NetWare Link/X.25 User Facilities

The ITU-T Recommendation X.25 addresses users' needs for versatility in their network requirements through a set of optional user facilities. These facilities give X.25 the capability of being tailored to meet varied network and user requirements, and allow a network installer to fine-tune the network's handling of such areas as security, accounting, routing, and performance. These facilities can be selectively and incrementally specified to the needs of the users on that network.

Many user facilities can be used within an X.25 connection to a PDN. The user facilities available with NetWare Link/X.25 include the following:

• Flow Control Negotiation ---Allows negotiation, on a per-call basis, of the window size and maximum user data field length that can be used on the call in each direction.
• Throughput Class Negotiation ---Specifies, on a per-call basis, the throughput of data that can be transferred on a virtual circuit. The range is 75 bps to 64 Kbps.
• Fast Select ---Expands the Call and Clear user data fields from the normal 16 octets to 128 octets, enhancing the data field's usefulness for short-duration, low-volume, transaction-oriented applications. This facility is often used in the retail point-of-sale and credit card authorization terminal environment.
• Reverse Charging ---Offers the equivalent of a collect call. It is allowed on a per-call basis and is specified in the Call Request packet by the calling DTE.
• Closed User Group (CUG) ---Allows the configuration of one or more virtual private networks within a larger public network. It allows a user to collect a number of DTEs into a single logical group and restrict access to the group having the ability to receive incoming calls from or to make outgoing calls to the restricted open portion of the network. The number of CUGs is network-dependent. A single DTE can belong to one or more CUGs.

  Within the CUG category, you can specify whether a user connection has incoming access (CUG with Incoming Access), outgoing access (CUG with Outgoing Access), or both. If a DTE belongs to more than one CUG, you must also specify a preferred (or primary) CUG.

• Bilateral Closed User Group (BCUG) ---Offers a finer degree of access control than the CUG offers. Bilateral signifies a CUG relationship that has been limited to a pair of DTEs. Access between the pair of DTEs is unrestricted; however, access to or from any other DTE is not possible.

A DTE subscription with a PDN can include a provision to allow or disallow a remotely originated, reverse-charged call from reaching that DTE (Reverse Charging Acceptance). Additionally, a DTE subscription with a PDN can include a provision to disallow any locally charged calls; that is, all locally generated call requests must specify reverse charging.

NetWare Link/X.25 additionally provides local configurable options for both of the preceding items; that is, regardless of a customer's PDN subscription, all inbound reverse-charged calls can be rejected and all outbound call attempts that do not specify reverse charging can be disallowed.