Specifications

4-6 Cisco MGX 8220 Reference, Release 4.1
Frame Service Module
The main function of the FRSM service module is to perform the necessary conversions between the
frame formatted data on its 4 or 8 T1 or E1 lines and ATM/AAL5 cell formatted data received and
transmitted over the cell bus. The FRSM performs the FRSM frame to ATM cell conversion and the
address translation between frame relay port/DLCIs, FUNI port/frame address, or Frame
Forwarding port, and the ATM virtual connection identifiers (VPI/VCIs).
For frame relay, the FRSM can be configured to perform network interworking or service
interworking. Network interworking and service interworking connections can be freely intermixed
on the same FRSM and the same physical port of the FRSM. The type of interworking is specified
on a PVC by PVC basis.
Fr to ATM Network Interworking
Using the MGX 8220 shelf, FR-ATM network interworking permits a permanent virtual connection
to be established between two frame relay service users over a Stratagem or multi-vendor network.
Across the network the traffic is carried in ATM cells.
By specifying “network interworking” as the channel type when adding a frame relay PVC to an
FRSM, all PVC data is subject to network interworking translation and mapping.
Figure4-5 shows a BPX 8620 network with network interworking connections.
Figure4-5 BPX 8620 Network with Networking Interworking Connections
Cell Loss Priority
In addition, to frame to cell and DLCI to VPI/VCI conversion, the network interworking feature
maps cell loss priority (CLP) and congestion information from frame relay to ATM formats.
Frame Relay to ATM Direction
Each Frame Relay/ATM network interworking connection can be configured as one of the following
DE to CLP mapping schemes:
• DE bit in the frame relay frame is mapped to the CLP bit of every ATM cell generated by the
segmentation process.
• CLP is always 0.
• CLP is always 1.