IBM BC-201 manual BC-231

Overview of IBM Networking

DSPU and SNA Service Point

Figure 105 shows a router functioning as a DSPU concentrator.

Figure 105 Router Acting as a DSPU Concentrator

LU

LU

							PU 2 + 3 LU
	Token	RSRB			Token
	Ring				Ring
			PU 2	PU 5			PU 2 + 1 LU
Mainframe				DSPU concentrator
				supporting 4 PUs
with 1 PU and
				and 8 LUs
8 LUs defined						PU 2 + 2 LUs		S3223

Typically, a router establishes one or more upstream connections with one or more hosts and many downstream connections with PU type 2 devices. From an SNA perspective, the router appears as a PU type 2 device to the upstream host and assumes the role of a system services control point (SSCP) appearing as a PU type 5 device to its downstream PUs.

The SSCP sessions established between the router and its upstream host are completely independent of the SSCP sessions established between the router and its downstream PUs. SNA traffic is routed at a logical unit (LU) level using a routing algorithm that maps downstream LUs onto upstream LUs.

Figure 106 illustrates the SNA perspective of DSPU.

Figure 106 SNA Perspective of DSPU

Upstream PU

(PU type 2)

LU routing algorithm

Downstream PU A

(PU type 5)

Downstream PU B

(PU type 5)

S3224

	Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02		BC-231