ATM - Asynchronous Transfer Mode

Definition:ATM is ahigh-speed networking standard designed to support both voice and datacommunications. ATM is normally utilized by Internet service providers on theirprivate long-distance networks. ATM operates at the data link layer (Layer 2 inthe OSI model) over either fiber or twisted-paircable.

ATMdiffers from more common data link technologies like
Ethernet in several ways. For example, ATMutilizes no routing. Hardware devices known as ATM switches establishpoint-to-point connections between endpoints and data flows directly fromsource to destination. Additionally, instead of using variable-length packetsas Ethernet does, ATM utilizes fixed-sized cells. ATM cells are 53 bytes in length, that includes 48 bytes of dataand five (5) bytes of header information.

Theperformance of ATM is often expressed in the form of OC (Optical Carrier)levels, written as "OC-xxx." Performance levels as high as 10 Gbps (OC-192) are technically feasible with ATM.More common performance levels for ATM are 155 Mbps (OC-3) and 622 Mbps(OC-12).

ATMtechnology is designed to improve utilization and quality of service (QoS) on high-trafficnetworks. Without routing and with fixed-size cells, networks can much moreeasily manage bandwidth under ATM than under Ethernet, forexample. The high cost of ATM relative to Ethernet is one factor that haslimited its adoption to "backbone" and other high-performance,specialized networks. 

ATM letscompanies settle on a single technology standard for all their differentcommunication needs. With ATM technology voice, audio, video & datacommunications can all be carried over the one seamless network.

Four ATM packages are available:

• E1 Access:- 2MB access over copper or fibre optic cable. E1 Access can be configured either as a 2MB permanent virtual path (PVP) or divided into 2x1MB paths.
   
• E3 Access:- 34 MB Access over fibre optic cable. E3 Access can be configured as a 34MB Permanent Virtual Path (PVP) or divided into smaller paths to serve multiple locations in a company WAN Environment.
   
• STM1 Access:-155MB over fibre optic cable. STM1 Access can be configured as a 155MB Permanent Virtual Path (PVP) or divided into smaller paths to suit your WAN (Wide Area Network) environment.
   
• STM4 Access:- 622Mb over fibre optic cable.
  
  Please note that backup facilities can be provided for E1, E3 and STM1 Links. Backup facilities are not available for STM4 Access.