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Basic Introduction to SS7 Moshe Haviv  September 2009 [email_address]
Contents ,[object Object],[object Object],[object Object]
Signalling and methodology ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Introduction to SS7 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Basic SS7 properties ,[object Object],[object Object],[object Object],[object Object],[object Object]
[object Object],[object Object],[object Object],[object Object],[object Object],Basic SS7 properties (Contd.)
SS7 Features ,[object Object],[object Object],[object Object],[object Object],[object Object]
A General SS7-PSTN-IP network
And now an SS7 network- Standalone
SSP  –  Service Switching Point ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
SSP  Call setup scenarios ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
STP  – Signalling Transfer Point ,[object Object],[object Object],[object Object],[object Object],[object Object]
SCP  – Service Control Point ,[object Object],[object Object],[object Object],[object Object]
SS7 Protocol Stack
SS7 transported over other networks
Addressing in SS7 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Addressing in SS7 (Contd.) ,[object Object],[object Object],[object Object],[object Object],[object Object]
GT Usage example
SS7 Protocol Stack elements ,[object Object],[object Object],[object Object],[object Object],[object Object]
ISUP ,[object Object],[object Object],[object Object],[object Object],[object Object]
ISUP   Elements in detail
Basic ISUP messages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
A basic ISUP call scenario
ISUP-ISUP Successful call trace
ISUP-ISUP Successful Call trace
 
 
 
ISUP messages list 05 00000101 Continuity 07 00000111 Connect 2F 00101111 Confusion 31 00110001 Charge information  1B 00011011 Circuit group unblocking acknowledgement  19 00011001 Circuit group unblocking 29 00101001 Circuit group reset acknowledgement  17 00010111 Circuit group reset 2B 00101011 Circuit group query response 2A 00101010 Circuit group query 1A 00011010 Circuit group blocking acknowledgement  18 00011000 Circuit group blocking 2C 00101100 Call progress 15 00010101 Blocking acknowledgement  13 00010011 Blocking 09 00001001 Answer 06 00000110 Address complete HEX  Binary  ISUP Messages
ISUP messages list (Contd.) 0C 00001100 Release 28 00101000 Pass-along 30 00110000 Overload 32 00110010 Network resource management 24 00100100 Loop back acknowledgement 01 00000001 Initial address 03 00000011 Information request 04 00000100 Information 37 00110111 Identification response 36 00110110 Identification request 08 00001000 Forward transfer 1F 00011111 Facility request 21 00100001 Facility reject 20 00100000 Facility accepted 33 00110011 Facility 11 00010001 Continuity check request 05 00000101 Continuity HEX  Binary  ISUP Messages
ISUP messages list (Contd.) 2D 00101101 User-to-User information 34 00110100 User Part test 35 00110101 User Part available 2E 00101110 Unequipped CIC 16 00010110 Unblocking acknowledgement 14 00010100 Unblocking 0D 00001101 Suspend 02 00000010 Subsequent address 38 00111000 Segmentation 0E 00001110 Resume 12 00010010 Reset circuit 10 00010000 Release complete HEX  Binary  ISUP Messages
SIP to PSTN Call trace- brief
 
 
 
 
SIP to PSTN Call trace-  detailed
 
 
 
 
 
 
 
 
General ISUP Message format
IAM  message contains ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
 
MTP L1
MTP L1 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
MTP L2
MTP-L2 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
MTP-L2(Contd.) Three kinds of Signalling Units

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Ss7 Introduction Li In

  • 1. Basic Introduction to SS7 Moshe Haviv September 2009 [email_address]
  • 2.
  • 3.
  • 4.
  • 5.
  • 6.
  • 7.
  • 9. And now an SS7 network- Standalone
  • 10.
  • 11.
  • 12.
  • 13.
  • 15. SS7 transported over other networks
  • 16.
  • 17.
  • 19.
  • 20.
  • 21. ISUP Elements in detail
  • 22.
  • 23. A basic ISUP call scenario
  • 26.  
  • 27.  
  • 28.  
  • 29. ISUP messages list 05 00000101 Continuity 07 00000111 Connect 2F 00101111 Confusion 31 00110001 Charge information 1B 00011011 Circuit group unblocking acknowledgement 19 00011001 Circuit group unblocking 29 00101001 Circuit group reset acknowledgement 17 00010111 Circuit group reset 2B 00101011 Circuit group query response 2A 00101010 Circuit group query 1A 00011010 Circuit group blocking acknowledgement 18 00011000 Circuit group blocking 2C 00101100 Call progress 15 00010101 Blocking acknowledgement 13 00010011 Blocking 09 00001001 Answer 06 00000110 Address complete HEX Binary ISUP Messages
  • 30. ISUP messages list (Contd.) 0C 00001100 Release 28 00101000 Pass-along 30 00110000 Overload 32 00110010 Network resource management 24 00100100 Loop back acknowledgement 01 00000001 Initial address 03 00000011 Information request 04 00000100 Information 37 00110111 Identification response 36 00110110 Identification request 08 00001000 Forward transfer 1F 00011111 Facility request 21 00100001 Facility reject 20 00100000 Facility accepted 33 00110011 Facility 11 00010001 Continuity check request 05 00000101 Continuity HEX Binary ISUP Messages
  • 31. ISUP messages list (Contd.) 2D 00101101 User-to-User information 34 00110100 User Part test 35 00110101 User Part available 2E 00101110 Unequipped CIC 16 00010110 Unblocking acknowledgement 14 00010100 Unblocking 0D 00001101 Suspend 02 00000010 Subsequent address 38 00111000 Segmentation 0E 00001110 Resume 12 00010010 Reset circuit 10 00010000 Release complete HEX Binary ISUP Messages
  • 32. SIP to PSTN Call trace- brief
  • 33.  
  • 34.  
  • 35.  
  • 36.  
  • 37. SIP to PSTN Call trace- detailed
  • 38.  
  • 39.  
  • 40.  
  • 41.  
  • 42.  
  • 43.  
  • 44.  
  • 45.  
  • 47.
  • 48.  
  • 50.
  • 52.
  • 53. MTP-L2(Contd.) Three kinds of Signalling Units

Editor's Notes

  1. Each SP has one or more addresses associated with it. Those addresses are called Signaling Point Codes, PC . It is also possible to use an alias which is not PC . That is called Global Title ( GT ). Global title is not an SS7 address and needs to be translated to one to be useful. Nodes in the SS7 network are addressed by their Signaling Point Code ( SPC ). When locations like an SCP (we will explain later what this is) are addressed, Point Code is not enough. Another value must be used to identify the service application that is sought. For this purpose, the SS7 simply uses a value (represented in the message packet by a byte, and therefore, in the range of 0 to 255) which is called a Subsystem Number ( SSN ). Subsystem numbers typically identify databases. However, they may also identify other services. For example, a switch may offer several features. Because several features are offered, simply sending the request to the SPC of the switch is not enough. A subsystem number will be used as well in order to specifically address the exact service that is required.
  2. We will show all of the above when we go deeper into the protocol.
  3. In the third case where the dialled number is, say an 800 number, the SSP reaches to SCP with the help of an STP using TCAP protocol. In turn SCP returns a new Global Title (destination address) that can be routed in the SS7 network. A global title is an address (e.g., a dialled 800 number, calling card number or mobile subscriber identification number) that is translated by SCCP into a destination point code and subsystem number
  4. In SS7, Global Title is an alias for PC or (PC + SSN). If the SSP does not know the destination of a global title, it sends a query in the form of TCAP messages to its local STP. When the query gets to the STP, the global title digits are given to the STP's SCCP. The STP will then translate the SCCP address fields and determine, through its own translation tables the address of the application (SCP). The Global Title Translation provides the SSN of the database and point code of the SCP that interfaces that database application.
  5. One, two or all three may be present in an SS7 message as Calling or Called party address. If the associated message requires to be routed over the SS7 network, translation is required. Translation of the GT will result in a DPC being produced and possibly also a new SSN and GT. A field is also included in the address indicator to identify the format of the global title. The MTP part of SS7 stack only needs PCs but at higher levels other addressing types in various combinations are used. When a DPC (Destination Point Code) has more than one application running on it we need something additional to distinguish between them. So comes the usage of SSN. The different applications in a node (Usually an SCP) can be Call Center, Credit card billing application, 1-800 data base etc. So SSN can be an application identifier and/or a data base identifier.
  6. http://www.dialogic.com/support/helpweb/signaling/iw1414.aspx
  7. ISUP functionality can be further broken down into three procedural categories. The first of these is Signalling Procedure Control (SPRC) which directly interfaces with the services of the MTP. The SPRC, in turn, provides support for Circuit Supervision Control (CSC) and for Call Processing Control (CPC). The application which deals with the circuit connection requirements of the switch, and simultaneously with SS7 signalling, is usually referred to as a Call Control application.
  8. IAM- Initial Address Message. The ISUP message with all the info required to establish a connection and also to reserve a circuit for that purpose. In addition to Called address, BW requirement, type of call etc. is also relayed. SAM- For cases where all the digits were not included in IAM an additional message ( SAM ) is sent with the additional digits. ACM- Acknowledgment to IAM. It means that the receiving switch has reserved circuit asked in IAM. When ACM is received a “Ringing”, ring back tone is sent to the connection initiator. CPG- An optional, Call progress advancing message. ANM- When the destination user picks up the phone the switch send a DC current to the phone and also send back to the neighbouring switch the ANM message which is carried back from switch to switch all the way back the source switch. REL- If the destination is Busy the destination exchange sends back that message. As a result the source exchange sends back to the originating client a Busy tone. To make sure that Busy signal does not arrive before a ringing tone a delay is introduced before sending a ringing tone.
  9. Taken from http://dbrbbs.net/simple/index.php?t9546.html
  10. ST is last digit state.
  11. tacm - This is the Receipt of A ddress C omplete M essage at outgoing international exchange. T9 in ISUP . Time out value is 2-4 minutes.
  12. When the called party answers, the destination switch terminates power ringing of the called line, removes audible ringing tone from the calling line and sends an Answer Message ( ANM ) to the originating switch. The originating switch initiates billing after verifying that the calling party's line is connected to the reserved trunk .
  13. PT (Payload Type) 0 above in “m=audio 49172 RTP/AVP 0” is PCMU according to RFC3551. Above “a=rtpmap:0 PCMU/8000 “ the rtpmap can be found in RFC4566 . The format for attribute (a) is : a=rtpmap:<payload type> <encoding name>/<clock rate> [/<encoding parameters>] If the Alice INVITE request did not include a max-request header filed than the proxy must add one with the value of 70! When a UAC sends a request to a proxy server, the proxy server may decide to authenticate the originator before the request is processed. The proxy can challenge the originator to by returning a 407 response (Proxy Authentication Required) with a Proxy-Authenticate header containing the challenge. The client can re-send the request with a Proxy-Authorization header which provides the credentials that match the challenge. A client may provide the credentials also before being challenged in order to avoid the delay and extra processing of the 407 response (the credentials may be built according to cached challenges). Both challenge and credentials are built using a cryptographic hash so that certain values, such as password, are not sent in the clear
  14. AOR- Address of Record in SIP protocol- RFC3261. It is a SIP or SIPS URI that points to a domain with a location service that can map the URI to another URI where the user might be available. Typically, the location service is populated through registrations. An AOR is frequently thought of as the "public address" of the user. If a proxy wishes to remain on the path of future requests in a dialog created by this request (assuming the request creates a dialog), it MUST insert a Record-Route header field value into the copy before any existing Record-Route header field values, even if a Route header field is already present.
  15. Satellite Call Indicator is used to indicate if one or more satellite links are used. Excessive use of satellite might reduce the call quality. Forward Call Indicators include National/International Call End to End method (Pass along or SCCP-Connectionless) SUP indicator (Whether ISUP is used for every leg of the connection) Calling Party Category can be “Regular Subscriber”, “payphone”, “operator” or “test call”
  16. An MTP-L2 message is called Signalling Unit.
  17. LSSU- Link Status Signalling Unit. This unit is transmitted in both direction and carries Link Status information between Signalling Points. MSU- Message Signalling Unit. This unit carries all call control, data base query answer/info FIU- Fill In Signalling unit. This unit is transmitted in the absence of MSU/LSSU frames.