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Chapter Objectives

Chapter Objectives. At the end of this chapter you will be able to: Describe standardisation in the data communications area Describe the following technologies: X.25, Frame Relay, ISDN, PPP, Modem, XDSL and ATM Analyse the protocols of the X.25, Frame Relay and ISDN technologies.

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Chapter Objectives

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  1. Chapter Objectives At the end of this chapter you will be able to: • Describe standardisation in the data communications area • Describe the following technologies: X.25, Frame Relay, ISDN, PPP, Modem, XDSL and ATM • Analyse the protocols of the X.25, Frame Relay and ISDN technologies

  2. Leased Line and Dial-Up • Leased Line • With a leased line connection, a data user has a permanent dedicated transmission path which can be end to end across the network, locally, nationally or internationally. • Dial-up • This method is used for modem to modem data communication over the Public Switched Telephone Network (PSTN). Both the source and destination must have compatible modems

  3. Circuit Switching and Packet Switching • Circuit Switching • In a circuit switched network, a dedicated communications path is established between two terminals through the nodes of the network and for information transfer • Packet Switching • In this case it is not necessary to dedicate transmission capacity along a path through the network. Rather, data is sent out in a sequence of small chunks, called packets. Each packet is passed through the network from node to node along some path leading from the source to the destination

  4. HDLC Variations HDLC Subset Uses NRM Multipoint networks that typically use SDLC LAP Early X.25 implementations LAPB Current X.25 implementations LAPD ISDN D channel and frame relay LAPM Error-correcting modems (specified as part of V.42)

  5. X.25 Network PSE Modem X.25 Port Modem X.75 port to other packet switching networks X.28 Port Modem Modem PSE Modem X.25 Port Modem X.28 Port Modem Modem Dumb Terminal

  6. User Process User Process OSI Layers Multi-channel Logical Interface Layer 3 Packet Packet Layer 2 Link Access Link Access LAPB Link Level Logical Interface Layer 1 Physical Physical X.21 Physical Interface X.25 Interface User Data X.25 Packet Layer 3 Header User Data LAPB Frame LAPB Header Layer 3 Header User Data LAPB Header

  7. LAPB Commands and Responses

  8. X.25 Packet Header 8 7 6 5 4 3 2 1 Bits General Format Identifier Logical Channel Group Number Octet #1 Logical Channel Number Octet #1 P(R) M P(S) 0 Octet #1 User Data User Data

  9. X.121 Addressing

  10. User Network Interface User Network Interface X.25 Operation User System B User System A Network A Initiates a virtual call to B Call Request Incoming Call Call Accepted When A is informed that the call is connected it can begin to send data packets Call Connected Data R=0 S=0 The packets are delivered in sequence Data R=0 S=1 Data R=0 S=0 Data R=0 S=1 B has no data packet with which to acknowledge packet S-1, so it sends a supervisory packet Data R=2 S=0 Data R=2 S=0 Receive Ready R=1 Data R=1 S=3 Data R=1 S=3 Receive Ready R=3 Data R=4 S=1 Data R=4 S=0 A Initiates clearing of the virtual call Clear Request Clear Indication Clear Confirmation Clear Confirmation

  11. Frame Relay and X.25 Protocol Stacks X.25 Packet Level Implemented by end system but not network LAPB LAPF Control Implemented by end system and network LAPF Core Implemented by end system and network Physical Layer Physical Layer Frame Relay X.25

  12. LAPF Formats

  13. Frame Handler Operation Frame relay control point TE A DLCI=0 DLCI=0 TE D DLCI=312 DLCI=334 TE B DLCI=0 DLCI=342 DLCI=306 TE E DLCI=0 TE C DLCI=0 DLCI=322 DLCI=306 Frame Handler

  14. Frame Relay Network Access

  15. Basic AT Commands

  16. Applications of ISDN in Internetworking Dial Backup ISDN Network DDR SOHO ISDN NT BRI PRI

  17. ISDN Access • Basic Rate Interface (BRI) • Primary Rate Interface (PRI)

  18. Customer Premises Local Exchange Terminal equipment ISDN interface Network termination equipment basic termination (DSU/CSU) TE1 Network termination equipment basic termination (DSU/CSU) Network termination equipment PBX or internetworking device Transmission Line NT1 NT2 ISDN Switch TA TE2 Terminal adapter Terminal equipment (Non-ISDN) S T U U ITU-T Physical Interface Points ISDN Functional Devices and Physical Interfaces

  19. Length in Octets 1 FLAG Service Access Point Identifier (SAPI) C/R O 1 1 Terminal Endpoint Identifier (TEI) Control 1-2 Information 0-128 or 0-260 Frame Check Sequence 2 FLAG 1 LAPD Frame Format

  20. Messages for Circuit-mode Connection Control

  21. Main Components of PPP • Encapsulation Scheme • Link Control Protocol • Network Control Protocols

  22. PPP Encapsulation Maximum Receive Unit (MRU) Padding Information Protocol 8 or 16 bits

  23. LCP Management Functions • Determine encapsulation format options • Negotiate optimal packet size • Terminate the link • Authenticate the identity of the peer on the link (optional) • Negotiate PPP Multilink Data Compression (optional) • Link quality monitoring (optional)

  24. Network Control Protocol (NCP) NCPs are a series of independently-defined protocols that encapsulate network layer protocols such as TCP/IP, DECnet, AppleTalk, IPX, XNS, and OSI.

  25. PPP Link Phases • In the process of configuring, maintaining and terminating the point-to-point link, the PPP link goes through several distinct phases: • Link dead (Physical layer not ready) • Link establishment • Authentication • Network-layer protocol • Link termination

  26. PPP Peer to Peer Connection • Setting up a PPP connection between two peers involves four phases: • LCP negotiation • LCP steady state • NCP negotiation • Network layer protocol data flow

  27. UNI ATM Switch UNI UNI ATM Switch UNI Private UNI ATM Switch ATM Network Private UNI

  28. ATM Connections • ATM supports two types of connections: • Point-to-point, which connects two ATM end systems and can be unidirectional (one-way communication) or bidirectional (two-way communication). • Point-to-multipoint connects a single-source end system (known as the root node) to multiple destination end systems (known as leaves). Such connections are unidirectional only. Root nodes can transmit to leaves, but leaves cannot transmit to the root or each other on the same connection. Cell replication is done within the ATM network by the ATM switches where the connection splits into two or more branches.

  29. XDSL

  30. Copper Access

  31. DMT Subchannels

  32. VDSL Connection

  33. HDSL

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