1. WAN Transport Methods
Chapter 7

2. Learning Objectives
Explain the X.25 communications protocol and understand how to implement X.25 WAN connections
Explain frame relay for use in WANs
Describe ISDN communications for voice, data, and video networks; explain how to connect to ISDN
Define SMDS networking and explain how it is implemented
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3. Learning Objectives
Describe DSL network communications for high-speed networking
Explain how SONET works and how it is implemented
Describe Ethernet-based MANs
Discuss additional WAN protocols: SLIP, PPP, and SS7

4. X.25
Older, very reliable packet-switching protocol for connecting remote networks
Offers bandwidth up to Mbps
Defines communications between DTEs and DCEs
Globally accepted
Can connect older LANs to WANs and older mainframes and minicomputers to a WAN

5. X.25 and the OSI Model

6. X.25 Transmission Modes Switched virtual circuits (SVCs)
Permanent virtual circuits (PVCs)
Datagrams

7. X.25 Connectivity Communications accomplished by:
DTE
DCE
Packet assembler/disassembler (PAD)
Protocols important to maintaining X.25 network
X.3 protocol
X.20 protocol
X.28 protocol
X.29 protocol

8. X.25 Network

9. X.25 Frame Structure

10. Layer 3 Header and Data

11. X.25 Deployment Provides worldwide connectivity between LANs
Designed to release unused bandwidth when nodes are not communicating
For WAN connectivity, being replaced by faster technologies (frame relay, SMDS, SONET, Optical Ethernet)

12. Frame Relay
Communications protocol that relies on packet switching and virtual connection technology (SVC or PVC) to transmit data packets
Uses frame relay assembler/disassembler (FRAD) to convert packets
Achieves higher transmission rates (up to 45 Mbps) by leaving extensive error-checking functions to intermediate nodes
Can transport IP, IPX, AppleTalk, PPP, SLIP

14. Frame Relay Layered Communications

15. Switching and Virtual Connections
Virtual connections are logical rather than physical
Types of virtual connections
Permanent
Switched

16. Frame Relay Format

17. Frame Format Data link connection identifier (DLCI)
Contained in address field
Identifies an individual virtual connection on a frame relay network

19. Frame Relay Local management interface (LMI) protocol LMI extensions
Used by frame relay for signaling communications
Enables frame relay to determine when to:
Create a new virtual circuit
Delete a virtual circuit that is no longer in use
Identify a virtual circuit that has failed
LMI extensions
Added to frame relay frame for additional functions

20. Voice over Frame Relay (VoFR)
Transmits voice signals over the network to reduce long-distance telephone costs between sites
Voice transmission techniques
Voice compression
Pulse code modulation (PCM)
Adaptive differential pulse code modulation (ADPCM)
Sub-band adaptive differential pulse code modulation (SB-ADPCM)
Silence compression

21. Vendor Services Committed information rate (CIR)
Permanent virtual connection (PVC)
Port

22. Integrated Services Digital Network (ISDN)
Standard for delivering data services over telephone lines
Current practical limit of Mbps
Theoretical limit of 622 Mbps

23. ISDN Applications LAN-to-LAN connectivity
Home offices and telecommuting
Off-site backup and disaster recovery
Connecting a PBX to the RBOC
Transferring large image and data files
LAN-to-LAN video and multimedia applications

24. Benefits of ISDN
Provides voice, data, and video services over one network
Layered protocol structure compatible with OSI reference model
Communications channels offered in multiples of 64 Kbps, 384 Kbps, and 1536 Kbps
Switched and non-switched connection services
Broadband ISDN capabilities 155 Mbps and higher

25. I.200 Services for Networking
Bearer services
Circuit-mode options
Packet-mode options
Virtual call circuits and permanent virtual call circuits
Teleservices
Speech and telex
Supplementary services (voice communications)
Caller ID and conference calling

27. Digital Communications Services
Basic rate interface (BRI) ISDN
Three channels
Two 64-Kbps channels for data, voice, and video transmissions
One 16-Kbps channel used for communications signaling
Primary rate interface (PRI) ISDN
Switched communications in multiples of Mbps

28. Connecting to ISDN
Equip computer with a TA that also contains a network terminal (NT1) network terminator
Connect ISDN line into external TA that is equipped with a U interface
Network Termination Unit (NTU)

29. Connecting via an NTU

30. Connecting to ISDN PRI

31. Broadband ISDN (B-ISDN)
Data transfer rate of 155 Mbps and higher
Currently under development; not widely implemented

32. How ISDN Works
Time-compression multiplexing
Echo cancellation

33. ISDN and OSI

34. Link Access Procedure D Channel (LAPD) Frame Format

35. Q.931 Connection Control Protocol
Contains information elements
Setup
Call proceeding
Connect
Connect acknowledgement
Suspend
Resume
Disconnect
Release
Release Complete

36. ISDN Considerations Available locally?
Which protocol used by provider?
Twisted-pair copper wire or fiber-optic cabling?

37. Connecting to ISDN Through a T-carrier
Circuit mode services
Packet mode services

38. Switched Multimegabit Data Service (SMDS)
High-speed WAN technology, often implemented over T-1 carrier lines
High-speed bus with bandwidth of up to 155 Mbps
Compatible with wide range of LAN-based protocols

39. SMDS Applications High-speed links for regional networks
Transmission of large image files (medical X-rays)
Transmission of CAD graphics
Fast access to library holdings and electronic catalogs

40. SMDS Architecture

41. SMDS and OSI

42. SMDS Cell

43. SMDS Considerations Advantages Disadvantages
High-speed network communications
Compatible with B-ISDN, T-carrier, SONET, and ATM
Strong security options for users
Disadvantages
Not as universally available as X.25, frame relay, and ISDN
Designed to transport data only

44. Digital Subscriber Line (DSL)
Uses advanced modulation technologies on existing telecommunications networks for high-speed networking between subscriber and telco
Can turn existing twisted-pair telephone wire into a high-speed WAN for communications up to 55 Mbps (downstream)

45. DSL Applications Residential lines for telecommuting Internet access
Accessing multimedia over a network
Quick transmission of a large image file
Taking an interactive class or seminar
Implementing a distributed client/server application among geographically dispersed users

46. DSL Basics

48. Synchronous Optical Network (SONET)
Fiber-optic communication technology capable of high-speed data transmissions (over one gigabit per second)
Advantages
Nonproprietary
Can connect to interfaces for ATM, ISDN, routers, and other equipment
High-speed communications possible over long distances
Enables delivery of voice, data, and video communications

49. SONET Communications Media and Characteristics
Uses single-mode fiber-optic cable and T-carrier communications (starting at T-3)
Main transport method occurs at OSI Physical layer
Operates at base level of Mbps or optical carrier level 1 (OC-1)

50. SONET Transmission Rates

51. SDH Levels Compared to SONET

52. SONET Network Topology and Failure Recovery
Ring topology
Methods of failure recovery
Unidirectional path switching
Automatic protection switching
Bidirectional line switching

54. SONET and OSI

55. SONET Frame

56. Point-to-Point Protocol (PPP) over SONET
Work is underway to implement RFC 2615, which outlines how to enable Point-to-Point (PPP) protocol to be directly transported over SONET and SDH

57. Ethernet-based MANs (Optical Ethernet)
High-speed Ethernet carried on fiber-optic cable and used for MANs
Consists of:
Gigabit or 10 Gigabit Ethernet backbone
Multimode fiber-optic cable connections of up to 6 miles
Single-mode fiber-optic cable connections of up to 43.4 miles

59. Additional WAN Protocols
Serial Line Internet Protocol (SLIP)
Point-to-Point Protocol (PPP)
Signaling System 7 (SS7)

60. SLIP
Designed for UNIX environments for point-to-point communications between computers, serves, and hosts using TCP/IP
Compressed Serial Line Internet Protocol (CSLIP)
Compresses header information in each packet sent across a remote link
Reduces overhead of SLIP by decreasing header size

61. SLIP

62. SLIP and CSLIP Do Not Support…
Network connection authentication; no security
Automatic setup of network connection at multiple OSI layers at same time for faster communications
Synchronous connections
Remote set up of new account using remote administration tools in Windows NT Server or Windows 2000 Server over the Internet

63. PPP
Remote communications protocol that enables connections to networks, intranets, extranets, and VPNs through the Internet
Supplemented by Point-to-Point Tunneling Protocol (PPTP)
Recommended on network where users connect using multiple protocols

64. Advantages of PPP over SLIP or CSLIP
Lower overhead
Greater capabilities
Stronger security
Supports more network protocols

65. PPP and SLIP Compared

66. SS7 WAN protocol for telecommunications networks
Determines most efficient routes through telecommunication network
Performs functions using:
Service control points (SCPs)
Service switching points (SSPs)
Signal transfer points

67. How SS7 Enables Fast Communications
Keeps databases of routing information at different strategic points throughout a WAN
Quickly directs central site’s query about fastest route
Tracks every telecommunications call to determine fastest route

68. Chapter Summary Older WAN technologies Newer WAN technologies X.25
Frame relay
ISDN
Newer WAN technologies
SMDS
DSL
SONET
Ethernet-based MANs
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69. Chapter Summary
WAN protocols
SLIP
PPP
SS7