it would require modifying the software. Any
failure of an intermediate computer or the application of the
computer would cause a break in the chain of the messages that
are passed. The Internet uses the principle of network layer
interconnection. Using the OSI model as an example, the goal is
to build the functionality of the network in independent
modules. This allows a diversity of LAN technologies at Layers
1 and 2 and a diversity of applications functioning at Layers
5, 6, and 7. The OSI model provides a mechanism where the
details of the lower and the upper layers are separated. This
allows intermediate networking devices to “relay” traffic
without having to bother with the details of the LAN. This
leads to the concept of internetworking, or building networks
of networks. A network of networks is called an internet,
indicated with the lowercase “i”. When referring to the
networks that developed from the DoD on which the Worldwide Web
(www) runs, the uppercase “I” is used and is called the
Internet. Internetworking must be scalable with regard to the
number of networks and computers attached. Internetworking must
be able to handle the transport of data across vast distances.
It must be flexible to account for constant technological
innovations. It must be able to adjust to dynamic conditions on
the network. And internetworks must be cost-effective.
Internetworks must be designed to permit anytime, anywhere,
data communications to anyone. Figure summarizes the connection
of one physical network to another through a special purpose
computer called a router. These networks are described as
directly connected to the router. The router is needed to
handle any path decisions required for the two networks to
communicate. Many routers are needed to handle large volumes of
network traffic. Figure extends the idea to three physical
networks connected by two routers. Routers make complex
decisions to allow all the users on all the networks to
communicate with each other. Not all networks are directly
connected to one another. The router must have some method to
handle this situation. One option is for a router to keep a
list of all computers and all the paths to them. The router
would then decide how to forward data packets based on this
reference table. The forwarding is based on the IP address of
the destination computer. This option would become difficult as
the number of users grows. Scalability is introduced when the
router keeps a list of all networks, but leaves the local
delivery details to the local physical networks. In this
situation, the routers pass messages to other routers. Each
router shares information about which networks it is connected
to. This builds the routing table. Figure shows the
transparency that users require. Yet, the physical and logical
structures inside the Internet cloud can be extremely complex
as displayed in Figure . The Internet has grown rapidly to
allow more and more users. The fact that the Internet has grown
so large with more than 90,000 core routes and 300,000,000 end
users is proof of the soundness of the Internet architecture.
Two computers, anywhere in the world, following certain
hardware, software, and protocol specifications, can
communicate reliably. Standardization of practices and
procedures for moving data across networks has made the
Internet possible. Web Links Internet: The Big Picture
http://navigators.com/ internet_architecture.html
Content
9.2 Internet Addresses 9.2.1 IP
addressing For any two systems to communicate, they must be
able to identify and locate each other. While these addresses
in Figure are not actual network addresses, they represent and
show the concept of address grouping. This uses the A or B to
identify the network and the number sequence to identify the
individual host. A computer may be connected to more than one
network. In this situation, the system must be given more than
one address. Each address will identify the connection of the
computer to a different network. A device is not said to have
an address, but that each of the connection points, or
interfaces, on that device has an address to a network. This
will allow other computers to locate the device on that
particular network. The combination of letter (network address)
and the number (host address) create a unique address for each
device on the network. Each computer in a TCP/IP network must
be given a unique identifier, or IP address. This address,
operating at Layer 3, allows one computer to locate another
computer on a network. All computers also have a unique
physical address, known as a MAC address. These are assigned
by the manufacturer of the network interface card. MAC
addresses operate at Layer 2 of the OSI model. An IP address is
a 32-bit sequence of 1s and 0s. Figure shows a sample 32-bit
number. To make the IP address easier to use, the address is
usually written as four decimal numbers separated by periods.
For example, an IP address of one computer is 192.168.1.2.
Another computer might have the address 128.10.2.1. This way of
writing the address is called the dotted decimal format. In
this notation, each IP address is written as four parts
separated by periods, or dots. Each part of the address is
called an octet because it is made up of eight binary digits.
For example, the IP address 192.168.1.8 would be
11000000.10101000.00000001.00001000 in binary notation. The
dotted decimal notation is an easier method to understand than
the binary ones and zeros method. This dotted decimal notation
also prevents a large number of transposition errors that would
result if only the binary numbers were used. Using dotted
decimal allows number patterns to be more easily understood.
Both the binary and decimal numbers in Figure represent the
same values, but it is easier to see in dotted decimal
notation. This is one of the common problems found in working
directly with binary number. The long strings of repeated ones
and zeros make transposition and omission errors more likely.
It is easy to see the relationship between the numbers
192.168.1.8 and 192.168.1.9, where
11000000.10101000.00000001.00001000 and
11000000.10101000.00000001.00001001 are not as easy to
recognize. Looking at the binary, it is almost impossible to
see that they are consecutive numbers. Web Links IP
Addressing Fundamentals http://support.wrq.com/tutorials/
tutorial.html
Content 9.2
Internet Addresses 9.2.2 Decimal and binary
conversion There are many ways to solve a problem. There
are also several ways to convert decimal numbers to binary
numbers. One method is presented here, however it is not the
only method. The student may find other methods easier. It is a
matter of personal preference. When converting a decimal number
to binary, the biggest power of two that will fit into the
decimal number must be determined. If this process is designed
to be working with computers, the most logical place to start
is with the largest values that will fit into a byte or two
bytes. As mentioned earlier, the most common grouping of bits
is eight, which make up one byte. However, sometimes the
largest value that can be held in one byte is not large enough
for the values needed. To accommodate this, bytes are combined.
Instead of having two eight-bit numbers, one 16-bit number is
created. Instead of three eight-bit numbers, one 24-bit number
is created. The same rules apply as they did for eight-bit
numbers. Multiply the previous position value by two to get the
present column value. Since working with computers often is
referenced by bytes it is easiest to start with byte boundaries
and calculate from there. Start by calculating a couple of
examples, the first being 6,783. Since this number is greater
than 255, the largest value possible in a single byte, two
bytes will be used. Start calculating from 215. The binary
equivalent of 6,783 is 00011010 01111111. The second example is
104. Since this number is less than 255, it can be represented
by one byte. The binary equivalent of 104 is 01101000. This
method works for any decimal number. Consider the decimal