Specifications

4-10 Cisco MGX 8220 Reference, Release 4.1
Frame Service Module
Translation and Transparent Modes
Service Interworking can operate in either Translation or Transparent mode on a per connection
basis. In translation mode the FRSM performs protocol translation between the FR NLPID
encapsulation (RFC 1490) and the ATM LCC encapsulation (RFC 1483). In transparent mode, no
such translation takes place. Service Interworking also supports address resolution by transforming
Address Resolution Protocol (ARP, RFC 826) and Inverse ARP (inARP, RFC 1293) between their
Frame Relay and ATM formats when the PVC is configured as Translation Mode.
Frame Forwarding
The FRSM card can be configured as “Frame Forwarding” on a port by port basis.
When frame forwarding, the operation is the same as that for frame relay except:
• The 2 byte Q.922 header is not assumed/interpreted.
• All frames received are mapped to a specific connection if it exists. Otherwise, the frames are
dropped.
• No DE/CLP or FECN/EFI mapping is performed.
• “Illegal header count” and “Invalid DLCI” statistics are not kept.
• “Discarded frame count due to no connection” statistic is kept.
FUNI
The FRSM support the ATM Frame User to Network Interface (FUNI). Upon receiving a frame from
the FUNI interface, the 2 byte FUNI header is removed and the frame is processed into ATM cells
using AAL-5 for transmission over the network. In the reverse direction ATM cells are reassembled
into frames using AAL-5, the FUNI header is added and the frame is sent to the FUNI port.
Loss Priority Indication
Loss Priority Indication mapping is provided in both directions.
FUNI to ATM Direction
The CLP bit on the FUNI header is mapped to the CLP bit of every ATM cell that is generated for
the FUNI frame.
ATM to FUNI Direction
CLP bit in the FUNI header is always set to 0.