directly to a network segment is referred to as a
device. These devices are broken up into two classifications.
The first classification is end-user devices. End-user devices
include computers, printers, scanners, and other devices that
provide services directly to the user. The second
classification is network devices. Network devices include all
the devices that connect the end-user devices together to allow
them to communicate. End-user devices that provide users with a
connection to the network are also referred to as hosts. These
devices allow users to share, create, and obtain information.
The host devices can exist without a network, but without the
network the host capabilities are greatly reduced. Host devices
are physically connected to the network media using a network
interface card (NIC). They use this connection to perform the
tasks of sending e-mails, printing reports, scanning pictures,
or accessing databases. A NIC is a printed circuit board that
fits into the expansion slot of a bus on a computer
motherboard, or it can be a peripheral device. It is also
called a network adapter. Laptop or notebook computer NICs are
usually the size of a PCMCIA card. Each individual NIC carries
a unique code, called a Media Access Control (MAC) address.
This address is used to control data communication for the host
on the network. More about the MAC address will be covered
later. As the name implies, the NIC controls host access to the
medium. There are no standardized symbols for end-user devices
in the networking industry. They appear similar to the real
devices to allow for quick recognition. Network devices
provide transport for the data that needs to be transferred
between end-user devices. Network devices provide extension of
cable connections, concentration of connections, conversion of
data formats, and management of data transfers. Examples of
devices that perform these functions are repeaters, hubs,
bridges, switches, and routers. All of the network devices
mentioned here are covered in depth later in the course. For
now, a brief overview of networking devices will be provided. A
repeater is a network device used to regenerate a signal.
Repeaters regenerate analog or digital signals distorted by
transmission loss due to attenuation. A repeater does not
perform intelligent routing like a bridge or router. Hubs
concentrate connections. In other words, they take a group of
hosts and allow the network to see them as a single unit. This
is done passively, without any other effect on the data
transmission. Active hubs not only concentrate hosts, but they
also regenerate signals. Bridges convert network transmission
data formats as well as perform basic data transmission
management. Bridges, as the name implies, provide connections
between LANs. Not only do bridges connect LANs, but they also
perform a check on the data to determine whether it should
cross the bridge or not. This makes each part of the network
more efficient. Workgroup switches add more intelligence to
data transfer management. Not only can they determine whether
data should remain on a LAN or not, but they can transfer the
data only to the connection that needs that data. Another
difference between a bridge and switch is that a switch does
not convert data transmission formats. Routers have all the
capabilities listed above. Routers can regenerate signals,
concentrate multiple connections, convert data transmission
formats, and manage data transfers. They can also connect to a
WAN, which allows them to connect LANs that are separated by
great distances. None of the other devices can provide this
type of connection. Interactive Media Activity Drag and
Drop: Identifying Network Devices After completing this
activity, the student will be able to identify different
network devices. Interactive Media Activity PhotoZoom:
Cisco 1503 Micro Hub In this PhotoZoom, the student will view a
Cisco 1503 hub. Interactive Media Activity PhotoZoom:
Cisco Catalyst 1924 Switch In this PhotoZoom, the student will
view a Cisco Catalyst 1924 switch. Interactive Media
Activity PhotoZoom: Cisco 2621 Router In this PhotoZoom,
the student will view a Cisco 2621 router. Web Links
Hardware Channel Home Page http://www.howstuffworks.com/
category.htm?cat=Hardwar
Content 2.1
Networking Terminology 2.1.4 Network
topology Network topology defines the structure of the
network. One part of the topology definition is the physical
topology, which is the actual layout of the wire or media. The
other part is the logical topology, which defines how the media
is accessed by the hosts for sending data. The physical
topologies that are commonly used are as follows: - A
bus topology uses a single backbone cable that is terminated at
both ends. All the hosts connect directly to this backbone.
- A ring topology connects one host to the next and the
last host to the first. This creates a physical ring of cable.
- A star topology connects all cables to a central
point of concentration.
- An extended star topology
links individual stars together by connecting the hubs and/or
switches. This topology can extend the scope and coverage of
the network.
- A hierarchical topology is similar to an
extended star. However, instead of linking the hubs and/or
switches together, the system is linked to a computer that
controls the traffic on the topology.
- A mesh topology
is implemented to provide as much protection as possible from
interruption of service. The use of a mesh topology in the
networked control systems of a nuclear power plant would be an
excellent example. As seen in the graphic, each host has its
own connections to all other hosts. Although the Internet has
multiple paths to any one location, it does not adopt the full
mesh topology.
The logical topology of a network is
how the hosts communicate across the medium. The two most
common types of logical topologies are broadcast and token
passing. Broadcast topology simply means that each host sends
its data to all other hosts on the network medium. There is no
order that the stations must follow to use the network. It is
first come, first serve. Ethernet works this way as will be
explained later in the course. The second logical topology is
token passing. Token passing controls network access by passing
an electronic token sequentially to each host. When a host
receives the token, that host can send data on the network. If
the host has no data to send, it passes the token to the next
host and the process repeats itself. Two examples of networks
that use token passing are Token Ring and Fiber Distributed
Data Interface (FDDI). A variation of Token Ring and FDDI is
Arcnet. Arcnet is token passing on a bus topology. The diagram
in Figure shows many different topologies connected by network
devices. It shows a network of moderate complexity that is
typical of a school or a small business. It has many symbols,
and it depicts many networking concepts that will take time to
learn. Web Links Network Topologies
http://www.icoe.k12.ca.us/support/ network/topology.htm
Content 2.1 Networking Terminology
2.1.5 Network protocols Protocol suites are
collections of protocols that enable network communication from
one host through the network to another host. A protocol is a
formal description of a set of rules and conventions that
govern a particular aspect of how devices on a network
communicate. Protocols determine the format, timing,
sequencing, and error control in data communication. Without
protocols, the computer cannot make or rebuild the stream of
incoming bits from another computer into the original format.
Protocols control all aspects of data communication, which
include the following: - How the physical network is
built
- How computers connect to the network
- How the data is formatted for transmission
- How
that data is sent
- How to deal with errors
These network rules are created and maintained by many
different organizations and committees. Included in these