Gokul Blog — A conversation on VoIP, IMS, Cisco and Just about Anything

Deeper analysis of VoIP

Talk About Irony!!

Posted by tggokul on May 15, 2007

As most of you are aware a lot of sniffing tools, NMS ( Network Management Solutions) tools, Legal Intercept/Barge Solutions use the concept of SPAN port. For people who are unfamiliar with this, let us say there is a device connected to a switch. You configure another port in that switch to replicate all the packets going through the other port. So any packets going to that device will also go to this spanned port. If you connect any of your sniffer programs into the other port, you will see all the details going to device 1.

You probably would know that most of the calls you make to a call-center are recorded (I am sure most of you would have heard the ‘This call is being monitored for Quality/Training purposes). In a IP based contact center the above mentioned SPAN port mechanism is used to record the calls. So lets say, that one agent sitting with an ip phone is talking to you. The conversations you are having with him is sent as packets to the Recorder application that is connected to this SPAN port.

In a conventional contact center, agents will all reside in a single location and their ip phones will be in the LAN connected to a switch. So it is very easy to SPAN these ip phones and get the conversation. But then with the advent of IP contact centers you get the flexibility of mobility. So for all you might care, the agent can take a call sitting in his house with broadband connection. In that event he would not be in the same switch as the Recording application. So what do you do in that case?

If you know the architecture of a typical IPT ( IP telephony) or IPCC setup, Voice Gateways (Media Gateways) provide the link between the TDM and the IP world. So as a customer you would be dialing from a normal PSTN/mobile phone and the packet conversion happens at the Media Gateway level. So in the above case where a customer is talking to an agent who is sitting at home, irrespective of where he is located, the packets have to traverse through the Voice Gateway which always resides at the central location. So these contact centers span the Voice Gateway port and record the conversations from that port.

This solution is not too accurate for the following reason. The RTP packets flow from the Media Gateway to the agent phone through WAN and the packets that are recorded at the central site need not have have been delivered to the agent phone. Needless to say, this solution is at best ,passable. So the agent/customer might actually think that the call’s quality is miserable, whereas the recording solution would not give any indication to that (QoS is another issue. There is forward/reverse MoS which will address the issue I am talking about, but that is a conversation for another day, another time).

Though the solution is not accurate, you get atleast some kind of data. And how is that possible? Because you have a voice gateway. And why do you have a voice gateway? Because you have TDM integration. What if the world that we are all envisioning, the land of IP actually becomes true? There won’t be Voice Gateways. Most recording solutions will fail. In fact any application using the concept of SPAN ports shall fail. Most NMS solutions will fail, CALEA would die!!! That is the irony I am talking about. If not for TDM being in existence today, most of the IP solutions would be a goner!!!

Forget next generation networks where everything is in IP. Think of today’s world where a customer reaches a contact center through IP rather than through TDM. For example he clicks on the web page link that lets him call into a IP contact center which has mobile agents. In this call flow, there is no way the RTP packets can be traced in today’s solutions.

There are a couple of workarounds for these. Use of a Media Proxy ( i.e any call goes through the Media Proxy). Not very efficient. The only real way to fix this would be to have the intelligence on the agent phone and then ftp the data from the endpoints to the central server. This was actually how the initial logger solutions worked but were phased out because the TDM guys did not like to have the control at the agent desktop level. Talk about irony again.

Anyway, my point is a lot of solutions that exist today cater to a hybrid model ( who expect the TDM world to survive for sometime). Fact of the matter is ,the world is not yet ready for pure IP!!!


5 Responses to “Talk About Irony!!”

  1. anonymous said

    What about a classical SIP based approach of
    1. treating a recordig/monitoring server as a SIP end point
    2. INVITING it to join a call
    3. Call then gets recorded.
    4. Media gets stored in a Storage server.
    5. Accessed by normal HTTP mechanisms or add in streaming capabilities to a player running on Flash for realtime playback.


  2. tggokul said

    Hi Anonymous,

    There are ways, conferencing as you have suggested is surely a way out. My point was most solutions have not yet got that kind of capability.

    Everybody needs to quickly move to SIP. I am just not talking telecom. I am thinking of a day where I can control a washing machine or a fan thorugh SIP. Might sound weird and crazy now. But I can see consumer electronics following the telecom route.


  3. […] using a Voice Gateway to convert it into packets. I had briefly touched upon this last month when I wrote about NMS solutions in IP contact […]

  4. […] using a Voice Gateway to convert it into packets. I had briefly touched upon this last month when I wrote about NMS solutions in IP contact […]

  5. Fantastic site, I really like your writing style. Very distinctive and easy to follow. On a lot of blogs people just drone on and on, but not you – very nice. Keep up the great work! I find VoIP very interesting. I have learned a lot in implementing a small VoIP network at home, and am thinking of starting VoIP business in my area. There are a number of small businesses in my region that would benefit from it greatly.

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