Q-Lite Satellite Modem Installation and Operating Handbook
7-19
automatically be forwarded to the far modem. The M&C VLAN is filtered (pulled off) by
each modem and the commands processed. This is true also in a point-to-multipoint mode,
where the M&C messages for all the remote modems share the M&C VLAN, with each
modem acting on just the M&C messages addressed to that modem.
The M&C VLAN can be used in all modes (including bridging and routing) and for all
waveforms, regardless of whether VLANs are being used more generally or not. There is
no restriction on how much bandwidth can be used for the M&C VLAN and it will consume
as much or as little as required.
7.8.6 IP Over ESC
The Engineering Service Channel (ESC) is a low rate independent data channel from the
main data channel that exists within some framed satellite services such as IBS and
Closed Network plus ESC. It was originally intended for inter-earth station communications
and is often used for M&C control of remote equipment.
The ESC is implemented as an internal serial interface run at baud rates up to a maximum
of 115kbps. The ‘
ESC interface type
’ needs to be set to ‘
IP
’ to put the ESC into IP mode.
Because the ESC is a serial interface, IP will not run directly on top of it – the modem
encapsulates IP packets within PPP, much the same as a dial-up modem connecting to the
internet. When used for IP, the ESC channel runs in bridge mode, with the M&C port being
bridged to the ESC channel.
Since the ESC channel acts as a bridge, some bandwidth may be consumed by broadcast
traffic finding its way onto it and it is best to minimize this if possible.
The modem allocates private IP addresses to the two ends of the ESC link – no user
address set up is required.
The ESC channel in IP mode has some sophisticated M&C modes as described in the
following list (in all cases, IP packets destined for the remote network continue to be
bridged over the ESC):
•
Paradise Univeral Protocol (PUP) commands can be sent to the modem with an
‘
esc
’ prefix to force them to be sent over the ESC to the far modem e.g. ‘
esc get
RxRemoteEbNo
’.
•
If you don’t want packets to be indiscriminately forwarded over the ESC then you
can take the M&C port out of the bridge, meaning that packets on the M&C port will
not
normally
then go any further than the local modem. You can then force chosen
packets to be forwarded over the ESC if you want. Forwarding is controlled by the
‘
Remote M&C interface
’ setting. Setting this to ‘
IP – Forward to remote
’ causes the
modem to process TCP packets sent to ports 6703 and 6704 in a special way.
o
Packets sent to port 6703 are forwarded over the ESC to port 6703 on the
remote modem. At the remote modem (with the remote M&C interface
mode set to ‘
IP – Remote (Rem M&C)
’), the payloads of packets received
over the ESC on port 6703 are forwarded out of the serial RS485 M&C
interface (i.e. converted from IP to serial commands).
o
Packets sent to port 6704 are forwarded over the ESC to port 6701 on the
remote modem. At the remote modem, packets received over the ESC on
port 6701 are treated as local M&C commands for the modem and go no
further.
