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How a 0800(freephone) call is routed?

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aslamzohaib

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how a call is routed

Hi,
My question to all of you is that plz tell me how a 0800 (freephone) call is routed through the telecom network i.e through normal pstn and then through IN(Intelligent Network). Plz tell me all the parts that are involved in the process.
Thanks.
 

hossam.algewely

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Hi,
Basically , there are many types of Toll Free Numbers
Domestic TF DTFN
International TF ITFN
Universal TF UIFN

When DTFN or ITFN number is dialled , it is routed to the IN via Tandem switches to be translated into what we cal a Down Stream Number , this number can be a normal PSTN number (Domestic / International) according to Routing Decisions defined by the IN/SCP (Like when you dial McDonalled number for instance , the call is routed based on your Callinf Line Id CLID to the nearst branch)

When UIFN number is dialled , it is passed through international carriers to firms like France Telecom and it is formated into a special format , then is sent to the IN to be translated into down stream number that can be a normal PSTN number or a private dial plan number sent to the customer site via global VPN's controlled by companys like BT or Orange ,.....

I hope that i helped you
Thanx
 

aslamzohaib

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Thanks ...but your are using complicated language with abbreviation and all that kind of stuff....can you plz give me some links or some diagramatic presentaion of the process here....i will b more then thankfull to you..
 

irenepetes

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What happens when a toll free number is dialed? The SSP (Service Switch Point) in the phone network will determine the dialed number by looking at the prefix. Once confirmed that the call is a toll free service request, the SCP (Service Control Point) will be queried and then re-routes it to the appropriate subscriber who owns the number.
 

zhi_yi

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Hi Aslamzohaib,

There are 3 general items in SS7 network which is SSP (Service Switching Point), SCP (Service Control Point), and STP (Signaling Transit Point).

A SSP is just like a Switch in IP network, it uses for routing the call signaling. I believe that you have already known the different between signaling and the bearer.

A STP is just like a router in IP network, it use to centralize the SSP and hence it ease the operator to manage their network. Normally STP comes with some additional features and capabilities depends on its Vendor.

A SCP is just a database actually, so in this case regarding the toll free number, SCP equipment will contain a database which map the '0800' number towards the normal PSTN number (0800xxxxx = X PSTN numbers).

Subscribers are connected to the SSP. In a normal call setup, the SSP will use the ISUP protocol to establish the call.

For example:
Subscriber A (123456) is attached to SSP A, subscriber B (234567) attached to SSP B. and there is a connection between SSP A and SSP B. while Subscriber A dialed 234567, the SSP A will check the "digit" dialed by Subscriber A, and then it will figure out "oh okay, so this is a normal PSTN number, I will tell SSP B to notice Subscriber B that there is a call"

That is a normal call setup, and it uses ISUP protocol, but while there is a toll free call, for example:
Subscriber A dial to 0800888888, the SSP A will check the dialed number and then say "oh okay, so this is a toll free call, I may need to check with SCP first where to route this call", and then SSP A check to SCP and then find out "Oh Okay, so 0800888888 means I should route to 654321", and then the SSP A will route the call to another subscriber with ID 654321.

The communication to the SCP or to the IN network may use different protocols depends on the network, if it is PSTN it will use INAP, and if it is in mobile network GSM, it will use CAMEL.

Hope above explanation could helps, please correct me if I am wrong.


Regards,
Zhi Yi
 

Ankit C

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Hi Aslamzohaib,

There are 3 general items in SS7 network which is SSP (Service Switching Point), SCP (Service Control Point), and STP (Signaling Transit Point).

A SSP is just like a Switch in IP network, it uses for routing the call signaling. I believe that you have already known the different between signaling and the bearer.

A STP is just like a router in IP network, it use to centralize the SSP and hence it ease the operator to manage their network. Normally STP comes with some additional features and capabilities depends on its Vendor.

A SCP is just a database actually, so in this case regarding the toll free number, SCP equipment will contain a database which map the '0800' number towards the normal PSTN number (0800xxxxx = X PSTN numbers).

Subscribers are connected to the SSP. In a normal call setup, the SSP will use the ISUP protocol to establish the call.

For example:
Subscriber A (123456) is attached to SSP A, subscriber B (234567) attached to SSP B. and there is a connection between SSP A and SSP B. while Subscriber A dialed 234567, the SSP A will check the "digit" dialed by Subscriber A, and then it will figure out "oh okay, so this is a normal PSTN number, I will tell SSP B to notice Subscriber B that there is a call"

That is a normal call setup, and it uses ISUP protocol, but while there is a toll free call, for example:
Subscriber A dial to 0800888888, the SSP A will check the dialed number and then say "oh okay, so this is a toll free call, I may need to check with SCP first where to route this call", and then SSP A check to SCP and then find out "Oh Okay, so 0800888888 means I should route to 654321", and then the SSP A will route the call to another subscriber with ID 654321.

The communication to the SCP or to the IN network may use different protocols depends on the network, if it is PSTN it will use INAP, and if it is in mobile network GSM, it will use CAMEL.

Hope above explanation could helps, please correct me if I am wrong.


Regards,
Zhi Yi
For better understanding can you/someone please specify the name of the node (the SCP) to which this query goes for getting a routable number?

If it goes to IN then what happens in case when the calling party is a postpaid subscriber which do not have an IN trigger (CSI) defined for it in HLR?
 

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