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User Facility Support 191

User Facility Support

X.25 Facilities are encoded into the Facility field of the call request packet

without any interpretation on the part of the program. This allows you to specify

any optional User Facilities, except for the packet retransmission Facility and

extended packet sequence numbering (modulo 128).

The Facility field contains both Facility codes and their associated parameters.

The code format varies since some Facilities may have one, two, or more

parameters. Enter the contents of the User Facilities field as hexadecimal

numbers separated by commas, as ASCII characters within either single or

double quotation marks, or as a combination of both.

Facility Types

Facilities fall into two groups: those specified at subscription time, and those

specified on a per-call basis.

Subscription Facilities

The first group includes CCITT Facilities such as nonstandard default window

and packet sizes, Closed User Group definitions, barring of incoming or

outgoing calls, and Reverse Charging.

Per-Call Facilities

The second group of Facilities are agreed upon at the time of subscription but

can be used on a per-call basis. These Facilities include: Reverse Charging,

indexing of a Closed User Group (CUG), or specification of a Network User

Identification (NUI).

Facility Syntax

Facility codes are entered as a string of numbers and/or ASCII characters. The

first parameter of a Facility code indicates the Facility you want to use. The

subsequent parameters supply information about that Facility.

A request for CCITT Facilities must always precede all requests for non-

CCITT Facilities. The National Facility Marker (0,0) need only be included

when at least one request for a non-CCITT facility is present.

The following sections explain the syntax for Network User Identification, and

Flow Control Negotiation.

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Eicon Networks C21 Guia de Instalação Página 191