[MLB-WIRELESS] Transfer Rates

[Michael Weinbergs]

I don't know about the wireless side, but I can tell you that Ethernet uses
CSMA/CD (Carrier Sense, Multiple Access, Collision Detection) to modulate
the carrier (radio frequency) .
Only one device can talk at one time per "Carrier" - thus, on Ethernet if
you have multiple devices (MA) sharing the carrier and create "two way"
communications (ie. pings originating from both ends) - the packets could
collide, a pause will occur and they will retry. (/CD) - slowing down your
data path.
 
THEN, also don't forget, that whilst the CARRIER communicates at "10Mb" -
you are encoding with protocols to transport the data ie. 802.3 Frame, Ip
Protocol, TCP protocol etc. All of these carry the payload (read: data) that
you are sending. 
I would also guess that if you are also encrypting you should
(theoretically) have packet "padding"  to filling up any partially-filled
frames - so it will also affect the throughput of the of path (not
forgetting the time it takes (latency) to encrypt and decrypt etc)
 
Finally, there is Latency. This is the time it takes to get from one side of
a device to another. For example, in a router you expect latency, because
the router has to strip the Frame (802.11 or 802.3), investigate the IP
Addresses and protocol, make a decision and then forward it onto the next
interface. All of which takes time - thus affecting the throughput.
 
So I would assume that, like Ethernet, in wireless you wouldn't get actual
11Mbs of data passing over a link, just like you will not get "10Mb" of data
over an Ethernet link. (In fact, I believe that the throughput of Ethernet
is about 3.9Mb)
I can't tell you what to expect on a wireless link (I don't have those
figures) - but look for throughput - it is a better representation.

-----Original Message-----
From: Rowan Wainwright-Smith [mailto:Rowan at teleaudit.com]
Sent: Tuesday, 17 September 2002 9:15
To: Cameron Donaghey
Subject: Re: [MLB-WIRELESS] Transfer Rates


Cameron,

transfer rates are a little tricky, 'coz there are two ways of measureing
them

1    PURE Bandwidth - how many BITS per second!
2.   Transfer performance (usually measured in BYTES per second)

The stats you are getting are pretty reasonable, but you should be able to
get about 550(-600)k/sec 


these cards are 11 Mbit,

if you work it out, you are getting about 2.5mbit transfer rate (not
counting TCP overheads) Bear in mind that these devices are 11mbit TOTAL
bandwidth, so if you have two PC's communicating, then you can really only
expect up to approx 5Mbit transfer, 3PC's then about 3.5 Mbit & so on.

Wireless is NOT switched bandwidth like most modern wired networks, but
shared (like running a hub instead of a full switch)
 Personally not sure about what effect using an AP is having, but this
*could* be reasonable!

maybe the rest of the list can help you more....

well done on getting your WLan up & running!

Rowan

Cameron Donaghey wrote:


Hello Everyone,
  I have eventually got my wireless up and running, only on a private level
at the moment, and
yet I am not entirely sure it is running correctly. I have two machines and
in each one I have
a Compaq WL100 card set to infrastructure mode. I also have a linksys Wap11
access point
which is running as an access point only.
I have done some testing and I seem to have a max. transfer rate between the
two machines
of about 310kb/s and the machines are only a meter or so apart. I would have
assumed that
being a 11mb/s network that I would be able to achieve more so around
500-1000kb/s rather
than the 300kb/s max. I am currently achieving. Both card say they have
"excellent connections"
and at 11mb/s.
My question to you all, is the transfer speed of about 300kb/s typical for
802.11b or should I be
able to achieve higher rates of transfer? If I should be able to achieve
more would anyone have
any suggestions towards resolving the problem?
  Thanks very much,
     Cameron Donaghey



  
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