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D-Channel X.25
Recognized Private Operating Agency
Flow Control Parameter Negotiation
12-12
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.
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.
UTA220/UTA220k
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