Reference Guide

ZCOM Tables and Data Structures
Interface Table
Chapter 3 89
The list headers in this array function identically to ITXLSTA only for
the low priority transmit requests. A terminal may be linked to
ITXLSTX, ITXLSTA and ITXLSTB all at the same time, if it has express,
high, and low priority transmit requests in progress.
IPLIMIT - Port unacknowledged transmit limit (in bytes)
This array contains the limit (in bytes) of all unacknowledged transmit
messages to terminals belonging to the same port or subchannel of this
interface. This array contains one element, one for each port or
subchannel of the Mux card. If the DAM issues a transmit request to the
Mux card and the Mux card does not have enough free buffers to hold the
request data, the Mux will reject the request with an “out of buffers”
error. The DAM will retry the request after an unacknowledged transmit
request completes. This field is used to minimize the number of retries
(and thereby increase overall performance) by imposing a limit on the
size of unacknowledged transmit requests. This array is initialized by
TTGEN from the default value hpiplim in the ZCOM header. This value
is configured through the Port-Limit or E1T1-Port-Limit parameter in
the TTGEN configuration file.
IPBYTES - Port unack TX size (in bytes)
This array is maintained by the DAM and keeps track of the number of
256-byte buffers currently in use by all unacknowledged transmit
messages to a port of this interface card. The ipbytes array contains one
element for each port/subchannel on the Mux card. The DAM compares
the iplimit value for a port with the ipbytes value times 256 to determine
whether it should issue a transmit request immediately or wait until a
previously issued transmit request completes. The DAM uses this
method to predict when the Mux card will reject a request with an “out of
buffers” error and can thereby avoid sending a request now which has a
high probability of needing to be retransmitted later.
IPENDG_BUFS - Total pending transmit size (in # of buffers)
This field is used internally by the ZCOM drivers.
IPSTAT - Port/Subchannel status
Depending on the card type this interface table is for, this ipstat field
either contains the status of each subchannel in a 4-port E1/T1 ACC
card, or the status of each port in a non-4-port E1/T1 ACC card (e.g.,
2-port card or 8-port ACC card).
The individual ipstat bits are handled as follows: