internet telephony

Hardware requirement

To create a little VoIP system you need the following hardware:

1. PC 386 or more
2. Sound card, full duplex capable
3. a network card or connection to internet or other kind of interface to allow communication between 2 PCs

All that has to be present twice to simulate a standard communication. The tool above are the minimal requirement for a VoIP connection: next we'll see that we should (and in Internet we must) use more hardware to do the same in a real situation. Sound card has be full duplex unless we couldn't hear anything while speaking! As additional you can use hardware cards (see next) able to manage data stream in a compressed format (see Par 4.3).

Hardware accelerating cards

We can use special cards with hardware accelerating capability. Two of them (and also the only ones directly managed by the Linux kernel at this moment) are the

1. Quicknet PhoneJack
2. Quicknet LineJack
3. VoiceTronix V4PCI
4. VoiceTronix VPB4
5. VoiceTronix VPB8L

Quicknet PhoneJack is a sound card that can use standard algorithms to compress audio stream like G723.1 (section 4.3) down to 4.1 Kbps rate.

It can be connected directly to a phone (POTS port) or a couple mic-speaker.

It has a ISA or PCI connector bus.

Quicknet LineJack works like PhoneJack with some addition features (see next).

VoiceTronix V4PCI is a PCI card pretty like Quicknet LineJack but with 4 phone ports

VoiceTronix VPB4 is a ISA card equivalent to V4PCI.

VoiceTronix VPB8L is a logging card with 8 ports.

For more info see Quicknet web site and VoiceTronix web site

Hardware gateway cards

Quicknet LineJack and VoiceTronix cards can be connected to a PSTN line allowing VoIP gateway feature.

Then you'll need a software to manage it (see after).

Software requirement

We can choose what O.S. to use:

1. Win9x
2. Linux

Under Win9x we have Microsoft Netmeeting, Internet Phone, DialPad or others or Internet Switchboard (from Quicknet web site) for Quicknet cards.

Warning!!: Latest Quicknet cards using Swithboard (older version too) NEED to be connected to Internet to get working for managing Microtelco account (not free of charge), so if you plan to remain isolated from Internet you need to install OpenH323 software.

For VoiceTronix cards you can find software at VoiceTronix web site

Under Linux we have free software GnomeMeeting, a clone of Microsoft Netmeeting, while in console mode we use (also free software) applications from OpenH323 web site: simph323 or ohphone that can also work with Quicknet accelerating hardware.

Attention: all Openh323 source code has to be compiled in a user directory (if not it is necessary to change some environment variable). You are warned that compiling time could be very high and you could need a lot of RAM to make it in a decent time.

Gateway software

To manage gateway feature (join TCP/IP VoIP to PSTN lines) you need some kind of software like this:

• Internet SwitchBoard (only when connected to Internet) for Windows systems also acting as a h323 terminal;
• PSTNGw for Linux and Windows systems you download from OpenH323.

Gatekeeper software

You can download as gatekeeper the Free product Openh323 Gatekeeper (GK) from here.

Version 2.0 of it supports "proxy function" to enabe talking from/to a private network.

Other software

In addition I report some useful software h323 compliant:

• Phonepatch, able to solve problems behind a NAT firewall. It simply allows users (external or internal) calling from a web page (which is reachable from even external and internal users): when web application understands the remote host is ready, it calls (h323) the source telling it all is ok and communication can be established. Phonepatch is a proprietary software (with also a demo version for no more than 3 minutes long conversations) you download from here.

Same function can be obtained using "Proxy" function of Gatekeeper Gnugk (see before).

This entry was posted on Tuesday, January 02, 2007 at 2:52 AM. You can skip to the end and leave a response.