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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. 7. 7. 6. 6. 5. 5. 4. 4. 3. 3. 2. 2. 1. 1. Transport network. Signalling network. - PowerPoint PPT Presentation
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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
1
2
3
4
5
6
7
1
2
3
4
5
6
7
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
Telephony Gateway
CS Core
(POTS, ISDN)
GSM Core
Cellular
Access
Wireless
Access
PS Core (ATM)
Telephony Gateway
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
R S T S/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 partse.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 PartASE: Application Service ElementTUP: Telephone User PartDUP: Data User PartTCAP: Transaction Capabilities Application Part ISUP: ISDN User PartSCCP: 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 sizeLock on “flag” pattern: 0111110 - 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 MessageACM: 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
AB
SS#7 - TCAP Message Structure
SS#7 - 0800 Example
SS#7 - The ITU Standard
SS#7 - The ITU Standard
SS#7 - The ITU Standard
2 Signalling messages2.1 Address 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.2.2 Answer 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
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