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New Member

ATM PCR SCR MBS question

We have 2 ATM connected hub 3662 routers with RS8234 SAR ATM DS3 module, each with a PVC connecting remote sites using 2621 router with FRX over 384Kbps frac T-1.

Each PVC has 192 CIR and 384 burst. Running VOIP and will use LFI and FRTS. Do not want to exceed CIR at any time to prevent packet loss for voice.

Trying to do the math to determine the best value for PCR SCR and MBS. To restrict exceeding my CIR, research says to make SCR=PCR, but the formula to determine MBS is T = (burst cells x 424 bits per cell)/(PCR-SCR). Should my MBS be 0?

The frame relay research indicates Be should be 0. Do the MBS and Be paramaters operate similarly under these circumstances?

3662 config

interface ATMA/0.ab point-to-point

ip directed-broadcast

pvc A/abc

protocol ip (ip address) broadcast

vbr-nrt 192 192 16

encapsulation aal5snap

protocol ppp Virtual-TemplateZ

interface Virtual-TemplateZ

bandwidth 192

ip address X Y

service-policy output XYZ

ppp multilink

ppp multilink fragment-delay 10

ppp multilink interleave

Frame Relay Config

interface Serial0/0.X point-to-point

no cdp enable

frame-relay interface-dlci AB ppp Virtual-TemplateX

class frts-192kbps

interface Virtual-TemplateX

bandwidth 192

ip address (IP Address)

ip mroute-cache

service-policy output ABC

ppp multilink

ppp multilink fragment-delay 10

ppp multilink interleave

map-class frame-relay frts-192kbps

frame-relay cir 192000

frame-relay bc 1920

frame-relay be 0

frame-relay mincir 192000


Re: ATM PCR SCR MBS question

the way you have it configured is correct , when PCR is equal to SCR you will not be able to burst . you should remove the 16 it is ignoring that number

New Member

Re: ATM PCR SCR MBS question

ATM has about 15-20% of the overhead than the Frame-relay side. So you usually config 15-20% more on the parameter for the ATM traffic shaping compare to the FRTS side.



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