Cabletron Systems FRM User Manual - page 285
St atus Displays
19-13
switchovers. The tradeoff on this approach is more management overhead on the link,
so it is generally better to increase the applications timeout parameters.
Data Exchanges
Data packet (Q.922 UI frame) entries include the following, reading from the left:
●
Timestamp, if turned on.
●
T
or
R
, indicating whether the frame was transmitted or received by the port
being traced.
●
Four-digit DLCI.
●
Identification of any of these bits that are set:
◆
B
– Backward Explicit Congestion Notification (BECN).
◆
F
– Forward Explicit Congestion Notification (FECN).
◆
D
– Discard Eligibility Indicator (DE).
◆
C/R
– Command/Response.
●
Four-digit packet length, starting from the frame relay Q.922 control byte.
The type of link management used has no bearing on the format of the
Q.922 UI frame.
Trace Example
The following is an example of a frame relay port trace of Modulo 8 X.25 logical port
link activation (X.25 encapsulated in frame relay per RFC1490):
0016
(0008) 030851816780013F
(LAPB SABM)
0016
(0008) 0308518167800173
(LAPB UA)
0016
(0013) 03085181678003001000FB0700
(LAPB Information frame
0016
(0013) 03085181678001201000FB8700
(LAPB Information frame)
0016
(0008) 0308518167800121
(LAPB Receiver Ready)
0016
(0008) 0308518167800331
(LAPB Receiver Ready)
0016
(0008) 0308518167800331
(LAPB Receiver Ready)
In RFC1490 encapsulation, theLAPBb frame follows the T1.618 header, Q.922
control byte, Q.933 NLPID and the level 2 and 3 protocol IDs (2 bytes each). SNA,
APPN, X.25, IP, IPX traffic are identified on the DLCI based on their NLPIDs, as well
as (if applicable) level 2 and 3 headers (e.g., X.25: 0x03 Q.922 control, 0x08 Q.933
NLPID, T1.617 L2 LAPB PID 0x51 81, T1.617 L3 PID 0x67 80, LAPB frame. For
instance,
013F
is a LAPB SABM frame.)
Frame Format Examples (in hex)
IP/IPX over RFC1490:
Flag AddressCtrl PAD NLPID OUI
PID Data
FCS Flag
Routed IP
03
CC
(start of IP header 45..)
Routed IPX
03 00 80
000000
8137
X.25 over RFC1490:
Ctrl NLPID Lvl2PID Lvl3PID Data
FCS Flag
03
08
5181
6780
LAPB frame, X.25 packet