12-10 Cisco BPX 8600 Series Reference
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.
