Nortel Networks 8000 - Manual (Page 214)

Nortel Secure Router 8000 Series
Configuration -WAN Access 7 LAPB and X.25 configuration
lapb window-size k-value
The command configures the LAPB window parameter K.
Step 5 Run:
lapb max-frame nl-value
The command configures the LAPB parameter N1.
Step 6 Run:
lapb retry n2-value
The command configures the LAPB parameter N2.
Step 7 Run:
lapb timer { t1 tl-value | t2 tl-value | t3 t3-value }
The command configures the system timers T1 and T2 and T3 of LAPB.
—End
The two types of numbering modes for LAPB frames are as follows:
• Modulo 8
• Modulo 128
Each data frame (I frame) is numbered according to its sequence. The numbers are in the
range of 0 to modulo minus 1 and are selected in a cyclic way within this range.
LAPB window parameter K represents the maximum number of numbered I frames to be
acknowledged by DTE or DCE at any given time.
N1 indicates the maximum length (in bits) of I frames that DCE or DTE hopes to receive from
DTE or DCE.
The formula is as follows: N1 = 8 x (MTU + total bits of the protocol header).
The value of N1 must be integral multiple of 8. At present, it can only be 12032.
N2 indicates the maximum number of times that DCE or DTE sends a frame to DTE or DCE
successfully.
T1 is the sending timer. DTE (or DCE) retransmits the frame when the transmission timer T1
times out. You must make T1 greater than the maximum time between a frame and its
destination frame.
T2 is the receiving timer. When the T2 timer reaches the designated time, DTE or (DCE) must
send a confirmation frame so that the opposite DCE (or DTE) can receive the confirmation
frame before T1 times out (T2 < T1).
T3 is the idle channel timer. When the T3 timer reaches the designated time, DCE reports the
status of the long-time idle channel to the packet layer. You must make T3 larger than T1 in
DCE (T3 > T1). If T3 is 0, it indicates that the timer does not work.
By default, LAPB frame numbering mode is modulo 8. K is 7, n2 is 10, T1 is 3000 ms, T2 is
1500 ms and T3 is 0 ms.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 7-11