What is OTMA?

OTMA has similarities to network protocols.

Several architectural models for networks exist. The following figure shows two. The simplified four-layer model shown on the right is often used in descriptions of UNIX networks. In the open systems interconnection (OSI) model, shown on the left, OTMA is the session layer. Both models have a Transport, Network, and Data Link layer. The OSI model also includes layers for Application, Presentation, and Session, and the simplified model includes a process layer. In the four-layer model, OTMA is the process layer.

Figure 1. Network architecture models
Left column shows OSI Model and layers. Right column shows simplified four-layer model. OTMA sits between.
OTMA, however, does not exactly conform to the OSI model, because OTMA can process several sessions simultaneously using a single transport connection, if the following are true:
  • The z/OS® cross-system coupling facility (XCF) is the transport layer.
  • A session is the connection between IMS and a client.
  • A client or server only creates a single XCF connection.

OTMA performs some of the basic functions of the OSI transport layer (those not performed by XCF), so it is simplest to think of OTMA as a combined session and transport layer, with the transport layer comprised of both XCF and OTMA.

Although you can think of OTMA as a session and transport layer in a network architecture model, OTMA is designed to be a high-performance comprehensive protocol that allows z/OS programs to access IMS applications.

Definitions:  A z/OS program in this case means any z/OS application that is a member of an XCF group that includes IMS. The XCF group members that IMS communicates with are called OTMA clients.

By using OTMA, each client (z/OS application) can submit transactions to IMS or issue IMS commands and receive output from IMS application programs and from IMS itself.

Definition:  Because IMS can communicate with, or serve, many OTMA clients, IMS is called the server. However, OTMA only operates in the following IMS environments: