Signalling SIP SIGTRAN Overview Handout

1

Signalling, SIP,

SIGTRAN Overview

- 1 -

Name: Bartlomiej Puchalski (Bartek)

Country: Poland

Education:PhD in Optimization of analogue Circuit Testing at Silesian University of Technology in Poland

MsC in Telecommunications (Silesian University of Technology, Bournemouth University UK)

Professional Experience: Instructor, Leliwa – training for /// Ericsson Manager, Orange PolandConsultant, Kennedy Information

- 2 -

Course Agenda

• SS7 Signalling Overview ~ 3,5 Days

• SIGTRAN ~ 1 Days

• SIP 0,5 Days

Daily Agenda

Introduction to the Signaling Architecture

Vertically Integrated and Horizontally Integrated network

Figure 1-1: Vertically Integrated and Horizontally Integrated network design models

Old approach

PCM

IP

PPP ATM

SDH

New approach

AMR GPRS

PPP

SDH

IPAAL2 AAL5

SDH

ATM

AMR GPRS

Synchronous Digital Hierarchy

2

Figure 1-3: Monolithic Architecture vs Layered Architecture

Handout: Classical (monolithic) architecture and Mobile Network Development

Figure 1-2: Layered Core Network Model Showing the Logical Network Nodes

Vertical architecture protocol stack.

Control Layer

ISDNMSC

HLR

GMSCBSC

AUCIN

BSSAP ISUP ISUP

MAPINAPCAP

Figure 1-5: Protocols used in the Mobile Core Network for Circuit Mode services

BICC – Used by /// only (all other vendors use SIP-T)

ITU /// IETFH248 = GCP = MEGACO

/// uses GCP because complete H248 functionality was not implemented in R1

Future ….

Figure 1-6: The access signaling in the common GSM and WCDMA systems Network

Figure 1-7: User plane protocol stacks for IP and ATM backbones

Figure 1-8: PCM encoded vs. Compressed speech in the Core Network

Figure 1-9: TrFO for WCDMA and TFO for GSM

Figure 1-10: Target architecture for the Mobile Core Network

Introduction to Signaling

Signalling and network activities

Traffic control

Database communication

Network management

B-numberAddress complete

Clear forwardB-answer

data base 1

data base 2 MS=‘X’

MS=‘X’ is now in my area!

OK, I have updated!

Trunk seizure!

Trunk blocked!

O&

M

Trunk group ‘Y’ blocked!

Redirect traffic …, etc.!

Figure 2-1: Signaling in Telecommunication Networks

Signalling:

• Access signalling (or subscriber signalling), between a subscriberterminal and the local exchange.

• Trunk signalling (or inter-exchange signalling), between networknodes (exchanges, switches, databases, etc.).

Access Signalling:

• Subscriber line signalling (used in PSTN).

• Digital subscriber signalling (used in ISDN and PLMN).

A-subscriber Local exchange B-subscriber

Off hook / seizure

Dial tone

B-number

Ring tone Ring signal

speech / data / fax

On hookOn hook

Off hook / answer

Subscriber line signalling

3

Digital Subscriber Signalling system No.1 (DSS1)

Setup

Call proceeding Setup

Call proceeding

AlertingAlerting

ConnectConnect

Connect ackConnect ack

SS7SS7

call communication

Disconnect

Release

Release complete

Disconnect

Release

Release complete

Trunk Signalling:

• Channel Associated Signalling (CAS).

• Common Channel Signalling (CCS).

BSC

LAPD LAPDmD-channel signalling Dm-channel signalling

(m – modified)

GSM access signalling GSM

CC (call control)

ISDN

DSS 1

P ... C BA S Q ... P ... C BA S Q ...

17 16... 3 21 0 18 ... 31 17 16... 3 21 0 18 ... 31

0 31 16

a aa a p pp p b bb b q qq q

register signals / traffic channels17-31

line signals16

register signals / traffic channels1-15

frame synchronisation0

used fortime slot

Channel Associated Signalling (CAS)

In practice CAS is not implementednowadays. However some old PSTN exchanges still use it andmust be supported in MSC.

Figure 2-2: CCITT R2 Signals (MFC)

Figure 2-3: Simplified Call Setup using the CAS System

Signalling Terminal

Computer

Signalling Terminal

Computer

ExchangeExchange

Signalling link

Data packet

Signalling message

Common Channel Signalling (CCS)

Figure 2-4: OSI Reference Model

Figure 2-5: Schematic figure of Information added in each Layer

L1

L2

L3

Service Access Point

Signalling entity

Primitive

Characteristics

High flexibility

Many different types of telecommunication services can use SS7.

High capacity

A single signalling link can support several thousand traffic circuits.

High speed

Setting up a call through a number of exchanges takes less than a second.

High reliabilityThe system contains powerful functions for elimination of disturbances in the signalling network. One example is the possibility of choosing alternative links for signalling.

Economical

Wide range of telecommunication services and connections can use one and the same signalling system. is an important economical aspect.

Signalling System No. 7 Signalling System No. 7Figure 2-8: Relationship between OSI and CCITT SS7

Figure 2-6: CCITT SS No. 7 General Structure

L3 Addressing & Routing,

MTP L2 Reliable Transmission (ACK, ReTx, Flow Control)

L1 1 64 kbps Timeslot on E1

TUP – not used in practice

ISUP – connection related signalling

SCCP – non connection related signalling

Figure 2-7: ETSI / ITU-T Protocols in the Mobile Core Network

4

SS7 Terminology

SP

(SPC=10)

SP

(SPC=20)

SL (SLC=1)

SL (SLC=0)

circuit (CIC=1) circuit (CIC=29)

LS

0 311 2

circuit (CIC=2)

SP - Signalling Point – sender/receiver of signalling messageSPC - Signalling Point Code – address of the SPSL - Signalling Link – 64 kbps TS carrying SS7 signalling between two SPsSLC - Signalling Link Code – SL identifier (4 bits)LS - Link Set – set of SLs connecting two SPs. Max 16 SLs/LSCIC - Circuit Id. Code – Connection Id. Standard 12b (4000 connections)

may be extended to 16b (65 000 connections)Figure 2-9: Signaling Network Elements

SS7 Signalling LinksProblem with capacity – 16 Signalling Links/Link Set not enough for GSM

Solution 1. Allocation of 2 logical signalling points to one physical node.

SPC=A

SPC=A’

SPC=B

SPC=B’

1 LS

16 SLs

16 SLs

Solution 2.Proprietary modification (e.g. CISCO, not supported by ///).

SPC=B32 SLs

SPC=A

Solution 3. HSL – High Speed Signalling Link. Whole E1 allocated for SS7.

SPC=B16 HSLsSPC=ASS7oATMoE11 SL has 2Mbps capacityIn practice 50% is wasted by ATM1 HSL = 16 SL

SS7 Addressing

International level

National level

SP

2-20

SP

2-10

SP

2-10

SP

2-32

NI Network Indicator

0 – international net. 2 – national net.1 – not used3 – operator network (e.g. in Russia 2 – whole federation,

3 – whole republic)

SP

0-12 2-28

SP

0-10 2-23

SPC Signalling Point Code

SS7 Signalling Point Types Figure 2-10: Associated and Quasi-associated Signaling Modes

Topology guidelines

• Each SP that is not an STP is connected to at least two STPs of thelower level.

• Each STP of the lower level is connected to at least two STPs of thehigher level.

• STPs in the higher level are fully meshed (all STPs have direct link toeach other).

Figure 2-11: A Hierarchically Structured Network

SS7 Signalling Link Types (ANSI)

SP

STP

STP

STP

SP

SP

STP

STP

SP

STP

F

A

A

E

CB

B

D

D

CA – AccessB – BridgeC – Cross

D – DiagonalE – ExtendedF – Fully associated

Figure 2-12: North American Signaling Network Link Types

Message Transfer Part - MTP

5

SS7 Protocol Stack

MTP

TUP

SCCP

BSSAP ISUP

TCAP

MAP CAP/INAP

Figure 3-1: Functional Levels of the Message Transfer Part

MTP1

MTP2

MTP1

MTP2

MTP1

MTP2

MTP1

MTP2MTP1

MTP2

MTP1

MTP2

MTP1

MTP2

MTP1

MTP2

MTP 3LS

SL

Relations between MTP entities and SL

Regional Hardware& Software

Central Software

Figure 3-2: MTP Connections in an AXE Exchange

Figure 3-3: Traditional MTP versus ATM-based MTP

Figure 3-4: Message Processing on High-speed Signaling Links

Signal UnitFigure 3-5: MTP Signal Unit Formats

• MSU - Message Signal Unit

(LI = 3 ÷ 63) is used to carry upper layer messages protocol messages.

• LSSU - Link Status Signal Unit

(LI = 1 or 2) is used to start up the link and in case of failures.

• FISU - Fill-In Signal Unit

(LI = 0) is used for error supervision (it carries only error correction fields. It is sent when in the transmission buffer there is nothing else to be sent to keep the link running.

Figure 3-6: Bit Stuffing and De-stuffing

MTP L2: FSN, BSN, FIB and BIB usage

request for retransmission

retransmission

FSN=1 BSN=1 FIB=0 BIB=0









sequence error

positive ack.

MTP L2: FSN, BSN, FIB and BIB usageBackward Indicator Bit (BIB)

The BIB (1 bit) marks the signal unit as:

• Positive acknowledged if the logical value of the BIB bit is the same as that received in the latest signal unit.

• Negative acknowledged if the value of BIB is not equal to the value in the latest received signal unit.

Forward Indicator Bit (FIB)

• If the logical value of the FIB is equal to the one in the previous signal unit, the receiver is informed that the signal unit is sent for the first time.

• If the logical value of FIB is not equal to the one in the previous signal unit, the receiver is informed that it is a repetition of a previously sent signal unit.

Service Information OctetFigure 3-7: Service Information Octet

Signalling Information Field

DPC

CKF SIO LI FSN BSN FSIF

OPCCICISUP message

OPC Originating Point Code

DPC Destination Point Code

SLS Signalling Link Selection -> SLC (used for load sharing)

CIC Circuit Identity Code

ISUP ISDN User Part

routing label

SLS

6

MTP routing labels

Signalling information CICSLS OPC DPC

14 bits 14 bits

Management information SLS OPC DPC

4 bits

12 bits

Signalling information CIC OPC DPCSLS

Signalling information OPC DPCSLS

4 bits

MTP management messages (label type A):

TUP messages (label type B):

ISUP messages (label type C):

SCCP messages (label type D):

Status Field in the LSSU Figure 3-7: Service Information Octet

Alignment procedure

LSSU (SIO)

LSSU (SIN/SIE)

LSSU (SIOS)

Out of alignment (HELLO)

Normal/Emergency (faster) alignment

Proving period

Normal Operation

Out of Service (e.g. link failure, cannot transmit/receive MSU, due to other

reasons than processor outage)

FISU

Alignment Error Rate Monitor

AERM

Emergency 0.5s ≤1 error

Normal 8.2s ≤4 errors

If proving is aborted M (M=5) times, the link is returned to the out-of-service state.

Recommendation:

In each LS one SL shouldoperate in emergency mode.At restart of the SP, all routesbecome available very quickly

SP SP

SP

LS SIO

SIE

Figure 3-12: Signal Unit Error Rate Monitor

Processor outage Problems at a functional level higher than MTP level 2 preclude utilisation of the link.

MSU/FISU

MTP3

MTP2← LSSUs (SIPO)

FISUs →

MTP3

MTP2MSU/FISU

RxTx RxTxLSSU (SIB)

Re-Tx Re-Tx

BSN, BIB - stop

LSSU (SIB)RxTx Re-Tx

BSN, BIB - stop

link faulty

First SIB reception T6 (3-6s)

SIB reception -> restart T7 0,5÷2s)

T5 (80-120ms)

T5 (80-120ms)

Congestion in the receiver buffer

Figure 3-9: Overview of the Signaling Link Functions (level 2)

Figure 3-10: SU Acceptance Procedure

Signalling Network – MTP 3

Signalling Network functions

• Signaling Message Handling

• Signaling Network Management

Traffic handling sub-functions

• Message Routing

• Message Discrimination

• Message Distribution

Figure 3-13: Overview of the Signaling Network Functions

Figure 3-14: Signaling Message Handling Overview

Figure 3-15: MTP SIF Fields: Routing Labels and User Information

7

International Signalling Point Codes (ISPC)

Zone identification Area/network identification Signalling point identification

3 bits 8 bits 3 bits

Signalling Area/Network Code (SANC)

Zone identification

•7 – South America•5 – Australia, South East Asia•3 – North and Central America

•6 – Africa•4 – Asia and Middle East•2 – Europe

7-096 – Uruguay3-136 – Cuba

7-060 – Chile3-128 – Bahamas

7-048 – Brazil3-020 to 3-059 – USA

2-144 – Ireland

5-102 – Tuvalu6-110 – South Africa4-120 – China2-124 to 2-131 – Germany

5-050 – Singapore6-092 – Madagascar4-108 – Hong Kong2-080 to 2-081 – Sweden

5-040 – Thailand6-078 – Kenya4-080 – Japan2-072 – UK (Mercury)

5-010 – Australia6-010 – Tunisia4-040 Saudi Arabia2-068 – UK (BT)

5-004 – Malaysia6-004 – Egypt4-008 – India2-004 – Greece

MTP RoutingFigure 3-16: MTP Routing Table Example

Link Set identification

SP2-20

SP2-30

LS=2-30 LS=2-20

Figure 3-17: Load Sharing of Message Signal Units

Load SharingLoad sharing within a LS - Always applied, uses the least significant part of the SLS field.

Load sharing between LSs - one method, commonly used, can be applied by using a specific Load SHaring Bit (LSHB) in the SLS field (each signalling route set usually needs no more than two LSs).

Load SharingSLS is selected by upper layer protocols (ISUP, SCCP) that control load Sharing. Often SLS values are changed one-by-one.

In case of „sequence-sensitive” protocol Load Sharing is disabled in orderto cope with variable delays in different Signalling Links (loss of sequence)

IAM

ACM

CPG

ANM

SLS=Xfixed = lower bits of CIC

problem

Signalling Network Management

Signalling traffic management:

Signalling link management:

Signalling route management:

changeover, changeback, forced rerouting, controlled rerouting, MTP restart, management inhibiting, signalling traffic flow control

signalling link activation, restoration and deactivation, link set activation, automatic allocation of signalling terminals and signalling data links

transfer-controlled procedure, transfer-prohibited procedure, transfer-allowed procedure, transfer-restricted procedure, signalling-route-set-test procedure, signalling-route-set-congestion test procedure

Status of signalling link

available

failed or inactive;

blocked

(failed or inactive) and blocked

inhibited

inhibited and (failed or inactive)

inhibited and blocked

(failed or inactive), blocked and inhibited

unavailable:

Signalling link status:

Inhibited – may be

automatically

restored

Blocked – may only

be manually (by command) restored

Status of signalling route

Restricted – priority is decreased automatically. Faces some

problems, but still able to carry traffic.

Status of signalling routes:

available

restricted

unavailable

Status of signalling point:

available

unavailable

Status of signalling point

8

Congestion thresholds (international network)

Tx Re-Tx

congestion onset thr.congestion abatement thr.

Congestion thresholds (national network – available in ANSI)

Tx Re-Tx

cong. level 3 onset thr.cong. level 3 abatement thr.



cong. discard level 3 thr.



Congested Signalling Route Set (international network)

A

B

C

D

Route #1

Route #2

SL congested

SR congested

SRS congested

SL congestion -> SR congestion -> SRS congestion

Congested Signalling Route Set (international network)

A

B

C

D

Route #1

Route #2

SL congested

TFC

L4 SRS towards D congested

(congestion status not retained at level 3)

TFC Transfer Control

Signalling Link Changeover

COA SLC=0 FSN=123

Re-TxTx

MSU 123

MSU 124

MSU 125

MSU 126

Re-TxTx

MSU 72

MSU 73

MSU 74

MSU 75

MSU 76

MSU 77

MSU 78

Re-TxTx

MSU 81

MSU 82

MSU 83

Re-TxTx

MSU 64

MSU 65

MSU 66

MSU 67

MSU 68

unavailable

COO SLC=0 FSN=81

MSU 69

Changeover Order (CCO) Changeover Acknowledgement (COA)Diverted traffic has no priority in relation to normal traffic already conveyed on the SL.

Figure 3-21: Changeover Procedure

Figure 3-20: Fault in Local Signaling Link (SL)

Emergency Signalling Link Changeover Due to Signalling Terminal failure it may be impossible to determine FSN of the last MSU accepted over the unavailable link.

COA SLC=0 FSN=123

Re-TxTx

MSU 123

MSU 124

MSU 125

MSU 126

Re-TxTx

MSU 72

MSU 73

MSU 74

MSU 75

Re-TxTx

MSU 81

MSU 82

MSU 83

Re-TxTx

MSU 64

MSU 65

MSU 66

MSU 67

MSU 68

unavailable

ECO SLC=0

Figure 3-22: Emergency Changeover Procedure

9

Time-controlled changeover

Time-controlled changeover is initiated f any (or several) of the

following cases apply:

• No signalling path exists between the two ends of the unavailable link, so that the exchange of changeover messages is impossible.

• Processor outage indication is received on a link. In this case, if the remote processor outage condition is only transitory, sending of a changeover order could result in failure of the link.

• A SL currently carrying traffic has been marked (locally or remotely) inhibited. In this case, time controlled changeover is used to divert traffic for the inhibited link without causing the link to fail.

Traffic is transmitted via a new SL after expiry of a time T1 (500 to 1200 ms) in order to reduce the probability of message mis-sequencing.

If no changeover message in response to a CC0 is received within a timer T2 (700 to 2000 ms), new traffic is started on the alternative SL.

Figure 3-23: Changeover Procedure on No Response to COO

Signalling Link Changeback

CBA

CBDSPSP

ChangeBack Declaration (CBD)

ChangeBack Acknowledgment (CBA)

Forced Rerouting Procedure

A

Y

Z

X

�

�

�

� TFP (x)

� Destination X:

Route Y, unavailable

Route X, available

Figure 3-24: Fault on SL between A and B

Transfer Prohibited (TFP)

Case 1

RST every30s

Route Set Test (RST)

Figure 3-25: Forced Rerouting Procedure

TFP procedure (case 2 –broadcast method)

X

Destination X:


Route Z, available

B

A

C

Y

Z

TFP (x)

TFP procedure (case 3 – response method)

A

Y

Z

X

MSU X

Destination X:


Route Z, available

TFP (x)

Controlled Rerouting (case 1)

A

Y

Z

X

�

�

�

Destination X:

Route Y, available

Route X, available

Figure 3-26: Fault on SL between A and B Repaired

Figure 3-27: Controlled Rerouting Procedure

� TFA (x)

Transfer Allowed (TFA)

RST

10

Controlled Rerouting (case 2)

A

Y

Z

X

�

�TFR (x)

�

Destination X:

Route Y, restricted

Route Z, available

Link Management Procedure• Signaling link activation

Activates the SL at the operator’s request.

• Signaling link restoration

Performs an attempt to restore (activate) a faulty SL.

• Signaling link deactivationDeactivates the SL at the operator’s request. Can be performed even if the SL is in service.

•· Signaling link emergency restart

If the entire LS fails, the resource management indicates an “emergency” situation for all links in the group. In this case a restoration of each link is started and level 2 uses the short alignment period.

Link inhibiting

X Y

SL 0 unavailable, locally inhibited

SL 1 available

management system

LIN

LIA

SL 0 unavailable, remotely inhibited

SL 1 available

Inhibiting – disabling traffic for testing/troubleshooting purposes.e.g. too many changeovers and changebacks in a short time

Link Inhibit Message (LIN)

Link Inhibit Acknowledgement (LIA)Link Inhibit Denied (LID) - inhibiting will result in a destination becoming inaccessible

Link uninhibiting

X Y

SL 0 unavailable, locally inhibited available

SL 1 available

management system /

signalling routing control function

LUN

LUA

SL 0 unavailable, remotely inhibited available

SL 1 available

Link Uninhibit (LUN)

Link Uninhibit Acknowledgement (LUA)

Link Forced Uninhibit (LFU) - Signalling routing control will initiate SL uninhibit if an inhibited link is found to be a member of a LS in a route to a destination which has become inaccessible.

Signalling Link Test

SLTM

SLTA

A B

Signalling Link Test Message (SLTM) – initiates test. Sent every T2 (30-90s)

Signalling Link Test Acknowledgement (SLTA)

Fault Indication

A test run is unsuccessful if the following events occur:

• SLTA is not received within 10 seconds on the SL that has sent the corresponding SLTM.

• The bit pattern in the received SLTA does not agree with thebit pattern in the sent SLTM.

• The SL is indicated faulty if two consecutive tests fail.

Policing

STP Policing

• OPC restricted, all DPCs allowed• DPC restricted, all OPCs allowed• Both OPC and DPC restricted

SNM Policing – support for STM Policing. Limits the use of SNM messages.

Figure 3-28: Communication between Layers and Nodes

11

Signaling Transport in ATM Networks - SAAL

Figure 4-1: Broadband and Narrowband SS7 protocol stacks

Asynchronous Transfer Mode ATM

Figure 4-2: ATM cell format

Figure 4-3: The use of AALs

Figure 4-4: ATM Adaptation Layer type 1

Figure 4-5: ATM Adaptation Layer type 5

Figure 4-6: Message Transfer Part Functional Levels

Figure 4-7: AAL Architecture

• Segmentation and Reassembly sublayer (SAR)The SAR is responsible for the segmentation of the CS ProtocolData Unit (PDU) into 48 octet ATM SDUs.

• Convergence Sublayer (CS)The CS is responsible for adding information to the user-data,allowing acceptable recovery at the exit point of the ATMnetwork.

ATM Adaptation Layer for Signaling on the Network-to-Network Interface, (SAAL-NNI)

Figure 4-7: AAL Architecture

Common Part Convergence Sublayer (CPCS)

Performs functions that are common to all users of the specificAAL type (e.g. compressed voice and compressed video)

Service Specific Convergence Sublayer (SSCS)

Performs functions that are specific to the user application.

In SAAL – NNI the two lower sublayers SAR & CPCS are the same as inAAL5

SERVICE SPECIFIC CONNECTION-ORIENTED PROTOCOL (SSCOP)

SSCOP – almost the same capabilities as MTP-2, adaptedto broadband ATM transport

Figure 4-8: SSCOP Functions

Figure 4-9: SSCOP PDUs

Figure 4-10: Sequenced Data PDU

Invalid PDU :

· Has an unknown PDU type code· Is not 32 bit aligned.· Is not the proper length for a PDU of the stated type.

and should be discarded.

SSCOP PDU fieldsN(S) - functionally similar to the MTP-2 Forward Sequence Number (FSN).

Information field - in SD, MD or UD PDUs (upper layer info).

N(PS) - in POLL PDU, incremented each time a POLL PDU is sent

N(R) - although there is no explicit field like (BSN) receiver still maintains a variable containing the next in-sequence N(S) expected. Sent in STAT and USTAT PDUs

N(MR) - receiver window advertisement. Sent in STAT, STAT, RS, RSAK, ER, ERAK, BGN and BGAK

Source (S) bit - set (1) when the connection was released by the SSCOP entity. Sent in END PDU.

N(SQ) - incremented every time a new connection is initiated. Used by SSCOP entities to detect duplicate BGN, RS, or ER PDUs.

PDU Type field, PAD, Pad Length (PL)

SSCOP FUNCTIONSFigure 4-11: Connection Establishment and Release

Figure 4-12: SSCOP Error Free Operation

Figure 4-13: Error Correction using USTAT

Figure 4-14: Error correction using STAT

Figure 4-15: Coding of STAT element lists

Flow Control

N(MR) - For example, if the sender’s N(S) is 23 and the receiver Sets N(MR) to 87, the sender is permitted to send PDUs 23..86 Without further acknowledgement.

Keep Alive

No FISU. Heartbeat mechanism POLL->STAT

12

SERVICE SPECIFIC CONTROL FUNCTION (SSCF)

Figure 4-16: SSCF Functions

ISDN User Part - ISUP

ISUP Function

Figure 6-8: ISUP Message Structure Overview

ISUP is responsible for providing the necessary signalingcapability between exchanges in order to support the handling of the basic and supplementary ISDN services.

ISUP Message structure

Optional Part

Mandatory Variable Part

Mandatory Fixed Part

Message Type Code

Circuit Identification Code (CIC)

Routing label

CIC and SLS

CIC

SLS

4 bits

LSB

Ensures the in-sequence delivery of all messages related to a particular connection

Interaction between ISUP and MTP loadsharing

2-20

2-30

2-31

2-50

12-31

12-302-50

PriorityLSDPC

SLS=x0xx

SLS=x1xx

LSHB

SLS=xx00 SLS=xx01 SLS=xx10 SLS=xx11

path (message with SLS=1010)

CIC=0x1010

All the messages related with connection on CIC=0x1010 between exchanges 2-20 and 2-50 are exchanged under normal conditions over the same SLs and LSs.

Circuit Identity Code (CIC) format

CIC (most sig. bits)octet 2

CIC (least significant bits)octet 1

12345678Bit

Spare

For international applications, the four spare bits of the CIC field are reserved for CIC extension, provided that bilateral agreement is obtained before any increase in size is performed. For national applications, the four spare bits can be used as required.

13

Handout: ISUP message types

Formatting Principles

Figure 6-9: An IAM Example Message

Figure 6-3: Information Elements in an IAM Message

Call Setup

BA

Setup

CICB-no

IAM

Selection of outgoing route

BA

SetupB-no ?

called party numberconnection type required,network signalling capability required

CIC allocation (example)

CIC

=1

CIC

=2

CIC

=3

1

CIC

=3

2

CIC

=6

2

A B

A’B’

IAM (CIC=54)

2-11 2-10IAM (CIC=54)

ACM (CIC=54)

IAM (CIC=22)

Dual Seizure

Automatic repeat attempt

A B

�IAM�IAM

�!#$??

�IAM

�ACM�ACM

Params. in Initial Address Message -National/international call indicator

A B

IAM IAM IAM

national nationalinternational international

nat/international nat/international international

End-of-pulsing signal

IAM

A

Called Address Signals:

48323764433F

Removal of CC at last international exchange

A B

IAM IAM IAM


48323766305 32376630548323766305

Network protection timerIAM

A

T7 (20-30s)ind.

no ACM/CON/…

Completion of transmission path

� IAM

A B

� Setup� Setup

� ACM � Alerting� Alerting

� Answer� ANM Connect

� �

�

Figure 6-2: En-bloc, Non-auto Answer Call Set-up and Disconnection

14

Subsequent Address Messages (SAM)

A B

IAM(48)


004832376630

5

national

IAM(4832)SAM(32)IAM(4832)

SAM(3766) SAM(3766) SAM(3766)IAM

(48323766)

SAM(305) SAM(305) SAM(305) SAM(305)

Figure 6-4: Overlap, Non-auto Answer Call Set-up and Disconnection

Message Segmentation

IAM / ACM / CPG / CON

>272 octets

272 octets

IAM / ACM / CPG / CONSGM

simple segmentation indicator

Unsuccessful set-up

A B

IAM IAM

tones/ ann. RELREL

RLCRLC

causecause

A B

IAM IAM

tones/ ann. RELREL

RLCRLC

ACMACM cause

cause

CASE 1

CASE 2

Address incomplete (1)

A B

IAM IAM

tones/ ann.

c

RELREL

RLCRLC

cause: address

incomplete

cause: address

incomplete

(4832376630F) (4832376630F)

Address incomplete (2)

A B

IAM(48)

004832

IAM(4832)SAM(32)IAM(4832)

T35 (15-20s)RELRELREL

cause: address

incomplete

cause: address

incomplete

RLC RLC

cause: address

incomplete

RLCtones…

Call release

A B

REL

RLC

REL

RLC

on-hook/ disconnect

conversation

15

Suspend/resume (T6/T38 expires) Figure 6-6: Suspend/Resume Procedure

A B

SUS

REL

SUS

REL

on-hookT6 (1-2 min)

conversation

Propagation delay determination

A B

IAMpropagation delay counter = d1+d2

ACM/CONcall history information

= d1+d2+d3+d4

d1 d2 d3 d4

IAMpropagation delay

counter = d1+d2+d3

ACM/CONcall history information

= d1+d2+d3+d4

Echo (2-wire/4-wire hybrids)

2

2

2 2

trunk networkaccess network access network

ECHO

Echo (acoustic feedback) & (crosstalk in the handset cord)

IHECD and OHECD

2

2

2 2

trunk networkaccess network access network

A B

OHECD

IHECD

Incoming Half Echo Control Device IHECD

Outgoing Half Echo Control Device

Echo control procedure (decision in originating exchange)

A B

OHECD

IHECD

�

IHECD may be needed

IAM(OHECD included)

IAM(OHECD included)

IAM(OHECD included)

�

IHECD may be needed

IHECD may be needed

�

ACMACMACM �

�

(IHECD included, OHECD not included, OHECD requested)



16

Echo control procedure (decision in terminating exchange)

A B

OHECD

IHECD

IAM(OHECD not included)



� �

ACM(IHECD included, OHECD included,

OHECD requested)

ACMACM ��

OHECD may be needed

(IHECD included, OHECD included,

OHECD requested)

(IHECD included, OHECD included,

OHECD requested)

NRM(OHECD included)

NRM(OHECD included)

�

�

�(OHECD released)

�

�

�

�

�

�

(OHECD released)

NRM�

(OHECD released)

(OHECD included)

Continuity check

� IAM

continuity check required

TX

RX�

� COT

continuity check successful

�

�COT

�

Continuity check test call

� CCR

TX

RX� �

CIC mismatch

CIC

=1

CIC

=2

CIC

=0

CIC

=3

CIC

=4

CIC

=1

CIC

=2

CIC

=3

Swapped cables

DIP #1

DIP #2

Tx

Rx

TxRx

Reset of circuits

RSC

REL

GRS

GRA

Reset Circuit (RSC) – acknowledged with Release

Circuit Group Reset (GRS)Circuit Group Reset Acknowledgement (GRA)

Unreasonable messages

When a message format error (e.g. improper length, mandatory variable or start of optional parameter’s pointer points beyond themessage length) the message is discarded.

Unrecognized messages and parameters

release callXX1

discard message and send notification110

pass on message010

discard message100

pass on message000

discard message

indicator

send notification

indicator

release call

indicator

Required action

Instruction indicator

Message compatibility information parameter

Unrecognized messages and parameters

release callXXX1

1110discard message and send notification

0110

discard parameter and send notification1010

pass on parameter0010

1100discard message

0100

discard parameter1000

pass on parameter0000

discard parameter indicator

discard message indicator

send notification

indicator

release call

indicator

Required actionInstruction indicator

Parameter compatibility information parameter

17

Compatibility information missing

XXX

CFN

Message compatibility: - do not release call, - send notification, - discard message

message type non-existent or not implemented – discarded, diagnostic field = XXX

Confusion message

Signaling Connection Control Part - SCCP

Call related and call non-related signalling

Figure 12-1: Circuit-related vs. Non-circuit-related Signaling

AddressingNormally exchanges analyse B-number, which is a problem with the call non-related signalling (no B-number).

The only address available in MTP is DPC. Problem with mobilesubscribers, as national DPCs are not unique.

Additionally, to enable routing based on DPC each SP should know the routes to all SPs worldwide. Any network reconfigurationrequires updates in routing tables (manually configured).

Figure 12-14: SCCP Address Elements

Figure 12-3: SCCP in the Mobile Core Network

Global TitleE.164 numbering plan address.

GT = 46 501 563 432

SPC = 2-2745

GT = 46 501 456 501

SPC = 2-1024

GT = 46 501 767 453

SPC = 2-7038

GT = 46 501 273 454

SPC = 2-6053

2-70382-102446 501 456...

2-10242-703846 501 273...

SSPPSPGT series

Figure 12-15: Global Title Translation

SCCP & Load SharingHow to exceed LS above 16 SLs?

SPC=ASPC=B

SPC=B’

16 SLs

16 SLs

How to implement Load Sharing over 32 links?

MTP – impossibleSCTP – possible with GTT

GT48 607 0

48 607 148 607 2

48 607 348 607 448 607 4

GTRC = 1

GTRC = 2

GTRC PSP SSP1 B B’

2 B’ B

MGT Mobile Global Title

MSC HLRIMSI MGT

GT = 48 607 000 000

IMSI 260 01 221954

MGT 48 607 21954

MCC MNC MSIN

CC NDC SN

• Used in the GSM network during the registration procedure.• One-to-one relation between MCC Mobile Country Code (IMSI) and the CC Country Code.

• In MNC to NDC translation a first digit of the MSIN is taken into account because operator can use more than one NDC.

STP on the way are only analysing MGT series

In home network IMSI is used.

International STPsdo not

understand IMSI

18

SSN Subsystem Number

SPC = 2-2381GT = 49 601 000001

VLR

GMSC, MSC

HLR

AUC SSN = 10

SSN = 6

SSN = 7

SSN = 8

Result of GT translation

Termination indication (OWNSP) - The message terminates in this node.

DPC with intermediate indication - The message is sent to the next SCCPnode. The next SCCP node re-routes the message further. The DPC is used In the routing label of the message to route the message to another node forfurther GT translation. The GT is left unchanged for translation in the nextnode.

DPC with termination indication - The message is sent to the next SCCPnode. The message terminates in the next SCCP node. The DPC is used inthe routing label of the message together with the SSN of the called party address to route the message to its final destination.

Figure 12-16: Connectionless Signaling Sequence

SCCP exemplary proceduresFigure 12-26: SCCP Addressing during a Call to an MS

Figure 12-27: SCCP Addressing during Location Updating

Figure 12-28: SCCP Addressing between the MSC and the BSC

SCCP service classesFigure 12-4: SCCP Protocol Classes

Connectionless Connection oriented

SCCP CL 0 (MAP example)

This class of operation is used for ‘window size = 1’ procedures, i.e. there is never more than one message send in particular direction before the result or answer message is received from the opposite side.

MSCVLRHLR

SEND ROUTING INFORMATION PROVIDE ROAMING NUMBER

PROVIDE ROAMING NUMBERSEND ROUTING INFORMATION

GMSC

IAM

SCCP class 0, called address,

calling address


calling address


calling address

SCCP class 0,

called address, calling address

SCCP CL 0 & MTP load sharing

SCCP

MTP

00SCCP message

10SCCP message

20SCCP message

30SCCP message

40SCCP message

………

150SCCP message

00SCCP message

SLSClass

19

SCCP CL 1 (MAP example)This class of operation is used for ‘window size > 1’ procedures, i.e. there are multiple messages send in particular direction before the result or answer message is received from the opposite side (bigger portion of data).

VLR HLRMSC

UPDATE LOCATION

INSERT SUBSCRIBER DATA


UPDATE LOCATION





Class 0, called and calling address








The sameSLS


SCCP

MTP

40SCCP message

51SCCP message

31SCCP message

20SCCP message

10SCCP message

00SCCP message

60SCCP message

31SCCP message

51SCCP message

70SCCP message

31SCCP message

51SCCP message

80SCCP message

SLSClassoperations executed in

sequence

SCCP Class 2 is used across BSC-MSC interface in order to make relation between identity of the dedicated channelallocated to the MS, known by the BSC, and the identity of the MS (IMSI/TMSI), known by the MSC.

SCCP CL 2 & (BSSAP example)

Figure 12-19: Connection Establishment

Figure 12-21: Data Transfer Phase

Figure 12-23: Connection Release Phase

Figure 12-9: SCCP Messages

Figure 12-10: Parameters of Some SCCP Messages

Figure 12-11: Overview of the Structure of an SCCP Message

Figure 12-5: SCCP Service Primitives

Figure 12-6: Peer-to-peer Communication

Figure 12-7: Service Primitive - General Syntax and Examples

Figure 12-12: Detailed Structure of an SCCP Message

Figure 12-13: Unitdata (UDT) Message

Figure 12-20: Connection Establishment Data Flow

Figure 12-22: Data Transfer Data Flow

Figure 12-24: Connection Release Data Flow


SCCP

MTP

32SCCP message

42SCCP message

22SCCP message

22SCCP message

10SCCP message

00SCCP message

50SCCP message

22SCCP message

42SCCP message

32SCCP message

22SCCP message

42SCCP message

60SCCP message

SLSClassmessages belonging to

the same connection

SCCP Subsystem Status Management • Signalling Point status management (SSN=1 the whole SCCP)

- Inaccessible - Accessible - Congested

• Remote SCCP status management- Remote SCCP available,- Remote SCCP unavailable (reason unknown),- Remote SCCP unavailable (unequipped),- Remote SCCP unavailable (inaccessible).- Remote Subsystem prohibited,- Remote Subsystem allowed.

• Local Subsystem status management- In-Service- Out-Of-Service

• Subsystem status test• Broadcast

Figure 12-25: SCCP Subsystem Status Management

Base Station System Application Part - BSSAP

20

BSSAP introductionFigure 13-1: GSM infrastructure in 2G

Figure 13-2: MSC and SGSN in Pool for GSM and WCDMA

Figure 13-3: GSM access connected to Layered Architecture Core Network

Figure 13-4: BSC connectivity to the MSS infrastructure

Figure 13-5: Signaling between the MS and MSC

• Direct Transfer Application Part DTAP

Used for the transparent transfer of CM and MM messages between MS and MSC in SCCP CO mode.

• Base Station System Management Application Part BSSMAP

Used for sending of messages related to handover procedures, MS initial communication, cell or BSC management.

MSCBSC

CM, MMDTAP

BSSMAPInitial MS messages

DTAP and BSSMAP

BSSAP message format

1234÷n

DiscriminationDLCILength IndicatorCM, MM info

L3 message DiscriminationLength Indicator

123÷n

DTAP message

BSSMAP message

Discrimination

DTAP BSSMAP

DLCI

3 - SMS 0 – all other

Traffic channel assignment

MSCBSC

Assignment requestChannel activation

Channel activation ack

Assignment command

SABM

UAEstablish indication

Assignment complete Assignment

complete

Handover (A interface)

MSCBSC BSC

Handover requiredHandover request

Handover request ack.Handover command

Handover detect

Handover completeClear command

Clear complete

Other BSS Protocols and BSSAPFigure 13-5: Signaling between the MS and MSC

Figure 13-6: Overview of the Air Interface Layer 3 Functions

Figure 13-7: Example LAPDm Signaling

Figure 13-8: BSC-BTS Layer 3 Messages

Figure 13-9: BSSAP Signaling at Location Updating

BSC/TRC Application Part (BTAP)

0 1 2 3 4 5 6 7

BSC

Um A-bis

0 1 2 3 4 30 31

…

TRC

A-ter BTAP

MSC

A – TRC is transparent for BSSAP

signalling

Figure 13-10 … 13-19

21

Mobile Application Part - MAP

TCAP dialogues and transactionsFigure 14-1: TCAP – A Common Communication Protocol

Figure 14-2: TCAP in the Mobile Core Network

Binds response with request

MSC HLR

MAP req.

MAP req.

MAP req.

MAP resp.

MAP resp.

MAP resp.

Enables dialogs

MSC HLR

MAP

MAP

MAP

MAP

Begin, OTID=12

12

OTID=15Continue, DTID=12

OTID=12Continue, DTID=15

OTID – Originating Transaction IdentifierDTID – Destination Transaction Identifier

OTID=15

Emd, DTID=12

Invoke #1

Invoke #2

Result #2

Result #1

TCAP dialogues and transactionsFigure 14-3: Functional View of TCAP

CAP

INAP

MAP

TCAP

SCCP

MTP

CAP

INAP

MAP

TCAP

SCCP

MTP

dialogues

transactions

TCAP sub-layers

TCAP

MAP

TCAP

MAP

SCCP

TC_InvokeComponent #1

(MAP message)

TC_InvokeComponent #2 (MAP message)

TC_InvokeComponent #3 (MAP message)

co

mp

on

en

t su

b-la

ye

r

TC_Begin

TCAP message

Dialog ID ID ID ID

tra

nsa

ctio

nFigure 14-4: Structure of TC

Figure 14-5: TC Primitives

TCAP sub-layers

Many Upper Layer (MAP) messages may be embedded intosingle TCAP transaction

Figure 14-4: Structure of TC

TCAP message

Figure 14-12: An Embedded TCAP Message

Mobile Application Part - MAP

22

MAP StructureThere is no single node, where complete MAP functionalityis implemented.

Figure 15-1: Structure of the Mobile Application Part

ASE Application Service Entity. Functionality (set of messagescharacteristic for the particular procedure).

1982-1992 1991-1994 1994-...

GSM Phase 1

Services:• Speech• Data• Fax• SMS• International roaming• Call forwarding• Call baring

GSM Phase 2

Services:• calling line iiiidentification• call waiting• call hold• conference calling

GSM Phase 2+

Services:• interworking between iiiGSM 900, GSM 1800 iii& GSM 1900• HSCSD• EDGE• GPRS• interworking with UMTS

Figure 15-2: MAP Versions in Ericsson’s Mobile Core Network

MAP protocol fallback

HLRVLR

BEGIN Location UpdateApplication Context Name = Network Loc Up, ver 3

ABORT

Application Context Name = Network Loc Up, ver 2

Application context name not supported

BEGIN Location UpdateApplication Context Name = Network Loc Up, ver 2

I understand only ver 3

OK let’s proceed with 2

Figure 15-3: MAP Primitives Used by the MAP-CHECK-IMEI Service

Figure 15-5: MAP Messages between the MSC and EIR

MAP Services – Location UpdatingFigure 15-4: Messages in MAP version 2

„ack” – means the same

message in opposite direction

no separate „ack”

messages exist

PVLRVLR HLR

DDG

MSC

old LAI

TMSI

SEND IDENTIFICATION

SEND IDENTIFICATION ack

UPDATE LOCATION

CANCEL LOC

CANCEL LOC ack

ACTIVATE TRACE MODE

ACTIVATE TRACE MODE ack


INSERT SUBSCRIBER DATA ack

UPDATE LOCATION ack

Figure 15-6: MAP Messages at Location Updating

Roaming Management

Solution 1

ROAMINGvisited PLNM

MSC

unwanted

MSC

wanted

HLR

„black box” filters all UPDATE LOCATIONoperations from „unwanted” network

may allow access to „unwanted” networkafter predefined number of tries otherwise no coverage from „wanted” network -> no service

Xdiscarded

passed

how to cheat it?artificially generate a sequenceof many UPDATE LOCATIONoperations

Roaming Management

Solution 2

ROAMINGvisited PLNM

MSC

unwanted

MSC

wanted

HLR

„black box” only monitors and informs SIMApplication Toolkit Server

X

passed

Remote SIM control. Initially intended to facilitate GPRS configuration

„black box”

SIM

ApplicationToolkit

1

2reset preferrednetwork list(background SMS)

3„proper”

Location Update

HLR Restoration

MSCVLR HLRD

RESET

Loc Upd UPDATE LOCATION

ACTIVATE TRACE MODE

ACTIVATE TRACE MODE ack


INSERT SUBSCRIBER DATA ack

UPDATE LOCATION ack

FORWARD CHECK SS INDICATION

Figure 15-7: MAP Messages at HLR Restoration

23

MS Purging

VLR HLRD

PURGE MS

PURGE MS ack


MS Terminating Call


Basic Handover

VLRVLRMSC A MSC BE

PREPARE HANDOVER

PREPARE HANDOVER ack

PROCESS ACCESS SIGNALLING

SEND END SIGNAL

FORWARD ACCESS SIGNALLING


SEND END SIGNAL ack

Subsequent Handover

VLR

MSC AMSC B’E

SEND END SIGNAL

MSC BE

PREPARE SUBSEQUENT HANDOVER

PREPARE HANDOVER

PREPARE HANDOVER ack

PREPARE SUBSEQUENT HANDOVER ack


SEND END SIGNAL

SEND END SIGNAL ack

Subscriber Tracing

MSCVLR HLRD

Subscriber Tracing ActivationACTIVATE TRACE MODE

OMC

ACTIVATE TRACE MODE ackSubscriber Tracing Activation Acc.

Subscriber Tracing Information

Subscriber Tracing Information

Subscriber Tracing DeactivationDEACTIVATE TRACE MODE

DEACTIVATE TRACE MODE ackSubscriber Tracing Deactivation Acc.

Subscriber Deletion

VLR HLRD

Delete subscriberCANCEL LOCATION

OMC

Subscriber deletedCANCEL LOCATION ack

MO short message transfer

VLRIWMSC

SM

SC

MO FORWARD SM

MSC

SM

SM ackMO FORWARD SM ackSM ack

MT short message transfer

VLRGMSC

SM

SCMSC

SM

SM ack

SEND ROUTING INFO FOR SM

SM ack

HLR

SEND ROUTING INFO FOR SM ack

MT FORWARD SM

MT FORWARD SM ack

Vendor – specific MAP versions

Figure 15-9: Ericsson Variant MAP Compared to a Standard MAP

Figure 15-10: Extension Area and Extension Container

Handout: Message examples in ASN.1 x2 s

24

Signaling for Intelligent Networks

IN services

ACC Account Card Calling

FPH Freephone

PRM Premium Rate

UAN Universal Access Number

UPT Universal Personal Telecommunications

VOT Televoting

VPN Virtual Private Network

PNA Personal Number

UAN Universal Access Number

PPS Prepaid SIM Card

I&Bii Information & Business Service

Who’s who (VOT)

•Uses the service

•(TV viewers)•Service User

•Subscribes to the service(TV company)

•Service Subscriber

•Provides the VOT service (MIN owner)

•Service Provider

•Provides the network

•(GSM network owner)•Network Operator

Who’s who (VOT)

MSC/SSF

BSC

cell ID=11One number taxi = 800123456

SCP

�

�

trigg

er ta

xi s

ervic

e

Cell ID C-number

B-num

ber�

‘Hello’ Taxi‘Hello’ Taxi

�

Without SCP (database) routing tables should be modified in all exchanges taking into consideration their location

Similar service prompted development of IN for PSTN (freephone) in 1960s

Network architectureFigure 16-1: Intelligent Network Elements

Figure 16-2: IN in the Core Network Layered Architecture

Figure 16-3: Basic Principles of IN Call Handling

Figure 16-4: Handling of a Terminating IN Service

Figure 16-5: Handling of an Originating IN Service

Triggering

MSC

SSFVLR

GMSC

SSF HLR

MSC

A-sub category found in VLR

A

B-no

B-no

B-sub category found in HLR

B-no

CAP vs INAP

INAPIntelligent Network Application PartDedicated for PSTN

Capability Set 1 (CS1)

Capability Set 2 (CS2)

CAPCAMEL Application PartDedicated for PSTN

Phase 1

Phase 2

Phase 3

Phase 4

CAMEL Customised Application of Mobile Enhanced Logic

Figure 16-6: CAMEL Compared to CS-1 and CS-2

25

Description of CAMEL Subscriber Data

Originating – CAMEL Subscription Information

TDP List

gsmSCF address

Service Key

Default Call Handling

DP criteria

CAMEL Capability Handling

O-CSI

CSI state

Notification flag

TDP – triggering

detection pointdetermines whencontrol should be

passedto IN.

address to be used to access the gsmSCF

(E.164 number)enables roaming

indicates the service (logic to be used)

indicate whether the gsmSSF shall

request instructions from the gsmSCF

phase of CAMEL

what to do in caseof SSF error

indicates whether the O-CSI is active or not

indicates whether the change of the O-CSI shall

trigger Notification on change of Subscriber data

Example of service executionFigure 16-7: CS-1 Operations

Figure 16-8: Additional CS-1+ Operations and Extensions

Figure 16-9: Detection Points in the Basic Call State Model

Figure 16-10: Originated Call Request from a VPN Subscriber

Figure 16-11: InitialDP Operation

Figure 16-12: Response from the SCF

Figure 16-13: Event Reporting and Call Continuation

Documents

Signalling SIP SIGTRAN Overview Handout