Re: DHCP too slow - trying to cache
- From: "Paul G. Tobey [eMVP]" <ptobey no spam AT no instrument no spam DOT com>
- Date: Wed, 24 Aug 2005 08:39:32 -0700
So, when you *don't* use DHCP, the connection is 20-30 seconds faster? It
sounds like a fair test, if that's the case. I don't experience that sort
of latency myself, but I'm not turning on cards from nothing or resuming the
device. Our devices are always powered, so I can plug in an RF Ethernet
card. It takes about 3 seconds to establish a WEP-based connection to the
AP and another 7 or so to get the address. I guess that the only other
suggestion would be to use a DEBUG build of the OS and capture the serial
debug messages to see if something odd is going on.
Paul T.
"John Roberts" <john@xxxxxxxxxxxxx> wrote in message
news:eZqv8kJqFHA.2240@xxxxxxxxxxxxxxxxxxxxxxx
> Hi Paul,
>
>> Note that you haven't told us anything, including the OS version, what
>> QFEs are applied, etc. about the device...
>
> Windows CE 5.0 and the latest QFE roll-ups are applied. The device is a
> wi-fi television remote control designed to be used in the home. To
> prolong the battery life, the wi-fi connection is to be kept off as much
> as possible and in an ideal situation, the wi-fi connection should be able
> to connect promptly to give a good user experience. For example, imagine
> the user wants to find out the weather on their remote. They pick it up
> and go to the weather application which goes and fetches it. This should
> be as prompt as possible but at the moment, I'm seeing 30 seconds or more
> when DHCP is used - particularly on ad-hoc ICS connections. I realise
> there are other processes that contribute to this time but DHCP seems to
> be taking the lion's share - if I measure the time taken between the
> physical transport layer being established on the wi-fi network (NDIS
> Media Connect) and the Address Change notification (NotifyAddrChange API).
> This is 20-30 seconds with DHCP and 2-4 seconds with static IP.
>
> One question I have is whether this 20-30 second time is normal both when
> a new IP address is obtained and when there should be an IP address
> cached? I've tried a variety of DHCP servers (those embedded in different
> wi-fi routers and those on Windows 2000 and Windows XP when ICS is used).
> Times are variable but always longer than I'd hoped.
>
>> It's legal, but not maintainable, in my opinion. What assures that the
>> address you have will never be issued to some other device? If the lease
>> expires and you then show up on the network using an address that you
>> shouldn't have, you might find someone else using it and you'll have real
>> problems. Even if you've reconnected before the lease expires, once it
>> does expire, you may have a problem, as the DHCP server will call that
>> address fair game, again. If you can accurately duplicate the lease
>> behavior in DHCP, then you won't have a conflict problem, but that's a
>> pretty significant chunk of code.
>
> I'm pretty confident I can limit the use of the address to be within the
> original lease without writing too much code. After that time, I will
> simply use DHCP again for the next connection to avoid using an IP address
> beyond the lease time.
>
>> In that case, why not always use static addressing?
>
> End users will be able to use static IP but we anticipate most of our
> users will not have the networking know-how to set this up. This is a
> consumer device and we are trying to make setup as simple as possible.
>
>> What are the characteristics of the 802.11 connection? WEP? WAP? EAP?
> Just WEP or unsecured connections. Although establishing the connection
> does take some time, it is fairly good at about 4 seconds.
>
>> All of those things can take various amounts of time to work through
>> before you can communicate with the rest of the network. Are you sure
>> that you're fairly assigning the blame to DHCP?
> Comparing the results with static IP, I'm sure that DHCP is a problem.
>
> Thanks for your interest!
>
> - John
>
>
>
>
>
.
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- From: John Roberts
- Re: DHCP too slow - trying to cache
- From: Paul G. Tobey [eMVP]
- Re: DHCP too slow - trying to cache
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