Basic of Layer 4
Provides transparent transfer of data between end hosts.
Provides (or doesn't provide) various services to applications:
reliable data transfer
error recovery
data sequencing
flow control
Provides Layer 4 addressing (port numbers).
Identify the Application Layer protocol.
Provides session multiplexing.
In this context, port, does not refer to the physical interfaces/ports on network devices.
The following ranges have been designated by IANA (Internet Assigned Numbers Authority)
Well-known port numbers: 0 -1023
Registered port numbers: 1024 - 49151
Ephemeral/private/dynamic port numbers: 49152 - 65535
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