The resources of the CS/AIX system can be divided into the following types:
The following sections describe the various CS/AIX resources, and explain how those resources work together to support each type of user program.
| Note: | Some of the resources listed here do not appear in the Motif administration program, or are presented differently. These differences are indicated in the following sections where they apply. |
Connectivity to remote systems is supported by the following resources:
If you use the Motif administration program to configure a port, the corresponding DLC definition is created automatically. For command-line administration, the DLC is configured separately.
If you use the Motif administration program, you can define a connection network as part of port configuration. For command-line administration, a connection network is configured separately.
In addition, you can enable the High-Performance Routing (HPR) feature of APPN. This feature provides support for Rapid Transport Protocol (RTP), which minimizes cycles and storage requirements for routing network layer packets through intermediate nodes on a session route, and automatic network routing (ANR), which enables APPN networks to automatically reroute sessions if a portion of the originally computed route fails. HPR also provides end-to-end dynamic window sizes for communications, and reduces storage and processing requirements on intermediate nodes in the route.
A DLC is the component responsible for communication over a physical link (or multiple links) using a specific data link protocol, such as SDLC or token ring. Each DLC can manage one or more ports, as described in Ports.
CS/AIX provides support for the following data link protocols:
The following link protocols require additional products or features that are not included with CS/AIX:
| Note: | In the Motif administration program, DLCs are not shown directly. The information required for configuring a DLC is displayed as part of the configuration of a port owned by the DLC. |
A port represents the local end of a communications link as a unique access point in the network. In general, this corresponds to a single physical access point such as an adapter card. However, some link protocols (such as token ring) enable you to define multiple ports for a single adapter; in this case, the different ports are distinguished by addresses (such as the SAP address).
Each port is associated with a specific DLC. One or more ports can use the same DLC.
A link station represents the logical path through the SNA network between the CS/AIX local node and a remote computer. The remote computer can be any of the following:
A link station is associated with a specific port. One or more link stations can be defined on the same port.
Connection networks cannot be used by LEN nodes.
Nodes that are connected to the same token ring, Ethernet, FDDI, or IP network have a direct communications path between all nodes, so that in theory any two nodes can communicate directly. Such a network is referred to as a shared-access transport facility (SATF).
The local node can have an explicit link station defined for its communication path to another node on the SATF, but enabling communications between every pair of nodes on the SATF requires a large number of link station definitions, and results in a large volume of network topology information flowing on the network.
APPN enables you to set up this type of configuration without having to define each link station explicitly, by defining a connection network (CN) that represents the SATF. For each node on the SATF, you define one or more ports used to access the connection network. Instead of defining a link station to each remote node, you specify the name of a virtual routing node (VRN) as part of the port definition.
You can think of the VRN as an imaginary node that represents all the other nodes on the SATF; you can give it any name you like, but all nodes on the SATF must use the same VRN name (and it must not match the name of any of the real nodes on the SATF). The local node can establish communications with any other node that has a port associated with the same CN, by accessing the VRN (which represents all the other nodes attached to the SATF), instead of requiring an explicitly defined communications path between each pair of nodes.
When two nodes on the SATF need to communicate and both have a port defined with the same VRN name, APPN can dynamically establish a direct connection between them; you do not need any additional configuration.
Because the connection is direct and does not need to go through any intermediate nodes, using a connection network reduces traffic on the LAN and improves performance. You should use connection networks wherever possible to take advantage of this.
You can define CNs for communications using token ring, Ethernet, FDDI, or IP DLCs.
To use this feature, you first define a DLC and port for each node that accesses the SATF, and indicate that the port should be defined on the connection network. You do not need to define any link stations; CS/AIX sets up a dynamic link station to the CN (and hence to any port on it) when required.
| Note: | In the Motif administration program, CNs are not shown as a separate resource, but are included as part of the configuration of SATF ports. |
The following session resources are used by CS/AIX:
An LU is the node's point of contact with a user program (3270 emulation program, APPC TP, CPI-C application, or LUA application). LUs are divided into two categories:
LU types 0-3 are sometimes referred to as "old LUs," and are used to communicate with hosts using 3270 emulation or LUA.
Type 0-3 LUs can also be grouped into LU pools, as described in LU Pools. In addition, dependent type 6.2 LUs can be assigned to default pools, as described in Default LUs.
Type 6.2 LUs that are used to communicate with peer computers, or with newer SNA software on host computers, are referred to as independent LUs. Independent LUs can support multiple user sessions simultaneously.
Dynamic definition of dependent LUs (DDDLU) is a host feature that enables dependent LUs on the SNA system to be added to the host configuration when the communication link from the SNA system to the host is established. With DDDLU, LUs do not have to be configured statically at the host. (You must still define dependent LUs on the CS/AIX node.) This reduces the initial configuration required at the host, and makes later expansion easier.
CS/AIX can communicate with both DDDLU-capable and non-DDDLU-capable hosts, with no difference in the configuration required. When the communications link from the CS/AIX node to the host is established, a DDDLU-capable host informs the node that it supports DDDLU; the node then sends the required information to define the dependent LUs that use the link. If the host is not DDDLU-capable, CS/AIX does not send this information; it assumes that the LUs have already been defined statically at the host.
Type 0-3 LUs can also be grouped into LU pools, so that a user session can be assigned to a pool of LUs. For 3270 and LUA applications, you can use LU pools to simplify configuration and give greater flexibility.
All of the LUs in a pool must be the same type.
LU pools support the following operations:
If you are configuring type 6.2 dependent LUs for use with APPC or CPI-C applications, you may wish to define them as members of the default pool. An application that does not specify a particular local LU is assigned an unused LU from the pool of default LUs; it can be assigned to any of these LUs as available.
A mode specifies a set of characteristics that a type 6.2 local LU uses to communicate with its partner LU. These characteristics include information about the way data is transmitted between the two LUs (such as maximum RU size and pacing window sizes), and about whether the LUs can establish parallel sessions.
The definition of a mode can also include the name of a class of service (COS), which specifies minimum and maximum acceptable values for characteristics such as transmission time, transmission cost, and network security, together with weightings associated with different ranges of these values. This enables the node to calculate the best route across the network when two or more routes to the same remote LU are available. The configuration of the CS/AIX node specifies whether the node performs explicit mapping between modes and COSs. If explicit mapping is not supported, you do not need to associate a COS with the mode; the COS name is determined dynamically.
APPN network and end nodes maintain dynamic directory information about remote nodes and partner LUs. In addition, you can configure such information directly. On a LEN node, you must configure directory entries for each partner LU. You can also configure such resources directly on an APPN end node or network node (for example, to eliminate the need for a network node to locate a frequently used resource).
Information about domain resources such as CPI-C side information, and logging levels is stored in the domain configuration file.