Download Frame Relay network

Chapter 11
Wide Area
Networks
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OBJECTIVES
After reading this chapter, the reader should
be able to:
Understand point-to-point WAN technologies: T-lines and
SONET networks.
Understand X.25 technology and why it is losing popularity.
Understand Frame Relay technology and how it was designed
to replace X.25.
Understand ATM technology and its importance in today’s
market.
Understand ATM LANs.
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11.1
POINT-TO-POINT
WANs
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Figure 11-1
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T-1 line
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Note:
A T-1 line has a data rate of
1.544 Mbps
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Note:
A T-3 line has a data rate of
44.736 Mbps
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Technical Focus:
Fractional T-Lines
Many subscribers may not need the entire capacity of a Tline. To accommodate these customers, telephone companies
offer fractional T-line services, which allow several
subscribers to share one line by multiplexing their
transmissions.
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Figure 11-2
SONET
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11.2
SWITCHED
WANs
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Technical Focus:
Tunneling
To use an X.25 network, an IP packet uses a technique called
tunneling. Because X.25 does not allow IP packets to use their
own 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 11-4
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Frame Relay layers
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Technical Focus:
DLCIs
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:
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Note:
A cell network uses the cell as the basic
unit of data exchange. A cell is defined
as a small fixed-sized block of
information.
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Figure 11-5
ATM multiplexing
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Figure 11-6
Architecture of an ATM network
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Technical Focus:
VPIs 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).
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Figure 11-7
An ATM cell
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Figure 11-8
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ATM layers
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Note:
The IP protocol uses
the AAL5 layer.
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11.3
ATM
LANs
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Figure 11-9
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ATM LAN architectures
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Technical Focus:
LANE
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:
Connectionless vs. Connection-oriented
Physical Address vs. Virtual Connection Identifier
Multicasting and Broadcasting Delivery
Interoperability
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.
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