1. What are your long-range goals and objectives?
I have many goals.For example, I am going to have a job, my own big house, and big and happy family.
2. What are your short-range goals and objectives?
In several months I am going to graduate my university as telecommunication's engineering. That is my short-range goal.
3. In what ways do you think you can make a contribution to our organization?
I will invent new technology.
4. What have you learned from participation in extra-curricular activities?
I have learned the ability of self-educated and working in team.
5. How do you determine or evaluate success?
Everyone can reach the top, just day must do whatthey can and always try to develop.
Just like this, I will reach the peak.
6. How do you plan to achieve your career goals?
I always try to know about the new technologies, to be patient and bold.
7. What makes a job enjoyable for you?
I am interested in my profession a lot, that makes job enjoyeable for me.
8. Why did you decide to seek a position with this communication organization?
I want to begin my first job whit new technology and in big company.
9. What two or three things would be most important to you in your job?
In my opinion, the most important things are attention, responsiblity and hard working.
10. What do you know about the job?
My job connects all people whitch each other.
11. How important is communication and interaction with others on your job?
In my opinion, the most important thing is communication.
12. Do you prefer to work by yourself or with others?
I prefer to work in team.
Friday, December 10, 2010
new words
1. Development-ололт,дээшлүүлэлт,сайжруулах
2. Appropriate-тохирох,таарах
3. Peer-тэнцүү
4. Killer applications-нэмэлт үйлчилгээ
5. Capabilities-чадвар
6. Circuit switched-уламжлалт холболт
7. Value added-өртөг нэмэх үйлчилгээ
8. User installable-хэрэглэгч суурьлуулах үйлчилгээ
9. Reliance-итгэл, найдвар
10. Seamlesly-засваргүй
11. Appropriate-нэгдмэл
12. Perspective-хэтийн төлөв
13. Differentiator-ялгарагч
14. Fidelity-нарийн таарах, үнэнч
15. Trouble shooting-алдаа илрүүлэх
16. Critical-шийдвэрлэх
17. hard codded-нарийн кодчлол
18. approach-арга зам, ойртох, дөхөх
19. competition-өрсөлдөөн
20. relute-холбох, холбогдох
21. providers-нэмэлт үйлчилгээ
22. troubleshooting-алдаа илрүүлэх
23. session-сүлжээний холболт
24. sophisticated-нарийвчлал сайтай
25. migrate-шилжих
26. competition-өрсөлдөөн, тэмцэл
27. essiantial-үндсэн, гол чухал
28. appropriately-тохирох, таарах
29. alliances-биеэ даасан байгууллага
30. attract-анхаарал татах
31. operational-үйл ажиллагааны, шуурхай ажлын
32. illustrates-харуулах, дүрслэх, үзүүлэх
33. describe-тайлбарлах, дүрслэх, тодорхойлох
34. Apply – зөвшөөрөх, хэрэглэх, ашиглах
35. Simultaneous – нэгэн зэрэг, паралель, зэрэгцсэн
36. Required to meet – шаардлагад нийцэх
37. Offered – зөвшөөрөгдсөн, санал болгосон
38. Abandoned – татгалзсан, хаягдсан, орхигдсон
39. Term – зүйл анги, болзол нөхцөл, нэр томъёо, томъёолол
40. Blocked – хаалттай, хаалтанд орсон, саатсан, саатуулагдсан
41. Order – заавар, журам, тушаал
42. Accurate – нарийн, тодорхой
43. Distribution – тархалт
44. Allocation – хувиарлах, хувиарлалт, хуваах
45. Assumption – төсөөлөл, таамаглал
46. Separate – салгах, тусгаарлах, ангилах, хуваагдах
47. Simple – хялбар, энгийн, шударга
48. Entire – бүхэл бүтэн
49. Extreme – хэт туйлын, хязгаарын, үнэмлэхүй
50. Pathway – гол зам, маршрут, чиглүүлэгч
51. specialized – мэргэшсэн, тусгай
52. slightly – үл ялаг, алгуурхнаар
53. confirm – батлах, баталгаа өгөх, баталгаажуулах
54. inaccessible – хүрэх боломжгүй
55. spread - сунгах,тархац
56. remote – алслагдсан
57. demand – шаардлага, хүсэлт, хэрэгцээ
58. demonstration – баталгаа, нотолгоо, үзүүлэх, таниулах
59. portability – авсаархан, зөөвөрлөх болмжтой
60. evolution – хувьсал, хөгжил
61. discussion – хэлэлцээр, маргаан, хэлэлцүүлэг
62. capability – чадвар, нэвтрүүлэх чадвар
63. capacity – багтаамж, хүчин чадал эзэлхүүн
64. allow- зөвшөөрөх, болох өгөх, боломж олгох
65. apparently – илэрхий, тод, маргаангүй
66. major – үндсэн
67. increased – нэмэлт, өсөлт, өссөн
68. capabilities-боломж
69. wiring-цахилгаан утас
70. various-олон төрлийн, ялгаатай
71. tend-хэлбийх
72. significant-ач холбогдолтой
73. plexibility-уян хатан чанар
74. operators-утас залгагч
75. implementation-биелэлт, хэрэгжилт
76. facilitating-хөнгөвчилж байна
77. conjunction-залгах, нэгдэх, холбоос
78. arrangement-байрлал, тоног төхөөрөмж
79. circumstance-нөхцөл байдал
80. cross-солбисон, зөрсөн
81. portions-хэсэг, зангилаа, блок
82. Appropriate-нэгдмэл
83. Real time-бодит хугацааны
84. Trouble shooting-алдаа илрүүлэх
2. Appropriate-тохирох,таарах
3. Peer-тэнцүү
4. Killer applications-нэмэлт үйлчилгээ
5. Capabilities-чадвар
6. Circuit switched-уламжлалт холболт
7. Value added-өртөг нэмэх үйлчилгээ
8. User installable-хэрэглэгч суурьлуулах үйлчилгээ
9. Reliance-итгэл, найдвар
10. Seamlesly-засваргүй
11. Appropriate-нэгдмэл
12. Perspective-хэтийн төлөв
13. Differentiator-ялгарагч
14. Fidelity-нарийн таарах, үнэнч
15. Trouble shooting-алдаа илрүүлэх
16. Critical-шийдвэрлэх
17. hard codded-нарийн кодчлол
18. approach-арга зам, ойртох, дөхөх
19. competition-өрсөлдөөн
20. relute-холбох, холбогдох
21. providers-нэмэлт үйлчилгээ
22. troubleshooting-алдаа илрүүлэх
23. session-сүлжээний холболт
24. sophisticated-нарийвчлал сайтай
25. migrate-шилжих
26. competition-өрсөлдөөн, тэмцэл
27. essiantial-үндсэн, гол чухал
28. appropriately-тохирох, таарах
29. alliances-биеэ даасан байгууллага
30. attract-анхаарал татах
31. operational-үйл ажиллагааны, шуурхай ажлын
32. illustrates-харуулах, дүрслэх, үзүүлэх
33. describe-тайлбарлах, дүрслэх, тодорхойлох
34. Apply – зөвшөөрөх, хэрэглэх, ашиглах
35. Simultaneous – нэгэн зэрэг, паралель, зэрэгцсэн
36. Required to meet – шаардлагад нийцэх
37. Offered – зөвшөөрөгдсөн, санал болгосон
38. Abandoned – татгалзсан, хаягдсан, орхигдсон
39. Term – зүйл анги, болзол нөхцөл, нэр томъёо, томъёолол
40. Blocked – хаалттай, хаалтанд орсон, саатсан, саатуулагдсан
41. Order – заавар, журам, тушаал
42. Accurate – нарийн, тодорхой
43. Distribution – тархалт
44. Allocation – хувиарлах, хувиарлалт, хуваах
45. Assumption – төсөөлөл, таамаглал
46. Separate – салгах, тусгаарлах, ангилах, хуваагдах
47. Simple – хялбар, энгийн, шударга
48. Entire – бүхэл бүтэн
49. Extreme – хэт туйлын, хязгаарын, үнэмлэхүй
50. Pathway – гол зам, маршрут, чиглүүлэгч
51. specialized – мэргэшсэн, тусгай
52. slightly – үл ялаг, алгуурхнаар
53. confirm – батлах, баталгаа өгөх, баталгаажуулах
54. inaccessible – хүрэх боломжгүй
55. spread - сунгах,тархац
56. remote – алслагдсан
57. demand – шаардлага, хүсэлт, хэрэгцээ
58. demonstration – баталгаа, нотолгоо, үзүүлэх, таниулах
59. portability – авсаархан, зөөвөрлөх болмжтой
60. evolution – хувьсал, хөгжил
61. discussion – хэлэлцээр, маргаан, хэлэлцүүлэг
62. capability – чадвар, нэвтрүүлэх чадвар
63. capacity – багтаамж, хүчин чадал эзэлхүүн
64. allow- зөвшөөрөх, болох өгөх, боломж олгох
65. apparently – илэрхий, тод, маргаангүй
66. major – үндсэн
67. increased – нэмэлт, өсөлт, өссөн
68. capabilities-боломж
69. wiring-цахилгаан утас
70. various-олон төрлийн, ялгаатай
71. tend-хэлбийх
72. significant-ач холбогдолтой
73. plexibility-уян хатан чанар
74. operators-утас залгагч
75. implementation-биелэлт, хэрэгжилт
76. facilitating-хөнгөвчилж байна
77. conjunction-залгах, нэгдэх, холбоос
78. arrangement-байрлал, тоног төхөөрөмж
79. circumstance-нөхцөл байдал
80. cross-солбисон, зөрсөн
81. portions-хэсэг, зангилаа, блок
82. Appropriate-нэгдмэл
83. Real time-бодит хугацааны
84. Trouble shooting-алдаа илрүүлэх
Tuesday, December 7, 2010
abstract
Future Developments in Telecommunications
Pressures such as service providers, technology, regulators, governments, customers, embedded equipment, developers, and dozens of other factors are impinging on this technological colossus and it is moving; sometimes slowly, but it is always moving.
The next decade in telecommunications will be most interesting and replete with opportunities .
The giants and startups alike have assessed the industry, made their moves, and some have flopped spectacularly.
The telecommunications industry has several unmistakable trends that will shape products and services in the future. IP is becoming a global language, wire is giving way to wireless, and broadband access unleashes a plethora of new services.
This time the monopoly is not nationwide, but on a regional basis it bears more than a casual resemblance to the old Bell System. Other trends that are already well underway include movement toward Ethernet and open source. Ethernet, is well entrenched in the LAN and in its 1G and 10G versions it will increasingly serve the metropolitan network. Open source protocols, operating systems, and software are a major disruptive force to the traditional developers. The trend is unmistakable, and will continue to provide users with attractive alternatives, even extending to PBXs.
Cable and Cellular Competitors
Many people expect voice over WiFi to provide a viable alternative to cellular/PCS, but WiFi hotspots cannot offer a reliable alternative to cellular because the frequencies are too limited and the protocols have too many quality problems. Moreover, WiFi is designed as a private network, not a common carrier service. WiMax, on the other hand, is lurking in the future. Its protocols are far from complete, but by about 2007 WiMax should be ready for the market as a credible platform on which service providers can offer VoIP.
WiMax will not only compete with cell phones (including 3G and 4G cellular), it is expected to be suitable for access, competing directly with cable and DSL. In some localities it may become the primary means of access. WiMAX can potentially do for metropolitan area wireless what WiFi did for wireless LANs. Prestandard products are on the market now, well ahead of the expected 2007-8 protocol approval. Both the cable companies and the ILECs are studying the feasibility of IPTV: bringing video on demand to the customer over a broadband pipe. This displaces the old service model of passing all channels by every cable customer and replaces it with video that can be customized at the source. Instead of being restricted to a single view of live program material, the originator can send multiple views, which allows the viewers to select the ones they prefer.
IPTV, in trials today, holds out the promise of personalizing video reception beyond the limited manipulations that are possible with video hard disk drives. Another trend that is apt to occur is barely visible: a shift from broadcasting to narrowcasting. One of the hottest products on the market is the i-Pod, which gives users a choice of hours of their own musical selections. For video, devices such as DVD recorders, and the old standby VCR give users a choice of what to watch and when they want to watch it without being bombarded with annoying commercials. They are also subject to competition from satellite providers, but these cannot compete favorably for access, which gives the cable companies a big advantage.
Wireless
It is safe to predict that wireless will have a vigorous future.The spectrum is limited and competition for it is intense. Many people see WiFi as a key technology, but its limitations will prevent it from becoming more than is intended to be, which is a LAN alternative. Its spectrum and range are too limited to create a metropolitan network service. Hot spots in airports and other transportation centers have great potential. The airlines are preparing to offer WiFi in their cabins and this should prove to be enormously attractive.
The desire for cellular service is nothing short of astounding, particularly when you watch the development in third-world nations, and consider the amount of money that people pay for trivial accessories such as customized ringing tones. New cell phones support video, albeit on a miniature screen, and content providers are beginning to offer custom video clips. How far the market for this will extend is anyone’s guess, but society has demonstrated a boundless willingness to pay for entertainment. Fourth generation wireless standards are under development, and an industry group is working on an interim service known as Super 3G that may be ready in 2007. Super 3G would have downstream speeds as high as 100 Mbps.
Pressures such as service providers, technology, regulators, governments, customers, embedded equipment, developers, and dozens of other factors are impinging on this technological colossus and it is moving; sometimes slowly, but it is always moving.
The next decade in telecommunications will be most interesting and replete with opportunities .
The giants and startups alike have assessed the industry, made their moves, and some have flopped spectacularly.
The telecommunications industry has several unmistakable trends that will shape products and services in the future. IP is becoming a global language, wire is giving way to wireless, and broadband access unleashes a plethora of new services.
This time the monopoly is not nationwide, but on a regional basis it bears more than a casual resemblance to the old Bell System. Other trends that are already well underway include movement toward Ethernet and open source. Ethernet, is well entrenched in the LAN and in its 1G and 10G versions it will increasingly serve the metropolitan network. Open source protocols, operating systems, and software are a major disruptive force to the traditional developers. The trend is unmistakable, and will continue to provide users with attractive alternatives, even extending to PBXs.
Cable and Cellular Competitors
Many people expect voice over WiFi to provide a viable alternative to cellular/PCS, but WiFi hotspots cannot offer a reliable alternative to cellular because the frequencies are too limited and the protocols have too many quality problems. Moreover, WiFi is designed as a private network, not a common carrier service. WiMax, on the other hand, is lurking in the future. Its protocols are far from complete, but by about 2007 WiMax should be ready for the market as a credible platform on which service providers can offer VoIP.
WiMax will not only compete with cell phones (including 3G and 4G cellular), it is expected to be suitable for access, competing directly with cable and DSL. In some localities it may become the primary means of access. WiMAX can potentially do for metropolitan area wireless what WiFi did for wireless LANs. Prestandard products are on the market now, well ahead of the expected 2007-8 protocol approval. Both the cable companies and the ILECs are studying the feasibility of IPTV: bringing video on demand to the customer over a broadband pipe. This displaces the old service model of passing all channels by every cable customer and replaces it with video that can be customized at the source. Instead of being restricted to a single view of live program material, the originator can send multiple views, which allows the viewers to select the ones they prefer.
IPTV, in trials today, holds out the promise of personalizing video reception beyond the limited manipulations that are possible with video hard disk drives. Another trend that is apt to occur is barely visible: a shift from broadcasting to narrowcasting. One of the hottest products on the market is the i-Pod, which gives users a choice of hours of their own musical selections. For video, devices such as DVD recorders, and the old standby VCR give users a choice of what to watch and when they want to watch it without being bombarded with annoying commercials. They are also subject to competition from satellite providers, but these cannot compete favorably for access, which gives the cable companies a big advantage.
Wireless
It is safe to predict that wireless will have a vigorous future.The spectrum is limited and competition for it is intense. Many people see WiFi as a key technology, but its limitations will prevent it from becoming more than is intended to be, which is a LAN alternative. Its spectrum and range are too limited to create a metropolitan network service. Hot spots in airports and other transportation centers have great potential. The airlines are preparing to offer WiFi in their cabins and this should prove to be enormously attractive.
The desire for cellular service is nothing short of astounding, particularly when you watch the development in third-world nations, and consider the amount of money that people pay for trivial accessories such as customized ringing tones. New cell phones support video, albeit on a miniature screen, and content providers are beginning to offer custom video clips. How far the market for this will extend is anyone’s guess, but society has demonstrated a boundless willingness to pay for entertainment. Fourth generation wireless standards are under development, and an industry group is working on an interim service known as Super 3G that may be ready in 2007. Super 3G would have downstream speeds as high as 100 Mbps.
chapter 13
QUALITY OF SERVICE PROTOCOLS
Most quality problems resulting from congestion can be solved by providing plenty of bandwidth. Carriers that have their own fiber optic capacity can often provide enough bandwidth so that delays resulting from router queuing and packet discard are held to a minimum. Some carriers even use the Internet for part of their network, but to do so they must monitor quality and switch the traffic to a more stable platform if congestion begins to develop. The main factor in carrier networks is the use of QoS protocols to provide the stability and precedents that isochronous traffic needs. This is not feasible in the Internet because of the diverse ownership and lack of controls over the router protocols. Several protocols are available to ensure that the network reserves enough bandwidth and boosts time-sensitive traffic along without unacceptable delay. Although the QoS protocols discussed in this section are not technically part of the PSTN, they are discussed here because they are used with VoIP sessions that must emulate the PSTN. Chapters 36 and 37 provide additional details.
Reservation Protocol (RSVP)
RSVP is not a routing protocol; it is a signaling protocol that works through the routing protocol to set up the path. An application running under RSVP sends a reservation request forward through the IP network using RSVP messages following the path set up by the routing protocol. RSVP communicates with admission and policy control modules in the node. Admission control determines whether the node has resources to provide the requested QoS. Policy control determines whether the user has permission to request the reservation. If the checks succeed, RSVP sets a QoS class in its packet classifier. Each node in the path stores path-state indicators containing the IP address of the previous node. The path state is used to return the reservation confirmation over the same pathway using an RESV message. The RESV message provides receivers with information about the path and traffic load so they can reserve the bandwidth. If the path changes during the session, RSVP adapts to the change. Each node along the path must support RSVP and have the bandwidth available to reserve for the session. If either of these fails, the reservation request fails. If the session becomes inactive, RSVP sends keep-alive packets to confirm that the session is still alive. When these stop, the reservation times out and the resources are returned to the pool. RSVP emulates a circuit-switched connection by providing controlled latency and sufficient bandwidth to support the session. It is inefficient for short flows because the setup time becomes a significant part of the total session time. It is also reliable only in a network of known characteristics such as a carrier’s IP network. Three classes of service are defined. Guaranteed service provides bandwidth of known delay characteristics and no lost packets. Controlled load service is an intermediate service providing a better class of service than the third category, which is best effort, the service class now provided by the Internet. RSVP falls under a category the IETF defines as Integrated Services (IntServ).
Differentiated Services (DiffServ)
DiffServ takes a different approach than IntServ by identifying time-sensitive packets at the application and placing class-of-service information in the IPheader. The type-of-service (ToS) field in the IPv4 header marks packets to receive a particular forwarding treatment at each node; i.e., to forward it immediately or delay it in favor of a higher priority packet. With DiffServ, it is not necessary to exchange QoS requirements between the source and destination, which reduces the setup time compared to RSVP. RSVP’s setup time can be a substantial part of the total in short flows. DiffServ does not guarantee a level of service. It is designed to ensure that services requiring explicit QoS are identified and classified as priority traffic. It is less complex than RSVP and scales better, but it lacks admission control, so too much high-priority traffic can swamp the network.
Multiprotocol Label Switching (MPLS)
MPLS short cuts the routing process by mapping IP addresses to simple fixed length labels, which are numbers that identify a data flow. A sequence of labels and links is called a label-switched path (LSP) also known as an MPLS tunnel. MPLS supports a variety of QoS functions including bandwidth reservation, prioritization, traffic engineering, traffic shaping, and traffic policing on almost any type of interface. Routing is simplified because it happens only once at the edge of the network in the label edge router (LER). Routers in the path read the label instead of the packet header and route the call along a path that is defined by the label. Traffic is assigned to a forwarding equivalence class (FEC), which is a group of packets to the same destination and which share the same QoS requirements. An MPLS-compatible router is called a label switched router or LSR. Packets enter and leave the core network through ingress and egress LERs. The ingress LER inserts the label ahead of the IP header. As packets flow through the network, each MPLS device checks its label tables or label information base to determine how to forward the traffic. MPLS is at the heart of most VoIP carrier networks and in combination with RSVP it is capable of delivering QoS that is comparable to circuit switching, provided every node in the path supports the protocols. The only way this can be assured is for the carrier to control the network design. This limits the degree of network interoperability that the PSTN provides, and is contrary to the free-wheeling nature of the Internet.
Router Queue Scheduling Protocols
The method routers use to process their queues is an important factor in determining latency. In the absence of a prioritization scheme, routers process packets first come- first-served, which is unsuitable for time-sensitive packets unless the load is light. Most routers are capable of prioritizing traffic using a variety of techniques. Priority queuing is the technique in which the traffic is divided into various priorities and assigned to queues, which the router processes in priority order. All the traffic in the highest priority queue is processed ahead of traffic in the second priority queue, and so on. The problem with this approach is that since voice and video must be given highest priority, when the load is high they can preempt data and lengthen the response time. Custom queuing alleviates this somewhat by dividing the bandwidth on a percentage basis as part of the router setup process. The queues are processed in round robin fashion, but the only prioritization given to voice and video is the percentage of bandwidth they are allocated. Weighted fair queuing (WFQ) divides the bandwidth among all the traffic flows entering the queue. All flows by default have a precedence of zero, and are given a weighting of the precedence plus one. If five flows of equal priority were flowing into the router, each would get 20 percent of the bandwidth. If one of these were a voice flow, it might be given a precedence of, say, 5. This would mean that the voice flow would receive a precedence of 6 (5+1) and the other four flows would have a precedence of 1. The total weighting would be 10, so the voice flow would receive60 percent of the bandwidth, and the other four flows would each receive 10 percent. Priority classifications include source and destination addresses, protocol, and session identifier based on the three IP precedence bits in the packet header. Routers may use a combination of priority queuing and WFQ with voice applied to the priority queue and data applications distributed among queues using WFQ. Weighted random early detection (WRED) is a method of determining which packets are dropped when the router must discard traffic. In the absence of any prioritization, the last packets in are dropped first. WRED predicts the need to drop packets, and begins dropping low-priority packets to prevent congestion rather than waiting until congestion occurs. When WRED needs to drop TCP/IP packets, it drops all of them within a TCP window because if one packet within the window is dropped, all of them must be retransmitted anyway.
Classifying Traffic
A final QoS issue is how to classify the traffic or as some call it “coloring” the packets so they are forwarded to the appropriate queue in the switch or routers. The network devices then must apply the appropriate scheduling techniques for unloading their queues. The traffic class may be defined by the type of user, by port number, or by the applications such as voice, video, or e-mail. This classification is ideally handled by a policy management system, but policy management is largely proprietary and will remain so until standards are developed. The other alternative is to have the application dictate the appropriate class at the origin. The 802.1p Ethernet priority bits define a variety of parameters for providing QoS including such variables as frame error rate, loss, sequencing, duplication, data unit size, user priority, delay, and throughput. The 802.1p protocol provides a total of eight traffic classes and eight user priorities. The highest class is network control, which is given precedence because of its role in controlling the network. Voice and video are given controlled delay, which is next highest. From there the classes descend to the lowest, background class, which is suitable for such applications as games. The standard is implemented in network interface cards in response to priority requested by the application. In order to get end-to-end QoS, all the network elements have to support the standard. The advantage of using 802.1p to classify traffic is simplicity. Switches can read the information and forward frames with the prioritization intact. The drawback is that the information is stripped off when the frame passes through a router. This argues for the second method, which is setting the ToS field in the packet. This works in some cases, but it does not work with layer 2 switches, which do not read packet headers.
Essential Characteristics of the PSTN
The PSTN has certain characteristics that all circuit-switched class 5 and above central offices must support. This section provides an overview of how the PSTN functions, both from a technical and a regulatory standpoint.
The North American Numbering Plan
The North American Numbering Plan is a subset of ITU E.165. Neustar, Inc. is the North American Numbering Plan Administrator (NANPA). NANPA assigns area codes, which are also known as NPA codes, for all of the countries included in the North American plan. It also assigns central office codes in the United States. Area codes have the form NXX, where N is any digit from 2 through 9and X is any digit from 0 through 9. There are 800 possible combinations under this format, but some combinations are not available or have been reserved for special purposes. Codes with the format N11 are called service codes and are not used as area codes. These are used for such services as emergency calling (911), directory assistance (411), and travel information (511). Codes where the second and third digits are the same are called easily recognizable codes. These designate special services such as the series 800, 888, 877, etc., that are used for toll-free calling. Until recently an NPA always had an exclusive geographic boundary. As more and more prefixes were assigned to support CLECs, cellular and paging providers, and large companies that requested exclusive prefixes, NPAs were split into smaller areas and numbers assigned to the new NPA were changed. To forestall number changes, some state regulatory commissions elected to use overlay area codes. An overlay area code follows approximately, but not necessarily exactly, the same boundaries as the original NPA. Overlay area codes require the subscribers to dial 10 digits to complete local calls. In a non-overlay NPA, calls are completed with seven digits. Central office codes, also known as NXXs or prefixes, are digits 4, 5, and 6 of a 10-digit telephone number. NANPA assigns central office codes using guidelines from state and federal authorities. Several factors are leading to the exhaust of available numbers, so NXXs are assigned within strict rules, particularly where the available numbers in an area code are in danger of being exhausted. Among the factors contributing to number usage is the assignment of prefixes to entities that cannot use all the numbers. For example, many small communities have a switch that serves less than 1000 telephones and the rest of the prefix is unused. To make better use of prefixes, the industry has introduced thousands-block pooling, which subdivides the prefix into blocks of 1000 numbers. A major difference between the PSTN and an IP network is the fact that a PSTN number is associated with a physical location. Numbers can be ported or forwarded, but they are reached by a traceable path. Even with cell phones, which can roam anywhere the service provider supports, the number is associated with a switch that has a fixed location. This inflexibility is a disadvantage from a mobility standpoint, but it allows accurate dispatch of emergency vehicles for wired locations. Cellular emergency calls are a separate issue, which we discuss in Chapter 20.
Local Number Portability (LNP)
The Telecommunications Act of 1996 mandates that customers be permitted to change service providers without changing their telephone number. Within the bounds of a rate area, subscribers can change their geographic location or can change between classes of service such as from POTS to Centrex without a number change. To implement LNP, each wire line switch is identified with a 10-digit location routing number (LRN). The LRN for a particular switch is a “native” NPA-NXX that serves as a network address for that switch. Carriers query the LNP database to determine the LRN corresponding to the dialed telephone number. The originating switch routes the call to the terminating switch based on the LRN. Figure 13-2 illustrates how the process works. An LNP database serves the territory covered by each of the seven original RBOCs. After the caller dials the telephone number, the originating switch sends a query over SS7 to the LNP database through its STP. The SCP that hosts the LNP returns a message containing the LRN of the recipient switch. The originating switch sends the call to the recipient switch, which completes the call.
Access to the Local Exchange Network
Until AT&T’s divestiture in 1984, the telephone network in the United States was designed for single ownership in each exchange. In some countries it still is, butt hose countries that have deregulated long distance provide access to multiple IXCs. This section discusses the architectures of local and long distance telephone
networks, how the IXCs obtain local access, and the way IXCs sometimes bypass the local networks to provide service directly to end users.
Local Access Transport Areas (LATAs)
The terms of the agreement between AT&T and the Department of Justice prohibited the RBOCs from transporting long-distance traffic outside LATAs. The Telecommunications Act of 1996 provides for the eventual lifting of this restriction as local networks are opened to competition. At the time of this writing, the restrictions prohibiting the RBOCs from carrying inter-LATA toll have been lifted in most states, but the LATA boundaries remain. RBOCs that have been relieved of the inter-LATA restrictions provide long-distance service through a subsidiary. LATAs correspond roughly to Standard Metropolitan Statistical Areas defined by the Office of Management and Budget. Equal access requires intelligence in the class 5 office to route the call to the trunk group serving the primary IXC. Subscribers register their choice of PIC with their serving LEC. Separate PICs are provided for inter-LATA and intra-LATA traffic. IXCs select the method of accessing the LECs. They can connect to the LEC with direct trunks, or they can gain access to any exchange in the LATA through an access tandem. Every end office in the LATA, including CLEC offices, connects to the LATA tandem with direct trunk groups. Access through the tandem carries a usage charge, so IXCs use direct trunks to the end office where they are cost-effective.
Maintenance and Administrative Features
Central offices include many features to monitor the system’s health. These features enable the system to respond automatically to abnormal conditions through a local or remote maintenance and control center (MCC). The features in this section are essential for any carrier switch. Most enterprise network switches include the same features, although often to a less sophisticated degree.
Fault Detection and Correction
The central processor continually monitors all peripheral equipment to detect irregularities. When a peripheral fails to respond correctly, the processor signals an alarm condition to the MCC and switches to a duplicated element if one is provided. The MCC interfaces maintenance personnel to the fault-detecting routines of the generic program. At the MCC, the central processor communicates its actions with messages on a CRT, a printer, or both. Depending on the degree of sophistication in the program, the system may register the fault indication or may narrow the source of the fault down to a list of suspected circuits. For unattended operation the MCC transmits fault information to a control center over a data link. The processor also monitors its own operation through built-in diagnostic routines. If it detects irregularities, the on-line processor calls in the standby and goes off-line. All such actions to obtain a working configuration of equipment can be initiated manually from the MCC or from a remote center. The ultimate maintenance action, which can be caused by an inadvertently damaged database or a program loop, is a restart. A restart is usually done only manually and as a last resort because it involves total loss of calls in progress and loss of recent changes to the database.
Communications Assistance for Law Enforcement Act (CALEA)
CALEA requires all wire line, cellular, and broadband carriers to assist law enforcement personnel who are acting under court order. The act requires a carrier to ensure that its equipment, facilities, or services are capable of enabling the government to intercept wire and electronic communications. Carriers must provide access to reasonably available call-identifying information and deliver intercepted communications and information to law enforcement agencies. Circuit-switched networks have little difficulty in complying with CALEA requirements, but VoIP is another matter. Calls placed over residential broadband and calls between SIP endpoints can flow directly between endpoints in RTP packets. The soft switch controlling the packet flow does not have access to the voice packets, which makes it difficult, if not impossible, to comply with wiretapping requests. The FCC permits packet-mode providers to request exemption from CALEA requirements, but as VoIP gains popularity, it is difficult to see how a disparity between circuit-switched and packet-switched requirements can survive.
Emergency Calling
In North America, the E-911 system is designed to ensure that emergency vehicles from the correct jurisdiction are sent to an address from which a call originates, regardless of whether the caller is able to communicate with the emergency CHAPTER 13 The PSTN and Quality Requirements 231 services operator. In most jurisdictions, the LEC boundaries do not align with the boundaries of the emergency service agencies and the agencies’ boundaries do not align with one another. Furthermore, city and county boundaries are also no guide to which public safety answering point (PSAP) may handle an emergency call. Therefore, the E-911 system must have a database that correlates a calling number with the appropriate responding agency. Figure 13-3 shows the principal components in an E-911 system. Each locality has one or more central offices designated to route emergency calls to the correct PSAP. This switch is known as the selective router (SR). It may be known by another serving area connects to the SR with a trunk group for handling emergency calls. When a subscriber places a 911 call, the end office sends the voice call and the calling number to the SR. The SR looks up the emergency service number (ESN), which identifies the serving PSAP. The call is switched to the PSAP, which interrogates the 911 database for the address of the calling telephone number. The database returns the name, address, location, and the appropriate emergency responders for that address. The process of automatically displaying the caller’s number, address, and supplementary emergency information is known as automatic location identification (ALI). The 911 database is often known as the ANI/ALI database Providing accurate location information on emergency calls is a major issue for any organization that has private switches distributed over a wide area while sharing a common group of trunks. Unless other measures are taken, the host
switch location will display in the PSAP and emergency vehicles will be dispatched to the wrong address. The process of supporting private systems to the E-911 system is known as private switch automatic line identification (PS/ALI). PS/ALI identification of the source of a 911 call can be accomplished by several different methods:
A POTS line is connected to the CPE switch. The automatic route selection in the switch selects that line for 911 calls. A CAMA trunk can be connected to the serving central office. The CAMA trunk contains the calling station identity. If the PBX connects to its serving CO over PRI, the CO can receive the calling station identification and pass it to the SR. VoIP raises critical issues with respect to E-911 because the phone is mobile and the IP address has no fixed relationship to the location. The service provider maintains a default location address for the serving trunk group, but VoIP enables users to transport their phones to other jurisdictions, even to other area codes. The issues are similar to cell phones, but the solutions proposed there involve either the use of GPS or the triangulation from cell sites. GPS is technically a suitable method for VoIP, but requires an unobstructed view of at least three satellites, which is not reliable. The most practical solution relies on the fact that every phone is connected to a switch port that has a fixed geographical location. If a VoIP phone dials 911, the call controller communicates with a server that registers the physical location of the phone. The call switches to the PSAP through the SR while a gateway communicates location information through the PS/ALI process. The process for handling this is not standardized at this writing.
Essential Service and Overload Control
Switching systems are designed for traffic loads that occur on the busiest normal business days of the year. Occasionally, peaks occur that are higher than normal. Heavy calling loads can occur during unusual storms, political disorders, and catastrophes. During these peaks, the switching system may be overloaded to the point that service is delayed or denied to large numbers of users. Central offices include line load control circuitry that denies service to nonessential users so that users essential to public safety and health can continue to place calls. Nonessential users are assigned to two groups. When line load control operates, one group is denied service while the other group is permitted to dial. The two groups are periodicallyreversed to give equal access to both nonessential groups.Many local offices have network management provisions to prevent overloads. For example, dynamic overload control automatically changes routing tables to reroute traffic when the primary route is overloaded. Code conversion allows the system to block traffic temporarily to a congested central office code. This feature enables the blocked system to take recovery action without being overwhelmed by ineffective attempts from a distant central office. These provisions are circuit-related and not applicable to VoIP except in the case of gateways, which are subject to the overload conditions on their circuit side.
Telecommunications Service Priority
The Telecommunications Service Priority (TSP) Program provides national security and emergency preparedness (NS/EP) users with priority authorization of telecommunications services that are vital to coordinating and responding to crises such as hurricanes, floods, earthquakes, and other natural or human-caused disasters. During such a disaster, telecommunications service providers may become overwhelmed with restoration requests. The TSP Program provides service vendors with an FCC mandate for prioritizing service requests by identifying those services critical to NS/EP. A telecommunications service with a TSP assignment is assured of receiving full attention by the service vendor before a non-TSP service.
Trunk Maintenance Features
Local central offices have varying degrees of trunk maintenance capability. The system monitors trunk connections in progress to detect momentary interruptions or failures to connect. The system registers the failure and enters it on a trunk irregularity report, which technicians use to pattern trunk trouble. The system marks defective trunks out of service and lists them on a trunk out-of-service list. When all trunks in a carrier system fail, the system detects a carrier group alarm, marks the trunks out of service in memory, and through its alarm system reports the failure to the MCC.
Line Maintenance Features
Switching systems contain circuits to detect irregularities in station equipment and outside plant. Like trunk tests, these are made on a routine or per-call basis. On each call, many systems monitor the line for excessive external voltage (foreign EMF), which suggests cable trouble. Line insulation tests (LIT) are made routinely during low-usage periods to detect incipient trouble. The LIT progresses through lines in the office on a pre-programmed sequence and measures them for foreign voltage or low insulation resistance, which is low resistance between the tip and ring or from each side of the pair to ground. These tests detect outside plant troubles such as wet cable, and terminal, drop wire, and protector problems. Switching systems must deal with permanent signals, which are caused by a telephone receiver off hook, cable trouble, or a defective station protector. Any of these irregularities place a short circuit on the line, and the line circuit attaches the line to a register, which furnishes dial tone and prepares to accept digits. The system must be capable of detecting and dealing with receivers off hook and multiple short circuits that result from cable trouble. Such lines are marked out of service temporarily so they do not tie up common equipment in the central office. One method of resolving permanent signals is to connect the line to a series of tones and recordings such as a recording that asks the caller to hang up the line.Then after a suitable interval it may be connected to a progressively louder seriesof tones to attract the caller’s attention.
Configuration Management
When the office is initially configured, its software retains a map of equipped and spare facilities. When the office is upgraded the configuration management system informs the switch of the presence of new equipment. Daily service order activity modifies the software to add new subscribers, delete disconnected ones, or change features. The configuration management system enables technicians to enter order activity through a terminal or through file transfer. As discussed in the next section, the system samples call activity and reports traffic information such as call counts, call completions, and line, trunk, and feature usage. The system monitors CPU activity and reports grade of service measurements such as dial tone delay and common equipment usage.
Traffic-Measuring Equipment
Circuit switches are engineered based on usage. Usage information is based onthe number of times a trunk or line circuit is seized and the average holding timeof each attempt. Software registers measure the number of times the circuit isseized and elapsed time that the circuit is busy. The registers are periodicallyunloaded to a processing center for summary and analysis. Class 5 offices thathave integrated VoIP and separate VoIP gateways must also collect usageinformation toward the PSTN because it is needed to determine the bandwidth ofthe connecting trunks. Traffic-measuring equipment can provide a variety of otherdata for administering the central office. For example, database information isprovided to update the availability of vacant lines and trunks.
LOCAL CENTRAL OFFICE SERVICE FEATURES
All central offices provide certain basic features. This section discusses some of themost common features and explains their purpose.
Automatic Number Identification (ANI) and AutomaticMessage Accounting (AMA)
ANI automatically identifies the calling party for billing purposes. On POTS linesthe number is identified from the cable pair. In ISDN and VoIP lines call setupmessages identify the calling number. AMA equipment interrogates ANI equipmentto determine the identity of the calling party. AMA equipment is classifiedas local AMA (LAMA), in which call collection is done in the local central office,or centralized AMA (CAMA). A CAMA office connects calling subscribers toa center where call details are recorded for all subtending central offices. AMAequipment records call details at each stage of a connection. The calling and calledparty numbers are registered initially. An answer entry registers the time of connection,and the terminating entry registers the time of disconnect. The storagemedium is tape, disk, or solid-state memory. Call records are sent to distant dataprocessing centers over a datalink.
Local Measured Service (LMS)
Many telephone companies base their local service rates on usage. Flat ratecalling is often available, with LMS as an optional service class. With the LMSclass of service, calls inside the local calling area are billed by the number of calls,time of day, duration of call, and distance between parties. The method is similarto long distance billing except that calls may be bulk-billed with no individualcall detail.
Centrex
LECs furnish a PBX-like service through equipment located in the central office.The switching equipment is a partition in the end office called a Centrex commonblock. Centrex features allow direct inward dialing (DID) to a telephone numberand direct outward dialing (DOD) from a number. For calls into the Centrex, theservice is equivalent to individual line service. Outgoing calls require users to dialan access code such as 9, after which the central office returns the second dial tone.Stations within a common block can have an extended suite of features.Internal calls can be abbreviated to four or five digits instead of the seven digitsrequired for ordinary calls. Centrex users have access to all of the calling featuresof the central office, which are listed in a later section, as well as most of the featuresof a PBX such as call pickup, call hold, and class-of-service restrictions. Anattendant console located on the customer’s premises links to the central officeover a separate circuit. These features are discussed in Chapter 24, CustomerPremise Switching System Features.Centrex brings several advantages to the customer. Reliability is high since theLEC provides backup power and the stability of a switch that is more reliable thanmost PBXs. The customer avoids the expense of powering the switching equipment.The LEC handles problems of growth and obsolescence and the customer is relievedof many administrative tasks associated with switch ownership. Amajor advantageis the ability to link telephones in multiple locations with a single switch.Offsetting this to some degree is the difficulty of feature activation in analogCentrex. Telephone sets are POTS sets operating over cable pairs and the user activatesfeatures with a dial code. For example, call pickup might be *8. Users tendto forget the codes, and the features are consequently under-utilized. Some switchmanufacturers offer digital Centrex with TDM feature telephones similar to thoseprovided with PBXs. Feature telephones have displays, which improves usability,and functions such as call pickup and transfer are activated by pushing a button.Digital Centrex is limited, however, by the distance from the central office. Featuretelephones have a range limitation much less than POTS phones and will notwork outside the home central office.IP telephony offers the possibility of rejuvenating the LECs’ Centrex offerings.A media gateway (MG) can be placed on the subscriber’s premises. If the subscriberhas multiple locations, a separate MG can be placed on each, and the entirecomplex can be served from a single controller. This technology is described inmore detail in Chapter 16. IP telephones overcome the range restrictions of TDMtelephones and offer the benefits of expanded displays.
Routing to Service Facilities
All central offices provide access to service facilities such as operator and repairservice. All local switching systems also provide access to call progress tones suchas busy, reorder, vacant number tone, etc., and recorded announcements for interceptednumbers and permanent signals. Some systems also provide access to localtesting facilities.
Call-Processing Features
Local central offices provide a variety of service features that enhance call processing.The user signals the central office equipment with a momentary on-hookflash on a POTS line or a data message on IP or ISDN. On a POTS line the systemresponds to the flash with stutter dial tone to show that it is ready to receiveinstructions. Many call-processing features that once were reserved for businessuse are now becoming popular with residential subscribers. As residential usersincreasingly subscribe to second lines and custom calling features, such servicesas call pickup and do-not-disturb are becoming popular. The following is a briefdescription of the principal features provided by most end offices in addition tothe CLASS features discussed in Chapter 12:Call forwarding enables the user to forward incoming calls to anothertelephone number. While this feature is activated, calls to the user’snumber route automatically to the target telephone number. When the userof a forwarded line picks up the telephone to place a call, the system sendsstutter dial tone as a reminder that the line is forwarded.Call forward remote access permits the user to activate or deactivate callforwarding from a remote location.Call transfer allows the user to add a third party to a call as with three-waycalling. One party can then hang up, leaving the other two parties inconversation.Call waiting sends a tone to signal a user on a busy line of anotherincoming call. The user can place the original call on hold and talk to thewaiting call by pressing the switch hook. Some LECs offer “whisper” callwaiting so the other party is not aware of the interrupting call. A cancelcall-waiting feature enables users to disable the service temporarily to avoidhaving a modem call interrupted by call waiting.Distinctive ringing allows the LEC to assign as many as four separatedirectory numbers to a single line. By using an adapter that responds to theunique ringing pattern, the user can route calls to a separate telephone, faxmachine, modem, or other analog device. Most fax machines respond tothe distinctive ring without an adapter.Gab line enables callers to dial a number to which multiple callers can beconnected simultaneously. Some LECs use the gab line, which is popularwith teenagers, as a revenue-generating feature.Hot line automatically places a call to a directory number when the handsetis lifted.Multiline hunt connects incoming calls to the first idle line in a group.Speed calling enables the user to dial other numbers with a one- or two-digitnumber. Most telephones also provide speed calling without involving thecentral office.Three-way calling allows the user to add a third party to the conversation bymomentarily holding the first party while a third number is dialed.Voice mail allows callers to leave messages when the phone is busy orunanswered and alerts the user to waiting messages.Warm line is similar to hot line except that the predetermined number is notdialed until after an elapsed time. The service is useful for handicappedpeople who may be unable, at times, to dial the phone.
Most quality problems resulting from congestion can be solved by providing plenty of bandwidth. Carriers that have their own fiber optic capacity can often provide enough bandwidth so that delays resulting from router queuing and packet discard are held to a minimum. Some carriers even use the Internet for part of their network, but to do so they must monitor quality and switch the traffic to a more stable platform if congestion begins to develop. The main factor in carrier networks is the use of QoS protocols to provide the stability and precedents that isochronous traffic needs. This is not feasible in the Internet because of the diverse ownership and lack of controls over the router protocols. Several protocols are available to ensure that the network reserves enough bandwidth and boosts time-sensitive traffic along without unacceptable delay. Although the QoS protocols discussed in this section are not technically part of the PSTN, they are discussed here because they are used with VoIP sessions that must emulate the PSTN. Chapters 36 and 37 provide additional details.
Reservation Protocol (RSVP)
RSVP is not a routing protocol; it is a signaling protocol that works through the routing protocol to set up the path. An application running under RSVP sends a reservation request forward through the IP network using RSVP messages following the path set up by the routing protocol. RSVP communicates with admission and policy control modules in the node. Admission control determines whether the node has resources to provide the requested QoS. Policy control determines whether the user has permission to request the reservation. If the checks succeed, RSVP sets a QoS class in its packet classifier. Each node in the path stores path-state indicators containing the IP address of the previous node. The path state is used to return the reservation confirmation over the same pathway using an RESV message. The RESV message provides receivers with information about the path and traffic load so they can reserve the bandwidth. If the path changes during the session, RSVP adapts to the change. Each node along the path must support RSVP and have the bandwidth available to reserve for the session. If either of these fails, the reservation request fails. If the session becomes inactive, RSVP sends keep-alive packets to confirm that the session is still alive. When these stop, the reservation times out and the resources are returned to the pool. RSVP emulates a circuit-switched connection by providing controlled latency and sufficient bandwidth to support the session. It is inefficient for short flows because the setup time becomes a significant part of the total session time. It is also reliable only in a network of known characteristics such as a carrier’s IP network. Three classes of service are defined. Guaranteed service provides bandwidth of known delay characteristics and no lost packets. Controlled load service is an intermediate service providing a better class of service than the third category, which is best effort, the service class now provided by the Internet. RSVP falls under a category the IETF defines as Integrated Services (IntServ).
Differentiated Services (DiffServ)
DiffServ takes a different approach than IntServ by identifying time-sensitive packets at the application and placing class-of-service information in the IPheader. The type-of-service (ToS) field in the IPv4 header marks packets to receive a particular forwarding treatment at each node; i.e., to forward it immediately or delay it in favor of a higher priority packet. With DiffServ, it is not necessary to exchange QoS requirements between the source and destination, which reduces the setup time compared to RSVP. RSVP’s setup time can be a substantial part of the total in short flows. DiffServ does not guarantee a level of service. It is designed to ensure that services requiring explicit QoS are identified and classified as priority traffic. It is less complex than RSVP and scales better, but it lacks admission control, so too much high-priority traffic can swamp the network.
Multiprotocol Label Switching (MPLS)
MPLS short cuts the routing process by mapping IP addresses to simple fixed length labels, which are numbers that identify a data flow. A sequence of labels and links is called a label-switched path (LSP) also known as an MPLS tunnel. MPLS supports a variety of QoS functions including bandwidth reservation, prioritization, traffic engineering, traffic shaping, and traffic policing on almost any type of interface. Routing is simplified because it happens only once at the edge of the network in the label edge router (LER). Routers in the path read the label instead of the packet header and route the call along a path that is defined by the label. Traffic is assigned to a forwarding equivalence class (FEC), which is a group of packets to the same destination and which share the same QoS requirements. An MPLS-compatible router is called a label switched router or LSR. Packets enter and leave the core network through ingress and egress LERs. The ingress LER inserts the label ahead of the IP header. As packets flow through the network, each MPLS device checks its label tables or label information base to determine how to forward the traffic. MPLS is at the heart of most VoIP carrier networks and in combination with RSVP it is capable of delivering QoS that is comparable to circuit switching, provided every node in the path supports the protocols. The only way this can be assured is for the carrier to control the network design. This limits the degree of network interoperability that the PSTN provides, and is contrary to the free-wheeling nature of the Internet.
Router Queue Scheduling Protocols
The method routers use to process their queues is an important factor in determining latency. In the absence of a prioritization scheme, routers process packets first come- first-served, which is unsuitable for time-sensitive packets unless the load is light. Most routers are capable of prioritizing traffic using a variety of techniques. Priority queuing is the technique in which the traffic is divided into various priorities and assigned to queues, which the router processes in priority order. All the traffic in the highest priority queue is processed ahead of traffic in the second priority queue, and so on. The problem with this approach is that since voice and video must be given highest priority, when the load is high they can preempt data and lengthen the response time. Custom queuing alleviates this somewhat by dividing the bandwidth on a percentage basis as part of the router setup process. The queues are processed in round robin fashion, but the only prioritization given to voice and video is the percentage of bandwidth they are allocated. Weighted fair queuing (WFQ) divides the bandwidth among all the traffic flows entering the queue. All flows by default have a precedence of zero, and are given a weighting of the precedence plus one. If five flows of equal priority were flowing into the router, each would get 20 percent of the bandwidth. If one of these were a voice flow, it might be given a precedence of, say, 5. This would mean that the voice flow would receive a precedence of 6 (5+1) and the other four flows would have a precedence of 1. The total weighting would be 10, so the voice flow would receive60 percent of the bandwidth, and the other four flows would each receive 10 percent. Priority classifications include source and destination addresses, protocol, and session identifier based on the three IP precedence bits in the packet header. Routers may use a combination of priority queuing and WFQ with voice applied to the priority queue and data applications distributed among queues using WFQ. Weighted random early detection (WRED) is a method of determining which packets are dropped when the router must discard traffic. In the absence of any prioritization, the last packets in are dropped first. WRED predicts the need to drop packets, and begins dropping low-priority packets to prevent congestion rather than waiting until congestion occurs. When WRED needs to drop TCP/IP packets, it drops all of them within a TCP window because if one packet within the window is dropped, all of them must be retransmitted anyway.
Classifying Traffic
A final QoS issue is how to classify the traffic or as some call it “coloring” the packets so they are forwarded to the appropriate queue in the switch or routers. The network devices then must apply the appropriate scheduling techniques for unloading their queues. The traffic class may be defined by the type of user, by port number, or by the applications such as voice, video, or e-mail. This classification is ideally handled by a policy management system, but policy management is largely proprietary and will remain so until standards are developed. The other alternative is to have the application dictate the appropriate class at the origin. The 802.1p Ethernet priority bits define a variety of parameters for providing QoS including such variables as frame error rate, loss, sequencing, duplication, data unit size, user priority, delay, and throughput. The 802.1p protocol provides a total of eight traffic classes and eight user priorities. The highest class is network control, which is given precedence because of its role in controlling the network. Voice and video are given controlled delay, which is next highest. From there the classes descend to the lowest, background class, which is suitable for such applications as games. The standard is implemented in network interface cards in response to priority requested by the application. In order to get end-to-end QoS, all the network elements have to support the standard. The advantage of using 802.1p to classify traffic is simplicity. Switches can read the information and forward frames with the prioritization intact. The drawback is that the information is stripped off when the frame passes through a router. This argues for the second method, which is setting the ToS field in the packet. This works in some cases, but it does not work with layer 2 switches, which do not read packet headers.
Essential Characteristics of the PSTN
The PSTN has certain characteristics that all circuit-switched class 5 and above central offices must support. This section provides an overview of how the PSTN functions, both from a technical and a regulatory standpoint.
The North American Numbering Plan
The North American Numbering Plan is a subset of ITU E.165. Neustar, Inc. is the North American Numbering Plan Administrator (NANPA). NANPA assigns area codes, which are also known as NPA codes, for all of the countries included in the North American plan. It also assigns central office codes in the United States. Area codes have the form NXX, where N is any digit from 2 through 9and X is any digit from 0 through 9. There are 800 possible combinations under this format, but some combinations are not available or have been reserved for special purposes. Codes with the format N11 are called service codes and are not used as area codes. These are used for such services as emergency calling (911), directory assistance (411), and travel information (511). Codes where the second and third digits are the same are called easily recognizable codes. These designate special services such as the series 800, 888, 877, etc., that are used for toll-free calling. Until recently an NPA always had an exclusive geographic boundary. As more and more prefixes were assigned to support CLECs, cellular and paging providers, and large companies that requested exclusive prefixes, NPAs were split into smaller areas and numbers assigned to the new NPA were changed. To forestall number changes, some state regulatory commissions elected to use overlay area codes. An overlay area code follows approximately, but not necessarily exactly, the same boundaries as the original NPA. Overlay area codes require the subscribers to dial 10 digits to complete local calls. In a non-overlay NPA, calls are completed with seven digits. Central office codes, also known as NXXs or prefixes, are digits 4, 5, and 6 of a 10-digit telephone number. NANPA assigns central office codes using guidelines from state and federal authorities. Several factors are leading to the exhaust of available numbers, so NXXs are assigned within strict rules, particularly where the available numbers in an area code are in danger of being exhausted. Among the factors contributing to number usage is the assignment of prefixes to entities that cannot use all the numbers. For example, many small communities have a switch that serves less than 1000 telephones and the rest of the prefix is unused. To make better use of prefixes, the industry has introduced thousands-block pooling, which subdivides the prefix into blocks of 1000 numbers. A major difference between the PSTN and an IP network is the fact that a PSTN number is associated with a physical location. Numbers can be ported or forwarded, but they are reached by a traceable path. Even with cell phones, which can roam anywhere the service provider supports, the number is associated with a switch that has a fixed location. This inflexibility is a disadvantage from a mobility standpoint, but it allows accurate dispatch of emergency vehicles for wired locations. Cellular emergency calls are a separate issue, which we discuss in Chapter 20.
Local Number Portability (LNP)
The Telecommunications Act of 1996 mandates that customers be permitted to change service providers without changing their telephone number. Within the bounds of a rate area, subscribers can change their geographic location or can change between classes of service such as from POTS to Centrex without a number change. To implement LNP, each wire line switch is identified with a 10-digit location routing number (LRN). The LRN for a particular switch is a “native” NPA-NXX that serves as a network address for that switch. Carriers query the LNP database to determine the LRN corresponding to the dialed telephone number. The originating switch routes the call to the terminating switch based on the LRN. Figure 13-2 illustrates how the process works. An LNP database serves the territory covered by each of the seven original RBOCs. After the caller dials the telephone number, the originating switch sends a query over SS7 to the LNP database through its STP. The SCP that hosts the LNP returns a message containing the LRN of the recipient switch. The originating switch sends the call to the recipient switch, which completes the call.
Access to the Local Exchange Network
Until AT&T’s divestiture in 1984, the telephone network in the United States was designed for single ownership in each exchange. In some countries it still is, butt hose countries that have deregulated long distance provide access to multiple IXCs. This section discusses the architectures of local and long distance telephone
networks, how the IXCs obtain local access, and the way IXCs sometimes bypass the local networks to provide service directly to end users.
Local Access Transport Areas (LATAs)
The terms of the agreement between AT&T and the Department of Justice prohibited the RBOCs from transporting long-distance traffic outside LATAs. The Telecommunications Act of 1996 provides for the eventual lifting of this restriction as local networks are opened to competition. At the time of this writing, the restrictions prohibiting the RBOCs from carrying inter-LATA toll have been lifted in most states, but the LATA boundaries remain. RBOCs that have been relieved of the inter-LATA restrictions provide long-distance service through a subsidiary. LATAs correspond roughly to Standard Metropolitan Statistical Areas defined by the Office of Management and Budget. Equal access requires intelligence in the class 5 office to route the call to the trunk group serving the primary IXC. Subscribers register their choice of PIC with their serving LEC. Separate PICs are provided for inter-LATA and intra-LATA traffic. IXCs select the method of accessing the LECs. They can connect to the LEC with direct trunks, or they can gain access to any exchange in the LATA through an access tandem. Every end office in the LATA, including CLEC offices, connects to the LATA tandem with direct trunk groups. Access through the tandem carries a usage charge, so IXCs use direct trunks to the end office where they are cost-effective.
Maintenance and Administrative Features
Central offices include many features to monitor the system’s health. These features enable the system to respond automatically to abnormal conditions through a local or remote maintenance and control center (MCC). The features in this section are essential for any carrier switch. Most enterprise network switches include the same features, although often to a less sophisticated degree.
Fault Detection and Correction
The central processor continually monitors all peripheral equipment to detect irregularities. When a peripheral fails to respond correctly, the processor signals an alarm condition to the MCC and switches to a duplicated element if one is provided. The MCC interfaces maintenance personnel to the fault-detecting routines of the generic program. At the MCC, the central processor communicates its actions with messages on a CRT, a printer, or both. Depending on the degree of sophistication in the program, the system may register the fault indication or may narrow the source of the fault down to a list of suspected circuits. For unattended operation the MCC transmits fault information to a control center over a data link. The processor also monitors its own operation through built-in diagnostic routines. If it detects irregularities, the on-line processor calls in the standby and goes off-line. All such actions to obtain a working configuration of equipment can be initiated manually from the MCC or from a remote center. The ultimate maintenance action, which can be caused by an inadvertently damaged database or a program loop, is a restart. A restart is usually done only manually and as a last resort because it involves total loss of calls in progress and loss of recent changes to the database.
Communications Assistance for Law Enforcement Act (CALEA)
CALEA requires all wire line, cellular, and broadband carriers to assist law enforcement personnel who are acting under court order. The act requires a carrier to ensure that its equipment, facilities, or services are capable of enabling the government to intercept wire and electronic communications. Carriers must provide access to reasonably available call-identifying information and deliver intercepted communications and information to law enforcement agencies. Circuit-switched networks have little difficulty in complying with CALEA requirements, but VoIP is another matter. Calls placed over residential broadband and calls between SIP endpoints can flow directly between endpoints in RTP packets. The soft switch controlling the packet flow does not have access to the voice packets, which makes it difficult, if not impossible, to comply with wiretapping requests. The FCC permits packet-mode providers to request exemption from CALEA requirements, but as VoIP gains popularity, it is difficult to see how a disparity between circuit-switched and packet-switched requirements can survive.
Emergency Calling
In North America, the E-911 system is designed to ensure that emergency vehicles from the correct jurisdiction are sent to an address from which a call originates, regardless of whether the caller is able to communicate with the emergency CHAPTER 13 The PSTN and Quality Requirements 231 services operator. In most jurisdictions, the LEC boundaries do not align with the boundaries of the emergency service agencies and the agencies’ boundaries do not align with one another. Furthermore, city and county boundaries are also no guide to which public safety answering point (PSAP) may handle an emergency call. Therefore, the E-911 system must have a database that correlates a calling number with the appropriate responding agency. Figure 13-3 shows the principal components in an E-911 system. Each locality has one or more central offices designated to route emergency calls to the correct PSAP. This switch is known as the selective router (SR). It may be known by another serving area connects to the SR with a trunk group for handling emergency calls. When a subscriber places a 911 call, the end office sends the voice call and the calling number to the SR. The SR looks up the emergency service number (ESN), which identifies the serving PSAP. The call is switched to the PSAP, which interrogates the 911 database for the address of the calling telephone number. The database returns the name, address, location, and the appropriate emergency responders for that address. The process of automatically displaying the caller’s number, address, and supplementary emergency information is known as automatic location identification (ALI). The 911 database is often known as the ANI/ALI database Providing accurate location information on emergency calls is a major issue for any organization that has private switches distributed over a wide area while sharing a common group of trunks. Unless other measures are taken, the host
switch location will display in the PSAP and emergency vehicles will be dispatched to the wrong address. The process of supporting private systems to the E-911 system is known as private switch automatic line identification (PS/ALI). PS/ALI identification of the source of a 911 call can be accomplished by several different methods:
A POTS line is connected to the CPE switch. The automatic route selection in the switch selects that line for 911 calls. A CAMA trunk can be connected to the serving central office. The CAMA trunk contains the calling station identity. If the PBX connects to its serving CO over PRI, the CO can receive the calling station identification and pass it to the SR. VoIP raises critical issues with respect to E-911 because the phone is mobile and the IP address has no fixed relationship to the location. The service provider maintains a default location address for the serving trunk group, but VoIP enables users to transport their phones to other jurisdictions, even to other area codes. The issues are similar to cell phones, but the solutions proposed there involve either the use of GPS or the triangulation from cell sites. GPS is technically a suitable method for VoIP, but requires an unobstructed view of at least three satellites, which is not reliable. The most practical solution relies on the fact that every phone is connected to a switch port that has a fixed geographical location. If a VoIP phone dials 911, the call controller communicates with a server that registers the physical location of the phone. The call switches to the PSAP through the SR while a gateway communicates location information through the PS/ALI process. The process for handling this is not standardized at this writing.
Essential Service and Overload Control
Switching systems are designed for traffic loads that occur on the busiest normal business days of the year. Occasionally, peaks occur that are higher than normal. Heavy calling loads can occur during unusual storms, political disorders, and catastrophes. During these peaks, the switching system may be overloaded to the point that service is delayed or denied to large numbers of users. Central offices include line load control circuitry that denies service to nonessential users so that users essential to public safety and health can continue to place calls. Nonessential users are assigned to two groups. When line load control operates, one group is denied service while the other group is permitted to dial. The two groups are periodicallyreversed to give equal access to both nonessential groups.Many local offices have network management provisions to prevent overloads. For example, dynamic overload control automatically changes routing tables to reroute traffic when the primary route is overloaded. Code conversion allows the system to block traffic temporarily to a congested central office code. This feature enables the blocked system to take recovery action without being overwhelmed by ineffective attempts from a distant central office. These provisions are circuit-related and not applicable to VoIP except in the case of gateways, which are subject to the overload conditions on their circuit side.
Telecommunications Service Priority
The Telecommunications Service Priority (TSP) Program provides national security and emergency preparedness (NS/EP) users with priority authorization of telecommunications services that are vital to coordinating and responding to crises such as hurricanes, floods, earthquakes, and other natural or human-caused disasters. During such a disaster, telecommunications service providers may become overwhelmed with restoration requests. The TSP Program provides service vendors with an FCC mandate for prioritizing service requests by identifying those services critical to NS/EP. A telecommunications service with a TSP assignment is assured of receiving full attention by the service vendor before a non-TSP service.
Trunk Maintenance Features
Local central offices have varying degrees of trunk maintenance capability. The system monitors trunk connections in progress to detect momentary interruptions or failures to connect. The system registers the failure and enters it on a trunk irregularity report, which technicians use to pattern trunk trouble. The system marks defective trunks out of service and lists them on a trunk out-of-service list. When all trunks in a carrier system fail, the system detects a carrier group alarm, marks the trunks out of service in memory, and through its alarm system reports the failure to the MCC.
Line Maintenance Features
Switching systems contain circuits to detect irregularities in station equipment and outside plant. Like trunk tests, these are made on a routine or per-call basis. On each call, many systems monitor the line for excessive external voltage (foreign EMF), which suggests cable trouble. Line insulation tests (LIT) are made routinely during low-usage periods to detect incipient trouble. The LIT progresses through lines in the office on a pre-programmed sequence and measures them for foreign voltage or low insulation resistance, which is low resistance between the tip and ring or from each side of the pair to ground. These tests detect outside plant troubles such as wet cable, and terminal, drop wire, and protector problems. Switching systems must deal with permanent signals, which are caused by a telephone receiver off hook, cable trouble, or a defective station protector. Any of these irregularities place a short circuit on the line, and the line circuit attaches the line to a register, which furnishes dial tone and prepares to accept digits. The system must be capable of detecting and dealing with receivers off hook and multiple short circuits that result from cable trouble. Such lines are marked out of service temporarily so they do not tie up common equipment in the central office. One method of resolving permanent signals is to connect the line to a series of tones and recordings such as a recording that asks the caller to hang up the line.Then after a suitable interval it may be connected to a progressively louder seriesof tones to attract the caller’s attention.
Configuration Management
When the office is initially configured, its software retains a map of equipped and spare facilities. When the office is upgraded the configuration management system informs the switch of the presence of new equipment. Daily service order activity modifies the software to add new subscribers, delete disconnected ones, or change features. The configuration management system enables technicians to enter order activity through a terminal or through file transfer. As discussed in the next section, the system samples call activity and reports traffic information such as call counts, call completions, and line, trunk, and feature usage. The system monitors CPU activity and reports grade of service measurements such as dial tone delay and common equipment usage.
Traffic-Measuring Equipment
Circuit switches are engineered based on usage. Usage information is based onthe number of times a trunk or line circuit is seized and the average holding timeof each attempt. Software registers measure the number of times the circuit isseized and elapsed time that the circuit is busy. The registers are periodicallyunloaded to a processing center for summary and analysis. Class 5 offices thathave integrated VoIP and separate VoIP gateways must also collect usageinformation toward the PSTN because it is needed to determine the bandwidth ofthe connecting trunks. Traffic-measuring equipment can provide a variety of otherdata for administering the central office. For example, database information isprovided to update the availability of vacant lines and trunks.
LOCAL CENTRAL OFFICE SERVICE FEATURES
All central offices provide certain basic features. This section discusses some of themost common features and explains their purpose.
Automatic Number Identification (ANI) and AutomaticMessage Accounting (AMA)
ANI automatically identifies the calling party for billing purposes. On POTS linesthe number is identified from the cable pair. In ISDN and VoIP lines call setupmessages identify the calling number. AMA equipment interrogates ANI equipmentto determine the identity of the calling party. AMA equipment is classifiedas local AMA (LAMA), in which call collection is done in the local central office,or centralized AMA (CAMA). A CAMA office connects calling subscribers toa center where call details are recorded for all subtending central offices. AMAequipment records call details at each stage of a connection. The calling and calledparty numbers are registered initially. An answer entry registers the time of connection,and the terminating entry registers the time of disconnect. The storagemedium is tape, disk, or solid-state memory. Call records are sent to distant dataprocessing centers over a datalink.
Local Measured Service (LMS)
Many telephone companies base their local service rates on usage. Flat ratecalling is often available, with LMS as an optional service class. With the LMSclass of service, calls inside the local calling area are billed by the number of calls,time of day, duration of call, and distance between parties. The method is similarto long distance billing except that calls may be bulk-billed with no individualcall detail.
Centrex
LECs furnish a PBX-like service through equipment located in the central office.The switching equipment is a partition in the end office called a Centrex commonblock. Centrex features allow direct inward dialing (DID) to a telephone numberand direct outward dialing (DOD) from a number. For calls into the Centrex, theservice is equivalent to individual line service. Outgoing calls require users to dialan access code such as 9, after which the central office returns the second dial tone.Stations within a common block can have an extended suite of features.Internal calls can be abbreviated to four or five digits instead of the seven digitsrequired for ordinary calls. Centrex users have access to all of the calling featuresof the central office, which are listed in a later section, as well as most of the featuresof a PBX such as call pickup, call hold, and class-of-service restrictions. Anattendant console located on the customer’s premises links to the central officeover a separate circuit. These features are discussed in Chapter 24, CustomerPremise Switching System Features.Centrex brings several advantages to the customer. Reliability is high since theLEC provides backup power and the stability of a switch that is more reliable thanmost PBXs. The customer avoids the expense of powering the switching equipment.The LEC handles problems of growth and obsolescence and the customer is relievedof many administrative tasks associated with switch ownership. Amajor advantageis the ability to link telephones in multiple locations with a single switch.Offsetting this to some degree is the difficulty of feature activation in analogCentrex. Telephone sets are POTS sets operating over cable pairs and the user activatesfeatures with a dial code. For example, call pickup might be *8. Users tendto forget the codes, and the features are consequently under-utilized. Some switchmanufacturers offer digital Centrex with TDM feature telephones similar to thoseprovided with PBXs. Feature telephones have displays, which improves usability,and functions such as call pickup and transfer are activated by pushing a button.Digital Centrex is limited, however, by the distance from the central office. Featuretelephones have a range limitation much less than POTS phones and will notwork outside the home central office.IP telephony offers the possibility of rejuvenating the LECs’ Centrex offerings.A media gateway (MG) can be placed on the subscriber’s premises. If the subscriberhas multiple locations, a separate MG can be placed on each, and the entirecomplex can be served from a single controller. This technology is described inmore detail in Chapter 16. IP telephones overcome the range restrictions of TDMtelephones and offer the benefits of expanded displays.
Routing to Service Facilities
All central offices provide access to service facilities such as operator and repairservice. All local switching systems also provide access to call progress tones suchas busy, reorder, vacant number tone, etc., and recorded announcements for interceptednumbers and permanent signals. Some systems also provide access to localtesting facilities.
Call-Processing Features
Local central offices provide a variety of service features that enhance call processing.The user signals the central office equipment with a momentary on-hookflash on a POTS line or a data message on IP or ISDN. On a POTS line the systemresponds to the flash with stutter dial tone to show that it is ready to receiveinstructions. Many call-processing features that once were reserved for businessuse are now becoming popular with residential subscribers. As residential usersincreasingly subscribe to second lines and custom calling features, such servicesas call pickup and do-not-disturb are becoming popular. The following is a briefdescription of the principal features provided by most end offices in addition tothe CLASS features discussed in Chapter 12:Call forwarding enables the user to forward incoming calls to anothertelephone number. While this feature is activated, calls to the user’snumber route automatically to the target telephone number. When the userof a forwarded line picks up the telephone to place a call, the system sendsstutter dial tone as a reminder that the line is forwarded.Call forward remote access permits the user to activate or deactivate callforwarding from a remote location.Call transfer allows the user to add a third party to a call as with three-waycalling. One party can then hang up, leaving the other two parties inconversation.Call waiting sends a tone to signal a user on a busy line of anotherincoming call. The user can place the original call on hold and talk to thewaiting call by pressing the switch hook. Some LECs offer “whisper” callwaiting so the other party is not aware of the interrupting call. A cancelcall-waiting feature enables users to disable the service temporarily to avoidhaving a modem call interrupted by call waiting.Distinctive ringing allows the LEC to assign as many as four separatedirectory numbers to a single line. By using an adapter that responds to theunique ringing pattern, the user can route calls to a separate telephone, faxmachine, modem, or other analog device. Most fax machines respond tothe distinctive ring without an adapter.Gab line enables callers to dial a number to which multiple callers can beconnected simultaneously. Some LECs use the gab line, which is popularwith teenagers, as a revenue-generating feature.Hot line automatically places a call to a directory number when the handsetis lifted.Multiline hunt connects incoming calls to the first idle line in a group.Speed calling enables the user to dial other numbers with a one- or two-digitnumber. Most telephones also provide speed calling without involving thecentral office.Three-way calling allows the user to add a third party to the conversation bymomentarily holding the first party while a third number is dialed.Voice mail allows callers to leave messages when the phone is busy orunanswered and alerts the user to waiting messages.Warm line is similar to hot line except that the predetermined number is notdialed until after an elapsed time. The service is useful for handicappedpeople who may be unable, at times, to dial the phone.
Friday, December 3, 2010
Reading
1. read from begining to end.
2. what about this text? understanding in general.
3. to find main sentence.
4. see complex sentence.
5. to make know words
6. to examine carefully read and to see no knows words.
7. starting to translate.
8. choose appropicate words from dictionary.
9. find main idea of sentence by linking words understanding.
10. to join translated sentences.
11. compare the translated sentences another with sentences.
12. to revise to make a mistakes.
13. to correct a mistakes.
14. read the sentences and check sentences idea.
15. to put in order writing from begining.
2. what about this text? understanding in general.
3. to find main sentence.
4. see complex sentence.
5. to make know words
6. to examine carefully read and to see no knows words.
7. starting to translate.
8. choose appropicate words from dictionary.
9. find main idea of sentence by linking words understanding.
10. to join translated sentences.
11. compare the translated sentences another with sentences.
12. to revise to make a mistakes.
13. to correct a mistakes.
14. read the sentences and check sentences idea.
15. to put in order writing from begining.
Application
1.PERSONAL DATA
1. LAST NAME (as in passport) Myangan
2. FIRST NAME (as in passport) Narangaraw
3. PASSPORT NUMBER E0370152
4. HOME ADDRESS Bayanzurkh district, 10th khoroo,Apt#1435 Ulaanbaatar city, Mongolia
5a. PHONE 976-99234599
5b. CONTACT NUMBER BEIJING 65014433
6. CITIZENSHIP Mongolian
7a. COUNTRY OF BIRTH Mongolia
7b. DATE OF BIRTH 1989/July/15
8. FEMALE Yes
9. MARITAL STATUS Single
2.OCCUPATION
10. CURRENT OCCUPATION Secretary
PHONE 976-99234599
11. COMPANY’S NAME TETRAEDR GROUP CO.,1td
PHONE 976-99194203
12. BUSINESS ADDRESS Bayangol district, 6th khoroo, Building #-3-40 (Land organization center)
13. MONTHLY INCOME MNT 150000
14. OTHER INCOME (source and amount)
15. PORT AND DATE OF ENTRY INTO MEXICO by plane, 2006/Sep/13
16. PURPOSE OF YOUR TRIP Tourist
17a. MAIN DESTINATION AND
LENGTH OF STAY IN MEXICO In Mexico city, 3 weeks
17b. ADDRESS FOR BUSINESS VISA
18. IF VISITING THE NORTH BORDER OF MEXICO INDICATE CITIES
PURPOSE OF VISIT
19. IF VISITING THE SOUTH BORDER OF MEXICO INDICATE CITIES
PURPOSE OF VISIT
20. HAVE YOU EVER APPLIED FOR A MEXICAN VISA BEFORE
WHERE NO
I declare that all information herein is true. I authorize the Mexican Government to conduct its verification.
I am aware that the final admission into Mexico must be approved by sanitary and immigration authorities at the port of entry and that issuance of a visa by Mexican Consulate does not guarantee the admission.
I understand that sanitary and immigration officials have the right to verify my compliance with all legal requirements.
2010 december
Applicant signature: M.Narangaraw
1. LAST NAME (as in passport) Myangan
2. FIRST NAME (as in passport) Narangaraw
3. PASSPORT NUMBER E0370152
4. HOME ADDRESS Bayanzurkh district, 10th khoroo,Apt#1435 Ulaanbaatar city, Mongolia
5a. PHONE 976-99234599
5b. CONTACT NUMBER BEIJING 65014433
6. CITIZENSHIP Mongolian
7a. COUNTRY OF BIRTH Mongolia
7b. DATE OF BIRTH 1989/July/15
8. FEMALE Yes
9. MARITAL STATUS Single
2.OCCUPATION
10. CURRENT OCCUPATION Secretary
PHONE 976-99234599
11. COMPANY’S NAME TETRAEDR GROUP CO.,1td
PHONE 976-99194203
12. BUSINESS ADDRESS Bayangol district, 6th khoroo, Building #-3-40 (Land organization center)
13. MONTHLY INCOME MNT 150000
14. OTHER INCOME (source and amount)
15. PORT AND DATE OF ENTRY INTO MEXICO by plane, 2006/Sep/13
16. PURPOSE OF YOUR TRIP Tourist
17a. MAIN DESTINATION AND
LENGTH OF STAY IN MEXICO In Mexico city, 3 weeks
17b. ADDRESS FOR BUSINESS VISA
18. IF VISITING THE NORTH BORDER OF MEXICO INDICATE CITIES
PURPOSE OF VISIT
19. IF VISITING THE SOUTH BORDER OF MEXICO INDICATE CITIES
PURPOSE OF VISIT
20. HAVE YOU EVER APPLIED FOR A MEXICAN VISA BEFORE
WHERE NO
I declare that all information herein is true. I authorize the Mexican Government to conduct its verification.
I am aware that the final admission into Mexico must be approved by sanitary and immigration authorities at the port of entry and that issuance of a visa by Mexican Consulate does not guarantee the admission.
I understand that sanitary and immigration officials have the right to verify my compliance with all legal requirements.
2010 december
Applicant signature: M.Narangaraw
Essay
These topics say about me In the world, million people live together, but they are all different. So they talk about different side of one thing, and me. I am introducing by my opinion of success, why people go to University? and television. In my opinion hard work is the main thing that defines success, but in most cases luck also plays a very important role. So I think first we I need talk about success. Someone says: when people succeed, it is because of hard work. Luck has nothing to do with success. In my opinion, I agree that success need hard work, but sometimes luck is important too. As the old saying: no pains, no gains. Success mainly depends on hard work. When we talk about some famous people, we all think they are respectable, because we know, at the back of their success; there is how much hard work. For example, Tomas Addison, one of the most famous inventors in last century, spent most of his time in his lab. He often loses in his work and forgets his family and even sleeping or eating. But people all of the world respect him and remember he for ever, his endeavor bring people a lot of happiness and convenience. If Addison just sits in his home waiting for luck or magic, never will he succeed.Albert Einstein has said that the genius is 99 percent sweeter plus 1 percent luck. Although luck is secondary, we cannot omit it. In fact, in some extent, luck also plays an important role. Each people must have heard the story of an apple and Newton, the apple is Newton`s luck, it`s the God`s gift. Without that apple, may be Newton must spend more time to think and think. May be in our life, people have this kind of experience. For example, when you are working on a mathematics problem, you try and try but cannot get the answer. May be suddenly sometimes, you will think of something or find way, “aha”, the problem is solved. I would like to state that one`s life is what one makes out of it. Success is never a short instantly achieved path. It needs lots of hard work, determination and blessings. And success is always there for such people. So I would suggest to all the people younger to me to believe that hard work done today shall be paid back to you in near future.Any opinion of only emphasizing on hard work or luck is impartial. Hard work is main factor; luck can accelerate one`s success. So both hard work and luck are important. Finally, how they help your work or university.Nowadays, more and more young people attend the universities for different reasons. According to the survey, the main goal of what most of them do so is for career preparation. I think there are basically two main reasons: One is for a degree, which is important in finding a job; another is for knowledge that we acquire for the better understanding of the whole world and ourselves. To get a degree is a direct aim as well as a result to go to college. No one would be happy with four years hard work without a diploma. In the competitive job market, a degree is a very important factor in finding a good job. Admittedly, a higher degree does not mean that you have a higher capability or have abundant knowledge, it merely means your education background, but which is most employers wanted. Besides, your salary is related with your degree. In general, people possess a college diploma will earn twice or more income than those who just finish their high school. So, if you want to live a better life than the average, you have to attend college.Of course, another important reason, and I think it should be a primary reason for attending college is to acquire knowledge. Since universities are the cradle of many invents and discoveries in science and technology, people attend a university can expand their knowledge about history, society, culture, as well as the latest science development. To pursue knowledge is man`s nature, and to go to a university is a best way to do it. In sum, whether people attend college for career preparation or for their interests in knowledge, the experience in a university or college is important and unforgettable in one`s life. My university give me much knowledge and skills.Television is undoubtedly one of the most powerful means of communication in the history of humankind, rivaled only by such other forms of communication as the Internet, the telephone, movies, and, of course, simple, low-tech speech. Television, with its wide availability and rich media with image and sound, is difficult to ignore and even seductive in its appeal. Television is as much a part of our lives as are our meals, work, or school; studies consistently show that the average child spends almost as much time watching television as she does in school. Furthermore, because television is so rich in its media, it often requires our full attention or is more attraction to us than are our daily lives. Naturally, the more time one spends watching television, the less time she has with her family and friends. Thus, we can clearly see why some have claimed that television has been harmful for communication among family and friends. However, I believe that, while television has been somewhat harmful in its effects, it has hardly "destroyed" communication among family and friends for most people, although for some, this may be true.
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