low connection speed on ZTE 821

RouterOS General
1

Hello,
I have ZTE 821 USB modem (exists on compatibility list of routerOS). I have quite good radio signal (-67dBm). When the modem is connected directly to computer, I get speed about 70Mb/s down, 6 Mb/up. and ping about 40-50 ms. When the same device is connected to RB751G via active USB hub (to ensure enough power) the speed goes down to 4Mb/s down, 3Mb/s up, ping 100-200ms Modem is used as PPP client. I chose 3 for data channel and 3 for info channel (I’m not sure if it matters).
When I disable the client and check Info I get:

Status: call in progress
..
Functionality: full
…
Access technology: Evolved 3G (LTE)
Signal Strength -67dBm

I see nothing in Interfaces | LTE ( I guess it is reserved for MiniPCI cards).

I noticed that other people get better results on similiar modems and RB devices. Do you have any hints how to improve speed? It looks like buying LTE modem for a router is a waste of money. Probably the only way to have fast connection is to setup a computer with Windows playing role as a router.

kind regards
Piotr Rezmer

2

Yesterday I have made more tests. First I did system reset configuration /no default configuration. Then I connected USB modem again via active Hub to RB751G. I updated ppp-out2, changed masquerade output interface. Now the results are much better than before (test using speedtest.net):

ping 72ms, 24,2 Mb/s down / 5,6 Mb up

I also made another test with RB751+ Dovado Tiny (NAT mode) (connected to ether1) + active Hub + ZTE MF821:

ping 43ms, 37,66 Mb/s down / 6,64 Mb/s up

The results are better because dovado uses cdc driver instead of ppp daemon. I also checked if switching dovado from NAT to bridge mode affects performance. There is no difference.

When the modem was connected directly to PC:
ping 46ms, 66,5 Mb/s down /8,92 Mb/s up

kind regards
Piotr Rezmer

3

ideally attempt without such “active USB Hub” could be nice 2 be sure its not bottleneck.
no offense.

4

Ok,
I repeated the test with and without USB Hub (it’s Trust Piramid 7 port - http://www.trust.com/products/product.aspx?ProductCategory=CONNECT&ProductGroup=USB-HUBS&artnr=15140). The hub has its own power supply (max current 2A).
The test was performed in not optimal conditions (without external antenna, inside building), using speedtest.net. I slightly moved modem (10-15 cm) when changing connection from/to hub and rb751 USB port

With hub:
download 24Mb/s, upload: 1,2 Mb/s, ping 73ms

without hub:
download: 23Mb/s upload: 1,3 Mb/s, ping 56ms.

This was only one measurement, of course I should make many of them and calculate average, but I guess it is obvious that using a hub does not create a bottleneck.
Another good news is that RB751G is capable of providing enough power for USB LTE modem (ZTE MF 821).

kind regards
Piotr Rezmer