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Author Topic: SMS routing over SS7  (Read 697 times)
Abdulsalam
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« on: May 20, 2007, 18:57:10 UTC »

Hi,

Kindly, can any one guide about how SMS is routed over SS7 between mobile operators.
I am interseted about the lower layers of SS7. SCCP/MTP3/MTP2/MTP1.
As, I can't found any useful document about how SMS is carried over these layers.

Moreover, How the MSU's of the SMS look like in the SIF field of the MTP3?

Finally, Can the SMS traffic be forced to be routed to a specific point code without the care of the GTT?
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RussCrush
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« Reply #1 on: May 21, 2007, 02:54:49 UTC »

Lets see.....

Hi,

Kindly, can any one guide about how SMS is routed over SS7 between mobile operators.
I am interseted about the lower layers of SS7. SCCP/MTP3/MTP2/MTP1.
As, I can't found any useful document about how SMS is carried over these layers.
It is OSI standard model.
MTP1 is physical, as in the wire or fiber between the network entities or nodes.
MTP2 is communication integrity, checksums and the like (FIB, BIB, etc.)
MTP3 is where the Telephone junk starts. Point codes (OPC, DPC), redundancy routes (route costing), congestion controls (priority bits), that sort of thing.
SCCP is the application layer that identifies the message flow (RI, NPI, NAI, GT Addresses ). This is the upper level, where the SMS magic happens.
Moreover, How the MSU's of the SMS look like in the SIF field of the MTP3?
Got me. What is the SIF field?
Finally, Can the SMS traffic be forced to be routed to a specific point code without the care of the GTT?
Simply put, no.
SMS traffic is GT based, and must be signaled as such, in order to ensure delivery. It IS possible to signal without GT, but failure is the likely outcome.
The SCCP portion contains a field called the Routing Indicator (RI), and if this field is set wrong, or it is sent to an entity that does not support the RI setting, it will fail, for sure. The RI can be set to GT, for routing between networks, and DPC/SSN for routing to nodes.

 
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Abdulsalam
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« Reply #2 on: May 21, 2007, 10:24:01 UTC »

Hi,

Thanks for your reply.

About the SIF; Service Indication Field in the MSU of the MTP3, it contains the routing label and the application information of the upper layers. my question was how the SMS data is presented in this application information field?

About the final reply( to the final question about forced routing):
So, an SMS traffic can't be routed to a third party through SS7 using pointcodes?
Therefore, an SMS hub can't be interworking through SS7?(am i right?)
Let me calrify with an example:
suppose that a user from a  mobile operator A want to send an SMS to a user from a mobile operat B. But, mobile operator A doesn't have the operator B in his interworking list.
Moreover, a third party (SMS hub) has the mobile operator B in his interworking list. ( and connected with each other through SMPP or any other)
Now, can mobile operator A route the SMS traffic to the third party through SS7?and how?
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RussCrush
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« Reply #3 on: May 22, 2007, 01:42:21 UTC »

SIF.....
I am quite familiar with the Service Indicator (SI), but that is set to 3 for SCCP or TCAP, or 5 for ISUP.  I am not sure if it is the same thing that you are talking about. Please let me know if this is what you are talking about.

 You used the term "Hubbing"in your example. This is a new term to GSM, so new that only proof of concept trials have been completed, and none are production. Hubs will probably not hit the streets for years, due to the requirement to pass SMS from anyone to anyone with no blocking, and the numerous architectures being promoted (at least 6 last time I looked), most of which are not compatible with each other.

 In fact, the whole idea of hubbing is that if the SMS originated from an Operator A sub is not destined for another one of Operator A's subs, it goes to the Hub. The Hub knows to send it to Operator B, or to another Hub where Operator B resides. Operator A would not need to know anything about Operator B at all. Just dump the traffic to the Hub, and let them sort it out.

At first, Most Hubs will interconnect with other Hubs via SS7, but SMPP signaling between Hubs will follow on quickly, I am sure.

 Regarding forced routing. I was just saying that the network topology and GT signaling via SS7 is set and agreed upon by the adjacent SCCP providers, and unless you fully and completely understood the entire portion of the network, it would probably fail.

It is just easier to route according to the established procedures.
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Abdulsalam
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« Reply #4 on: May 22, 2007, 13:43:50 UTC »

Hi,
I guess that your are taking about SIO Service indicator octet(4bits). But, its set to 2 for SCCP and to 3 for ISUP (refer to http://www.cisco.com/univercd/cc/td/doc/product/tel_pswt/vco_prod/ss7_fund/ss7fun04.htm#wp1025505). Any way, the SIF field is behind the SIO as you  see from the document. So, my question was how the SIF field will be filled with the SMS traffic.
Do you have any idea about: what the SIO field will be set to? If the MSU carry an SMS traffic.( I guess it will be set to a value for MAP. But, then how the SMS messages will be differentiated form other MAP messages)

About SMS routing:
Ok, SS7 traffic is routed through GT.
The question is: can GTT (global title translation) be forced to translate many GT to one DPC (Destination point Code)?
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RussCrush
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« Reply #5 on: May 25, 2007, 02:39:26 UTC »

I see what you are going on about now........

 The "SIF" you mentioned is the entire message after MTP2!! 8 bit words, no more than 272 of them. It is a poor representation of what a message looks like. Cisco is probably not the best source for SS7 info.

 A better one is here:
http://www.pt.com/tutorials/ss7/stack.html

It shows the IP model next to the SS7 model.

MTP 3 contains the OPC and DPC. The SIO is either a 3 for TCAP (and SCCP) or 5 for ISUP.  The SCCP layer is a label that contains the CDPA and CGPA, NAI, NPI, TT, SSN, RI and some other stuff that I can't remember right of the top of my head.
The MAP layer is next, and this is the payload. It has the actual SMS in this layer, along with some other pertinent info.

 
About SMS routing:
Ok, SS7 traffic is routed through GT.
The question is: can GTT (global title translation) be forced to translate many GT to one DPC (Destination point Code)?

Yes. But I am not sure if I answered your question. If Comfone has 3 customers, and BT wants to route traffic to those customers, all the GTs associated with those 3 customers are routed to Comfone. Comfone then routes the traffic to those 3 customers after GT dipping.

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parasa
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« Reply #6 on: May 25, 2007, 14:50:37 UTC »

Do you have any idea about: what the SIO field will be set to? If the MSU carry an SMS traffic.( I guess it will be set to a value for MAP. But, then how the SMS messages will be differentiated form other MAP messages)
It will be set to SCCP ( value 0x09, stands for SCCP-UDT message). At SCCP the incoming GT gets translated to SSN 8 ( that stands for MSC - [SMSC is configured as MSC in the networks]). This happens only if the cofiguration at SCCP layer at SMSC's Stack are correct. MAP payload gets decoded at MAP layer and there appropriate action are taken depending on MAP operations.

Anyhow TCAP component portion has operation tag, which infact contains the value of MAP/INAP/CAP operation.


About SMS routing:
Ok, SS7 traffic is routed through GT.
The question is: can GTT (global title translation) be forced to translate many GT to one DPC (Destination point Code)?
yes it can be done.
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Thanks & regards,

Parasa kiran
India
Abdulsalam
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« Reply #7 on: May 28, 2007, 11:03:31 UTC »

Dear all,

Thanks a lot for your replies.

About the MSU of SMS: how many MSU needed to send or receive an SMS?

About SMS routing and a third party as an interworking network:
Ok, GT is used to route between networks. While, DPC/SSN is used to route between signaling node within the same network.
But, can the HLR of the third party be consider as a signaling node within an operator network that want to send SMS to another operator that don't have a roaming agreement with them while the third party have? So, the first operator will set their Routing Indicator to route using DPC/SSN and not the GT!
So, the DPC will be  the point code of the third party HLR while the SSN will be the MSC of the third party.
Am I right?

Moreover, do any one know about the 338 method?
It said that a third party may have its own short GT (338 or 3204). then operators that want to interconnect with this third party as an interworking network for SMS would add as a suffix the short GT to the called party GT.

About ISPC?
Do any one know how International Signaling Point Code is assigned?
Is there a third party that is responsible for this assignment?
In another word, how I assign a SPC to my Signaling nodes?
Does the SPC in SS7 look like the MAC address in the IP environment or like an IP address?
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RussCrush
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« Reply #8 on: May 29, 2007, 01:28:29 UTC »

SMS can be sent (within the same network) with only a single invoke and response. Remember, SS7 (C7, and by extraction SMPP) always, ALWAYS require a response.

GT signaling (also known as intermediate GT) is between networks and some network elements within a network. This message may or may not be passed on to whatever node receives it.  DPC/SSN signaling (also known as Final GT) is only to a SEP (signaling end point), meaning that it cannot go any further.  This is almost always done within the same network. DPC/SSN routing requires that the third party node know the DPC of the network element that is to be signaled to. This is usually not known outside of the network, and usually not reachable even if it is known.

I do not know what the 338 method is. I do know that ITU point codes are 3-8-3 formatted. Did you mean that? Can you link something? We like links.

 Every node on the SS7/C7 network must have an unique point code. In GSM, every node (MSC, SMSC, HLR, VLR...) must also have an address as well (a phone number). These addresses are usually country specific, and assigned by the numbering authority in the country (Think Bureaucracy).

The ITU-T doles out the point codes to the world, (except for ANSI). These are not that easy to get. You can't just ring them up and ask. Point codes are like IP addresses, only shorter.

Then there is your connection to the network. Please bear in mind that this is not the internet, and you have no "right" to get access. If you are going to offer a service to customers, then you can get an SCCP provider such as BT, FT, Belgacom, Comfone, or VSNL-Teleglobe to hook you up. If you intend to scam and spam, then you would get shut down rather quickly. Even though it is a worldwide network, there are only a few players. They all know each other.

 So Abdul....What are your plans, anyway?
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Abdulsalam
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« Reply #9 on: May 29, 2007, 10:15:04 UTC »

Hello,

Many thanks for your posts.
Ok, this the book by HenryLaborder Chapter 7 from where I got the 338 method:
http://www.artechhouse.com/GetBLOB.asp?Name=HenryLaborder_CH07.pdf
And about what I am planning to do:
Of course not scam nor spam. But, just as a legal GSMA member as a Roaming Broker.
So, I am planning to be a third party as an SMS interworker over SS7.

Back to our discussion:
Ok, no way for a signaling provider to make a routing over DPC/SSN as they are from the lower layers below SCCP. Therefore, they can do routing over GT only through the SCCP layer.
But, can I get my own GT from a signaling provider?
And if I can, then I  can ask my roaming partners to replace the destination GT ( of the network that they don't  have a roaming agreement with them but I do have)with my GT. But then, how would my signaling provider tell me the original destination GT? I mean can the SCCP handle the addressing of more than one destination GT.
But if I can't, what addresses can the SCCP provider give me?
Do you have any idea about if a mobile operator can have more than one SCCP provider?
And if they can, then how will the proper routing over GT between SCCP providers work?
Thanks in advance for your reply.
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Abdulsalam
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« Reply #10 on: June 05, 2007, 08:33:01 UTC »

Dear all,

Yet, I didn't get any answers about what addressing can the signaling provider host for his customers?( I guess that the signaling provider will assign me a dedicated GT! Am I right?)

Now, at the roaming mobile operator side:
Can the operators SMSC reroute the SendRoutingInfoForSM to a different SCCP address without modifying the content inside the GSM-MAP packet?

knowing that the above roaming operator willing to reroute this to a third party as he don't have a roaming agreement with the destination operator. ( while the third party do have).

If the answer depends on the vendor of the SMSC or other signaling points at the roaming mobile operator side. Please specify those vendors who can do this rerouting.
Or, may be it depends on the signaling provider of the roaming mobile operator!

Thanks in advanced for your reply.
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