Op3r

Play a bit with Asterisk. It’s a VoIP pbx (and much more).

- Be famaliar with the most commonly used Codecs, like G.711u/a, PCMU/PCMA, G.729a, GSM, etc.
- Something about the 3 primary protocols: SIP, H323, IAX.
- SIP is becomming dominant for stand-alone services and Windows based IP-PBX.
- IAX is dominant among IP-PBX Asterisk based services.
- Importance of QOS with VoIP.
- Importance of Latency, delayed and dropped packets and related issues that affect voice qualiy.
- Router issues for Port Forwarding and Triggering of SIP ports 5060-5070 and RTP ports 10,000-20,000, etc.
- NAT traversal issues and usage of STUN Servers.
- Know how to configure your own user configurable ATA’s and Softphones

I’m self-taught just by doing extensive research over the Internet.
I’ve tested using many different VoIP services.

I downloaded user configurable softphones like the X-Lite, SJPhone, NCH Express Talk softphone, and 3CX VoIP Client from 3CX corp.
My favorite to use is the 3CX VoIP Client Softphone.

3CX also has a free down-loadable Windows based IP-PBX for learning about using IP-PBX systems.

I learned to configure my own Linksys PAP2T-NA and SPA2102-NA VoIP ATA adapters. I recommend the SPA2102-NA because it has built-in router and QOS.

Learn to configure these devices with BYOD VoIP services like InPhonex, les.net, and CallCentric. Currently, my preferred provider is CallCentric. I use them on my ATA’s and Softphones.

The above should at least give you a starting point…

First of all get an introduction about VOIP. learn about TCP/IP networking from a forum likes.
Then you can start Asteriks PBX system.