SIP is the most popular signalling protocol in VOIP ecosystem. It is most suited to a caller-callee scenario , yet however supporting scalable conferences on VOIP is a market demand. It is desired that SIP must for multimedia stream but also provide conference control for building communication and collaboration apps for new and customisable solutions.
Role of SIP in conference involves
- initiating confs
- inviting participants
- enabling them to join conf
- leave conf
- terminate conf
- expel participants
- configure media flow
- control activities in conf
Centralised vs Mesh signalling for Multi participant conf
In a Centralised signalling model , all communication flows via a centralised control point
In a decentralised or mesh signalling structure , participants can communicate p2p
Unicast vs Multicast Media Distribution
Decentralised Media , Multi unicast streaming
Decentralised media , Multicast
Centralised Media / MCU
Conference types
1. Bridge
Centralised entity to book conf , start conf , leave conf . Therefore single point of failure potentially .
To create conf : conf created on a bridge URL , bridge registers on SIP Server, participants join the conf on the bridge using INVITES
To stop conf : either participant can Leave with BYE or conf can terminate by sending BYE to all
2. Endpoints as Mixer
Endpoints handle stream , decentralised media , therefore adhoc suited
mixer UAs cannot leave untill conf finishes
3. Mesh
complex and more processing power on each UA required
no single point of failure but endpoints have to handle NATIng
