CHAPTER 2
NETWORK
▪
Data networks
1.
Networking Devices
2.
Networking Topologies Types
▪
Physical topologies
▪
Logical topologies
▪ Data networks developed as a result of business applications that were written for microcomputers.
▪ Businesses needed a solution that would successfully address the following three problems:
▪ How to avoid duplication of equipment and resources
▪ How to communicate efficiently/ reduce duplicate copies of files
▪ How to set up and manage a network
▪ Businesses realized that networking technology could increase productivity while saving money.
▪ In the 1980s users with stand-alone computers started to share files using modems to connect to other computers. This was referred to as point-to-point, or dial-up communication
▪ Bulletin boards became the central point of communication in a dial-up connection. Drawbacks to this type of system were:
▪ That there was very little direct communication
▪ Availability was limited to only with those who knew about the location of the bulletin board
▪ Required one modem per connection. If five people connected simultaneously it would require five modems connected to five separate phone lines
▪ From the 1960s-1990s, the DoD developed large, reliable, WANs for military and scientific reasons.
▪ In 1990, the DoDs WAN eventually became the Internet
▪ One early solution was the creation of local-area network (LAN) standards.
▪ Because LAN standards provided an open set of guidelines for creating
network hardware and software, the equipment from different companies could then become compatible.
▪ This allowed for stability in LAN implementation.
▪ In a LAN system, each department of the company is a kind of electronic island.
▪ As the use of computers in businesses grew, it soon became obvious that even LANs were not sufficient.
▪
Network devices include all the devices that connect the end-user
devices together to allow them to communicate.
▪
End-user devices
include computers, printers, scanners, and other
devices that provide services directly to the user.
▪
End-user devices that provide users with a connection to the
network are also referred to as
hosts
.
▪
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)
▪
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 format
▪
management of data transfers.
▪
A
repeater
is a network device used to regenerate a
signal.
▪
Repeaters regenerate analoge or digital signals
distorted by transmission loss due to attenuation.
▪
A repeater dose not perform intelligent routing.
NETWORKING DEVICES
(REPEATERS)
▪
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 host, but they also
regenerate signals.
NETWORKING DEVICES
(HUBS)
▪
Bridges
convert network transmission data formats
as well as perform basic data transmission
management.
▪
Bridges provide connections between LANs.
▪
Bridges also perform a check on the data to
determine whether it should cross the bridge or not.
NETWORKING DEVICES
(BRIDGES)
▪
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.
NETWORKING DEVICES
▪
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.
NETWORKING DEVICES
(ROUTERS)
NETWORK TOPOLOGIES
▪ 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.
PHYSICAL TOPOLOGIES
PHYSICAL TOPOLOGIES BUS NETWORK TOPOLOGY
▪ A bus topology uses a single backbone cable that is terminated at both ends.
▪ All the hosts connect directly to this backbone.
▪ All devices connected to a common central cable
▪ Inexpensive
▪ Easily expanded
▪ If cable fails, the entire network will shut down
PHYSICAL TOPOLOGIES RING NETWORK TOPOLOGY
▪ Each node connected to two other nodes in a ring
▪ Similar to the buss, but with the ends of the buss connected together
▪ More reliable than buss or star
▪ If one node fails, data rerouted around failed node
▪ Expensive and difficult to install
▪ Usually used by larger organizations who can afford the expense and to whom the reliability is very important
PHYSICAL TOPOLOGIES STAR NETWORK TOPOLOGY
▪
A star topology connects all cables to a central point of
concentration.
▪
Star topology is centered around central routing device called a hub
▪
All network nodes connect to the hub
▪
Easy to install and update
▪
If hub fails, network fails
PHYSICAL TOPOLOGIES
EXTENDED STAR
▪
An extended star topology links individual stars together by
connecting the hubs and/or switches.
PHYSICAL TOPOLOGIES
HIERARCHICAL
▪
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.
PHYSICAL TOPOLOGIES
MESH NETWORK TOPOLOGY
▪ Every node connected to every other node
▪ Fast
▪ Reliable
▪ No hub or bus to fail
▪ If one device goes down, it is the only node affected
▪ Expensive
▪ Every node must be wired to every other node
▪ Difficult to add nodes
▪ If there are 32 nodes in a mesh network and you wish to add a new node, how many new cables must you add?
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PHYSICAL TOPOLOGIES
TREE NETWORK TOPOLOGY
▪
Combination of bus and star
▪
Two or more star networks connected using a bus for the
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PHYSICAL TOPOLOGIES
HYBRID TOPOLOGIES
▪
Combine two or more of the other topologies
▪
Bus used for LANs and ring used for campus backbone linking
LOGICAL TOPOLOGIES
▪
The logical topology of a network is how the hosts communicate
across the medium.
▪
The two most common types of logical topologies are broadcast
LOGICAL TOPOLOGIES
BROADCAST
▪
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.
BROADCAST
▪
Ethernet
▪
A set of rules for constructing message in a local network
▪
Most widely used protocol for transmitting data over LANs
▪
Listen before talk
▪
Simple
▪
Inexpensive
▪
Flexible
▪
Collisions
LOGICAL TOPOLOGIES
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
TOKEN PASSING
▪
Token Ring
▪
Also a set of rules for constructing message in a local network
▪
Only one node “talks” at a time
▪
Complex
▪
Expensive
▪
More fault tolerant than Ethernet
▪
No collisions
Copyright © 2005 Prentice Hall, Inc.
NETWORK SOFTWARE
▪
Network operating system
▪ Novell NetWare
▪ Microsoft Windows Server 2003
▪
Network management software
▪ Helps ensure security of network
▪ Monitors performance
▪ Helps administrators reconfigure network
▪ Remote administration via push technology
▪
Network monitoring software
▪ Packet sniffers – see data as it moves over network
Copyright © 2005 Prentice Hall, Inc.
TELECOMMUNICATIONS SERVICES
▪
Value Added Networks (VANs)
▪ Proprietary networks built using common carriers
▪ Provide enhanced services
▪ Video conferencing
▪ Electronic data interchange (EDI)
▪
Virtual Private Networks (VPNs)
▪ Use encryption to provide a secure end-to-end connection over common carriers or the Internet
▪ Remote access to internal networks w/o dialup
▪
