Defining Link Stations

To communicate with other nodes in an SNA network, you must configure the characteristics of a link station (LS) to an adjacent node in the SNA network. Before you can define a link station, you must define a port for the adapter (and link protocol) you are using. Most of the information needed to configure a link station is the same, whatever protocol is being used.

A link station represents the logical path through the SNA network between the SNAplus2 local node and a remote computer. The remote computer can be any of the following:

A host computer, on which SNAplus2 accesses a host program using 3270, RJE, or LUA communications (or uses APPC or CPI-C for program-to-program communications)
A peer computer, with SNAplus2 and the remote computer communicating as equal partners (the typical arrangement in an APPN network)
A downstream computer that uses the SNAplus2 PU concentration feature or DLUR feature in order to access a host

A link station is associated with a specific port; you can define one or more link stations on each port.

Each link station that supports dependent traffic has an associated PU (physical unit). Because PUs are associated with link stations, SNAplus2 does not treat them as separate resources; they are configured as part of link station configuration, and are started and stopped as part of starting and stopping link stations. Link stations are shown in the connectivity section of the Node window; PUs are not shown in any window.




	NOTE: In most circumstances, you need to add a link station to the port. However, if you want to use a dynamically created link station for APPC traffic only, for situations in which the link is always activated from the remote node, you do not need to explicitly configure one. If a remote node attempts to connect to the local node, but no link station is defined that matches the address specified on the incoming call, SNAplus2 can define one implicitly if a suitable port has been defined on the local node. This dynamically created link station appears in the connectivity section of the Node window for the duration of the connection.

To configure a link station, use one of the following methods:

Motif administration program

Select Connectivity and New link station from the Services menu on the Node window.

Command-line administration program

Issue the following command:

define_type_ls

In this command, type indicates the link protocol type (sdlc, tr, ethernet, fddi, qllc).

Advanced parameters for link stations provide additional control over transmission characteristics, XID exchange, optional link facilities, and reactivation procedures.

Link Station Configuration Parameters

In Motif, the Link Station Configuration dialog contains the following sections, each containing different categories of configuration parameters:

Link station: Use this area of the dialog to provide information that is required for all link stations, whether they support LU traffic for dependent LUs, independent LUs, or both. For descriptions of the parameters in this section, see “Common Link Station Parameters”.
Independent LU traffic: Provide this information only if you are using the link station for independent traffic. For descriptions of the parameters in this section, see “Parameters for Independent LU Traffic”.
Dependent LU traffic: Provide this information only if you are using the link station for dependent traffic. For descriptions of the parameters in this section, see “Parameters for Dependent LU Traffic”.

Common Link Station Parameters

The following parameters are required for all link stations, whether they support dependent traffic, independent traffic, or both.

For more information about the parameters on this dialog, refer to the online help or to HP-UX SNAplus2 Administration Command Reference.

Name

A name to identify the link station locally.

SNA port name

The port that is to be used to access the adjacent node.

Activation

Method used to activate the link station. Specify one of the following methods:

By administrator: The link station is activated only on the request of a local System Administrator.
On node startup: The link station is started automatically when the node starts up.
On demand: The link station is started automatically when required to provide connectivity for an application.

Link stations are activated separately from ports, so the link station must be activated even if the port is already active. Activating the port does not itself activate any link stations, and configuring the port to be initially active does not mean that any of its link stations are activated automatically when the node starts up. However, activating a port does make it possible to activate link stations. A link station cannot be activated unless the ports are active on both the local node and the adjacent node.

If the link is one for which you are charged for usage, avoid activating the link unnecessarily, in order to keep the cost down.

If you are not sure how to set this field, consult your SNA network planner.

LU traffic

The type of LU traffic to flow over the link. This choice determines what other parameters are needed for link definition.

Any: The link station can be used for both independent and dependent LU traffic. For this option, you must supply values for the fields described in “Parameters for Independent LU Traffic” and “Parameters for Dependent LU Traffic”, in addition to those described in this section.
Independent only: The link station can be used only for independent LU traffic. For this option, you must supply values for the fields described in “Parameters for Independent LU Traffic”, in addition to those described in this section.
Dependent only: The link station can be used only for dependent LU traffic. For this option, you must supply values for the fields described in “Parameters for Dependent LU Traffic”, in addition to those described in this section.

You also need to provide addressing information for contacting the adjacent node. The type of addressing information needed depends on the DLC type of the port. If you do not supply an address for the remote node, the link station acts as a nonselective listening link station, accepting incoming calls from any remote node.

Additional Link Station Parameters for SDLC

Poll address

The poll address of the remote station. Specify the address as a two-digit (one-byte) hex value, typically starting at C1. A primary link station polls the remote station using this value. A secondary link station responds to polling with this value. The poll address is entered differently depending on the link role:

If the link is a point-to-point link (not multi-drop), the address C1 is normally used.
If the parent port for this link is switched incoming, the poll address is configured on the port and cannot be configured independently for each link station.
If you are configuring a primary switched outgoing link station, and you do not know the poll address of the remote secondary with which you wish to communicate, you can specify a poll address of 0xFF on the primary. This value enables the node to accept responses from a secondary, regardless of the poll address it has configured. 0xFF is not a valid address for a nonprimary link or a link that is not switched outgoing.
If you are using a multi-drop configuration, all the secondary link stations that communicate with the same primary must have different poll addresses.

The poll addresses at both ends of the link must match. Contact your SNA network planner if you do not know the address configured at the remote system.

On a VTAM host, the poll address is configured as the ADDR= parameter in the VTAM PU definition.

On an AS/400 system, the poll address is the STNADR parameter of the Line Description.

Line encoding

The line encoding used on your SDLC line. In the U.S., this is usually NRZ. In Europe, this is usually NRZI. If you set this incorrectly, you will find that the frames being received are all discarded and do not appear in any trace.

On a switched outgoing port, the line encoding can be set independently for each link station. For other types of ports, the line encoding setting is taken from the port, so this field does not apply.

Dial string

An ASCII string to be sent to your modem in order to make it initiate the outgoing call. The dial string is required for a switched outgoing port. Refer to the documentation for your modem for more details. (Some modems do not support dial strings; in such cases, this field does not appear.)

For switched incoming ports, the dial string is configured on the port. For leased ports, this field does not apply.

By default, the dial string is sent to the modem at the rate of 1200 bits per second (the default baud rate) using asynchronous communications. You can match the baud rate to the modem's baud rate by placing one of the following numbers (enclosed by parentheses) in front of the dial string:

1 (300 baud)
2 (600 baud)
3 (1200 baud)
4 (2400 baud)
5 (4800 baud)
6 (9600 baud)
7 (19200 baud)

For example, you can specify a 9600 baud rate dial string by entering (6), as follows:

(6)AT &&D3 &&Q1 DT7,012345678

For details of the rest of the dial string, refer to your modem's documentation.

Additional Link Station Parameters for Token Ring, FDDI and Ethernet

MAC address

The MAC address of the remote station, entered as a series of hexadecimal digits. The MAC address uniquely identifies the adapter card on the remote system.

If you do not know what value to use, consult your SNA network planner.

If the remote end of this link is a VTAM host, you can find its MAC address in the MACADDR= parameter of the VTAM Port definition.

If you are configuring a link to an AS/400 system, the MAC address is the ADPTADR parameter in the Line Description.

SAP number

The SAP number of the port on the remote computer. The SAP number distinguishes between different links using the same adapter card. This is a hex number, normally 04. It must be a multiple of 4.

If you do not know what value to use, consult your SNA network planner.

If the remote end of this link is a VTAM host, the SAP number is the SAPADDR= parameter of the VTAM PU definition.

If you are configuring a link to an AS/400 system, the MAC address is the ADPTADR parameter in the Line Description.

Additional Link Station Parameters for X.25 (QLLC)

Circuit type

Specify either Permanent virtual circuit or Switched virtual circuit to indicate whether the circuit is permanent or switched.

Channel ID

The channel ID that identifies the virtual circuit the link station is to use (only applicable for a permanent virtual circuit). Channel IDs are numbered from 1 up to a maximum of 4096. If you have only one permanent virtual circuit, its channel ID is likely to be 1.

Remote X.25 address

The DTE address of the remote DTE as a series of hexadecimal digits (only applicable if the circuit is a switched virtual circuit).

Adapter/Port Number

The card number (if your card has only one port). If you have only a single card, use a value of 0.

If your card has more than one port, use the value npx, where n is the card number and x is the port number. For example, the first port on the first card should be specified as 0p1.

SpiderX25 stacks use an adapter number and a port number to support multiple X.25 cards, each with possibly multiple physical ports. Cards are numbered starting at 0; ports are numbered starting at 1.

To determine the card and port number to use, use a string that matches the end of the device name of the X.25 driver. For example, use an adapter/port number of 0p1 for an X.25 driver named /dev/x25_0p1.

Parameters for Independent LU Traffic

You need the following information to configure this link station for use by independent LUs (LUs of type 6.2 for use by APPC, 5250, or CPI-C applications):

Remote node name

The fully qualified CP name of the remote node.

If the remote system is a VTAM host, you can find the network name (the first eight characters of the fully qualified name) in the NETID parameter of the VTAM Start command. The last eight characters are in the SSCPNAME parameter of the VTAM Start command.

If you enter the name of a new remote node, you can add a definition for the remote node to enable you to define partner LUs on the new remote node.

To define a new remote node in this way, specify the remote node type for this definition rather than specifying a remote node type of Discover. (If the local node is a LEN node, you do not need to specify the remote node type, and the Remote node type field does not apply.) If the local node is an end node rather than a LEN node, and if you specify a remote node type of Discover, you do not have to supply the remote node name. If you do not supply a remote node name, any adjacent node can use the link station.

Alternatively, you can specify Discover dynamically. This leaves the remote node name empty and sets the remote node type to Discover, so that any adjacent node can use the link station. The Discover dynamically option is not available if the local node is a LEN node.

Remote node type

The level of APPN support on the remote node that is accessed through this link station (only applicable if the local node is an end node).

If you do not know whether the remote node is a LEN node or end node or whether it is a network node, you can choose Discover. Discovering the level of APPN support on the remote node can delay link activation slightly, so if you do know the type it is better to specify it. This also helps to ensure network configuration consistency.

You cannot choose Discover if the link station is activated on demand.

If the local node is a LEN node, this field does not apply.

Parameters for Dependent LU Traffic

Configuring a link station for dependent LU traffic automatically creates an appropriate PU with the same name as the link station.

You need the following information to configure a link station for use by dependent LUs (LUs of type 0-3 for 3270, RJE, or LUA applications):

Local node ID

A value to identify the local node in the SNA network.

You can usually use the same node ID (the default value) for all the links on the same node. However, if you need more than 255 dependent LUs to access a specific host, you must configure multiple link stations to the host, each with up to 255 dependent LUs, and each with a different local node ID.

To ensure that the remote node is configured to recognize the local node ID, contact your SNA network planner.

In a VTAM configuration, the first three digits should match the IDBLK parameter in the PU definition, and the last five should match the IDNUM parameter.

On an AS/400 system, the node ID is configured in the EXCHID parameter.

Remote node ID

The node ID for the remote link station (optional; only applicable if you need to restrict access to this link station). If you specify the remote node ID, the link is activated only if the node ID of the remote node matches the value specified in this definition. This can be useful if you have several link stations configured on a switched port, because it enables the link stations to be distinguished when they are activated by the remote nodes. Link stations can also be distinguished by the CP name of the remote node, but for remote nodes that do not send their CP name when activating a link, the remote node ID must be used instead.

If you do not specify the remote node ID, the node ID of the remote node is not checked when the link is activated.

Remote node role

The role of the remote (adjacent) node:

Host: The link station supports dependent LUs (such as 3270 LUs) that are used for sessions with a host computer (the most common case). If the link is to a node that provides host connectivity using PU concentration or DLUR, the adjacent node role should still be set to Host, even though the link is not directly to a host computer.
Downstream (PU concentration): The link station is to a downstream node that will communicate with a host using the PU concentration capabilities of the local node (to the host, the LUs on the downstream node appear to reside on the local node).

Additional Configuration

After performing the link station configuration, continue with the following configuration tasks:

To define a DLUR PU, see “Defining DLUR PUs”.
To configure passthrough services, see Chapter 9 “Configuring Passthrough Services”
To support specific user applications, see Chapter 8 “Configuring User Applications”
To support APPC communication, see Chapter 7 “Configuring APPC Communication”