The conversation, which is the primary task, and what went on behind the scene to make the conversation successful. This has been the essence of signalling in telecommunications for a long time. There is a uniform set of standard messages in the signalling repertoire. Over the years, there has been a vast improvement in signalling technology and the lady operator has long since been replaced by automatic digital switching exchanges.
They are still doing exactly the same job as the lady, but faster and more reliably over a global network. Many different factors have led to a variety of signalling systems being developed in telecommunications networks.
Different signalling standards were developed in different parts of the world. They were all doing the same task, but in a different way. This would obviously mean that when a call originates in one network with one type of signalling implementation and terminates in another network with another type of signalling system, some compromise, or adaptation would have to be used.
A large number of telephone exchanges in the world are still using this system, but its implementation is such, that it is only suitable for cases where traffic is low.
Another problem with CAS is that it is not possible to send signalling messages in the absence of a call. This causes bottlenecks and wastes bandwidth. One of the main advantages of this system was that signalling did not have to go along the same path as the speech. It is modular in design, although the modules are not as clearly defined as is the case with the OSI 7-layer model, which it pre-dates.
Let us take a closer look at this system in the following sections. The first part was responsible for transferring the message within a signalling network. The second part was the user of these messages. As an analogy we can compare it to two managers with their own message runners.
One manager writes a message, puts it in the envelope and gives it to the messenger. The messenger in turn looks at the address on the envelope, and gives it to the messenger of the other manager. The messenger of the receiving manager looks at the address and gives it to his manager, who will then read and act as necessary.
Figure 3. The part responsible for taking these messages from one network element to another network element is known as the Message Transfer Part MTP. The entire SS7 is built on the foundation of this MTP, which consists of three sublayers as shown in the figure below. Message Transfer Part layers The lowest level, MTP layer 1 physical connections , defines the physical and electrical characteristics. MTP layer 2 data link control helps in error free transmission of the signalling messages between adjacent elements.
MTP layer 3 network layer is responsible for taking the message from any element in a signalling network to any other element within the same network. But who is the user who receives, sends and acts on these messages? Those standard sets of messages that were mentioned previously are the standard TUP messages that help to set up the call, to supervise and clear it.
However, with the passing of time and the development of newer and more advanced technology, signalling requirements also started to become more stringent and demanding. The MTP guarantees the transfer of messages from any "signalling point" in the signalling network to any other "signalling point", safely and reliably.
However, each message could reach the destination signalling point by using different paths. This may cause situations where the order of messages that are received, are different from the original sequence.
Address Information Contains Address for Example : Two SCPs can be combined to form a subsystem service group that is accessed frothe relevant service switching point SSP via globa l title translation. Home Documents Telecom ss7 basic. Post on Apr views.
Category: Documents 6 download. Grp B Bwd Sig. Grp II Fwd Sig. Called Party 2. Calling Party 3. User Data Mandatory Variable 1. User Data 1. Return Cause 2. Hop Counter 1. Segmentation data Optional Variable 1. Hop Counter1. Address Indicator : a. In the drawing above, if the network were to go no further, then this switch could connect anytelephone it serves to any other telephone it serves. But, of course, there are other end offices ser-vicing their own collection of telephones.
If the drawing represents the entire network, none of thetelephones shown here could be connected to any of the telephones serviced by any other endoffice. That could be solved by running a transmission line from each end office to each of theother end offices. That would work; but, it would be very inefficient. A much better way would be to connect this local office to a switch whose main purpose would bethe interconnection of many local offices.
The local switch, then, would not need a transmissionline to every other local office. Instead, transmission lines going directly to the intermediateswitch would be sufficient. The result would look something like the above drawing. Here a switch is used simply to connectswitches.
Note the result in the rapid expansion of the number of telephones that can now be con-nected. We have elected to keep the example simple by showing an intermediate switch whichonly connects four end offices. Now picture that switch connecting as many end offices as eachend office connects telephones.
In our example, each end office could connect twenty telephones. If the intermediate switch con-nected twenty end offices, four hundred telephones could then be connected. In practice, ofcourse, an end office connects a huge number of telephones. The first intermediate switch like-wise connects many more end offices.
Taking our example one step further, the Tandem offices can be connected to another switchwhose job is to connect switches. In this case the new switch would likely be a switch for longdistance communication. As you can see, each time a switch at a higher hierarchical level is used to connect lower levelswitches, the network grows more rapidly.
So does the potential for disaster. Since each switchconnects more and more telephones, the loss of such switches would result in the loss of commu-nications to an ever greater number of phones. Home Documents Basics of SS7. Post on Oct 37 views. Category: Documents 5 download. Tags: ss7 ss8 networks forewordthose use of ss8 networks ss7 standards acronym ss7 ss8 networks written materials murat erkam handlethis page.
My thanks to all of the above. What is a network? The Fall of SS7. SS7 over 30 years ago. Protocolo SS7. SS7 Nortel. Ss7 Tutorial. SS7: Locate.
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