Sierra MC7455 TCP Congestion Control

[Tang Nguyen]

I agreed with Dan that TCP congestion is controlled by host - not by modem itself.
I experienced pretty low data rate on  LTE modem (MC7350) due to MTU setting between host and modem interface.  By default, Sierra has set MTU as 1430, and if MTU of wwanX  has default value, which is 1500 ,  then you would get pretty low data rate.

To be sure data is not fragmented along the path, you can set MTU of wwanX as 1430 and use iptable utility  with option  "clamp-mss-to-pmtu" on wwanX interface.
Doing that, performance would be improved a lot.

Regards

--tang

----------------------------------------------

On Tue, 1/10/17, Dan Williams <dcbw at redhat.com> wrote:

 Subject: Re: Sierra MC7455 TCP Congestion Control
 To: "Noah Taber" <noahtaber at gmail.com>, "Bjørn Mork" <bjorn at mork.no>
 Cc: "libqmi (development)" <libqmi-devel at lists.freedesktop.org>
 Date: Tuesday, January 10, 2017, 12:14 PM
 
 On Tue, 2017-01-10 at
 07:58 -0800, Noah Taber wrote:
 > It's
 something that android has access to.  I figured it
 might
 > improve
 >
 things through the internet if we had direct access to that
 parameter
 > as
 >
 well.
 
 I could be wrong, but
 typically all TCP congestion control would be
 handled on the host side (eg, in the Linux
 kernel) and using the
 kernel's
 congestion control algorithms.  The modem doesn't care;
 it
 just passes along a data stream to the
 network, possibly subjecting it
 to QoS
 inside the modem.
 
 So do you
 mean QoS instead?  QMI has some capabilities to define QoS
 on
 each packet itself, and you can also
 create data bearers with specific
 QoS
 settings ("requested" and "minimum"
 QoS).  These are actually
 controlled/handled by the modem and by the
 network.
 
 Dan
 
 > I have no knowledge about
 how to do this through the mc7455 though.
 > 
 > On Tue, Jan 10, 2017
 at 12:26 AM, Bjørn Mork <bjorn at mork.no>
 wrote:
 > 
 > > Noah
 Taber <noahtaber at gmail.com>
 writes:
 > > 
 > >
 > Hi,
 > > > 
 > > > Is there a way to change the TCP
 Congestion Control algorithm on
 > >
 > the
 > > 
 >
 > Sierra
 > > > MC7455 through AT
 commands?  I'm hoping this isn't something that
 > > > is set
 > >
 
 > > by
 > > >
 the carrier.
 > > 
 >
 > Sorry, don't know the answer to that.  But
 I'm curious how you
 > > detect
 > > this.  Did you measure it?  Any
 data and/or procedures you can
 > >
 share?
 > > 
 > >
 
 > > Bjørn
 > >
 
 > 
 >
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