Telecommunications Management 273-436/635

1. Telecommunications Management273-436/635 Lecture 7: Communication Networks - Part 3: WAN transmission services

2. Wide area network service alternatives • Dedicated circuit (leased line) services • Switched circuit services Grant

3. Wide area network service alternatives Dedicated circuit (leased line) services • Digital data services • T Carrier Circuits • SONET/SDH Grant

4. Wide area network service alternatives Switched circuit services • X.25 • Narrowband ISDN • Frame relay • Asynchronous transfer mode (ATM) • Switched Multimegabit Data Services (SMDS) • Broadband ISDN Grant

5. Digital data services • Digital carrier systems permit the transmission of voice data and video signals of over high capacity transmission links such as • wire pairs, coaxial cable, optical fiber, and microwave. • Digital transmission services use digital signaling units rather than modems. • Digital carrier systems use synchronous time division multiplexing techniques for transmitting signals. • Signals can be transmitted through channel structures of different capacities. • North American and International signaling standards have been developed. Grant

6. North American and International Digital Carrier Standards Grant

7. T Carrier Circuits • is a special form of digital services. • are leased circuits with wide range of transmission capacities. • is the North American telephone industry standard for interconnecting digital communication systems. • is a hierarchy of digital transmission and multiplexing standards designated T-1 to T-4. • correspond to the digital services standard DS-1 to DS-4. Grant

8. T Carrier Circuits Grant

9. T-1 Circuits • The T-1 facility is widely used by large organizations to expand their communications capabilities and to control costs. • The facilities can be used for a number of applications including: • Private voice networks • Private data networks • Video teleconferencing • High speed digital facsimile • Internet access Grant

10. SONET/SDH • SONET (synchronous optical network) is the optical transmission interface developed by Bellcore and standardized by ANSI. • An equivalent standard Synchronous digital hierarchy (SDH) was adopted by the ITU-T Grant

11. SONET/SDH Grant

12. X.25 • This is a packet switching standard developed by the ITU • It specifies the interface between the host system and the packet switching network. • Functionally, X.25 is specified at three levels: • physical level • link level • packet level Grant

13. X.25 - physical level • The physical level is concerned with the physical interface between the communicating devices (computer, terminal, workstation) and the packet switching node. Grant

14. X.25 - link level • The link level provides for the reliable transfer of data across the physical link, by transmitting data in a sequence of frames. • It uses the link standard referred to as LAPB (link access protocol - balanced) which is a subset of High-level Data Link Control (HDLC) protocol. Grant

15. X.25 - packet level • The packet level provides the logical connection between two subscribers to the network. • This is usually referred to as the external virtual-circuit. Grant

16. User data and X.25 protocol Grant

17. Narrowband ISDN • ISDN is both a concept and an application. • The concept focuses on the development of a truly digital network that will allow the transmission and processing of all data types. • ISDN has been manifested in a variety of applications around the world. • It is intended to be a worldwide telecommunications network that replaces the existing public network. • Implementations and use of ISDN technology is not as widespread as anticipated but work is continuing on the development of the technology and the standards associated with it. Grant

18. ISDN Network Architecture • ISDN has the following specification: • a physical connection for subscribers • a digital link from the subscriber to the network • ISDN-specific features for the network switching office • The common physical interface allows the connection of a variety of equipment to the network including telephones, individual workstations, PBXs, LANs, etc. • The type of connection and service is defined by the protocols used Grant

19. ISDN Network Architecture Grant

20. ISDN Transmission structure ISDN transmission has the following structure: • B channel: 64 kbps • D channel: 16 or 64 kbps • H channel: 384, 1536, or 1920 kbps. Grant

21. ISDN Transmission structure B channel: • This is the basic user channel which can carry digitized voice, digital data or a mixture of other types of traffic. • Four kinds of connections are possible: • Circuit-switched - switched digital service • Packet-switched - packet switching service such as X.25 • Frame mode - Frame relay • Semi-permanent - similar to a leased line. Grant

22. ISDN Transmission structure D channel: This has two purposes: • For control messages such as acknowledgements, call set up and termination and other services such as caller identification. • Packet switching, low speed data transmission such as videotex, teletex and for telemetry services. Grant

23. ISDN Transmission structure H channel: • These are provided to users who want to transmit data at higher bit rates. • The user may configure the channel to suit its own needs. • Examples of such uses are fast facsimile. video, high-speed data, high quality audio. Grant

24. ISDN Service structure Basic access service • consists of two full-duplex 64 kbps B channels and a full duplex 16-kbps D channel. • is actually provided at 192 kbps. This is to take into account transmission overhead requirements. • are targeted at small businesses and residential subscribers. Grant

25. ISDN Service structure Primary access service • is typically offered to large commercial concerns that have high transmission requirement. • configuration depends on the digital transmission hierarchies being used in the country. • In the USA, Canada and Japan primary access services are configured to be transmitted at speeds of up to 1.544 mbps. • In Europe they are provided at speeds of up to 2.048 mbps. Grant

26. ISDN Service structure Primary access service • In the USA/Canada/Japan the primary rate service consists of 23 B channels of 64 kbps each and 1 D channel of 64 kbps. • In Europe the equivalent service is provided using 30 64 kbps B channels and 1 64 kbps D channel. Grant

27. Conceptual view of ISDN Connection Grant

28. Frame Relay • Frame relay is a newer form of packet switching technology that transmits data faster than X.25. • X.25 transmission includes considerable error controlling overhead with each packet transmitted. • This reduces the data transmission capacity and speed of transmission. • Modern digital technologies are less prone to transmission errors. • Therefore the large error correcting overhead carried by the X.25 frame is no longer necessary. • Frame relay is designed to eliminate much of this overhead. Grant

29. Frame Relay Transmission • With X.25 error checking is done at each node on the network between the source and the destination. • In frame relay transmission the acknowledgement is sent only by the destination node. • The advantage of frame relay lies in the streamlining of the communications process. • It requires less protocol functionality at the user-network interface. • Reduced internal network processing leads to higher throughput and less delay. Grant

30. X.25 packet network C B D E A Grant

31. Frame relay packet network C B D E A Grant

32. Asynchronous Transfer Mode (ATM) • ATM (also called cell relay) is similar to frame relay, except that it is more streamlined and can transmit data at much higher speeds. • ATM is a packet switched service and like frame relay does not do error control at intermediate nodes in the network. • Error control takes place at the source and destination. Grant

33. Asynchronous Transfer Mode (ATM) ATM differ from frame relay in three important ways. • 1. ATM uses fixed length packets of 53 bytes (5 bytes for overhead and 48 bytes for user data) called cells. • This makes it more suitable for voice transmission which cannot tolerate much delay. • The small fixed length packets simplifies routing making it possible to do this using the hardware. Grant

34. Asynchronous Transfer Mode (ATM) • 2. ATM is scaleable. • Basic ATM circuits can be multiplexed into much faster ATM circuits. • ATM circuits provide the same data rates as SONET. • 3. ATM provides forward error correction in the header that minimizes the number of packets that are discarded due to errors. Grant

35. Asynchronous Transfer Mode (ATM) • The logical connections in ATM is the virtual channel • It is the basic unit of switching in an ATM network. • Virtual channels with the same end points can be bundled together to form a virtual path. • This allows all the cells flowing through the same virtual path to be switched together. • This simplifies the network architecture, increases the efficiency of the network, improves performance, and reduces processing and connection setup times. Grant

36. Asynchronous Transfer Mode (ATM) Grant

37. Switched Multimegabit Data Services (SMDS) • was originally developed by Bellcore on behalf of the seven regional Bell operating companies in the US to serve the metropolitan area network market. • is essentially a switched version of the T carrier and SONET services. • The current specification of SMDS provides for user access at DS-1 (1.544 Mbps) and DS-3 (44.376 Mbps). • The primary advantage of SMDS is that it is switched. • Instead of a company leasing six T-1 lines to handle its communication between six sites it can use one or two. Grant

38. Broadband ISDN • Broadband ISDN is being developed to cater for the requirement to transmit high volumes of voice, data and video traffic. • In the future, such services such as video-on-demand and other interactive services will require transmission circuits with large bandwidths. • B-ISDN takes advantage of many of the technological developments in switched and non-switched services. • It is essentially a switched version of SONET. Grant

39. Broadband ISDN service structure Three levels: • A full-duplex 155.52 Mbps service • An asymmetrical service with two simplex channels, one from the subscriber at 155.52 Mbps and one from the host at 622.08 Mbps. • A full-duplex service at 622.08 Mbps Grant

40. Broadband ISDN service structure • The full-duplex services are intended for normal bi-directional information exchange while the asymmetrical service will support digital broadcast television. • Broadband ISDN architecture will support current narrowband services as well as the new services. • This protects the users’ narrowband investments and facilitates migration to broadband services. Grant