Cisco Systems 8600 Series manual Routing, Bandwidth Management, User Interface

Management

Routing

Interworking connections use the complex gateway feature of the AIT trunk card to repackage data from frames to ATM cells, and vice-versa. All BPX switch-IPX switch hops these connections route over must provide the complex gateway function. IPX switch-IPX switch hops (frame relay connections) can be any trunk card type. This requirement simplifies the routing mechanism when dealing with structured networks, as software does not know the type of trunks in remote domains.

Bandwidth Management

Bandwidth calculations for interworking connections assume a large frame size, which minimizes the loading inefficiency of packets vs. cells. In other words, the translation between packets and cells assumes 100 percent efficiency, so the conversion is simply based on 20 payload bytes per fastpacket vs. 48 payload bytes per ATM cell.

This mechanism keeps the fastpacket/cell conversion consistent with the bits per second/cells per second conversion. Thus, conversion of endpoint rates to trunk loading is straightforward.

User Interface

ATM connection classes are added for convenience. Classes can be configured as interworking or regular ATM. The cnfcls command is used to configure a class. The class is specified as part of the addcon command. ATM connection classes are maintained on all BPX switch. IPX switch nodes do not know about these classes.

A special ATM class is defined as the default interworking class. When an interworking connection is added from the frame relay end, the ATM-only parameters for this connection are taken from this default class.

Network-wide ForeSight parameters are supported for the frame relay end of interworking connections. The cnffstparm command is used to configure these parameters. Since the ATM end of interworking connections has per-virtual circuit ForeSight parameter configurability, the network-wide ForeSight parameters do not apply.

Note that the default ATM ForeSight parameters will match the default frame relay ForeSight parameters, with appropriate units conversion.

Port Management

The cnfport command supports the following new features:

•An ASI-1 card can be configured to be UNI or NNI.

•An ASI-1 UNI or NNI port can be configured to transmit Backwards Congestion Messages (BCM) to indicate congestion to the foreign ATM network.

•An ASI-1 UNI or NNI port can be configured for LMI, ILMI or no local management.

The cnfportq command supports configuration of queue depth, EFCN threshold, and CLP thresholds for all port egress queues (CBR, VBR, VBR w/ForeSight).

Frame Relay to ATM Network and Service Interworking 12-17