Layer 1 & Layer 2 Protocols • 7-9 •
The H.110 Basic Rate ISDN Board
Check Response message. If the option is set to 0, one response message
is sent containing all TEI’s, if the option is set to 1, each TEI is reported in
a separate message. The default for these options is 0, and in most cases
it will not be necessary to issue this command.
The application can query the board at any time for the TEI’s that are
assigned. This is done by sending a command of the form TQxx where xx
is the port number. The response will take the form TQxxtttttttttttttt,
where xx is the port number and each tt pair is one of the eight TEI’s. The
Packet TEI is the last one. If a TEI is not assigned, the value returned for
that TEI will be “FF”. As an example, a port with the TEI’s 64 and 65
assigned would return “TQxx4041FFFFFFFFFFFF”. This command can
be issued for either a TE or an NT port.
Normally, once a TEI is assigned, the data link is in the multi-frame
established state. However, the link can be disconnected or reestablished
by using commands of the form TDxxtt and TExxtt where xx is the port
number and tt is the TEI. A data link that is disconnected is placed in the
TEI assigned state. If an attempt is made to send a Layer 3 message on a
data link in the TEI assigned state, an attempt to reestablish the multi-frame
established state will automatically be made by the board.
7.5 The Packet Data Link
One Data Link is reserved for sending X.31 Packet Data using the D
Channel. The TEI for this data link is managed in a slightly different
manner than the other seven data links. The TEI will default to a value of
0 on a power up or restart of the board. The Packet TEI can be set to any
value in the range 00-126 using a command of the form TPxxtt where xx
is the port number and tt is the TEI. If a fixed packet TEI is used, the TEI
may be set to any value in the range 00-63. If dynamic TEI’s are to be
used for packet data, then it will be necessary to set the TEI to the same
value as one of the seven data links. This can be done after the TEI has
been assigned.
The Packet Data Link is put in the Multi-frame Established state by sending
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