- Data Communications Operator's guide Ethernet CMG-DCM

CMG-DCM
The options will take effect immediately whenever possible. Some changes may
take some time to complete, since services may need to be restarted. The
gcfgdbset command performs only simple checks on the new value, so you
should check the syntax of the option carefully.
Wi-Fi
Optionally, a DCM may be supplied with 802.11 (“Wi-Fi”) hardware in place of
Ethernet. There are two modes in which an 802.11 network may operate:
• In ad hoc mode, data packets are sent out over the wireless connection
indiscriminately and are received by all machines on the network. This is
the simplest style of Wi-Fi network, but consumes more power and
cannot easily be extended to large networks.
• In infrastructure mode, dedicated 802.11 hubs collect data packets,
collate, and distribute them efficiently around the network. These hubs
may also act as transparent extensions to existing (wired) TCP/IP
networks.
The DCM is capable of running in either situation, depending on your
requirements. As far as the computers on the network are concerned, there is no
difference between a TCP/IP network running over Ethernet and one using
802.11 connections, or a mixture of the two.
Once the 802.11 system is running, you will need to run a DHCP service on
your network, or manually set the IP address of the DCM as above.
Connecting to the Internet
If the local network is already connected to the Internet through some other
means (perhaps through a gateway machine), you can create a default route with
gcfgdbset net.eth.0.gateway network-gateway
where network-gateway should be replaced with the IP address of the
gateway on your local network.
The DCM can perform more complex routeing if required. See “Static routes”
in Section 4.4 for more details.
As supplied, the DCM module will accept requests to its on-board Web server
and logins over SSH. In addition, the DCM can be requested by Scream! or
other GCF-compatible software to send GCF streams to your computer.
If the instrument is located on a private network, you may be able to connect to
it from the wider Internet by using a feature implemented by SSH known as
tunnelling. You can use this technique to connect to the DCM through a chain
16 Issue A