|
|
Hi Guy's,
On this matter. We are clearly talking about GSM SMS implementation generally.
Whilst implementations differ, this is roughly how it works.
Originator ->originating networks SMC->receiving Subscriber. You may be wondering where the receiving networks SMC has gone, literally speaking the receiving networks SMC plays no real role in the delivery. It appears largely transparent to the originating SMC, which will basically set up a signalling* path directly to the recipient handset.
Signalling/IP* communication done purely between machines, often takes wholly differents paths from the speech circuit it can set up.
The issue with replying is that, depending on SMS software in the handset, this will generally try to reply using the original senders SMC. Across most networks this will fail because the majority preclude submission of SMS from another network. The obvious reason for this is that no one would pay for SMS as you would just change your SMC no. to one which could not bill you.
Moreover, some handsets, within message settings have the ability to set "reply via same centre"(doomed to fail X net) and others have the ability when sending to "prevent reply".
Interoperability problems arise, particularly internationally, because GSM is basically a hybrid technology somewhere between IP and circuit switched comms. Different networks are at different levels of development with the European networks particularly driving further into IP technologies in order to support our ever growing desire for more services. There are also compatibility issues between different network element vendors.
As most signalling is done in a varying standard IP or ATM realm(differing, ocassionally proprietary protocols floated on top) and this is the layer most SMS is passed over, there is fairly heavy scope for **** up. This results in Political reason no1 for stating "we support the sending of SMS to this network", when a supported service fails, customers complain. Though in fairness, it is our desire for gadgetry in the developed world which results in many of these issues.
There have also been issues felt when some networks provide GatewaySMC services to some slightly dubious web based sources(spam anyone?). From an Operators point of view it makes complete sense to bar these networks from submitting SMS to you. They have to increase SMC capacity in line with the deluge or the service to paying customers suffers, the customers themselves don't get spammed(or reduces).
When roaming, even if your network has a send/receive agreement with that network, there are a few reasons why you cannot send. When you roam a copy of your Home Location Register details(subscriber database) is exported to the "foreign" network, this is done in the signalling realm obviously(see the pattern  ). Occasionally what are known as basic or core services either go missing or the status of them is misconstrued by the recipient network.
On message duplication, the Mobiles relationship with the originating networks SMC is simple. Mobiles states "here have this", SMC signals back "got it". The way this reflects on the mobile is "message sending" and then "message sent", "message sending failed" would be seen when either, the SMS did not make it to the SMC, it was rejected by the SMC or the SMC "got it" message didn't make it to the handset. In this third scenario your SMS is actually sent and received by the SMC, for forwarding to the intended recipient, you believing the message sending failed, re-send, two SMS on the SMC!
On the receiving leg the SMC says "here have this" and the Mobile says "got it". From an SMC perspective it can see "message sending failed" if the SMS fails to make it to the mobile or if the "got it" from the handset doesn't get back to the SMC, the SMC re-sends. In the second scenario, this will result in two SMS on the handset.
Blimey, the ramblings of a drunk man, sorry if I bored ya all, hope it helps someone better understand what goes on behind the scenes 
|
|
|
Posting Permissions
Originally Posted by wahili
