Subject: Advanced Network Technologies

Topic: WAN Technologies

Difficulty: High

QOS parameters of ATM are:-

1.Constant Bit rate (CBR):-

This class is used for emulating circuit switching. The cell rate is constant with time. CBR applications are quite sensitive to cell-delay variation. Examples of applications that can use CBR are telephone traffic (i.e., nx64 kbps), videoconferencing, and television.

2.Variable Bit Rate - non-real time (VBR–NRT):-

This class allows users to send traffic at a rate that varies with time depending on the availability of user information. Statistical multiplexing is provided to make optimum use of network resources. Multimedia e-mail is an example of VBR–NRT.

3. Variable bit rate–real time (VBR–RT):-

This class is similar to VBR–NRT but is designed for applications that are sensitive to cell-delay variation. Examples for real-time VBR are voice with speech activity detection (SAD) and interactive compressed video.

4. Connection oriented packet transfer or available bit rate (ABR):-

This class of ATM services provides rate-based flow control and is aimed at data traffic such as file transfer and e-mail. Although the standard does not require the cell transfer delay and cell-loss ratio to be guaranteed or minimized, it is desirable for switches to minimize delay and loss as much as possible. Depending upon the state of congestion in the network, the source is required to control its rate. The users are allowed to declare a minimum cell rate, which is guaranteed to the connection by the network.

5. Connectionless data transfer or unspecified bit rate (UBR):-

This class is the catch-all, other class and is widely used today for TCP/IP.