[Nanog] VoIP over Asymmetric routing
Hello, We are going to roll out a network to carry VoIP only, between the P routers, there will be 3xOC3 links. Each site has 2xPEs, PE1 is connected to the P router in the local premises with 10GE and PE2 is connected with 2xOC3s to remote P sites for backup incase local P fails. VoIP is going to be generated by Ericsson Media Gateways and the network designers are suggesting to take traffic in the outgoing direction through the PE1 path and come back through the PE2 path (if that makes sense), so traffic will take a different link for outgoing over incoming.
From your experiences, I am wondering what are future unforeseen pitfalls we can get into?
Regards, KO _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog
If there are any firewalls in the path they tend to dislike asymmetric routing(just standing the obvious).. It tends to play hell on the VoIP ALG's and can cause them to eat CPU/Hang/Crash depending on what vendor you have. This assumes that you have a firewall in the network path. Other items that would concern me is link utilization (What if one network link became completely saturated?)
From a application stand point most VoIP systems will do ok with asymmetric routing RTP doesn't *need* to be symmetric but I would have concerns of designing it to be asymmetric out of the gates.
Just my 2 copper. Tim Eberhard On Mon, Apr 21, 2008 at 1:34 AM, Kim Onnel <karim.adel@gmail.com> wrote:
Hello,
We are going to roll out a network to carry VoIP only, between the P routers, there will be 3xOC3 links.
Each site has 2xPEs, PE1 is connected to the P router in the local premises with 10GE and PE2 is connected with 2xOC3s to remote P sites for backup incase local P fails.
VoIP is going to be generated by Ericsson Media Gateways and the network designers are suggesting to take traffic in the outgoing direction through the PE1 path and come back through the PE2 path (if that makes sense), so traffic will take a different link for outgoing over incoming.
From your experiences, I am wondering what are future unforeseen pitfalls we can get into?
Regards, KO _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog
_______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog
Hi, In _Theory_ asymmetric routing _should_ be ok, but that's in theory. I would be concerned as to why they are designing it this way. Have they gave you a good technical reason it has to be this way? I would ask them to justify it. Also, if there are routing problems on one path but not the other, this could cause a scenario where voice is heard but not received, or vice-versa. This situation is much more frustrating to customers as they will try and continue the conversation. Opposed to if it just doesn't work at all because of a routing problem, customer will just use their cell phones. Also, are they implementing any local PSTN access for local calls or failover? That's my experiences. -----Original Message----- From: Kim Onnel [mailto:karim.adel@gmail.com] Sent: Monday, April 21, 2008 2:35 AM To: NANOG list Subject: [Nanog] VoIP over Asymmetric routing Hello, We are going to roll out a network to carry VoIP only, between the P routers, there will be 3xOC3 links. Each site has 2xPEs, PE1 is connected to the P router in the local premises with 10GE and PE2 is connected with 2xOC3s to remote P sites for backup incase local P fails. VoIP is going to be generated by Ericsson Media Gateways and the network designers are suggesting to take traffic in the outgoing direction through the PE1 path and come back through the PE2 path (if that makes sense), so traffic will take a different link for outgoing over incoming.
From your experiences, I am wondering what are future unforeseen pitfalls we can get into?
Regards, KO _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog
Having the 2 sessions take different paths is fine as long as they both always work as well as each other. If one has more latency or jitter than the other you are likely to run into noticeable echo or other quality issues. What's more important, however, is that each RTP session traverses only 1 path. If you have different packets (or groups of packets) that are part of one session taking different paths, you will run into issues with out of order packets that basically just get dropped. The other thing to think about it what are you actually gaining here? Not redundancy because 1 direction of a call's media is not an acceptable loss (i.e. "in" link goes down but "out" link stays up). Also you aren't gaining much on capacity because modern backhaul links such as 10GE links or OC-X's are symmetrical, so if you only carry traffic in one direction (RTP is UDP so has no ACKs or any reverse direction traffic within the one session) you are actually wasting half of your circuits. -Scott -----Original Message----- From: endzer [mailto:endzer@verizon.net] Sent: Monday, April 21, 2008 7:55 AM To: 'Kim Onnel'; 'NANOG list' Subject: Re: [Nanog] VoIP over Asymmetric routing Hi, In _Theory_ asymmetric routing _should_ be ok, but that's in theory. I would be concerned as to why they are designing it this way. Have they gave you a good technical reason it has to be this way? I would ask them to justify it. Also, if there are routing problems on one path but not the other, this could cause a scenario where voice is heard but not received, or vice-versa. This situation is much more frustrating to customers as they will try and continue the conversation. Opposed to if it just doesn't work at all because of a routing problem, customer will just use their cell phones. Also, are they implementing any local PSTN access for local calls or failover? That's my experiences. -----Original Message----- From: Kim Onnel [mailto:karim.adel@gmail.com] Sent: Monday, April 21, 2008 2:35 AM To: NANOG list Subject: [Nanog] VoIP over Asymmetric routing Hello, We are going to roll out a network to carry VoIP only, between the P routers, there will be 3xOC3 links. Each site has 2xPEs, PE1 is connected to the P router in the local premises with 10GE and PE2 is connected with 2xOC3s to remote P sites for backup incase local P fails. VoIP is going to be generated by Ericsson Media Gateways and the network designers are suggesting to take traffic in the outgoing direction through the PE1 path and come back through the PE2 path (if that makes sense), so traffic will take a different link for outgoing over incoming.
From your experiences, I am wondering what are future unforeseen pitfalls we can get into?
Regards, KO _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog _______________________________________________ NANOG mailing list NANOG@nanog.org http://mailman.nanog.org/mailman/listinfo/nanog
participants (4)
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endzer -
Kim Onnel -
Scott Berkman -
Tim Eberhard