Signaling System No 7System No. 7 (Zeichengabesystem Nr. 7) · Signaling System No. 7 global...

Signaling System No 7Signaling System No. 7(Zeichengabesystem Nr. 7)

SS#7, SS7, ...Common Channel Signaling System No. 7,

C7, CCS7, ...(ZGS Nr 7)(ZGS-Nr. 7)

www.comnets.uni-bremen.de SS7 - 10 - 1

Terms (Begriffe) Communication Networks I + II

(Kommunikationsnetze I + II)(Kommunikationsnetze I II)http://www.lkn.e-technik.tu-muenchen.de/itg/empfehlung.html(old: http://www.comnets.rwth-aachen.de/~itg/FG521/home_ger.html)http://www.comnets.uni-bremen.de/itg/itgfg521/FG521/home_ger.html

German Version of Script: see web sitem V f p w


Signaling System No. 7 global standard for telecommunications defined

by the International Telecommunication Union(ITU) T l c mmunic ti n St nd diz ti n S ct(ITU) Telecommunication Standardization Sector(ITU-T) (Q.700-Q.795)

standard defines the procedures and protocols standard defines the procedures and protocolsby which network elements in the public switched telephone network (PSTN) exchange inf m ti n di it l i n lin n t k t information over a digital signaling network to effect wireless (cellular) and wireline call setup,routing and controlg

ITU definition of SS7 allows for national variants such as the American National St d d I tit t (ANSI) d i N th Standards Institute (ANSI) used in North America and the European Telecommunications Standards Institute (ETSI) standard used in


( )Europe

SS7 network and protocol used for:

basic call setup, management, and release mobile services, mobile roaming, and mobile , g,

subscriber authentication local number portability (LNP) p y toll-free (800) and toll (900) wireline services enhanced call features such as call forwarding, g

calling party name/number display, and three-way calling, conference calls

assures efficient and secure worldwide telecommunications


Advantages of SS7 faster call setup times

(compared to in-band signaling using multi-frequency (MF) signaling tones)

more efficient use of voice circuits support for Intelligent Network (IN) services

which require signaling to network elementsith t i t nk ( d t b t m )without voice trunks (e.g., database systems)

improved control over fraudulent network usage


Protocol Architecture SS7User of SS#7

“TCAP U ”

OSIlayers

“TCAP User”(e.g., MAP, INAP)

TransactionISDN

U T l h7

Capabilities ApplicationPart (TCAP)

User

Part(ISDN-UP,

ISUP)

TelephoneUser Part

(TUP)(level 4)4-6

( t )

Signalling Connec-tion Control Part(SCCP, level 4)

ISUP)(level 4)

( )(empty)

Other MTP Users(SCCP, level 4)3

21

Other MTP Users

MTP (level 1-3)1


Message Transfer Part The Message Transfer Part (MTP)

is divided into three levels (Ebenen). The lowest level, MTP Level 1, is equivalent to the OSI Physical , , q y

Layer. MTP Level 1 defines the physical, electrical, and functional characteristics of the digital signaling link. Physical interfaces defined include E1 (2048 kbit/s; 32 x 64 kbit/s channels) DS 1 (1544 kbit/s; 24 x 64kbit/s channels) V 35 channels), DS-1 (1544 kbit/s; 24 x 64kbit/s channels), V.35 (64 kbit/s), DS-0 (64 kbit/s), and DS-0A (56 kbit/s). (64 kbit/s -> 2 Mbit/s)

MTP Level 2 ensures reliable transmission of a message across a MTP Level 2 ensures reliable transmission of a message across a signaling link. Level 2 implements flow control, message sequence validation, and error checking. When an error occurs on a signaling link, the message (or set of messages) is retransmitted. MTP Level 2 is equivalent to the OSI Data Link Layer (Frame similar to HDLC).

MTP Level 3 provides message routing between signaling points in th SS7 n t k MTP L l 3 t t ffi f m the SS7 network. MTP Level 3 re-routes traffic away from failed links and signaling points and controls traffic when congestion occurs. MTP Level 3 is equivalent to the OSI Network Layer (lower part of OSI layer 3, connection-less


Network Layer (lower part of OSI layer 3, connection less communication).

TCAP UserTCAP User

TCAP (L7) ISUP(L4)

TUP(L4)

SCCP (L4)

(L4) (L4)

MTP (level 1-3)


ISDN User Part (ISUP) The ISDN User Part (ISUP) defines the

protocol used to set-up, manage, and release p ptrunk circuits that carry voice and data between terminating line exchanges (e.g., between a c llin p rt nd c lled p rt )calling party and a called party).

Today ISUP is used for both ISDN and TCAP Userfor both ISDN and non-ISDN calls.

However calls thatTCAP (L7) ISUP

(L4)TUP(L4)

However, calls thatoriginate and terminate at the same switch do

SCCP (L4)

not use ISUP signaling. Why?

MTP (level 1-3)


Telephone User Part (TUP) In some parts of the world

(e.g., China, Brazil), (e.g., China, Brazil), the Telephone User Part (TUP) is used to support basic call setup and tear-down.support basic call setup and tear down.

TUP handles analog circuits only TCAP Useranalog circuits only.

In many countries, ISUP has replaced

TCAP (L7) ISUP(L4)

TUP(L4)ISUP has replaced

TUP for call management

SCCP (L4)

management. MTP (level 1-3)


Signaling Connection Control Part (SCCP)

SCCP provides connection-less and connection-oriented network services and global title trans-lation (GTT) capabilities above MTP Level 3.

A global title is an address (e.g., a dialed 800 b lli d b bil number, calling card number, or mobile

subscriber identification number) which is translated by SCCP into a destination point code translated by SCCP into a destination point code and subsystem number. A subsystem number uniquely TCAP Usery q yidentifies an application at the destination signaling point. SCCP i d th t t

TCAP (L7)

SCCP (L4)

ISUP(L4)

TUP(L4)

SCCP is used as the transport layer for TCAP-based services.

Partially used by ISUP

SCCP (L4)

MTP (level 1-3)


Partially used by ISUP.

Transaction Capabilities Applications Part (TCAP) TCAP t th h f i it l t d d t TCAP supports the exchange of non-circuit related data

between applications across the SS7 network using the SCCP connectionless service (connection-less).

Queries and responses sent between SSPs (Service Switching Point) and SCPs (Service Control Point) in the Intelligent Network (IN) are carried in TCAP messages.Intelligent Network (IN) are carried in TCAP messages.

For example, a switching point (SP) sends a TCAP query to determineth tin n mb i t d

TCAP User

TCAP (L7) ISUP TUPthe routing number associated with a dialed 800 number or to check the personal identification

b (P N) f ll d

TCAP (L7)

SCCP (L4)

ISUP(L4)

TUP(L4)

number (PIN) of a calling card user.

In mobile networks (IS-41 and GSM), TCAP carries

MTP (level 1-3)

In mobile networks (IS 41 and GSM), TCAP carries Mobile Application Part (MAP) messages sent between mobile switches and databases to support user authentication equipment identification and roaming


authentication, equipment identification, and roaming.

Signaling Network and Bearer Network

STP1 STP2STP1

SP A

STP2

SP CSignaling Network

Switch B

Switch CSwitch A

Traffic/Bearer raff c/Bearer Network


Network Nodes SS7 SP: Signaling Point

(Zeichengabeknoten)

layer 1-7ISUP TUP ISUP, TUP, ...co-located or part of a switching node

STP: Signaling Transfer Point(Transit-Zeichengabeknoten)

layer 1-3Router for SS7Router for SS7


1 SS#7 channel per traffic channel

a)

Signaling Point / SP1 SS#7 channel per traffic channel0 STP

b)

Signaling Point / SP

Signaling Transfer Point (STP)

Signaling Channel SS#7b) Signaling Channel SS#7

Traffic Channel

2 SS#7 channels per traffic channel1 STP

c) d)




2 STP 3 STP


Number of switching nodes (Vermittlungsknoten)

for a typical ISDN end-to-end connection

localconnection

nationalconnection

internationalconnection

Number of switching nodes 1-4 5-7 8-10


ISDN QoS (ITU-T E.721) D-channel access time (D-Kanal-Zugriffszeit)

C ti t ti (V bi d fb it) ti Connection setup time (Verbindungsaufbauzeit) time between sending dialling information (Setup) and the alerting (Alerting) or busy signal (Indication)

Time of answer delay (Antwortverzögerungszeit)time between sending the connection acknowledgement (Connect: called party) until it reaches the caller (Connect: called party) until it reaches the caller (Connect: calling party)

Connection release time (Verbindungsabbauzeit)ti b t di th di t t (Di t) time between sending the disconnect request (Disconnect) and receiving the Release answer (Release)

Congestion Probability (gassenbesetzt)g y (g )Probability that the network cannot set-up a connection to the B subscriber, although the B subscriber is not busy


SS7 message types for ISDN connection setup and release

IAM Initial Address Messagegsent to install a traffic channel between A and B, Parameters: calling and called number

ACM Add C l t M ACM Address Complete Messagesignals that the information for connection setup is complete

CPG Call Progress Messagesignals state of connection set-up, e.g., that B is being alertedg , g

ANM Answer Messagesignals that traffic channel can be activated

REL Release Message REL Release Messagesignals that traffic channel can be released

RLC Release Complete Message


p gsent after release of the traffic channel

Callingsubscriber A

SubscriberLocal Exchange A

Transit Exchange SubscriberLocal Exchange B

Calledsubscriber B

SetupIAM

IAMACM Setup

Alerting

ConnectCPG

CPG

ACM

ConnectANMAlerting

ANM

CPG

Connect

Traffic Channel

Connect

DisconnectRelease REL

RLC RELRLC RELRLC Disconnect

Successful ISDN SS7


Successful ISDN connection set-up

SS7

Type Code ISUP: Message typeype Code SU : ess ge ypeACM 06 Address CompleteANM 09 AnswerANM 09 AnswerBLA 15 Blocking AcknowledgementBLO 13 BlockingBLO 13 BlockingCCR 11 Continuity Check RequestCFN 2F C f iCFN 2F ConfusionCGB 18 Circuit Group BlockingCGBA 1A Circuit Group Blocking Acknowledgement


CGU 19 Circuit Group UnblockingCGUA 1B Circuit Group Unblocking AcknowledgementCMC 1D Call Modification CompletedCMR 1C Call Modification RequestCMRJ 1E Call Modification RejectCON 07 ConnectCOT 05 ContinuityyCPG 2C Call ProgressCQM 2A Circuit Group QueryCQ C cu G oup Que yCQR 2B Circuit Group Query Response


CRG 31 Charge informationDRS 27 Delayed ReleaseFAA 20 Facility AcceptedFAR 21 Facility RequestFOT 08 Forward TransferFRJ 1F Facility RejectGRA 17 Circuit Group Reset Acknowledgementp gGRS 29 Circuit Group ResetIAM 01 Initial Address Message0 dd ess ess geINF 04 Information


INR 03 Information RequestLPA 24 Loop Back AcknowledgementOLM 30 OverloadPAM 28 Pass AlongREL 0C ReleaseRES 0E ResumeRLC 10 Release CompletepRSC 12 Reset CircuitSAM 02 Subsequent Address MessageS 0 Subseque dd ess ess geSUS 0D Suspend


UBA 16 Unblocking AcknowledgementUBL 14 UnblockingU U b oc gUCIC 2E Unequipped Circuit Identification CodeUSR 2D User to User InformationUSR 2D User to User Information

0A Reserved0B Reserved0B Reserved0F Reserved22 R d22 Reserved23 Reserved25 Reserved26 Reserved


Callingsubscriber

SubscriberLocal Exchange

Transit Exchange SubscriberLocal Exchange

Calledsubscriber

SetupIAM

IAMACM Setup

AlertingCPG

CPG

ACM

AlertingCPG

DisconnectRelease REL

RLC RELRLC RELRLC Disconnect

ISDN ti t ( b ib B d t )


ISDN connection set-up (subscriber B does not answer)

Callingsubscriber A

SubscriberLocal Exchange

Transit Exchange SubscriberLocal Exchange

Calledsubscriber Bsubscriber A L E ng Local Exchange

SetupIAM

IAMIAM

REL (busy)

RLCREL (busy)Indication RLC

RLCREL (busy)

ISDN connection set-up (subscriber B busy)


QoS circuit switched ISDN services

Quality of service parameter (ITU-T E.721) Normal load (100%) Higher load (115%)

mean 95 % mean 95%

D-channelaccess time

0.6 s 1.0 s 1.0 s 2.0 saccess time

Connection setup time

local connectionti l ti 3.0 s 6 0 snational connection

international connection3.0 s5.0 s8.0 s

6.0 s8.0 s11.0 s

Time of answer delay

local connectionnational connection

international connection

0.75 s1.5 s2.5 s

Congestion Probability Congestion Probability

local connectionnational connection

international connection

2%3%5%


international connection 5%


Maximum time allowed for l d

ti t ti

total connection set-up time according to I.352

connection set-up time

mean 7.5 s

95 % 8.45 s95 . 5

I.352 (03/93) Network performance objectives for connection processing delays in ISDN


for connection processing delays in ISDN

Reference Connection between two users

MPT MPI MPI MPT

Reference Connection between two users

T or S/T IB IB T or S/TIB IB T or S/TTransit AE(nat. part)

Transit AE(nat. part)

User User AE Transit AE(int part) User AE User(int. part)

AE Access ElementIB I t ti l B dIB International BorderMPT Measurement Point MPI Measurement Point Int.


MPI Measurement Point Int.

Connection set-up delay Connection set up delay

connection set-up delay

mean 1.7 s

95 % 2.3 s

connection set-up delay

Connection set-up delay of international network part

mean 2.9 s

95 % 3 6 95 % 3.6 s

Connection set-up delay of national network part


MPI1 ISCISC MPI2ISC

MPI M P i I i lMPI Measurement Point InternationalISC International Switching Center

Worst-Case Reference Connection for international network part

MPT LE MPIPC SC ISC

p

MPT Measurement Point - TerminalLE Local ExchangePC, SC Transit Switching Nodes, gISC International Switching CenterMPI Measurement Point - International

Worst-Case Reference Connection for national network part


Worst Case Reference Connection for national network part

Maximum number of SPs and STPs

Numb f SPs Numb f STPs

Maximum number of SPs and STPs

Number of SPs Number of STPs

International Network Part 3 4

NationalN t k P t 4 5Network Part 5


Parameters for the calculation of connection processing delaysf p g y


Current "SS7" Developments Fixed and mobile telephone network operators are designing a so-

called All–IP architecture including support for signaling system 7 (SS7) signaling protocols( ) g g p

The benefits of using an IP network in comparison to a legacy TDM-(time division multiplex)–based network include: Ease of deployment—When using signaling gateways, there is no need to

d h k d f h disrupt the existing SS7 network, and future enhancements are transparent.

Less costly equipment—There is no need for further expensive investments in the legacy signaling elements. investments in the legacy signaling elements.

Better efficiency—Signaling over an IP network does not require the physical E1/T1 over synchronous digital hierarchy (SDH) rings. Using new technologies like IP over SDH and IP over fiber, for instance, can achieve much higher throughput achieve much higher throughput.

Higher bandwidth— Signaling information over IP does not constrain link capacity as it does in the SS7 network. The IP network is much more flexible than the TDM-based legacy network.

Enhanced services—Implementing a core IP network facilitates a variety of new solutions and value-added services (VAS).

see e.g. SIGTRAN IETF group


Current "SS7" Developments SIGTRAN (Signaling Transport) is a

working group within the IETF standard organization. Its primary purpose is to address the transport of packet-based public switched telephone network (PSTN) signaling over IP networks taking into over IP networks, taking into account the functional and performance requirements of the PSTN signaling. g g

In order to interwork with the PSTN, IP networks need to transport signaling such as i t t d i di it l li integrated service digital line (ISDN) (e.g. Q.931) or SS7 (e.g. ISDN user part (ISUP), SCCP, and so on) messages between IP nodes so on) messages between IP nodes such as a signaling gateway (SG), a media gateway controller (MGC), a media gateway (MG), or an IP–b d d b


based database.

ISDN Numbering Plan ITU T E 163 E 165ISDN Numbering Plan ITU-T E.163-E.165

CC NDC SN

CC Country Code, defined in E.164 (Landeskennzahl)NDC National Destination Code (Ortsnetzkennzahl)( )SN Subscriber Number (Teilnehmernummer)

+49 421 2182277


References http://www.pt.com/tutorials/ss7/


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