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Community Member

Traffic flow control over ATM

We have the following scenario:

Between two locations we will have a 50Mb/s ATM link. This link will be utilized for general purpose IP traffic as well as for 25Mb/s MPEG video contribution. We want to be able to use the full capacity for IP traffic as long as there is no Video contribution taking place. When Video contribution starts we want to guarantee capacity for this and use the rest of the available bandwidth for IP traffic, and this flow control mechanism should be transparent for the users.

What would the best way to implement this ?

5 REPLIES
Community Member

Re: Traffic flow control over ATM

What platform is this on? Since it is a 50meg link, I'm assuming it is a 7200/7500 series router or higher. A Low-Latency Queueing QoS solution might work for you since this is interactive video. To be honest, since this is 25meg MPEG streams, I don't see how the users won't notice the affect on IP traffic when the video is taking half of the bandwidth, but LLQ will at least guarantee the video goes out the interface first. You need to setup a service-policy and then build two classes beneath it: one for the video and one as a class-default. You also need to make sure that the codec or some other device can mark packets with ip precedence.

ip cef

.

.

.

class-map match-any Video

match ip precedence 5

!

!

policy-map Video

class Video

priority 25000

class class-default

fair-queue 4096

.

.

.

! Then on the ATM sub-interface:

!

interface ATM2/0.100 point-to-point

description ATM Link

bandwidth 50000

ip address xxx.xxx.xxx.xxx sss.sss.sss.sss

pvc 2/100

vbr-nrt 50000 49000 100

encapsulation aal5snap

service-policy output Video

This is one possible solution, and there certainly may be other ways to do this. What happens here is that as long as the mpeg video stream is marked at ip precedence 5 the traffic will go through the priority queue and will be honored first before other ip traffic. It will limit itself to 25meg so other ip traffic flows are not eliminated. As a matter of fact, if the video traffic exceeds 25meg, it will be dropped. Traffic from the priority queue will not default to the weighted fair-queues.

There will have to be some mechanism to mark the packets with IP precedence or Diffserve codepoints. IP precedence is easier if video is the only thing you want to prioritize. The entire bandwidth should be available to the users until the video kicks in, and this should be transparent to the users. Understand that once the video starts the other traffic will only have half the bandwidth so they will be dropped, or if they are tcp based flows they will window down considerably to fit the available bandwidth.

This is just one "possible" solution. I'd be interested in others myself.

Community Member

Re: Traffic flow control over ATM

I may not have been perfectly clear describing our scenario, but will give it another shot. The important thing to note is that we have two independent systems utilizing the same ATM link, one is the Cisco WAN (3662 one end, 7200 the other). The other is a Thomson ATM adaptor (http://www.magnasys.com.au/Partners/Nextream/bxna.pdf).

The normal situation would be 50Mb being used for WAN traffic. When the Thomson ATM adaptor is used to set up a video transmission, we would like the Cisco router to detect this and throttle down the WAN traffic to use whatever capacity is left on the ATM link. Likewise we would like the Cisco router to detect when the video transmission stops and start using the available bandwidth for WAN traffic.

I'd be happy to hear from you or anyone else who has a solution to this.

Community Member

Re: Traffic flow control over ATM

I'm not sure I can help with this one. I don't think a router is designed to do this. It sounds like you have two seperate pvc's and you want to borrow bandwidth from one pvc and use it on the other, which you cannot do, as far as I can tell. I guess I still don't fully understand the situation.

Is the video stream using H.320 video? The Thomson ATM adapter does circuit emulation, which sounds like H.320 video. Before I could give an answer I would need to see a diagram or at least your current router configuration.

Sorry I'm not more help. Thanks!

Community Member

Re: Traffic flow control over ATM

Interesting question!! Are you geting SVC services on three different physical ATM interface??? Or ATM PVP between two site and ATM switch on one end to connect both router and video codec???

I did somthing like this long time ago by using PVP. The traffic control was done on the ATM switch, not on the router.

Community Member

Re: Traffic flow control over ATM

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