> This is not the case in v120. The type of the control field is
> FT_STRING, and the length of the field seems to be variable (8 or 16
> bits).
> But the according to the following URL :
> http://www.acacia-net.com/Clarinet/Protocol/v12029v7.htm
> the control field is 8 bits long.
Well, that page does indeed say
The structure of frame is that specified in Q921:
bits 8 _ _ _ _ _ _ 1 field
octet 1 Address (High order octet)
octet 2 Address (Low order octet)
octet 3 Control
octets 4-n Information
but the page at
http://www.acacia-net.com/Clarinet/Protocol/v1206pd0.htm
says:
V120 frame structure: control field
See also
Q921 frame structure: control field
and if you follow the link on the last line to
http://www.acacia-net.com/Clarinet/Protocol/q9211dk4.htm
it speaks of the control field as having 2 octets when it's an I-format
frame, so I'd say the page at
http://www.acacia-net.com/Clarinet/Protocol/v12029v7.htm
is incorrect (which agrees with the way I read the V.120 and Q.922 specs
- the V.120 spec says that Q.922 is used for the address and control
field, not Q.921; Q.921 is LAPD, and Q.922 is LAPF, for Frame Relay, as
I read the spec - and also agrees with the actual packet trace).