Introduction to SS7- Part 1
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This document provides an introduction to the SS7 signaling protocol, detailing its history, components, and function within telecommunications. It outlines the different network elements, types of links, and stack layers involved in SS7, as well as the messaging formats used in the protocol. Additionally, it describes the roles of signaling points and the types of frames employed in communication, emphasizing reliability and error management.
Introduction to SS7- Part 1
- 1. ارتباط ساعیان 1 Introduction to SS7 سیگنالینگ پروتکلSS7
- 3. What is SS7? • Signaling System 7 – CCSS7, C7, number 7, CCIS7 • Official Standard by ITU in 1980 • Common Channel Signaling (CCS) – Signaling channel, CICs • 2 versions…ITU and ANSI • Universal signaling via a suite of sub- protocols – ISUP, TUP, DUP, etc 3
- 4. What is SS7 Network Elements? 4 • 3 types of Switches: • Signal Switching Points (SSP) – Terminate signaling links – Start, end, and switch calls • Signal Transfer Points (STP) – Main routing switches • Signal Control Points (SCP) – Switches attached to Databases
- 6. SS7 Link Types 6 • A Links – Link between an end point and an STP – “A” stands for Access – Purpose is to deliver signaling messages – Connects an SSP to an STP – Connects an SCP to an STP • C Link – Link between 2 STPs (making them a “mated” pair) – “C” stands for Cross Link
- 8. SS7 Link Types 8 • B Links – Link between 2 mated STP pairs – “B” stands for Bridge Link • D Links – Link between 2 mated STP pairs (different hierarchical levels) – “D” stands for Diagonal Link
- 10. SS7 Link Types 10 • E Links – Link between an SSP and a secondary mated STP – “E” stands for Extended Link • F Links – Link between 2 SSPs – “F” stands for Fully Associated
- 12. SS7 Stack layers 12 MTP1 MTP2 MTP3 ISUP SCCP Physical Data Link Network Presentation Transport Session Application TCAP MAP/INAP
- 13. MTP Layers 13 MTP2 • Data Link Layer Protocol • Ensures reliable communications on a signaling link • Error checking, flow control, and sequence checking • Defined in ITU Q.702, Q.703. ANSI equivalents exist
- 14. MTP Layers 14 MTP3 • Network Layer Protocol • Ensures reliable communications to other nodes in the network • Addressing, routing, and congestion control • Defined in ITU Q.703, Q.704. ANSI equivalents exist
- 15. MTP2 Messages 15 BSN/BIB 7 bits/1 bit FSN/FIB 7 bits/1 bit LI/Spare 6 bits/2bits CRC 16 bits BSN/BIB 7 bits/1 bit FSN/FIB 7 bits/1 bit LI/Spare 6 bits/2bit CRC 16 bits SF 8/16 bits BSN/BIB 7 bits/1 bit FSN/FIB 7 bits/1 bit LI/Spare 6 bits/2bits CRC 16 bits SIO 8 bits SIF >=24 bits FISU – Fill In Signal Unit LSSU – Link Status Signal Unit MSU– Message Signal Unit
- 16. MTP2 Messages 16 • BSN – Backwards Sequence Number – Increments to acknowledge reception of a valid frame • BIB – Backward Indicator Bit – Toggles to indicate negative acknowledgement of the last frame • FSN – Forward Sequence Number – Increments to indicated transmission of a valid frame • FIB – Forward Indicator Bit – Toggles to indicate the beginning of retransmission
- 17. MTP2 Messages 17 • LI – Length Indicator – 0 = FISU, 1-2 = LSSU, >2 = MSU • SF – Status Field – Indicates state of link alignment • SIO – Service Information Octet – Indicates type of layer 4 frame • SIF – Service Information Field – Layer 4 data
- 18. FISU 18 • Used to idle the signaling link and keep track of transmitted and received frames • Even though HDLC framing is used on signaling linking frames; MTP does not allow for more then 2-3 idle flags to be transmitted, instead FISU frames are transmitted repeatedly
- 19. LSSU 19 • Used to sync the state machines on both sides of the link • Frame length can be 1 or 2 (normally 1 and normally switches are supposed to be compatible with both) • 6 types of frames identified by the value of the status field (Status Indication X) • Service Information Octet (ITU Q.703, 11.1.3, page 23): – 0, SIO, “out of alignment” – 1, SIN, “normal alignment” – 2, SIE, “emergency alignment” – 3, SIOS, “out of service” – 4, SIPO, “processor outage” – 5, SIB, “busy”
- 20. MSU 20 • Used to carry higher layer traffic (MTP3 mng/test, ISUP, SCCP frames) • Service Information Field divides into 2 fields: – Sub-Service Field, type of layer 4 traffic – Service Indicator, network indicator (aka NI) • Service Indicator(ITU Q.704, 14.2.1, page 70): – 0, network management messages – 1, network test messages – 3, SCCP – 5, ISUP • Sub-Service Field (ITU Q.704, 14.2.2, page 71): – 0, International Network – 1, Spare (international use only) – 2, National Network – 4, Reserved for national use
- 21. ارتباط ساعیان 21 باشید همراه ما با...