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Status Displays 20-13
The format of status exchanges depends on the type of link management. Annex D
frames always use DLCI
0000
, and LMI frames always use DLCI
1023
. Examples of
both formats are shown below:
Annex D
LMI
0000 Full Status Enquiry 001/000 T 1023 Full Status Enquiry 001/000
0000 Full Status 001/001 R 1023 Full Status 001/001
016:N 017:N 141: N 241: A
0000 LIV Status Enquiry 002/001 T 1023 LIV Status Enquiry 002/001
0000 LIV Status 002/002 R 1023 LIV Status 002/002
0000 LIV Status Enquiry 003/002 T 1023 LIV Status Enquiry 003/002
0000 LIV Status 003/003 R 1023 LIV Status 003/003
0000 LIV Status Enquiry 004/003 T 1023 LIV Status Enquiry 004/003
0000 LIV Status 004/004 R 1023 LIV Status 004/004
0000 LIV Status Enquiry 005/004 T 1023 LIV Status Enquiry 005/004
0000 LIV Status 005/005 R 1023 LIV Status 005/005
0000 LIV Status Enquiry 006/005 T 1023 LIV Status Enquiry 006/005
0000 LIV Status 006/006 R 1023 LIV Status 006/006
0000 Full Status Enquiry 007/006 T 1023 Full Status Enquiry 007/006
0000 Full Status 007/007 R 1023 Full Status 007/007
016: A 017:A 141: A 241: A
0000 LIV Status Enquiry 008/007 T 1023 LIV Status Enquiry 008/007
The pair of 3-digit numbers at the end of each line are the send/receive sequence
numbers. For example,
LIV Status Enquiry 002/001
means that the DTE received
sequence 001 and sent sequence 002.
If the timestamp is turned on, it will be displayed at the left of each line. Note that the
T
or
R
in LMI frames indicates whether the frame was transmitted or received by the
port being traced.
Note that in the above example the frame relay DTE port is configured for an
N1
Polling Count
of
6
, meaning that every six polling cycles the DTE will send a Full
Status Enquiry to the DCE, asking for the status of the DLCIs on the link. The interval
between
N1
polls is governed by the frame relay port parameter
T1 Link Integrity Timer
.
If
N1
is set to 6 and
T1
is set to 10, the status of DLCIs will be reported every 60
seconds. If you are using DLCI backup, you may have to lower these parameters
(thereby learnng the DLCI status sooner) to avoid application timeouts on
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.