| TCP/IP is not a single protocol but a
suite comprised of a number of protocols operating at most of the
layers of the OSI model. The Defense Advance Research Projects Agency
(DARPA) originally developed TCP/IP to interconnect defense department
computer networks across the country to form a fault tolerant network.
It was adopted and further developed as the standard networking
communications component of the UNIX operating system.
Many networking protocols have come and
gone over the years. Proprietary protocols are rapidly losing ground
in favor of open protocols like TCP/IP. Proprietary protocols include
Novell's' IPX and Apple computer's AppleTalk. In fact, current
versions of both Novell's and Apple's network operating systems
support TCP/IP as a primary protocol. TCP/IP is an open standard and
is the only protocol that is supported by every major operating system
and nearly every networking equipment vendor. Virtually every computer
manufactured in the world today, from laptops to the largest
mainframes can communicate using the TCP/IP protocol. TCP/IP was
originally developed as a WAN protocol but has recently become a
required LAN protocol since most PCs on LANs need access to the
Internet. With some LANs, TCP/IP runs along with other protocols such
as IPX and AppleTalk, however it is becoming increasingly common to
build LANs using only the TCP/IP protocol.
TCP/IP is the language of the Internet,
which is the largest international network in the world with millions
of nodes. The Internet is a packet-switched network that uses the
Internet Protocol or IP to identify and encapsulate its packets.
TCP/IP is the de facto UNIX standard and is the most widely used
protocol suite in the world. Nearly every network equipment
manufacturer has developed or is developing products that support
TCP/IP.
The name TCP/IP is a combination of the
two most important protocols in the suite: Transmission Control
Protocol (TCP) and Internet Protocol (IP). TCP is one of
the layer four transport protocols in the suite and IP is the layer
three routing protocol in the Suite. TCP provides connection-oriented
services to ensure that all packets reach their destination. Most
Internet communication such as Hypertext Transfer Protocol (HTTP) use
TCP as their transport mechanism. UDP is the other layer 4 protocol
that provides connectionless services which can be used when
delivery does not need to be guaranteed and for real-time applications
such as voice and video transmission. Whether TCP or UDP, all packets
ride over the Internet on IP. All computers (hosts) such as
workstations and servers that wish to communicate over the Internet
must have an IP address and must run the TCP/IP protocol. As a result,
TCP/IP is fast becoming the protocol of choice for LANs and WANs.
TCP/IP is a “routed” or “routable”
protocol. A host IP address has in it both the network’s address the
address of the host on that network. This provides a way for one host
to send packets to a host on another network while allowing each
packet to be directed from the source host to a destination host
sometimes through many routers along the way.
Any computer running the TCP/IP
protocol is considered to be a “host”. A host is uniquely
identified on the Internet by a 32-bit IP address. This address is
divided into 4 set of 8 bits each which are referred to as octets. In
addition to an IP address, TCP/IP computers are also given a host name
such as www.sun.com. Most TCP/IP networks will allow a user to refer
to the user-friendly host name as when browsing the Internet and a
network naming service such as Domain Name System (DNS) or Network
Information Server (NIS) will translate the host name into an IP
address. Figure
shows an example of an IP host address and a host name. Figure
shows two hosts communicating over the Internet using TCP/IP. Figures
and
compare the OSI model to the TCP/IP protocol stack.
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