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CNS 479R Voice Over IP

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CNS 479R Voice Over IP

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  1. CNS 479R Voice Over IP Signaling System 7 Gary D. Brown, Guest Lecturer

  2. Signaling System 7 (SS7) • Introduction • SS7 Network Architecture • SS7 Protocols • SS7 Call Signaling • VoIP Issues • NG9-1-1 Architecture

  3. Introduction • Public Switched Telephone Network (PSTN) • Time-Division Multiplexed (TDM) Technology • Wire-line Network • Wireless Network • SS7 Network • Business Models • Applications

  4. Wire-line Network • Terminals • Telephones • Facsimile machines • Modems • Video Conferencing Systems • 143 Million (2004) in the United States • 1 Billion+ terminals worldwide

  5. Wire-line Network • Switches • Central Office (End Office) Switches • Connect terminals to PSTN (lines) • Interconnect with tandem switches (trunks) • 142 Million (2004) in the United States • 17,932 CO switches (2004) in the United States • Tandem Switches • Interconnect CO and tandem switches • Form PSTN “back-bone” network • National tandems • International tandems (same network between countries) • International Gateway tandems (different network types)

  6. Wire-line Network Architecture Central Office Lines National Network Trunks National Tandem International Network International Gateway Tandem

  7. Wireless Network • Wireless Terminals • Mobile Phones • Laptop Computers • Personal Digital Assistants (PDA) • 213 Million (2005) in the United States • 1 Billion+ worldwide

  8. Wireless Network • Base Station Controllers (BSC) • Control multiple Antennas (cell towers) • TDM-to-radio conversion and frequency control • Limited switching capability • Mobile Switching Centers (MSC) • Wireless equivalent of “Central Office” switch • Control multiple Base Station Controllers • Interconnect with tandem switches • 1,000+ in the United States

  9. Wireless Network Architecture Radio Central Office BSC National Network Trunks MSC Lines National Tandem International Network International Gateway Tandem

  10. SS7 Network • Created in late 1970s—deployed 1980s • About same time as IP network • Purpose-built for PSTN • Specifically designed for voice calls and services • Interconnects PSTN switches and networks • Wire-line CO and tandem switches • Wireless MSC • National/International networks

  11. SS7 Network Interconnection Radio Central Office BSC National Network Trunks MSC Lines National Tandem SS7 International Network International Gateway Tandem

  12. SS7 Network • Interconnects all wire-line and wireless networks • Interconnects with VoIP networks via SS7/VoIP signaling gateways • Very important infrastructure network • AT&T’s “Black Monday” in 1980s • Entire 1-800 network failed • Congressional hearings held to determine blame!

  13. PSTN Business Models • Carriers or Service Providers • Local Exchange Carriers (LEC) • Incumbent LEC (ILEC) (e.g.Qwest Communications) • Competitive LEC (CLEC) (e.g. Veracity) • Local Telephone Companies • Inter-exchange Carriers (IXC) • Long Distance Telephone Companies (e.g. AT&T, Sprint) • Switch-less Resellers • Mobile Network Operators (MNO) (e.g. Sprint PCS, T-Mobile) • Mobile Virtual Network Operators (MVNO) (e.g. TracPhone) • Geographic Area/Coverage • Interconnected via SS7 Network

  14. Applications • POTS (Plain Old Telephone Service) • 800 toll-free service • 900 premium service • Directory Assistance • Operator Assistance • Conferencing Service • Local Number Portability (LNP) • Wireless Local Number Portability (WLNP) • Line Information Database (LIDB) • Billed Number Screening (BNS)

  15. SS7 Network Architecture • Network Elements (components) • Redundancy • Addressing • Interconnections

  16. SS7 Network Elements • Circuits • TDM-based • Voice Circuits • Signaling Circuits

  17. SS7 Network Elements • Nodes • Service Switching Point (SSP) • Central Office Switches (CO) • Mobile Switching Centers (MSC) • [Access] Tandem Switches (AT) • Controls calls • Asks for services • Signal Transfer Point (STP) • Forwards SS7 Messages • Service Control Point (SCP) • Provides services

  18. SS7 Network Elements ≡ IP Network LAN Router Server SS7 Network SSP STP SCP Service Switching Point Switches between computers Signaling Transfer Point Forwards packets Service Control Point Provides services

  19. SS7 Network Elements MSC Switch Tandem Switch CO Switch Voice Circuits Voice Circuits SS7 Messages SS7 Messages SS7 Messages SS7 Messages SS7 Messages STP Home Location Register (HLR) Global Title Translation (GTT)

  20. SS7 Signaling Links • Physical Connection • DS0 channel in T1/E1 circuit (very common) • V.35 modem (older technology) • IP network (newer technology) • Bandwidth • 56Kbps (robbed-bit T1) • 64Kbps (clear channel T1 and E1) • Link Sets • Dual data links for Redundancy

  21. SS7 Signaling Links/Redundancy • A-links – links between STP and SSP or SCP endpoints • B-links – bridge links between mated pairs of STPs STP Pair STP Pair SCP SCP • C-links – cross link between STPs within STP pair • D-links – diagonal links between mated STP pairs in different networks • E-links – extended links between SSP and alternate STP Voice Circuits SSP SSP • F-links – links between SSPs

  22. SS7 Addressing • Point Codes and Circuit Identification Codes • ANSI • 24-bit point code (16,777,216 nodes) • 14-bit circuit identification code (16,384 circuits) • North America, Japan, China • ITU • 14-bit point code (16,384 nodes) • 12-bit circuit identification code (4,096 circuits) • Rest of World (RoW)

  23. SS7 Addressing • Origination Point Code (OPC) • Sender of SS7 message • Destination Point Code (DPC) • Receiver of SS7 message • Circuit Identification Code (CIC) • Identifies physical circuit between SSPs • Circuits have common numbering between SSPs • SS7 Call Signaling Messages contain OPC, DPC and CIC

  24. SS7 Interconnections • SSP-to-SSP (switch-to-switch) • F-link used to directly interconnect switches • Uses one DS0 channel of T1 circuits between switches • Sometimes used in North America SS7 F-link Voice Circuits SSP SSP

  25. SS7 Interconnections • SSP-to-STP (switch-to-SS7 network) • Uses A-link to interconnect SSP and STP • Uses one DS0 channel of T1 or E1 circuit—no channels used for voice • Commonly used throughout the world—required in Europe STP STP SSP SS7 A-links Voice Circuits SSP SSP SSP

  26. SS7 Interconnections • SS7 Signaling Transport Companies • AT&T Wholesale • Was SNET (Southern New England Telephone) • Connecticutt ILEC • ISUP Gateway Service • LNP Gateway Service • 8XX Gateway Service • SOA (Service Order Administration) Service Bureau • Ports subscribers to other carriers (LNP) • CLASS (Custom Local Area Signaling Services) gateway

  27. SS7 Interconnections • SS7 Signaling Transport Companies • VeriSign • Illuminet (purchased in 2001) • 15 STP Pairs • Largest independent U.S. SS7 transport network • Interconnects with nearly all carriers in North, Central and South America • IXCs (e.g. Sprint LD, MCI) • LECs (Qwest, Verizon)

  28. Wireless 1-800 Call Mobile phone dials 1-800 number. MSC verifies phone is a customer. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  29. Wireless 1-800 Call MSC asks for Global Title Translation of 1-800 number, which gives actual destination. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  30. Wireless 1-800 Call MSC switch passes call information to and requests circuit from Tandem switch. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  31. Wireless 1-800 Call Tandem switch passes call information to and requests circuit of CO switch. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  32. Wireless 1-800 Call Circuit path completed and called party alerted. Answer supervision returned when called party answers and billing starts. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  33. Wireless 1-800 Call Call in conversation. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  34. Wireless 1-800 Call Call torn down when one party disconnects. Circuits are released and billing terminates. MSC Switch Tandem Switch CO Switch STP Home Location Register (HLR) Global Title Translation (GTT)

  35. Signaling System 7 (SS7) Next lecture on SS7 Protocols used between SS7 network elements