Extending the economic and technical usefulness of existing investments in networking infrastructure is one of SOGA's strong points. Most organizations have existing leased-line SDLC connections that can be used with branch-based deployments, as well as with distributed deployments as backup connections. See Figure 2.2 for a depiction of a traditional branch-based deployment leveraging existing investments in leased-line SDLC connections.
SNA Server supports the following vendors' SDLC adapters:
Organizations make use of existing X.25 private or public Packet Switched Networks (PDNs) to link branch-based SNA gateways with central-site host computers. These X.25 connections are primarily used in branch-based deployments to link remote SNA Server computers with central-site host systems.
In a distributed deployment model, X.25/QLLC connections can be used as a means to provide fault tolerance in cases of general WAN failure. See Figure 2.2 for a depiction of a traditional branch-based deployment leveraging existing investments in X.25 PDNs.
SNA Server supports the following vendors' X.25 adapters:
One of the most popular methods for integrating SNA and TCP/IP networks is to use router-based DLC encapsulation within IP to extend SNA from the branch offices to the central site. An industry standard called Data Link Switching has emerged as the open, interoperable way to accomplish this integration. Under
SOGA, the branch-based SNA Server computers that connect to the host using the DLC protocol often rely on the DLSw support in routers to transmit the SNA traffic to the central-site LAN. See Figure 2.3 for a depiction of a branch-based configuration using DLSw.
RFC1490 is emerging as an industry standard for routing DLC traffic over frame relay networks. Implemented as a software option in the branch-based router or FRAD, RFC 1490 picks up DLC traffic from the branch LAN and passes the SNA traffic through one or more virtual circuits across the frame relay network to the central site. This capability in routers and FRADs is a natural complement for branch-based deployments of SNA Server computers. See Figure 2.3 for a depiction of a branch-based configuration using frame relay.
Additionally, a central-site SNA gateway could leverage frame relay to connect the branch-office LANs with the central-site LAN. Frame relay is also an essential component of a distributed deployment configuration. Branch-based SNA gateways can communicate with the central site over a frame relay WAN. See Figures 2.4 and 2.5 for depictions of a frame relay WAN used in centralized and distributed deployment models respectively.
Centralized deployments can use an ATM WAN to connect branch LANs with central-site LANs. The branch-based desktops connect to the centrally located SNA Server computers across the ATM WAN. ATM can also be used in a distributed deployment configuration to link remote SNA Server computers in branch offices to SNA Server computers located near host systems in central offices. See Figures 2.4 and 2.5 for depictions of a WAN using ATM technology to deploy a centralized and distributed configuration respectively. See Figure 2.3 for a depiction of a branch-based configuration using ATM.
The TN3270 standard is gaining popularity as a way to access 3270 applications on IBM mainframes over a TCP/IP network. This approach has the same attractiveness as the distributed link service: the enterprise network can be entirely based on TCP/IP with no DLC tunneling or encapsulation. In addition to split-stack SNA client support, SNA Server can also act as a TN3270 server, connecting to the mainframe via SNA protocols.
A channel-attached SNA Server can act as a centralized TN3270 server, providing a more complete TCP/IP-to-SNA off-load than the IBM 3172 controller. SNA Server supports TN3270, TN3287, and TN3270E, as well as split-stack TCP/IP clients for LU0 and LU6.2 applications. Other TCP/IP-to-SNA gateways support only the base TN3270 capability. For more information see "Integrating IBM Mainframes with TCP/IP Networks" on Microsoft's World Wide Web site at http://www.microsoft.com/sna.