ss7 by masoodalam

8/7/2019 SS7 by MasoodAlam

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By Masood Alam


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Introduced by ITU by its

recommendations

Q.700-Q.716, Q.721-Q.766, Q.771-Q795 International standard forCommon

Channel Signaling System, anothername

CSS7

Call setup, communication, teardown,management ,maintenance


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Signaling method in which a single

channel conveys, by means of labeled

messagesMessage structure iswell organized, and

are Packetized

High speed 56 kbps and 64 kbps

Networktopology (e.g. Redundant paths)Number portability, databases


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Cellular providers were dependent on

X.25 networkto carry IS-41 signaling

information.This did not allow them to interconnect

through PSTN.

Now they are deploying their own SS7

networks.


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Service Switching Point (SSP).

Service Control Point (SCP).

Signal TransferP

oint (STP

).


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SSPs are switches that originate,

terminate calls.

Send messages to other SSP

sMay also send query to SCP


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Interfaces to telephone company

databases.

SSP

may use information from thesedatabases to manage calls.


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It is a Packet Switch.

Networktraffic between signaling points

is routed.Acts as network hub


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The transport, session, and presentation

layers are not used in SS7

Instead transport, session andpresentation layers are grouped together

atthe application layer, which is known

as Level 4 in SS7.


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Message TransferPartLevel 1 (MTP-1)

corresponds to Physical Layer ofOSI

model.Physical , Electrical and functional

characteristics are defined.

examples

E1 (2.048 Mbps)

DS1 (1.544 Mbps)

See Q.701 Specs ofITU.


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SS7 message is called a signal unit (SU) Fill-In Signal Units (FISUs)

Link Status Signal Units (LSSUs)

Message Signal Units (MSUs)


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Transmitted continuously on a signaling link in bothdirections unless other signal units (MSUs orLSSUs)are present

Carry basic level 2 information only (e.g.,

acknowledgment of signal unitreceipt by a remotesignaling point). Because a CRC is calculated foreach FISU, signaling link quality is checkedcontinuously by both signaling points at either end ofthe link.

Inthe ITU-T Japanvariant, signaling link quality ischecked by the continuous transmission of flag octets(8-bit bytes)ratherthan FISUs; FISUs are sent only atpredefined timer intervals (e.g., once every 150milliseconds).


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LSSUs carry one ortwo octets (8-bit

bytes) of link status information between

signaling points at either end of a link.The link status is used to control link

alignment and to indicate the status of a

signaling point (e.g., local processor

outage)to the remote signaling point


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Carry all call control, database query andresponse, network management, andnetwork maintenance data inthe signaling

information field (SIF)Have a routing labelwhich allows an

originating signaling pointto sendinformationto a destination signaling point

across the network.Have Service InformationOctet (SIO)that

specified MTP user ofthis message


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Signaling message handling functions. Message discrimination, distribution and routing

to appropriate user part according to SIO.

provides message routing betweensignaling points inthe SS7 network

Signaling network managementfunctions. Reroutes traffic away from failed links and

signaling points and controls traffic whencongestion occurs.


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Defines necessary telephone signaling

functions Initial Address Message

Address complete Message

Answer Message

Clear back Message

Clear Forward Message etc. etc.


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To establish, maintain and release trunk

circuits that carry voice & data calls over

P

STN.Used for both ISDN and non-ISDN calls.


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TUP was specified before DSS1 (ISDN user signaling) during1980s

ISUP2 specs was released after DSS1 Changeover from TUPto ISUP is well under way

internationally. Innetwork core development path is

CAS -> TUP -> ISUP Changing TUPto ISUP is easy by a software upgrade in

exchanges. Limitations ofTUP

DSS1 terminal info cannot be transported inTUP

ISDN Suspend/Resume is not supported inTUP TUP does not support all supplementary services (call waiting, call

hold etc) in Euro-ISDN.

InTUP, release is non-symmetric.


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Provides connection-less network services. Provides connection-oriented network services

by using Sequence Control.

Transfer information between exchanges andspecialized centers

Makes use of MTP services. Networkto multiple network communication. This is essentially a data network combining

the features ofIP and X.25, offering bothconnection-oriented and connectionlessoperation


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Used extensively in cellularnetworks Base Station Subsystem Mobile ApplicationPart

(BSSMAP)

DirectTransfer ApplicationP

art (DTAP

)to transferradio-related messages in GSM

In conjunction with TCAP, also usedthroughoutthe GSM Network SwitchingSubsystem (NSS)to transport MAP signalingbetweenthe core GSM components toenable subscriber mobility and textmessaging


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SCCP connection-oriented control

(SCOC)

SCCP

connectionless control (SCL

C)SCCProuting control (SCRC)

SCCP management (SCMG)


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Class 0: Basic connectionless class

Class 1: In-sequence delivery

connectionless classClass 2: Basic connection-oriented class

Class 3: Flow control connection-oriented

class


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Temporary Signaling Connections connection establishment phase

data transfer phase

connectionrelease phase

Permanent Signaling Connections The setup/release service is controlled by the

administration (e.g. OMAP

)


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Routing Label one octet

Message Type code one octet

CR,CC,CREF,RLSD,RLC,DT1,DT2,AK,UDT,UDTS,

ED, EA,RSR,RSC,ERR,IT,XUDT,XUDTS,LUDT,LUDTS

mandatory fixed parameters (MF)

Pointers to mandatory variable parameters

Pointers to optional parts

Mandatory variable parameters (MV)

Optional parts (O)


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ParameterName code

End of optional Parameters 0

estination lo

al reference

Source local reference 2

Called party address 3

Calling party address 4

Protocol class 5

Segmenting/reassembling 6

Receive sequence number 7

Sequencing/segmenting 8

Credit 9

Release cause 0

Returncause

Resetcause

2Errorcause 3

Refusal cause 4

ata 5

Segmentation 16

Hop counter 17

Importance 18

Long data 19


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Routes messages received from the MTPtoappropriate local subsystem

Routes messages from local subsystems toother local subsystems

Routes messages from local subsystems tosubsystems inremote nodes by utilizingMTP's transport services. The destination

is specified inthe called party (CdPA)

address parameter, which is supplied by thesubsystem. The address can contain acombination of point code, system number,

and global title.


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Types ofnetworkrouting Point Code (PC)routing

x MTP layer can only use point code routing

x Using MTP point code routing, MSUs pass through the

STPs until they reach the SPthat has the correct DPC

Subsystem Number (SSN)routing

Global Title (GT)routing


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A subsystem is the name givento an

applicationthat uses SCCP

SSN is used to identify the SCCP user in

much the same way as the SIO identifies

the MTP3 user.

SSN examples

SCMG (1), ISUP (3), MAP(5), HLR(6), VLR(7)MSC(8), EIR(9), AC(10)


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Point code indicator indicates thatthe address contains a signaling point code

SSN indicator indicates thatthe address contains a SSN

Global title indicator (GTI) no global title included (0) includes nature of address indicator only (1) includes translationtype only (2) includes translationtype, numbering plan and encoding

scheme (3) includes translationtype, numbering plan, encodingscheme and nature of address indicator (4)

Routing Indicator Route on SSN or Route on GT.


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Signaling Point Code it, when provided, is represented by two octets

Subsystem Number (SSN) identifies an SCCP user and, when provided, consists

of one octet coded e.g. SCMG (1), ISUP (3), MAP(5),HLR(6), VLR(7)MSC(8), EIR(9), AC(10)

Global title (GT) variable length

Nature of Address indicator (NAI), Even/Oddindicator andGlobal title Address information


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Provides functions and protocols to largevariety of applications distributed overswitches and specialized centers (e.g.Databases)

TC refers to a set of communicationcapabilities that provide interface betweenapplications and network layer services

The original implementations ofTCAP were

created to support calling card and 800-number applications inNorth America bythe North AmericanT1 standards committeein around 1986


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designed to be generic to accommodate

the needs of a wide variety of different

services

Most services can be viewed as a

dialogue of questions and answers

Non-circuitrelated services


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Used to transport INAP inIntelligent

Networks

Used to transport MAP in mobile phone

networks.

Supports remote control ability to

invoke features in anotherremote

network switch.Calling card calls are validated using

TCAP query and response messages.


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MTP provides transfer across data link.SCCP provides transfer across signaling

points.TCAP core functionality is to enable the

feature inthe remote switch/SP/exchangeand querying Toll free number application.Intoll free number application ( 800)

TCAP uses SCCP because itneeds end to

end transport protocol forretrieving therouting number from the SCP which may belocated any where inthe large network


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Above transport layer ofOSI model

depends uponthe SCCP's transport

services

Transaction sublayer

Component sublayer


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Component the means by which TC conveys a requestto perform

an operation, or a replyx operation is an actionto be performed by the remote end

x reply carries an indication of success or failure in carryingoutthe operation

Components are passed individually between a TC-user and the Component sublayer

Components in a message are delivered to theremote TC-user inthe same order as they areprovided atthe originating interface

Provides dialogue facility


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Successive components exchangedbetweentwo TC-users in ordertoperform an application

Unstructured dialogueTC-users can send components that do not expect

replies without forming an explicit association

betweenthemselves

Structured dialogueAlternatively,TC-users indicate the beginning, ortheformation of a dialogue, the continuation, and the end

of a dialogue


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provides the capability forthe exchange

of components

provides the capability to send

transaction messages between peerTR-

layer entities by means ofthe services

provided by SCCP


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the neural system interconnecting thedistributed computer infrastructure of GSM(VLRs, MSCs, HLRs and other entities).

Can be interfaced via procedure callsAProtocol first presented in 1988Features

Roaming

Call handling Non-interruptive handover

Remote switching management

Management of security functions


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MAP protocol stack TCAP

SCCP

MTP

Maximum outage allowed 15 min/yr

Tighttime budget 100 ms


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When a mobile subscriberroams into a

new mobile switching center (MSC) area,

the integrated VLR requests service

profile information from the subscriber's

HLR using mobile application part (MAP)

information carried withinTCAP

messages.


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IN Architecture to quickly create and deploy customer

SERVICES Supports many services

Is a standard - multi-vendor Distributed platform Example services supported by IN

Freephone Premium Rate Voice mail Call Diversion Call baring Local NumberPortability


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Nortel HLR features network connectivity is implemented using IP

based signaling with full support for Sigtran

17 million GSM subscribers or up to 10 millionUMTS subscribers in a single rack of equipment


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ss7 by masoodalam

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