VOIP Technologies for idiots (paraphrased)

Michael Krele and Rajatish Mukherjee attempted to give people like me a complete overview of how telephony systems worked from. Starting with a primer on terminology… how many do you know? I knew quite a few (although I did used to work with PBXs on teletype machines)

 
 

Telephone System

• PBX Private Branch Exchange
  
• POTS Plain Old Telephone System
  
• IP-PBX IP based PBX
  
• Hybrid PBX IP enabled PBX
  
• Switch PBX
  
• Node Specific PBX in a network
  
• Trunk Access to PSTN
  

 
 

Telephony

• PSTN Public switched telephone network
  
• ISDN Integrated services digital network
  
• TDM Time Division Multiplexing
  
• PRI Primary rate interface
  
• E1 30 voice channels (Europe)
  
• T1 23+1 voice channels (USA)
  
• BRI Basic rate interface (2 voice channels)
  

Computer Telephone Integration

• CTI Computer Telephone Integration
  
• CSTA Computer Supported Telephone Application
  
• GETS Genesys Enterprise Telephony Server
  
• CUPS Cisco Unified Presence Server
  

   
   

  Protocols and Codec
  

  • QSig ISDN based signaling protocol to connect different PBXs
    
  • SIP IETF Standard, signaling protocol (Session Initiation Protocol)
    
  • H.323 ITU Standard, signaling protocol
    
  • G.711 Standard voice codec (ISDN quality)
    
  • RTAudio Microsoft's dynamic voice codec (superior voice quality)
    

   
   

  Others
  

  • QoS Quality of Service
    
  • QoE Quality of Experience
    
  • CDR Call Detail Record
    

   
   

 
 

PBX are massive racks of kit with built in inelegance. Then you add cards for subscribers. e.g analog / digital cards (16 or 24 lines, add another card after 24 lines) once the whole lot is full then you need to add another system. It's actually more complicated than that as sometimes dependent on what type of cards you have you may need to leave some slots empty for power / CPU reasons. Other cards you can add would be Mgmt cards / Networking (Qsig) and a card for connection to the network (PRI / BRI).

They you can play with all the cards such as putting in all networking cards to create an IP PBX or a hybrid.

Now then, you can then do a corporate GSM Mobile approach, this involves giving everyone a GSM mobile phone. This means that when back at base you can get free calls and they still work outside the workplace. Thus you can have 4-5 digit numbers inside the branch and full mobile numbers outside. This means that you can replace the PBX (aside from a few bits and pieces) .

 
 

So then, how can we make everything better? How can we blaze our way into the future? Well… no prizes for guessing that it's called VOIP and it's got a Microsoft flavour… It's a three step process.

• Build a foundation with a single identity in AD, install IM and presence with OCS2007
  
• Add VOIP software to OCS2007
  
• Finally OCS Standalone
  

   
   

  Sounds great, however…. problems still exist such as lack of emergency call (including information as to where people are), receptionist, teams and hunt group, hold music etc...
  

  So.. How about keep your existing phone and link in to Office Communicator, then you can have the best of both worlds (as long as your PBX supports call forking). There also seems to be a need for a SIP mediation server to link the PBX to OCS2007, however I was a bit confused about that.
  

   
   

  Implications for Lancaster?
  

  I guess the big question for me is how does our Cisco VOIP system interop with LCS? If this can be tightly linked then this might be very good news, we should be able to do things like:
  

• Ring people on your VOIP phone from link on your PC, or global address list, or from SharePoint / outlook.
  
• Conference call across the VOIP network from communicator.
  

   
   

  Ah ha… good news. You can do this now with a CSTA interface, but it's very expensive and not many people do it so DRAT!