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New Member

IP telephony and the Internet


I have many customers enquiring about IPT and the Internet. They typically utilise ASDL lines to access the Internet and VPN's to transport data between branch/remote offices and their HQs, and are interested in running IP telephony alongside.

Does anyone know if Cisco have any design guidelines/suggestions for this scenario, or are we only limited to IP telephony on a private network (or MPLS).

I would really appreciate some input.

Thanks in advance.


Cisco Employee

Re: IP telephony and the Internet

I can say from experience that it will work, but you will not be able to guaratee quality of service over the Internet. I have a vpn 3002 at home that vpn's to a vpn concentrator over my cable modem. My phone registers and I have had good success with voice quality. I would say about 95% of the time the voice quality is excellent. 2 points I would make I am not sure you will see official guidelines and support since you have not control of the QOS on the Internet. The next point is as long as the users understand not to expect 100% of the time excellent vocie quaitly they will probably be happy with it. Keep in mind that the reason you cannot quarentee the voice quality is because of the Internet and the inablity to control QOS not because of the IP phones and callmanager. You can sometimes get deals with service providers to provide that QOS for you but you cannot leave their network and it will cost you big $$.

My $.02,


Re: IP telephony and the Internet

Pretty much a ditto here. I am rolling this out right now with a little different scenario. As long as you convey to the users upfront what it actually is capable of and not then you should be fine. The official Cisco line is that it is not recommended but that's only due to the lack of QoS. If possible, keep your hops to a minimum and the latency below 200ms. ADSL is a little more unpredictable than SDSL so plan for some jitter and robot voice from time to time but overall you should be ok.

New Member

Re: IP telephony and the Internet

My experience with DSL shows that you can get different SLA's. We have QWEST here which provides the following at different costs:

- ABR - Available bit rate

- VBR - Variable bit rate

- VBRNRT - VBR Non-real time

- VBRRT- VBR Real-time (this is recommended for voice and video)

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