Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!ut-emx!dell!Kepler!mjhammel
From: mjhammel@Kepler.dell.com (Michael J. Hammel)
Newsgroups: comp.dcom.lans
Subject: Re: X.25
Message-ID: <4586@dell.dell.com>
Date: 4 Dec 89 23:44:05 GMT
References: <2050001@hp-and.HP.COM> <1100@sumax.UUCP>
Sender: news@dell.dell.com
Reply-To: mjhammel@Kepler.dell.com (Michael J. Hammel)
Organization: Dell Computer Corp.
Lines: 25

In article <2050001@hp-and.HP.COM>, panek@hp-and.HP.COM (Jon Panek) writes:
> The actual x.25 specification doesn't address "operating systems" per se.
> I do believe (from old memory) that the number of bits allocated in the
> standard message frame for addressee is 8 bits.  This would effectively
> limit the number of addressable sites (on the link level, at any rate)
> to 256.
> 
I couldn't remember if this was true so I looked it up in a manual I got
in an X.25 class I took.  Now I'm more confused.  According to this text
there is a Logical Channel Number of 8 bits and a Logical Channel Group
Number of 4 bits.  Together these are used to maintain a call.  This would
then allow upto 4095 maintained calls.  To establish a call there are 3
fields:  the calling DTE address length field, the called DTE address
length field, and the actual address field.  By this definition the
address length can be any specified length (as long as the address fits
between the 4th and 19th octets of the X.25 packet).  So in establishing
the call the address field is quite large (a bit more than 8 bits), but
as far as X.25 is concerned the logical addresses are no more than 8 bits
or 12 bits if coupled with the group number.


Michael J. Hammel   | internet:mjhammel@Kepler.dell.com
Dell Computer Corp. | Also: ...!dell!mikeh  or 73377.3467@compuserve.com
"I know engineers, they looooove to change things" L. McCoy
Disclaimer equ standard