[Fwd: Correction: summary: ca client connection pattern]

[Wolfgang Maschmann <maschi@heraqc.desy.de>]

-------- Original Message --------
Subject: Correction: summary: ca client connection pattern
Date: Thu, 05 Apr 2001 16:41:28 -0500
From: Geoff Savage <savage@fnal.gov>
To: tech-talk@aps.anl.gov

I have the directions of the TCP messages reversed.  The client, in this
case IOC A, must initiate the connection based on the information
returned in the directed UDP message.

Sorry for the confusion.

Geoff

Geoff Savage wrote:
> 
> Hi,
> 
> Make sure you close channels using ca_clear_channel when you are done.
> 
> I changed my version (R3.13.1.1) of ca_test to call ca_clear_channel at
> the end and connections were made flawlessly.  I also avoided the
> problem by usig a connection callback and extending the ca_pend_io
> timeout to 5 seconds.
> 
> Here's the problem with some details.  With two IOCs, A and B, you run a
> client on A that connects to a PV on B.  If you reboot A without closing
> the connection then B still thinks that the connection still exists.
> More importantly B's TCP layer has an expected sequence number that was
> generated when the initial connection was made.  Now reboot A and run a
> ca client that attempts to connect to a PV on B.  When B initiates the
> connection with A the sequence number is not understood by A so A tells
> B and B tells A to reset.  A few seconds (~3 seconds) B attempts to
> connect again and things go as expected.
> 
>                         Succesful connection
>         IOC A                           IOC B
> 1       UDP broadcast   -->     Looking for a PV                -->     UDP received
> 2       UDP received    <--     PV located here                 <--     UDP directed
>         Establish TCP connection (these are TCP messages)
> 3       SYN received    <--     <SEQ=100><CTL=SYN>              <--     SYN sent
> 4       SYN received    -->     <SEQ=300><ACK=101><CTL=SYN, ACK>-->     Established
> 5       Established     <--     <SEQ=101><ACK=301><CTL=ACK>     <--     Established
> 
>                         Failed connection
>         IOC A                           IOC B
> 1       UDP broadcast   -->     Looking for a PV                -->     UDP received
> 2       UDP received    <--     PV located here                 <--     UDP directed
>         Establish TCP connection (these are TCP messages)
> 3       SYN received    <--     <SEQ=500><CTL=SYN>              <--     SYN sent
> 4       SYN received    -->     <SEQ=350><ACK=150><CTL= ACK>    -->     SYN sent
> 5       Listen          <--     <SEQ=150><CTL=RST>              <--     SYN sent
>         After a few seconds
> 6       SYN received    <--     <SEQ=100><CTL=SYN>              <--     SYN sent
> 7       SYN received    -->     <SEQ=300><ACK=101><CTL=SYN, ACK>-->     Established
> 8       Established     <--     <SEQ=101><ACK=301><CTL=ACK>     <--     Established
> 
> For more information on TCP see RFC 793.
> 
> Thanks for the assistance and suggestions.
> 
> Geoff