Internet Architecture- Addressing

Physical Addresses
The physical address, also known as the link address, is the address of a node as defined by
its LAN or WAN. It is included in the frame used by the data link layer. It is the lowest-level address.
The size and format of these addresses vary depending on the network. For example, Ethernet uses
a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC).
Most local area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal
digits; every byte (2 hexadecimal digits) is separated by a colon.

Logical Addresses
Logical addresses are necessary for universal communications that are independent of
underlying physical networks. Physical addresses are not adequate in an internetwork environment
where different networks can have different address formats. A universal addressing system is
needed in which each host can be identified uniquely, regardless of the underlying physical network.
The logical addresses are designed for this purpose. A logical address in the Internet is currently a 32-
bit address that can uniquely define a host connected to the Internet. No two publicly addressed and
visible hosts on the Internet can have the same IP address.

Port Addresses
The IP address and the physical address are necessary for a quantity of data to travel from a source to the destination host. However, arrival at the destination host is not the final objective of data communications on the Internet. Computers are devices that can run multiple processes at the same time. The end objective of Internet communication is a process communicating with another process. For example, computer A can communicate with computer C by using TELNET. At the same time, computer A communicates with computer B by using the File Transfer Protocol (FTP). For these processes to receive data simultaneously, we need a method to label the different processes.
In other words, they need addresses. In the TCP/IP architecture, the label assigned to a process is called a port address. A port address in TCP/IP is 16 bits in length.
A port address is a 16-bit address represented by one decimal number as shown.