IBM BC-201 manual Advantages of the Client/Server Model, Extended Scalability, BC-228

Overview of IBM Networking

NCIA

After the peer session has been established, the NDLC protocol establishes the circuit between the client and server. This circuit is used to transfer end-user data between the client and the server. Because the client and its target station are not on the same transport, they cannot form a direct, end-to-end circuit. Each client must form a circuit between the client and server, and the server must form another circuit between the server and the target station. The server links those two circuits to form an end-to-end circuit. The server acts as a mediator between the client and the target station so that packets can be transferred between them.

In the NCIA server only peer keepalive is maintained. There is no keepalive at circuit level.

The NCIA server acts as a data-link provider, like Token Ring or Ethernet, in the router. It uses CLSI to communicate with other software modules, just as other data-link providers do. The network administrator configures the router to communicate with specific modules. For data-link users, such as SNASw, DLSw+, and DSPU, the NCIA server can interface to them directly. For other data-link providers, the NCIA server must go through a DLSw+ local peer to communicate with them. The DLSw+ local peer passes packets back and forth among different data-link providers.

Advantages of the Client/Server Model

The client/server model used in the NCIA Server feature extends the scalability of NCIA. In addition, it provides support for both the installed base of RSRB routers and the growing number of DLSw+ routers.

Extended Scalability

The client/server model minimizes the number of central site RSRB or DLSw+ peer connections required to support a large network of NCIA clients (see Figure 102). Rather than each client having a peer connection to a central site router, the clients attach to an IP backbone through an NCIA server that, in turn, has a single peer connection to a central site router. This scheme can greatly reduce the number of central site peer connections required. For example, in a network with 1000 clients and 10 NCIA servers, there would be only 10 central site peer connections. Note that there would still be 1000 LLC2 connections that must be locally acknowledged at the central site router, but this can easily be handled in a single central site router. When the number of LLC2 connections (or the number of clients) is in the tens of thousands, NCIA servers can take advantage of downstream PU concentration to minimize the number of LLC2 connections that must be supported by the central site routers.

Figure 102 NCIA Server Provides Extended Scalability to Support Large Networks

RSRB	RSRB
IP	Token
backbone
	Ring

Mainframe

with FEP

NCIANCIA

server client

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	Cisco IOS Bridging and IBM Networking Configuration Guide
BC-228	78-11737-02