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Wireshark-users: Re: [Wireshark-users] PSH/ACK in all packets

From: "ronnie sahlberg" <ronniesahlberg@xxxxxxxxx>
Date: Sat, 26 Jul 2008 16:03:50 +1000
Cant you kind of implicitely set the PSH bit by playing with
cork/uncork on these boxens?


On Sat, Jul 26, 2008 at 7:26 AM, Guy Harris <guy@xxxxxxxxxxxx> wrote:
>
> On Jul 25, 2008, at 12:10 PM, Troy Tate wrote:
>
>> I have an application where all packets seem to have the PSH/ACK
>> flags set (from both sides of the conversation). This is a barcode
>> application. Is this a typical behavior for these types of
>> applications? The user is reporting slow performance, but I am not
>> seeing any network issues other than these flags set in every packet.
>
> It is typical behavior for the type of application called "TCP-based
> application" to have ACK set on all but some of the initial packets;
> to quote RFC 793:
>
>        Acknowledgment Number: 32 bits
>        If the ACK control bit is set this field contains the value of the
> next sequence number the sender of the segment is expecting to
> receive. Once a connection is established this is always sent.
> Whether PSH is set depends on whether the TCP implementation sets it;
> that's probably not application-specific.  In Mac OS X, for example,
> there's nothing the application can do to explicitly request PSH;
> looking at the versions of the {Free,Net,Open}BSD TCP code I had
> handy, the same is true there.  I don't have the Linux or Solaris code
> handy so I don't know whether they can explicitly force a push, and I
> don't know what other UN*Xes or Windows do.
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