Newbie Digital Telephony / Networking Question

[oliverlennox]

Hi There,

I'm a bit of a novice at this so apologies if this is a stupid question! 

I'm currently working with a client (a Cisco customer) who operates a large site spread across several buildings. Each building contains a comms cabinet and the cabinets are connected together with fibre optic lines. Inside each building is a standard CAT6 network.

From my basic understanding of networking the fibre lines in this setup are acting like long patch cables and connecting the switches in each comms cabinet together - is that right? So you have one continuous network across the whole site? So from a routing / IP perspective it's fine because the routers at each end of the fibre can direct traffic and you can shunt data around your network between the buildings.

The bit I'm a bit confused with is the telephony side of things. These guys don't actually use an IP telephony system (yet!) they still use a digital switchboard system which is house near one comms cabinet and connected to a bundle of ISDN phone lines. From my (again, very limited) experience of these switchboards you have a port on the box corresponding to a digital line and these ports are connected on a 1-to-1 basis to a CAT5/6 port which connects to a digital telephone. 

My question is: How do you go about sending a series of digital phone ports down a fibre optic line and then separating them out again at the other end? I'm guessing this system is completely different from TCP/IP and so needs to happen apart from your network switches? Also is it possible to use the same fibre line for both your TCP/IP data traffic and your digital phone lines? Or is there some aspect of this which I'm completely missing?

Any advice/explanation would be extremely helpful! Thanks very much for your time

[Dennis Mink]

as always the answer is, depends. sounds like your phone system is physically separated from your data network. if you want the two to merge together, which has always be a mayor selling point for 'VOIP'. your phone system will need to become TCP/IP capable, which in your scenario, it isnt.

usually, traditional digital phone systems have dedicated tie lines (trunks) between buildings or campuses. do if you want to convert to fibre, something will need to translate between TCP/IP and a protocol like for instance QSIG that traditionally ties PBX's together. this will allow it to have your tie lines to go across fibre, by 'becoming" IP.

for example:  http://www.cisco.com/c/en/us/solutions/collateral/enterprise-networks/empowered-branch-solution/white_paper_c11_459092.html

[oliverlennox]

Wonderful Dennis thank you very much for your help, this makes things much clear