kommunikationsnetze i v10c ws1112 ss7 org
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.(Zeichengabesystem Nr. 7)
SS#7, SS7, ...
Common Channel Signaling System No. 7,
C7, CCS7, ...- r.
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Terms (Begriffe)
Communication Networks I + IIi i +
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 o Scri t: see web site
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Signaling System No. 7
global standard for telecommunications definedby the International Telecommunication Union
e eco ca o a ar za o ec or(ITU-T) (Q.700-Q.795)
by which network elements in the publicswitched telephone network (PSTN) exchange
n orma on over a g a s gna ng ne wor oeffect wireless (cellular) and wireline call setup,routin and control
ITU definition of SS7 allows for national
variants such as the American Nationalan ar s ns u e use n orAmerica and the European TelecommunicationsStandards Institute ETSI standard used in
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SS7 network and protocol used for:
basic call setup, management, and release
mobile services mobile roamin and mobilesubscriber authentication
local number portability (LNP) toll-free (800) and toll (900) wireline services
enhanced call features such as call forwardin ,
calling party name/number display, and three-way calling, conference calls
assures efficient and secure worldwide
telecommunications
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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 elements
w ou vo ce run s e.g., a a ase sys ems improved control over fraudulent network usage
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Protocol Architecture SS7
User of SS#7
OSIlayers
ser(e.g., MAP, INAP)
Transaction ISDN7
Capabilities ApplicationPart (TCAP)
ser
Part(ISDN-UP,
e ep oneUser Part
(TUP)level 44-6
Signalling Connec-tion Control Part
(level 4)
empty
3
2
MTP (level 1-3)
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Message Transfer Part The Message Transfer Part (MTP)
is divided into three levels (Ebenen). The lowest level MTP Level 1 is e uivalent to the OSI Ph sical
Layer. MTP Level 1 defines the physical, electrical, andfunctional characteristics of the digital signaling link. Physical
interfaces defined include E1 (2048 kbit/s; 32 x 64 kbit/sc anne s , - s; x s c anne s , .(64 kbit/s), DS-0 (64 kbit/s), and DS-0A (56 kbit/s).(64 kbit/s -> 2 Mbit/s)
signaling link. Level 2 implements flow control, message sequencevalidation, and error checking. When an error occurs on asignaling link, the message (or set of messages) isretransmitted. MTP Level 2 is equivalent to the OSI Data LinkLayer (Frame similar to HDLC).
MTP Level 3 provides message routing between signaling points ine ne wor . eve re-rou es ra c away romfailed links and signaling points and controls traffic whencongestion occurs. MTP Level 3 is equivalent to the OSI
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communication).
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ISDN User Part (ISUP)
The ISDN User Part (ISUP) defines theprotocol used to set-up, manage, and releasetrunk circuits that carry voice and data between
terminating line exchanges (e.g., between aca ng par y an a ca e par y .
Today ISUP is usedTCAP User
non-ISDN calls. TCAP (L7) ISUP
(L4)TUP(L4)
,originate and terminate
at the same switch do
SCCP (L4)
not use ISUP signaling.Why?
MTP (level 1-3)
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Telephone User Part (TUP)
In some parts of the worldC i i
the Telephone User Part (TUP) is used toi -
TUP handlesTCAP User.
In many countries, TCAP (L7) ISUP(L4)
TUP(L4)
TUP for call SCCP (L4)
. MTP (level 1-3)
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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 800num er, ca ing car num er, or mo i esubscriber identification number) which is
and subsystem number.A subs stem number uni uel TCAP User
identifies an application at
the destination signaling point.
TCAP (L7)
ISUP(L4)
TUP(L4)
s use as t e transportlayer for TCAP-based services.
MTP (level 1-3)
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r y se y .
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Transaction Capabilities Applications Part (TCAP)
suppor s e exc ange o non-c rcu re a e a abetween applications across the SS7 network using theSCCP connectionless service (connection-less).
Queries and responses sent between SSPs (Service
Switching Point) and SCPs (Service Control Point) in the
For example, a switching point (SP)sends a TCAP query to determine
TCAP User
e rou ng num er assoc a ewith a dialed 800 number or tocheck the personal identification SCCP (L4)
(L4) (L4)
num er PIN o a ca ing car user.
In obile networks IS-41 and GSM TCAP carries
MTP (level 1-3)
Mobile Application Part (MAP) messages sent betweenmobile switches and databases to support user
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, , .
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Signaling Network and Bearer Network
SP A SP CSignaling Network
Switch B
Switch CSwitch A
Traffic/BearerNetwork
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Network Nodes SS7
SP: Signaling Point(Zeichengabeknoten)
layer 1-7, , ...
co-located or part of a switching node
STP: Signaling Transfer Point(Transit-Zeichengabeknoten)
layer 1-3
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a)
0 STP Signaling Transfer Point (STP)
Traffic Channel
2 SS#7 channels per traffic channel1 STP
c) d)
3 SS#7 channels per traffic channel
4 SS#7 channels per traffic channel
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Number ofswitching nodes (Vermittlungsknoten)
for a typical ISDN end-to-end connection
localconnection
nationalconnection
internationalconnection
Number of switching nodes 1-4 5-7 8-10
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SS7 message types for ISDN
connection setup and release IAM Initial Address Messa e
sent to install a traffic channel between A and B,
Parameters: calling and called numberress omp e e essage
signals that the informationfor connection setup is complete
CPG Call Progress Messagesignals state of connection set-up,e. . that B is bein alerted
ANM Answer Messagesignals that traffic channel can be activated
e ease essagesignals that traffic channel can be released
RLC Release Complete Message
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Callingsubscriber A
SubscriberLocal Exchange A
Transit Exchange SubscriberLocal Exchange B
Calledsubscriber B
SetupIAM
IAMACM Setup
Alerting
CPG
ACM
ANMAlerting
ANM
Traffic Channel
Disconnect
Release REL
RLC Disconnect
Success ul ISDN
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connection set-up
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T e Code ISUP: Messa e t e
ACM 06 Address Complete
BLA 15 Blocking Acknowledgement
CCR 11 Continuity Check Request
on us on
CGB 18 Circuit Group Blocking
CGBA 1A Circuit Group Blocking Acknowledgement
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CGU 19 Circuit Group Unblocking
CGUA 1B Circuit Group Unblocking Acknowledgement
CMC 1D Call Modification CompletedCMR 1C Call Modification Request
CMRJ 1E Call Modification Reject
CON 07 ConnectCOT 05 Continuity
CPG 2C Call Progress
C M 2A Circuit Grou uer
CQR 2B Circuit Group Query Response
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CRG 31 Charge information
DRS 27 Delayed Release
FAA 20 Facility AcceptedFAR 21 Facility Request
FOT 08 Forward Transfer
FRJ 1F Facility RejectGRA 17 Circuit Group Reset Acknowledgement
GRS 29 Circuit Group Reset
IAM 01 Initial Address Messa e
INF 04 Information
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INR 03 Information Request
LPA 24 Loop Back Acknowledgement
OLM 30 OverloadPAM 28 Pass Along
REL 0C Release
RES 0E ResumeRLC 10 Release Complete
RSC 12 Reset Circuit
SAM 02 Subse uent Address Messa e
SUS 0D Suspend
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UBA 16 Unblocking Acknowledgement
UBL 14 Unblockin
UCIC 2E Unequipped Circuit Identification Code
0A Reserved
0F Reserved
eserve
23 Reserved
25 Reserved
26 Reserved
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Callingsubscriber
SubscriberLocal Exchange
Transit Exchange SubscriberLocal Exchange
Calledsubscriber
SetupIAM
IAMACM Setup
Alerting
CPG
ACM
Alerting
Disconnect
Release REL
RLC Disconnect
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connec on se -up su scr er oes no answer
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QoS circuit switched ISDN services
Quality of serviceparameter (ITU-T E.721)
Normal load (100%) Higher load (115%)
mean 95 % mean 95%
D-channel
0.6 s 1.0 s 1.0 s 2.0 saccess me
Connection setup time
local connection
3.0 s na ona connec on
international connection
5.0 s8.0 s
.8.0 s11.0 s
Time of answer delay
local connectionnational connection
international connection
0.75 s1.5 s2.5 s
local connectionnational connection
2%3%5%
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Maximum time allowed for
total connection set-up time according to I.352
connec on se -up me
mean 7.5 s
95 % 8.45 s
I.352 (03/93) Network performance objectives
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MPT MPI MPI MPT
T or S/T T TTransit AE(nat. part)
Transit AE(nat. part)
User User AE Transit AE
User AE User.
AE Access Element
n erna ona or er
MPT Measurement Point
i
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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
. s
Connection set-up delay of national network part
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MPI1 ISCISC MPI2ISC
easurement o nt nternat onaISC International Switching Center
Worst-Case Reference Connection for international network art
MPT LE MPIPC SC ISC
MPT Measurement Point - TerminalLE Local Exchange
PC, SC Transit Switchin NodesISC International Switching CenterMPI Measurement Point - International
- i i
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um er o s um er o s
International NetworkPart
3 4
National
4 5e wor ar
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Parameters for the calculation
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Parameters for the calculationo connection rocessin dela s
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Current "SS7" Developments
Fixed and mobile telephone network operators are designing a so-called AllIP architecture including support for signaling system 7SS7 si nalin rotocols
The benefits of using an IP network in comparison to a legacy TDM-(time division multiplex)based network include:
Ease of deploymentWhen using signaling gateways, there is no need toisrupt t e existing SS7 networ , an uture en ancements are
transparent. Less costly equipmentThere is no need for further expensive
invest ents in the le ac si nalin ele ents.
Better efficiencySignaling over an IP network does not require thephysical E1/T1 over synchronous digital hierarchy (SDH) rings. Using newtechnologies like IP over SDH and IP over fiber, for instance, can
. 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 servicesImplementing a core IP network facilitates avariety of new solutions and value-added services (VAS).
see e.g. SIGTRAN IETF group
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Current "SS7" Developments
SIGTRAN (Signaling Transport) is aworking group within the IETFstandard organization. Its primarypurpose is to address the transportof packet-based public switched
telephone network (PSTN) signaling,account the functional andperformance requirements of thePSTN signaling.
In order to interwork with thePSTN, IP networks need totransport signaling such asn egra e serv ce g a ne(ISDN) (e.g. Q.931) or SS7 (e.g.ISDN user part (ISUP), SCCP, and
such as a signaling gateway (SG), amedia gateway controller (MGC), amedia gateway (MG), or an IP
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ase ata ase.
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- . - .
CC NDC SN
CC Country Code, defined in E.164 (Landeskennzahl)
NDC National Destination Code Ortsnetzkennzahl
SN Subscriber Number (Teilnehmernummer)
+49 421 2182277
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R f
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References
http://www.pt.com/tutorials/ss7/
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