A look at SS7

1. 03/16/12
Tinniam V Ganesh tvganesh.85@gmail.com
SIGNALING SYSTEM 7 (SS7)
1
Tinniam.V. Ganesh
tvganesh.85@gmail.com
http://gigadom.wordpress.com/

2. WHAT IS COMMUNICATION ?
03/16/12
 Communication is used between 2 network
elements to exchange information.
Tinniam V Ganesh tvganesh.85@gmail.com
 There are 2 types of domains in the
communication world
 Data communication
 Telecommunication
2

3. DIFFERENCES BETWEEN TELECOM &
DATACOM
03/16/12
Telecommunication Data Communication
Tinniam V Ganesh tvganesh.85@gmail.com
Network used for making voice Network used for transferring
calls between telephones data from one computer to
another
Telephones were the end points Computers were the end point
Uses protocols like ISUP, ISDN Predominantly uses TCP/IP
Network elements are MSC, Network elements are Routers,
HLR, SCP etc hubs, ATMs, bridges etc
Uses circuit switching Uses packet switching
3

4. NETWORKS OF TODAY …
03/16/12
 In the networks of today telecommunication
networks are used to download data e.g.GPRS
Tinniam V Ganesh tvganesh.85@gmail.com
 Data networks are used for making Voice Calls
e.g. VOIP
4

5. WHAT IS SIGNALING ?
03/16/12
 Signaling refers to the exchange of information
between network elements
Tinniam V Ganesh tvganesh.85@gmail.com
 Signaling between network elements follows a
specific protocol
 A Protocol refers to the set of rules for
communicating between the elements
5

6. WHAT IS SS7 SIGNALING ?
03/16/12
 Signaling System 7 was devised by ITU-T
(formerly known as CCITT)
Tinniam V Ganesh tvganesh.85@gmail.com
 Initially the signaling in trunks used to happen
on the same channel in which the voice call used
to occur. Hence call setup, digits etc would use
the same line as the actual voice circuit
 In SS7 a separate channel is allocated just for
signaling. This is known as Out-Of- Band
signaling
6

7. SS7 SIGNALING
03/16/12
 Signaling happens in a separate channel
outside of the voice channels
Tinniam V Ganesh tvganesh.85@gmail.com
 A separate timeslot is used to transfer signaling
messages like call setup, teardown etc
 This is also known as Common Channel
Signaling (CCS)
7

8. ADVANTAGES OF OUT OF BAND
SIGNALING
03/16/12
 Allows signaling at any phase of the call
 Allows upto 56 Kbps of signaling information
Tinniam V Ganesh tvganesh.85@gmail.com
Switch A Switch B
Voice Trunk
8
Signaling Link

9. SS7 STACK
03/16/12
CAP,MAP
Tinniam V Ganesh tvganesh.85@gmail.com
…
Application
ISUP,TUP..
layer
TCAP
SCCP Network layer
MTP 3 Network layer
MTP 2 Data link layer
MTP 1 Physical layer
9

10. SS7 LAYERS
03/16/12
 MTP – Message Transfer Part
 SCCP – Signaling and Connection Control Part
Tinniam V Ganesh tvganesh.85@gmail.com
 TCAP – Transaction Capabilities Application
Part
 CAP – CAMEL Application Part
 ISUP – ISDN User Part
 MAP – Mobile Application Part
10

11. 03/16/12 Tinniam V Ganesh tvganesh.85@gmail.com
11
SS7 VS OSI STACK

12. SS7 PROTOCOLS
03/16/12
SS7 protocols can be classified as call related and
non-call related
Tinniam V Ganesh tvganesh.85@gmail.com
 Call related protocols – ISUP (ISDN User Part),
B-ISUP (Broadband – ISUP)
 Non-call related protocols –
 INAP (Intelligent Network Application Part)
 CAP (CAMEL Application Part)
 MAP (Mobile Application Part)
 … 12

13. SS7 STANDARD BODIES
03/16/12
 The SS7 standard body for North American
market is ANSI (American National Standards
Institute). The ANSI versions are ANSI ISUP,
Tinniam V Ganesh tvganesh.85@gmail.com
ANSI TCAP etc.
 The SS7 standard body for European market is
ETSI (formerly CCITT). The ETSI versions of the
protocols are ETSI ISUP, ETSI TCAP etc.
 There are minor variations in the protocols by
the two standard bodies.
13

14. SS7 Link speeds
There are 2 main standards in the world for
03/16/12
transmission of PCM signals
T-Carrier – This is used in the North American market
Tinniam V Ganesh tvganesh.85@gmail.com
E-Carrier – This is used for European market
T1 – 24 channels * 64 Kbps = 1.544 Mbps
E1 – 32 channels * 64 Kbps = 2.048 Mbps
Level North American European
0 64 Kbps 64 kbps
1 1.544 Mbps (T1) 2.048 Mbps (E1)
2 6.312 Mbps (T2) 8.448 (E2)
3 44.736 Mbps (T3) 34.368 (E3) 14

15. MTP LAYER 1 – PHYSICAL LAYER
03/16/12
 This is the Physical Layer and defines the
electrical and physical characteristics of SS7
links.
Tinniam V Ganesh tvganesh.85@gmail.com
 Signaling links use DS-0 channels and carry data
at 56 Kbps or 64Kbps.
15

16. MTP LAYER 2 – DATA LINK LAYER
03/16/12
 The data link level provides the network with
sequenced delivery of all SS7 message packets
between adjacent nodes
Tinniam V Ganesh tvganesh.85@gmail.com
 It also provides for flow control and error
checking
16

17. MTP LAYER 3 – NETWORK LAYER
03/16/12
 This provides network layer functionality. It
delivers messages between signaling end points
Tinniam V Ganesh tvganesh.85@gmail.com
 The network level depends on the services of
Level 2 to provide alternate routing, and message
distribution functions.
17

18. SCCP (SIGNALING CONNECTION CONTROL
PART)
03/16/12
 Signaling Connection Control Part (SCCP) is a
higher level protocol than MTP that provides
end-to-end routing.
Tinniam V Ganesh tvganesh.85@gmail.com
 SCCP is required for routing TCAP messages to
their proper database.
 SCCP also does Global Title Translation to
determine the end signaling point.
18

19. TCAP (TRANSACTION CAPABILITIES APPLICATION
PART)
03/16/12
 Transactional Capabilities Application Part
(TCAP) facilitates connection to an external
database.
Tinniam V Ganesh tvganesh.85@gmail.com
 Information/data received is sent back in the
form of a TCAP message
19

20. APPLICATION LAYER
03/16/12
 At the application layer there are the following
protocols
Tinniam V Ganesh tvganesh.85@gmail.com
 Call related
 ISDN User Part (ISUP) supports basic telephone call
connect/disconnect between end offices.
 Non-call related
 CAP – Camel Application Part is used to access a
database ,the SCP and influence the call
20

21. SS7 SIGNALING ARCHITECTURE
03/16/12
There are 3 main elements in SS7 signaling
architecture
Tinniam V Ganesh tvganesh.85@gmail.com
SSP – These are SS7 capable digital switches
STP – These are SS7 capable network elements
that route incoming SS7 messages to the correct
destination
SCP – These are databases which take part in non-
call related SS7 signaling
21

22. ISUP CALL FLOW
03/16/12
Switch A Switch B
A dials digits
Initial Address Message (IAM) B’s phone rings..
Tinniam V Ganesh tvganesh.85@gmail.com
Address Complete Message (ACM)
B Answers
Answer Message (ANM)
A disconnects
Release Message (REL)
B disconnects
Release Complete (RLC)
22

23. 03/16/12 Tinniam V Ganesh tvganesh.85@gmail.com
23
Thank You !!!