How SMS Works

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.

1. The SMS message is submitted to your wireless service provider’s SMS Center.
2. 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.
3. The SMS Center sends the message to the Mobile Switching Center (MSC).
4. The MSC collects the recipient’s information from the Visitor Location Register (VLR) and, sometimes, proceeds with an authentication operation.
5. The MSC forwards the message to a Mobile Server
6. The MSC returns the outcome of the Forward Short operation to the SMS Center.
7. 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.

  Mike