Question: In a Public Land Mobile Network (PLMN), what does the 'protocol on the signalling channel' attribute at an access/reference point typically characterize, and which of the following is NOT a possible value for this attribute in terms of protocol stacks?
Option 1: Characterizes data transmission speed; manual, V-series, X-series
Option 2: Characterizes signalling protocol type; HTTP/FTP, V-series, I-series stack
Option 3: Characterizes network architecture; Wi-Fi, V-series, X-series
Option 4: Characterizes signalling protocol type; manual, appropriate V-series protocol, appropriate X-series protocol
Explanation: The correct characterization is related to the 'signalling protocol type'. Among the options, only one correctly identifies a scenario where the provided choices do NOT match the possible values for the attribute as described. HTTP/FTP are not signalling protocols in the context of PLMN's signalling channels, making Option 2 the correct answer due to its incorrect protocol suggestions (HTTP/FTP) alongside correct characterization (signalling protocol type).