[mythtv-users] LAN bandwidth consumption

James C. Dastrup jc at dastrup.com
Sat Dec 31 18:23:58 EST 2005

I have MRTG running on my network and I can easily see how much bandwidth is used on all my computers, backends, frontends, etc. In regards to just network bandwdith (ignoring any other limitations - CPU, HDD speed, other network traffic, etc), over a 100Mbit network:
1080i HD content uses a good 19 Mbit/sec.  So, I bet you could easily get 3 frontends showing HD content from one backend.  A fourth would bring it to 76 Mbit/sec, which would be pushing it, but maybe would work.
SD content is up to 6 Mbit/sec, so theoretically you could have over 10 frontends pulling content from the same backend. But for some reason I find that unlikely due to other factors, but I don't know.


From: mythtv-users-bounces at mythtv.org on behalf of John P. Mitchell
Sent: Sat 12/31/2005 3:36 PM
To: Discussion about mythtv
Subject: Re: [mythtv-users] LAN bandwidth consumption


    Let me start by saying I am NOT a computer scientist and do not
fully understand all of the mechanisms involved with the complex systems
we play with now days. So take everything I say with a grain of salt,
and PLEASE feel free to correct me, since I want to know if I have
something wrong.

John Andersen wrote:
> On 12/31/05, Larry's Club Cars <larrysclubcars at yahoo.com> wrote:
>>Newbie here.
>>I have a 100Mb LAN.
>>I plan to have 1 Myth backend and 2 frontends.
>>Assuming that the 2 frontends are running simultaneously.
>>How much of the 100Mb LAN will be used?

    Very good question. But your question does not include enough
information as the answer depends on the bit rate of the recorded
content. I will use my system as an example since I have two frontends
and a backend just like you (I convert roughly to megabytes since that
is what I think in):

    I record my content at 4400kilobit/second, which I understand is
something like half quality DVD. I usually have two 4400kilobit/second
or ( (4400 / 8) / 1000 = .55 ) .55megabyte/second streams running across
my ( (100 / 8) * .8 = 10 ) 10megabyte/sec LAN, for a consumption of
about 1.1megabyte/second of a 10megabyte/second network. (The .8
reflects real world utilization versus specification throughput of the
network. Yes I know that certain special built applications can get the
full 12.5megabyte/second throughput, but for general network
applications I think 80% is a safe number. Even at 80% utilization it
would seem you are doing REALLY well or the network is only being
utilized by a single application.)

   Which leads into the next interesting question: what do you want to
do with your content? This question usually dictates your requirements
for recorded bit rate.
    I wanted a flexible platform agnostic format that would be easy to
archive to a format that would be platform agnostic once in archived
format. I also wanted to minimize the number of encodings to preserve
the end result content quality as much as possible. Therefore I choose
MPEG2 hardware encoders that record my content at 4400kilobit/second.
This creates about 2gigabyte/hour of recorded content. This fits an
average two and a half hour movie or three average one hour length TV
episodes sans commercials nicely on a DVD-R for archival. The DVD-R
plays nicely on almost every device I have put it in and is easy enough
for the family members (besides me :-) ) to manipulate.

> According to my quick glance at gkrellm, I'm pulling
> 600 to 800k bytes per second across lan from my backend
> to my laptop.
> I've pulled two streams over the cat5 100mb lan with
> no problem what so ever.

    Interesting response, but still not super helpful as we do not know
the content bit rate.

> --
> ----------JSA---------
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     John P. Mitchell <john at cepros.com>
     Email Sticker: My Boss is a Jewish carpenter
     http://www.GoboLinux.org | User #00010110
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