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McGraw-Hill ©2003 The McGraw-Hill Companies, Inc. Chapter 11 Wide Area Networks
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McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Chapter 11
Wide AreaNetworks
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Understand point-to-point WAN technologies: T-lines andUnderstand point-to-point WAN technologies: T-lines andSONET networks.SONET networks.
Understand X.25 technology and why it is losing popularity.Understand X.25 technology and why it is losing popularity.
Understand Frame Relay technology and how it was designedUnderstand Frame Relay technology and how it was designedto replace X.25.to replace X.25.
Understand ATM technology and its importance in today’sUnderstand ATM technology and its importance in today’smarket.market.
After reading this chapter, the reader should After reading this chapter, the reader should be able to:be able to:
OOBJECTIVESBJECTIVES
Understand ATM LANs.Understand ATM LANs.
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
POINT-TO-POINTPOINT-TO-POINTWANsWANs
POINT-TO-POINTPOINT-TO-POINTWANsWANs
11.111.1
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Figure 11-1T-1 line
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A T-1 line has a data rate ofA T-1 line has a data rate of1.544 Mbps1.544 Mbps
Note:Note:
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A T-3 line has a data rate ofA T-3 line has a data rate of44.736 Mbps44.736 Mbps
Note:Note:
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Technical Focus:Technical Focus: Fractional T-LinesFractional T-Lines
Many subscribers may not need the entire capacity of a T-line. To accommodate these customers, telephone companies offer fractional T-line services, which allow several subscribers to share one line by multiplexing theirtransmissions.
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Figure 11-2
SONET
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
SWITCHEDSWITCHEDWANsWANs
SWITCHEDSWITCHEDWANsWANs
11.211.2
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Technical Focus:Technical Focus: TunnelingTunneling
To use an X.25 network, an IP packet uses a technique called tunneling. Because X.25 does not allow IP packets to use theirown network layer protocol, the IP packets are encapsulated in the network layer of the X.25 protocol.
This can be compared to a car entering a tunnel. To an observer, the car disappears at one side of the tunnel and reappears at the other side. Likewise, an IP packet disappears at the entry point of an X.25 network and reappears at the exit point.
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Figure 11-3
Frame Relay network
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Figure 11-4Frame Relay layers
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Technical Focus:Technical Focus: DLCIsDLCIs
A Frame Relay network uses data link connection identifiers (DLCIs) which act as addresses. Each DLCI defines a channel between two adjacent devices (DTEs or DCEs). A path between a device at one end and another device at the other end is made of several DLCIs as shown in the following figure:
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
A cell network uses the cell as the A cell network uses the cell as the basic unit of data exchange. A cell is basic unit of data exchange. A cell is defined as a small fixed-sized block of defined as a small fixed-sized block of
information.information.
Note:Note:
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Figure 11-5
ATM multiplexing
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Figure 11-6
Architecture of an ATM network
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Technical Focus:Technical Focus: VPIs and VCIsVPIs and VCIs
In an ATM network, connection between two end points is accomplished through transmission paths, virtual paths, and virtual circuits as shown in the following figure:
The outer cylinder shows a transmission path. The inner cylinders show the virtual path identifiers (VPIs). The lines show virtual circuit identifiers (VCIs).
McGraw-Hill ©2003 The McGraw-Hill Companies, Inc.
Figure 11-7
An ATM cell
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Figure 11-8
ATM layers
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The IP protocol usesThe IP protocol usesthe AAL5 layer.the AAL5 layer.
Note:Note:
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ATMATMLANsLANsATMATMLANsLANs
11.311.3
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Figure 11-9ATM LAN architectures
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Technical Focus:Technical Focus: LANELANE
Connectionless vs. Connection-orientedConnectionless vs. Connection-oriented
Physical Address vs. Virtual Connection IdentifierPhysical Address vs. Virtual Connection Identifier
Multicasting and Broadcasting DeliveryMulticasting and Broadcasting Delivery
InteroperabilityInteroperability
At the surface level, the use of ATM technology in LANs seems plausible. However, on close inspection, we see that many issues need to be resolved, as summarized below:
An approach called local area network emulation (LANE) solves the above-mentioned problems and allows stations in a mixed architecture to communicate with each other.
