Version 8a, 08/2001

munchdrabΔίκτυα και Επικοινωνίες

30 Οκτ 2013 (πριν από 4 χρόνια και 2 μήνες)

292 εμφανίσεις

SIGNALING NETWORKS

SS7 TUTORIAL

Version 8a, 08/2001


30/10/2013


Generic Training SS7

2

SUMMARY

Signaling basics

Signaling characteristics (User Part & Network Part)

SS7 General principles

SS7 Signaling Modes

SS7 architecture

SS7 protocols & Examples of call transactions

SS7 Usage

SS7 & Intelligent networks (IN)

SS7 Operation, Administration & Maintenance

SS7 / IP convergence

SS7 in GSM + IN convergence

SS7
-
based applications :
an introduction to NMG’s solutions


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Generic Training SS7

3

Signaling Definition

Signaling refers to the exchange of information between call
components required to provide and maintain service.

Signaling includes all the necessary signals for managing
connections:


Establishment and release of circuit
-
related connections,


Control and billing,


Supervision and maintenance …


GSM and IN management

communication

establishment

Release

control


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Signaling Types

Network 1

Network 2

User Network

Interface (UNI)

-

Access signaling
(DSS1,V5)

-

ISDN signaling (D)

-

PABX signaling (QSIG)

Network Network

Interface (NNI)

-

SS7 signaling


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Signaling characteristics (1)

from UNI to NNI

From analog to digital signaling


On customer accesses, signaling today remains mostly analog
(DTMF tones)


The evolution goes towards digital packet signaling at the user
access (e.g. ISDN D channel) and in the core network


More information


Faster access to the information


More secure information


and enhanced QoS



This revolution is still operating for a long date in
the core network
.



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6

Signaling characteristics (2)

from UNI to NNI

Use of communication channels based on
Out
-
of
-
Band

signaling or
Common
Channel

signaling (CCS)


On customer accesses, signaling information is today carried
over the same links than voice or user data


The evolution goes towards separate channels for signaling and
user information (e.g. ISDN D channel)


Permanent access to signaling information (ability to signal during a
call)


Enhanced performance (reduced delay and reduction in fraud)



This revolution is also operating for several years
in the core network (1980)


…. SS7 ….


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7

Out
-
of
-
Band signaling: General
principles

Signaling links:

SS7 network

User information links:

Data/Voice trunk

Signaling

channels

D channel s

B channel s


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8

SS7 Signaling choices

SS7 messages are exchanged between network elements over
64 kb/s bidirectional channels (called signaling links).

Signaling occurs out
-
of
-
band on dedicated channels rather
than in
-
band on voice channels.

Compared to in
-
band signaling, out
-
of
-
band signaling
provides:



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 without voice trunks (e.g., database systems)


improved control over fraudulent network usage



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9

Full network architecture

Subscriber line

Voice trunk

Signaling link

Network 1

Network 2


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SS7 Architecture (1)

Each signaling point in the SS7 network is uniquely
identified by a numeric point code.



Point codes are carried in signaling messages exchanged between
signaling points to identify the source and destination of each message.



The SS7 network is composed of 3 types of signalling
points
.



SSP

(Service Switching Point)


SEP (Signaling End Point)


STP

(Signal Transfer Point)


SCP

(Service Control Point)


STEP (Signaling Transfer and End Point)




This type of architecture allows
a maximum of flexibility in
the network topology


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STP : Signaling Transfer Point

SP : Switching Point

TSw : Transit Switch

Sw : Local Switch

Signaling network

Circuit groups and Switches

SP

SSP

SSP

SSP

Sw

Sw

Sw

Sw

TSw

TSw

TSw

STP

STP

STP

STP

SS7 Architecture (3)


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12

SS7 Signaling Modes (1)

Associated Signaling


With this type of signaling, the signaling link directly parallels associated voice
trunks.


Thus, dedicated links must be provisioned between every interconnected
switch.

Quasi
-
Associated Signaling


This type of signaling employs a minimal number of nodes, thus minimizing
delays.


Quasi
-
associated signaling is the preferred signaling mode for SS7
.

(Non
-
Associated Signaling)


With this type of signaling, voice/data and signaling are carried on separate,
logical paths. Multiple nodes in the signaling path to the final destination can
causes delays.


Although used in the SS7 network, it is not preferred.



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STP
1

STP
2

STP
3

STP
4

SSP1

SSP2

SSP3

Associated

Mode

Voice Trunks

SS7 links

link

linkset

relation

Quasi
-
Associated Mode

SS7 Signaling Modes (2)


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SS7 Protocols (1)



SS7 services are described by
ISO 4 to 7 upper layers:


ISUP

= ISDN User Part


TUP

= Telephone User Part


SCCP

= Si gnaling
Connection Control Part


TCAP
= Transaction
Capabilities Application Part




SS7 Transmission part is
described by ISO layers 1 to 3:


MTP

= Message Transfer Part



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15

MTP

Message Transfer Part (Q.701


Q.704)

ISUP

ISDN User Part (Q.761


Q.766)

TUP

Telephone User Part (Q.721


Q.725)

SCCP

Signaling Connection Control Part (Q.711


Q.714)

MAP

Mobile Application Part

INAP

Intelligent Network Application Part

SSN

Sub System Number (SCCP)

SIO

Service Information Octet (SIO=NI+SI, Network Indicator and Service Indicator)

M T P

SCCP/TCAP

ISUP

TUP

MAP

INAP

SIO

SSN

--

3

--

5

--

4

--

0

SS7 Protocols (2)


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Layer 3 : signaling network

-
Route management

-
Linkset management

-
Load management of links within a linkset

L3 : Routing

The system is able to send a
message from a SP to any other SP
through the same signaling network.

Layer 2 : signaling link

-
Correction methods (Basic and PCR)

-
Error detection by CRC, acknowledgement

-
Sequence numbering (NSA, NSR) and mngt

-
Link management (LSSU exchange)

-
Signal unit delimitation by Flag

-
Alignment procedures

Layer 1 : Data link

(
PDH hierarchy)

-
Full duplex data links at 64 kbits/s timeslots
embedded in a 2048kbit/s PCM (E1)

L2 : Adressing, flow and
error control

The system is able to send

messages both way on a link

(between two SP) without error and
in the right order.

Application layers (ISUP, …)

MTP functions

L1: transmission

32 timeslots based on 64kbit/s data
links:

TS0 is for synchro

TS1 to TS31 support SS7 links


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An SS7 message is called a signal unit (SU).

There are three kinds of signal units:


Fill
-
In Signal Units (FISUs),


Link Status Signal Units (LSSUs),


and Message Signal Units (MSUs)




FISU (Fill
-
In Signal Unit)

F
:

Flag

BSN:

Backward sequence number

FSN:

Forward sequence number

BIB:

Backward indicator bit

FIB:

Forward indicator bit

LI:

Length indicator



FISU is recognized by LI = 0

CK:

Check bits


CK

LI

FSN

BSN

F

F

I

B

16

2

6

1

7

1

7

8

B

I

B

Layer 2 Signaling Messages (1)


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18


LSSU (Link Status Signal Unit)




MSU (Message Signal Unit)



SF:

Status field

LSSU is recognized by LI= 1 or 2

CK

LI

FSN

BSN

F

F

I

B

16

2

6

1

7

1

7

8

SF

8 oder 16

B

I

B

Layer 2 Signaling Messages (2)

CK

LI

FSN

BSN

F

F

I

B

16

2

6

1

7

1

7

8

B

I

B

8n

272>n>1

8

SIF

SIO

SIO :

Service information octet, contains :


-

NI, Network indicator (national, international, …)


-

SI, Service indicator (ISUP, TUP, SCCP)

SIF :

Signaling information octet : maximum 272 bytes

MSU is recognized by LI > 2


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Layer 3 Message

Layer 2

SIO

DPC

OPC

SLS

CIC

Info

32

Layer 2

8

14

14

4

16

16

DPC :

Destination point code

OPC :

Originating point code

SLS :


Signaling link selection

CIC :

Circuit identification code

Layer 3: Signaling Messages (3)

CK

LI

FSN

BSN

F

F

I

B

16

2

6

1

7

1

7

8

B

I

B

8n

272>n>1

8

SIF

SIO

Layer 2 MSU

Layer 3

Upper Layers


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SS7: ISUP & TUP functions

Upper Layers:


ISDN User Part (ISUP)

The ISDN User Part (ISUP) defines
the protocol used to set
-
up,
manage, and release trunk circuits
that carry voice and data between
terminating line exchanges.

ISUP is used for both ISDN and
non
-
ISDN calls.


TUP (Telephone User Part)

The TUP protocol is specified for
telephony signaling. TUP handles
basic establishment functions only.
In many countries, ISUP has
replaced TUP for call management

SEP

SEP


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SS7: SCPP & TCAP functions

Upper Layers:


SCCP (Signaling Connection Control Part)

provides connectionless
and connection
-
oriented network services above MTP Level 3. SCCP is
used as the transport layer for TCAP
-
based services

It allows signaling exchanges between SS7 networks (MTP is unable to
do it)


TCAP (Transactions Capabilities Applications Part)

supports the
exchange of non
-
circuit related data between applications across the
SS7 network using the SCCP connectionless service.



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.



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SS7: MAP and INAP functions

MAP supports:



MAP and SMS capabilities for IS
-
41 and GSM networks


Acting as the VLR, HLR, and MSC


MAP
-
GSM acting as the VLR, HLR, MSC, and SGSN/GGSN in GPRS


Implementing GSM Phase 1, Phase 2, and Phase 2+. It also supports
MAP
-
GSM extensions for GPRS and CAMEL

INAP supports:



Capability Set 1 (CS1), as defined by the ITU, ETSI, and the Generic
Requirement (GR) standards of the Bellcore Advanced Intelligent Network
(AIN)


The interaction between the SSF, SCF, Specialized Resource Function
(SRF), and the Service Data Function (SDF) B
-
ISUP supports:


Establishing, maintaining, and releasing broadband
-
switched network
connections across an SS7/ATM network. It can act as the originating,
destination, or intermediate exchange


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Signaling protocols

at the User Interface (UNI)

Calling

Terminal

Called
Terminal

ESTABLISH / SET
-
UP

(Adress,VPI,VCI,Bitrate, QoS)

ACCEPT / CONNECT

(REJECT / RELEASE)

DISCONNECT / RELEASE

EFFICIENT COMMUNICATION



Future networks will negociate their characteristics ( bitrate, QoS, etc…)

during the call setup.


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Network
-
to
-
Network signaling
protocols (NNI)

Subscriber line

Voice trunk

Signaling link


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Call Simulation (1)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

IAM1

IAM2

IAM3


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Call Simulation (2)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

ACM1

ACM2

ACM3


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Call Simulation (3)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

ANM3

ANM2

ANM1


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Call Simulation (4)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

REL1

REL2

REL2


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Call Simulation (5)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

REL1

REL2

REL2


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Call Simulation (6)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

RLC1


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Call Simulation (7)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

RLC2


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Call Simulation (8)

PTS

PTS

PTS

PTS

PS

PS

PS

PS

RLC3


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Call Simulation (9)

PTS

PTS

PTS

PTS

PS

PS

PS

PS


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Messages are linked by label (OPC, DPC,CIC)

The sequence is analysed and the call is classified in a Cause Family

The most important information for each call is recorded in the CDR.

Message linking and sequence analysing

Signaling units (MSU)

CDRs

CDR Generation mechanisms


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Successful call hang
-
up by calling party

Switch A (calling)

IAM

Initial Address

SAM

Subsequent Address

ACM

Address Complete

Switch B (called)

ANM

Answer

REL

Release

RLC

Release Complete

SAM

Subsequent Address

Setup time

Ring time

Conversation

time

Release time

ISUP Sequence (1)


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No Answer
-

Cause Family = NA

Switch A (calling)

IAM

Initial Address

SAM

Subsequent Address

ACM

Address Complete

Switch B (called)

REL

Release

RLC

Release Complete

SAM

Subsequent Address

Setup time

Ring time

Release time

ISUP Sequence (2)


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Hang
-
up during establishment
-

Cause Family=HE

Switch A (calling)

IAM

Initial Address

SAM

Subsequent Address

Switch B (called)

REL

Release (by calling)

RLC

Release Complete

SAM

Subsequent Address

Setup time

Release time

ISUP Sequence (3)


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Operation, Administration &
Maintenance

The operations, Maintenance and Administration Part
(OMAP) provides the procedures for network management
and supervision from central control points in the SS7
network.



It defines application protocols and procedures to monitor, test,
coordinate, and control SS7 network resources.

OMAP procedures are used for a number of functions,
including:


MTP route verification, to detect route loops, excessive delays, or
inaccessibility of signaling points.


SCCP route verification, to verify routing and global title translation.


Routing data management.


Traffic data collection.


Link failure management.


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SS7 Usage


basic call setup, management, and tear down


enhanced call features such as call forwarding, calling party
name/number display, and three
-
way calling



wireless services such as personal communications services (PCS),
wireless roaming, and mobile subscriber authentication & localisation


Short message transportation (SMS)



IN applications


toll
-
free (800/888) and toll (900) wireline services


local number portability (LNP)



efficient and secure worldwide telecommunications



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40

IN Definition



An intelligent network (IN) is a service
-
independent
telecommunications network where Intelligence is
taken out of the switch and placed in computer
nodes that are distributed throughout the network.


This provides the network operator with the means to develop
and control services more efficiently.


New capabilities can be rapidly introduced into the network.


Once introduced, services are easily customized to meet
individual customer's needs.


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41

SS7 Architecture for IN application

SSP

(Service Switching Point)

STP

(Signal Transfer Point)

SCP

(Service Control Point)


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Meshed IN Architecture


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Benefits of IN

The main benefit of intelligent networks is the
ability to improve existing services and develop
new sources of revenue.



To meet these objectives, providers require the
ability to accomplish the following:



introduce new services rapidly


provide service customization


establish vendor independence


create open interfaces



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SS7 in GSM


MAP protocols

A: BSC
-
MSC

B: MSC
-
VLR

C: GMSC
-
HLR

D: VLR
-
HLR

E: MSC
-
MSC

F: MSC
-
EIR

G: VLR
-
VLR

H: HLR
-
AUC

PSTN

MailBox

Interface MAP B to G

Interface A

(DTAP / BSSAP)

ISUP


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Access to IN services through CAMEL

(Mobile / IN Convergence)

CAMEL = Customized Applications for
Mobile Network Enhanced Logic


Connects home and visited mobile
networks to IN platforms


Allows roaming subscribers to
access IN services


Such as:


Pre
-
paid calling


Personal numbering


Location dependent applications


Available through the
CAP = Camel
Application Part

protocol.




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SS7 / IP Convergence

New Generation Networks (NGN)

Signaling Gateway

SIP Client

SIP Server

STP

E1/T1

Media Gateway

RTP

MGCP

IP

network

Media Gateway

Controller

DSS 1

Voice trunks

Signaling

SIP

SIP

SIP

ISUP/IP

ISUP/MTP

SS7


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SS7
-
based Supervision:

PrOceSS7 applications

PrOceSS7
takes advantage of SS7
data richness to develop performance
and Customer Traffic Efficiency
applications:


Real
-
time CDRs for all call attempts


Quick handling of customer
complaints


Traffic analysis


QoS expertise (roaming QoS)


Interconnection arbitration


Network planning


Traffic engineering


Protocol analysis

SS7 protocols analyzed are:


ISUP, INAP, MAP, etc…

Data processing

Workstations

Alarm Workstations

Maint enance

Web Browser

Alarm Server

Lan
-

Wan

Real Time
Data Base

Real Time
Data Base

SS7 Probe

SS7 Probe


Off Line
Data Base

Open Applications

SNMP/Q3

SS7 Network

SS7 Network


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SS7
-
based Simulation:

EVA applications

EVA
traffic simulator is designed for
network equipment providers for:


Traffic testing; performance and QoS


End
-
to
-
end QoS measurements


Functional service tests

Signaling protocols emulated are:


ISDN, SS7


H323, SIP (VoIP applications)


IP ?

Z

T2

Z

Z

S0


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SS7
-
based Services:

VAS & SMS applications

Value Added Services (VAS)

for
mobile communications are based on
data capture over signaling links:


Mobile subscriber authentication


Mobile localisation (Cell
-
ID, VLR
tracking,…)


Mobile presence (WIM)


Mobile subscriber accounting


Wireless roaming traffic & QoS


SMS/EMS handling

Significant applications:


SMS
-
Welcome, SMS
-
Bon Voyage,
SMS
-
Advertizing,…

SS7 protocols concerned:


MAP, BSSAP …


HLR

VLR

Statistics

SMS C

BSC

MSC

SCCP

Gateway

Data Collection

System

VAS Platform

Process

System


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Annex: Relevant standards




SS7 Level


ITU Standard


ANSI Standard


JTC (Japan) Standard


MTP Level 2


ITU Q.701
-

Q.703,
1992


ANSI T1.111.2
-
.3,
1992


JT
-
Q.701
-

JT
-
Q.703,
1992


MTP Level 3


ITU Q.704
-

Q.707,
1992


ANSI T1.111.4
-
.7,
1992


JT
-
Q.704
-

JT
-
Q.707,
1992


SCCP


ITU Q.711
-

Q.714,
1992


ANSI T1.112, 1992


JT
-
Q.711
-

JT
-
Q.714,
1992


TUP


CCITT Q.721
-

Q.724,
1988


N/A


N/A


ISUP


ITU Q.761
-

Q.764,
1992


ANSI T1.113, 1992


JT
-
Q.761
-

JT
-
Q.764,
1992


TCAP


ITU Q.771
-

Q.775,
1992


ANSI T1.114, 1992


JT
-
Q.771
-

JT
-
Q.775,
1992