Cisco Systems MGX 8230 manual Frame Forwarding, ATM Frame-to-User Network Interface

Chapter 2 Module and Service Descriptions

Frame Relay Service Modules

Command and Response Mapping

Command/Response Mapping is provided in both directions.

Frame Relay–to–ATM Direction

The FRSM maps the C/R bit of the received Frame Relay frame to the CPCS-UU least-significant bit of the AAL5 CPCS PDU.

ATM to Frame Relay Direction

•The least-significant bit of the CPCS-UU is mapped to the C/R bit of the Frame Relay frame.

Translation and Transparent Modes

Each service interworking (SIW) connection can exist in either translation or transparent mode. In translation mode, the FRSM translates protocols between the FR NLPID encapsulation (RFC 1490) and the ATM LCC encapsulation (RFC 1483). In transparent mode, the FRSM does not translate. Translation mode support includes address resolution by transforming address resolution protocol (ARP, RFC 826) and inverse ARP (inARP, RFC 1293) between the Frame Relay and ATM formats.

Frame Forwarding

The FRSM card can be configured as “Frame Forwarding” on a port-by-port basis.

Frame forwarding operates the same as standard Frame Relay except that the FRSM:

•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.

ATM Frame-to-User Network Interface

All FRSMs support the ATM Frame-based User-to-Network Interface (FUNI). When a frame arrives from the FUNI interface, the FRSM removes the 2-byte FUNI header and segments the frame into ATM cells by using AAL5. In the reverse direction, the FRSM assembles ATM cells from the network into a frame by using AAL5, adds a FUNI header to the frame, and sends it 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.

	Cisco MGX 8230 Edge Concentrator Installation and Configuration
2-26	Release 1.1.31, Part Number 78-11215-03 Rev. B0, May 2001