FIN ACK TCP延迟

时间:2014-12-23 13:46:01

标签: java sockets tomcat tcp httpclient

我有两台与HTTP通信的服务器:查看客户端代码的一部分

 PostMethod postMethod = new PostMethod(strURL);
    int bodylength=UCIPBodyRequestGen.toStringBodyRequest(_request, DEFAULT_CHARSET).length();
    setRequestHeader(postMethod,bodylength);
    postMethod.setRequestBody(requestBody);
    HttpClient myClient = new HttpClient();
    myClient.setConnectionTimeout(mcf.getTimeout());
    myClient.setTimeout(mcf.getTimeout());
   int statusCode = myClient.executeMethod(postMethod);
   responseBody=postMethod.getResponseBodyAsString();

我在某个请求中有一点延迟~500ms,另一个平均值为~20ms

TCPDUMP show that the delay is in TCP FIN-ACK

2014-12-23 09:38:59.069230  HTTP/XML    1534    POST /Servlet HTTP/1.1 
2014-12-23 09:38:59.070450  HTTP    514 HTTP/1.1 200 OK 
2014-12-23 09:38:59.110758  TCP 66  14783?9770 [ACK] Seq=1469 Ack=450 Win=33920 Len=0 TSval=2321949059 TSecr=2321949019
2014-12-23 09:38:59.602623  TCP 66  14783?9770 [FIN, ACK] Seq=1469 Ack=450 Win=33920 Len=0 TSval=2321949551 TSecr=2321949019

关于这种延迟的任何线索?

1 个答案:

答案 0 :(得分:2)

FIN ACK数据包汇总为:

http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/TCP_CLOSE.svg/375px-TCP_CLOSE.svg.png

在第一个服务器FIN和ACK之间,是另一个服务器的ACK和FIN对,因此这个连接终止阶段(四次握手)需要时间。

问候