Cisco Systems 8600 Series manual AIT/BTM Control Mapping, Frames and Cells

AIT/BTM Control Mapping, Frames and Cells

AIT/BTM Control Mapping, Frames and Cells

In addition to performing DLCI to PVC/VCC conversion, the network interworking feature provided by the AIT card in the IPX switch or BTM in the IGX switch maps cell loss priority, congestion information, and management information between frame relay and ATM formats as follows:

CELL LOSS PRIORITY, Frame Relay to ATM Direction

Each frame relay to ATM network interworking connection can be configured as one of the following DE to CLP mapping choices:

•The DE bit in the frame relay frame is mapped to the CLP bit of every ATM cell generated by the segmentation process.

The following 2 choices are not available on IPX/IGX switch NIW (network interworking):

•

•

CLP is always 0.

CLP is always 1.

CELL LOSS PRIORITY, ATM to Frame Relay Direction

Each frame relay to ATM network interworking connection can be configured as one of the following CLP to DE mapping choices:

•If one or more ATM cells belonging to a frame has its CLP field set, the DE field of the frame relay frame will be set.

The following choice is not available:

•Choosing no mapping from CLP to DE.

CONGESTION INDICATION, Frame Relay to ATM direction

•EFCI is always set to 0.

CONGESTION INDICATION, ATM to Frame Relay Direction

•If the EFCI field in the last ATM cell of a segmented frame is set, then FECN of the frame relay frame will be set.

For PVC Status Management

The AIT/BTM does convert OAM cells to OAM fastpackets, and vice-versa, including the AIS OAM. Also, “A-bit” status is now propagated via software messaging.

The ATM layer and frame relay PVC Status Management can operate independently. The PVC status from the ATM layer will be used when determining the status of the FR PVCs. However, no direct actions of mapping LMI A bit to OAM AIS will be performed.

12-10Cisco BPX 8600 Series Reference