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On Wed, 23 Sep 2009, Henry Bremridge wrote:
However as I will be going VoIP at some point I want to be able to grant default low priority access to visitors, and give full QoS to VoIP. Current box will not allow this.
Be careful what you mean by QoS... QoS (now really called diffserv) is a set of extra bits in the IP headers that tell switches, routers, etc. about this packet and what priority weighting to give it.
To my knowledge, no ISPs in the UK honour QoS bits over their network - if they did, then all the P2P etc. users would simply enable it and really annoy others...
You can use QoS when you have control over all the network devices - in a corporate environment with private leased lines to form a WAN for example. You will want to promote interactive traffic over bulk data transfers.
Another form is traffic shaping - which is often confused with QoS as it can provide a degree of quality of service - or a degree of traffic throttling! You can "shape" traffic based on many more criteria than just the QoS/Diffserve bits - IP address, ports, packet size, etc. Actually, in the Linux world you can use the back-end traffic shaping as teh control mechamisn to handle the managemnt of the QoS/Diffserve bits in data packets.
(And if you want to blunder about in a huge black hole, then start with the lartc site http://lartc.org/ look at wondershaper and if you're still alive at that point sell yourself as a Linux traffic manglement specialist ;-)
For the home/SOHO user you may be able to gain something in your router if it supports traffic shaping and it may support QoS (DiffServe), giving it the ability to queue up packets it recieves and then select which ones to send out to the outside world. It can do this if it has a large enough buffer and all the timings are met - it can't stall a packet forever and at some point it will have to start sending data out else it's internal buffer will overflow.
However, for incoming data, there is nothing you can do about it as the data has already been clocked over the wire into the device. Download data packets are 1500 bytes long, VoIP data packets are 160 bytes long and need to come in at 50 packets per second. Do a bit of math and you'll run out of time when downloading a big file and taking a VoIP stream at the same time, although jitter buffers can help here. Incoming data is generally not an issue in this country as it's usually much faster than outgoing, so it's only outgoing data you need to wory about. VoIP will suffer when you do a bit upload, send large emails, etc. unless you can control it in the router.
Nothing's perfect though - even if you can perfectly shape outgoing traffic, you've then for the BT wholesale network to wory about and after that, your chosen ISP - and then there's the ISPs that may be inbetween your ISP and the end-point of your VoIP call... It's a miracle it works at all, really... (Er, Actually it works very well which is a testament to just how good our intrastructure is in the UK - as long as you pick reputable ISPs to carry your data over)
And although I like Drayteks, they're not perfect and the next generation of my PBXs will actually have router functions built-it and 2 Ethernet Interfaces. (Well, they already have 2 Ethernet interfaces, I just need to write the code :)
Gordon -- 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