Handbook of Local Area Networks, 1998 Edition:Advanced LAN Interconnectivity Issues and Solutions
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SNA FRAME RELAY NETWORKS
IBM provides connections for frame relay networks on all its current networking products, including 3745 communication controller, 3172 interconnect controller, OS/2 RouteXpander/2, 3174 network server, AS/400, and the 6611 network processor. Users can evolve their current SNA networks from an SDLC multidrop backbone to a frame relay WAN. IBM supports all SNA topologies: Intermediate Network Node, Boundary Network Node, SNA Network Interconnect, and APPN across a frame relay network.
IBM’s frame relay products are configured as frame relay DTE devices, except the FEP (3745 communication controller), which can also be configured as a frame relay data communications equipment (DCE) device and can act as a frame relay switch.
Intermediate Network Node (INN)
IBM’s NCP software provides an INN connection—PU4-to-PU4—between FEPs over a frame relay network. This support was first announced for NCP Version 6, Release 1 (V6R1) in 1992. IBM supports mixed-media, multiple-link transmission groups that can include frame relay, SDLC, and Token Ring links. Thus, frame relay can be incorporated with other data link types in a transmission group to give users flexibility in network design.
Because frame relay is an OSI level 2 routing protocol, it provides fast INN routing, which is an efficient means of interconnecting multiple FEPs. Level 2 frame relay eliminates SNA processing on intermediate FEPs. Furthermore, as each pair of FEPs appears to be directly linked, the intermediate network configuration is transparent to SNA routing algorithms.
SNA Network Interconnect (SNI)
NCP Release 6, Version 1 also introduced SNA over frame relay for interconnecting multiple SNA networks. Two traditional SNA networks can be connected using an SNI link over frame relay so the users of one SNA network can access the resources or applications of another across a frame relay network.
Boundary Network Node (BNN)
NCP Version 7, Release 1 fully expands the role of the NCP to that of providing SNA Boundary Network Node—PU4-to-PU2—connectivity between an NCP and an SNA node (PU2/2.1). The FEP can establish an SNA/BNN connection across a frame relay network with users on a 3174 network processor or users connected through an IBM 6611 network server or RouteXpander/2.
AS/400
IBM’s AS/400 supports direct frame relay connectivity to another AS/400 or through a frame relay bridge to a 5494 remote controller or PC workstation. SNA nodes connected to an AS/400 across a frame relay network must be SNA Type 2.1 nodes, such as an IBM 5494 remote controller.
APPN
IBM’s APPN Network Node products, 6611 IBM Network Processor, AS/400, and OS/2 Communication Manager (RouteXpander/2) can be configured to establish an APPN network across a frame relay WAN. APPN end-node applications can thus take advantage of the combined frame relay and APPN network.
IBM Legacy Devices
Many IBM networks include legacy devices that are incapable of supporting frame relay network access, such as 3274 controllers, System 3X computers, and 5394 controllers. A frame relay assembler/disassembler (FRAD) provides connection to a frame relay network for a non-frame relay capable device.
A FRAD translates the SNA controller’s SDLC data stream into frame relay frames for transport over the network. FRADs based on RFC 1490 can interoperate across a frame relay network with IBM’s frame relay products. Interoperability with IBM requires that the SDLC be converted to LLC2 for encapsulation in frame relay.
In addition to basic framing functions, a FRAD usually concentrates a number of low- or medium-speed SDLC lines into a single, high-speed frame relay link. By combining data from multiple, low-speed controllers onto one or more high-speed lines, FRADs reduce overall network costs.
Private Frame Relay Network
NCP Version 6, Release 2 (V6R2) adds DCE support to the front-end processor. The FEP functions as a frame relay switch (i.e., DCE) for frame relay DTE equipment, such as an OS/2 RouteXpander, so users can create private frame relay networks based on the IBM FEP. Private frame relay networks support both SNA and LAN protocols. In summary:
• All current IBM SNA products provide frame relay network access.
• All SNA topologies are supported across a frame relay network.
• FRADs can be used to provide high-performance connectivity for Legacy IBM SDLC and BSC devices.
IBM MULTIPROTOCOL SUPPORT
IBM’s frame relay access products use the RFC 1490 standard, which specifies the frame format and characteristics for multiplexing multiple protocols across a frame relay network on a single, frame relay link.
Treatment of LAN protocols is similar to that described for SNA-over-frame relay. The RFC 1490 header for LAN protocols indicates whether the packet is being bridged or routed. A bridged frame header includes what media it is originating on—802.3, 802.4, 802.5, FDDI, or 802.6—whether it is being source routed or transparently bridged, and its destination medium access control (MAC) address.
Some routed protocols have an assigned Direct Network Layer Protocol Identifier, or NLPID, such as IP. For these protocols the NLPID is used to identify the frame. Otherwise, the Subnetwork Access Protocol (SNAP) header for the frame is used to identify frame contents.
RFC 1490 specifies the transport of both bridged and routed LAN protocols across a common frame relay interface and provides a standard format for the frame relay packets. RFC 1490 specifies for bridged data the protocol being used—source route or transparent—and thus facilitates multivendor networking based on industry standard implementations. For routed data, however, there is currently no means of specifying the routing protocol being used for a given LAN protocol, so interoperability of routed protocols is more complicated.
All of IBM’s frame relay products provide for multiprotocol support over frame relay. This support is available over public and private frame relay networks and includes both the bridging and routing of LAN protocols. The IBM 6611 also allows SNA/SDLC traffic to be transported across a frame relay WAN.
NETWORK MANAGEMENT
With the addition of frame relay as a packet-mode WAN supported by IBM’s NCP software, IBM incorporates support for frame relay WANs in NetView network management software, including NPM and NTune and NetView/6000, its SNMP manager. IBM provides a complete picture of the SNA and frame relay internetwork including both SNA and non-SNA traffic and DTE devices. Exhibit 4-2-5 shows the SNA network management topology.
Exhibit 4-2-5. SNA Network Management Topology
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