Do SMS' ever get lost?
January 26, 2011 2:43 AM Subscribe
Where does my SMS go on it's way to where I've sent it? Does it hang out at the phone company at all or does it go out like a phone call?
What are the technical details of an SMS' trip from my phone to the recipients'? Would a (albeit fictional, which is to say they 'how' is marginally less important than the 'if possible') hacker steal SMS messages off the sim card in my phone or could they get them from some storage device at the phone company?
Secondly, where could I find an example of a 'raw' SMS, one with all the information that (I'm assuming) gets stripped when it shows up on my phone?
I've browsed a couple message boards but I've yet to find an answer to these (I thought) pretty straight-forward/stupid obvious questions.
Thanks!
What are the technical details of an SMS' trip from my phone to the recipients'? Would a (albeit fictional, which is to say they 'how' is marginally less important than the 'if possible') hacker steal SMS messages off the sim card in my phone or could they get them from some storage device at the phone company?
Secondly, where could I find an example of a 'raw' SMS, one with all the information that (I'm assuming) gets stripped when it shows up on my phone?
I've browsed a couple message boards but I've yet to find an answer to these (I thought) pretty straight-forward/stupid obvious questions.
Thanks!
Best answer: The trip that your SMS takes can be quite complicated, but the basic process is described fairly well on Wikipedia. Your phone (a.k.a. your "mobile station") sends the message over the air network (via the MAP part of the SS7 protocol) to a part of the network switching subsystem called a mobile switching centre (MSC), or to a part of the GPRS core network called a serving GPRS support node (SGSN). From there, it is forwarded to a short message service centre (SMSC). The SMSC tries to deliver the message to your friend's phone; if it can't be delivered (for example, if your friend's phone is off), the SMSC may store it for a while, re-attempting delivery until it considers the message to be expired (called the "validity period"). Once the message is delivered, you have a chain of acknowledgements going all the way back to your phone.
It can get a lot more complicated than that, and once you start involving multiple operators, multiple countries, mobile number portability (MNP), home location registers (HLRs), firewalls, filtering software, and many other variables. So yes, it's very possible that your messages are lost along the way. Google some of the terminology above, and you'll learn a lot (including even more acronyms!).
posted by neushoorn at 3:20 AM on January 26, 2011 [3 favorites]
It can get a lot more complicated than that, and once you start involving multiple operators, multiple countries, mobile number portability (MNP), home location registers (HLRs), firewalls, filtering software, and many other variables. So yes, it's very possible that your messages are lost along the way. Google some of the terminology above, and you'll learn a lot (including even more acronyms!).
posted by neushoorn at 3:20 AM on January 26, 2011 [3 favorites]
Would a (albeit fictional, which is to say they 'how' is marginally less important than the 'if possible') hacker steal SMS messages off the sim card in my phone
SMSes are generally stored in an "Outbox" or "Sent Messages" folder on your phone (which may store the messages directly on the SIM or on the phone's internal memory), so theoretically if someone could "hack" into your phone they'd be able to read messages that you'd sent (assuming you hadn't deleted your sent messages after sending).
posted by EndsOfInvention at 4:29 AM on January 26, 2011 [1 favorite]
SMSes are generally stored in an "Outbox" or "Sent Messages" folder on your phone (which may store the messages directly on the SIM or on the phone's internal memory), so theoretically if someone could "hack" into your phone they'd be able to read messages that you'd sent (assuming you hadn't deleted your sent messages after sending).
posted by EndsOfInvention at 4:29 AM on January 26, 2011 [1 favorite]
To answer your title question - Do SMS' ever get lost?
Yes, they can get lost or may simply not be delivered. Simplest reason for this would be if the recipient's hand set is off for a lengthy period of time and the message expires. There are a couple of other less common scenarios.
You can select to enable delivery receipts which will tell you whether the message was delivered or not. Might be days before you get a delivery failure message.
posted by w.fugawe at 5:05 AM on January 26, 2011
Yes, they can get lost or may simply not be delivered. Simplest reason for this would be if the recipient's hand set is off for a lengthy period of time and the message expires. There are a couple of other less common scenarios.
You can select to enable delivery receipts which will tell you whether the message was delivered or not. Might be days before you get a delivery failure message.
posted by w.fugawe at 5:05 AM on January 26, 2011
Delivery receipts are a feature of the SMS (and email, for that matter) client, not the protocol.
posted by gjc at 5:09 AM on January 26, 2011 [1 favorite]
posted by gjc at 5:09 AM on January 26, 2011 [1 favorite]
Best answer: To answer your other questions:
It is theoretically possible that some hacker could see your messages. Not so likely in your phone, I think, but as I described above, the message hits quite a few network entities in its journey, and can probably be comprised at pretty much any point (well, during any operation that contains the "user data", which is the message that you wrote).
Also, various people who work for network operators can see the content of your messages, unless you live in a country where that information must be hidden from them (I doubt such a country exists). If you live in certain countries, I can guarantee that your messages are being read, and that there is automatic filtering in place to censor or outright block messages that contain whatever text the operators/government thinks needs to be censored.
The way a "raw" message looks depends on the encoding. There's some information about it here.
posted by neushoorn at 5:16 AM on January 26, 2011 [1 favorite]
It is theoretically possible that some hacker could see your messages. Not so likely in your phone, I think, but as I described above, the message hits quite a few network entities in its journey, and can probably be comprised at pretty much any point (well, during any operation that contains the "user data", which is the message that you wrote).
Also, various people who work for network operators can see the content of your messages, unless you live in a country where that information must be hidden from them (I doubt such a country exists). If you live in certain countries, I can guarantee that your messages are being read, and that there is automatic filtering in place to censor or outright block messages that contain whatever text the operators/government thinks needs to be censored.
The way a "raw" message looks depends on the encoding. There's some information about it here.
posted by neushoorn at 5:16 AM on January 26, 2011 [1 favorite]
Best answer: Check out the source code for gnokii - it's capable of sending raw sms using one's phone, or a usb gsm modem. Even if you don't have cables / blue tooth to connect your phone to the computer (or if your phone isn't supported), you can look at the code to see how the message gets put together. Turn up debugging, and you see the data as you send.
posted by nobeagle at 6:53 AM on January 26, 2011 [1 favorite]
posted by nobeagle at 6:53 AM on January 26, 2011 [1 favorite]
Just as as anecdote, SMSes routinely get lost when they're sent between two of the major cell phone providers here (Rogers and Telus). Rogers-to-Rogers is fine, Telus-to-Telus is fine, but anything between the two runs a not-insignificant risk of being delayed or lost altogether. It doesn't happen a lot, but enough that a pattern has emerged and is well documented in the interwebs.
posted by cgg at 7:24 AM on January 26, 2011 [1 favorite]
posted by cgg at 7:24 AM on January 26, 2011 [1 favorite]
neushoorn's answer is correct but only considers the situation in which the sender and the receiver are on the same operator and in the same country.
If, for example, you are on AT&T and you send me a text message then your phone would send this message to AT&T's SMSC who would then forward that onto O2 UK's SMSC which would then send this to my mobile phone. In short, your phone only ever communicates with your operators SMSC and your operators SMSC handles the sending of messages to the correct SMSC and the receiving of messages intended for you.
The best way to think of an SMSC is that it is like the postal service. You send an SMS (post the message into the post box), the SMSC redirects the message to the correct recipient SMSC (the post is shipped to the UK postal service), the recipient SMSC sends the message to the phone (the UK postal office sticks the letter through my door).
(Those of you old enough will remember many many years ago, it was allegedly possible to change your phones SMSC to get free text messages - although I never knew anyone who actually got it to work)
Finally, just because you're on the same operator doesn't mean you'll use the same SMSC. For example, if I send a text message to someone on O2 in Germany then it'll still have to pass from O2 UK's SMSC to O2 Germany's SMSC. Even big players like Vodafone do not have one SMSC which handles multiple countries.
This is for GSM phones as I have very little experience with CDMA.
posted by mr_silver at 10:54 AM on January 26, 2011 [1 favorite]
If, for example, you are on AT&T and you send me a text message then your phone would send this message to AT&T's SMSC who would then forward that onto O2 UK's SMSC which would then send this to my mobile phone. In short, your phone only ever communicates with your operators SMSC and your operators SMSC handles the sending of messages to the correct SMSC and the receiving of messages intended for you.
The best way to think of an SMSC is that it is like the postal service. You send an SMS (post the message into the post box), the SMSC redirects the message to the correct recipient SMSC (the post is shipped to the UK postal service), the recipient SMSC sends the message to the phone (the UK postal office sticks the letter through my door).
(Those of you old enough will remember many many years ago, it was allegedly possible to change your phones SMSC to get free text messages - although I never knew anyone who actually got it to work)
Finally, just because you're on the same operator doesn't mean you'll use the same SMSC. For example, if I send a text message to someone on O2 in Germany then it'll still have to pass from O2 UK's SMSC to O2 Germany's SMSC. Even big players like Vodafone do not have one SMSC which handles multiple countries.
This is for GSM phones as I have very little experience with CDMA.
posted by mr_silver at 10:54 AM on January 26, 2011 [1 favorite]
Response by poster: Thanks!
It's not something I ever really think about, and as I don't work in telecom in any way, I had no idea even where to start.
posted by From Bklyn at 11:43 AM on January 26, 2011
It's not something I ever really think about, and as I don't work in telecom in any way, I had no idea even where to start.
posted by From Bklyn at 11:43 AM on January 26, 2011
This thread is closed to new comments.
posted by Salvor Hardin at 3:14 AM on January 26, 2011 [1 favorite]