TCP/IP transport layer has UDP and TCP protocols.

These are the two most important and common protocols in the 
      TCP/IP transport layer.

The transport protocols deliver data to applications executing on
    on the IP host.

What additional functionality can the transport level protocols provide?

     Congestion control,
     reliable data delivery,
     duplicate data suppression, and
     flow control.

PORTS and SOCKETS

    Provides a uniform and standard way to uniquely identify connections
    and the programs and hosts that are engaged in them.  The process ID
    that is specific to that process on that operating system is thus
    effectively abstracted from.  But in the packet, is the PID number
    stored somewhere?

    Two kinds of ports:

    Well-known:
        Controlled by IANA (Internet Assigned Number Authority).

        Can only be used by system processes or by programs executed by
        privileged users on most systems.
 
        Well known port numbers are typically odd numbers.  Why?
        Because early systems required an odd/even pair of ports
        for duplex operations.

        Most servers only require a single port, but ftp (20 and 21) and
             BOOTP (67 and 68) use two ports.
 
    Ephemeral:
        The client can use any number allocated to it,
        as long as the combination of 
               <transport protocol, IP address, port number> is unique.

        Normally in range 1024 to 65535.

        Client process is allocated the ephemeral port number for
            as long as it needs it.