IBM BC-203 - Manual (Page 24)

Overview of IBM Networking
SNA FRAS
BC-226
Cisco IOS Bridging and IBM Networking Configuration Guide
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
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.
DLCI
Q.922
Address Control
0x30 NLPID
Q.933
0x08 L2
Protocol ID
0x4c (802.2) 0x08 L3
Protocol ID DSAP
SSAP Control F
C
S
S3217