NETWORKING
What is Computer Networking?
In the world of computers, networking is the practice of linking two or more
computing devices together for the purpose of sharing data. Networks are built with a mix of
computer hardware and computer software.
InternetWorking Devices
What is a Router???
The method by which information (Internet Protocol packets) is
transferredfrom one system on a network to another. Routers perform this
function.
It looks like this..
Its purpose can be seen from this diagram..
What is a Hub??
A network device that allows a number of computers to be connected. Allsystems
on a hub can see all the traffic on that network.Internet Control Message Protocol
(ICMP)A protocol used to verify that the network is working correctly.
It looks like this..
What Are Bridges and Switches?
Bridges and switches are data communications devices that operate principally at
Layer 2 of the OSI reference model. As such, they are widely referred to as data link
layer devices.
Bridges became commercially available in the early 1980s. At the time of their
introduction, bridges connected and enabled packet forwarding between homogeneous
networks. More recently, bridging between different networks has also been defined and
standardized.
Several kinds of bridging have proven important as internetworking devices.
Transparent bridging is found primarily in Ethernet environments, while source-route
bridging occurs primarily in Token Ring environments. Translational bridging provides
translation between the formats and transit principles of different media types (usually
Ethernet and Token Ring). Finally, source-route transparent bridging combines the
algorithms of transparent bridging and source-route bridging to enable communication in
mixed Ethernet/Token Ring environments.
What is a Lan Switch?
LAN switches are used to interconnect multiple LAN segments. LAN switching provides
dedicated, collision-free communication between network devices, with support for
multiple simultaneous conversations. LAN switches are designed to switch data frames at
high speeds. Figure 4-4 illustrates a simple network in which a LAN switch interconnects
a 10-Mbps and a 100-Mbps Ethernet LAN.
CABLES
Cabling play an important role in networking and the type of network media
used determines how fast the data travels along the media, and also the
maximum data rate that can be carried. The four main types of networking
media are:
Shielded twisted-pair (STP)
Unshielded twisted-pair (UTP)
Coaxial cable
Fiber-optic cable
Shielded twisted-pair:
This is a type of copper telephone wiring in which each of the two copper wires
that are twisted together and are coated with an insulating coating that
functions as a ground for the wires.
Unshielded twisted-pair:
Unshielded Twisted-pair are not shielded and thus interfere with nearby
cables.
They are used in LANs to bit rates of 100Mbps and with maximum length of
100m.
UTP cables are typically used to connect a computer to a network.
Coaxial cable:
Has a grounded metal sheath around the signal conductor.
Interference among cables is reduced due to the sheath around signal
conductor.
Allows higher data rate transfer.
Typically they are used at bit rates of 100 Mbps for maximum lengths of 1
km.
Fiber-optic cable:
Do not interfere with nearby cables.
Give greater security.
Allows extremely high bit rates over long distances.
They provide more protection from electrical damage by external equipment
and greater resistance to harsh environment.
Safer in hazardous environment
Network Operating Systems
DEFINITION: A network operating system (NOS) is a computer
operating system system that is designed primarily to support
workstation, personal computer, and, in some instances, older
terminal that are connected on a local area network (LAN). Artisoft's
LANtastic, Banyan VINES, Novell's NetWare, and Microsoft's LAN
Manager are examples
Note 1: A network operating system is most frequently used with local area networks and
wide area networks, but could also have application to larger network systems.
Note 2: The upper 5 layers of the OSI Reference Model provide the foundation upon
which many network operating systems are based.
Source: from Federal Standard 1037C
NOS was also the name of a proprietary time-sharing operating system on the CDC 60-bit
6000 and Cyber series mainframe computers; in the mid 1980s, NOS was replaced with
NOS/VE on the 64-bit Cyber-180 systems.
Network Operating System (NOS) is an operating system that includes special functions
for connecting computers and devices into a local-area network (LAN) or Internetworking. Some popular NOSs for DOS and Windows systems include Novell
NetWare, Windows NT, 2000, 2003, 2008 Server, Sun Solaris and IBM OS/2. The Cisco
IOS (Internet Operating System) is also a network operating system with a focus on the
Internetworking capabilities of network devices.
Features
1.Some of the features of Network Operating System are:
2.Basic support for ethernet ports
3.Provide basic operating system features such as support for processors, protocols,
automatic hardware detection and support multi-processing of applications
4.Security features such as authentication, authorization, logon restrictions and access
control
5.Provide name and directory services
6.Provide file, print, web services, back-up and replication services
Various Networking Topologies
What is a Topology?
The physical topology of a network refers to the configuration of cables, computers, and
other peripherals. Physical topology should not be confused with logical topology which
is the method used to pass information between workstations. Logical topology was
discussed in the Protocol chapter .
Main Types of Physical Topologies
The following sections discuss the physical topologies used in networks and other related
topics.






Linear Bus
Star
Star-Wired Ring
Tree
Considerations When Choosing a Topology
Summary Chart
Linear Bus
A linear bus topology consists of a main run of cable with a terminator at each end (See
fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear
cable. Ethernet and LocalTalk networks use a linear bus topology.
Fig. 1. Linear Bus topology
Advantages of a Linear Bus Topology


Easy to connect a computer or peripheral to a linear bus.
Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology




Entire network shuts down if there is a break in the main cable.
Terminators are required at both ends of the backbone cable.
Difficult to identify the problem if the entire network shuts down.
Not meant to be used as a stand-alone solution in a large building.
Star
A star topology is designed with each node (file server, workstations, and peripherals)
connected directly to a central network hub or concentrator (See fig. 2).
Data on a star network passes through the hub or concentrator before continuing to its
destination. The hub or concentrator manages and controls all functions of the network. It
also acts as a repeater for the data flow. This configuration is common with twisted pair
cable; however, it can also be used with coaxial cable or fiber optic cable.
Fig. 2. Star topology
Advantages of a Star Topology



Easy to install and wire.
No disruptions to the network then connecting or removing devices.
Easy to detect faults and to remove parts.
Disadvantages of a Star Topology



Requires more cable length than a linear topology.
If the hub or concentrator fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of the
concentrators.
The protocols used with star configurations are usually Ethernet or LocalTalk. Token
Ring uses a similar topology, called the star-wired ring.
Star-Wired Ring
A star-wired ring topology may appear (externally) to be the same as a star topology.
Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that
allows information to pass from one device to another in a circle or ring (See fig. 3). The
Token Ring protocol uses a star-wired ring topology.
Tree
A tree topology combines characteristics of linear bus and star topologies. It consists of
groups of star-configured workstations connected to a linear bus backbone cable (See fig.
4). Tree topologies allow for the expansion of an existing network, and enable schools to
configure a network to meet their needs.
Fig. 4. Tree topology
Advantages of a Tree Topology


Point-to-point wiring for individual segments.
Supported by several hardware and software venders.
Disadvantages of a Tree Topology



Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.
5-4-3 Rule
A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule.
One aspect of the Ethernet protocol requires that a signal sent out on the network cable
reach every part of the network within a specified length of time. Each concentrator or
repeater that a signal goes through adds a small amount of time. This leads to the rule that
between any two nodes on the network there can only be a maximum of 5 segments,
connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be
populated (trunk) segments if they are made of coaxial cable. A populated segment is one
which has one or more nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The
furthest two nodes on the network have 4 segments and 3 repeaters/concentrators
between them.
This rule does not apply to other network protocols or Ethernet networks where all fiber
optic cabling or a combination of a fiber backbone with UTP cabling is used. If there is a
combination of fiber optic backbone and UTP cabling, the rule is simply translated to 76-5 rule.
Considerations When Choosing a Topology:




Money. A linear bus network may be the least expensive way to install a
network; you do not have to purchase concentrators.
Length of cable needed. The linear bus network uses shorter lengths of
cable.
Future growth. With a star topology, expanding a network is easily done
by adding another concentrator.
Cable type. The most common cable in schools is unshielded twisted pair,
which is most often used with star topologies.
Summary Chart:
Physical Topology
Common Cable
Common Protocol
Linear Bus
Twisted Pair
Coaxial
Fiber
Ethernet
LocalTalk
Star
Twisted Pair
Fiber
Ethernet
LocalTalk
Star-Wired Ring
Twisted Pair
Token Ring
Tree
Twisted Pair
Coaxial
Fiber
Ethernet
Mesh topology
A type of network setup where each of the computers and network devices are
interconnected with one another, allowing for most transmissions to be
distributed, even if one of the connections go down. This type of topology is
not commonly used for most computer networks as it is difficult and expensive
to have redundant connection to every computer. However, this type of
topology is commonly used for wireless networks. Below is a visual example of
a simple computer setup on a network using a mesh topology.
Hybrid topology
A network topology that uses two or more network topologies.
Ring topology
Also known as a ring network, the ring topology is a type of
computer network configuration where each network
computer and device are connected to each other forming a
large circle (or similar shape). Each packet is sent around
the ring until it reaches its final destination. Today, the
ring topology is seldom used. Below is a visual example of a
simple computer setup on a network using a ring topology.