Overview of IBM Networking
SNA FRAS
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 224
•RFC 1490 Bridged Format for LLC2 (BAN), page 225
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
Figure 98 Frame Relay Encapsulation Based on RFC 1490
DLCI | Control | NLPID | L2 | L3 | DSAP | Control | F |
|
Q.922 | 0x30 | Q.933 | Protocol ID | Protocol ID | SSAP |
| C | 51911 |
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.
Figure 99 SNA BNN Support for Frame Relay
Frame Relay
NCP
SDLC
Token
Ring
S3218
The frame format that communicates across the Frame Relay BNN link is defined in RFC 1490 for routed SNA traffic. From the perspective of the SNA host (for example an NCP or AS/400), the Frame Relay connection is defined as a switched resource similar to a Token Ring BNN link. Because the frame format does not include link addresses to allow the NCP to distinguish among SNA devices on the same
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