husain@stsusa.com (12/11/89)
I know these questions are very specific to my application
but I cannot think of any other group that could answer
them. I did post this to the telecom group and got no
response.
I am using a DS0 on a DS1 signal for a data communication
application. The layer 1 protocol is HDLC and LAPD (Q921)
for layer 2. Layer 3 is a test version of a simpler Q931
implementation and will eventaully evolve into IP.
I do NOT get/send messages across to my test set which I have
configured for Q931/Q921/HDLC.
However, if I set the test set for just "user-data" [at]
Q921/HDLC I see my messages come in and can display them.
**question #1:
Is a function of the Q931 protocol to drop any
messages that are not connect requests if a
connection has not been established on the
incoming channel?
The second "problem" is as follows:
When the HDLC chip has no message to send I have it programmed
to send out idle flags ( %01111110 patterns ). I can see this
on a scope as 0xFC (i.e. %11111100 instead of %01111110). This
simply means that we are not on DSO boundary.
**question #2:
Is'nt it true that since HDLC is BIT oriented protocol, so any
information on a DS0 does NOT have to be frame (BYTE) aligned?
In other words, the information in the DS0 is going to be
shifted bit by bit in the flag recognition circuitry in the chip
and byte alignment is a moot point. Am I right? or what?
***question #3:
When I read the TR303 and q921 specs I say the structures
defined in OCTETs: which I presume mean "8 bit quantities"
and NOT a byte which implies some sort of boundary restriction.
Nowhere was any requirement that this information has to be on
a 8-bit boundary. Am I correct?
HOWEVER when the HDLC chip does tranemit it does so as a DSO
aligned frame. There are therefore a few bits between the last
idle flag and the flag for my start of message. These are ignored
by my test set. I cannot replicate the problem to the HDLC receiver
from my test set.
**** Now for the last question:
Is there are a minimum frame requirement for I-frames in HDLC?
Are these bits ignored or will they cause framing errors in other
chips? Is there somewhere I can look for answers ???
Please mail me the answers/suggestions/etc.
Thanks in advance.
Kamran Husain
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