Securing views Berg

SMS may seem like a very trivial service. The daughter sent the scarce 3000 SMS in November (which 1200 + to the same guy). She has of course no idea how it works behind the scenes and do not care, of course, in which, but since I wrote a kilometer post to a mailing list to explain, I felt that the job was done and that I might as well share it with others. I may well take this opportunity to warn that it is difficult to explain in lekmannanivå without becoming completely unmanageable. Some knowledge of network nodes and GSM topology should bear this in mind before you understand fully below.

The question is when will the text messages back and what factors influence this?

I often say that they understand the GSM that moment when you are infinitely packed, just before the roosters. The moment you understand where the universe ends and the other big issues. Then fall asleep and forget it in the morning.

It's completely irrelevant who you are delivering your subscription to one but there are two things that are important;
* In which network carries HLR (Known HPMN - Home Public Mobile Network. HLR Home Location Register - that the operational database in which your subscription is registered. It is not the actual customer list - your billing address and when customer service has been in contact with you but your SIM identity and related services))
* In which network / during which the VLR is it updated (Known VPMN - Visited Public Mobile Network. VLR means Visited Location Register, which can be regarded as a local working copy of your CPR that includes all of its own and visiting customers who are registered under this VLRs pickup)

The sending SMSC t have to have a relationship with both. Are you in your hammanät are these the same and it's a minor problem. Grid of SMSCs t is called APMN. (Associated Public Mobile Network)

Whoever designed the SMS was a "genius" who thought that the normal chain of client - server - server - client went to optimize. Much would be easier if he thought the whole chain out and also stops
smoking weed in the spec no! I am sure that the technician's favorite saying "broken" is something that is used to comment on this.

Introduction to SMS *** ***

Telephony is based on having payload (the actual voice traffic - typically a 64 kbit / s circuit-switched connection), and signaling. In the past signaled it on the voice channel / payload which enabled BlueBox technology could be used to make free calls (see the movie Sneakers for how it could look like). They emulated the signaling and could call that they wanted. Now there is signaling of a logical separate packet switched network. Signalling is thus the control signaling between network nodes.

Now I'm a little unsure of the terminology - if I use the "stack" right, but I am after all a lawyer and not technologies why I allow myself to slip on the concepts sometimes

# In the United States uses an ANSI (Named SS7) stack defined and in Europe a CCITT - now ITU - (Named C7) defined variant, so you need via a gateway if you must travel between systems.
# On top of that you follow

• ISUP for pure link signaling (connection, disconnection, caller ID info, etc.);
• MAP (Mobile Application Part - besöksnät a roamare knocking on and check with CPR if he can roam and everything else needed to maintain mobility) and
• CAP (CAMEL Application Part - available in several phases used for real-time charging, code conversion, driven from its home network, and so on).

SMS is a service which uses the MAP.

SMS goes like this:

1) The mobile phone sends to its SMSC regardless of where you are. SMSC is defined in international format in the phone - taken from the SIM, and it's SMSCs such that then is the sender. By the sender is the Swedish SMSCs such as use of the Swedish numbering plan and that is why you can send 71xxx and 72xxx even from abroad. (SMS tested in IR.24 tested, which means that if roaming works, you MUST text message also Funka both in and out for postpaid - or is something wrong. For prepaid, it may be different). As far as the client - server: it is now the freaking out.

2) SMSC: t now takes out where the receiver is by sending an SRI (Subscriber Routing Information) to the recipient's CPR - in return, it receives a reference to the VLR where you are updated. If something goes wrong here, you know SMSCs such that it went wrong and you get a proper error message.

3) SMSC: t is now delivering SMS.et to the network on which you are updated.

Sounds of course easy, but because it may be that all these parts go wrong, it is not so simple.

What could go wrong?

a) For an SMSC to send an SRI then there must be an established signaling relationship between the two networks - one has implemented one another Global Title "rants" and it shall be open
through C7 carriern. The premise is that it is closed, so there's normally an active effort to open. It usually opens for networks that have been roaming (SMS come with "on the house") or you must have opened special (unusual). Sometimes you're lucky and signaling suppliers have opened a little more than just some GT ranks (sometimes they open the whole country at once), but in return we know of course not if it will continue to function. So it is always good to make sure that it is green from the supplier.

Normally, this is one of SMSC.t out which networks are open (a whitelist) and uses an SMS broker case you do not reach himself. So this is a special player in the market for SMS delivery that sells capacity to terminate SMS for an attractive price and to as many destinations as possible. There are an incredible number of players in this market.

Here's the catch; ACK for delivering text messages are usually sent by the broker for their platform received the SMS. You will receive a message that got through but it's not true - the only thing that is clear is that the broker received it, this is not the same as the recipient received it. A case in point when you text and it says that the recipient received it and you learn that it does not - then it is typically so that a broker has been used and it has not managed to deliver SM et.

A magical dimension is how to find the right network if all you have is the number and the recipient's operator is in a country with nummerpotrabilitet. "It dissolves in signaling dimension" I have received in response but did not become wiser from it.

b) You must have a sensible VLR address back to your SRI request.

Some networks allow the SMSC to other networks simply send to their customers if there is a special agreement signed SMS (SMS Interworking). This is manifested, for example, by sending SHAM back, but in a properly formatted message. (I so clearly do not point to any one here - especially Vodafone in Germany

c) When one now knows which VLR to which the receiver is in it's SMSC for sending it. If there is a roaming network (ie, HLR and VLR for the receiver is not the same network) so it can go very wrong. As before, we know that the HLR and VLR network has roaming (and thus signaling) - otherwise the receiver had not been able to update itself in this network. The snag is that APMN (SMSC network) not need to have roaming with a visit to the network (VPMN). This is the single most common error case, you get reasonable response to your question SRI, but nurtured then you must deliver, it's a network you can not reach.
- If there is a signaling relationship between SMSC network and VLR network it goes well (delivered or you happen to be on). SM goes up - ACK comes back.
- If this relationship is missing, can it be that the SMSC: t can still send the message to the VLR because it happens to be open. Unless failar the (correct error) - SM does not approach.
- The receiver receives and will now visit the web send an ACK back. If it goes forward as it succeeded and we have a properly delivered message. SMS goes up - ACK comes back.
- BUT the real circus show up on SMSC St. successful send but receiver network may not return an ACK. Then SMSC e.g. into its retry
schedule. Depending on how it is defined, you can SMSC: t here to bomb the recipient of messages. When 3 was a young operator and had an extremely aggressive retryschema so would my boss texting his brother (a customer of T-Mobile) and swapped the two figures. The receiver was in Morocco and roamed the provider Telia were roaming with us on 3 had the other. The receiver was slightly hysterical after about 250 messages in less than a day.

What can you do?

An operator can protect their own customers by always returning their own (virtual or real) VLR address of all SRI issues. This will avoid the sending SMSC: t send to the recipient. When you create a classic client -> server -> server -> client brand that works.

There is much more to delve into the substance SMS

SRI issues can be used to a lot of things that are legal and ethical gray areas.

- Some network scans number series with SRI to find out which number includes subscribers. It can be done in order to measure a competitor or as preparation for gathering data before a SMS spam campaign. An alternative to damsuga internet for email addresses before they have to send email spam. I can not say I know that this happens often, but I personally have insight into a case of an Indian operator did this to a British operator (and the British suffered a text message spam attack just a week later).

- You can build some services on SRI: If you have a visitor in her at roamare. If you lose that visitor, you can ask a question SRI. Is roamaren in another country, so thank you for stopping by and wishing to welcome back ("Au Revoir SMS") but if he is on another network in the same country, you can send "Win Back SMS" (marketing to the customer to actively change the network to yours). Note that Winback SMS course goes directly into the normal case, the home service provider does not even see that this message will go. All proceedings in which visits the networks sending SMS is normally prohibited, unless your provider has given its consent. This is regulated by the GSM Association's documents BA.47 which was signed by and delivered a number of lines. My contribution was to create public opinion and also other types of marketing through other means - such as Bluetooth's broadcast that occurs in Italy - should be covered. The point is that you are a customer of his home operator and not in the visitors' net so all communication must go from the home network or be with the home network's consent. Few things are broken it to a greater extent than this!