Telecom SS7 basic

TELECOM BASICS

CCS Associated

CCS Quasi associated

CCS Non associated.

CCS STRUCTURE

E1 a) 256 bytes per frameb) 8 bits Each TS in E1 Framec) 0.125uS time taken by one framed) Total 8000 frames in One Second

Voice Theorma) Voice Frequency ~ 300 to 3300 Hz , bandwidth = 4000 Hzb) Nyquist theorm = Min 8000 sampling rate reqd ( 4000*2 )c) One Sample = 8 bits ( Reprsntation of 256 Voice Levels , 2 pow 8 = 256)d) 8000 samples in One Sec = 8 bits * 8000 = 64000 bits per sec required

Erlanga) Unit of Traffic descibes total traffic volume in one hour b) Erlang = Busy time for ckts / Avl Time for measurment , Ex : 20/60 = 3Er15ckt - 8.1 Er 31ckt - 21.5 Er 3 E1 - 77 Er 10 E1 - 286 Er 20 - 59230ckt - 20.3 Er 02 E1 - 48 Er 5 E1 - 136 15 E1 - 439 Er 30 - 901

E1 Physical Interfacea) 0th TS used for synchronization ( 0011011)b) Modes of Operation 1. Unframed - No TS at all 2. Framed - All 32 TS used for data 3.Multiframe - 0 TS for sync, rest 31 for datac) Bit '1' - 3V , Bit '0' - 0~0.3 V

CAS ( Channel Associated Signalling )a) Uses INBAND Signalling ( Voice frequencies )b) Signaliing Associated in that E1 only - TS = 16 Line Sig. And TS=All Registered Signalling

CAS Line Signallinga) Uses TS = 16 for indication of ckt. Status only ( I.e. FREE , SIEZ , FREE BY A/B , BUSY etc….)

ABCD Fwd ABCD Bckwd STATUS10XX 10XX IDLE00XX 10XX SIEZ00XX 11XX SIEZ ACK00XX 01XX ANS00XX 11XX B PARTY REL10XX 0/10XX A PARTY REL

Ist Frame : TS-1 & TS-17 (4+4 bits)IInd Frame : TS-2 & TS-18........15th Frame : TS-15 & TS-31

CAS Registered Signallinga) Uses voice TS for Registered Signalling .b) Types : DECADIC , DTMF , R2 Semi C , R2Fully Cc) R2MF - R2 Multi Freq Fully Compled (Ack Reqd)d) MF - Combination of 2 Freq to represent one info

CAS Registered Signalling Grp A Bwd Sig. Grp B Bwd Sig.1 Send Next Dig. 2 Changed No.2 Restart 3 Called Line Busy3 Change over grp B 4 Congestion4 CLI 5 Unallocated No.5 Send Cat of A Party 6 Normal subs free6 Switch to speech7 Send last but 2 digits8 Send last but 3 digits9 Send last but 1 digit

Grp 1 Fwd Sig. Grp II Fwd Sig.1 Digit '1' 1 Ordinary Subs2 Digit '2' 2 Priority Subs3 Digit '3' 5 Operator4 Digit '4' 6 STD Coin Box

CCS 7 Layers8 7 1 7 1 6 2 8

Layer#2 FLAG BSN BIB FSN FIB LI SPARE DATA CRC

Layer#3 SIF SIO

SubService Field Service Indicator

DPC OPC USER PART

ISUP Message Type Mandatory FIX Mandatory Variable Optional FIX Optional Variable

IAM A Party Category , Forward Call Indicator B Party No , User service Info CLI , Carrier , NW , HOPs

Network Indicator NAT0/1, INAT0/1

Priority - 1,2,3 ( Low to High )

SLS ( 4 Bits , Max

16 Selection )Signalling

Link Selection

CIC (only ISUP)

0 FISU1-2 LSSU3-63 MSU

Layer-2 : CRC , Retransmission ( PCR ) , Error Correction and detection Etc

Layer-3 : b. Signalling Route Management - Traffic / Sharing / Overloading Routingc. Signalling Link Management - Control / Monitor / Status of Linkse Signalling Traffic Management - Change over/ Back in case of Faile. Alignment - SIO , SIN , SIE , SIOSf. Message Distribution - Distributing the MSG to ISUP , SCCPg. Message Discrimination - Mine or Other DPC / NWh. Message Routing - Linkset / DPC findout from Routing Table

Service Indicator0 - SNM ( Signalling NW Management Message )1 - MTN ( Mtc Regular Msg )2 - MTNs ( Mtc Special Message )3 - SCCP ( Carry Non-Voice Traffic Ex: SMS )4 - TUP5 - ISUP ( Voice related traffic )6 - Data User Part ( Call & ckt Related )7 - Data User part ( Facility Regn & Cancellation )

ISUP Message Type :IAM ( Initial Address Message )INR ( Information Request )ACM ( Address Complete )ANM ( Answer Message )REL ( Release Message )RLC ( Release Complete )BLO ( Blocking )UBL ( Uublocking )BLA ( Blocking Acknowledment )CPG ( Call Progress )

Layer-3 TimersT1 Delay to avoid message mis-sequencing on changeover .5 to 1.2 sec.T2 Wait for changeover Ack .7 to 2. 0 secT3 Delay to avoid message mis-sequencing on changeback .5 to 1.2 sec.T4 Wait for changeback Ack (1st attempt) 5 to 1.2 sec.T5 Wait for changeback Ack (2nd attempt) 5 to 1.2 sec.

SCCP Message Type Mandatory FIX Mandatory Variable Optional FIX Optional Variable Used for

UDT

XUDT

UDTs 1. Segmentation data

XUDTs 1. Segmentation data

1. Called Party2. Calling Party3. User Data

Used to transport user data and SCCP management messages in the

connection-less mode. It can Segment / DeSegment data as per

its size1. Called Party2. Calling Party3. User Data

1. Return Cause2. Hop Counter

1. Called Party2. Calling Party3. User Data

Used to indicate to the originating SCCP user that a UDT message

cannot be delivered to the specified destination. The data field of the UDT

message and the reason for the return are included in the UDTS

message.

1. Return Cause2. Hop Counter

1. Called Party2. Calling Party3. User Data

Protocol Class :Class -0 : Basic Connectionless ( Non Critical, TCAP )Class -1 : Sequenced Connectionless (Critical , TCAP )Class -2 : Basic Connection Oriented ( BSSAP )Class -3 : Flow Control Connection Oriented (BSSAP )Class -4 : Flow Control + Err Recovery Connection Ori.

Calling / Called party :1. Address Indicator : a. Routing Indicator : GT based or ( DPC + SSN ) b. GTT Indicator : No GT or GT - 1 or 2 or 3 or 4 c. SSN Indicator : Present / Not Present d. Point Code Indicator : Present / Not Present

2. Address : a. Point Code b. SSN

c. GT - 1 : i. Nature of Address Ind : Subscriber Number / National Sig. No. / International No. ii. Odd / Even Indicator ( Spr) iii. Address Information ( 919839212499 ) d. GT - 2 : i. Translation Type ii. Address Information ( 919839212499 ) e. GT - 3 : i. Translation Type ii. Encoing Scheme - Unknown / BCD Odd / BCD Even iv. Address Information iii Numbering Plan - ISDN / Telephony / Data / Telex / Land Mobile / Mobile e. GT - 4 : i. Translation Type ii. Encoing Scheme - Unknown / BCD Odd / BCD Even iii. Numbering Plan iv. Nature of Address Indicator v. Address Information ( Contains Address for Example : 919839212499 )

User Data :1. Length Indicator2. User Data Ex: TCAP etc

Connection Oriented- Only used in BSSAP where heavy data transfer is required for ex. Between MSC/VLR to BSC to BTS

SCCP - Routing Protocol

Hop Counter ( 15 to 1 ) : Counter is decremented upon GTTSegmentation : Max 16 Segments , each carries 246 bytes

GTT CASES1. SPC + SSN2. SPC + SSN + GT3. SSN + GT4. SPC + GT5. GT only

GT is performed on given SPC + SSN on the basis of GT info , to find out the final A/B Party Address

SSN1 SCCP Management 3 ISDN user part 4 OMAP (Operation, Maintenance and Administration Part) 5 MAP (Mobile Application Part) 6 HLR (Home Location Register) 7 VLR (Visitor Location Register) 8 MSC (Mobile Switching center) 9 EIR (Equipment Identifier register) 10 AUC (Authentication Centre) 11 ISDN Supplementary Services (SSAP) 13 Broadband ISDN edge-to-edge applications 254 Base Station System Application Part (BSSAP)

SCMG Functions- Signaling point status management : Failure, recovery, and congestion information of signaling points, provided by MTP

- Subsystem status management : Subsystem failure and recovery information, and SCCP (SSN 1) congestion received in SCCP management messages.

- Subsystem status test : SSP , SSA , SST , SOR , SOG

GTT> Method of hiding the SS7 point code and sub-system number from the originator of a message

a) GT Consists of – Translation type (TT) – Numbering plan (NP) – Nature of address (NA) – Global title digits (GTDIG)

b) GT Benefits– Central administration of routing information makes it easier to restructure the network– It is possible to set up alternative routing schemes and load sharing– More compact and dyanmic routing tables– The function is required for the introduction of certain new services (such as call completion to busy subscriber, CCBS and 800 free phone)

a) The result of a global title translation can be:– the point code for a signaling destination– a subsystem service group ( this is used in the intelligent network to guarantee a fail-safe service control point (SCP). Two SCPs can be combined to form a subsystem service group that is accessed from the relevant service switching point (SSP) via global title translation. )– a translator service group ( this consists of up to four signaling points, each of which can perform the necessary translation )– a further translation in the same network node

TRANSACTION DIALOG TAG COMPONENT TAG

Message type FunctionInvoke Initiates/invokes a desired operation at the remote peer application entity.Return result not last Used to carry a segment of the result of a successfully completed operation. It is used when a success reply is physically too large to fit into a single message.Return result last Represents the final success reply to an operation invocation. If the success reply was segmented, this component would represent the final segment of the replyReturn error Indicates an operation invoked previously has failed due to some processing error. Error codes are supplied by TCAP users, and are passed transparently by TCAP.Reject Indicates that one of the Invoke, Return Result, or Return Error components received from the remote user/CSL could not be understood or was not expected.Unidirectional Used to transport data in an unstructured dialogueBegin First message, to start a structured dialogue, sent onceContinue Used to sustain the structured dialogue, more continue messages can be sentEnd Used to terminate the structured dialogue in a normal wayAbort Used to terminate the structured dialogue in an off normal way.

TCAP :1. Transaction Part : ( Deals with SCCP Message ) a. TCAP Message Type : BEGIN / UNI / END / CONTINUE / ABORT b. Length Indicatior of Transaction Tag ( Max 2048 , SCCP takes Care of Segmenting / Breaking ) c. Transaction Info ( Not Valid for UNI ) i. Origination Transaction Id ( Mandatory for BEGIN , CONTINUE ) - Length Indicator & Value i. Destination Transaction Id ( Mandatory for END , ABORT , CONTINUE ) - Length Indicator & Value i. P_Abort Cause ( Mandatory for TC_P_Abort Request ) - Reason for Abort

2. Dialog Part : a. Dialog Indicator Tag b. Length Indicatior of Dialog Tag c. Dialog Information - Depend on USER For Ex : MAP , INAP

3. Message Component Part : ( Deals with USERs such as MAP , INAP ...) a. Component Indicator Tag b. Length Indicatior of Component Tag c.Component Type : ( Invoke / Return Result Last / Return Result Not Last / Return Error / Reject ) d. Component length e. Component User Information by MAP , INAP , CAMEL , OMAP , SSAP Etc..........

Functions of TCAP are to control:· The transaction between both endpoints in the network · The communication to the users of TCAP.

SMSC1. SMS are stored in SMSC before they can be sent to MS ( 140 bytes each SMS )2. MAP USED is > Forward Short Message Submit > Send Routing Info for SM > Forward Short Message Deliver

3. MO Forward SM : A party MS to SMSC ( Forward Short Message Submit )4. MT Forward SM : SMSC to B Party MS ( Forward Short Message Deliver )

HLR

GMSC

MSC/VLR

TCAP Begin/Invoke - SRI for SMTCAP End / Retrun Res - SRI Ack MSISDN

SM_DELIVER BTS

TCAP Begin/Invoke - Forward SMTCAP End / Retrun Res - Forward SM Ack

SCP

SCP

STP

STP

STP

STP

SSP (Service Switching Pt )

A-Acces

s

A-Access

A-Acce

ss

E-Extended

C-Cross D-Diagonal

B-Bridge Other STP NWService Control Pt C-Cross

VLR VLR

BTS

GMSCHLR

AUC-SIM

MSC

SMSC EIR

EC

G

B

HF

D D

A

HLR

GMSC

MSC/VLR

TCAP Begin/Invoke - Provide MSRNTCAP End / Retrun Res - MSRN AckTCAP Begin/Invoke - SRI

TCAP End / Retrun Res - SRI Ack MSISDN

IAM - MSISDN

IAM - MSISDN

BTS

IMSI

IMEI

Mobile Terminating Call ( MTC )

GSM Overview

C7 Network

GPRS ( General Packet Radio Services )a) Key Features Speed immediacy New applications Better applications Service access

b) Key Network Features of GPRS Packet switching Spectrum efficiency Internet aware Supports tdma and gsm

c) Limitations of GPRS Limited cell capacity for all users Speeds much lower in reality Support of gprs mobile terminate by terminals is not ensured Suboptimal modulation Transit delays No store and forward

d) SGSN - Serving GPRS Support Node handles session management, mobility management, billing and traffic measurements bit level encryption of data which is to be sent over the air interface. Put GPRS data received from the BSC in IP format for sending to the GGSN and vice-versa. Provide GPRS routing to BSC’s

d) GGSN - GPRS Gateway Support Node The GGSN is the gateway in and out of the GPRS system. It routes packets from an external network ( "the Internet" ) to the SGSN which is currently serving the MS, and routes packets from the SGSNs to which it is connected to the external network. This concept is called tunnelling.

d) Similar Techniques Enhanced Data rates for GSM Evolution (EDGE) Universal Mobile Telephone System (UMTS)

FLAG

DPC

UDT MESSAGE TRANSACTION ID , BEGINBSNBIB DIALOG IDFIBFSN

OPCUSER DATA

COMPONENT TYPE = INVOKELISIOSIF

SPARE USER DATACRC SLS

MTP - 2 LAYER 3 SCCP TCAP

PROTOCOL CLASS = 0 / 1B PARTY - GT(N) /

SSN / SUB NOA PARTY - GT(N) / SSN / SUB NO

COMPONENT USER DATA , MT Forward SM , MSIN DIGIT

GSM OverviewIMSI : International Mobile Subs Identity [ SIM , MCC(3) + MNC(2) + MSISDN (<10) ]TMSI : Temporary Mobile Subs Identity [ VLR , MCC(3) + MNC(2) + MSISDN (<10) ]MSISDN : Mobile Stn Integrated Services Digital NW [ CC(1-3) + NDC(1-3) + MDN(10) ]MSRN : Mobile Subs Roaming Number [ VLR , CC(1-3) + NDC(1-3) + MDN(10) ]IMEI : International Mobile Eqpt. Identity [ By Nokia ]LAI : Location Area Identifier [ MCC(3) + MNC(2) + LAC(<10) ]

VLR VLR

BTS

GMSCHLR

AUC-SIM

MSC

SMSC

EIR

EC

G

B

H

F

D D

A

IMSI

IMEIGSM Overview

IMSI Vs TMSIOne can't take hacking benefits with TMSI as it is dyanmically allocated by VLR , moreover TMSI is 4 octet shorter than IMSI .

MAP D ( HLR-VLR )Provide MSRN / MSRN AckUpdate Location / Cancel Location / AckInsert / Delete Subs Data / AckSend Param / AckResetDeregister Mobile DataNote MS Present

MAP C ( HLR-MSC )Send Routing info SRI / AckSend Routing info for SM / AckSet Message waiting dataAlert Service CentreRegisster charging info

MAP E ( GMSC - MSC )Process access sigmnalling CCS 7Forward access Signalling CCS 7Send End Signal CCS 7Perform Handovers / Subsequent HOPerform Internal HandoversTrace subs activity

MAP I ( Subservices - MSC )Get Pwd / Register PwdActivate / Deactivate / Erase / Register SSInterrogate / Invoke SSForward SS Notification

MAP F ( EIR - MSC )Check IMEI

MAP H ( SMSC - MSC )Forward Short Message

MAP G ( VLR - VLR )Send Param

Intelligent Network ( IN )Requirement / Advantages Rapid deployment of Vendor / SSP Free Services which are centrally administered

SSP CCF - Call Control Functions ( Takes Care of all call related processing in Switch ) SSF - Service Switching functions ( Provides IN Triggering and IN Accessibility ) SRF - Specialized resource function ( Provides interactioon bw Call processing SW in SSP)

SCP SCF - Service Control Functions ( Executes IN service logic and interfaces witrh SSP via SSF ) SDF - Service data function ( Maintains all customer and nw data ) SMP - Service Management Point ( Administration and Operation of IN ) SIB - Service Independ Service Blocks ( Generic purpose reusable software codes in IN ) BCP - Basic Call Process SCEP - Service Environment creation function ( Allows sevices in IN to be defined , tested ... )

Erlanga) Unit of Traffic descibes total traffic volume in one hour b) Erlang = Busy time for ckts / Avl Time for measurment , Ex : 20/60 = 3Er15ckt - 8.1 Er 31ckt - 21.5 Er 3 E1 - 77 Er 10 E1 - 286 Er 20 - 59230ckt - 20.3 Er 02 E1 - 48 Er 5 E1 - 136 15 E1 - 439 Er 30 - 901

CAS Line Signallinga) Uses TS = 16 for indication of ckt. Status only ( I.e. FREE , SIEZ , FREE BY A/B , BUSY etc….)

ABCD Fwd ABCD Bckwd STATUS10XX 10XX IDLE00XX 10XX SIEZ00XX 11XX SIEZ ACK00XX 01XX ANS00XX 11XX B PARTY REL10XX 0/10XX A PARTY REL

Ist Frame : TS-1 & TS-17 (4+4 bits)IInd Frame : TS-2 & TS-18........15th Frame : TS-15 & TS-31

GTT> Method of hiding the SS7 point code and sub-system number from the originator of a message

a) GT Consists of – Translation type (TT) – Numbering plan (NP) – Nature of address (NA) – Global title digits (GTDIG)

b) GT Benefits– Central administration of routing information makes it easier to restructure the network– It is possible to set up alternative routing schemes and load sharing– More compact and dyanmic routing tables– The function is required for the introduction of certain new services (such as call completion to busy subscriber, CCBS and 800 free phone)

a) The result of a global title translation can be:– the point code for a signaling destination– a subsystem service group ( this is used in the intelligent network to guarantee a fail-safe service control point (SCP). Two SCPs can be combined to form a subsystem service group that is accessed from the relevant service switching point (SSP) via global title translation. )– a translator service group ( this consists of up to four signaling points, each of which can perform the necessary translation )– a further translation in the same network node

FunctionInitiates/invokes a desired operation at the remote peer application entity.Used to carry a segment of the result of a successfully completed operation. It is used when a success reply is physically too large to fit into a single message.Represents the final success reply to an operation invocation. If the success reply was segmented, this component would represent the final segment of the replyIndicates an operation invoked previously has failed due to some processing error. Error codes are supplied by TCAP users, and are passed transparently by TCAP.Indicates that one of the Invoke, Return Result, or Return Error components received from the remote user/CSL could not be understood or was not expected.Used to transport data in an unstructured dialogueFirst message, to start a structured dialogue, sent onceUsed to sustain the structured dialogue, more continue messages can be sentUsed to terminate the structured dialogue in a normal wayUsed to terminate the structured dialogue in an off normal way.

Functions of TCAP are to control:· The transaction between both endpoints in the network · The communication to the users of TCAP.

SMSC1. SMS are stored in SMSC before they can be sent to MS ( 140 bytes each SMS )2. MAP USED is > Forward Short Message Submit > Send Routing Info for SM > Forward Short Message Deliver

3. MO Forward SM : A party MS to SMSC ( Forward Short Message Submit )4. MT Forward SM : SMSC to B Party MS ( Forward Short Message Deliver )

GPRS ( General Packet Radio Services )a) Key Features Speed immediacy New applications Better applications Service access

b) Key Network Features of GPRS Packet switching Spectrum efficiency Internet aware Supports tdma and gsm

c) Limitations of GPRS Limited cell capacity for all users Speeds much lower in reality Support of gprs mobile terminate by terminals is not ensured Suboptimal modulation Transit delays No store and forward

d) SGSN - Serving GPRS Support Node handles session management, mobility management, billing and traffic measurements bit level encryption of data which is to be sent over the air interface. Put GPRS data received from the BSC in IP format for sending to the GGSN and vice-versa. Provide GPRS routing to BSC’s

d) GGSN - GPRS Gateway Support Node The GGSN is the gateway in and out of the GPRS system. It routes packets from an external network ( "the Internet" ) to the SGSN which is currently serving the MS, and routes packets from the SGSNs to which it is connected to the external network. This concept is called tunnelling.

d) Similar Techniques Enhanced Data rates for GSM Evolution (EDGE) Universal Mobile Telephone System (UMTS)

GMSC

MAP I ( Subservices - MSC )Get Pwd / Register PwdActivate / Deactivate / Erase / Register SSInterrogate / Invoke SSForward SS Notification

SMS

FLAG

DPC

UDT MESSAGEBSN PROTOCOL CLASS = 0 / 1BIB B PARTY - GT(N) / SSN / SUB NO DIALOG IDFIB A PARTY - GT(N) / SSN / SUB NOFSN

OPC

USER DATA

LISIOSIF

SPARE

CRC SLS

MTP - 2 LAYER 3 SCCP TCAP

TRANSACTION ID , BEGIN

COMPONENT TYPE = INVOKE

COMPONENT USER DATA , MT Forward SM ,

MSIN DIGIT

USER DATA

Some Useful Definitions:-

Protocls must provide reliable, error free transmission of user data as well as network managament functions.

In the case of Dbase, the Dbase is considered as an application entity and the protocol used to acccess and interfaceto this application is TCAP.

MTP-2 Functionalities…1) S.U. Delimination.. Flag…01111110… Correct start and end of SU… If not bit insertion is used.

ie No " 1s density " violation should be there. If its there then Bit stuffig is used.2)S.U. Alignment SU should be received in sequence

Conditions for error free transmissionSU must be a multiple of 8SIF of MSU should not exceed 272 octet capacity

Counter used to check the max number of errors on a 64Kbps SDLEach link keeps its unique couterWhen the number of errors increase the threshold limit then the link is taken out of service.Error due to clock signals being not synchronised prperly at Tx and Rx

L-3 ( Realigns the Link, by taking the link out of service)

L-2 (Reports any error to L-3 link Mgmnt)This phenomena is called the"Alignment Procedure" phenomena

PROTOCOL:- It is a set of rules governing the way, the data will be Tx and Rx over the data communication network.

PRIMITIVE:- A primitive is an interface which provides access from one level of protocol to another level of protocol.

CIC:- It is of 16 bits of which 4 bits are spare

SUERM: Signalling unit error rate monitor

Protocls must provide reliable, error free transmission of user data as well as network managament functions.

In the case of Dbase, the Dbase is considered as an application entity and the protocol used to acccess and interface

Conditions for error free transmission

When the number of errors increase the threshold limit then the link is taken out of service.

It is a set of rules governing the way, the data will be Tx and Rx over the data communication network.

A primitive is an interface which provides access from one level of protocol to another level of protocol.