TCP/IP协议栈的process model一般有几种方式.
1. TCP/IP协议的每一层是个独立进程.链路层是个进程,ip层是个进程,tcp层是个进程.这样的好处是网络协
议的每一层都非常清晰,代码的调试和理解都非常容易.不过最大的坏处数据跨层传递时会引起上下文转换(context switch)。对于接收一个TCP segment要引起3次context switch(从网卡驱动程式到链路层进程,从链路层进程到ip层进程,从ip层进程到TCP进程)。通常对于操作系统来说,任务转换是要浪费时间的.过频的context swich是不可取的.
2. 另外一种方式是TCP/IP协议栈在操作系统内核当中.应用程式通过操作系统的系统调用(system call)和协议栈来进行通讯. 这样TCP/IP的协议栈就限定于特定的操作系统内核了.如windows就是这种方式.
3. LwIP的process model:所有TCP/IP协议栈都在一个进程当中,这样tcp/ip协议栈就和操作系统内核分开了.而应用层程式既能是独立的进程也能驻留在TCP/IP进程中.如果应用程式是独立的进程能通过操作系统的邮箱,消息队列等和TCP/IP进程进行通讯.如果应用层程式驻留TCP/IP进程中,那应用层程式就利用内部回调函数口(Raw API)和TCP/IP协议栈通讯.对于uc/os来说进程就是个系统任务
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