Quantum and Evolution Series Installation and Operating Handbook
8-38
Header compression on the IP Traffic card works to 29000 packets per second one way,
22000 two way.
1.32.4 Jumbo Ethernet Frame Support
Leaving aside preamble, a standard Ethernet frame has 18 bytes of overhead and varies in
size between 64 bytes and 1518 bytes. Some protocols extend the Ethernet frame e.g.
VLAN and MPLS both add 4 bytes.
The base modem supports Ethernet frames up to 1536 bytes in length.
The IP Traffic card supports Ethernet frames up to 1600 bytes in length.
1.32.5 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
