Why does the sockets buffer fill up sooner than expected?
From Paul W. Nelson (nelson@thursby.com): In the traditional BSD socket implementation, sockets that are atomic such as UDP keep received data in lists of mbufs. An mbuf is a fixed size buffer that is shared by various protocol stacks. When you set your receive buffer size, the protocol stack keeps track of how many bytes of mbuf space are on the receive buffer, not the number of actual bytes. This approach is used because the resource you are controlling is really how many mbufs are used, not how many bytes are being held in the socket buffer. (A socket buffer isn’t really a buffer in the traditional sense, but a list of mbufs). For example: Lets assume your UNIX has a small mbuf size of 256 bytes. If your receive socket buffer is set to 4096, you can fit 16 mbufs on the socket buffer. If you receive 16 UDP packets that are 10 bytes each, your socket buffer is full, and you have 160 bytes of data. If you receive 16 UDP packets that are 200 bytes each, your socket buffer is also full,
