VOIP

hey guys, u all want a hadrcore VoIP ?! take this

VoIP stands for Voice Over Inetnet Protocol. repeat the acronym once more and if u are smart u can find the power of this acronym.

There are also other different methods to transport voice such as
Voice over frame relay VoFR and voice over ATM VoATM.
People also transport voice over MPLS.

However, our major cocern is VoIP. IP doesnt really care what physical layer u are really using. be it a LAN, WAN or frame relay or wireless, the voice should get just transported between any interconnetced networks.

Any network that supports IP and there u go u r VoIP instantaneous.

How it Works and what are its advantages ?

lets concentrate on the advantage factor first,
when u are deploying VoIP we are really meaning voice and data network convergence. There is no hefty international (ILD) Phone bills on the companys pocket. An international call is just a local call.
because the call gets routed over IP.
with this u can also do a TOLL bypass. This means that bypass and ILD (International Long distance call) and just connect to the other end thru local exchange PSTN (Public switched telephone Network)

now lets see how it is made to work ?
people from the electrical and electronics background have sufficient information regarding PCM (Pulse code Modulation).
our speech has an alloted bandwidth of 4Khz by the telephone company. to digitize it, this 4khz signal is sampled at 8000 samples per second. each sample is then coded to an 8bit word.
This means our speech signal in digital form is 64kbps.
Imagine this Bandwidth is a dream to achieve in india.

Here comes into picture an important technology called (DSP)
Digital Signal Processing. The DSP compresses these 64kbps and outputs an 8kbps. { 70% of the content in the speech is redundancy and silence. DSP takes advantage of this}

we know that voice and speech are real time entities. a voice sample delayed is as good as lost. Hence TCP is the worst trasnport protocol for VoIP. Hence UDP is used in this technlogy.
However there needs to be another robust protocol which provides the reliablity of TCP but the fastness of UDP. This protocol is called RTP (Real Time Transport protocol ).
an voice sample contains the combination (IP+UDP+RTP).
the headers of all these three protocols are 20, 8 and 12 bytes respectively. so an overhead of 40 bytes will be there.

theres something known as paket frequency. how much packets are needed to complete one second of voice ?

lets assume each voice sample contains 20ms of voice data.
then we need 50 packets per second.
assuming dsp generates 8kbps, and (50*40*=16kbps header overhead. the total BW = 24Kbps.

the BW depends upon the codecs used.


thanx for reading such a long post and forgive me for the aconyms.



with regards
tsunami

Nice synopsis Tsunami

Another great location for VoIP information, and available plans is Which VoIP.

This is available at www.whichvoip.com

My school recently installed VoIP, so I was wondering, other than not having a phone bill, what are the advantages of a VoIP telephone system over POTS (Plain-Old Telephone System)?

I am not a VoIP expert but from what I have seen at work here in a large corporate environment these are some of the benefits:

- Ease of administration - most setup can be done from a single workstation via Cisco CallManager (for Cisco VoIP obviously) and is very easy to do.

- Ability to 're-route' calls through the network in case of congestion, network downtime, etc.

- You can easily remove your phone from the jack and plug it in anywhere else on the network and it will still work.

- Nice little quirks, such as if someone's phone is dialed and they don't answer after x amount of rings the call can be forwarded (via CallManager) to another phone for x amount of rings, and then onto another, etc until someone answers. Or it can be routed to a phone that has been idle the longest to give that person some work to do!

- Can also use a 'soft phone' which is basically just installing software on your computer and using a headset so you can basically VPN to your network from anywhere in the world and you will have access to your phone and voicemail and everything else.

Where do you get the idea that VoIP is free?

I don´t now enough about VoIP, but from what I understand, it is only free if you use it to talk to other IP phones, and even this I am not shure that it is totaly free!

If have a gateway that allows you to call normal phone numbers via you telecom company, than you are paying tha same as with normal phones.

If you don´t have a gateway, and want to call normal phone numbers, than you need to sign up with a VoIP ISP, and this will cost you money (maybe cheaper).

There is also the problem of people calling you. If you don't have a POTS line going through a gateway, then no one will be able to reach you from a normal POTS phone. Unless your VoIP can attribute a number for that efect. But then again you are paying for the service.

If I sayed something that is not true, please correct me. I am mostly interested in this technology.

[quote="... other than not having a phone bill, what are the advantages of a VoIP telephone system over POTS (Plain-Old Telephone System)?[/quote]