Ss7 Introduction Li In
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description
This is an introductury SS7 presentation. More of a guide than a full presentation from a data(TCP/IP) person perspective
Transcript of Ss7 Introduction Li In
Contents
Signalling and methodology
Introduction to SS7
SS7 protocol stack
Signalling and methodology
Two basic approaches:
Channel Associated Signalling- CASSignalling and voice/media take the same path/Time slot Robbed bit/Wink MFCR2/TS16 Multiframe
Common Channel Signalling- CCS Q.921/Q.931
Introduction to SS7
Network wide CCS for PSTN
SS7 Defines the elements and procedures for User Identification Routing Billing Setting up/disconnect calls Manage Calls
Basic SS7 properties
A private network consisting well defined Network Elements and links
Network Elements are called Signalling Point (SP)
Each SP is identified with a unique address-Point Code (PC)
Various types of SPs and Links are defined
Basis for Intelligent Networking (IN)
Out of Band Signalling (CCS)
High Signalling data rates- 56KBPS/64KBPS and higher
Packet Switching
Connectionless, bursty and short duration messages
Reliable and Flexible
Basic SS7 properties (Contd.)
SS7 Features
Flow Control
Error detection and retransmission capability
Controls for congestion control
Peer entity status detection
Security mechanisms
A General SS7-PSTN-IP network
And now an SS7 network- Standalone
SSP – Service Switching Point
It is basically a switch with SS7 interfaces Class 5 - Local Exchange Class 4 - Tandem switch
Determines how to setup, manage and terminate a call
Based on dialled numbers, sets up SS7 messages
Sends messages using ISUP - ISDN User Part TCAP - Transaction Capabilities Application Program
SSP Call setup scenarios
Call originating and terminating on the same switch (SSP)No SS7 signalling required
Call targeting a known SSPThe SSP routes the call with the help of its routing tables using ISUP messages
Call destined to an unknown SSP The Global Title (dialled number) is either an 800
number or ported one The SSP gives the address of the next hop SSP The IAM message is sent to that SSP with the help of
STP(s)
STP – Signalling Transfer Point
Router/switch/Gateway of the SS7 Network
They are normally paired for reliability
Routes messages based on destination Point Codes on the message header
For cases where the local SSP does not know the destination GT it must provide GT translation
Can provide multiple Signalling routes to destination
SCP – Service Control Point
Provides Application access such as to a data base
An SCP communicates with applications using primitives
The protocol to use and access a data base is called TCAP
SCP may consist of various Sub Systems each with its own SSN (Sub system Number)
SS7 Protocol Stack
SS7 transported over other networks
Addressing in SS7
Point Code (PC) is the Basic Addressing units for each SP.
It should be unique throughout the network. Two major versions:
ITU Basic - A number in the range of 0- 16383 International- 14 bits [3-8-3][Zone: 0-7]- [Area: 0-255]-[Point: 0-7]
ANSI24 bits [8-8-8 bits][Network ID]-[Cluster ID]-[Network Cluster Member]
Addressing in SS7 (Contd.)
Addressing in SS7 makes use of three distinct elements
Point Code –PC
Sub-System Number - SSN
Global Title - GTThe Global Title (GT) may comprise of dialed digits or another form of address that is not recognized in the SS7 network. It is basically an alias for (PC + SSN)
GT Usage example
SS7 Protocol Stack elements
ISUP
TCAP
MTP-L1
MTP-L2
MTP-L3
ISUP
Most widely used part of SS7- ITU Q.764
Protocol to establish/tear down connections
It defines two types of services Basic Services- To establish tear down connections Supplementary Services- To maintain connections
ISUP Elements in detail
Basic ISUP messages
IAM – Initial Address Message
SAM- Subsequent Address Message
ACM – Address Complete Message
CPG – Call Progress Message
ANM – Answer Message
REL - Release Message
RLC - Release Complete Message
A basic ISUP call scenario
ISUP-ISUP Successful call trace
ISUP-ISUP Successful Call trace
ISUP messages list
ISUP Messages Binary HEX
Address complete 00000110 06
Answer 00001001 09
Blocking 00010011 13
Blocking acknowledgement 00010101 15
Call progress 00101100 2C
Circuit group blocking 00011000 18
Circuit group blocking acknowledgement 00011010 1A
Circuit group query 00101010 2A
Circuit group query response 00101011 2B
Circuit group reset 00010111 17
Circuit group reset acknowledgement 00101001 29
Circuit group unblocking 00011001 19
Circuit group unblocking acknowledgement 00011011 1B
Charge information 00110001 31
Confusion 00101111 2F
Connect 00000111 07
Continuity 00000101 05
ISUP messages list (Contd.)
ISUP Messages Binary HEX
Continuity 00000101 05
Continuity check request 00010001 11
Facility 00110011 33
Facility accepted 00100000 20
Facility reject 00100001 21
Facility request 00011111 1F
Forward transfer 00001000 08
Identification request 00110110 36
Identification response 00110111 37
Information 00000100 04
Information request 00000011 03
Initial address 00000001 01
Loop back acknowledgement 00100100 24
Network resource management 00110010 32
Overload 00110000 30
Pass-along 00101000 28
Release 00001100 0C
ISUP messages list (Contd.)
ISUP Messages Binary HEX
Release complete 00010000 10
Reset circuit 00010010 12
Resume 00001110 0E
Segmentation 00111000 38
Subsequent address 00000010 02
Suspend 00001101 0D
Unblocking 00010100 14
Unblocking acknowledgement 00010110 16
Unequipped CIC 00101110 2E
User Part available 00110101 35
User Part test 00110100 34
User-to-User information 00101101 2D
SIP to PSTN Call trace- brief
SIP to PSTN Call trace- detailed
General ISUP Message format
IAM message contains
Nature of Connection Indicator (NOC) Satellite Indicator Continuity Indicator Echo Indicator
Forward Call Indicators Calling Party’s category Transmission Media Requirement (ITU) User Service Info (ANSI) Called Party Number Optional Parameters
MTP L1
MTP L1
The SS7 Physical layer that defines the electrical/optical signal cable definitions
The physical interfaces include E1 - 2048 KBPS 32 *64KBPS channels DS1 - 1544 KBPS 24 *64KBPS V35 - 64 KBPS DS-0 - 64 KBPS DS-0A – 56KBPS
MTP L2
MTP-L2
This layer provides a reliable means of data (signalling info) transfer between adjacent SPs
Equivalent to Layer 2 in OSI model
ITU-T Q.703 standard
Signal Unit Delimitation and Alignment
Make sure blocks of data are delivered in correct order: Adding the correct sequence number to each frame sent
Check the integrity of link.
Signal Unit Error detection and correction
Flow control: Send back busy signal when the buffer exceeds a threshold
MTP-L2(Contd.)
Three kinds of Signalling Units
