WAN Transport Methods

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WAN Transport Methods

• Chapter 7

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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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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

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X.25

• Older, very reliable packet-switching protocol
  for connecting remote networks
• Offers bandwidth up to 2.048 Mbps
• Defines communications between DTEs and DCEs
• Globally accepted
• Can connect older LANs to WANs and older
  mainframes and minicomputers to a WAN

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X.25 and the OSI Model
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X.25 Transmission Modes

• Switched virtual circuits (SVCs)
• Permanent virtual circuits (PVCs)
• Datagrams

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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

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X.25 Network
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X.25 Frame Structure
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Layer 3 Header and Data
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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)

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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

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Frame Relay Layered Communications
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Switching and Virtual Connections

• Virtual connections are logical rather than
  physical
• Types of virtual connections
• Permanent
• Switched

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Frame Relay Format
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Frame Format

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

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Frame Relay

• Local management interface (LMI) protocol
• 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

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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

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Vendor Services

• Committed information rate (CIR)
• Permanent virtual connection (PVC)
• Port

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Integrated Services Digital Network (ISDN)

• Standard for delivering data services over
  telephone lines
• Current practical limit of 1.536 Mbps
• Theoretical limit of 622 Mbps

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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

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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

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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

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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 1.536 Mbps

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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)

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Connecting via an NTU
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Connecting to ISDN PRI
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Broadband ISDN (B-ISDN)

• Data transfer rate of 155 Mbps and higher
• Currently under development not widely
  implemented

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How ISDN Works

• Time-compression multiplexing
• Echo cancellation

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ISDN and OSI
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Link Access Procedure D Channel (LAPD) Frame
Format
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Q.931 ConnectionControl Protocol

• Contains information elements
• Setup
• Call proceeding
• Connect
• Connect acknowledgement
• Suspend
• Resume
• Disconnect
• Release
• Release Complete

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ISDN Considerations

• Available locally?
• Which protocol used by provider?
• Twisted-pair copper wire or fiber-optic cabling?

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Connecting to ISDNThrough a T-carrier

• Circuit mode services
• Packet mode services

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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

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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

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SMDS Architecture
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SMDS and OSI
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SMDS Cell
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SMDS Considerations

• Advantages
• 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

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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)

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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

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DSL Basics
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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

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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 51.84 Mbps or optical
  carrier level 1 (OC-1)

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SONET Transmission Rates
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SDH LevelsCompared to SONET
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SONET Network Topology and Failure Recovery

• Ring topology
• Methods of failure recovery
• Unidirectional path switching
• Automatic protection switching
• Bidirectional line switching

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SONET and OSI
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SONET Frame
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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

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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

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Additional WAN Protocols

• Serial Line Internet Protocol (SLIP)
• Point-to-Point Protocol (PPP)
• Signaling System 7 (SS7)

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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

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SLIP
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SLIP and CSLIPDo 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

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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

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Advantages of PPPover SLIP or CSLIP

• Lower overhead
• Greater capabilities
• Stronger security
• Supports more network protocols

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PPP and SLIP Compared
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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

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How SS7 Enables Fast Communications

• Keeps databases of routing information at
  different strategic points throughout a WAN
• Quickly directs central sites query about
  fastest route
• Tracks every telecommunications call to determine
  fastest route

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Chapter Summary

• Older WAN technologies
• X.25
• Frame relay
• ISDN
• Newer WAN technologies
• SMDS
• DSL
• SONET
• Ethernet-based MANs

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Chapter Summary

• WAN protocols
• SLIP
• PPP
• SS7