voip pstn | what is voip | sip | ip phone | voip phone | pbx | voip


What is voip ?

Voip (voice over ip ) is relatively new telephony. The voip telephony  is based on protocols e.g. Sip ( session initiation protocol) , rtp protocol etc.  The voip uses same internet network for telephony. While Pstn was using pstn based (E1/T1 channels and ss7 signaling for telephony).

A voip call can be setup using voip phone/ip phone  or softphone. A softphone is the software which can be installed in PC or in mobile device , while ip phone is a hardware which comes with voip software.

Benefits of voip:

  • Voip uses already existing internet network , so its easy to deploy new services. 
  • Low cost call, as voip uses the existing internet , so user has to pay only for data not for call. 


Session Initiation Protocol or SIP:
This protocol is used to setup a  media session over ip. This is a signaling protocol, which is used to set session, update session and terminate session.

SIP messages

INVITE: This is the fist message , which is send from sip client to SIP server for call initiation.
Re-INVITE: This message is used to modify a sip session.
ACK: This message is send by called to indicate that the call has been setup.
BYE: Use to terminate SIP session.
REGISTER: Use to register a SIP user agent with SIP register.
SUBSCRIBE :
NOTIFY:
OPTIONS:
UPDATE:

SIP Trunk, 
A sip trunking is service provides by companies , those can connect voip phone on your office or home and you can call or receive calls from traditional telephony. A trunk may carry multiple call on same trunk.

Sip base rfc 3261



Voip Call Setup:




  • Caller sends SIP INVITE to called 
  • Called responds with 180 ringing and caller starts hearing ringing.
  • Called pick up the call, caller receives 200 OK, and caller responds with ACK.
  • Now media session starts , in this session actual voice packets are transferred over ip network.
  • Caller disconnects the call, a BYE is send from caller to called. 
  • Called send ACK in response to BYE. 


     
  

No comments:

Post a Comment

TeleCom Core Signaling | ss7 | Diameter protocol | GTP | 3G | 4g| LTE

This is all about telecom core signalling. Core network signalling is used to make a call, SMS and data in 3G, 4G  and LTE network. There a...