I have a QOS issue

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Dec 29th, 2009

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Hello everybody

I need help in QOS issue, we have 2 branches A and B, A connected via MPLS "Frame-relay" with 2 Mbps connection and B the same like A but with 256Kbps connection, both of the 2 branches connected via the MPLS cloud with many other branches, but only A and B configured with QOS.

And here is the configuration

1-Router A

Class match-any voice

Match protocol rtp

Match access-group 101

Policy-map voice

Class voice

  Set dscp ef

  Priority 1024

Class-default

  Set dscp default

Policy-map voiceA

Class-default

  Shape average 2048000

  Service-policy voice

Int serial 0/3/0.1

Max-reserved bandwidth 90

Service-policy out voiceA

Access-list 101 permit ip 20.1.0.0 0.0.255.255  20.1.0.0 0.0.255.255

Note:all voice lans have this range

2-Router B

Class match-any voice

Match protocol rtp

Match access-group 101

Policy-map voice

Class voice

  Set dscp ef

  Priority 128

Class-default

  Set dscp default

Policy-map voiceB

Class-default

  Shape average 256000

  Service-policy voice

Int serial 0/1.1

Max-reserved bandwidth 90

Service-policy out voiceB

Access-list 101 permit ip 20.1.0.0 0.0.255.255  20.1.0.0 0.0.255.255

the problem

when there is a traffic from A to B "DATA not VOICE" it saturate the INBOUND link of branch B, ok and no voice calls initiated yet.

BUT, when a call initiated voice from B to A is good "outbound of B"

And voice from A to B "inbound to B" so so bad, WHY??

The inbound to B only come from A ok, and data marked with dscp=0 and voice marked with dscp = ef, and the Service provider assure the QOS through its network

Note both A and B policy maps match the pakets and mark it, I checked it using sh policy-map int

Note during saturation of data I traced from A to B using voice subnet and delay = 50 ms in all hops except the last hop "from service provider to B" it equals 300 ms

Any one has any idea??

Thnx for your time  
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Marwan ALshawi Tue, 12/29/2009 - 04:56

the problem here is your connection in site A is sending traffic in a higher rate than B

can handel in the case your link i A side will start dropping in the SP side


as long you are using MQC not frame-relay traffic shaping


in router A you need to shape the interface that sending traffito site B


if you have a specific DCLI going to Site B

than instead of using class-default for the shaper

create class map that match the DLCI going to Site B


class-map map1

match fr-dlci [dlci toward site b]


Policy-map voiceA

Class map1

  Shape average 256000

service policy ---- this one need to be reconfigured to accommodate the new shaped bandwidth

if you do not have a DLCI for Site B only use ACL that match source and destination that represent traffic gong to Site B and use this class instead of class map1 in the example above

this way you will shape the traffic from Site A to B with 256K .

good luck

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Zeinovich Tue, 12/29/2009 - 13:41

dear Marwan, thnx for your reply

but i did what u talked about , i did this shaping with an ACL "which match the data traffic only" where we didn't have specific dlci for branch B, but what is the result?? nothing only the sound sounds better when i shape in a low rate ,

Shape average 256000 >>>>bad sound in B

Shape average 128000>>>>good sound in B

Shape average 96000>>>>very good sound in B


any soln????

or i should shape the all traffic (voice and data)???

Marwan ALshawi Tue, 12/29/2009 - 16:03

you need to shape all of you traffic to 256k and within the 256 k you can prioritize

your voice traffic


with your shaper use bc of 2560 to make the tc to the lowest interval which is 10ms best practice with voip


shape avarrage 256000 bc 2560


good luck

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