signaling hcna uc

Signaling Technologies

What is Signalling ?

In telecommunication, signaling (signalling in British English) has the following meanings:

the use of signals for controlling communicationsthe information exchange concerning the establishment and control of a telecommunication circuit and the management of the network, in contrast to user information transferthe sending of a signal from the transmitting end of a telecommunication circuit to inform a user at the receiving end that a message is to be sent.

What is Signalling ?• Signaling systems may be classified based on

several principal characteristics:

In-band and out-of-band signaling Line versus register signaling Channel-associated versus common-channel signaling Compelled signaling Subscriber versus trunk signaling Many be some more…….

In-band and out-of-band signaling• In-band signaling is the exchange of call control

information within the same channel that the telephone call itself is using. – Example: dual-tone multi-frequency signaling (DTMF), which is

used on most telephone lines to customer premises.

• Out-of-band signaling is telecommunication signaling on a dedicated channel separate from that used for the telephone call. – Example: Signaling System No. 6 (SS6) was introduced in the

1970s, and also in Signalling System No. 7 (SS7) in 1980.

Signaling Techniques

• In-channel signaling

•SF Signaling (2600 Hz)•MF Signaling•DTMF Signaling

In-band•DC Current (on-/off-hook•Dial pulses (10 pps)•20 Hz Ringing voltage

Out-of-band

Line Vs register signaling• Line signaling is concerned with conveying

information on the state of the line or channel, such as on-hook, off-hook (answer supervision and disconnect supervision, together referred to as supervision), ringing current (alerting), and recall.

Line Vs register signaling• Register signaling is concerned with conveying addressing

information, such as the calling and/or called telephone number.

Channel-associated (CAS) versus common-channel signaling (CCS)

• CAS – Employs a signaling channel which is dedicated to a specific

bearer channel.

• CCS – Employs a signaling channel which conveys signaling

information relating to multiple bearer channels. These bearer channels therefore have their signaling channel in common.

Signaling Techniques

• Common Channel Signaling (CCS)SignalingNetwork

Dedicated data link between systems• Trunk group associated• Trunk group disassociated

Advantages of CCS

• Value-added services of a signaling control point– Shared processing for small offices– Allows centralized decision making (flow

mgmt)– Permits Advanced Intelligent Network (AIN)

services

Disadvantages of CCS

• CCS links can be a single point of failure• No inherent testing of speech path by call

setup signaling• CCS response time is critical

Compelled signaling• Compelled signaling refers to signaling where receipt of

each signal from an originating register needs to be explicitly acknowledged before the next signal is able to be sent.– Most forms of R2 register signaling are compelled), while R1

multi-frequency signaling is not.

Summary of Signalling• Every signaling system can be characterized along each of

the above axes of classification. A few examples:1. DTMF is an in-band, channel-associated register signaling

system. It is not compelled.2. SS7 (e.g., TUP or ISUP) is an out-of-band, common-channel

signaling system that incorporates both line and register signaling.

3. E and M signaling (E&M) is an out-of-band channel-associated signaling system. E&M line signaling is however usually paired with DTMF register signaling.

4. Loop start, ground start, reverse battery etc. are all DC, thus out of band, and all are channel-associated, since the DC currents are on the talking wires

Subscriber versus trunk signaling• The PSTN Signaling methods are generally broken

into following groups

User-to-Network Signaling

Network-to-Network Signaling

User-to-Network Signaling(Famous Types)


Analog CommunicationAnalog Local Loop

Digital CommunicationDigital Local Loop

DTMF ISDN ADSL

Other examples of User to Network Signaling ?

DTMF Signaling• DTMF stands for Dual-Tone Multi-Frequency• In DTMF a combination of two tones is transmitted for each

number

Frequencies (Hz) 1209 1336 1477 1633

697 1 2 3 A

770 4 5 6 B

852 7 8 9 C

941 * 0 # D

Why Two frequencies……????

Other Tones & Events on the Subscriber Line

• In addition to the tones to represent dialed digits, the ITU-T defines other tones and events that can appear on a subscriber line – Off-Hook– On-Hook– Busy Tone– Ringing Tone– Call Waiting Tone– Congestion Tone– Many more

Other Tones & Events on the Subscriber Line

On-hook Voltage 48 V dc

Off-hook voltage5-10 V dc,

depending on loop resistance

Dial Tone 350 & 440 Hz

Ringing Voltage (at phone)Approximately 8o v ac,

superimposed on 48 V dc

Ringback Voltage440 and 480 Hz

pulsed 2s on,4s off

Many more …



… … C7 (SS7)

Other Examples of Network to Network Signaling ?

Channel-associated signalling (CAS)

CAS means in-band signalling over voice channels.

2) Signalling to/from databases is not possible (setting up a circuit switched connection to the database would be extremely inconvenient).

Exchange Exchange

circuit switched connection

signalling possible signalling not possible (yet)

CAS has two serious draw-backs:1) Setting up a circuit switched connection is very slow.

Database

E-1 Structure

Common channel signalling (CCS)

The packet-switched signalling network is separated from circuit switched connections. Consequently:

In practice, CCS = SS7 (except maybe North America). In Finnish: CCS = yhteiskanavamerkinanto (YKM)

Exchange Exchange

signalling possible anywhere anytime

Database

1) Signalling to/from databases is possible anytime.2) End-to-end signalling is possible before call setup and also during the conversation phase of a call.

C7 (SS7)

C7 (SS7)

The full name is

Common Channel Signaling System # 7 (CCS7)

Switch A Switch B

Switch C Switch D

Signal Transfer Point

C7 (SS7)

Uses of C7 (SS7)

Basic Call Setup & Tear down

Database Access

Wireless Roaming Applications

Intelligent Network (IN) Services

Local Number Portability

Few more

C7 (SS7)

SS7 Network Architecture

SS7 Protocol Suite and Messages

SS7 Examples and Call Flows


Signaling Elements Signaling Links



SS7 Signaling Elements

Service Switching Point (SSP) Signal Transfer Point (STP) Service Control Point (SCP)


SS7 Signaling Links

A links B links C links D links E links F links

SS7 Signaling Elements

SS7 Signaling Elements• An SS7 point code is similar to an IP address in an

IP network. It is a unique address for a node (Signaling Point, or SP), used in MTP layer 3 (will be discussed later ) to identify the destination of a message signal unit (MSU).

• OPC (Originating Point Code) and a DPC (Destination Point Code); sometimes documents also refer to it as a signaling point code.

SS7 Signaling Elements• Depending on the network, a point code can be

– 24 bits (North America, China)– 16 bits (Japan), or 14 bits (ITU standard, International

SS7 network and most countries) in length.

SS7 Signaling Elements• ANSI point codes use 24 bits, mostly in 8-8-8

format.• ITU point codes use 14 bits and are written in 3-8-

3 format.• Fourteen bit point codes can be written in a

number of formats. – The most common formats are :

• decimal number• hexadecimal number• or 3-8-3 format (3 most significant bits, 8 middle bits, 3 least

significant bits).

SS7 Signaling Elements• Signalling Bits will be discussed in the

last…………………….

Service Switching Point (SSP)

Signal Transfer Point (STP)

Signal Transfer Point (STP)

• STPs are configured in pairs and are mated to provide redundancy and higher availability

• These mated STPs perform identical function and are considered the home STPs for directly connected SSP or SCP

STP Hierarchy

• STP implementation can occur in multiple levels, such : Local STP Regional STP National STP International STP Gateway STP

STP Hierarchy

• The local, regional, and national STPs transfer SS7 messages within the same network using the same national standard of SS7 protocol

• International STP provide international connectivity where the same International ITU-T standard SS7 are deployed in both networks

Gateway STP• Gateways STPs can provide the following functions:

Protocol conversion from a national standard ( such as ANSI , ETSI ) to international standard ( ITU-T), or some other standard.

Network-to Network Interconnection Network security features such as screening

Screening is the capability to examine all incoming and outgoing packets and allow only those which are authorized

Service Control Point (SCP)

IN Services• Televoting• Call screening• Telephone number portability• Toll free calls/Freephone• Prepaid calling• Account card calling• Virtual private networks (such as family group

calling)• Mass-calling service• Many many more………..

What are other IN Services ??

Service Control Point (SCP)• SCP provides the interface to the databases where

additional information is stored • The interface between the SCP and database system

is accomplished by a standard protocol, which is usually X.25

• The database stores information related to its application and is addressed by a subsystem number, which is unique for each database

Service Control Point (SCP)

800 Database

900 Database

Local Number Portability Database

Home Location Register (HLR)

Visitor Location Register (VLR)

SCP

STP

STP

STP

STP

SSP SSP

Signaling Links

Signaling Data Links TypesSignaling Data Links Types

SS7 Signaling Links

A links B links C links D links E links F links

Signaling Data Links Types

75

SS7 Architecture

STP pair STP pair

SCP

STP pair

A-link

B-linkC-link

D-link

E-link

F-linkSSP SSP

A-linkA-link

Trunk

NETWORK 1NETWORK 2

Voice/Data Trunk

SS7 Signaling Link

– Service Switching Point (SSP) is a telephony switch that performs call processing.

– Service Control Point (SCP) contains databases for providing enhanced services.

– Signal Transfer Point (STP) is a switch that relays SS7 messages between SSPs and SCPs.

Signaling Data Links Types

Access Links ( A )

• Mostly SSPs or SCPs has at least two A-links that connect to the “home” STP pair

• It is possible to have only one A-link to an STP; however, this is not common practice

• The STP routes the A-link signaling messages received from the originating SSP or SCP toward the destination

Access Links ( A )

Bridge Links ( B )

Cross Links ( C )

Cross Links ( C )

• The STP pairs perform identical functions and are mated to provide redundancy in the network

• C-links are used only when failure or congestion occurs

Diagonal Links ( D )

Extended Links ( E )

Fully Associated Links ( F )

Fully Associated Links ( F )

• These links are used when STPs are not available or when high traffic volumes exist between the SSPs

SS7 Protocol Overview

SS7 Protocol Stack Vs. OSI Model

INAP :Intelligent Network Application Protocol / Intelligent Network Application PartMAP: Mobile Application Part

Application protocols

Protocol layers (”levels”) of SS7

MTP - Message Transfer PartSCCP - Signalling Connection Control Part

UP - User Part AP - Application Part

CAP INAPMAP ISUP TCAP

SCCP

TUP

MTP level 3 MTP level 2 (link-layer protocol)

MTP level 1 (64 kbit/s PCM time slot)

routing

Application protocols in SS7

TUP (Telephone User Part) – is being replaced by ISUP ISUP (ISDN User Part) – for all signalling related to setting up, maintaining, and releasing circuit switched connections MAP (Mobile User Part) – for transactions between exchanges (MSC, GMSC) and databases (HLR, EIR, AuC) in mobile networks INAP (Intelligent Network Application Part) for IN applications in fixed networks CAP (CAMEL (Customized Applications for Mobile networks Enhanced Logic ) Application Part) for extended IN functionality in mobile networks (where MAP is not sufficient ...)

• GSM network signaling, based on the GSM architecture.• Fig. 10.1 shows various network signaling protocols used by the

entity interface in GSM.• The GSM architecture can be partitioned into three part.• Databases• Switches• Radio Systems

GSM NETWORK LAYOUT

• Mobile Application Part (MAP) is an SS7 protocol that provides an application layer for the various nodes in GSM and UMTS mobile core networks and GPRS core networks to communicate with each other in order to provide services to mobile phone users.

• MAP is used to access • Home Location Register• Visitor Location Register• Mobile Switching Center• Equipment Identity Register• Authentication Centre• Short message service center • and Serving GPRS Support Node (SGSN).

GSM NETWORK LAYOUT

94

GSM Protocol layers(GSM has MAP just like IS41)

• MAP makes use of the Transactions Capabilities Part (TCAP) transport protocol.

• MAP functions: – Updating of residence information in VLR– Storage of routing information in HLR– Updating and supplementing of user profiles in HLR– Handoff of connections between MSCs

ISUP• ISDN (Integrated Services Digital Network) User Part

• Used to set up telephone calls in the public switched telephone network (PSTN)

• When a telephone call is set up from one subscriber to another, several telephone exchanges could be involved, possibly across international boundaries. To allow a call to be set up correctly, where ISUP is supported, a switch will signal call-related information like called party number to the next switch in the network using ISUP messages.

ISUP• The telephone exchanges may be connected via E1 or T1

trunks which transport the speech from the calls. • These trunks are divided into 64 kbit/s timeslots, and one

timeslot can carry exactly one call.• Regardless of what facilities are used to interconnect

switches, each circuit between two switches is uniquely identified by a circuit identification code (CIC) that is included in the ISUP messages.

• The exchange uses this information along with the received signaling information (especially the called party number) to determine which inbound and outbound circuits should be connected together to provide an end to end speech path.

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

• The SS7 protocol stack consists of only four levels• The OSI model consists of seven layers• SS7 protocol stack does not perfectly align with the

OSI model

SS7 Protocol Stack

This is due to the fact that SS7 was developed before the OSI model

Application protocols

Protocol layers (”levels”) of SS7

MTP - Message Transfer PartSCCP - Signalling Connection Control Part

UP - User Part AP - Application Part

CAP INAPMAP ISUP TCAP

SCCP

TUP

MTP level 3 MTP level 2 (link-layer protocol)

MTP level 1 (64 kbit/s PCM time slot)

routing

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 )

MTP Level 1

• Physical layer of SS7 protocol is MTP Level 1• This Level defines the physical, electrical, and

functional characteristics of the digital signaling link• The signaling data link should mostly be

Terrestrial , although Satellite links are supported in the standards

• Physical interfaces defined include • DS-0 (64 kb/s) • DS-0A (56 kb/s)

MTP Level 1

MTP Level 2

• Data Layer of the SS7 protocol is MTP Level 2 • MTP2 has the following mechanisms

MTP Level 2

MTP Level 2

MTP Level 3

MTP Level 3• Routing in the signalling network (using

OPC, DPC) between SPs.

MTP Level 2 (in detail)

• There are three types of signal units

MTP Level 2

Message Signal Unit ( MSU )

Link Status Signal Units ( LSSU )

Fill-In Signal Units ( FISU )

• LI indicates the signal unit type & length in octets of the upper level fields

• The 6-bit LI store values between zero and 63

Length Indicator ( LI )

LI value Signal Unit Type

0 FISU1,2 LSSU

3……63 MSU ( MSUs are of variable length )

Message Signal Unit ( MSU )

SS7 Level 4

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)

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 SS7ISDN user part (ISUP) does not refer to the ISDN userISDN user part ( ISUP ) is user of lower layers of SS7

ISUP Message Format

ISUP Message Format• ISUP information is carried in the Signaling Information Field (SIF)

of an MSU • ISUP message consists of fields organized into the following parts

Routing Label

14 14 4DPC OPC SLS

Routing Label

Routing Label

Circuit Identification Code (CIC)

ISUP Message Types

Mandatory Fixed Part

• Contains those parameters that are mandatory for a particular message type and are of fixed length

Mandatory Variable Part• Contains those parameters that are mandatory for a

particular message type and are of variable length

Optional Part

• Parameters that may or may not occur for a particular message type

ISUP MESSAGES

Initial Address Message ( IAM )• IAM is the first message used to initiate a call• An Initial Address Message (IAM) is sent in the

forward direction by each switch needed to complete the circuit between the calling party and called party until the circuit connects to the destination switch

• IAM contains the called party number in the mandatory variable part

• Subsequent Address Message (SAM) is used when the called number is sent in more than one message

• An IAM contains the calling party number in the optional part

Address Complete Message (ACM)• This message is sent by distant exchange in the

backward direction upon receipt of all address signals ( IAM, SAM ) 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

000

358 99

123456712345671234567

International numberNational numberUser number

PrefixCountry codeArea code

3589

In each exchange, the B number is analyzed at call setup and a routing program (algorithm) selects the next exchange to which the call is routed.

or mobile network code 40

What is E.164 numbering scheme ?

Some more Topics..

• SCCP sits on top of Message Transfer Part 3 (MTP3) in the SS7 protocol stack.

• SCCP provides additional network layer functions to provide transfer of noncircuit-related (NCR) signaling information, application management procedures and alternative and more flexible methods of routing.

• Signaling Connection Control Part (SCCP) provides additional functions such as Global Title Translation (GTT) to the MTP.

SCCP (Signalling Connection Control Part)

• A Global Title (GT) is an address used in the SCCP protocol for routing signaling messages on telecommunications networks

SCCP (Signalling Connection Control Part)

147

• provides the capability to exchange information between applications using non-circuit-related signaling.

• Operations, Maintenance, and Administration Part (OMAP) is a TCAP application for network management.

• Mobile Application Part is a TCAP application that supports mobile roaming management.

Transaction Capabilities Application Part (TCAP)

TCAP

• It manages to communicationin MAP.

• It likes a secretary • Transaction Capabilities Application Part

(TCAP) provides the capability to exchange information between applications using non-circuit-related signaling.

A interface

Signalling in GSM core network

MAPTCAP

MM / CMRR

BSSMAP / DTAPMAP

ISUPBSSAP TCAPBSSAP

SCCPMTP

SCCPMTP

BSC MSC / VLR to GMSC

HLRSCCP SCCP

MTP

ISUP for signalling between exchanges (MSC, GMSC)MAP for signalling to/from databases (VLR, HLR, AuC, EIR)

MSCMSC BSCBSC HLRHLRMTPMTP It provides to It provides to

transfer the transfer the messages of SS7 messages of SS7 between different between different network network componentscomponents

It provides to It provides to transfer the transfer the messages of SS7 messages of SS7 between different between different network network componentscomponents

It provides to transfer the messages of SS7 between It provides to transfer the messages of SS7 between different network componentsdifferent network components

TUP/ISUPTUP/ISUP It provides to set It provides to set up, manage and up, manage and control the callscontrol the calls

No existNo exist No existNo exist

SCCPSCCP It provides It provides connectionless connectionless communication communication and virtual and virtual connectionsconnections

It provides virtual It provides virtual connection connection between MSC and between MSC and

MSMS Connectionless CommunicationConnectionless Communication

BSSAPBSSAP It provides GSM It provides GSM communication communication between BSC and between BSC and MSMS

MSC and GSM MSC and GSM communicationcommunication

No existNo exist

MAPMAP It It pprovides basic rovides basic communication communication between HLR and between HLR and other MSCother MSC

No existNo exist It provides basic communication between MSC and It provides basic communication between MSC and HLRHLR

TCAPTCAP It provides to It provides to connect service to connect service to MAP MAP

No existNo exist It provides to connect service to MAPIt provides to connect service to MAP

INAPINAP It provides It provides communication via communication via Intelligent NetworkIntelligent Network

No existNo exist It provides communication via Intelligent NetworkIt provides communication via Intelligent Network

THANKS

signaling hcna uc

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