First message after a pause always slower in 3G than 2G using EHS5-E | Telit Cinterion IoT Developer Community
May 19, 2017 - 1:05pm, 2160 views
Hi,
I have noticed that the first ping after a long pause takes a while in 3G using the EHS5-E modem. Below is a trace that shows the issue:
1) Ping 8.8.8.8 just after connection, first ping takes ~9934ms, then goes to ~320:
root@Phoenix /appfs/apps/share#ping 8.8.8.8 -c3
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=56 time=934.448 ms
64 bytes from 8.8.8.8: seq=1 ttl=56 time=330.330 ms
64 bytes from 8.8.8.8: seq=2 ttl=56 time=320.128 ms
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/*** = 320.128/528.302/934.448 ms
Quickly request PIN again several *****, now the first message is not delayed...
root@Phoenix /appfs/apps/share#ping 8.8.8.8 -c3
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=56 time=324.081 ms
64 bytes from 8.8.8.8: seq=1 ttl=56 time=320.523 ms
64 bytes from 8.8.8.8: seq=2 ttl=56 time=330.353 ms
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/*** = 320.523/324.985/330.353 ms
root@Phoenix /appfs/apps/share#ping 8.8.8.8 -c3
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=56 time=344.319 ms
64 bytes from 8.8.8.8: seq=1 ttl=56 time=320.470 ms
64 bytes from 8.8.8.8: seq=2 ttl=56 time=320.122 ms
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/*** = 320.122/328.303/344.319 ms
Now wait for like 10 min. It takes 2s for the first ping and 1 sec for the 2snd one:
root@Phoenix /appfs/apps/share#ping 8.8.8.8 -c3
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=56 time=2004.842 ms
64 bytes from 8.8.8.8: seq=1 ttl=56 time=1005.411 ms
64 bytes from 8.8.8.8: seq=2 ttl=56 time=100.340 ms
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/*** = 100.340/1036.864/2004.842 ms
I also see "psinfo" URC being sent when the long delay happens:
066233.582HEX DUMP: Buffer address = 0x4004B2B4, size = 21
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 0123456789ABCDEF.
----------------------------------------------- ----------------.
000| 0D 0A 2B 43 49 45 56 3A 20 70 73 69 6E 66 6F 2C ..+CIEV: psinfo`.
010| 36 0D 0A 0D 0A 6.... .
----------------------------------------------- ----------------.
066234.242HEX DUMP: Buffer address = 0x4004B2B4, size = 22
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 0123456789ABCDEF.
----------------------------------------------- ----------------.
000| 0D 0A 2B 43 49 45 56 3A 20 70 73 69 6E 66 6F 2C ..+CIEV: psinfo`.
010| 31 30 0D 0A 0D 0A 10.... .
----------------------------------------------- ----------------.
Is this something related to the cell putting the module in low priority after a delay in traffic? I do not see the same issue when using a 2G modem, like the BGS2-W.
Is there any way to prevent this? My application is very sensitive to latency.
Many thanks in advance,
Jose
Hello,
I think that the reason for that behavior is in the nature (architecture) of 2G/3G networks. The network resources are assigned by the network according to the current ***** of the mobile and possibilities on the network side. So in case of idle connection or when there haven't been data transfer yet there may be greater latency. Some additional signaling may be needed and allocation of traffic channels. While in idle **** the traffic channels are released. The "+CIEV: psinfo" URC's confirm this theory as they indicate the status of the mobile device related to packet switched data calls which starts to change when there is no data transferred and the data is sent after that.
At the moment I can't explain why you can't see this in 2G for BGS2-W module - that would require more detailed analysis of the network signaling for 2G and 3G. This might also depend on the particular network configuration or area. Please also try EHS5-E in 2G for comparison.
The latency should be much lower in 4G networks.
Best regards,
Bartłomiej
Hi,
Many thanks for your input. To be honest I also see the issue with the 2G modem, but is much less pronounced. The 1st ping after a pause on a 2G connection takes around 900ms ***, then goes down to ~400ms (for both BGS2-W and EHS5-E). Never seen it more than 900ms, while with 3G I have seen even a delay of 3secs.
I guess there is no way to keep the network active by configuring the modem in a particular way, so the only solution is to periodically connect to or ping a remote host? I don't like that idea, it meas lots of additional traffic.
Regards,
Jose
Hello,
This is controlled by the network so there's not much you can do - you could try some other operator for comparison - generally 3G should rather be a little faster than 2G but according to your measurements it's the opposite way. It should be much better in LTE (ELS61 works in LTE for example).
Regards,
Bartłomiej