1.1 Addressing and Internet Service: An Overview

In many ways, Internet addressing scheme has similarities to the postal addressing system.

	The addressing in the Internet is referred to as Internet Protocol (IP) addressing.
	An IP address defines two parts: one part that is similar to the postal code and the other part that is similar to the house address; in Internet terminology, they are known as the Net-ID and the Host-ID.
	Net-ID is used to identify a network (postal code) and Host-ID is used to identify a host within a network (house address).
	Thus, a host is the end point of communication in the Internet and where a communication starts. A netid identifies a contiguous block of addresses.

Like any service delivery system, there is a need for a delivery model for the Internet also.

For example, in the postal system, one can request guaranteed delivery for an additional fee. The Internet's conceptual framework, known as TCP/IP (Transmission Control Protocol/Internet Protocol), relies on a delivery model in which TCP is in charge of the reliable delivery of information, while IP is in charge of routing, using the IP addressing mechanism. IP, however, does not worry about whether the information is reliably delivered to the address or is lost during transit.

1.1 Addressing and Internet Service: An Overview

	Suppose that a document that we want to download from a host (web-server) is 2 MB. Actually, it cannot be accommodated entirely into a single fundamental unit of IP, known as packet or datagram, due to a limitation imposed by the underlying transmission system. This limitation is known as the Maximum Transmission Unit (MTU).
	MTU is similar to the limitation on how many people can fit into a single car. Thus, the document would need to be broken down into smaller units that fit into packets. Each packet is then labeled with both the destination and the source address, which is then routed through the Internet toward the destination.