[mythtv-users] LAN bandwidth consumption

John P. Mitchell john at cepros.com
Sat Dec 31 17:36:31 EST 2005


    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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