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