Problem in SCPC link

If there are no CRC errors then the satellite link is error free and the problem must be elsewhere.

Is the link very congested with traffic due to intensive use, VoIP/skype calls, large file transfers, viruses etc ?  That would cause a proportion of pings to be lost, particularly at peak traffic times.

Leave a ping running for a long time ( -t option ) and see if you can observe what else occurs when the lost pings appear.

Do the pings to the IP address of the local modem and also to the IP address of the remote modem. Starting with your your PC you need to go step by step, testing further each time, till the problem is localised.

If there is a ping generator inside the local modem, use it outwards in both directions, as well as testing from your PC.

Turn off all the pingers when you have finished !

Best regards, Eric.

If you're using Microsoft's PING utility, the default wait time I believe is about 500ms. In many circumstances, that's not long enough for satellite hops. Bottlenecks in the path can delay the PING return beyond the default timeout. In those occasions the packet is counted as dropped, even if it actually did make it back.

When I experience suspected dropped packets, first thing I do is extend the PING wait time with the -w suffix. Another way to PING the IP address rather than the PLA. Example: rather than PING satsig.net, try PING 82.197.70.19 -w2000. That will eliminated the DNS conversion lag and wait 2 seconds for the PING to return to be counted. If the number of dropped packets decreases, then I run TRACERT to see if I can isolate the bottleneck.

If you are interested in the other PING (and TRACERT) variants, type PING /? (or TRACERT /?) at a command prompt.

//greg//

Try testing each part of the link to localise the problem.

Local router to local modem.
Local modem to distant modem (over satellite).
Distant modem to distant router.

The CDM570-IP modem contains its own ping generator, so try testing with that.

I said earlier "If there are no CRC errors the satellite link must be error free."  I am now not quite sure about this. If the system is idle and no traffic then there are no packets being sent or received, so no CRC count. There could be errors occurring which are not detected because no traffic is flowing.

Do you have any congestion - too much traffic at times ?

Added thoughts....

Are the clocks slipping?.  This might cause some regular brief outage.   Check how the clocks are configured at each end. Do you have exactly the same bit rate set at each end ?

If the modem is set to revert to home state it may loose connection very briefly, every so often.

The FEC and scrambling etc must match exactly between both ends.

On your routers, set the ethernet port speeds fixed, rather than leaving them to autonegioate from time to time, which causes brief outages.

Familiarise yourself with the CDM570 "IP Statistics Page", "Ethernet Statistics page" and the "WAN statistics".  If you have some problem that only occurs at time during the day, save the data and reset the counters to zero, every hour, for example.

Do you have any device on the network with wrong IP address or subnet mask?.  

Maybe ping packets are set to low priority in QoS, so they are delayed or dropped in favour of normal customer traffic during high traffic periods.

Check you don't have default route (0.0.0.0/0 Point-to-Point ToSat) pointed at satellite at both ends. If so, a packet with invalid address will go round and round till the TTL expires, causing a brief traffic spike.

Best regards, Eric.