Here’s a summary of my understanding of how SMS works….
SMS works on a store-and-forward basis. Instead of being sent directly to the recipient, SMS messages travel through several important nodes before reaching the recipient.
- The SMS message is submitted to your wireless service provider’s SMS Center.
- After the message is processed internally, the SMS Center sends a request to the Home Location Register (HLR) and receives the routing information for the recipient.
- The SMS Center sends the message to the Mobile Switching Center (MSC).
- The MSC collects the recipient’s information from the Visitor Location Register (VLR) and, sometimes, proceeds with an authentication operation.
- The MSC forwards the message to a Mobile Server
- The MSC returns the outcome of the Forward Short operation to the SMS Center.
- The SMS Center reports delivery status of the short message back to the sender.
Remember for serving a search warrant on undelivered SMS, they are stored at the originator’s SMSC. Here is a graphic
In relation to the great debate about interception of communications, here is an US interpretation:
- In order for the SMS to fall under wiretap (Title III in US, RIPA for UK) the SMS would need to be recieved in real time.
- Since the SMS is in fact stored at the provider level it is not in real time
- Therefore, considering the second point, the SMS is a stored electronic communication and subject to the Electronic Comunications Privacy Act (ECPA) and can be obtained via probable cause and a search warrantHope this is helpful to the Community.