Voice over ATM

ATM regarded as “a very complex technology, perhaps the most complex ever developed by the networking industry” [1]

Short for Asynchronous Transfer Mode is similar to frame relay, very high speed packet switched service which can be used for sending data or voice between two points either within a LAN, MAN or WAN, the transfer rates are up to 622Mbps, or faster, furthermore ATM is a very scalable, nevertheless it is an expensive technology.

In ATM data is sent in small packages of 53 byte called cells, which are relatively small compared to units used with older technologies, the reason for keeping the cells small is when a cell reaches a node in the ATM network, the cell will be able to pass quickly through the node to the destination. The small cell size enables ATM equipment to transfer audio, video and computer data over the same network.

ATM differs from TCP/IP, in TCP/IP messages are divided into packets and each packet can take a different route from source to destination, whereas in ATM a fixed channel or route is created, between two points whenever data transfer begins. This difference makes it easier to track and bill data usage across an ATM network, however it makes it less adaptable to sudden surges in network traffic. [2]

One of primary benefits of end to end ATM is the capability to integrate voice and data traffic.

However there are two methods of transmitting voice traffic over ATM and they are: CBR which is the most popular method for voice transport among ATM concentrators and switches, since the ATM Forum’s standard has promoted interoperability between vendors. The second method is real-time VBR which offers a more cost effective, since the ATM network doesn’t use any bandwidth during periods of silence. The unused bandwidth during these periods will be available to other ATM service categories.

References

1. Anthony Alles, 1995, "ATM Internetworking" http://www.cisco.com/warp/public/614/12.html
2. Teligent, http://www2.teligent.se/?sid=514&parentsid=27