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ATM (Asynchronous Transfer Mode) Switch Architecture

This page covers ATM (Asynchronous Transfer Mode) Switch Architecture basics. It also describes VP/VC switch and VP ATM switch with table.


Refer Following links to subtopics on this ATM tutorial:
ATM Network Architecture & Interfaces   ATM Protocol Stack  ATM services  ATM Switch  ATM Call Flow  ATM vs STM  ATM vs TDM  ATM versus Frame Relay  ATM AAL Layer Types 


ATM Switch: The Switch which works on packet switching technology to allow voice, data, image and video traffic over high speed single access circuit is known as ATM Switch. It divides the information as mentioned into equal size cells of size equal to 48 bytes and adds header (of size 5 bytes) before transmission. Here 48 bytes contain information and 5 bytes contain control information.

ATM (Asynchronous Transfer Mode) Switch works on same size cells and hence cell delay is manageable and predictable.

ATM Switch differs from conventional switch due to high speed interface i.e. 50 Mbps to 2.4 Gbps. The switch is designed to take care of broadband applications as well as to take care of certain types of traffic based on priority through ATM network. EXAMPLE: Voice traffic can not tolerate much delay and hence need to be taken on high priority compare to E-mail.

ATM network composed of more than one ATM switches between source and destination systems. The switch consists of input ports and output ports. These ports are interconnected with users, other ATM switches and other network elements.

ATM Switch

➨ATM (Asynchronous Transfer Mode) Switch functions are categorized into three planes viz. user plane, control plane, management plane. ATM cells are divided into data cells and control cells.

➨USER PLANE: ATM Switch relays data cells from input to output ports. The switch operates on cell headers and not on payload. The payload is carried transparently through the switch. When cell arrives at input port, switch checks VPI/VCI and routes cells accordingly to the output ports.

➨CONTROL PLANE: Information in the payload part of control cells is not transparent here. It is verified and checked by ATM switch and based on the same appropriate actions are taken by it. The control plane takes care of establishment and control of VP and VC connections.

➨Management plane takes care of monitor and control of the ATM network.

The figure-1 depicts typical modules in an ATM switch. It s composed of Input modules, output modules, CAC (connection admission control), switch management and cell switch fabric.

VP/VC ATM Switch

VP/VC ATM Switch

ATM switch uses two types of switches viz. VP switch and VP-VC sitch. Typically, switches connected to users are VPI/VCI switches while all intermediate switches are only VPI switches All VPIs and VCIs field have local significance across particular link. These values are re-arranged or re-mapped as required at the ATM (Asynchronous Transfer Mode) switch.


Incoming Outgoing
VPI VCI VPI VCI Interface
10 122 11 41 1
121 213 10 158 1
12 11 211 111 2
11 151 321 210 2

• As shown in figure-2, When cell arrives at the input of ATM switch, it looks up connection value in local table referred as translation table to determine appropriate outgoing port for the connection.
• It also assigns new VPI/VCI value of the connection on the same outgoing link.
• The switch re-transmits cell on the outgoing link with appropriate identifier.

VP ATM Switch

VP ATM Switch

VP switch routes cells based on VPI only. Here VPI values do not change but VCI values remain same during switching. It uses translation table for switching.


Incoming Outgoing
VPI VPI Interface
22 65 1
121 99 2
312 201 1
11 21 2

Networking related links

What is Bridge
What is Router
What is Gateway
Firewall basics
TCP-IP Packet format
Difference between OSI and TCPIP layers
Difference between TCP UDP
Packet Switching vs Message Switching

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