HTTP Error 503 - Service is unavailable (how fix?)
i have a web site for download mobile files and there many users in my web site.  
sometimes i have the error below :  
`HTTP Error 503 - Service is unavailable`  

1-so why this error happens and what is that mean?  

2-as i know appache free up itself when it's oveloaded, but what about iis?  

how can i put some limitations in my server (i have remote access to my server) for prevent this error happening?  

a-is limitation of dowload's **speed** efficient for prevent that error's occur?  
how can i do that?   is squid useful for this job or i can do that with another iis extension.

b.is limitation of download's **Bandwidth** efficient for prevent that error's occur?  
how can i do that (with iis or another extension)? 

in right side of iis -> configure area -> i found some limits.  
what do those limits mean and can i use them for keep my server alive all the time?  

thanks in advance  
best regards
HTTP Error 503 - Service is unavailable (how fix?)
===

i have a web site for download mobile files and there many users in my web site.  
sometimes i have the error below :  
`HTTP Error 503 - Service is unavailable`  

1-so why this error happens and what is that mean?  

2-as i know appache free up itself when it's oveloaded, but what about iis?  

how can i put some limitations in my server (i have remote access to my server) for prevent this error happening?  

a-is limitation of dowload's **speed** efficient for prevent that error's occur?  
how can i do that?   is squid useful for this job or i can do that with another iis extension.

b.is limitation of download's **Bandwidth** efficient for prevent that error's occur?  
how can i do that (with iis or another extension)? 

in right side of iis -> configure area -> i found some limits.  
what do those limits mean and can i use them for keep my server alive all the time?  

thanks in advance  
best regards