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Seán
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Chateau LTE12 cell lock LTE link flapping with CA

Tue Jun 23, 2020 1:26 pm

I have a Chateau LTE12 with firmware v7.0beta8 and am connecting to a cell approx. 53km (33 milles) across a bay with a pair of outdoor directional LOG antennae. The cell (Three Ireland) operates on band 20 (EARFCN 6300), band 3 (EARFCN 1275 and 1700) and band 1 (EARCN 525). I can connect on band 20 only as the primary band and use bands 3 and 1 for aggregation only due to that cell distance.

When I configured the APN and chose band 20 only, the Chateau connected and the connection was stable, but very slow (<10Mbps) due to high congestion on band 20. When I tried selecting bands 20, 1 and 3, the Chateau lost the connection and endlessly showed this status:
[admin@MikroTik] > interface lte monitor
number: 0
status: searching
model: EG12-EA
revision: EG12EAPAR01A05M4G
imei: [removed]
imsi: [removed]
uicc: [removed]
I think it was trying to connect on band 3 or 1 as the primary band, which I can only use for aggregation due to the distance. I ran the following command based on SiB's post here to lock the Chateau on cell 127 on EARFCN 6300 (band 20):
interface/lte/at-chat lte1 input="at+qnwlock=\"common/4g\",1,6300,127"
The Chateau connects to this cell and aggregates with a cell on both EARFCN 1700 and 525:
[admin@MikroTik] > interface lte monitor 0
status: connected
model: EG12-EA
revision: EG12EAPAR01A06M4G
current-operator: 3
current-cellid: 828423
enb-id: 3236
sector-id: 7
phy-cellid: 127
access-technology: LTE
session-uptime: 24s
imei: [Removed]
imsi: [Removed]
uicc: [Removed]
primary-band: B20@10Mhz earfcn: 6300 phy-cellid: 127
ca-band: B3@20Mhz earfcn: 1700 phy-cellid: 115,B1@15Mhz earfcn: 525 phy-cellid: 115
cqi: 8
ri: 1
mcs: 0
rssi: -63dBm
rsrp: -97dBm
rsrq: -14dB
sinr: -2dB
The speed is now very fast (100-150Mbps). However, the connection keeps interrupting every minute or two, e.g. downloads stall, VoIP voice, video calls freeze, etc. When I print the LOG, the LTE Link keeps going down and up as shown in this snip:
11:56:43 interface,info lte1 link up
11:57:13 interface,info lte1 link down
11:57:13 interface,info lte1 link up
11:57:43 interface,info lte1 link down
11:57:43 interface,info lte1 link up
11:59:13 interface,info lte1 link down
11:59:13 interface,info lte1 link up
12:00:58 interface,info lte1 link down
12:00:58 interface,info lte1 link up
12:01:13 interface,info lte1 link down
12:01:13 interface,info lte1 link up
12:01:43 interface,info lte1 link down
12:01:43 interface,info lte1 link up
12:01:58 interface,info lte1 link down
12:01:58 interface,info lte1 link up
12:02:13 interface,info lte1 link down
12:02:13 interface,info lte1 link up
12:02:29 interface,info lte1 link down
12:02:29 interface,info lte1 link up
12:03:28 interface,info lte1 link down
12:03:28 interface,info lte1 link up
When I enable LTE debugging, this is what it logged the moment the link down:
19:18:28 lte,async,raw lte1: sent AT+QENG="servingcell"
19:18:28 lte,async,raw lte1: rcvd +QENG: "servingcell","NOCONN","LTE","FDD",272,05,CA407,127,6300,20,3,3,A34A,-99,-16,-66,8,255,140,-
19:18:28 lte,async,raw lte1: sent AT+QCAINFO
19:18:28 lte,async,raw lte1: rcvd +QCAINFO: "pcc",6300,50,"LTE BAND 20",1,127,-99,-16,-65,8
19:18:28 lte,async,raw lte1: rcvd +QCAINFO: "scc",1700,100,"LTE BAND 3",1,115,-101,-12,-81,0
19:18:28 lte,async,raw lte1: rcvd DL
19:18:28 lte,async,raw lte1: rcvd +QCAINFO: "scc",525,75,"LTE BAND 1",1,115,-110,-10,-90,0
19:18:28 lte,async,raw lte1: rcvd DL
19:18:28 lte,async,raw lte1: sent AT+QRSRP
19:18:28 lte,async,raw lte1: rcvd +QRSRP: -100,-98,-140,-140
19:18:28 lte,async,raw lte1: sent AT+QNETINFO="cmr"
19:18:28 lte,async,raw lte1: rcvd +QNETINFO: "cmr",9,12,1,2
19:18:28 lte,async,event lte1: +CGEV: NW DETACH
19:18:28 lte,packet,raw lte1 mbim: wdm <<< recv #0
19:18:28 lte,packet,raw 07000080 48000000 00000000 01000000
19:18:28 lte,packet,raw 00000000 a289cc33 bcbb8b4f b6b0133e
19:18:28 lte,packet,raw c2aae6df 0a000000 1c000000 00000000
19:18:28 lte,packet,raw 01000000 00000000 00000000 00000000
19:18:28 lte,packet,raw 00000000 00000000
19:18:28 lte,debug lte1 mbim: service: connect, command: packet service, notify
19:18:28 lte,packet lte1 mbim: status data:
19:18:28 lte,packet 00000000 01000000 00000000 00000000
19:18:28 lte,packet 00000000 00000000 00000000
19:18:28 lte,debug lte1 mbim: packet service: attaching nwe: 0 class: 0
19:18:28 lte,debug lte1 mbim: state 16=>14
19:18:28 lte,account lte1 session: 90s 7358/7482 bytes 96/101 packets
19:18:28 interface,info lte1 link down
19:18:28 lte,packet,raw lte1 mbim: wdm <<< recv #0
19:18:28 lte,packet,raw 07000080 48000000 00000000 01000000
19:18:28 lte,packet,raw 00000000 a289cc33 bcbb8b4f b6b0133e
19:18:28 lte,packet,raw c2aae6df 0a000000 1c000000 00000000
19:18:28 lte,packet,raw 02000000 20000000 00e1f505 00000000
19:18:28 lte,packet,raw 0046c323 00000000
19:18:28 lte,debug lte1 mbim: service: connect, command: packet service, notify
19:18:28 lte,packet lte1 mbim: status data:
19:18:28 lte,packet 00000000 02000000 20000000 00e1f505
19:18:28 lte,packet 00000000 0046c323 00000000
19:18:28 lte,debug lte1 mbim: packet service: attached nwe: 0 class: 32
19:18:28 lte,debug lte1 mbim: state 14=>15
19:18:28 lte,debug lte1 mbim: state 15=>16
19:18:28 interface,info lte1 link up
This is what cell-monitor reports:
[admin@MikroTik] > interface lte cell-monitor 0
Columns: PHY-CELLID, BAND, EARFCN, RSRP, RSRQ, RSSI, AGE
PHY BAN EARF RSRP RSRQ RSSI AG
0 B3 1700 8s
6 B3 1275 -116dBm -20dB -87dBm 5s
6 B3 1700 -106dBm -17dB -81dBm 2s
67 B20 6300 -105dBm -20dB -73dBm 2s
115 B1 525 -114dBm -10dB -95dBm 2s
115 B3 1275 -99dBm -10dB -81dBm 5s
115 B3 1700 -98dBm -10dB -80dBm 2s
117 B1 525 -120dBm -16dB -95dBm 2s
117 B3 1275 -104dBm -14dB -81dBm 5s
117 B3 1700 -103dBm -15dB -80dBm 2s
127 B20 6300 -97dBm -13dB -67dBm 2s
195 B20 6300 -101dBm -19dB -73dBm 2s
231 B20 6300 -104dBm -20dB -73dBm 2s
344 B20 6300 -105dBm -20dB -73dBm 2s
If I set the Chateau to band 20 only (i.e. no carrier aggregation), the link stays up even hours later. However, if I enable band 1, 3 or both, the LTE link starts flapping again. So I'm not sure if this due to the modem or network still trying to hand over to a band 1 or 3 cell when CA is enabled.

Is there anything I can try to stop the link dropping with CA? This issue also occurs in the original firmware (v7.0beta6) and the previous modem firmware (EG12EAPAR01A05M4G).
 
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SiB
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Re: Chateau LTE12 cell lock LTE link flapping with CA

Tue Jun 23, 2020 6:34 pm

We know about that #bug #behaviour and we write the post to SoC team, please register and attach to that case: https://forums.quectel.com/t/eg12-and-c ... 5/14?u=sib

Of course good idea is write to MikroTik Support too, that way MikroTik as bigger SoC buyer then we can do maybe more in that case.
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Seán
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Location: Ireland
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Re: Chateau LTE12 cell lock LTE link flapping with CA

Sat Jun 27, 2020 1:01 am

I posted my issue on that Quectel forums thread and got a response to e-mail their support the log. Unfortunately, I got a reply saying I've been put through to the wrong support channel and that the e-mail support request needs to be generated from their customer MikroTik. So I will try contacting MikroTik support.

From own testing, I found that if I enable LTE passthrough, TCP connections do not break when the link flaps. Instead it causes a brief ~400ms latency spike. I downloaded a few large (1GB) files and each one downloaded successfully. I think this is due to my PC not seeing the split-second LTE link interruptions, causing outgoing packets to buffer instead of drop. I would be happy to put up with split-second latency spikes than broken TCP connections. :)

I would like to figure out a way of creating a virtual Ethernet interface on the MikroTik router that I can set the LTE passthrough and firewall NAT out interface to use instead, so I can still use the MikroTik as a router instead of a modem, otherwise I need to use another router for this LTE passthrough workaround. Basically I want to configure the MikroTik router in such a way that when the link flaps, that the gateway is still appears like it is "up" during the split-second the LTE link is down, so that WAN destined packets are not dropped as unreachable

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