Infrastructure/QOS, Ip Phone System

Edwards Finance > Phones

Q. I work for a UK charity (We currently have three small offices where I could not conceive of more than two VOIP 'lines' at each) we do also have a lot of home based broadband enabled users. I am currently experimenting with a single line Camrivox Flexor 151 / Gradwell out over a Draytek Vigor 2800VG latest firmware QOS enabled (Manual says when Qos enabled prioritises SIP by default) to Zen Internet on a 256u/512down ADSL circuit and then on to Gradwell. The Draytek/Zen/ADSL link is shared with typical Broadband applications like surfing and email + the occasional bit of downloading. Voice performance is 'not bad' but occasionally get 'words missing' which I suppose could be network packet loss. Primarily the reason we are interested in VOIP is to save money on Small Office to PSTN UK land- line calls (Each office currently spends about ?k/year to BT 75% of which is to UK PSTN national numbers!)

A. Anyhow we have just received a grant to spend on infrastructure and I would like to 'spend some capital' to save ongoing running (Dreaded BT phone bill! costs). How would you recommend I spend this money to optimise our VOIP experience (and to minimise things such as packet loss and other drop outs) Should I (for example): 1/ Spend it on CISCO kit (to replace the Draytek's) - We may have access to some refurbished but fully supported units? 2/ Change ISP to somebody who is 'best' at prioritising SIP traffic? Who might that be? 3/ Upgrade the ADSL to MAX e.g. 512up/8M down or even ADSL2? 4/ Implement duplicate ADSL circuits (one for VOIP, one for everything else?) 5/ Going for a more 'homogeneous' ISP environment (We currently use plusNET, Zen and Daemon) All of the above? none of the above? etc.... If you had a few thousand pounds to 'improve' your VOIP QOS (From handset to UK PSTN national numbers) via infrastructure improvements, where would you spend the money? What would be the priority as far as QOS is concerend? But do be aware that you can only efectively apply traffic shaping/QoS to outbound traffic. There is nothing you can really do to inbound traffic, because once it's been clocked over the wire, and arrived at the router, it's too late for the router to do anything with it, other than to pass it through. On the outboumd side, it can buffer up a small amount of data and prioritise VoIP packets, (but it can only store so much if it gets 160 byte VoIP packets and 1500 byte email packets, you quickly run out of time if you store too many!) So QoS on a router will do the right thing when you send a large email, upload big data, etc. but will struggle to make any difference when someone downloads a huge email/file/web page... So a better solution is to get a completely separate 2nd BT line installed and use it purely for VoIP. You don't even need QoS then. You might even be able to front both routers with a 3rd router with 3 Ethernet interfaces on to automagically work out the right circuit to put traffic on, and fail-over to one line should the other go down - I've done this with Linux routers, but don't know any commercial ones that can do this. But either way, you're still at the mercy of the ISP that carries your data (and really BT before it gets to the ISP), and whatever networks are between your ISP and the telco. Telco (Gradwell) might be able to tell you who they have the "best" peering with from that point of view, so you can base your choice on that, but simply do a few traceroute from each site on a different ISP to get a feel for it yourself.

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