[THIN] Re: Session Reliability

  • From: "Steve Greenberg" <steveg@xxxxxxxxxxxxxx>
  • To: <thin@xxxxxxxxxxxxx>
  • Date: Sat, 17 Jan 2009 08:58:42 -0700

I agree with Rick- Session Reliability is recommended when you have a known
situation of recurring short term disconnects. However it may not be a
benefit to turn on "just because". As Rick explains it does not really make
sessions more reliable, it just presents a less frustrating appearance
during the period of time the session is off line and is trying to




Steve Greenberg

Thin Client Computing

34522 N. Scottsdale Rd D8453

Scottsdale, AZ 85266

(602) 432-8649





From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf
Of Rick Mack
Sent: Friday, January 16, 2009 11:53 PM
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: Session Reliability


Hi Angela,


The concept behind session reliability is to hide the disconnect/reconnect
event from users. It doesn't actually improve things for your users, but
instead of their sessions disconnecting and reconnecting, the session just
appears to hang for a bit and then starts again. Session reliability is
actually a really bad name for this enhancement because it doesn't do what
it implies.


Session reliability is functionally a wrapper for standard ICA that
encapsulates the ICA protocol and allows you to handle stuff like
transparent session reconnection. However it uses a different port to ICA,
TCP port 2598. The session reliability listener is the Citrix XTE service
which then passes the ICA traffic on to the ICA listener.


So far so good, but there are 2 potential problems. 


The first is that the XTE service hasn't been totally stable in the past
with recurring instances of memory leaks and instability depending on hotfix
levels. If the XTE service starts playing up, session reliability just
became your worst enemy.

The second problem relates to the use of a different TCP port. It's fairly
common these days to set network QOS to favour ICA traffic when you use
Citrix. Everyone, especially your average comms person, knows that ICA is on
TCP port 1494 and that is what is used to identify ICA packets for QOS


When you switch on session reliability you are no longer using port 1494. So
any QOS optimization you've got for ICA suddenly disappears, and in a worst
case scenario, session performance can go out the door, you start seeing a
lot more disconnections and session reliability becomes "session liability".


However if your users are suffering a reasonable number of disconnections
and that is creating annoyance and political problems for you, then by all
means investigate using session reliability. But make sure that if you are
using QOS, that you co-ordinate with your comms people and ISP so that when
you enable session reliability nothing will break. Make absolutely certain
that they know ICA can use port 1494 AND port 2598.


And good luck :-)






Ulrich Mack
Quest Software
Provision Networks Division

On Sat, Jan 17, 2009 at 1:28 PM, Angela Smith <angela_smith9@xxxxxxxxxxx>


Im looking at enabling session reliability on my CPS 4 farm.  Are there any
gotchas I need to be aware of or could this cause more issues?  Im aware of
the port changes but I wanted to know if most people are using this or
whether session performance is slower due to the additional connection



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