IBM SC30-3681-08 manual Understanding Closed User Groups, Bilateral Closed User Groups

Using the X.25 Network Interface

Understanding Closed User Groups

A closed user group (CUG) is a group of X.25 DTEs allowed to establish connections with other speci®c DTEs. CUG numbers are de®ned by your network provider and you can only use the CUGs the provider assigns you. You can con®gure an address-speci®c CUG, a protocol-speci®c CUG, or an interface-speci®c CUG. If all of three types of CUG numbers are con®gured for a DTE, the closed

user group facility uses the address-speci®c destination CUG in a call request when contacting another DTE. If only a protocol-speci®c and an interface-speci®c CUG are con®gured for a DTE, the closed user group facility uses the protocol-speci®c CUG in a call request when contacting another DTE.

A single DTE can belong to multiple CUGs. You must specify a preferred CUG for that DTE. The preferred CUG is used when the router initiates calls to other DTEs. A single DTE cannot have more than a total of 5 preferred or normal closed user groups.

Bilateral Closed User Groups

A bilateral closed user group (BCUG) is a closed user group consisting of only two DTEs. The DTEs within the BCUG can originate calls to members of the BCUG and any DTEs that are not members of any CUG or BCUG. A single DTE cannot have more than a total of 5 preferred or normal bilateral CUGs.

A DTE uses a BCUG to establish circuits in the same way the DTE uses CUGs to establish circuits (see Table 49 on page 325), however, if both a BCUG and a CUG is de®ned for an interface, protocol, or address, the BCUG is used to establish the circuit.

Types of Extended Closed User Groups

The following extensions to closed user groups are supported:

CUG with Outgoing Access

The DTE can belong to one or more CUGs. The DTE can originate calls to members of the CUG and to any DTE belonging to other CUGs with Incoming Access.

CUG with Incoming Access

The DTE can belong to one or more CUGs. The DTE can receive calls from DTEs not belonging to any CUG or from DTEs belonging to other CUGs with Outgoing Access.

BCUG with Outgoing Access

The DTE can belong to one or more BCUGs. The DTE can originate calls to members of the BCUG and to any DTE not belonging to any BCUG.

Establishing X.25 Circuits with Closed User Groups on a Device

When you have enabled the closed user group facility, and a DTE receives a call request, it uses the CUG in the call request to determine whether to accept or reject the call from the DTE. If the CUG in the call request does not match a con®gured CUG on the interface, protocol, or on the destination associated with the calling DTE, the request is rejected. Table 49 on page 325 summarizes how X.25 circuits are established based on CUGs, if the interface, protocol, and address CUG numbers are different and incoming access is not enabled.

324MRS V3.2 Software User's Guide