n which Namespace the ObjectList class present

Hi, I am using chat application using Remoting, ie from the following site http://www.c-sharpcorner.com//internet/remoting_chat_server.asp i download the zip file of Remotingchat, in that the file ChatServerImpl consists of some code ie public class ChatServerImpl : MarshalByRefObject,ChatServer { private ObjectList chatters = new ObjectList(); when i compile it is giving an error ie ObjectList class is not found. I am expecting the ObjectList class is from System.Collection Namespace but in that namespace there is no class with the name ObjectList. I want to know in which Namespace the ObjectList class is present. For overcomming the error.