This post showcases the MS-initiated point-to-point call flow. Please see below for more information on the topic.
The point-to-point call service is one of the major railway services. For example, when a train driver calls the dispatcher, the train driver is the calling party in the point-to-point call. The following figure shows the flow of an MS-initiated point-to-point call in GSM-R networks.
1. Steps (1) through (8) in the figure on the previous slide describe the random access and immediate assignment processes, in which the BSS assigns signaling channels for the MS.
2. Steps (10) and (11) may involve the authentication, encryption, and classmarkquery or update.
Based on different data configurations on the MSC, the MSC may deliver the following messages instead of the CM Service Accepted message after links are established over the A interface:
a) the Cipher Mode Command message for starting the encryption process (in this case, the MSC does not send the CM Service Accepted message);
b) the Authentication Request message for starting the authentication process;
c) the ClassmarkUpdate message for starting the classmarkupdating process.
3. Steps (14) through (22) in the figure on the previous slide describe the TCH assignment process, in which the BSS allocates voice channels and circuit resources over the A interface to the MS.
4. Steps (30) through (40) in the figure on the previous slide describe the release process.
