06-05-2002 09:31 AM - edited 03-12-2019 07:06 PM
Need to be clarified something with with frame-relay bc command.
If I want to be very strict with my traffic shapping which set of commands should I use and why, I have work out my oun calculations but need some advise.
Example A
map-class frame-relay VOICE
frame-relay cir 64000
frame-relay bc 300
frame-relay be 0
frame-relay mincir 64000
frame-relay voice bandwidth 64000
frame-relay fragment 80
no frame-relay adaptive-shaping
frame-relay fair-queue
EXAMPLE B
map-class frame-relay VOICE
frame-relay cir 64000
frame-relay bc 6400
frame-relay be 0
frame-relay mincir 64000
frame-relay voice bandwidth 64000
frame-relay fragment 80
no frame-relay adaptive-shaping
frame-relay fair-queue
frame relay bc tc and be have me confused
The amount of data to send per each Tc interval in bits. Ideally for data PVCs Bc = CIR/8 so that Tc = 125msec. If we are doing voice on the PVC, then Bc = CIR/100 is preferable, so that the interval Tc = 10msec (as voice packets cannot tolerate a longer delay). The value of Bc by default is the CIR in bits.
06-12-2002 06:32 AM
The formula for the relation of bc to tc is this:
Tc = Bc/Cir ! time interval (the internalized version of Tc where the
time interval can't exceed 125ms)
CIR = Average rate you want to send out (This is generally not the
same as the CIR you get from your provider unless you aren't
allowed to send above CIR) This is measured in bits/second.
Bc = Amount of data to send per each Tc interval. This is
measured in bits.
(this also gets internalized and real amount of data sent per
interval is expressed in bytes by the "increment" variable).
Be = Amount of excess data allowed to be sent during first
interval once credit is built up. Also measured in bits.
Mincir = Minimum amount of data to be sent during periods of congestion.
This defaults to half of CIR.
Interval = Bc/CIR with the maximum size being 125ms.
byte increment = Bc/8 . Must be > 125. Upper side has no bound
or limitation except if interval is locked at 125ms.
limit = byte increment + Be/8 (measured in bytes)
so for Tc to be 10ms, Bc must be 1/10th of CIR.
also see here:
06-12-2002 02:03 PM
The URL is saying BC=1000 is enough so way not the small amout allowed by the IOS which is BC=300?
Make Bc small so that Tc (shaping interval) is small (Tc = Bc/CIR)
The minimum Tc value is 10 ms, which is ideal for voice. With a small Tc value, there is no risk of large packets using all the shaping credits. Large Tc values can lead to large gaps between packets sent because the traffic shaper waits an entire Tc period to build up additional credits to send the next frame. Making Bc = 1000 bits is usually a low enough value to force the router to use the minimum Tc of 10ms. This setting should not affect data throughput.
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