Gary D. Brown, Guest Lecturer CNS 479R Voice Over IP UVSC CS 479R -- Telecommunications and VoIP -- Signaling System 7 -- Lecture 1 Signaling System 7 Gary D. Brown, Guest Lecturer (C) Copyright 2007 by Gary D. Brown

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

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

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

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)

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

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

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

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

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

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

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!

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

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)

SS7 Network Architecture Network Elements (components) Redundancy Addressing Interconnections

SS7 Network Elements Circuits TDM-based Voice Circuits Type T-Carrier (NA/Japan) Capacity DS0 64 Kbps 1 T1 1.544 Mbps 24 T3 44.736 Mbps 672 Circuits TDM-based Voice Circuits Signaling Circuits Type E-Carrier (RoW) Capacity DS0 64 Kbps 1 E1 2.048 Mbps 30/31 E3 34.368 Mbps 480/496 Type Optical Carrier OC-1 51.84 Mbps OC-3 155.52 Mbps OC-12 622.08 Mbps OC-48 2.488 Gbps OC-192 9.953 Gbps

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

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

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

SS7 Signaling Links Physical Connection Bandwidth Link Sets 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

SS7 Signaling Links/Redundancy A-links – links between STP and SSP or SCP endpoints STP Pair STP Pair B-links – bridge links between mated pairs of STPs 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

SS7 Addressing Point Codes and Circuit Identification Codes ANSI ITU 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)

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

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

SS7 Interconnections SSP-to-STP (switch-to-SS7 network) UVSC CS 479R -- Telecommunications and VoIP -- Signaling System 7 -- Lecture 1 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 (C) Copyright 2007 by Gary D. Brown

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

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)

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

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

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

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

Home Location Register (HLR) Global Title Translation (GTT) 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 Home Location Register (HLR) STP Global Title Translation (GTT)

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

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

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