Originally Posted by merrimac
.....My opinion: do some research
on which router (software) works well, and then publish that here. OpenCPN development has taken thousands of manhours, all contributed for free. See this as an opportunity to do something in return.
Based on research
done so far; an ASUS RTN16 running Tomato (Version Shibby 1.28.0000 MIPSR2-117 K26 USB VPN) with some configuration changes to IGMP/Multicast will allow the multicast from the scanner through to OpenCPN over wireless. The router is configured to run 11N only for wireless connections, to give it a fighting chance of handling the data volume. It also has 4x100Mb ethernet ports
Changes effected were:
Advanced>Firewall>Multicast - Enable "IGMProxy" & "LAN"
Advanced>Routing>Miscellaneous - Enable "Efficient Multicast Forwarding"
Advanced>Wireless - Set "Multicast Rate" to 54Mbps (the max allowed)
Advanced>Wireless - Set "Wireless Multicast Forwarding" to Enable
As I can see from the router throughput charts
, the radar
data load usually sits around 50-52Mbps but can increase to 70 or so. I expect that some packets are being dropped but have no way of proving that. Other wireless traffic continues, mostly internet
connections for other devices, but is slowed by the multicast traffic (of course this could also be parts
of the network external to mine as I'm connecting through the ASUS router via a WiFi
extender into a local business as I tested and wrote this). The observed CPU load at the ASUS router has not exceeded 20% whilst carrying out these tests so it would appear to be well capable.
The NSS/Radar is connected to the ASUS router by putting a hub between the radome and the RI10 interface box, this tees the radome output into the RI10 and ASUS router. The NSS MFD picks up an address from the ASUS in the same way as any of my other devices do. By creating a connection in OCPN for the address of the NSS with a port of 10110 a plethora of NMEA
data is being sent, including GPS
messages, which OCPN picks up.
data is useful because it provides a backup for the instances of kPlex that also run on the router. The kPlex instances take inputs from Serial/USB connections from the older instrumentation on the boat giving both GPS
messages into an OCPN connection. kPlex also has an outbound instance that takes autopilot
data from a separate OCPN connection back to one of the Serial/USB connections, overcoming the limitation OCPN had until recently with input and output through the same connection ( I havent been able to test muttnik's changes for this yet).
Since the ASUS is my main existing router, my research has focussed on whether that (and its firmware) are capable of running the functions I desire. It acts as the hub for onboard comms so handles external internet
as well as intranet function, does some processing to packetise NMEA data into IP and handles VPN centrally for all connected devices when needed.
One limitation I'm aware of is that it uses a Broadcom SOC, the drivers for the wireless parts
of the Broadcom chip are proprietary hence the 2.6 kernel used by Tomato. In turn this means that IGMP snooping is not part of the kernel and I risk swamping wireless devices because the multicast implementation on Linux
based routers has limitations. This may be resolved if I change to the current
development OpenWRT branch (around 3.10 I believe), which I've been looking at. That would upgrade the Linux
kernel and may fix some other problems I've seen but at the risk of it bricking the router on installation
- not something I want to do whilst cruising. So thats a project
that is under consideration for risk!
There may well be a better router, but as I've found, the criteria governing that choice is going to be rather individual. My choices suit my usage so far, but I'm open to change. So far as researching multicast use goes, most references
I've found are from people trying to use IPTV which is sort of relevant to this but not complete. As muttnik points out, this seems to be a grey area for standards.
I cant so far find reference to any router firmware with a > 54Mbps setting for multicast over wireless, they must be there given the number of ISPs with IPTV offerings. If I find one it will also need to have USB ports
, ethernet, wireless, WAN, VPN; the processing power to run all that and the ability to recompile kPlex for it - oh and run off 12V!