为啥 wcf 中 System.Web.HttpContext.Current.Session 总是为Null

为什么 wcf 中 System.Web.HttpContext.Current.Session 总是为Null
为什么 wcf 中 System.Web.HttpContext.Current.Session 总是为Null。网上说的各种节点配置都尝试过还是不行。下面直接贴 源码，各位大神们求解。
契约：

方法：


web.Config

	<system.serviceModel>

		<bindings>

			<wsHttpBinding>
				<binding name="WSHttpBinding_ICCFlowServer" maxReceivedMessageSize="8388608"  maxBufferPoolSize="524288" allowCookies="true"
       closeTimeout="00:01:00" openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00" >
					<reliableSession enabled="true"/>
					<readerQuotas maxStringContentLength="8388608"/>
					<security  mode="None">
						<!--此属性控制安全上下文令牌是否通过客户端与服务之间的 WS-SecureConversation 交换建立。将它设置为 true 要求远程方支持 WS-SecureConversation。-->
						<message establishSecurityContext="true"/>

					</security>

				</binding>
			</wsHttpBinding>
		</bindings>
		<services>
			<service behaviorConfiguration="CCFlowServer" name="flowSDKWcf.ServerFun.CCFlowServer">
				<endpoint  address="" binding="wsHttpBinding" bindingConfiguration="WSHttpBinding_ICCFlowServer" contract="flowSDKWcf.ServiceContract.ICCFlowServer" />
			</service>
		</services>

		<behaviors>
			<serviceBehaviors>
				<behavior name="CCFlowServer">
					<serviceMetadata httpGetEnabled="true" />
					<serviceDebug includeExceptionDetailInFaults="false" />
				</behavior>
				<behavior name="">
					<serviceMetadata httpGetEnabled="true" />
					<serviceDebug includeExceptionDetailInFaults="false" />
				</behavior>
			</serviceBehaviors>
		</behaviors>
		<serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />

	</system.serviceModel>

客户端调用：

CCFlowServerClient flowclient = new CCFlowServerClient();
                    flowclient.SetCookie();
                    string s = flowclient.GetCooie();

客户端 config

	<system.serviceModel>
		<bindings>
			<wsHttpBinding>
				<binding name="WSHttpBinding_ICCFlowServer">
					<reliableSession enabled="true" />
					<security mode="None">
						<!--<transport clientCredentialType="Windows" />
						<message clientCredentialType="Windows" />-->
					</security>
				</binding>
			</wsHttpBinding>
		</bindings>
		<client>
			<endpoint address="http://localhost:8088/ServerFun/CCFlowServer.svc"
			 binding="wsHttpBinding" bindingConfiguration="WSHttpBinding_ICCFlowServer"
			 contract="CCWorkFlowServer.ICCFlowServer" name="WSHttpBinding_ICCFlowServer" />
		</client>
	</system.serviceModel>

返回回来的s 都是 "null of sessions"

哪里配置不对或者代码有问题 还望大神们指点啊
------解决方案--------------------
WCF中实例模式(InstanceContextMode)与会话模式(SessionMode)