Separation of control and data

Why?

• Allows concurrent control and data flow
• simplifies processing of data/control streams
• Provide QoS appropriate for control/data streams

Why not?

• Separate channels complicate management, increases resource requirements
• can increase latency

Maintaining network state

#definition State: Information stored in network nodes by network protocols

• Updated when network “conditions” change
• Stored in multiple nodes
• Often associated with end-systems generated call or sessions

In this context:

• Sender: Node that generates signalling messages to install, keep-alive, remove state from other nodes
• Receiver: Node that creates, maintains, removes state based on signalling messages received from sender

Hard State vs Soft State

Hard State:

• State installed by receiver via setup messages from sender
• State removed by receiver via teardown message from sender

Soft State:

• State installed by receiver via setup message from sender
• State removed by receiver via timeout
• Sender sends periodic refresh message indicating receiver should continue to maintain state

Allows “Easy” handling of changes:

• No need for network to signal failure/change to end system
• Less signalling than hard-state from network to end system
• More signalling than hard-state from end-system to network for refreshes

How to set the refresh/timeout timers?

• State timeout interval = n * refresh-interval
• the value of n determines the amount of signalling traffic
  • Small timers: Fast response to changes, more signalling
  • Long timers: Slow response to changes, less signalling