gtps2m0hACF/SNA Data Communications Reference

Subarea (PU_5) Environment

Cross-Domain Links

A cross-domain link interconnects locally attached NCPs and hosts. Cross-domain links are shown in Figure 3. SNA CTC support requires the channel-attached major node to reside in the same network as VTAM, with no SNI support.

Note:
In communications terms, local or locally attached refers to direct channel attachment. Remote or remotely attached refers to a link (communications line) attachment.

Figure 3. Cross-Domain Communication Link


Cross-domain links present an identical appearance to each domain. Both domains share equally in enabling a cross-domain link. Multiple links provide additional "bandwidth" among domains. Therefore, all interdomain communication does not depend on 1 link. Figure 4 represents a network with multiple links.

Figure 4. Multiple Cross-Domain Links


A cross-domain link must be enabled before cross-domain communication can take place. The network operators in each domain jointly enable the link.

Note:
The network operators must activate the link before the path can be enabled.

Cross-Domain Resource Manager (CDRM)

The system services control point (SSCP) manages the resources for a single domain. In this capacity, the SSCP is often called a domain resource manager (DRM). The DRM activates the network and controls session startup and termination. In a multiple-domain network, SSCP (DRM) functions are extended to include management of cross-domain communication. A cross-domain resource manager (CDRM) to CDRM session must be established before data can be transmitted between domains. In this type of session, the CDRMs work in tandem to activate, maintain, and terminate sessions between LUs in their respective domains.

Cross-Domain Sessions

A cross-domain LU-LU session must be established before a TPF logical unit can communicate with a second domains logical unit. Only after the SSCP to physical unit and SSCP to logical unit sessions are established in the respective single domains can a cross-domain session be initiated. Requests for a cross-domain LU-LU session also require that a session first be established between the SSCPs in the 2 domains. The processing to request a cross-domain session is outlined below. To aid in understanding the processing paths, LUs and SSCPs are numbered. The numbers have no additional significance.

Figure 5 shows the data flow paths for a cross-domain LU-LU session.

Figure 5. Cross-Domain LU to LU Session Data Flow