do 'llama' to enter the engineering mode.
Then do a 'flow stat' and you should see the number of free FCB/ total FCB.
Each FCB represent 1 flow.
This will give you the total number of concurrent connections.
If you do not own a CSS11501 and are just looking for the information, you can get it from this web page :
http://www.cisco.com/en/US/products/hw/contnetw/ps792/products_data_sheet0900aecd800f851e.html
Each module will handle +/- 200,000 concurrent connections. Since there is only 1 module in the 11501, this is the amount of concurrent connections.
Gilles.