When datastreams diverge

When multiple connection streams occur simultaneously in the protocol stack, all the data comes in on the same wire of the network interface card, so the divergence of individual datastreams happens between the physical layer and the application layer using ports or service access points. Where do the individual datastreams diverge, and why?

When multiple connection streams occur simultaneously in the protocol stack (for example, Telnet, FTP session and e-mail), all the data comes in on the same wire of the network interface card, so the divergence of individual datastreams happens between the physical layer and the application layer using ports or service access points, depending on which protocol stack you’re running. Where do the individual datastreams diverge, and why?

Datastreams are split early and often to accelerate processing on the way up the network stack to the application.

Data link frames coming into the machine are separated by type to determine which protocol software module should process the frame.

IP frames go to the IP stack. The IP stack separates datastreams based on the protocol type field in the IP datagram header.

UDP processing software places datagrams in queues based on source and destination ports.

TCP also distinguishes source and destination address to provide connection-oriented session services for applications.

On the way back to the network wire, each layer in the stack that needs to will add a header used at the other end to make layer-specific decisions about which application process gets the data.