The 2800 is a low end access switch.  It does not have the capability of throttling traffic on a connection.  The CoS feature allows you to set priority levels on the different traffic which is different.   If that connection and traffic is not handled properly you may need to look at getting an upgraded switch that has more of a full feature set that allows specific traffic shaping.
Anyone know if there are any setting to specify traffic shaping on the Dell PowerConnect 2816 or 2824 web managed switches?
traffic shaping on PowerConnect 28XX series