Thats right,
cisco hdlc is not compatible with other vendors implemenation of hdlc.
An HDLC frame format is shown below:
1 1 1 2 variable
2 1
+----+----+----+--------+---------------------------------------+--------+--
--+
|flag|addr|ctrl|protocol| data |
FCS |flag|
|0x7E| |0x00| | |
|0x7E|
+----+----+----+--------+---------------------------------------+--------+--
--+
flag = start/end of frame = 0x7E
(Other special characters: Idle = 0xFF, Abort = 0x7F)
address = this is really a frame type field
0x0F = Unicast Frame
0x80 = Broadcast Frame
0x40 = Padded Frame
0x20 = Compressed Frame
Protocol = the Ethernet type of the encapsulated data:
0x0800 = IP 0x6003 = DECnet ...
0x6558 = Bridged Frame
0x8035 = Keepalive Frame
0x80C4 = CDP
The bits in the frame (not counting the flag bytes) are 0 bit
stuffed to insure
that there is never more then 5 1 bits in a row on the wire.
Therefore 0xFF,
0xFE, 0xFC, 0x7E, 0x7F, 0x3F bytes could never be in the data
portion of the
frame - so they are free to be used for start/end framing and
other special
functions on the wire.
/Stuart.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Jeremy Dumoit
Sent: Friday, February 09, 2001 1:45 PM
To: [EMAIL PROTECTED]
Subject: HDLC
Getting some good info here.. So cisco has their own implementation of
HDLC.. is it compatible with other non-cisco devices (nothing particular in
mind here)? What does the control field of a cisco HDLC frame look like?
Thanks!!!
Jeremy
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