OCS 2007 Message Limits

Yesterday I went looking for what the maximum message size I could send in an IM through OCS 2007 was and I couldn’t find an answer anywhere in the documentation or across the web. So I sat down and did it the old fashioned way – copying and pasting items until I got some errors and I found some pretty interesting results. OCS actually has 2 different limits. One is a limit on the first message you send to a recipient and the second limit applies to subsequent messages, with the first limit being 10% of the second. So what are the limits?

  • Initial Message: 800 characters
  • Subsequent Messages: 8000 characters

Interestingly enough, these limits come from two different places. If you send an initial message of over 800 characters you’ll get a message back in your IM window saying "This message was not delivered to [Username] because it is too large:
server

If you enter more than 8000 characters you’ll actually get a message back from Office Communicator "The message is too long. Please shorten your message and try sending again.": toolong

I’ve also managed to make Communicator truncate the text I enter if it’s over 8000 characters, but I can’t consistently figure out when it truncates the text and gives me the server-side message as opposed to the Communicator dialog box above that the text is too long.

I think the question more people are asking though is "how can I change these limits?". From what I can tell we’re stuck with the latter limit. If you search around it appears SQL itself is limited to a varchar value of 8000. For all practical purposes, I think the 8000 limit should accommodate most everyone. If it’s bigger than that, it’s probably a candidate for email, not IM. I set about trying to change the initial limit.

First, I looked in the OCS 2007 snap-in, but couldn’t find any options for changing this. Next, I checked out the registry. Nothing there so I fired up ADSIEdit. I found some global config settings in CN=Global Settings,CN=RTC Service,CN=Microsoft,CN=System,DC=ptown,DC=com, but nothing related to a maximum message size.

The only other place I could think of to look was the actual OCS database instance so I opened up SQL Server Management Studio Express to take a look. I did find a table (MSFT_SIPProxySetting) in the rtcconfig database that looked promising with a columns titled MaxBodySizeClientMsg and MaxBodySizeServerMsg. These are also apparently properties in the WMI class: http://msdn2.microsoft.com/en-us/library/bb632153.aspx.

MaxBodySizeClientMsg was set to 128 and MaxBodySizeServerMsg was at 5000. These values are in KB, not characters. I changed these to 256 and 10000, respectively, restarting the services after each change, but nothing seemed to make a difference. The only thing I can think of is that these values are hard-coded into the OCS and Communicator products. Anyone got any other ideas? Did I miss something?

Peanut Gallery

  1. 1 Joshua Shoemaker

    Thanks for taking the time to figure out those limits and the apparent inability to modify that setting concerns me. I am getting ready to deploy this to my firm and I am sure that we will bump into that limit on the first message. (that is what prompted me to google the error and end up here). Going to check the OCS forums to see if anyone has posted about this there and if not will link to your blog and your investigative work to see if any SQL people can carry it further.

     
  2. 2 Simon Barratt

    Thanks for the info. I was so hoping for an answer too though! At least I was able to send my pased IM to the recipient I wanted to, by initiating an IM first before pasting it in!

     
  3. 3 Oliv

    Many thanks for the information. Too bad there is not way to make the limit bigger !

     
  4. 4 Marc

    thx for this info. Just what I was looking for

     
  5. 6 Josh (MSFT)

    This is hard coded. Furthermore it’s not a character limit so much as a SIP message size limit. You’ll find if you do lot of formatting on in the text you send you’ll be able to send fewer overall characters.

    The reason for the difference between the first and other messages has to do with toast. If you are signed on to multiple endpoints then we’ll establish the conversation with the endpoint you answer from. We need a few seconds to let the user answer when they see the toast so we don’t establish the dialog until a ~10 sec delay has happened. With no “message+ok” to establish the conversation we wouldn’t see any text in the popup toast. Therefore a copy of the first message sent is piggybacked on the invite. Piggybacked messages will have a smaller size to work with hence the ~800 instead of ~8000. (and I’m not positive those are the exact numbers…taking your word for it).

    A rushed answer but hopefully it helps.

     
  6. 7 Joe

    Ha, I love it. Send a 1 char message, then send the big one. Silly MS and their attempts at software!

    Thanks!

     

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