McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Chapter 18

Virtual CircuitSwitching:Frame Relay

andATM

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

18.1 Virtual Circuit Switching

Global Addressing

Virtual Circuit Identifier

Three Phases

Data Transfer Phase

Setup Phase

Teardown Phase

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.1 Virtual circuit wide area network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.2 VCI

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.3 VCI phases

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.4 Switch and table

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.5 Source-to-destination data transfer

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.6 SVC setup request

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.7 SVC setup acknowledgment

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Frame Relay(FR)

Frame relay is a virtual circuit wide-area-network that was designed in response todemands for a new type of WAN.• Prior to FR, X.25 was being used. But it is being replaced by other WANs.

• X.25 has several drawbacks:•It has a low 64-kbps data rate.•X.25 has extensive flow and error control at both data link and network layer.Flow and error control at both layers create a large overhead and slow downtransmission.•Originally X.25 was designed for private use, not for the Internet.

•Disappointed with X.25, some organization started their own private WAN byleasing T-1 0r T-3 lines from public service providers. This approach has also somelimitations:

•If an organization has n branches spread over an area, it needs n(n-1)/2 lines.•This type of service is not suitable for bursty data. Because T-1 or T-3 providesfixed data rate and bursty data require bandwidth-on-demand.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.8 Frame Relay network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

VCIs in Frame Relay are called DLCIs.(data link connection identifier)

Note:

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.9 Frame Relay layers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Frame Relay operates only at the physical and data link layers.

Note:

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.10 Frame Relay frame

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Frame Relay frame

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Frame Relay frame

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Frame Relay does not provide flow or error control; they must be provided by

the upper-layer protocols.

Note:

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.12 FRAD

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

18.3 ATM(Asynchronous Transfer Mode)

Design Goals

Problems

Architecture

Switching

Layers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Design Goals

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Problems

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Problems contd..

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

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.

Note:

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

ATM multiplexing

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.16 Architecture of an ATM network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.17 TP, VPs, and VCs

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.18 Example of VPs and VCs

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Note that a virtual connection is defined by a pair of numbers:

the VPI and the VCI.

Note:

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.19 Connection identifiers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.20 Virtual connection identifiers in UNIs and NNIs

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.21 An ATM cell

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.22 Routing with a switch

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.23 ATM layers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.24 ATM layers in endpoint devices and switches

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.25 ATM layer

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.26 ATM headers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.27 AAL1

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.28 AAL2

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.29 AAL3/4

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 18.30 AAL5