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Gordon Henderson wrote: > > So before I start: Disclaimer: I sell VoIP, PBXs and adapters, etc. I > also don't sell VoIP to save money - I sell it to increase flexibility. > It is possible to save money on calls, but that's not my primary reason > for it. > > > On Tue, 23 Dec 2008, Henry Bremridge wrote: > >> I am trying to move to VoIP and currently use Vonage, but am told by >> "the powers that be" that voice quality is not good enough. > > Quality means a lot of things to a lot of people. It's one of the > biggest headaches I have - almost as bad a hearing "my computer doesn't > work" is "the phone sounds bad" ... Narrowing down the actual "quality" > part of a connection is sometimes quite hard. > > In terms of pure audio quality, (assuming no packet loss), if the device > you are using (ATA, desk phone, soft phone, etc.) is using a G.711 CODEC > then the quality of the call should not be discernible from the quality > of a standard call placed over the BT network - because BT use G.711 > CODEC inside their own digital network once the analogue call hits the > exchange. > > In many cases it should actually be better, as you don't have the > analogue signal going over 50 year old copper wires to the exchange > before the conversion to digital happens. > > So what can go wrong, quality wise. > > Firstly the provider (or device) might be using a compressed CODEC. In > simple terms there is G.711 which although compressed in one manner of > speaking isn't "lossy", then there is everything else which is "lossy". > (Compare PNG which is compressed but not lossy vs. JPG which is both > compressed and lossy) > > G.729 is popular, but there are others. GSM we're all familiar with as > it's used on our mobile phones. G.726 is typically used between DECT > handsets and their base-stations. > > Transcoding degrades quality - like copying copies of VHS tapes, or > continually edit/save/edit/save JPG images. DECT phones typically use > G.726 between the handsets and base stations, so a DECT phone connected > to an analogue adapter which when converts to VoIP can be quite "lossy" > indeed: analogue -> G.726 -> analogue -> G.711 -> VoIP ... > > Compression is often used on international links too - especially if the > call is bridges to the PSTN at some point. That can really make things > worse. One of my wholesale providers gives me the option of 2 different > rates - one which they call their "gold" rates and that's using better > routes for some calls (presumably lower/no compression). Costs more though. > > The other issues you might get is echo. But that's another bag of wurms > in it's own right )-: > > Then there's the quality of the phone you're using. If a headset on a > PC/Laptop, how good is it really? Do some local recordings and check. > Sure, sound cards might be dolby zippity doo dah on the output side, but > what's their input quality like? > > > And not all desk phones are created equal. Grandstreams, which I like, > and sell a lot of are inferior, sound quality wise to Snoms. But Snoms > are twice the price. ATL250s are better too, and half the price, but > utterly useless as a phone. So you pay your money and takes the chances... > > So the above is all quality at the audio end. If we're sorted that out, > then we're left with Internet quality. > > In this country, Packet loss is what we're up against. Latency isn't > normally an issue, but jitter is (jitter is the variance between packet > times - we can tolerate high latency, as long as the time between each > packet is relatively similar) > > So why do we get packet loss... > > Your ISP and what you're doing with your own broadband connection are > the major contributors. Some ISPs do have internally congested networks, > and some people use p2p downloads ... and expect everything else to just > work... > > Unless you pay for it, (and pay dearly!) all Internet access is > contended. (Ye canny change the laws o' fizix!) The "trick" is to pick a > system with the least contention for the best price. > >> Can anyone provide recommendations to improving voice quality? > > The biggest single thing I've found is to use a GOOD ISP, and employ > good working practices on your own network. > > But what makes a good ISP? > > Pick 2 of these 3: Speed, Service, Price. > > I reckon there's a good number of ISPs in the middle-range - ones who > still have a UK based call centre, not too small to have their own > internal networks swamped, but not too big to not really care about > customer service. You'll find a few, but for most home users, IME, > you'll find them out of your price range. Which is why I deal with SMEs :) > > So for example: If you're currently paying £15 a month for the ISP, but > upgrade to a £23 a month ISP - wouldn't that £7 a month be better off > being spend on BT to move yourself to option 3 rather than to a better > ISP to then get free VoIP calls? > > It's a real minefield in the residential area - much easier for SMEs to > make that decision. > > So if you're looking to using VoIP to reduce call charges, then > investing in a good ISP, good routers, VoIP phones, headsets, etc. may > well be counter productive in the money savings department. > >> Issues that I have seen / heard are the following >> >> - Implement QoS on the router >> - Upgrade the router >> - Change from Vonage to another provider >> - Change Internet Connection to a fixed line speed (rather than a >> variable max rating) >> - Make sure ISP does not limit VoIP >> - Get VoIP phone rather that relying on Vonage > > Right now I'm not aware of any ISPs that limit VoIP. Some do > "accidentally" by providing you with a router that might be locked into > their own VoIP solution which won't allow VoIP on the inside. (BT...) > and some routers break VoIP because they've got buggy software in them > anyway. > > QoS/Traffic shaping will only work on outgoing data. > > By the time incoming data has clocked its way over the wire into the > device, it's too late to do anything about it. This is generally OK > though because it's the outgoing data that's going to be the more > problematic because our output speed here in the UK is typically 10 to > 20 times slower than incoming. I've used Draytek and Zyxels with their > traffic shaping/QoS in the past with good results, but when the network > is managed in a business sense (ie. no streaming media, no p2p, no pron, > etc.) then it's OK too. > > No amount of QoS will protect you against a rubbish ISP or a determined > teenager stealing music & videos. Ever had random slow downloads? Web > pages only half loaded? Imagine that on a VoIP call... I know I keep > going on about it, but getting a good ISP is 90% of the problem solved. > > > > Some other information: A single VoIP call, using a G711 CODEC needs > 80Kb/sec *each way* and 50 packets per second *each way* to work. A lot > of people overlook the packets per second requirement, and the full > duplex nature of voice communications plays havoc with Wi-Fi which is > only a half-duplex solution, so don't use Wi-Fi and VoIP. (It can work > and I have Wi-Fi VoIP handsets which do work, but I really don't > recommend it) > > > And then it really depends on what you want out of VoIP. If you want > cheap phone calls, then look into one of the standard BT packages. > (seriously). Or use one of the prefix-diallers - eg. one of the Betamax > resellers "18866", etc. (I think) Or use a cheap VoIP provider, but with > a cheap ISP, be prepared for call quality issues, but maybe you can put > up with that for cheap or even free calls? Your choice... > > > Right now, I think it's hard for your average home user to benefit from > VoIP - unless they're really keen and prepared to spend their own time > in testing, experimenting, etc. but if you've got the time, there are > free VoIP carriers and free calls to be made out there! I don't use > these services for my business customers because they've got no backup, > but for home use, where you're not depending on it, they're OK. > > I think I've witterd on enough now :) I'll bring some kit/toys along > with me to Paignton... Wonder if we can get a wired connection to their > network.. > > Cheers, > > Gordon > Wow that really was in-depth! I'm really looking forward to this Asterisk talk. I managed to unlock my Vonage box (Linksys router) but never did manage to get it to work with another provider (I tried Sipgate without success). Saying that though, if I could get Sipgate working, maybe I wouldn't need to implement Asterisk. Rob -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html