Clarification needed about WCF Concurrency in REST Services

Question

hi all,

 I have created WCF Rest services. When i am hitting the same request continuously  from client(i.e from Android mobile) it is using diifrerent threads and thread.sleep is also not working.

My code is  below like this..

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Single)]

    public class Service1 : IService1

    {

      [WebInvoke(Method = "POST", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Bare, UriTemplate = "VerifyLogin")]

        public bool VerifyLogin(Login loginCred)

        {

            bool res = false;

            string strThreadPrint= "";

            try

            {

               strThreadPrint= Thread.CurrentThread.ManagedThreadId.ToString() + "  time at : "+DateTime.Now;

               Thread.Sleep(5000); 

               dbcon = new DBConnection();

//for testing here i am throwing an exception so that its going to catch block and responce sent back to client with exception details as shown in catch block.

               dbcon.VerifyLogin(loginCred.Username.Trim(), loginCred.Password.Trim()); 

            }

            catch (Exception sqlex)

            {

                objErrorClass = new ErrorClass("Login class", sqlex.Message + " --- " + strThreadPrint, "CNMK");

                throw new WebFaultException<ErrorClass>(objErrorClass, System.Net.HttpStatusCode.BadRequest);

              

            }

        }

    }

when i am sending request using fiddler with following Requestbody {"Username":"13","Password":"dgdf"}

At that time i am getting the responce as in Json format

{"ErrorDesc":"login failed --- 33 time at :09/04/2013 12:31:30"}

{"ErrorDesc":"login failed --- 35 time at :09/04/2013 12:31:30"}

{"ErrorDesc":"login failed --- 41 time at :09/04/2013 12:31:30"}

{"ErrorDesc":"login failed --- 45 time at :09/04/2013 12:31:30"}

So the instance mode and concurrency mode not working for wcf restful services????

or am i doing any wrong in my code?? please help me