Large Waiting time for an HTTP request

I'm working on developing a web site using cakephp. I'm analyzing the website now using firebug + Yslow and Google chrome developer tools. In an Ajax request I get a large waiting time about 6s while the receiving开发者_如何学C time is too small 66ms which cause a great latency in the request. Does anybody know why the waiting time is too large??

Waiting time - From the time of request to the time first byte is received, which involves a round trip time. There can be latency if your server away from your machine. Usually it requires 3 round trips. 1 for DNS lookup and 1 for establishing TCP Connection, 1 for request and response pair.

Receiving Time : It will be less if there is less amount of data being downloaded from the server to the client.

For further reference : http://www.webperformancematters.com/journal/2007/7/24/latency-bandwidth-and-response-times.html

My guess is that you might be performing a SQL query as part of the resource that you are calling via Ajax. If this is the case, you may need to tune your query or indexes to improve the speed of the query. Can you post some code so we may review?