参见：http://en.wikipedia.org/wiki/Keepalive#TCP_keepalive

通常，保持活动时间（ net.inet.tcp.keepidle ）默认为7200秒。
我不知道在iOS中是否属实，但不少于2小时 / html / rfc1122＃page-101> RFC 1122 。

Usually, keepalive time (net.inet.tcp.keepidle) is 7200sec by default. I don't know that is true in iOS or not, but "no less than 2 hours" is clearly required by RFC 1122.

此间隔必须是
可配置且必须默认为不少于两个小时。

This interval MUST be configurable and MUST default to no less than two hours.

那么，你怎么能在你的应用程序中配置它？尝试：

So, how could you configure it in your application? try:

#import <sys/types.h>
#import <sys/socket.h>
#import <netinet/in.h>
#import <netinet/tcp.h>

int on = 1;
int delay = 120;
setsockopt(socket_handle, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on));
setsockopt(socket_handle, IPPROTO_TCP, TCP_KEEPALIVE, &delay, sizeof(delay));

参见 man tcp 。

我确认这适用于iOS模拟器（iPhone 5s / iOS 8.0）。

I confirmed this works on iOS Simulator (iPhone 5s / iOS 8.0).