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# Introducing BEA eLink TCP for TUXEDO

The BEA eLink for Mainframe TCP for TUXEDO (hereafter referenced as eLink TCP for TUXEDO) product is a domains-based gateway connectivity feature that makes it possible for application programs on BEA TUXEDO systems to perform non-transactional tasks with application programs in other OLTP systems that support eLink TCP for TUXEDO gateways. These include:

- CICS on IBM MVS systems

- IMS/TM on IBM MVS systems

- IMS/DC on IBM MVS systems

- IMS/OTMA on IBM MVS systems

  The BEA eLink TCP for TUXEDO is designed to provide transparent access to services that reside outside a BEA TUXEDO region. The eLink TCP for TUXEDO gateway validates and acts on behalf of a remote client making a request, without performing user authentication. In addition, eLink TCP for TUXEDO can provide remote application programs with access to local services if this is supported by the release of eLink TCP for TUXEDO software installed on the remote system.

  This document provides information about the following topics:

  - BEA eLink TCP for TUXEDO and the BEA TUXEDO Architecture

  - BEA eLink TCP Functionality

  - GWIDOMAIN Gateway Component

  - How eLink TCP for TUXEDO Affects BEA TUXEDO Application Programs

  - How eLink TCP for TUXEDO Affects BEA TUXEDO Administration

  ## BEA eLink TCP for TUXEDO and the BEA TUXEDO Architecture

  A BEA TUXEDO region consists of client and server programs that operate across a network of BEA TUXEDO systems or compatible systems. Any client program can request services that are offered by any server program running on any computer in the region. Further, by way of a directory that maps services to servers, the location of server programs is kept transparent.

  As Figure 1-1 shows, eLink TCP for TUXEDO extends this transparent access by sending requests to and receiving requests from remote regions and systems through TCP/IP network software.

  > Figure 1-1 Routing Service Calls through BEA eLink TCP for TUXEDO

  .

  As Figure 1-1 suggests, inside a single region, eLink TCP for TUXEDO fits between the BEA TUXEDO software and TCP/IP.

  - When local client programs send requests to remote systems, eLink TCP for TUXEDO transforms those requests into messages formatted appropriately for transmission to the remote system. Also, when remote systems respond, eLink TCP for TUXEDO transforms these responses into replies that local client programs can process.

  - When remote client programs send request messages, eLink TCP for TUXEDO transforms those messages into requests that local service routines can process. Also, when local service routines send replies, eLink TCP for TUXEDO transforms those replies into messages that remote services can process.

  BEA eLink TCP for TUXEDO is implemented as a TUXEDO domain gateway. It accepts standard BEA TUXEDO service requests and returns standard replies.

  One eLink TCP for TUXEDO gateway connects to multiple communications targets, also referred to as gateways. Each communications target, or gateway, is a unique network endpoint.

  The remote gateways must also support eLink TCP for TUXEDO. BEA eLink TCP for TUXEDO servers associated with the local gateway communicate with remote eLink TCP for TUXEDO gateways to non-BEA TUXEDO TP monitors, such as eLink TCP for CICS and eLink TCP for IMS.

  Although remote systems are identified in the eLink TCP for TUXEDO configuration, they remain unknown to BEA TUXEDO software. For example, remote systems that are accessible through eLink TCP for TUXEDO are not identified in the *MACHINES section of the UBBCONFIG file.

  BEA eLink TCP for TUXEDO maintains its own control information in shared memory, in much the same way that BEA TUXEDO software itself maintains the Bulletin Board. Although eLink TCP for TUXEDO accesses the BEA TUXEDO Bulletin Board, BEA TUXEDO does not access eLink TCP for TUXEDO control information.

  ## BEA eLink TCP Functionality

  The following functionality is available in this version of eLink TCP.

  ### Domains-based Gateway Connectivity

  The eLink TCP product has a domains-based architecture supporting bidirectional communications, request/response support, and concurrent support for MVS BMP and Open Transaction Manager Access (OTMA) interfaces.

  ### Security

  The eLink TCP for TUXEDO product grants access to BEA TUXEDO services based on a user name that the remote gateway supplies.

  The eLink TCP for CICS product can initiate transactions or link to programs. BEA TUXEDO security provides the USERID value to the eLink TCP product to test for appropriate security prior to initiating the transactions.

  The eLink TCP for IMS product has an OTMA interface that supports enhanced security. This interface allows a BEA TUXEDO requester to pass a USERID through the OTMA server interface for authorization through a third-party security package, such as RACF.

  ### Connection Multiplexing

  The eLink TCP for TUXEDO allows multiple requests to process simultaneously over a single connection. This is known as connection multiplexing. Two connecting gateways determine a multiplex count that is acceptable to both sides at connection time. After establishing the connection, clients can send multiple requests (up to the number in the multiplex count) to the server gateway. Connection multiplexing allows for more efficient use of sockets and other system resources by the eLink TCP gateways.

  Note: Each connection is one-directional, which means clients on opposing platforms cannot use the same connection to communicate with remote servers.

  ### Domain Name Server Support

  The eLink TCP product supports domain name server (DNS) resolution of IP addresses. This support allows you to change the IP address at the Domain Name Server to implement address changes without reconfiguring the eLink TCP gateway.

  ## GWIDOMAIN Gateway Component

  The eLink TCP product consists of a single component, the GWIDOMAIN gateway. This gateway is responsible for the processing of all incoming and outgoing requests. It also maintains connections with all remote gateways.

  ## How eLink TCP for TUXEDO Affects BEA TUXEDO Application Programs

  BEA eLink TCP for TUXEDO preserves the high degree of location transparency that BEA TUXEDO software provides. In fact, in virtually all cases, programmers do not need to know that particular services are provided by remote systems.

  BEA eLink TCP for TUXEDO supports the main BEA TUXEDO communication paradigm: request/reply communications (either synchronous or asynchronous).

  All BEA TUXEDO buffer types can be employed for data exchange. These include:

  - X/Open standard XATMI buffer types

  - X_OCTET

  - X_C_TYPE

  - X_COMMON

  - BEA TUXEDO ATMI buffers

  - CARRAY

  - STRING

  - FML

  - VIEW

  Each of the three X/Open buffer types is equivalent to a BEA TUXEDO ATMI buffer type. The following information provides these equivalencies.

  - X_OCTET is equivalent to CARRAY

  - X_C_TYPE is equivalent to VIEW

  - X_COMMON is equivalent to VIEW, but represents only the subset of field types that are common to both the C and COBOL languages

  ### VIEW Definitions

  In some circumstances, you must convert typed buffers to formats that are acceptable to target systems. The standard BEA TUXEDO system VIEW definition mechanism is employed for this purpose.

  VIEW definitions make it possible to map input data and output data between different programming environments (such as C and COBOL). They also enable eLink TCP for TUXEDO to convert data representations automatically between different systems

  VIEW definitions can be created by programmers or system administrators. See "Getting Ready to Configure BEA eLink TCP for TUXEDO," for details. For more detailed information about programming considerations, see "Understanding How BEA eLink TCP for TUXEDO Works."

  ### FML Buffer Support

  When communicating with systems or regions that do not support FML buffers directly, the eLink TCP for TUXEDO gateway can convert FML buffers to or from user-defined record layouts in a manner transparent to the FML application. Thus, once a VIEW definition that describes the remote application's record layout is created, it can be used to convert the record to or from an FML buffer. The GWICONFIG and DMCONFIG files (eLink TCP for TUXEDO configuration file) contains VIEW specifications as part of the service description.

  Through this conversion between ATMI buffers and record structures, eLink TCP for TUXEDO supports sending fielded buffers containing FML data between regions. The eLink TCP for TUXEDO software converts the data from FML buffers to user-defined records using the VIEW definitions and field descriptions at the originating region.

  ## How eLink TCP for TUXEDO Affects BEA TUXEDO Administration

  BEA eLink TCP for TUXEDO administration tools and features are thoroughly integrated with BEA TUXEDO administration tools and features. Here are some specific examples:

  - System administrators define eLink TCP for TUXEDO in the BEA TUXEDO configuration as a regular TUXEDO domain gateway.

  - The eLink TCP for TUXEDO configuration file (GWICONFIG) specifies how local BEA TUXEDO service names are mapped to remote service names. Also, the GWICONFIG file identifies VIEW definitions that eLink TCP for TUXEDO uses to convert and translate input and output data.

  - At runtime, system administrators use BEA TUXEDO `tmadmin` subcommands to manage eLink TCP for TUXEDO and related processes.

  For more detailed information about configuring eLink TCP for TUXEDO, see "Getting Ready to Configure BEA eLink TCP for TUXEDO," and "Configuring BEA eLink TCP for TUXEDO." For detailed information about commands for administering eLink TCP for TUXEDO, refer to the BEA TUXEDO Administrator's Guide and the BEA TUXEDO Domain User Guide.

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