husain%sdcsvax@ucsd.edu (12/06/89)
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.
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:
Isn't it true that since HDLC is BIT oriented protocol, 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
===)------------------ "Dr. StrangeCode"
------------------(*************)--------------------------
"It is better to have loved and lost than to have paid for
it and not liked it." - anon.
------------------(*************)--------------------------
UUNET: ..!uunet!stsusa!killer::husain
or try husain@killer.stsusa.com
Brain Loaned to: Siemens Transmission Systems
8620 N 22nd Ave, Phx, Az 85029
Voice phone: (602) 395 5222
------------------(*************)--------------------------