Hitachi manual Bandwidth Planning Considerations, Routing Capacity of GR2000 on ATM Interface

4.6.1Bandwidth Planning Considerations

4.6.1.1Routing Capacity of GR2000 on ATM Interface

The routing capacity of GR2000 on ATM interface is 50 kpps transmission per line. Plan the network so that the traffic exceeding the router’s capacity will not rush into the router.

4.6.1.2Cellularization Overhead

When relaying packets from a network of different medium such as Ethernet to an ATM network, the output traffic becomes higher than the input traffic because of the cellularization overhead. Figure 4-9 illustrates a sample cellularization process that converts an Ethernet frame (IP packet) to ATM cells.

For example, if a 64-byte frame is received from an Ethernet network, the IP packet length is 46 bytes. When transmitting this frame to an ATM network, PAD is added to normalize the data length on 48-byte boundary as shown below.

Header (8 bytes) + IP packet (46 bytes) + PAD and Trailer (42 bytes) = 96 bytes