View figure.
The components of CS/AIX and their relationships are shown in Figure 17.
Figure 17. Components of CS/AIX
| View figure. |
The local node--including its associated connectivity resources (DLCs, ports, and link stations)--is implemented as a set of STREAMS components in the kernel of the AIX system.
The APPC transaction programs, CPI-C applications, LUA applications, and the remote command facility (RCF) are user-space programs. CS/AIX supports multiple APPC TPs, CPI-C applications, and LUA applications running concurrently.
A server running CS/AIX implements an SNA node. It can also provide passthrough services between an SNA host and computers in an APPN or TCP/IP network.
CS/AIX provides SNA node type 2.0 and 2.1 (LEN node) support for communicating with host and peer computers; it also implements an APPN node, providing end node, branch network node, or network node function according to its configuration.
CS/AIX implements an APPN node to communicate with other nodes on the SNA network. This provides logical unit (LU) 6.2 support for APPC and CPI-C capabilities and for 5250 emulation, in addition to LU 0, 1, 2, and 3 support for 3270 and LUA communications.
CS/AIX can operate as any of the APPN node types (LEN, end, network, or branch network node), depending on its configuration. Certain functions are supported only on particular node types, as defined by the APPN architecture. These differences are indicated where necessary in this manual; where no differences are indicated, the information applies to all node types.
Passthrough services enable downstream computers on a LAN to access host resources through a server running CS/AIX, or enable computers to access SNA resources across mixed SNA and IP networks. CS/AIX provides the following passthrough services:
In addition to providing direct access to a host computer, CS/AIX can provide SNA gateway facilities. This feature enables other computers to access a host computer through the CS/AIX node, instead of requiring a separate connection to the host from each computer.
The SNA gateway feature is shown in Figure 18.
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The downstream computer must contain an SNA PU type 2.0 or 2.1 to support dependent LUs. For example, the downstream computer could be a PC running Communications Server for Windows NT, or another CS/AIX computer.
When the local CS/AIX node uses the SNA gateway feature, all the data transferred between the host and the downstream computer is routed through the local node. This enables a downstream computer to share a host connection with CS/AIX or with other downstream computers, instead of requiring a direct link. For example, you could set up several downstream computers connected to CS/AIX over a local token ring network, so that they could all access the same long-distance leased line from CS/AIX to the host.
Using SNA gateway also simplifies the configuration at the host, because you do not need to define the downstream computers and the communication links to them. The host configuration needs to include only the CS/AIX computer and its host communication link; the LUs at the downstream computers are configured as part of the resources of the CS/AIX computer. The host computer is not aware that SNA gateway is being used.
This section does not apply to LEN nodes.
In addition to providing direct access to a host computer, CS/AIX can provide dependent LU requester (DLUR) facilities. This feature enables sessions for dependent LUs to span multiple nodes in an APPN network, instead of requiring a direct connection to the host.
DLUR on the CS/AIX node works in conjunction with dependent LU server (DLUS) at the host. Together, they route sessions across the network from dependent LUs in the APPN network to the DLUS host. The route to the host can span multiple nodes and can take advantage of APPN's network management, dynamic resource location, and route calculation facilities.
If the local node is a network node, dependent LUs on downstream computers connected to the CS/AIX node can also use passthrough DLUR on the CS/AIX node--in the same way that LUs internal to the node do--to access the host across the network.
3270 emulation programs that communicate over TCP/IP (rather than over an SNA network) are referred to as TN3270 programs (Telnet 3270 emulation programs).
TN3270 programs can also include support for TN3270E (Telnet 3270 standard extensions). TN3270E supports 3270 device emulation (including both terminals and printers) using Telnet. It enables a Telnet client to select a particular device (by specifying the LU name), and provides enhanced support for various functions, including the ATTN and SYSREQ keys and SNA response handling.
| Note: | This guide uses the term TN3270 for information that applies equally to the TN3270, TN3287, and TN3270E protocols. |
CS/AIX TN server provides access to 3270 host computers for TN3270 users on other computers. TN server enables TN3270 users to share a host connection with CS/AIX or with other TN3270 users, instead of requiring a direct link. TN server also enables TN3270 users to access hosts that are not running TCP/IP.
CS/AIX TN server supports all TN3270 client emulation programs that correctly implement the protocols defined in RFCs 1123, 1576, 1646, and 1647.
The CS/AIX TN server function is shown in Figure 19.
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The CS/AIX TN server feature provides an association between a TN3270 user and CS/AIX 3270 LU. All data from the TN3270 user is routed to the LU. This means that the configuration for both the host and the TN3270 user is as though they were connected directly; neither needs to be aware that data is being routed through TN server.
When a TN3270 program communicates with TN server, CS/AIX identifies the program by the TCP/IP address of the computer where the TN3270 program is running. CS/AIX cannot distinguish between two different TN3270 programs being used by different users on the same computer. In the CS/AIX manuals, the term TN server user refers to the computer where a TN3270 program is running, not to an individual user of that program.
Each TN server user is normally configured to access a single 3270 LU, and so is restricted to one host session at a time. However, you can also configure a TN server user to access a pool of 3270 LUs, instead of having a single dedicated 3270 LU for each user. This enables the user to access as many sessions as there are available LUs in the pool.
CS/AIX TN Server supports data encryption, server authentication, and client authentication, using Secure Sockets Layer (SSL) software:
This feature is only available on AIX 4.3.1 and above, and requires some additional software in addition to the standard CS/AIX product. See Communications Server for AIX Quick Beginnings for more information.
CS/AIX TN Server also supports Service Location Protocol (SLP), providing service location and load balancing functions. If you use SLP, each TN Server advertises:
Because SLP is concerned with providing services that are available for use by any TN3270 client, it operates only if you have defined a default TN3270 access record to allow access by any client. The TN Server's services are not advertised if you restrict access to specific named clients and do not include a default record.
An SLP-capable TN3270 client can then select the "best" server to connect to (the least loaded server that provides the functions it requires). It does this either by querying TN Servers directly, or by querying a Directory Agent that in turn collects information advertised by TN Servers.
A large SLP network can be divided into "scopes" (typically based on departments or geographical areas), so that information about a TN Server is advertised only to TN3270 clients and Directory Agents that have the same scope as the TN Server. This allows you to control the range of TN3270 clients that can use the services of each TN Server.
The CS/AIX TN Redirector feature provides passthrough services for 3270, 5250 or VT sessions over TCP/IP. The Telnet user communicates with CS/AIX over a TCP/IP connection; CS/AIX then communicates with the host over another TCP/IP connection.
CS/AIX TN Redirector supports data encryption, server authentication, and client authentication, using Secure Sockets Layer (SSL) software, in the same way as for TN Server for 3270. This allows you to use Secure Sockets Layer (SSL) security checking where necessary, and not on the complete user-to-host connection. For example:
Enterprise Extender (HPR/IP) provides a mechanism for integrating SNA applications with an IP network.
SNA applications are designed to use SNA protocols to communicate over SNA networks with other SNA applications. When installed in a TCP/IP network using Enterprise Extender, SNA applications can still communicate; the Enterprise Extender function provides a mechanism for transporting SNA protocols over the IP network. In particular, it provides APPN High-Performance Routing (HPR) functionality, giving the applications the benefits of both APPN and IP connectivity.
Enterprise Extender in CS/AIX is implemented simply as a communications link. To connect two SNA applications over IP, you define an Enterprise Extender link, in the same way as for any other link type such as SDLC or Ethernet.
CS/AIX includes two AnyNet features that support protocol conversion and communication between applications across a non-native network. AnyNet Sockets over SNA enables socket applications to communicate across an SNA network, and AnyNet APPC over TCP/IP enables LU 6.2 (APPC) applications to communicate across a TCP/IP network. For more information about these features, refer to Communications Server for AIX AnyNet Guide to Sockets over SNA and Communications Server for AIX AnyNet Guide to APPC over TCP/IP.
CS/AIX supports the following user applications:
You can use 3270 emulation software to log on to and use SNA host systems from your computer, control display and printer emulation sessions, and to transfer files between the local and host computers. 3270 emulation uses the node's LU type 0-3 resources.
For more information about configuring support for 3270 emulation, see Chapter 8, Configuring User Applications.
Using 5250 emulation software , you can log on to and use AS/400 systems from your computer. You can use emulation software to control display and printer emulation sessions and to transfer files between the local computer and the AS/400. 5250 emulation uses the node's LU type 6.2 resources.
| Note: | CS/AIX does not provide a 5250 emulation program; it just provides support for third party 5250 emulation software. |
For more information about configuring support for 5250 emulation, see Chapter 8, Configuring User Applications.
CS/AIX includes the IBM APPC Application Suite, which provides the following set of APPC applications using independent LU 6.2: ACOPY, AFTP, ANAME, APING, APPC Remote EXECution (AREXEC), and APPC Tell (ATELL). For more information, refer to Communications Server for AIX APPC Application Suite User's Guide.
CS/AIX provides several standard programming interfaces that you can use to develop application programs:
In addition, CS/AIX includes the following proprietary programming interfaces:
For more detailed information about an API, refer to the programming guide for the API (see the Bibliography).
The following back-level APIs are included to provide support for existing TPs. Because these APIs may not be supported in future releases, it is recommended that you do not develop new applications using these APIs:
For more information about these APIs, refer to CS/AIX Transaction Program Reference V4R2.
An APPC application uses the node's LU type 6.2 resources to communicate with another APPC or CPI-C application on a host or peer computer, using a specified mode. The APPC API includes TP server support, enabling applications to have greater control over starting transaction programs (TPs) and distributing conversations to those TPs.
If the TP on the CS/AIX computer is the invoking TP (the TP that starts the APPC conversation), the additional node resources required depend on the APPC features used by the TP, and on the type of remote system it is communicating with:
In the Motif administration program, directory entries and partner LUs are not shown explicitly, but are included under the "Remote Systems" heading in the Node window for the local node.
If the TP on the CS/AIX computer is the invoked TP (the TP that accepts a conversation started by the invoking TP), the additional resources required depend on the APPC features used by the TP, and on how it is to be started:
For more information about TP configuration, see Defining TPs.
For more information about the APPC API, refer to Communications Server for AIX APPC Programmer's Guide.
A CPI-C application uses the node's LU type 6.2 and mode resources to communicate with another APPC or CPI-C application on a host or peer computer. You define the same resources for a CPI-C application as for an APPC application, as described in APPC API.
In addition, if the TP on the CS/AIX computer is the invoking TP (the TP that starts the conversation), you may need to define one or more side information entries for it. Each of these entries provides information about a partner TP, the LU and mode resources used to access the partner TP, and any security information required.
For more information, refer to Communications Server for AIX CPI-C Programmer's Guide.
The Common Service Verb (CSV) API provides utility verbs that enable an application program to perform functions such as character set conversion and trace file control.
For more information, refer to Communications Server for AIX CSV Programmer's Guide.
The LUA API enables application programmers to write applications that communicate with host applications at the request unit and response unit (RU) level, and to send and receive data on both the SSCP-LU session and the PLU-SLU session. This API can be used to support LU 0, 1, 2, or 3 communication with the host.
An LUA application uses the node's LU type 0-3 resources to communicate with a host application. You do not need to define any additional resources.
For more information, refer to Communications Server for AIX LUA Programmer's Guide.
The Management Services (MS) API enables an application to communicate with other MS products in an APPN network. An application can be either NMVT-level or MDS-level, depending on the type of MS data it sends and receives. CS/AIX performs any data conversion that is required.
For more information, refer to Communications Server for AIX MS Programmer's Guide.
The NOF API can be used to write applications that administer CS/AIX configuration and management resources. For more information, refer to Communications Server for AIX NOF Programmer's Guide.