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Your terminology is a little off. TCP does not provide anything for the application layer as it is transport layer. The application layer rides on top of that.

Your terminology is a little off. TCP does not provide anything for the application layer as it is transport layer. The application layer rides on top of that. Examples of transport protocols are TCP and UDP while application protocols are things like http, ssh, irc, and all those things your applications use. The network layer on which the transport layer rides is packet switched. The TCP uses segments with each segment having its own header and sequence numbers. Streams are just a series of segments populating across a single established handshake without a prior defined termination segment.

Matthias247 6y ago
I didn't meant to talk about OSI terminologies. It was more about: [user-space] applications which use the TCP/IP stack do not observe packet boundaries, whereas the Kernel certainly does. Obviously this is a bit ambiguous, and you can even get packet boundaries in user-space by running a TCP stack there. But for most TCP/IP usages it holds true.
- austincheney 6y ago
  > It was more about: [user-space] applications which use the TCP/IP stack do not observe packet boundaries That is still a bit imprecise. Userland applications won't directly see TCP as they are just looking at an application protocol. Typically it's the OS that packages and unpacks the application protocol data into a TCP segment, so of course the userland application won't see it since its not managing that part of the communication. https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Network_function https://en.wikipedia.org/wiki/Transmission_Control_Protocol#... There are some exceptions where some application platforms allow developers to write custom TCP protocols, such as Node.js, but these exceptions generally apply to network services and don't commonly apply to the end user application experiance. https://nodejs.org/dist/latest-v14.x/docs/api/net.html#net_net https://nodejs.org/dist/latest-v14.x/docs/api/net.html#net_n...

Matthias247 6y ago

I didn't meant to talk about OSI terminologies. It was more about: [user-space] applications which use the TCP/IP stack do not observe packet boundaries, whereas the Kernel certainly does. Obviously this is a bit ambiguous, and you can even get packet boundaries in user-space by running a TCP stack there. But for most TCP/IP usages it holds true.

austincheney 6y ago
> It was more about: [user-space] applications which use the TCP/IP stack do not observe packet boundaries That is still a bit imprecise. Userland applications won't directly see TCP as they are just looking at an application protocol. Typically it's the OS that packages and unpacks the application protocol data into a TCP segment, so of course the userland application won't see it since its not managing that part of the communication. https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Network_function https://en.wikipedia.org/wiki/Transmission_Control_Protocol#... There are some exceptions where some application platforms allow developers to write custom TCP protocols, such as Node.js, but these exceptions generally apply to network services and don't commonly apply to the end user application experiance. https://nodejs.org/dist/latest-v14.x/docs/api/net.html#net_net https://nodejs.org/dist/latest-v14.x/docs/api/net.html#net_n...