18.1
Chapter 18
Virtual-Circuit Networks:
Frame Relay and ATM
18.2
18-1 FRAME RELAY
Frame Relay is a virtual-circuit wide-area network that was designed in response to demands for a new type of WAN in the late 1980s and early 1990s.
Architecture�Frame Relay Layers
Extended Address
FRADs
VOFR
LMI
Topics discussed in this section:
18.3
Figure 18.1 Frame Relay network
18.4
VCIs in Frame Relay are called DLCIs.
Note
18.5
Figure 18.2 Frame Relay layers
18.6
Frame Relay operates only at the physical and data link layers.
Note
18.7
Figure 18.3 Frame Relay frame
18.8
Frame Relay does not provide flow or error control; they must be provided
by the upper-layer protocols.
Note
18.9
Figure 18.4 Three address formats
18.10
Figure 18.5 FRAD
18.11
18-2 ATM
Asynchronous Transfer Mode (ATM) is the cell relay protocol designed by the ATM Forum and adopted by the ITU-T.
Design Goals�Problems�Architecture
Switching
ATM Layers
Topics discussed in this section:
18.12
Figure 18.6 Multiplexing using different frame sizes
18.13
A cell network uses the cell as the basic unit of data exchange.
A cell is defined as a small, fixed-size block of information.
Note
18.14
Figure 18.7 Multiplexing using cells
18.15
Figure 18.8 ATM multiplexing
18.16
Figure 18.9 Architecture of an ATM network
18.17
Figure 18.10 TP, VPs, and VCs
18.18
Figure 18.11 Example of VPs and VCs
18.19
Note that a virtual connection is defined by a pair of numbers: �the VPI and the VCI.
Note
18.20
Figure 18.12 Connection identifiers
18.21
Figure 18.13 Virtual connection identifiers in UNIs and NNIs
18.22
Figure 18.14 An ATM cell
18.23
Figure 18.15 Routing with a switch
18.24
Figure 18.16 ATM layers
18.25
Figure 18.17 ATM layers in endpoint devices and switches
18.26
Figure 18.18 ATM layer
18.27
Figure 18.19 ATM headers
18.28
Figure 18.20 AAL1
18.29
Figure 18.21 AAL2
18.30
Figure 18.22 AAL3/4
18.31
Figure 18.23 AAL5
18.32
18-3 ATM LANs
ATM is mainly a wide-area network (WAN ATM); however, the technology can be adapted to local-area networks (ATM LANs). The high data rate of the technology has attracted the attention of designers who are looking for greater and greater speeds in LANs.
ATM LAN Architecture�LAN Emulation (LANE)
Client/Server Model
Mixed Architecture with Client/Server
Topics discussed in this section:
18.33
Figure 18.24 ATM LANs
18.34
Figure 18.25 Pure ATM LAN
18.35
Figure 18.26 Legacy ATM LAN
18.36
Figure 18.27 Mixed architecture ATM LAN
18.37
Figure 18.28 Client and servers in a LANE
18.38
Figure 18.29 Client and servers in a LANE