XMPP protocol extension for managing peer to peer video and audio sessions.

XMPP

• Based on XML.
• Formally known as Jabber.
• RFC3920 and RFC3921.
• Extensions using XEP (extension proposals).
• JID - looks like an email address.
• juliet@domain.com/resource - multiple clients on same account.
• message, presence, info/query

Jingle

• Extension to XMPP
• Supports RTP

MUC - Multi User Chat

Multi User Jingle

• Should work ok for clients that don’t support Multi-user Jingle.
• Joining Multi User Jingle session split into two stages to prevent race conditions.

Steps to join a session:

1. Announce that you’re preparing to start or join the session. Send a presence message.
2. After all clients that nnounced they were preparing to join have done so, update your presence with payload mapping.

Multi User Jingle

• only needs basic infrastructure.
• each client can present conference in different manner.
• does not scale to large groups, due to bandwidth requirements.
  • Limited to number of streams a client can decode.
  • upstream bandwidth
  • local bandwidth

Further work

Problem: not scalable

• RTP relay. Clients send streams to a relay, which relays to multiple clients.
• Mixer - client send streams to a mixer which combines streams into one stream. Unfortunately clients no longer have control over presentation.
• Combined relay and mixer. Clients choose if they want to receive a mixed stream or not. Allows clients to decide on tradeoff.

Problem: each client encodes data once, so must do so using method that is compatable with all other clients.

• Scalable Video codecs. Low resolution low quality base layer. Add extra layers for extra quality. Client decides which layers it wants to send. H264/SVC exists but is heavily patented. No free standard available.

https://telephathy.freedesktop.org/wiki/MultiUserJingle
https://www.nlnet.nl/project/mujingle/
https://farsight.freedesktop.org/
https://nice.freedesktop.org/