How to Setup a VOIP Server ?

VoIP stands for ‘V’oice ‘o’ver ‘I’nternet ‘P’rotocol.Sending voice of humans through IP packets

on the internet is done by VoIP. Accelerating hardware might be used by VoIP for this purpose

and can also be used in a Pc environment.Now we will see how VoIP is setup.

Setup :

1) Simple communication :- IP to IP

       X (Sound card)   -  -  -    Y (Sound card)

        192.168.1.2     -  -  -     192.168.1.3

192.168.1.2 calls 192.168.1.3 and viceversa.

X and Y should have :-

1.Properly installed and configured application like Microsoft Netmeeting,
  Internet Switchboard,Openh323 (under Windows environment) or Ohphone,
  Gnomemeeting (under Linux).

2.A kind of TCP/IP interface or a network card to talk to each other.

  In this kind of view X can make a H323 call to Y (if Y has server side
  application active)using Y IP address. Then Y can answer to it if it wants.
  After accepting call, VoIP data packets start to flow.

2)Using names

NetBIOS name can be used instead of an IP address Under Microsoft Windows :-

          X            -  -  -             Y 

     192.168.1.2       -  -  -        192.168.1.3

         Win           -  -  -            Jane

                    Win calls Jane

Win call request to Jane is converted to IP calling by the NetBIOS protocol.
This is the reason that it possible.

2 Examples given above are very easy to implement but aren't scalable.

In a more big view such as Internet it is impossible to use direct calling cause,
usually,the callers don't know the destination IP address. Furthermore NetBIOS
naming feature cannot work cause it uses broadcast messages, which typically
don't pass ISP routers .

You can also use DNS to solve name in IP address: for example you can call
''box.domain.com''.

3)Internet calling using a WINS server

The NetBIOS name calling idea can be implemented also in a Internet environment,
using a WINS server: NetBIOS clients can be configured to use a WINS server
to resolve names.

If WINS server is the same used by the PCs then it is possible for them to make
direct calling between them.

X (WINS Server is G) - - - - I  - - - -  Y (WINS Server is G)
                             N
                             T
                             E  - - - - -   G (WINS Server)
E (WINS Server is G) - - - - R
                             N
                             E  - - - -  F (WINS Server is G)
                             T

                   Internet communication

X,Y,E,F are different subnets ,but they can call each other in a NetBIOS name
calling fashion.The need is that all are using G as WINS Server.

Note: WINS server doesn't have very high performance because it uses NetBIOS
feature and should only be used for joining few subnets.

4)ILS Server

ILS is a kind of server which allows you to solve your name during an H323 calling:
when you start VoIP application you first register to ILS server using a name,
then everyone will be able to see you.

5)The masquering:A big problem.

A problem of few IPs is commonly solved using the so called masquering
(also NAT, network address translation): there is only 1 IP public address
(that Internet can directly "see"),the others machines are "masqueraded" using
all this IP.

           X  - - -

           Y  - - -   Router with NAT  - - -  Internet

           E  - - -

                       This doesn't work

In the example X,Y and E can navigate, pinging, using mail and news services
with Internet people, but they CANNOT make a VoIP call.This because H323 protocol
send IP address at application level,so the answer will never arrive to source
(that is using a private IP address).

Solutions:

there is a Linux module that modifies H323 packets avoiding this problem.
You can download the module here. To install it you have to copy it to source
directory specified, modify Makefile and go compiling and installing module with
“modprobe ip_masq_h323″. Unfortunately this module cannot work with ohphone
software at this moment (don’t know why).

           X  - - -   Router with NAT 

           Y  - - -         +           - - -  Internet

           E  - - -  ip_masq_h323 module

                         This works

There is a application program that also solves this problem:

           X  - - -   

           Y  - - -    PhonePatch   - - -  Internet

           E  - - -  

                         This works

6)Open Source applications

Ohphone Sintax

Sintax is:

“ohphone -l|–listen [options]”

“ohphone [options]… address”

“-l”, listen to standard port (1720)
“address”, mean that we don’t wait for a call, but we connect to “address” host
“-n”, “–no-gatekeeper”, this is ok if we haven’t a gatekeeper
“-q num”, “–quicknet num”, it uses Quicknet card, device /dev/phone(num)
“-s device”, “–sound device”, it uses /dev/device sound device.
“-j delay”, “–jitter delay”, it change delay buffer to “delay”.

Also, when you start ohphone, you can give command to the interpreter directly

(like decrease AEC, Automatic Echo Cancellation).

Gnomemeeting

Gnomemeeting is an application using GUI interface to make call using VoIP.

It is very simple to use and allows you to use ILS server, chat and other things.

7)Setting up a Gatekeeper

You can also experiment gatekeeper feature

Example

        (Terminal H323) X  - - -
                                 \
        (Terminal H323) Y  - -  - Z (Gatekeeper)
                                 /
        (Terminal H323) E  - - -  

                   Gatekeeper configuration

Hosts X,Y and E have gatekeeper setting to point to Z.
At start time each host tells Z own address and own name (also with aliases)
which could be used by a caller to reach it.
When a terminal asks Z for an host, Z answers with right IP address, so
communication can be established.

We have to notice that the Gatekeeper is able only to solve name in IP address, it

couldn’t join hosts that aren’t reachable each other (at IP level), in other words it couldn’t

act as a NAT router.

You can find gatekeeper code here: open323 library is also required.

Program has only to be launch with -d (as daemon) or -x (execute) parameter.

In addition you can use a config file (.ini) you find here.

8)Setting up a Gateway

As we said, gateway is an entity that can join VoIP to PSTN lines allowing us to made

call from Internet to a classic telephone. So, in addition, we need a card that could manage

PSTN lines: Quicknet LineJack does it.

From open323 website we download:

driver for Linejack
PSTNGw application to create our gateway.

If executable doesn’t work you need to download source code and open323 library,

then install all in a home user directory.After that you only need to launch PSTNGw to

start your H323 gateway.

9)Compatibility Matrix

First Matrix refers to:

Software intercommunications (i.e. Netmeeting with SwitchBoard)
Software/Driver/Hardware talking (i.e. Netmeeting can use a PhoneJACK card).

 _____________________________________________________________________________________________________________________
|            | Netmeeting |SwitchBoard |  Simph323  |  OhPhone   | LinPhone    |Speak-Freely|HW PhoneJACK|HW LineJACK |
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
| Netmeeting |      V            V            V           V             X            X            V            V
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|SwitchBoard |      V            V            V           V             X            X            V            V
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|  Simph323  |      V            V            V           V             X            X            X            X
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|  OhPhone   |      V            V            V           V             X            X            V            V
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
| LinPhone   |      X            X            X           X             V            X            X            X
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|SpeakFreely |      X            X            X           X             X            V            X            X
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|HW PhoneJACK|      V            V            X           V             X            X            _            _
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|
|HW LineJACK |      V            V            X           V             X            X            _            _
|____________|____________|____________|____________|____________|_____________|____________|____________|____________|

Second Matrix refers to Gateway softwares that manage LineJACK card.

 ___________________________________________________________
|              |HW LineJACK GW| SwitchBoard  |    PSTNGW    |
|______________|______________|______________|______________|
|HW LineJACK GW|      _       |      V       |       V      |
|______________|______________|______________|______________|
| SwitchBoard  |      V       |      _       |       _      |
|______________|______________|______________|______________|
|    PSTNGW    |      V       |      _       |       _      |
|______________|______________|______________|______________|

Notation: