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QoS on Cisco 2611 and 1720 Routers.

Hi All,
We are soon going to upgrade our old PBX system with a new Toshiba CIX/CTX systems in our two locations. We have a PTP T1 leased line between these two locations carrying data traffic. One of these locations is also the Internet gateway for the 2nd location.

The phone guys are telling me that our internal (between locations call) as well as voice mail traffic (centralized) will be on T1. So the T1 will carry both, voice and data. To hook up their new digital PBXs to our data network, they just need two separate IP addresses in each location and they can then connect  cat5 cables to our cisco switch in ea. location. Outward and Inward calls will be made through our Telco lines. So we are on VOIP, but partially.

What kind of configuration I would require to do in the routers? QoS? If yes, does Cisco 2611 and 1720 support QoS?
IP TelephonyVoice Over IPRouters

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8/22/2022 - Mon

Yes, you will need QoS and both Cisco routers will support that.
What needs to be done :
* apply marking, so you can differentiate between voice traffic and other, less critical, packets
* we will want to put all voice stream into the Low Latency Queue, this LLQ will get first priority when sending out packets over the T1
* a T1 has a, relatively, low bandwidth, the VoIP guys should be doing so when implementing, but you should use G.729 or some other low bandwidth codec over the WAN
* QoS can only protect voice traffic from other traffic, with LLQ you will allow all combined voice traffic x amount of bandwidth, if you will have more calls over the WAN than can be carried in that bandwidth, you will again run into issues, to prevent more calls than supported being set up, it's a good practice to set up Call Admission Control, CAC is applied by the VoIP equipment, Cisco CallManager can do it through Locations, or an H.323 gatekeeper, I suggest you ask your VoIP supplier to ask about this scenario

As a general comment, do take QoS and CAC serious, you will probably not even notice the first months if you do not configure it, but the point where a lack of WAN design becomes apparent WILL come up and haunt you sooner or later.

Thanks for the reply, KIBe.
Unfortunately, there is not much help available from our phone guys on VOIP. They are just phone guys who are installing their digital PBX. Their knowledge in IP networking is limited.
The T1 is going to be utilized only during internal calls and voice mails for the 2nd location. We still have Verizon lines (analog) in ea. location for external (out/in) calls.
The guys (from their experiences at other clients' locations) are telling me that we should just be fine w/o QoS, but in the event it has to be done, it has to be done by us. They are also talking about QSIG. What is it?
Many Thanks,


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How many users on PBX?  

my first inclination would be to use a CISCO ASA - its bandwidth management options are somewhat more extensive than i've seen in CISCO routers - also, have you considered CISCO's VOIP solution?  Depending on the number of users, it could be a better all round solution -
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William Peck

Thank you for responding again.
There will be 6 internal lines (between buildings) configured with additional VM traffic over the T1.
Although, they are saying we should be fine w/o any router config change, I would however like to configure QoS on both routers. That will be more sensible thing to do.
How complicated router configuration do you see in this situation?

I would appreciate if you could give me a high-level overview of the router config in both locations pertaining to QoS.
Thanks, S


Thanks,, Kibe for your insight and some valuable suggestions. They are helpful.
I will open up a new thread for some configuration help.