Unanswered Question
May 9th, 2007
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I currently have a TAC case open, and may have stumped the technician. My company is using radio communications at a central dispatch offic to communicate with rolling trucks. Some trucks are beyond the RF range, so an application is converting the radio transmissions into UDP to be relayed across a carrier MPLS WAN to other Antenna locations that are in RF range of these trucks. Multiple problems here. First, the application uses multicast, which is not supported on the MPLS network, resulting in the need for GRE. This is working. The second problem is trying to provice LLC QoS for these transmissions. The application requires 50k for the radio communications, and must be treated like voice. I have configured QoS but when applied it is degrading the quality of the communications to the point where it is totally unusable. When the service-policy is removed, the quality improves. My current QoS configs are as follows:

class-map match-all DINET_RADIO

match access-group name DINET





set dscp ef

priority 51

class class-default


interface Serial0/1/0

service-policy out OUTBOUND_POLICY

interface Serial0/1/0.777 point-to-point

frame-relay interface-dlci 777 IETF

ip access-list extended DINET

permit ip host host

I have looked at FRF, but don't know if it can be used on MPLS links. Any help in understanding why the QoS configs are making the communications worse, and how to fix it would be greatly appreciated.

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bjornarsb Wed, 05/09/2007 - 11:00
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I quess that your application requires more than you have reserved.

I would rather use the priority percent cmd.

The 75 percent rule of thumb is actually ok.

(i.e. the sum of the bandwidth percentage allocated to the high priority traffic and the bandwidth percentage allocated to the non-priority traffic cannot exceed 75 percent of the total bandwidth available on the interface. )

Keep in mind that GRE generates overhead.




bssmith10 Wed, 05/09/2007 - 11:43
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Actually, I have measured the amount of bandwidth used when communications is going through, and it is less than 50k. However I did at one point configure priority 102k, which made no difference. Exactly how much overhead does GRE add?

bjornarsb Thu, 05/10/2007 - 03:53
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Gre adds 24 byte overhead to each packet.

So it depens on your packet size.

On the other side, how much bandwith do you have available on your link?



bssmith10 Thu, 05/10/2007 - 07:21
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The circuit is a full T1, with enterprise PVC CIR at full T1. The circuit normally runs less than 30% utilization.

Would configuring frame-relay traffic shaping to get the dual FIFO help?


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