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Communication Sequences
MES-originated Duplex Telephone Call
MES
Mobile Earth Station
Listens to NCS common
channel.
OFF-HOOK
ESC
MES operator dials
subscriber's international
telephone number.
Transmits "Access Request"
SU.
Sets SCPC channel in "In-
band Signalling" mode.
Transmits "Service Address"
SUs and "Scrambling Vector
Advice" SU alternately.
"Return Carrier Identifier"
SUs
Changes to MESV/SUB
mode
"Ringing tones"
Transmits "MES
Connect" SUs.
Transmits speech
and "MES Connect"
SUs continuously.
12
INMARSAT-B
LES
Land Earth Station
NCS Common Channel
MESRQ
Adds MES to LES
busy list.
LESI
"Request for Channel
Adds MES to NCS
Assignment" SU
busy list.
NCSI
Transmits "Channel
Assignment" SU.
NCSA
NCSA:
Once for maritime
MES. Three times for
Land mobile MES.
MES-SIG
Returns "Scrambling
LES-SIG
Vector Acknowledge"
SU.
MES-SIG
Changes to
LESV/SUB mode.
Terrestrial call set-up
procedure.
LESV & SUB
Transmits "Ringing
LES Voice Channel
Tone" & "Fill-in" SUs.
and sub-band
signalling
SUB
Sends answer signal
& "LES Connect" SUss
SUB
SUB
"Fill-in" SUs when
quiet.
Maintains burst SU
every 5 secs to
prevent clearing by
MES.
For call release, see
separate diagram
NCS
Network
Mobile Earth Station
Coordination
Station
Listens to NCS common
channel.
Transmits "MES
Response" SU on the
TDMA channel.
Sets SCPC channel in "In-
band Signalling" mode.
Transmits "Scrambling
Vector Advice" SU
repeatedly.
RINGING
Transmits "Return Carrier
Identifier" SUs.
Switches to MESV/SUB
mode
OFF-HOOK
Transmits "Connect" SUs
Transmits speech
ESC
and "MES Connect"
SUs continuously.
S y s t e m D e s c r i p t i o n
S y s t e m D e s c r i p t i o n
S y s t e m D e s c r i p t i o n
INMARSAT-B
Fixed-originated Duplex Telephone Call
LES
MES
Land Earth Station
NCS Common Channel
Validates MES
authorization.
Adds MES to LES
MES number from
busy list. "Request
telephone network.
for Call
Announcement" SU.
MESRP
MES-SIG
Returns
LES-SIG
"Scrambling Vector
Acknowledge" SUs
repeatedly.
MES-SIG
Ringing tone
(generated by LES)
SUB
SUB
"Fill-in" SUs when
quiet.
Maintains burst SU
every 5 secs to
prevent clearing by
LES.
For call release, see
separate diagram
NCS
Network
Coordination
Station
LESI
Adds MES to NCS
busy list.
NCSC
"Call Announcement"
SU. Repeated once if
no response from
Land Mobile MES.
NCSI
Transmits "Channel
Assignment" SU.
NCSA
NSCA: Once for
maritime MES. Three
times for Land
mobile MES.
Saturn Bp Portable – Technical Manual
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