Q wrote on Jun 28
th, 2011 at 11:42pm:
There is none. You can have as many channels as you like on just about any number you like. We flex the number of channels up during busy periods at work and that 'flex' might be another 90 channels for 30 days.
When you start getting up to running contact centres you tend to use 30 channel ISDN lines, as the name gives away you can have 30 calls going on at any one time. Easy - thats a single line usually presented as BNC plugs or an RJ45 which you plug into your phone system. As you only have one number (In this case lets presume its the old 020 7222 1234 one) the 1st call will come in on channel one, and then 2 and 3 all the way to 30. When you hit all 30 channels in use you get the busy tone (As a user calling in).
To deal with this shortage you add another ISDN30 (which gives another 30 calls) brining your total simultainious calls upto 60, if thats still not enough you add more and more and more till you cant plug any more lines into your phone system. As all the lines relate to the same number (in this case) the BT (or whoevers exchange you use) is told that any call for 020 7222 1234 should be directed down any of the channels listed within the dial plan for that route. That way you add more lines but don't need more numbers or anything like that.
If you have ever come across featureline the principle is the same, but that's done using analogue copper lines, not fully digital lines as in the world of ISDN.
Quote:You might run into problems when trying to add more spans from the non serving exchange, but the wonders of datafill allow you to do all kinds of things like re-map DDI's etc on the fly, you can also split off the SS7 and send that over another line all together if your demand is high enough.
A span or a trunk is just another name used for the (in this case) ISDN30 lines we are talking about.
If you try and bring in 30 lines from say Wood Green exchange, and another 30 from Muswell Hill you can sometimes run into configuration problems where the telco makes a mess of things and your calls end up going to odd places. The problem is all to do with number blocks and the way there allocated, configured & routed over the network, and explains why they where so slow to offer number portability to people who wanted to keep there 'old' home phone number when they moved out of the serving exchange area.
Datafill is the the routing and config behind the public phone network. It tells exchanges how to route numbers and calls and all sorts of fun stuff. If your a big enough player in the telecomes world (or pay enough) you can have services from the telcos where you can have 1x30 channel trunk from Wood Green with the numbers 020 8521 0000 -> 0999 and a backup line from Muswell Hill that has no numbers on it. If your main line fails you can fail over and take the numbers with you onto the Muswell Hill trunk in one hit without having downtime or to re-advertise your entire number block in times of trouble.
SS7 is the guts of it all - wiki is your friend as there's a lot to cover off. When you start getting lots and lots of voice lines you need to deal with all the call setup stuff (On an ISDN line you have the 'D' channel for that) there comes a point where you can lump all of that SS7 traffic together and connect it into the public network anywhere you like (well almost) That way *all* your call setup traffic is pushed over 1 line and not split into each ISDN line. (If that makes sense)
Quote:Adding network routing is by the by in this case (While the contact centre is in London) all calls will still transit the same bits of the PSTN and end up within the 020 cloud. If we drop the DJSU's we have bigger problems than people not being able to find out where there train is.
DJSU's are (or where as I'm not sure how many are left in traffic now) Digital Junction Switching Units. They where installed into the BT network when 'London' started getting big (Prob goes back to the 01 to 071 and 081 move) The idea of those is to keep calls within London that never need to go outside of London. Before DJSU's a call from London to London might of gone a 'long' way round phone network in order to get up the road. That was and is silly so they stuck in some extra switches at key exchanges to manage London only calls and number routing.
If the DJSU's fell offline or all broke there would be issues with the call volumes in and around London which may break other parts of the public network because thats the only way the traffic can flow.
Quote:What they mean is they didn't want to get the from there existing provider so moved to a new provider (at the same time they moved all there internal numbers etc) they decided to get more channels off the new provider, and add a few more channel cards to there PBX... They could also be SIP trunking from there telco as well.
I spoke to TfL at length about all these changes some time ago, and part of it was they where changing there phone systems, suppliers and everything - they did it in one hit and this is the result. I can't give any details but they have numbers in the 020 3 block as apposed to the 020 7.
True its 'easier' to divert a 08xx number, and true you can get some funky services (like in-coming geographic call hand off) Think National Rail Enq - a caller from 0191 will have there call routed to a northern call centre, while someone from 020 goes to India!