cis 725 telephone protocols. telephone systems circuited switched system call control software

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CIS 725 Telephone protocols

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725_S08_Lecture20

CIS 725Telephone protocols1Telephone systemsCircuited switched systemCall control software2OCM = originating call machineTCM = terminating call machineA places a call to B An OCM for A is instantiated with initial state as idleWhen signal reaches B, a TCM for B is instantiated3

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5Off_hookdialtonenumberringingringbackOff_hookconnectconnectOff_hookdialtonenumberbusy

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C places a call to A An OCM for C is instantiatedA TCM for A is instantiated with state as busy7

C places a call to B An OCM for C is instantiatedA TCM for B is instantiated with state as busy

8Off_hookdialtonenumberringingringbackOff_hookconnectconnectOff_hookdialtonenumberringbackCW_alertFlash_hookOn_holdconnectconnectCall waiting feature9Feature InteractionLimited terminal equipmentSame key used for different purposesExample: 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 B10 Before listening to the tone, B presses # to call D using 3WC CW will intercept # and connect to B to C instead.11Call control interactions: 911 calls: only emergency operator can terminate the call

12 Distributed Interactions: Call number delivery vs call number blocking Call screening vs call forwarding

13Interaction DetectionModel each feature using a formal modelDepending on the current state, a feature may or may not accept a signalFi = accepts a signal S in state siFj = accepts a signal S in state sjCan Fi and Fj be in the states si and sj simultaneously14Explore all reachable states and check whether si and sj are simultaneously reachableIf you find interaction then avoid them15Assign prioritiesAssign priorities and use layeringExample: CW and CF: CW has priority over CF16Feature 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 layer17

- CW has priority over CF18

- CW has priority over 3WC19Multimedia systemsDifferent streams of dataWhat are the new requirementsQoS requirements: - picture quality, brightness, color, tint - jitter, glitches, lip_sync, delay20Intra-media requirementsLatency: - elapsed time from packet generation to packet playback - low latency: real-time applications - high latency: email21 Jitter: - disruption in continuous playback - low jitter for real-time applicationsPacket loss: - % of packets lost - video = packet loss could be high - text = low packet loss Successive packet loss22Intermedia requirementsAsynchrony: - synchronization between different streams - tight synch for tele-conferencing23Conflicts between QoS parametersJitter and latency conflict - To control jitter, value of latency must be large enough to smooth out variations in networkAsynchrony conflicts with latency 24Specifying QoS parametersLatency - two thresholds: lat_max, lat_minJitter Gap_maxPacket loss pktloss_max over time time_pktloss % of successive packet loss25Asynchrony: Async_negthres, Async_posthres

26QoS ControlCan be implemented inside the network - streams are synchronized - virtual circuit-based systemsCan be implemented at end-systemsCombination of both techniques27Inter-media synchronizationUse a single channel to send all types of data - perfect synchronizationMaster/slave channels - use one of the media as the master and synchronize others with respect to this channel28Marker-based synchronization: - periodically insert markers in the streams; - wait for markers to arrive on all streams29QoS Protocol DesignReceiver-based QoS controlQoS control module: - computes the playback time for each pkt - monitors QoS packets - adjusts the playback time - may buffer packets or drop them30Playback timeEach QoS parameters influences the playback time.LatencyJitterAsynchrony31Real-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 32