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PDA's connection lost (WIFI microcuts)

3 posts in General Discussion (old) Last posting was on 2010-03-05 07:57:51.0Z
Carlos López Posted on 2010-03-04 13:48:18.0Z
From: =?iso-8859-1?Q?Carlos_L=F3pez?= <clopez@unisoftx.com>
Newsgroups: sybase.public.sqlanywhere
Subject: PDA's connection lost (WIFI microcuts)
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Hi all.

We've developed a PDA application with Pocket Builder, and now we're testing
we've found that the PDA's DB connection is severed when changing form one
Wifi antenna to another. (in Spain we call it "micro-cortes", but I don't
know if
microcuts is the appropiate translation... excuse me ;-) )

Is there anyway to avoid that?

May programming some kind of re-connect?

Thanks in advance.


"Nick Elson [Sybase iAnywhere]" < Posted on 2010-03-04 17:25:54.0Z
From: "Nick Elson [Sybase iAnywhere]" <@nick@dot@elson@at@sybase@dot@com@>
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Subject: Re: PDA's connection lost (WIFI microcuts)
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Article PK: 866769

I believe the English word for "micro-cortes" would be a "cell"
which has the same meaning as the use of that word with Cellular
Phone technology.

The problem you are describing is a problem with 'handing off'
(aka a hand-off) a TCP/IP connection when moving across access
points. WIFI was not originally design with 'persistent hand-offs
of TCP connections across cells' in mind and so it is very common
to drop connections. Older and lower price WIFI gear can be
expected to have this behaviour. Unconfigured gear will likely
default to this behaviour as well.

It does appear that some WIFI access points (sometimes called
controllers in some newer products) can be configured for
'stateful failover' so you should look into that feature more. A
quick google search indicates this is an advanced feature that
may only (currently) be available in more expensive models.

If your equipment and IP-stack software cannot address this for
you then you need to address it in the application logic. From a
database API level about all you can do is reconnect and redo
any unfinished transactions from the beginning again. One alternative
(when running 'wirelessly') would be to only use small transactions
and handle disconnects on the transactional boundaries in your
application design. Of course autocommit mode that may be
easier to do, but that usually requires a significant redesign of the
application logic and will present other problems.

In the past there were proprietary (and somewhat costly) virtual
IP stacks available that could provide a stable virtual IP address;
though that approach has it's detractions and did not seem to
have caught on. I don't believe any such technology is currently
available as part of available operating systems or as an add on.

There was also some research done in adhoc routing and dynamic
load balancing that would also provide cell-independence. But I
don't personally know of any products that have implemented
something like that so those may not be available. [it may also
be the underlying technology under the 'virtualization' features being
promoted in some those WIFI 'controllers' I see being advertised.]

HTH

"Carlos López" <clopez@unisoftx.com> wrote in message
news:4b8fba22@forums-1-dub...
> Hi all.
>
> We've developed a PDA application with Pocket Builder, and now we're
> testing
> we've found that the PDA's DB connection is severed when changing form one
> Wifi antenna to another. (in Spain we call it "micro-cortes", but I don't
> know if
> microcuts is the appropiate translation... excuse me ;-) )
>
> Is there anyway to avoid that?
>
> May programming some kind of re-connect?
>
> Thanks in advance.


Carlos López Posted on 2010-03-05 07:57:51.0Z
From: =?iso-8859-1?Q?Carlos_L=F3pez?= <clopez@unisoftx.com>
Newsgroups: sybase.public.sqlanywhere
References: <4b8fba22@forums-1-dub> <4b8fed22$1@forums-1-dub>
In-Reply-To: <4b8fed22$1@forums-1-dub>
Subject: Re: PDA's connection lost (WIFI microcuts)
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Date: 4 Mar 2010 23:57:51 -0800
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Article PK: 841544

Thank you very much Nick.

I'm goin to talk with my customer in order to try something that you're
talking about.

I'll notice you.

Thanks again.


"Nick Elson [Sybase iAnywhere]" <@nick@dot@elson@at@sybase@dot@com@>
escribió en el mensaje de noticias news:4b8fed22$1@forums-1-dub...

>I believe the English word for "micro-cortes" would be a "cell"
> which has the same meaning as the use of that word with Cellular
> Phone technology.
>
> The problem you are describing is a problem with 'handing off'
> (aka a hand-off) a TCP/IP connection when moving across access
> points. WIFI was not originally design with 'persistent hand-offs
> of TCP connections across cells' in mind and so it is very common
> to drop connections. Older and lower price WIFI gear can be
> expected to have this behaviour. Unconfigured gear will likely
> default to this behaviour as well.
>
> It does appear that some WIFI access points (sometimes called
> controllers in some newer products) can be configured for
> 'stateful failover' so you should look into that feature more. A
> quick google search indicates this is an advanced feature that
> may only (currently) be available in more expensive models.
>
> If your equipment and IP-stack software cannot address this for
> you then you need to address it in the application logic. From a
> database API level about all you can do is reconnect and redo
> any unfinished transactions from the beginning again. One alternative
> (when running 'wirelessly') would be to only use small transactions
> and handle disconnects on the transactional boundaries in your
> application design. Of course autocommit mode that may be
> easier to do, but that usually requires a significant redesign of the
> application logic and will present other problems.
>
> In the past there were proprietary (and somewhat costly) virtual
> IP stacks available that could provide a stable virtual IP address;
> though that approach has it's detractions and did not seem to
> have caught on. I don't believe any such technology is currently
> available as part of available operating systems or as an add on.
>
> There was also some research done in adhoc routing and dynamic
> load balancing that would also provide cell-independence. But I
> don't personally know of any products that have implemented
> something like that so those may not be available. [it may also
> be the underlying technology under the 'virtualization' features being
> promoted in some those WIFI 'controllers' I see being advertised.]
>
> HTH
>
> "Carlos López" <clopez@unisoftx.com> wrote in message
> news:4b8fba22@forums-1-dub...
>> Hi all.
>>
>> We've developed a PDA application with Pocket Builder, and now we're
>> testing
>> we've found that the PDA's DB connection is severed when changing form
>> one
>> Wifi antenna to another. (in Spain we call it "micro-cortes", but I don't
>> know if
>> microcuts is the appropiate translation... excuse me ;-) )
>>
>> Is there anyway to avoid that?
>>
>> May programming some kind of re-connect?
>>
>> Thanks in advance.
>