Signalling:

#definition Exchange of messages among network entities to enable/provide a service.

Signalling is about maintaining state. Exchange of information between network components required to provide and maintain a service

Examples:

1. TCP Handshake (Connection setup and teardown)
2. RSVP (Resource Reservation Protocol)
3. SIP (Session Initiation Protocol)

Signalling in the Internet:

No network signalling protocols in initial IP design =

• Connectionless (stateless forwarding by IP routers) +
• best effort service However, Transport protocols need state and variable initialisation

Application Layer protocols enable users to be reachable independent of the device and location.

SIP - Session Initiation Protocol:

• IETF protocol
• all telephone calls and vide conference cals take place over the internet
• People are identified by email addresses rather than phone#
• Callee reachable independent of the location and device

Setting up a call:

Provide mechanism for :

• the caller to let callee know she wants to establish a call
• caller and callee to agree on media type and encoding
• end call

Determine current IP address of callee

• Require a mapping of mnemonic identifier to IP Address

Call Management:

• Add new media streams during call
• Change encoding during call
• Invite others
• Transfer and hold calls

Reserve resources along end-to-end path for QoS for multimedia application

RSVP - Resource Reservation Protocol

• Allows users to communication requirements to network in robust and efficient way
• Designed with multicast

Multicast Service Model:

Multicast Group:

• Host sends IP datagram to multicast group using the multicast group address
• Hosts that have joined the group will receive the packets
• Routers forward multicast datagram to hosts

Routers actively participate in multicast making copies of packets as needed and forwarding them towards multicast receivers.

Group Semantics:

• Anyone can join multicast group
  • Host informs local multicast router of desire to join group - IGMP
  • Local router interacts with other routers to receive multicast datagrams - DVMRP, MOSPF, PIM etc.
• Anyone can send to multicast group
• No network layer identification to hosts of members

We need infrastructure to deliver multicast datagrams to all hosts that have joined that group

IGMP - Internet Group Management Protocol:

• Host sends IGMP report when application joins mcast group
  • IP_ADD_MEMBERSHIP socket option
  • Host need not explicitly “unjoin” group when leaving
• Router sends IGMP query at regular intervals
  • Hosts belonging to a multicast group must reply to query