IBM BC-203 manual Sna Fras, RFC 1490 Routed Format for LLC2 BNN, BC-226

Overview of IBM Networking

SNA FRAS

SNA FRAS

Using Frame Relay Access Support (FRAS), the Cisco IOS software allows branch SNA devices to connect directly to a central site front-end processor over a Frame Relay network. FRAS converts LAN or Synchronous Data-Link Control (SDLC) protocols to a Frame Relay format understood by the Network Control Program (NCP) that runs in an FEP. The Cisco IOS software and the NCP support two frame formats:

•RFC 1490 routed format for LLC2, specified in the FRF.3 Agreement from the Frame Relay Forum and known in NCP literature as Frame Relay Boundary Network Node (BNN) support. Support for this feature requires NCP 7.1 or higher.

•RFC 1490 802.5 source-route bridged format, known in NCP literature as Frame Relay Boundary Access Node (BAN) support. Support for this feature requires NCP 7.3 or higher.

Management service point support in FRAS allows the SNA network management application, NetView, to manage Cisco routers over the Frame Relay network as if it were an SNA downstream PU.

FRAS provides dial backup over RSRB in case the Frame Relay network is down. While the backup Public Switched Telephone Network (PSTN) is being used, the Frame Relay connection is tried periodically. As soon as the Frame Relay network is up, it will be used.

This section contains a brief overview of SNA FRAS which is described in the following topics:

•RFC 1490 Routed Format for LLC2 (BNN), page 226

•RFC 1490 Bridged Format for LLC2 (BAN), page 227

RFC 1490 Routed Format for LLC2 (BNN)

RFC 1490 specifies a standard method of encapsulating multiprotocol traffic with data link (Level 2 of the OSI model) framing. The encapsulation for SNA data is specified in the FRF.3 Agreement.

The Frame Relay encapsulation method is based on the RFC 1490 frame format for “user-defined” protocols using Q.933 NLPID, as illustrated in Figure 98.

Figure 98 Frame Relay Encapsulation Based on RFC 1490

DLCI	Control	NLPID	L2	L3	DSAP	Control	F	S3217
Q.922	0x30	Q.933	Protocol ID	Protocol ID	SSAP		C
Address		0x08	0x4c (802.2) 0x08				S

Note The protocol ID for SNA subarea FID4 is 0x81. The protocol ID for SNA subarea FID2 is 0x82. The protocol ID for APPN FID2 is 0x83.

FRAS allows the router acting as a FRAD to take advantage of the SNA BNN support for Frame Relay provided by ACF/NCP 7.1 and OS/400 V2R3. Downstream PU 2.0 and PU 2.1 devices can be attached to the router through SDLC, Token Ring, or Ethernet links. The router acting as a FRAD is connected to the Network Control Program (NCP) or AS/400 through a public or private Frame Relay network, as illustrated in Figure 99.

Cisco IOS Bridging and IBM Networking Configuration Guide

BC-226