TCP/IP : Introduction, Underlying Network
Technologies, Internet Architecture, Internet Addresses
An Internet consists of a set of connected networks.
The chief advantage of an Internet is that it provides universal
interconnection while allowing individual groups to use
whatever network hardware is best suited to their needs.
The technology TCP/IP provides the basis for the global
Internet, which helps in connecting individuals, universities,
corporation and government department in many countries
around the globe. The global Internet is expanding rapidly.
2. Underlying Network Technologies
(i) Approaches to Network Communication:
The two approached to network communications are
Circuit switched (Connection Oriented)
Packet switched (Connectionless)
Circuit switched network operates by forming a dedicated
connection between two points.
In a Packet switched network, data to be transferred
across a network is divided into small pieces called packets
that are multiplexed onto high capacity intermachine connections.
(ii) Wide Area and Local Area Networks
The Packed switch technology is divided into two broad
Wide Area Network
Local Area Network
Wide Area Network:
WAN technologies, sometimes called long haul networks,
provide communication over large distances. Most WAN technologies
do not limit the distance spanned. A WAN can allow the endpoints
of a communication to be arbitrarily far apart. For example,
a WAN can span a continent or can join computers across
an ocean. Usually WANs operate at slower speeds that LANs,
and have much greater delay between connections. The typical
speed of WAN ranges from 56 Kbps to 155 Mbps. Delay across
a WAN can vary from a few milliseconds to several tenths
Local Area Networks:
LAN technologies provide the highest speed connections among
computers, but sacrifice the ability to span large distances.
For example, a typical LAN spans a small area like a single
building or a small campus and operates between 10 Mbps and
2 Gbps (Billion bits per second). Because LAN technologies cover
short distances, they offer lower delays than WANs. The delay
across a LAN can be as short as a few tenths of a millisecond,
or as long as 10 milliseconds.
(iii) Ethernet Technology
Ethernet is the name given to a popular packet switched LAN
technology; most medium or large corporations use Ethernet.
The Ethernet is a 10/100 Mbps (Recently extending in to Gbps
range) broadcast bus technology with distributed access control.
It is a bus because all stations share a single communication
channel; it is a broadcast because all transceivers receive
(iv) Fiber Distributed Data Interconnect
FDDI is a popular local area networking technology that provides
higher bandwidth than Ethernet. Unlike Ethernet and other LAN
technologies that use cables to carry electrical signals, FDDI
uses glass fibers and transfers data by encoding it in pulses
of light. FDDI has ability to detect and correct network problems,
such as a break in the network. The network is called Self-healing
because the hardware can automatically accommodate failure
(v) Asynchronous Transfer Mode (ATM):
ATM is a high-speed connection oriented networking that has
been used in both local area and wide area networks. ATM can
switch data at gigabit speeds. To achieve high transfer speeds,
an ATM network uses special-purpose hardware and software techniques.
3. Internet Architecture
An Internet is more than a collection of networks interconnected
by computers. Internetworking implies that the interconnected
systems agree to conventions that allow each computer to communicate
with every other computer.
The networks interconnect to form an internetwork.
Then, how a packet flows from one network to another? Physically,
a device that attaches to both of them can only connect two
networks. Devices that interconnect two networks and pass
packets from one to the other are called Internet gateways or
routers. A router reads the destination address, and routs the
packet to the destination.
Consider an example consisting of two physical networks shown
as below. In the figure, router R connects to both network 1
and 2. For R to act as a router, it must capture packets on
network 1 that are bound for machines on network 2 and transfer
them. Similarly, R must capture packets on network 2 that are
destined for machines on network 1 and transfer them.
In the above figure, two physical networks interconnected
by R, a router (IP gateway). In a TCP/IP Internet, computers
called routers or gateways provide all interconnections among
physical networks. Routers use the destination network, not
the destination host, when routing a packet.
4. Internet Addresses
Each host on a TCP/IP Internet is assigned a unique 32-bit
Internet address that is used in all communication with that
host. Conceptually, each IP address consists of a network
id that identifies a network, and host id identifies
a host on that network.Given an IP address, its class can be
determined from the three high-order bits, with two bits being
sufficient to distinguish among the three primary classes.
(i) ARP (Mapping Internet Addresses
to Physical Addresses)
Address Resolution Protocol, ARP, allows a host to find the
physical address of a target host on the same physical network,
given only the target's IP address.
ARP is a low-level protocol that hides the underlying networks
physical addressing, permitting one to assign an arbitrary IP
address to every machine. ARP is a part of physical network
system, and not as part of Internet protocols.
(ii) RARP (Reverse Address Resolution
At system startup, a computer that does not have a disk (diskless
computers) must contact a server to find its IP address before
it can communicate using TCP/IP. It is found that the RARP protocol
that uses physical network addressing to obtain that machine's
Internet address. The RARP mechanism supplies the target machine's
physical hardware address to uniquely identify the processor
and broadcasts the RARP request. Servers on the network receive
the message, look up the mapping in a table, and reply to the
sender. Once a machine obtain its IP address in memory and does
not use RARP again it reboots.