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WAN Protocol

The router solution to this issue is to encapsulate all traffic in IP packets for transmission over the frame relay (or other) network in conjunction with a proprietary routing protocol. Thus, the router solution is based on adding IP framing overhead to all data prior to adding frame relay framing for transmission over the network. Because most router protocols are proprietary and noninteroperable, a single vendor’s product must reside on both sides of the network.

SNA Support

The router solution is to use data link switching (DLSw) to terminate SDLC and LLC2 traffic in the router and encapsulate the SNA data in IP using the DLSw routing protocol over the WAN. This provides a single backbone protocol for SNA and non-SNA traffic over the WAN. Once the SNA data is encapsulated in IP, the WAN treats it as any other IP traffic. The router solution requires a second DLSw-compatible router on the destination side of the frame relay network to remove the SNA data from the IP packet. However, DLSw only covers SNA/BNN PU2 data on SDLC lines and Token Ring LANs and NetBIOS traffic.

IBM uses RFC 1490 for the transmission of SNA data over a frame relay WAN network. RFC 1490 provides for the transport of SNA/BNN PU 2 and type 2.1, but also SNA Intermediate Network, APPN, and SNA Network Interconnect traffic across a frame relay network. Therefore, RFC 1490 covers all SNA traffic without encapsulation in IP, and DLSw covers only SNA/BNN PU2 traffic and adds the IP overhead.

Network Management

SNMP is the principal network management tool used with routers, whereas NetView is the network management tool of choice for SNA networks. The SNMP management stations are not usually located in corporate data centers, which necessitates a separate set of DLCIs for SNMP management to each remote location.

Such a scheme creates a redundant tier of network overhead that reduces bandwidth availability for data, impedes SNA session responsiveness and reliability, obstructs NetView visibility, and complicates network design and problem solving. This results in poor SNA network performance in terms of efficiency and cost.

When SNA is internetworked using routers that do not provide NetView support, a “black hole” is created in the network, preventing the NetView operator from viewing, managing, or monitoring the frame relay DTE devices. In particular, routers usually do not support SDLC LL2, LPDA-2, or NPM statistic collection.

IBM provides an integral NetView connection in all its frame relay products. NetView connections share the same PVCs as SNA data, thereby eliminating the need for a separate management network for communication with NetView and its component applications.

SUMMARY

Frame relay—multiplexing multiple protocols over a common link—is an efficient solution for unifying LAN and SNA networks. Frame relay is the WAN of choice for organizations moving to APPN. The wide-scale deployment of APPN networks will soon be served by IBM’s High Performance Routing (HPR) technology to deliver connectionless routing, and frame relay will be supported by IBM’s initial implementations of HPR. Exhibit 4-2-8 illustrates frame relay as the unifying network for LAN and SNA.


Exhibit 4-2-8.  Frame Relay as the Unifying Networks for LAN and SNA Networks

Current frame relay network specifications and service-provider implementations are designed for permanent virtual circuits. PVCs provide a direct replacement for leased-line SNA connections, but SNA networks often include switched, dial-up SDLC connections for casual SNA host access. This capability is being added to frame relay. A number of vendors have initiated standardization of switched virtual circuits (SVCs).

Frame relay is also being positioned as the access network for ATM. An RFC that specifies a frame relay interface to ATM networks is currently being worked through the standards process. This interface, referred to as data exchange interface (DXI), covers ATM adaptation layer 1 (AAL 1).

Frame relay provides users with short-term payback and long-term preparedness—immediate economic benefits and a migration path to future, high-performance routing and networking.


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