I had and online training session today for desktop sharing using the NX protocol with two participants, both in Namibia. The FreeNX server was used on Ubuntu 10.04 and the NoMachine NX client on the connecting hosts. We all connected to the server by one participant making the connection and the other two participants attaching to the session by option of shadow on the NX clients. We connected via Skype conferencing for voice.
One person was connected via MTC 3G mobile Internet connection and the other with Telecom ADSL connection. Both reside in Windhoek. I was connected from Grahamstown in South Africa through the Rhodes University LAN. The NX Server was in Namibia connected on Telecom leased line.
We connected on a session with resolution set at 1024×768 and all other configuration set at default such as encoding and caching on the NX client. The connection status of the participants were as follows from a speed test done on www.speedtest.net host IT in Windhoek before starting the session:
- Telecom ADSL: ping=69ms; download=1.69mbps; upload=0.24mbps
- MTC 3G: ping=166ms; download=1.01mbps; upload=0.33mbps
- Rhodes LAN: ping=153ms; download=19.11mbps; upload=3.54mbps
There was the problem that the person connected from MTC kept losing connection on Skype. Me and the other person could communicate on Skype without connection loss. The voice also kept breaking up for the person connecting from MTC. This caused a delay in the training session and we tried to keep moving on so that the person can catch up once regaining connection. The person did however not loose connection from the NX connection and could see the screen updates despite not having voice over Skype. The lose of Skype connection would probably be because of the high network latency and cause a high packet lose. The total network latency would be that of to the host IT in Windhoek plus the International connection latency which would be about 200+ms Round Trip Time (RTT).
Another issue was the coordination of conversations when participants asked question. Two or more people may start to speak at the same time and may put conversation out of sync. An idea that was presented is for somebody wanting to ask a question should type it in the chat box.
The network packets were captured with Wireshark on the server and on the local machine here at Rhodes LAN. These would need to be analysed for the statistics of network transfer for display and for the Skype audio. There might be difficulty in analysing the Skype audio, cause from time to time when one person loosed the connection from the conference call, we had to redial and sometimes made direct connection call to each other. I do not know whether this would be significant to results at this time.
ADDITIONAL NOTES: The Wireshark summary statistics for each of the connections are shown below.The data only include that for the screen sharing by NX. This is achieved by filtering of traffic for IP packets with TCP port 22 and relevant IP addresses. All users are connected to the eLC server
| My PC | 3G | ADSL | |
| Elapsed time | 3328 sec | 1858 sec | 3229 sec |
| Avg. Mbit/sec | 0.128 | 0.030 | 0.029 |
| Avg. packets/sec | 118.8 | 9.2 | 10.2 |
| Avg. packets size | 135 bytes | 401 bytes | 358 bytes |
| Data transferred | 50.710 MB | 65.357 MB | 11.296 MB |
It would seem that the IP address of the person connecting from the ADSL connection is changed a few times during session so the total transferred is very low is shown in table above.
