SNA access methods for Db2 data sharing (deprecated)

Systems Network Architecture (SNA) is a proprietary IBM® architecture that describes the logical structure, formats, protocols, and operational sequences for transmitting information units through, and controlling the configuration and operation of, networks. SNA access for Db2 for z/OS® is deprecated, which means that it is supported but not recommended, and support might be removed eventually.

Tip: TCP/IP is the recommended communication protocol for communication with Db2. Although SNA communication remains supported in Db2 13, SNA communication (including the VTAM interface) is deprecated, and support might be removed in the future. You can disable SNA communication by setting the value of the DB2 TCP/IP IPNAME setting. See DB2 TCP/IP IPNAME field.

SNA contains several functional layers and includes the following components:

An application programming interface (API) called Virtual Telecommunications Access Method (VTAM®)
A communications protocol for the exchange of control information and data
A data link layer called Synchronous Data Link Control (SDLC)

SNA also includes the concept of nodes, which can contain both physical units that provide certain setup functions, and logical units (LUs), each of which is associated with a particular network transaction.

A data sharing group can simultaneously serve requesters that use member-routing access, group-generic access, and single-member access. As a server, the group is flexible about the access methods that requesters use. A requester can use member-routing access in one session and use group-generic access in another session. However, as a requester, the group always uses the same access method when communicating with a particular server.

Recommendation: Configure a data sharing group to use member-routing access whenever possible, unless your requester does not support it. It provides better workload balancing and two-phase commit support than group-generic access.

In SNA networks, each member of a data sharing group has its own LU name (in addition to the net ID that the member obtains from VTAM when the DDF starts). You can also define a generic LU name that represents all the members in the group.

An SNA requester can use one of several access methods to connect to a data sharing group:

Member-routing access: A requester can define a server location name that is associated with many LU names. Unlike with the generic LU name, a requester can establish sessions with one or more subsystems in the group. For member routing, the requests are distributed to members of the data sharing group based on their capacity.
Group-generic access: A requester uses the group's generic LU name to make an initial connection to any member of the group. With this access method, VTAM chooses one of the group members and establishes a session with that member on behalf of the requester. Subsequent queries from the requester are also directed to that same member.
Single-member access: A requester uses a member's LU name to connect and send queries to a single member of the group. All connection and query requests from that requester are directed to the same member.