1 / 51

Chapter 10

Chapter 10. ISDN and DSL. 1 PSTN Today. The overview of the modern public switched telecommunications network is presented in Figure ( see next slide ).

arthur-harris
Download Presentation

Chapter 10

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 10 ISDN and DSL Bahman R. Alyaei

  2. 1 PSTN Today • The overview of the modern public switched telecommunications network is presented in Figure (see next slide). • The structure and functionality of the network are only reviewed here because most of the elements in the figure are discussed in previous lectures and some new topics such as ISDN and ADSL will be explained in this lecture. Bahman R. Alyaei

  3. Overview of the public switched telecommunications network Bahman R. Alyaei

  4. Continue… • Figure presents a simplified diagram of a Regional or National PSTN that has connections to the Global Internet and PSTN. • The Network contains the Public Land Mobile Network (PLMN), which provides Wireless Access for Cellular Subscribers and is connected to the PSTN/ISDN Network at the Trunk Exchange Level. Bahman R. Alyaei

  5. Continue… • Internet users are connected to the Global Internet via the hosts of their ISPs. • Networks of NationalISPs are connected and this interconnection is extended to the networks of ISPs of neighboring countries, and these networks together make up the Global Internet. • Figure also shows two main methods for Accessing the Internet. Bahman R. Alyaei

  6. Continue… • A Telephone or ISDN Network is used for dial-up connections and ADSL provides permanent higher rateInternet Service. • Digital PABX is connected to a Local Exchange with a 1,544/2,048 kbpsDigital Line that has the capacity of 23/30 Channels. • For Data Communication via an Analog Network or Digital Network with Analog Subscriber Interfaces, a Modem is required. Bahman R. Alyaei

  7. Continue… • Also in the Figure, one office site of a company has high-data-rate Access to its ISP. • All employees have access to the Internet via the Company’s Private LAN. • Leased Lines, which interconnect two offices in the Figure, are often the most economical solution for high-data-rate circuits that are needed, for example, for LAN interconnections. Bahman R. Alyaei

  8. 2 The Internet • The name ‘Internet’ is derived from the term ‘inter-networking’. • Each of these networks is based on a special form of switching designed specifically for handling data, using a standard way of packaging and addressing the data: the so-called Internet Protocol (IP). • The subject of IP and Data Networks is covered in detail in (Computer Networks). Bahman R. Alyaei

  9. Continue… • A huge range of applications by Business and ResidentialUsers now exploits the Internet. • The most common of these applications are e-mails and other peer-to-peer applications such as Gaming, InformationGathering from Web Pages, and Internet Shopping. • Figure in the next slide presents a simplified schematic diagram of the Internet. Bahman R. Alyaei

  10. The Internet Concept Bahman R. Alyaei

  11. Continue… • Each of the component networks in the Internet constellation are owned and operated by Internet Service Providers (ISPs). • Users and Providers of information (in the form of Web Pages) subscribe to an ISP for their Internet service. • Users access their ISPsover Links provided by one of a range of networks such as PSTN, ISDN, Mobile, Leased Line, ADSL/broadband and Cable TV (CATV). Bahman R. Alyaei

  12. Continue… • ISPNetworks usually comprise a number of IP switching units known as ‘Routers’ located at various points in the country and linked by high capacity transmission circuits leased from a network operator (PSTN), so-called Leased Lines or Private Circuits. • ISP Networks link with one another in order to obtain full interconnectivity between users. Bahman R. Alyaei

  13. Continue… • The smaller ones connect to larger ISPs. • The larger in turn connect to the largest ISPs, those with a National or International coverage–the ‘Backbone ISPs’. • The interconnection of the largest ISPs in the United Kingdom is achieved by Jumpering cables between each of their Routers collocated in CentralBuildings, known as Internet Exchange (INX). Bahman R. Alyaei

  14. Continue… • The largest is located in the City of London: ‘Telehouse’. • This provides participants with full interconnectivity within the UK and to links going to the United States, Asia and Mainland Europe. Bahman R. Alyaei

  15. 2 Access to the Internet • Internet can be access from: • Dial-up via the PSTN • Over ISDN. • Over ADSL. • Over a Cable Modem. • Leased line access. Bahman R. Alyaei

  16. 3 Internet Access Through The Dial-up Network (PSTN) • The original and still a common way of Accessing the Internet is through a Telephone Call, thus taking advantage of the full interconnectivity of the PSTN. • The procedure is in two stages: • The first stage is a Telephony Call to the ISP. • The second stage is a Data Transfer session between the Computer and the Internet via the ISP. Bahman R. Alyaei

  17. Continue… Dial-Up Access to the Internet Bahman R. Alyaei

  18. Continue… • For the first stage, a standard call is set up from the Computer, which is connected to a Telephone Line in the normal way. • A ModemCard in the Computer makes it behave like a Telephone Instrument, providing the equivalent of lifting the receiver (‘off-hook’), detecting dial tone, and sending out the dialed digit tones. • The Modem also enables Data to be passed over the standard LocalTelephone Line. Bahman R. Alyaei

  19. Local-access network and digital local exchange site Bahman R. Alyaei

  20. Continue… • The ISP is connected to the PSTN over a standard Local Line or by an ISDN (Integrated Services Digital Network) Local Line, but in either case standard Telephone Numbers are allocated. • Once through to the ISP the second stage begins, the call connection through the PSTN now just acts as a two-waypath between the Computer and the ISP. Bahman R. Alyaei

  21. Continue… • An interchange of Data occurs so that the ISP can verify the identity of the user and establish a data session to the Internet. • IP is used between the Computer and the ISP’s equipment (an IP router), passing over the transparent PSTN call connection path. • The ISP then routes the Data between the Computer and the Internet for the duration of the session. Bahman R. Alyaei

  22. Continue… • When the user indicates that the session is over, the Modem Card in the Computer creates the equivalent of the ‘on-hook’ condition so that the Telephone Exchange clears the call to the ISP in the normal way. Bahman R. Alyaei

  23. 3.1 Modem • It is a contraction of the words Modulator and Demodulator. • The Modem converts a computer’s Digital Bit Stream into a signal (ASK, PSK, FSK) suitable for transmission over the Telephone Line and vice versa. • Modems are available in two forms: • Internal Modems. • External Modems. Bahman R. Alyaei

  24. Continue… Typical direct-connection installation Bahman R. Alyaei

  25. Continue… Analog- ASK, PSK, FSK Internet service over PSTN the dial-up network Bahman R. Alyaei

  26. 3.2 Modem Transmission Modes • Three transmission modes of operation used by modems: • Simplex: • Data are received or sent in one direction. • Half-Duplex: • In which the communication channel is shared between sending and receiving stations in a manner that receiving or transmission of the data is performed alternatively. Bahman R. Alyaei

  27. Continue… • Full-Duplex: • In which transmission receiving of the data is performed simultaneously. • In two-wire telephone circuit, this is performed using FDM. Bahman R. Alyaei

  28. 4 Internet Access Over ISDN • ISDN stands for Integrated Services Digital Network. • It is a design for a completely Digital Telephone and Telecom Networks. • It is designed to carry Voice, Data, Images, and Slow Scan Video. • The concept of the ISDN is that the Network of Digital Telephony Exchanges is enhanced to allow the Switching of Data Calls. Bahman R. Alyaei

  29. Continue… • Accessing the Internet via ISDN is essentially the same as for the PSTN, except that the Interface of the ISDNLine to the Computer is Digital rather than Analogue, so the Modem Card does not convert the Computer output to Analogue and consequently higher speeds up to 64 kbps or even 128 kbps are possible. • The ISDN Modem is also referred to as Terminal Adapter (TA) or Digital Modem. Bahman R. Alyaei

  30. Local-access network and digital local exchange site Bahman R. Alyaei

  31. Continue… Dial-up and ISDN Modem Bahman R. Alyaei

  32. Continue… • Two forms of internationally standardized ISDN are available: • Basic Rate Interface (BRI) ISDN. • Primary Rate Interface (PRI) ISDN. • In each of the above ISDN services, there are two types of Channels: • Bearer Channels (B-Channels) for Data Transmission purposes. • Delta Channel (D-Channel) for Signaling purposes. Bahman R. Alyaei

  33. 4.1.1 Basic Rate Interface ISDN • It consists of the following channels: • Two 64 kbpsB-Channels that is equivalent to two Time Slots. • One16 kbps Signaling orD-Channel. • The BRIISDN is designated “2B + D”. • The User Rate is 144 kbpsRb = 2 × 64 kbps + 16 kbps = 144 kbps and is normally carried over a Single Copper Pair. Bahman R. Alyaei

  34. 4.1.2 Primary Rate Interface ISDN • It consists of the following channels: • 30 × 64 kbps B-Channels. • One 64 kbps signaling D-Channel. • This PRI ISDN is designated ‘30B + D’. • The user rate is 2 MbpsRb = 30 x 64 kbps + 64 kbps = 2 Mbps and this is carried over an Optical Fiber or Microwave Radio Link. Bahman R. Alyaei

  35. 4.2 ISDN Exchanges • The main task of the Telephone or ISDN exchange is to build up a PhysicalConnection between two parties. • In practice, most PSTNExchanges today are combined ISDN and Telephony Systems. • When a subscriber wishes to have Basic Rate ISDN Service the existing Copper Line is shifted from the Analogue Line Card to an ISDN Line Card on the same Concentrator Switch-Block (requiring a Re-jumpering at the MDF). Bahman R. Alyaei

  36. ISDN Lines on a Digital Local Exchange Bahman R. Alyaei

  37. Continue… • A Network Terminating Unit (NTU) is installed at the subscriber’s premises to terminate the Digital Line System and present a set of Sockets for the subscriber’s Data and Telephony Terminals. • There is usually a Terminal Adaptor (ISDNModem) associated with the NTU to provide a conversion of the AnalogueTelephone to Digital so that it can use the ISDNLine. Bahman R. Alyaei

  38. Continue… • In the case of PRI ISDN service the termination at the SubscriberConcentrator is at the 2 Mbps level, requiring an appropriate Digital Line Termination–as provided for Digital PABX. • Figure also shows the arrangement for ISDN, with an indication of how the BORSCHT functions are spread between the ISDN Line Card and the NTU on the subscriber’s premises, instead of being solely in the Line Card as for Analogue Subscriber Lines. Bahman R. Alyaei

  39. Continue… • The acronym of BORSCHT is: • Battery: -48 V dc power supply. • Overload: for protecting the switch. • Ringing current. • Supervision. • Codec: ADC and DAC. • Hybrid: 2-to-4 wire conversion. • Test: testing the end point of the local loop. Bahman R. Alyaei

  40. Continue… • Non-Data Calls from ISDN subscribers are routed through the Switch Network as for Telephony with each B-Channel being treated separately. • Data Calls are also normally handled on a single B-Channel basis, with the required extra features indicated through the call set-up across the network through the ISDN signaling system. • ISDN Lines are given standard Telephony Numbers. Bahman R. Alyaei

  41. 4.3 ISDN Waveform • The Line Coding technique used by the BRI ISDN is called 2B1Q (2 Binary 1 Quarternary). Bahman R. Alyaei

  42. 4 Over ADSL • The use of ADSL enables a high-speed data service to be carried in addition to telephony over the copper pair of a standard telephone line. • Figure on the next slide shows how the Internet is accessed via ADSL. • At the subscriber premises, the internal telephone line and the computer are separately connected to the splitter within the ADSL termination equipment. Bahman R. Alyaei

  43. Access to the Internet via ADSL Bahman R. Alyaei

  44. Continue… • This device directs the computer output to the high speed data channel on the line, and similarly in the reverse direction; while enabling the telephone signal to be carried in the normal way on the local line. • The ADSL splitter and terminating equipment located at the exchange similarly separate the telephony and high speed data signal. • The telephony is carried over a copper pair to the input of the local exchange switch. Bahman R. Alyaei

  45. Continue… • The data stream carrying the Internet-bound traffic is connected to the DSLAM (digital subscriber line access multiplexer) equipment. • DSLAM combines the data from many such lines onto a high speed transmission link to a data network. • This network carries the Internet-bound data in an efficient way, interleaving it with data streams from other sources, to the connecting points of the various ISPs in the country. • A corresponding process applies in the reverse direction from the Internet to the computer. Bahman R. Alyaei

  46. 5 Over A Cable Modem • Cable TV Networks are able to provide a high speed data link to an ISP over one of the Spare TV Channels carried through the Network. • The technique requires a so-called Cable Modem, which converts the output of the Computer into a signal compatible with the TV distribution system. • Figure on the next slide shows how the Internet is accessed via Cable Modem. Bahman R. Alyaei

  47. Access to the Internet via Cable Modem Bahman R. Alyaei

  48. Continue… • The computer is connected to a Splitter-like device which segregates the received TV signal from the Broadband Data Stream at the subscriber’s premises, where both are carried as a composite TV signal over the Coaxial Cable from the Street Cabinet. • The Street Cabinet therefore performs a similar aggregating function as the DSLAM. Bahman R. Alyaei

  49. 6 Leased Line Access • The private-circuit service network provides point-to-point un-switched links, known as ‘private circuits’ or ‘leased lines’, between business premises (e.g. offices, factories or warehouses). • Although the private-circuit service provided to the business customers is non-switched, the network may use automatic digital cross-connection units (DXC). • See the figure on the next slide. Bahman R. Alyaei

  50. Continue… A Private-Circuit Services Network (Leased Line Access) Bahman R. Alyaei

More Related