Managed Systems Network Architecture (SNA) Services

As companies move from IBM s host-centric (i.e., mainframe) to the distributed computing environment (i.e., Local-Area Networks [LANs]), the major carriers are offering Wide-Area Network (WAN) services that address the specific needs of SNA users. Typically, these managed SNA services operate over Frame Relay connections, but they can also operate over well-managed IP backbones. Such services are especially suited to organizations that have many remote locations that must be tied into one or more hosts. Among the advantages of managed SNA services over Frame Relay are the following:

• Frame Relay s Permanent Virtual Circuits (PVCs) replace expensive Synchronous Data Link Control (SDLC) and Binary Synchronous Communications (BSC) multi-drop networks between the host and branch offices.
• Consolidating connections through Frame Relay eliminates costly Serial-Line Interface Coupler (SLIC) ports on Front End Processors (FEPs) while increasing performance.
• WAN access extends the useful lives of SDLC/BSC controllers and 3270 terminals.
• The availability and reliability of SNA connections are increased by enabling controllers to take advantage of WAN connections that have multiple host paths.

A managed Frame Relay service includes the Frame Relay Access Devices (FRADs) leased or purchased that transport SNA traffic over the PVCs. FRADs are more adept than routers at congestion control and prioritization. Some FRADs multiplex multiple SNA/SDLC devices onto the same PVC instead of requiring separate PVCs for each attached device, resulting in even greater cost savings.

The FRADs encapsulate SNA/LLC2 frames with minimal overhead and enable...