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CIS 725

CIS 725. Telephone protocols. Telephone systems. Circuited switched system Call control software. OCM = originating call machine TCM = terminating call machine A places a call to B An OCM for A is instantiated with initial state as idle When signal reaches B, a TCM for B is instantiated.

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CIS 725

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  1. CIS 725 Telephone protocols

  2. Telephone systems • Circuited switched system • Call control software

  3. OCM = originating call machine • TCM = terminating call machine • A places a call to B • An OCM for A is instantiated with initial state as idle • When signal reaches B, a TCM for B is instantiated

  4. Off_hook Off_hook dialtone dialtone number number ringing ringback busy Off_hook connect connect

  5. C places a call to A • An OCM for C is instantiated • A TCM for A is instantiated with state as busy

  6. C places a call to B • An OCM for C is instantiated • A TCM for B is instantiated with state as busy

  7. Call waiting feature Off_hook dialtone number ringing ringback Off_hook connect connect Off_hook dialtone number ringback CW_alert Flash_hook On_hold connect connect

  8. Feature Interaction • Limited terminal equipment • Same key used for different purposes • Example: CW and 3WC A is talking to B C calls B B receives the call; Call is accepted by CW; issues a tone to B Now, CW is in state ready to accept # from B

  9. Before listening to the tone, B presses # to call D using 3WC CW will intercept # and connect to B to C instead.

  10. Call control interactions: 911 calls: only emergency operator can terminate the call

  11. Distributed Interactions: Call number delivery vs call number blocking Call screening vs call forwarding

  12. Interaction Detection • Model each feature using a formal model • Depending on the current state, a feature may or may not accept a signal • Fi = accepts a signal S in state si • Fj = accepts a signal S in state sj • Can Fi and Fj be in the states si and sj simultaneously

  13. Explore all reachable states and check whether si and sj are simultaneously reachable • If you find interaction then avoid them

  14. Assign priorities • Assign priorities and use layering • Example: CW and CF: CW has priority over CF

  15. Feature at layer N processes a signal before a feature at layer N - 1 • If feature N does not accept a signal, it passes it to the next layer

  16. - CW has priority over CF

  17. - CW has priority over 3WC

  18. Multimedia systems • Different streams of data • What are the new requirements • QoS requirements: - picture quality, brightness, color, tint - jitter, glitches, lip_sync, delay

  19. Intra-media requirements • Latency: - elapsed time from packet generation to packet playback - low latency: real-time applications - high latency: email

  20. Jitter: - disruption in continuous playback - low jitter for real-time applications • Packet loss: - % of packets lost - video = packet loss could be high - text = low packet loss Successive packet loss

  21. Intermedia requirements • Asynchrony: - synchronization between different streams - tight synch for tele-conferencing

  22. Conflicts between QoS parameters • Jitter and latency conflict - To control jitter, value of latency must be large enough to smooth out variations in network • Asynchrony conflicts with latency

  23. Specifying QoS parameters • Latency - two thresholds: lat_max, lat_min • Jitter Gap_max • Packet loss pktloss_max over time time_pktloss % of successive packet loss

  24. Asynchrony: Async_negthres, Async_posthres

  25. QoS Control • Can be implemented inside the network - streams are synchronized - virtual circuit-based systems • Can be implemented at end-systems • Combination of both techniques

  26. Inter-media synchronization • Use a single channel to send all types of data - perfect synchronization • Master/slave channels - use one of the media as the master and synchronize others with respect to this channel

  27. Marker-based synchronization: - periodically insert markers in the streams; - wait for markers to arrive on all streams

  28. QoS Protocol Design • Receiver-based QoS control • QoS control module: - computes the playback time for each pkt - monitors QoS packets - adjusts the playback time - may buffer packets or drop them

  29. Playback time • Each QoS parameters influences the playback time. • Latency • Jitter • Asynchrony

  30. Real-time Transport protocol(RTP) • Application Level Framing: - application knows its own needs - application knows how to segment data * Defines format for data packets (RTP) and control packets (RTCP) * Provides timing-related information to the application to process packets and make decisions

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