9/14/20151msc ernakulam signaling system #7 kamalasanan.pk

04/21/2304/21/23 11MSC ErnakulamMSC Ernakulam

Signaling System #7Signaling System #7

Kamalasanan.PK Kamalasanan.PK

04/21/2304/21/23 MSC ErnakulamMSC Ernakulam 22

Types of Signaling Types of Signaling

Signaling in Telecommunications Network

•Channel Associated Signaling (CAS)

•Common Channel Signaling (CCS)

Signaling System Number (SS7) is a form of Common Channel Signaling.


Common Channel SignalingCommon Channel Signaling• Out of Band signaling• Employs separate, dedicated path for

signaling.• Voice trunks are used only when a

connection is established, not before.• Faster Call Setup.

SwitchA

SwitchB

Voice Trunks

Signaling Link


Advantage of CCS over CASAdvantage of CCS over CAS• Faster call setup• No interference between signaling tones by

network and frequency of human speech pattern.

• Greater Trunking Efficiency:- CCS has shorter call set up time that result in less call holding time, thereby reducing the traffic on the network.

• Information Transfer:- CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification


SS7 PrincipleSS7 Principle• Out of band Signaling• Higher Signaling data rates (56Kbps & 64

Kbps) for LSL and 2Mbps for HSL• Signaling traffic is bursty and of short duration,

hence operates in connectionless mode using packet switching

• Variable length signal units with maximum size limitation

• Optimum use of bandwidth• Reliability and flexibility


SS7 or Signaling System Number 7 is a set of protocols that describes a means of communication between telephone switches in public telephone networks. SS7 is a highly sophisticated and powerful form of Common Channel Signaling (CCS). The use of out-of-band signaling procedures offers considerable benefits over and above other signaling methodologies.

SS7 is a layered system, in which each layer (level)contains a well-defined functionality, including theinterface (functions and procedures).

DefinitionDefinition


SS7 NetworksSS7 Networks

STP

STP

STP STP

STP


Service switching point (SSP)Service switching point (SSP)– SSPs are switches that have SS7 software

and terminating signaling links– SSPs create packets (signal units) and

send those messages to other SSPs, as well as queries to remote shared databases to find out how to route calls

– SSPs communicate with the voice switch via the use of primitives and have the ability to send messages using ISUP (call setup and teardown) and TCAP (database lookup) protocols.

– The switch can originate, terminate, or switch calls


Signaling transfer point (STP)Signaling transfer point (STP)

–STPs are packet switches, and act like routers in the SS7 network.–Routes each incoming message to an outgoing signaling link, based on routing information contained in the SS#7 message and a pre-defined route table–Does not offer termination services–STPs are paired to ensure redundancy


Service control point (SCP)Service control point (SCP)– An SCP is usually a computer used as a front end

to a database system.– It is an interface to application-specific databases.– The address of an SCP is a point code, and the

address of the database it interfaces with is a subsystem number.

– The database is an application entity which is accessed via the TCAP protocol.

– Databases that provides information necessary for advanced call processing capabilities

– Accepts a query for information from a subsystem at another node


SS7 Link TypesSS7 Link Types

STP STP

STP

STP

STP

STP

STP

STP


SS7 Link TypesSS7 Link TypesA link (access) Connects signaling end point (SCP or SSP) to

STP.

B link (bridge) Join mated STP pairs to other mated STP pairs of equal hierarchy and forms a quad structure.

C link (cross) Connects STPs performing identical functions, forming a mated pair (for greater reliability). Provide alternate routing.

D link (diagonal)

Connects local and regional STP pairs.One level of STP pairs ,the secondary or local level,supports SSPs.

E link (extended)

Connects an CSP,SSP or signaling point to a remote STP pair to perform transaction services. (Note: E links are not recommended)

F link(fully associated)

Connects SCPs,SSPs and signaling points directly with one another.F links donot connect to STPs

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Common Channel Signaling ModesCommon Channel Signaling Modes

• There are three types of CCS signaling modes:– Associated– Quasi-associated– Non-associated

• SS7 runs in associated or quasi-associated mode, but not in non-associated mode. Associated and quasi-associated signaling modes ensure sequential delivery, while non-associated does not. SS7 does not run in non-associated mode because it does not have procedures for reordering out-of-sequence messages.

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Associated SignalingAssociated Signaling

• both the signaling and the corresponding user traffic take the same route through the network.

• Associated mode requires every network switch to have

signaling links to every other interconnected switch (this is known as a fully meshed network design).

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Quasi-Associated SignalingQuasi-Associated Signaling

• In quasi-associated mode, signaling follows a different route than the switched traffic to which it refers, requiring the signaling to traverse at least one intermediate node. Quasi-associated networks tend to make better use of the signaling links.


NODE A

NODE C

NODE B

LINK LINKSET

ROUTE

ROUTSET

PC = 1 PC = 2

PC = 3


•LINK – Physical channel used for signaling. LSL (Low Speed Link )- having a speed of 64Kbps HSL (High Speed Link) – Having a speed of 2Mbps

•LINKSET – Group of links between two nodes. For LSL max of 16 links can be in a Linkset For HSL max of 4 links can be in a Linkset

•LINKSET GROUP – Group of Linkset in which priority has been given

•ROUTE – Logical path between two nodes utilizing the linkset .

•ROUTESET – Group of Routes two a specific destination.


What goes What goes overover Signaling Link Signaling Link

Signaling information is passed over the signaling link in form of messages, which are called signaling units (SUs)

3 Types of SUs are:•Message signal units(MSUs)•Link status signal units(LSSUs)•Fill-in signal units(FISUs)


Message signal unit (MSU)

Carries signaling associated with call setup & database query and response and SS7 network input

BSN/BIB

FLAG LengthIndicator

FSN/FIB

Checksum

SignalingInfo. field

ServiceInfo. octet

1 1 11 1 8-272 1

Signaling UnitsSignaling Units


• FLAG: Beginning of a new SU and is 01111110• BSN: Used to acknowledge receipt of SUs• BIB: Indicate the negative acknowledgement by the

remote SP when toggled• FSN: Sequence number of the SU• FIB: Used in error recovery like BIB• SIO: Service Information Octet• SIF: Signaling Information Field• CRC: Cyclic Redundancy check



Signaling Units Passing in Physical LayerSignaling Units Passing in Physical Layer

F

SPARE

SIFBIB

LICK BSN FFSNFIB

SIO

Direction of transmission

F SFBIB

LI BSN FFSNFIB

FBIB

LI BSN FFSNFIB

Format of Message Signal Unit (MSU)

Format of Link Status Signal Unit (LSSU)

Format of Fill-in Signal Unit (FISU)

F – Flag (8) SIF – Signaling Information Field (8n, n>2)CK – Checksum (16) SIO – Service Information Octet (8)LI – Length Indicator (6) FIB – Forward Indicator Bit (1)FSN – Forward Sequence Number (7) BIB – Backward Indicator Bit (1)BSN – Backward Sequence Number (7) SF – Status Field (8 or 16)

CK

CK

SPARE

SPARE


LENGTH INDICATORLENGTH INDICATOR

LI = 0 indicates a FISU.

LI = 1 or 2 indicates an LSSU.

LI > 2 indicates a MSU


Link status signaling units (LSSU)

– Inform the far end about the changes in status of link

– Message length can be 1 or 2 bytes

FLAG BSN/BIB

FSN/FIB

LengthIndicator

CheckSum

1 1 1 1 1

Status Field

1 or 2



Network Management (LSSU)Network Management (LSSU)FORMAT..

USAGE OF CBA


FLAG BSN/BIB

FSN/FIB

LengthIndicator

CheckSum

1 1 1 1 1

Fill-In Signal Units (FISU)– Fill the gaps between MSU and LSSU

messages– Sent only when the buffer is empty, to keep the

signaling link active– Facilitate in constant monitoring of link quality.



F

SPARE

SIFBIB

LICK BSN FFSNFIB

SIO

8 716282-272 Bytes16 1 7 8

01111110 01111110

279 Bytes

Message Signaling UnitMessage Signaling Unit

Total Time required to transmit 1 MSU with 272 bytes SIF

1 bytes = 125 Micro secondOne MSU = 279 X .000125

= 0.0348 Seconds1 Second = 28 MSU’s

Q:How many MSU’s with fully loaded SIF’s will tranfer in One second?


SS7 Protocol StackSS7 Protocol StackOSI SS7


Message Transfer Part (MTP Level 1) Physical

• Provides an interface to the actual physical channel over which communication takes place

• CCITT recommends 64Kbps transmission as LSL whereas ANSI recommends 56 Kbps

• HSL provides a transmission speed of 2Mbps

ProtocolsProtocols

SS7 Protocol OverviewSS7 Protocol Overview

• The SS7 physical layer is called MTP level 1 (MTP1)• The data link layer is called MTP level 2 (MTP2),• The network layer is called MTP level 3 (MTP3).

Collectively they are called the Message Transfer Part (MTP).

• The MTP transfers the signaling message, in the correct sequence, without loss or duplication.

• The MTP provides reliable transfer and delivery of signaling messages.

MTP2MTP2

• MTP2 ensures reliable transfer of signaling messages.

• It encapsulates signaling messages into variable-length SS7 packets.

• SS7 packets are called signal units (SUs).• MTP2 provides delineation of SUs, alignment of

SUs, signaling link error monitoring, error correction by retransmission, and flow control.

• The MTP2 protocol is specific to narrowband links (56 or 64 kbps).

MTP3MTP3• MTP3 performs two functions:

– Signaling Message Handling (SMH) Delivers incoming messages to their intended User Part and routes outgoing messages toward their destination. MTP3 uses the PC to identify the correct node for message delivery. Each message has both an Origination Point Code (OPC) and a DPC. The OPC is inserted into messages at the MTP3 level to identify the SP that originated the message. The DPC is inserted to identify the address of the destination SP. Routing tables within an SS7 node are used to route messages.

– Signaling Network Management (SNM): Monitors linksets and routesets, providing status to network nodes so that traffic can be rerouted when necessary. SNM also provides procedures to take corrective action when failures occur, providing a self-healing mechanism for the SS7 network.

SCCPSCCP

• SCCP provides a more flexible means of routing and provides mechanisms to transfer data over the SS7 network.

• Such additional features are used to support non circuit-related signaling, which is mostly used to interact with databases (SCPs). It is also used to connect the radio related components in cellular networks and for inter-SSP communication supporting CLASS services.

• For example, in cellular networks, SCCP transfers queries and responses between the Visitor Location Register (VLR) and Home Location Register (HLR) databases.


F CK SIO LI FIB FSN BIB BSN F

SCCP InformationSCCP

Message

Optional PartMandatory

VariablePart

MandatoryFixed Part

SLS OPC DPC

Message Signal Unit 1st Bit Transmitted

- - >

MessageType

MTPRouting Label

SIF

Format of SCCP message.Format of SCCP message.


ProtocolsProtocolsTransaction Capabilities Applications Part (TCAP)• To establish more then one transaction between two ss7

nodes

• Exchange of non-circuit related data

– Between applications across the SS#7 network

– Using the SCCP service

• Queries and responses sent between Signaling Switching Point (SSPs) and Signaling Control Point (SCPs)

• Sends and receives database information

– Credit card validation

– Routing information


Transaction Portion Package TypesTransaction Portion Package Types

Begin

End

Abort

Continue

Starts a dialog between two nodes

Continues the dialog (for example, more messages can be sent)

Ends a dialog between two nodes

Terminates the dialog abruptly without transmitting any pending component


Basic ERROR CORRECTION -With ErrorBasic ERROR CORRECTION -With Error


Service Information Octet (SIO)Service Information Octet (SIO)

In message signal units (MSUs), the service information

octet (SIO) is used to perform message distribution.

This octet is divided into a four-bit service indicator (SI)

and a four-bit subservice field. This subservice field is

further divided into a two-bit network-indicator code

and two bits that are spare if the indicator code is 00

or 01, or are available for national use if the indicator

code is 10 or 11.


SIGNALLING NETWORK FUNCTIONSSIGNALLING NETWORK FUNCTIONSSignaling Message Handling – SERVICE INFORMATION OCTET

D C B A D C B A

Sub-service field (4 bits)

Service indicator (4 bits)

Direction of transmission

Bit D Bit C Network Indicator

0

0

1

1

0

1

0

1

International Network

Not used

National network

Reserved for national use

Sub-service field = Network Indicator(Bits A & B are spare)


THANK YOUTHANK YOU

KamalasananKamalasanan

9/14/20151msc ernakulam signaling system #7 kamalasanan.pk

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