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What’s SS7

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  • #32702

    Could anybody the explain me the SS7 signaling in details? Is an existing SS7 over satellite? And what is the difference of SS7 to R2 MFC?

    Thank you, and I hope someone will answer my questions.


    Aaron, SS7 is a very complex interofice signalling protocol. It has the following blocks:

    • OMAP (Operation and Maintenance Part)
    • TCAP (Transaction Capability Part)
    • ISUP (ISDN Userp Part)
    • SCCP Signalling Connection Control Part)
    • MTP (Message Transfer Part)

    Each part is applied based on what type of portion of the protocol is needed. You may require a further definition of ‘each’ part.

    All these messages are totally digital and each part has their own set of information.

    R2 is based on tones. An extreme simple protocol compared with the complexity of SS7. For every R2 tone there is another tone back. Message on R2 are defined in Forward (2 types) and Backward (2 Types).


    For an over all explaination of how SS7 works you may want to vist the web site where you can find several tutorials on SS7 and other topics that you may be interested. An excelent book on SS7 is a book entitled ISDN and SS7 by Uyless Black

    Wallis Dudhnath

    SS7 is Signallng System Number 7.

    In a nutshell, Signalling allows two communicating entities, e.g. SPC Time-Space-Time Switch, to initiate, maintain and clear a telecommunication connection.

    SS7 is related to a Digital Network. SS7, e.g. ISUP, is used beteen two Digital SPCs. R2 MFC (Multifrequency Compelled) is an analogue Voice Frequency signallin that is used between Analog nodes. This was very popular during the 1950s to the 1970s. Most Networks are ss7 / IP / Sigtran orientated.


    What is ss7 how does it work?

    Wallis Dudhnath

    SS7 is Signalling System Number 7. It is a Signalling system that was Standardised, designed and implemented as a part of the move from Analog Switches to Digital Switches.
    Regardless of SS7, Signalling is used to initiate, maintain and cleardown a telephony session.

    A Switch is basically a traditional Telephone Exchange. For a Digital Switch a “software Group Switch” using Control software will help to connect incoming / outgoing Time Slots. SS7 has been the backbone or the central nervous system for Digital Telecommunication Networks.

    The main reason to enhance Analog Switches and the Analog (e.g. Voice Frequency) signalling were:-

    -Fraud: With Analog Signalling it was easy to mimic the Voice Frequency signals so that frauds (extensive free calls) could be made. In fact, the first generation of Hackers were the
    Phone Phreakers using their “blue boxes” to operate Telecommunication Equipment from the once ubiquitous

    -Advanced Services: Analog Systems supported POTS – Plain Old Telephony Services. The move to Digital SS7 Signalling and the introduction of Digital Switches meant that PANS – Pretty Amazing Network Services – could be deployed.

    Look at ISDN and the numerous Services based around Calling Identity, Ring Back, Call Forwarding, Charging, etc..Services.

    SS7 is a message based Signalling system that aligns with OSI’s classic stack. GSM Network solutions are based
    on SS7 and ISDN signalling.

    VBR/ Wallis Dudhnath

Viewing 6 posts - 1 through 6 (of 6 total)
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