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Information Field
The 3708 normally sets the terminal ID field of the XID response to O. However, if
nonstandard operating bit 11 is set to 1, the 3708 sends the last 5 nibbles of the
serial number. This function gives host programs the ability to distinguish between
individual 3708s in a network.
The information frame is used to transmit message data. When transmitted, the 1
frame contains a maximum of 256 bytes of RU message data preceded by 6 bytes of
transmission header (TH) and, optionally, 3 bytes of request/response header (RH).
For more information, see "SNA Commands" on page 3-15.
Sequence Error Recovery Procedures
Abort· Function
A sequence error occurs when the 3708 receives an 1 frame with an incorrect NS
sequence count and valid frame check sequence (FCS) bytes. The 3708 does not
accept the 1 frame that caused the sequence error and rejects all following 1 frames
until an 1 frame is received that contains the correct NS value. The sequence error
condition is then reset.
The 3708 transmits 1 frames in the sequence indicated by the last NS count received,
which may include retransmission of previously transmitted 1 frames that have not
been acknowledged.
All 1 frames are transmitted in contiguous sequence according to the NS value
within the constraints of the modulo count.
The abort function is used by the SNA host or by the 3708 when a frame being
transmitted is to be discarded. The abort function is performed by transmitting
eight contiguous 1 bits with no 0 inserted as soon as possible after an abort situation
is recognized. No FCS is transmitted. When, for example, the 3708 receives seven
contiguous 1 bits, it discards the aborted frame. The 3708 uses the abort function
when an equipment malfunction causes an incorrect transmission.
Chapter 3. SDLC and SNA Communication
3-5
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