2 Mobile Network Architecture
Reference: Tobias Engel, SS7-Locate-Track-maniuplate, Presentation: https://berlin.ccc.de/~tobias/31c3-ss7-locate-track-manipulate.pdf, Video: https://www.youtube.com/watch?v=-wu_pO5Z7Pk
As the above figure , there are several important nodes that needs be familiarized with and what are their functions.
Home Location Register (HLR): Each operator has one or more HLR depending on its capacity. HLR operator's database each subscriber’s profile/info is stored in only one HLR. The HLR hold the below critical info:
- IMSI
- IMEI
- MSISDN
- Authentication keys of subscriber
- Subscriber latest location
- subscription profile
- Services allowed (call forwarding, barring,..etc) ..etc
Visitor Location Register (VLR): Each VLR is responsible for a specific region. Every subscriber roaming in a specific region is attached/connected to the VLR responsible for this region. The VLR acts as a temp database for the period of the roaming subscriber. It has the same info as the home network HLR.
Mobile Switching Centre (MSC): Each group of cells/BTS/towers are connected to an MSC. The MSC is responsible to route and switch calls,SMS and data from and to the subscribers attached to it.
Short Message Switching Centre (SMSC): Responsible for sending and delivering short messages (SMS) to subscribers.
Signal Transfer Point (STP): It acts as the gateway (i.e router) of the operators,which is responsible for all the routing, path determination and relaying of the SS7 messages.