Hardware Reference
In-Depth Information
Networking Protocols
A
protocol
is set of language rules used between two devices or two points in a process.
Networking involves many different protocols operating at different levels of the
transmission.
The
Open Systems Architecture (OSI) model
defines seven different
layers of network communication, each with its own protocols. The
levels, from lowest to highest, are 1: Physical, 2: Data Link, 3: Network,
4: Transport, 5: Session, 6: Presentation, and 7: Application. You don't
have to know these for the Strata exam, but knowing at which levels the
various protocols take place may help you in your overall understanding
of network communication. The CompTIA A+ exam does require you to
know these layers. Throughout the rest of this chapter, we'll mention at
which OSI layer a particular protocol operates for your reference. For more
information, see
http://en.wikipedia.org/wiki/OSI_model
.
TCP/IP
Transmission Control Protocol/Internet Protocol (TCP/IP)
is the most widely used
protocol in the world. It's actually an interconnected set of protocols, rather than a single
one; the IP portion operates at the Network layer, and the TCP portion operates at the
Transport layer. TCP/IP is important not only because most LANs use it internally as their
primary means of communication, but because it's the protocol used on the Internet, so all
Internet-capable devices also employ TCP/IP.
IP Addresses
Each device on a network has a unique
IP address
, which consists of four numbers (each
between 0 and 255) separated by periods like this:
204.52.0.23
. This is known as
IP
version 4 (IPv4)
.
Even though the numbers are written as decimals, to make them easier to read, in reality
an IPv4 address is a 32-bit binary number. Each of the four numbers is machine-translated
into binary, so the previous example IP address looks like this to a computer:
11001100.00110100.00000000.00010111
IPv4 is the original type of IP addressing used on the Internet, and it's also widely
used in local area networking. Each IP address is allocated to a particular company,
organization, or individual, and there are complex rules as to who may own and use which
IP addresses on the Internet. (Within a private network that isn't connected to the Internet,
you may use whatever IP addresses you like.) About 4 billion possible IP addresses are
