Wavecom W61PC V7.5.0 - Manual (Page 282)

272  SAT System WAVECOM Decoder W61PC/LAN Manual V7.5
MES Identification
A MES is called from the terrestrial network by its Inmarsat Number (IMN) which is identical to its public
telephone number with a country code prefix according to Table 2. Internally the system uses two differ-
ent (24 bits) IDs:
The Forward MESID, used on the forward path, i.e. in the direction from the Land Earth Station (LES) to
the Mobile Earth Station (MES).
The Return MESID, used on the return path, i.e. from the MES to the LES.
These IDs are unrelated to the publicly published IMN and are only known to the Inmarsat system, which
maintains a database describing the relationship between the IMN and the MESID pairs. These IDs are
hard coded into the satellite terminals at manufacturing time.
Session Signaling
In its idle state, the MES continuously listens to the NCSC, updating its internal network status database
(control channels, frequencies, etc) through the Bulletin Board messages.
There are two possibilities for starting a session:
 Fixed station initiates the session;
 MES initiates the session.
Fixed Station Initiated Session
Through the terrestrial network, the fixed station connects to a LES. The LES sends a signaling message to
the NCS, which in turn pages the MES via the NCSC. The MES receives the session oriented signaling mes-
sage with its Forward MESID, and sends a response back to the NCS with its Return MESID. The NCS in
turn sends a channel assignment signaling message to both the MES and LES, and both stations will tune
to the assigned traffic channel, where the session will take place. The traffic channel carries all user data
(voice, fax, data) plus signaling messages as required. At the end of the session, the traffic channel is re-
leased and the LES informs the NCS, that the channel is free again. The NCS returns the assigned channel
and channel equipment to its pool of available resources.
MES Initiated Session
On a MES Request Channel, the MES sends a request signaling message to the NCS containing its Return
MESID. The NCS then sends the traffic channel assignment using the Forward MESID to both the LES and
the MES. The remaining part of the protocol is as in the case above.
SAT Operation
The decoder displays the session output in two windows, a Session Window and a Session List Window.
The Session Window continuously displays control channel information:
Field
MODE: B, M, mM
SERVice DATA (data), FAX (fax), TEL (voice),TELX (telex)
EVeNT srt Traffic channel start
ass Assignment
ccs Control channel start
end End
MES_ID Mobile earth station ID
FREQ Traffic channel frequency
TX_CHA_ID Channel ID of the uplink channel from the MES
The result (a file) of a monitoring session is listed in the Session List Window. Bold font indicates that a
file is unread by the user, while normal font indicates that the file has been read (Display Status). In order