TSS-Lecture-09-SS7-1.pdftransmission and switching systems in engineering

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1. Unit-09:
Signaling System 7
Department of Telecommunication, MUET UET Jamshoro 1
Transmission and Switching Systems Dr. Abdul Latif

2. SS7 signaling
•WhatisSignaling?
–Signalingreferstotheexchangeofinformationbetween
callcomponentsrequiredtoprovideandmaintainservice.
•Signalingisofthreetypes.
Department of Telecommunication, MUET UET Jamshoro 2
Transmission and Switching Systems Dr. Abdul Latif
Sub-Exch Inter Exch WithinExch
CAS CCS7
Signaling

3. SS7 signaling
•CAS
•SS7
Department of Telecommunication, MUET UET Jamshoro 3
Transmission and Switching Systems Dr. Abdul Latif

4. SS7 signaling
•Signaling is done to:
➢Establish Call
➢Billing
➢Routing
➢Info exchange function of PSTN
•Signaling information for many voice channels is combined
onto one signaling channel which is effectively a data channel.
Department of Telecommunication, MUET UET Jamshoro 4
Transmission and Switching Systems Dr. Abdul Latif

5. SS7 signaling
•Out of band signaling.
•Allows fast allocation, test, and release of circuits
•Fast call setup: from 15-20 to 3-5 seconds
•Efficient routing
•Supports Intelligent Network services
•Bandwidth allows for signaling at any time
•Allows signaling to network elements to which there is no
direct trunk connection
•High-speed packet data switching
Department of Telecommunication, MUET UET Jamshoro 5
Transmission and Switching Systems Dr. Abdul Latif

6. Out of band signaling
•Out-of-band signaling is signaling that does not take place
over the same path as the conversation.
•Out-of-band signaling has several advantages that make it
more desirable than traditional in-band signaling.
➢Allows signaling at any time in the entire duration of the
call
➢Allows for the transport of more data at higher speeds.
➢Enables signaling for NE that have no direct signaling
links.
Department of Telecommunication, MUET UET Jamshoro 6
Transmission and Switching Systems Dr. Abdul Latif

7. SS7 Network Architecture
Department of Telecommunication, MUET UET Jamshoro 7
Transmission and Switching Systems Dr. Abdul Latif
SS7 Network
Architecture
Signaling
Elements
Signaling
Links

8. SS7 Network Architecture
•C7 Network can have three different types of architectures.
•Associated Signaling N/W Architecture
➢path is allocated between each interconnected pair of
switches as the signaling link.
➢Simple, economic and easy to control.
Department of Telecommunication, MUET UET Jamshoro 8
Transmission and Switching Systems Dr. Abdul Latif

9. SS7 Network Architecture
•Non-Associated Signaling N/W Architecture
➢Separate paths for speech and control information
➢Network topologies for speech and signaling are different
➢Flexible from routing point of view
Department of Telecommunication, MUET UET Jamshoro 9
Transmission and Switching Systems Dr. Abdul Latif

10. SS7 Network Architecture
•Quasi-Associated Signaling N/W Architecture
➢Signaling messages are sent through one intermediate node
for short distances.
➢Simplified predetermined paths between exchanges.
➢The signaling paths are not associated but are fixed for
given speech connections.
Department of Telecommunication, MUET UET Jamshoro 10
Transmission and Switching Systems Dr. Abdul Latif
Fig. 7.10. Three modes of CCS signaling

11. SS7 Network Architecture
•It consists of three essential parts:
•Signal switching points (SSPs)
➢telephone switches which originate, terminate and switch
calls
•Signal transfer points (STPs)
➢packet switches that receive and route signaling messages
based on routing information contained in messages
➢It may perform global title translation (GTT)-a procedure
by which the destination signaling point is determined from
digit present in the signaling message.
•Signal control points (SCPs)
➢SCP’s are databases that provide information necessary for advanced
call processing capabilities in Intelligent Networks (IN).
Department of Telecommunication, MUET UET Jamshoro 11
Transmission and Switching Systems Dr. Abdul Latif

12. SS7 Service Switching Point
Department of Telecommunication, MUET UET Jamshoro 12
Transmission and Switching Systems Dr. Abdul Latif

13. SS7 Signaling Transfer Point
•It is “Router” for SS7
signaling.
•It simplifies network
topologies.
Department of Telecommunication, MUET UET Jamshoro 13
Transmission and Switching Systems Dr. Abdul Latif

14. SS7 Service Control Point
•The SS7 node delivers
following services to
network:
•Database Services
–Caller Name database
(CND)
–Home Location Register
(HLR)
–Toll Free Number
database
•Messaging services
Department of Telecommunication, MUET UET Jamshoro 14
Transmission and Switching Systems Dr. Abdul Latif

15. SS7 Network Architecture
Department of Telecommunication, MUET UET Jamshoro 15
Transmission and Switching Systems Dr. Abdul Latif

16. SS7 Network Architecture
Department of Telecommunication, MUET UET Jamshoro 16
Transmission and Switching Systems Dr. Abdul Latif

17. SS7 Network Architecture
Department of Telecommunication, MUET UET Jamshoro 17
Transmission and Switching Systems Dr. Abdul Latif
SS7 Signaling Links
A linksB linksC linksD linksE linksF links

18. SS7 Signaling Types
Department of Telecommunication, MUET UET Jamshoro 18
Transmission and Switching Systems Dr. Abdul Latif
•A links
➢An "A" (access) link connects a signaling end point (e.g.,
an SCP or SSP) to an STP.
➢Only messages originating from or destined to the signaling
end point are transmitted on an "A" link.
•B links
➢A "B" (bridge) link connects an STP to another STP.
Typically, a quad of "B" links interconnect peer (or
primary) STPs (e.g., the STPs from one network to the
STPs of another network).
➢The distinction between a "B" link and a "D" link is rather
arbitrary. For this reason, such links may be referred to as
"B/D" links.

19. SS7 Signaling Types
Department of Telecommunication, MUET UET Jamshoro 19
Transmission and Switching Systems Dr. Abdul Latif
•C links
➢A "C" (cross) link connects STPs performing identical
functions into a mated pair.
➢A "C" link is used only when an STP has no other route
available to a destination signaling point due to link
failure(s).
➢Note that SCPs may also be deployed in pairs to improve
reliability; unlike STPs, however, mated SCPs are not
interconnected by signaling links.

20. SS7 Signaling Types
Department of Telecommunication, MUET UET Jamshoro 20
Transmission and Switching Systems Dr. Abdul Latif
•D links
➢A "D" (diagonal) link connects a secondary (e.g., local or
regional) STP pair to a primary (e.g., inter-network
gateway) STP pair in a quad-link configuration.
➢Secondary STPs within the same network are connected via
a quad of "D" links.
➢The distinction between a "B" link and a "D" link is rather
arbitrary. For this reason, such links may be referred to as
"B/D" links.

21. SS7 Signaling Types
Department of Telecommunication, MUET UET Jamshoro 21
Transmission and Switching Systems Dr. Abdul Latif
•E links
➢An "E" (extended) link connects an SSP to an alternate
STP.
➢"E" links provide an alternate signaling path if an SSP's
"home" STP cannot be reached via an "A" link.
➢"E" links are not usually provided unless the benefit of a
marginally higher degree of reliability justifies the added
expense.

22. SS7 Signaling Types
Department of Telecommunication, MUET UET Jamshoro 22
Transmission and Switching Systems Dr. Abdul Latif
•F links
➢An "F" (fully associated) link connects two signaling end
points (i.e., SSPs and SCPs).
➢"F" links are not usually used in networks with STPs.
➢In networks without STPs, "F" links directly connect
signaling points.

23. SS7 Network Architecture
Department of Telecommunication, MUET UET Jamshoro 23
Transmission and Switching Systems Dr. Abdul Latif

24. SS7 Protocol Stack
•The hardware and software functions of the SS7 protocol are
divided into different functional "levels".
Department of Telecommunication, MUET UET Jamshoro 24
Transmission and Switching Systems Dr. Abdul Latif

25. Message Transfer Part (MTP)
•Responsible for reliable transfer of signaling
message between users.
•Consists of three levels
➢Level 1 for signaling data link connection
➢Level 2 for signaling link functions
➢Level 3 for signaling network functions
Department of Telecommunication, MUET UET Jamshoro 25
Transmission and Switching Systems Dr. Abdul Latif

26. Message Transfer Part (MTP)
•Level 1
➢Deals with physical characteristics of data link.
➢Defines physical and electrical characteristics of the
signaling links.
➢Utilizes DS-0/E1 channels to carry signaling data at the rate
of 56 kbps or 64 kbps.
•Level 2
➢Provides data link layer functionality ensuring that the two
endpoints are reliably exchanging signaling messages.
➢It incorporates capabilities such as error checking, flow
control and sequence checking.
Department of Telecommunication, MUET UET Jamshoro 26
Transmission and Switching Systems Dr. Abdul Latif

27. Message Transfer Part (MTP)
•Level 3
Its functions are divided into two parts.
➢Message handling function involves
❖Discrimination- filters messages
❖Distribution- directs messages to correct destination
❖Routing-directs messages to correct signaling link
➢Network Management Function involves
❖Traffic management
❖ Route management
❖ Link management
Department of Telecommunication, MUET UET Jamshoro 27
Transmission and Switching Systems Dr. Abdul Latif

28. Telephone User Part (TUP)
•Uses messages to control circuit related activities like
➢Call setup
➢Supervision
➢Call release
•TUP is now replaced with ISUP for all basic operations of
non-ISDN and ISDN subscriber
•Can handle analog circuits only.
Department of Telecommunication, MUET UET Jamshoro 28
Transmission and Switching Systems Dr. Abdul Latif

29. ISDN User Part (ISUP)
•Performs all functions of TUP
•Used for both ISDN and Non ISDN calls
•Supports 3 classes of services
➢Bearer services / data services
➢Tele services
➢Supplementary services
•Defines the messages and protocols used in the establishment
and release of voice and data calls.
Department of Telecommunication, MUET UET Jamshoro 29
Transmission and Switching Systems Dr. Abdul Latif

30. Signaling Connection and Control Part (SCCP)
•Provides capability for:
➢Set up of logical signaling connection
➢Release of logical connection
➢Transfer of data with or without logical signaling
connection
•Global Title Translation (GTT)
➢Global Title is an address which is translated by SCCP into
DPC & subsystem number (application number within a
node)
•Supports both connection-oriented and connectionless services
Department of Telecommunication, MUET UET Jamshoro 30
Transmission and Switching Systems Dr. Abdul Latif

31. Signaling Connection and Control Part (SCCP)
•Connection oriented services are characterized by
➢Two way exchange of data
➢Data sent in sequence
➢Reliable
➢Data acknowledgement
•Connection less services are characterized by
➢Flow of data in one direction
➢Contains both routing information and data
➢Each piece of data is routed independently
Department of Telecommunication, MUET UET Jamshoro 31
Transmission and Switching Systems Dr. Abdul Latif

32. TCAP & MAP
•Transaction Capability Application Part (TCAP) message
contains non circuit related information like queries and
responses sent between SSPs.
•It is used to
➢execute remote processes –provide means for transfer of
data between nodes
➢Used extensively in intelligent Networks (INs)
➢ Essentially in application layers
•Mobile Access part (MAP) Contains messages related to
mobile switches and database like
➢User authentication
➢Equipment Identification
➢Roaming
Department of Telecommunication, MUET UET Jamshoro 32
Transmission and Switching Systems Dr. Abdul Latif

33. Signaling Unit Structure
•An SS7 message is called signaling unit (SU).
•It has three types
➢FISU (Fill in Signaling Unit)
❖Are transmitted continuously on SL in both directions
unless other SUs are present.
➢LSSU (Link Status Signaling Unit)
❖Carry one or two octets (8-bit bytes) of link status
information between signaling points at either end of a
link.
Department of Telecommunication, MUET UET Jamshoro 33
Transmission and Switching Systems Dr. Abdul Latif

34. Signaling Unit Structure
➢MSU (Message Signaling Unit)
❖Carry all call control, database query and response,
network management, and network maintenance data in
the Signaling Information Field (SIF).
❖Also contains Routing label for proper delivery of
messages between nodes.
Department of Telecommunication, MUET UET Jamshoro 34
Transmission and Switching Systems Dr. Abdul Latif

35. Signaling Unit Structure
Department of Telecommunication, MUET UET Jamshoro 35
Transmission and Switching Systems Dr. Abdul Latif
Type of SU FISU LSSU MSU
LI Value 0 1,2 3,..63

36. Fill-in Signal Unit (FISU)
•FISUs do not carry any information from upper layers
•FISUs are transmitted on the signaling links when the MSUs
and LSSUs are not present.
•FISUs are sent to provide constant error checking on the link
using CRC checksum.
•To acknowledge the receipt of message using BSN & BIB
Department of Telecommunication, MUET UET Jamshoro 36
Transmission and Switching Systems Dr. Abdul Latif

37. Link Status Signal Unit (LSSU)
•LSSUs are sent between two signaling points to indicate the
status of the signaling link in the Status field (SF) between two
adjacent signaling points.
•Status Field is used for this purpose.
Department of Telecommunication, MUET UET Jamshoro 37
Transmission and Switching Systems Dr. Abdul Latif

38. Message Signal Unit (MSU)
•MSUs are Work Horses of SS7
•Functionality lies in
➢Service Information Octet (SIO)
➢Signaling Information Field (SIF)
Department of Telecommunication, MUET UET Jamshoro 38
Transmission and Switching Systems Dr. Abdul Latif

39. Signaling Unit Structure
•Flag
–Indicates beginning of a new SU.
–Binary value is 0111 1110
•BSN (Backward Sequence Number)
–Used to acknowledge the receipt of SU by remote SP
–Contains the sequence number of SU being acknowledged.
•BIB (Backward Indicator Bit)
–Indicates a negative acknowledgment when toggled
•FSN (Forward Sequence Number)
–Contains incremented sequence number of SU being
transmitted.
•FIB (Forward Indicator Bit)
–Indicates retransmitted SU when toggled
Department of Telecommunication, MUET UET Jamshoro 39
Transmission and Switching Systems Dr. Abdul Latif

40. Signaling Unit Structure
•SIO (Service Information Octet)
➢Contains network indicator, message priority and service
indicator
•SIF (Signaling Information Field)
➢Contains routing label and signaling information
(e.g TCAP, SCCP, ISUP data)
Department of Telecommunication, MUET UET Jamshoro 40
Transmission and Switching Systems Dr. Abdul Latif
Transmission Direction
SIFSIO
DataHeading CodeLabelSSF SI
H1H0CICOPCDPC

41. Service Information Octet (SIO)
Department of Telecommunication, MUET UET Jamshoro 41
Transmission and Switching Systems Dr. Abdul Latif
SIO (8 bits)
Service Indicator
(4bits)
Subservice
Indicator (4bits)

42. Common Service Indicator Values
Department of Telecommunication, MUET UET Jamshoro 42
Transmission and Switching Systems Dr. Abdul Latif
Value Function
0 Signaling Network Management
1 Signaling Network Testing and
Maintenance
3 Signaling Connection Control
Part (SCCP)
5 ISDN user part (ISUP)

43. Subservice Indicator
Department of Telecommunication, MUET UET Jamshoro 43
Transmission and Switching Systems Dr. Abdul Latif
•It indicates
➢National SS7 Protocol
➢International SS7 Protocol
XX two bits indicate Priority
4 possible values 3 Highest Priority, then 2 and so on.
00XX International Network
10XX National Network

44. Signaling Information Field (SIF)
Department of Telecommunication, MUET UET Jamshoro 44
Transmission and Switching Systems Dr. Abdul Latif
•SIF field in MSU contains
•Routing Label (OPC, DPC, SLS)
•Information from Upper level protocols (TUP, ISUP, SCCP
or Network Management data)
•Routing Labels route the MSU through the network to its
final destination.

45. Signaling Information Field (SIF)
Department of Telecommunication, MUET UET Jamshoro 45
Transmission and Switching Systems Dr. Abdul Latif
Octet Group Function Number of
Octets
Involved
Destination Point
Code (DPC)
Contains the address of
the node to which the
message is being sent
3 Octets
Originating Point
Code (OPC)
Contains the address of
message originator
3 Octets
Singling Link
Selection (SLS)
Distributes load among
redundant routes
1 Octet

46. Signaling Unit Structure
•H0 & H1(Header 0 & 1)
➢H0 indicates the message
group to which SU
belongs.
➢H1 indicates the message
within that group.
➢e.g H0=1 means
Forward Address
Message Group (FAM)
H1=1 means Initial
Address Message (IAM)
Department of Telecommunication, MUET UET Jamshoro 46
Transmission and Switching Systems Dr. Abdul Latif

47. Signaling Information Field (SIF)
Department of Telecommunication, MUET UET Jamshoro 47
Transmission and Switching Systems Dr. Abdul Latif

48. Signaling Unit Structure
•DPC (Destination Point Code)
➢Indicates destination SP of the SU
•OPC (Originating Point Code)
➢Indicates originating SP of the SU
•CIC (Circuit Identification Code)
➢Identifies the circuit to which SU refers between the origin
and destination SP. Also called SLS Signaling Link
Selection.
Department of Telecommunication, MUET UET Jamshoro 48
Transmission and Switching Systems Dr. Abdul Latif

49. Basic Call Setup
Department of Telecommunication, MUET UET Jamshoro 49
Transmission and Switching Systems Dr. Abdul Latif
STP STP
SSP SSP
IAM= INITIAL ADDRESS MESSAGE
ACM= ADDRESS COMPLETE MESSAGE
ANM= ANSWER MESSAGE
REL= RELEASE MESSAGE
RLC= RELEASE COMPLETE MESSAGE

50. Example: signaling a PSTN call
Department of Telecommunication, MUET UET Jamshoro 50
Transmission and Switching Systems Dr. Abdul Latif
1. caller goes offhook,
dials callee. SSP A
decides to route call
via SSP B. Assigns
idle trunk A-B
A
B
W
X
Y
2. SSP A formulates
Initial Address Message
(IAM), forwards to STP
W
3. STP W forwards IAM
to STP X
4. STP X forwards IAM
SSP B

51. Example: signaling a PSTN call
Department of Telecommunication, MUET UET Jamshoro 51
Transmission and Switching Systems Dr. Abdul Latif
5. B determines it serves callee, creates address
completion message (ACM[A,B,trunk]), rings
callee phone, sends ringing sound on trunk to A
A
B
W
XY
Z
7. SSP A receives ACM,
connects subscriber line to
allocated A-B trunk (caller
hears ringing)
6. ACM routed to Z to Y to A

52. Example: signaling a PSTN call
Department of Telecommunication, MUET UET Jamshoro 52
Transmission and Switching Systems Dr. Abdul Latif
8. Callee goes off hook, B
creates, sends answer
message to A
(ANM[A,B,trunk])
A
B
W
XY
Z
10. SSP A receives ANM,
checks caller is connected
in both directions to trunk.
Call is connected!
9. ANM routed to A