Download Networks concepts - EN

Telecoms Networks
Mohamed Mokdad
HES – Biel/Bienne
Agenda
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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
A real SS#7 network
Management network
Network Overlaying
The networks
Edge
Core
Access
Current architectures
Fixnet
CS Core
(POTS, ISDN)
Telephony
Gateway
PS Core (IPSS IP
Based)
Wireline
xDSL
Access
Mobile
Wireless
PS Core (ATM)
Access
Telephony
Gateway
Wi-Fi
Cellular
Access
GSM-GPRS-UMTS
GSM Core
Networks modelling
• 1 component = 1 objet
– Switch
– Access Point
– Router
• 1 objet = Σ fonctions
• 1 Dialog protocole with the object
– MIB & SNMP
ISDN Interfaces
TE1
TE2
NT2
NT1
TA
R
S
T
S/T
GSM Interfaces
TE2
MT0
BS/MSC
TE1
MT1
BS/MSC
TA
MT1
BS/MSC
MT2
BS/MSC
TE2
R
S
Um
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 2 simply monitors and reports to
the layer above. It assembles the outgoing
messages into packets known as signalling
units.
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 Messages
# of bits >
Up to 279 bytes packet size
Lock on “flag” pattern: 0111110 - zeros at both ends & 1s in the middle.
Bit stuffing could be necessary
Bit Stuffing
Byte Stuffing
MTP level 2 Messages
Backward Sequence Number (BSN).
Forward Sequence Number (FSN)
Length Indicator (LI)
Backward Indicator Bit (BIB)
Forward Indicator Bit (FIB)
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
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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#7 - 0800 Example
SS#7 - The ITU Standard
SS#7 - The ITU Standard
SS#7 - The ITU Standard
2 Signalling messages
2.1 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 semiautomatic 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