Embed Size (px)
DESCRIPTION
b
Citation preview
SS7 Protocol Stack Vs. OSI Model
SS7 Protocol Stack
MTP Message Transfer Part
TUP Telephone User Part
ISUP ISDN User Part
SCCP Signaling Connection Control Part
TCAP Transaction Capabilities Application Part
Message Transfer Part ( MTP )
• MTP is divided into three levels
MTP Level 1 ( Signaling Data Link )
MTP Level 2 ( Signaling Link )
MTP Level 3 ( Signaling Network )
Message Transfer Part ( MTP )
• Physical layer of SS7 protocol is MTP Level 1
• This Level defines the physical, electrical, and
functional characteristics of the digital signaling link
• Physical interfaces defined include • V.35 (64 kb/s), for use with high speed modems
• DS-0 (64 kb/s), and
• DS-0A (56 kb/s)
MTP Level 1
• Data Layer of the SS7 protocol is MTP Level 2
• MTP2 has the following mechanisms
MTP Level 2
MTP Level 2
• There are three types of signal units
MTP Level 2
Message Signal Unit ( MSU )
Link Status Signal Units ( LSSU )
Fill-In Signal Units ( FISU )
Fill-in Signal Unit (FISU)
Can be used to monitor quality of
signalling link at receiving end
Link Status Signal Unit (LSSU)
Contains signalling messages for MTP
level 2 (signalling link) supervision
Message Signal Unit ( MSU )
Contains actual SS7 signalling messages
Message Signal Unit ( MSU )
Service Information Octet ( SIO )
Signaling Information Field ( SIF )
Service Information Octet ( SIO )
SIO (8 bits)
Service Indicator (4bits) Subservice Indicator (4bits)
Service Indicator of SIO
Service Indicator of SIO
ISDN User Part (ISUP)5
Data User Part ( circuit-related messages)6
Data User Part (facility registration/cancellation
messages)
7
Telephone User Part (TUP)4
Signaling Connection Control Part (SCCP)3
Maintenance Special Message (MTNS)2
Maintenance Regular Message (MTN)1
Signaling Network Management Message (SNM)0
MTP3 UserService
Indicator value
Sub-Service Indicator of SIO
00XX International Network
10XX National Network
Signaling Information Field ( SIF )
Routing Label
• Network Layer of the SS7 protocol is called MTP3
• MTP Level 3 provides
MTP Level 3
Signaling Message Handling (SMH)
Signaling Network Management (SNM)
Routes SS7 messages during normal conditions
Reroutes Link traffic during network failure conditions
SS7 Level 4
Telephone User Part (TUP)
ISDN User Part (ISUP)
Signaling Connection Control Part (SCCP)
Transaction Capabilities Applications Part (TCAP)
Mobile Application Part ( MAP)
Operations, Maintenance and Administration Part
(OMAP)
Intelligent Network Application Part (INAP)
SS7 Level 4
• Level four in the SS7 network consists of different
protocols , called User Parts and Application Parts
• For basic telephone call connection and disconnect,
following protocols are used
– TUP (Telephone User Part )
– ISUP (ISDN user Part )
• To access databases, the TCAP and SCCP are used
ISDN User Part ( ISUP )
However, calls that originate and terminate at
the same switch do not use ISUP signaling.
ISDN User Part ( ISUP )
• The term User Part is unfortunate, since this does
not refer to the ISDN user ; rather it refers to the
fact that ISUP is a user of the lower layers of SS7
ISDN user part (ISUP) does not refer to the ISDN
user
ISDN user part ( ISUP ) is user of lower layers of
SS7
ISUP Message Types
Message Type Binary
Contents
Hex
Contents
IAM (Initial Address Message ) 0000 0001 01 H
SAM(Subsequent Address Message) 0000 0010 02 H
ACM (Address Complete Message) 0000 0110 06 H
ANM ( Answer Message) 0000 1001 09 H
REL ( Release Message) 0000 1100 0C H
RLC ( Release Complete ) 0001 0000 10 H
Many More
ISUP MESSAGES
Initial Address Message ( IAM )
• IAM is the first message used to initiate a call
• An Initial Address Message (IAM) is sent inthe forward direction by each switch neededto complete the circuit between the callingparty and called party until the circuitconnects to the destination switch
Address Complete Message (ACM)
• This message is sent by distant exchange in the
backward direction upon receipt of all address
signals to indicate that the end office is ringing the
called subscriber
• The originating switch responds to an ACM
message by connecting the calling party's line to the
trunk to complete the voice circuit from the calling
party to the called party.
• The originating switch also sends a ringback tone to
the calling party's line
Answer Message (ANM)
• When the called party answers, the destination
switch terminates the ringing tone and sends an
Answer Message (ANM) in the backward
direction to the originating switch
• Answer message (ANM) when received is used
to begin metering of the call for billing purposes
Release (REL)
• Release (REL) is a forward or backward
message requesting an immediate release of a
connection
• The forward and backward nature of the REL
message is based on the ability of the called and
calling users to initiate a release
Release Complete ( RLC )
• A Release Complete Message (RLC) is sent in
the opposite direction of the REL to indicate that
the exchange released the trunk at its end
Setup of a call using ISUP
LE A LE BTransit exchange User A User B
Setup IAMIAM
Setup
Alert
Connect
ACM
ANM
ACM
ANM
Alert
ConnectCharging of call starts now
Number analysis
SS7 Protocols—Call Setup Message Flow
Calling Party Called Party
Lifts handset
Plays dialtone
Dials number
IAM
backward talk path connected IAM
backward talk path connected
ACM
ACM Alerting (Ring)
Plays ringing
Called Party Answers
ANM talk path connected
ANM forward talk path connected
Stops ringing forward talk path connected
talk path connected
Tandem SwitchCalling Switch Called Switch
All circuits now connected and call is in conversation
SS7 Protocols—IAM Message Flow
CO
Switch
Tandem
Switch
CO
Switch
STP
Calling CO switch sends Initial Address Message (IAM) in forward direction to called CO
switch via tandem switches, and each switch seizes an outbound circuit and connects the
backward talk path.
Tandem
Switch
STP
IAM
IAM
IAM
IAM
IAM
IAM
IAM
SS7 Protocols—ACM Message Flow
CO
Switch
Tandem
Switch
CO
Switch
STP
Called CO switch alerts called party (ring), sends Address Complete Message (ACM) in
backward direction to calling CO switch via tandem switches, and calling CO switch plays
ringing.
Tandem
Switch
STP
ACM
ACM
ACM
ACM
ACM
ACM
ACM
SS7 Protocols—ANM Message Flow
CO
Switch
Tandem
Switch
CO
Switch
STP
Called party answers, called CO switch sends Answer Message (ANM) in backward direction to
calling CO switch via tandem switches, and all switches connect forward talk paths.
Tandem
Switch
STP
ANM
ANM
ANM
ANM
ANM
ANM
ANM
SS7 Protocols—REL Message Flow
CO
Switch
Tandem
Switch
CO
Switch
STP
Caller hangs up, calling CO switch sends Release Message (REL) in forward direction to called
CO switch via tandem switches, and each switch sends Release Complete Message (RLC) in
backward direction, disconnects the talk path and idles the circuit.
Tandem
Switch
STP
REL
REL
REL
REL
REL
REL
REL
RLC
RLC
RLC
RLC
RLC
RLC
RLC
Telephone User Part (TUP)
• In some parts of the world (i.e., China and
Brazil), the Telephone User Part (TUP) is
used to support basic call setup and tear-
down.
• TUP handles analog circuits only.
• In many countries, ISUP has replaced TUP for
call management.
Signaling Connection Control Part
(SCCP)• SCCP provides connectionless and connection-
oriented network services and global title translation
(GTT) capabilities above MTP Level 3.
• A global title is an address (e.g., a dialed 800
number, calling card number or mobile subscriber
identification number) that is translated by SCCP
into a destination point code and subsystem number.
• A subsystem number uniquely identifies an
application at the destination signaling point.
• SCCP is used as the transport layer for TCAP-based
services.
Transaction Capabilities
Applications Part (TCAP)• TCAP supports the exchange of non-circuit related
data between applications across the SS7 network
using the SCCP connectionless service.
• Queries and responses sent between SSPs and SCPs
are carried in TCAP messages.
• For example, an SSP sends a TCAP query to
determine the routing number associated with a
dialed 800/888 number and to check the personal
identification number (PIN) of a calling card user.
