CS294 3 Distributed Service Architectures in Converged Networks Randy H Katz Computer Science Division Electrical Engineering and Computer Science Department University of California Berkeley CA 94720 1776 1 Outline Historical Background Structure of the PSTN Intelligent Network Services SS7 Structure Common Themes and Observations 2 The Telegraph Learns to Speak Alexander Graham Bell 1876 Demonstrates the telephone at US Centenary Exhibition in Philadelphia Bell offers to sell patents to Western Union for 100 000 they refuse Bell Telephone Company founded 9 July 1877 1878 Western Union enters into competition with rival system designed by Thomas Edison and Elisha Gray Bell sues and wins 3 Bell s Early Telephones 4 Building the Network Almon Brown Strowger 1839 1902 1889 Invents the girl less cuss less telephone system also known as the mechanical switching system 5 Ma Bell Bell s patents expire in 1890s over 6000 independent operators spring up 1910 Bell System controls 50 of local telephone market 1913 AT T U S government reach Kingsbury Agreement AT T becomes regulated monopoly while promising universal telephone service Controls toll services in U S Long distance interconnection withheld as a competitive weapon 1950 Bell System controls 84 of the local telephone access market 6 Bell Telephone Equipment 7 Public Switched Telephone Network PSTN Time Division Multiplexed Network Single application uncompressed voice i e POTS Plain Old Telephone Service 99 9994 uptime Low latency and jitter Highly scalable call routing through SS7 infrastructure Value added voice services e g voice messaging caller ID 8 Structure of the PSTN Separation of data switching and control signaling planes Hierarchical switches Local Loop Central Office End Office Intermediate Regional Switches Trunks Long Distance Control signaling evolution Old PSTN 1960s analog signaling encoded in voice band Dual tone multifrequency DTMF between CPE and EO I e touch tone dialing Single frequency SF between COs New PSTN 1980s digital signaling separate control network SS7 SF still exists though made obsolete by SS7 9 Old vs New Signaling Call I m busy Voice Trunk Call Set up I m busy message Control Voice Trunk Free 10 Kinds of Signaling Messages I m forwarding to you a call placed from 212555 1234 to 718 555 5678 Look for it on trunk 067 Someone just dialed 800 555 1212 Where do I route the call The called subscriber for the call on trunk 11 is busy Release the call and play a busy tone The route to XXX is congested Please don t send any messages to XXX unless they are of priority 2 or higher I m taking trunk 143 out of service for maintenance 11 Advantages of Out ofBand Signaling for PSTN It allows transport of more data at higher speeds due to digital encoding rather than audio analog encoding Signaling takes place any time during call not only at beginning Allows signaling to network elements to which there are no direct trunk connections 12 PSTN Hierarchy Before Deregulation Class 5 End Office Local Office Interconnection among EOs only within a geographic service area Class 4 Tandem Office Also known as a toll office Higher bandwidth trunking among service areas Class 3 Primary Center Part of toll long distance network Class 2 Sectional Center Class 1 Regional Center Not a strict hierarchy in that Class 5 switch can be connected to switch other than a Class 5 or 4 switch 13 PSTN Hierarchy Local Area 510 LATA 8778 Analog local loop Twisted Pair Digital CO CO 642 CO CO CO CO LEC Trunk IXC 64 Kbps links time division multiplex demultiplex Voice band 3 4 KHz between 350 Hz and 3750 Hz 8000 samples second x 8 bits Law 14 PSTN Hierarchy Post AT T Breakup 1980s IXC Interexchange Carrier LATA Local Access Transport Area POP Tandem Office Class 4 Switch Intra LATA connections Inter LATA connections TO EO EO Allocate a facility circuit per switch per call AT TO EO Local Loop CPE Customer Premises Equipment EO EO EO End Office Central Office Class 5 Switch ILEC incumbent CLEC competitive Reciprocal Termination Revenue 15 PSTN Hierarchy Deregulation Complexities RBOCs traditional service areas divided into LATAs originally 146 now 300 Local operating company must use long distance provider to interconnect LATAs Long distance carriers gain access to local networks through Point of Presence POP center Every LATA must have a POP LATA further divided into local market and toll market Intra LATA toll calls also open for competition 16 PSTN Hierarchy Synchronous Network Maintaining clock synchronization PRS Stratum 1 PRS Primary Rate Source PRS Stratum 2 Toll Office Stratum 3 End Office Stratum 4 Sync Region Sync Region PBX Channel Banks Sync Region Sync Region 17 PSTN Hierarchy Digital Signal Bandwidth Destination DS0 DS1 DS1C DS2 DS3 DS3 Channels Carrier DS0s Designation 64 kbps 1 channel 1 544 mbps 24 channels 3 152 mbps 48 channels 6 312 mbps 96 channels 44 736 mbps 672 channels 274 176 mbps 4032 channels None T 1 T 1c T 2 T 3 T 4 Digital Signaling Hierarchy SS 7 uses DS0s for signaling links Channel banks divide DS1 into 24 DS0s Copper facilities replaced by fiber SONET speeds to 9 6 gbps and beyond OC 1 51 84 mbps OC 3 155 52 mbps OC 12 622 08 mbps OC 48 2488 32 mbps OC 96 4976 64 mbps OC 192 9953 28 mbps 18 Intelligent Network Motivation More rapid evolution of the network Easier to configure Tailored services for subscribers Services on demand voice communication audio video But the most common services are redirection e g 800 numbers cellular network support call forwarding etc but also services like call waiting caller id voice mail etc Implemented by GUI to switching networking Service Creation Environment SCE SS 7 is IN s backbone Network that links together the Service Switching Points Old PSTN command signaling embedded in audio channel New PSTN interoffice signaling between switches via orthogonal network 19 Intelligent Network Basic Call Sequencing Features services invoked on state transitions Disconnect Put down phone Quiescent Talking Pick up phone Off hook Send dial tone Dial Collect dial string Remote user Picks up phone Ringing Dialing Setup complete Setup Waiting for Setup Complete Busy detection Three way calling 20 Intelligent Network Call Sequencing Call set up and tear down handled by conventional SS 7 protocols Dialed digits determine how to connect call Request for call handling instructions sent to SCP DB provides handling instructions E g to map 800 number to local number under rules Routing
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