Northern UTA220/UTA220k Recognized Private Operating Agency, Flow Control Parameter Negotiation

D-Channel X.25

Recognized Private Operating Agency

The Recognized Private Operating Agency (RPOA) facility permits the user to specify the particular international gateway to be used when initiating an international virtual call.

Format: T <xxxx>

<xxxx>: four decimal digits

If four decimal digits are not specified, the response ERR displays.

Flow Control Parameter Negotiation

This facility permits the negotiation on a per-call basis of the packet and window sizes (flow control parameters) for each direction of transmission. The packet size designates the maximum data field length of the data packets. The window size designates the number of data packets that may be sent before acknowledgment of the received packets (i.e., permission to transmit more data packets) is received. Window sizes do not have to be the same at both ends of the virtual connection.

The TA cannot initiate negotiation of this facility, but will respond to negotiation from the network. The packet window size is changed by using the AT command !X0 (receive window size), !X1 (transmit window size) for the D-Channel or %D0 (receive window size), %D1 (transmit size) for an X.25 configured port (see AT commands).

If the window size is not the default value of two, the specified window size value is requested in the call request packet when the virtual call is being established. The default packet size supported by the TA is 128 bytes and can be changed using the AT commands !X2 (receive packet size), !X3 (transmit packet size), for the D-Channel or %D2 (receive packet size), %D3 (transmit packet size) for an X.25 configured port.

To allow maximum flexibility, the user may configure various parameters, such as packet size, window size, call type/LCN ranges, and packet modulus, for the D-Channel, Port, or Session (session not yet implemented) differently for each X.25 call.

The rules to determine the parameters used areas follows:

•If a session parameter (window or packet) is non-zero, the session parameter is used.

•If the session parameter is zero and the port parameter is non-zero, the port parameter is used.

•If the session and port parameters are zero, the D-Channel parameter is used.

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