Telecoms Networks Mohamed Mokdad HES – Biel/Bienne

Agenda OSI Model Networks modelling Connection types Interfaces SS#7 –Transfer Message Part –User Parts Standards

OSI Layers dynamics

Transport network

Signalling network

A real SS#7 network

Management network

Network Overlaying

The networks Core Edge Access

Current architectures xDSL Fixnet Wireline Access GSM-GPRS-UMTS Wi-Fi Mobile PS Core (IPSS IP Based) Telephony Gateway CS Core (POTS, ISDN) GSM Core Cellular Access Wireless Access PS Core (ATM) Telephony Gateway

Networks modelling 1 component = 1 objet –Switch –Access Point –Router 1 objet = Σ fonctions 1 Dialog protocole with the object –MIB & SNMP

ISDN Interfaces NT1NT2TE1 TATE2 RSTS/T

GSM Interfaces BS/MSCMT0 BS/MSCMT1TE1 BS/MSCMT1TATE2 BS/MSCMT2TE2 UmSR

Circuit/Packet Switched? Circuit switching –1 circuit dedicated to a connection –Connection must exist before data transfer –Connection oriented Paquet switching –1 paquet can follow any connection –Connection doesn’t exist before data transfer –Connectionless

Interconnexion PTS (Provider of Telecom Services) –What is it? Interconnexion –Transport –Signaling –Billing TDM & IP voice services interconnection –Présentation and discussion

SS#7 example = CCBS ?

SS#7 Architecture - STP examines the destination of messages it receives, consult a routing table, and send the messages via Cross Links - C links.

SS#7 Architecture - SEP End point in the SS#7 in the same way that a telephone is an end point in the PSTN. This is located in the local switch and is addressed by the Signalling Point Code. These are linked via Access Links - A links.

SS#7 Architecture – B&D Links Bridge Links - B links - connect 2 STPs in a redundant way and at the same hiercharchy level.

SS#7 Architecture – D Links

SS#7 Architecture – E Links Extended links - E links – can be connected for redundancy and reliability reasons to another pairs of STPs.

SS#7 Architecture – F Links SEP can be providing services to another SEP (data, special processing, data concentration, etc.). Connection is made via Fully Associated Links – F Links.

SS#7 - The Userparts Possible Future extentions.

Mapping OSI-SS#7

The Layered Model Different networks can share common resources. e.g. “transport mechanism” for signalling New specific user parts e.g. MAP integration afterwards Easier protocol conversions and encapsulation in different networks, e.g. not just SS#7, but genrally speaking

SS#7 - Userparts OMAP: Operations, Maintenance and Administration Part ASE: Application Service Element TUP: Telephone User Part DUP: Data User Part TCAP: Transaction Capabilities Application Part ISUP: ISDN User Part SCCP: Signalling Connection Control Part MTP: Message Transfer Part

OSI-Primitives

OSI-Primitives - 2

Message Transfer Part MTP level 1 considers the links, the control of clocking, and all of the physical considerations of sending messages over wires. Electrical Design Engineers job. No interest for software designers MTP level 2 simply monitors and reports to the layer above. It assembles the outgoing messages into packets known as signalling units.

MTP level 2 Messages Up to 279 bytes packet size Lock on “flag” pattern: zeros at both ends & 1s in the middle. Bit stuffing could be necessary # of bits >

Bit Stuffing

Byte Stuffing

MTP level 2 Messages Backward Sequence Number (BSN).Backward Indicator Bit (BIB) Forward Sequence Number (FSN)Forward Indicator Bit (FIB) Length Indicator (LI)

MTP 2 - Transmission

MTP 2 – Basic Error Correction

Basic Error Correction When the packet is received at the transmitting side the difference in the FIB and the BIB trigger a series of actions: –Transmission is stopped. –Messages beginning with FSN #19 are retransmitted in sequence. –Messages which were in the buffer before FSN #19 are deleted. –Transmission begins again

MTP 2 - Frames

SS#7 – MTP level 3 Signalling Network Management (SNM) Signalling Message Handling (SMH) Major part of the job of Level 3 is to control traffic on the traffic resources over which it has control, e.g. congestion, redirection, changeover, changeback

Signalling Network Management Force Rerouting Controlled Rerouting Changeover Changeback MTP Restart

Signalling Message Handling

Userparts SCCP: Signalling Connection Control Part –Sequence control and delivery ISUP: ISDN User Part –Digital networks TUP: Telephone Users Part –Analog telephony DUP: Data Users Part –Data

Architecture

Stack & message coding

ISUP Example

SS#7 - Call Setup IAM: Initial Address Message ACM: Address Complete Message - Switch can alert - Off Hook: ANM: ANswer Message - All switches connect the path - Busy: The caller can release - REL - the call setup

SS#7 – Call Release REL – Release - and – RLC – Release Complete

SS#7 - Simple Call Setup

RingBack Tones

SS#7 - More complete Figure

SS#7- IAM Fields

SS#7 - TCAP Queries SS#7

SS#7 - ISDN SS CCBS SS#7 A B

SS#7 - TCAP Message Structure

SS# Example

SS#7 - The ITU Standard

2Signalling messages 2.1Address Complete Message (ACM): A message sent in the backward direction indicating that all the address signals required for routeing the call to the called party have been received. 2.2Answer message (ANM): A message sent in the backward direction indicating that the call has been answered. In semi- automatic working, this message has a supervisory function. In automatic working, this message is used in conjunction with charging information in order to: –start metering the charge to the calling subscriber (see Recommendation Q.28 [2]); and –start measurement of call duration for international accounting purposes (see Recommendation E.260 [3]).

SS#7 - The ITU Standard 2.46Unequipped Circuit Identification Code message (UCIC): A message sent from one exchange to another when it receives an unequipped circuit identification code. 2.47User Part Available message (UPA): A message sent in either direction as a response to a user part test message, to indicate that the user part is available. 2.48User Part Test message (UPT): A message sent in either direction to test the status of a user part marked as unavailable for a signalling point. 2.49User-to-user information message (USR): A message to be used for the transport of user ‑ to ‑ user signalling independent of call control messages.

SS#7 and IP SIGTRAN –SIGnalling TRANsport SCTP –Stream Control Transport Protocol Interworking SS#7 and MGCP –Media Gateway Control Protocol

SIGTRAN Stack

SCTP

IMS or some thing else Which one to use –SIGTRAN? –SS#7? –IMS? 3GPP Signalling –Also valid for VoIP (SIP) IMS –IP Multimedia Subsystem