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 SubsetUses NRMMultipoint networks that typically use SDLC LAPEarly X.25 implementations LAPBCurrent X.25 implementations LAPDISDN D channel and frame relay LAPMError-correcting modems (specified as part of V.42)

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

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

7. LAPB Commands and Responses

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

9. X.121 Addressing

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

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

12. LAPF Formats

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

14. Frame Relay Network Access

16. Basic AT Commands

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

19. ISDN Access  Basic Rate Interface (BRI)  Primary Rate Interface (PRI)

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

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

22. Messages for Circuit-mode Connection Control

23. Main Components of PPP  Encapsulation Scheme  Link Control Protocol  Network Control Protocols

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

25. 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)

26. 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.

27.  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 PPP Link Phases

28. 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

29. ATM Network ATM Switch UNI Private UNI UNI ATM Switch UNI Private UNI

30. 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.

31. XDSL

32. Copper Access

33. DMT Subchannels

34. VDSL Connection

35. HDSL