COMPUTER NETWORT
AND DESIGN
CSCI 3385K
BY: ALBERTO DE LA CRUZ
What is a network?
• A network is a connected collection of devices and end systems, such as computers and
servers, which can communicate with each other. Networks carry data in many types of
environments, including homes, small businesses, and large enterprises. In a large
enterprise, there may be a number of locations that need to communicate with each other,
locations in terms of where the workers are located is as follows:
Main Office:
• a site where everyone is connected via a network and where the bulk of corporate information is located. Main
offices can have hundreds or even thousands of people who depend on network access to do their jobs. A main
office may use several connected networks, which can span many floor in an office building or cover a campus that
contains several buildings.
Remote Location:
• Branch Offices: Small group of people work and communicate with each other via a network. Although some
information may be stored in the local branch office, it is more likely that they need to have local network resources
such printer, etc. but must access information directly from the main office.
• Home Offices: Users are often require to have on-demand connection to the main offices
• Mobile Users: Users connect to the main office network while at the main office, branch, or traveling
BY: ALBERTO DE LA CRUZ
What is a network?
You may use a network in your home office to communicate via the Internet to locate information, place orders for merchandise and send messages
to friends. Or you may have a small office that is set up with a network that connects other computers and printers in the office. Or you may work in a
large enterprise in which there are many computers, printers, storage devices and servers that are used to communicate and store information from
many departments over large geographic areas.
BY: ALBERTO DE LA CRUZ
Common Physical Components
• Four major categories of physical components in a computer network:
• Personal computers (PCs): The computer serve as end points in the network, sending and
receiving data
• Interconnections: the interconnections consist of components that provide means for data
to travel from one point to another point in the network. This category includes components
such as the following:
• Network Interface Cards: translate the data produced by the computer into a format that can be transmitted
over the local network
• Network media: cables or wireless media that provides the means by which the signals are transmitted from
one networked device to another
• Connectors: provides the connection points for the media
• Switches: Switches are devices that provide network attachment to the end systems and
intelligent switching of the data within the local area network
• Routers: Routers interconnect networks and choose the best path between networks
BY: ALBERTO DE LA CRUZ
Common Physical Components
BY: ALBERTO DE LA CRUZ
Interpreting a Network Diagram
The network diagram is used to capture information related to the network. The amount of information and the
details differs from organization. The network topology is represented by a series of lines and icons
BY: ALBERTO DE LA CRUZ
Interpreting a Network Diagram
BY: ALBERTO DE LA CRUZ
Resources-sharing function and benefits
• Network allows end users to share both information and hardware resources. The major
resources that are shared in a computer network include the following:
• Data and applications: when users are connected through a network, they can share
files and even software application programs, making data more easily available and
promoting more efficient collaboration on work projects
• Resources: resources that can be shared include both input devices, such cameras and
output devices such printers
• Network storage: today there are several ways in which the network makes storage
available to users. Direct attached storage (DAS) directly connects physical storage to a
PC or a shared server. Network attached storage (NAS) makes storage available
through special network appliance. Finally, storage area networks (SANs)
• Backup devices: a network can also include backup devices, such tape drives, that
provide central means to save files from multiple computers. Network storage is also
used to provide archive capabilities, business continuance and recovery disaster.
BY: ALBERTO DE LA CRUZ
Resources-sharing functions and benefits
BY: ALBERTO DE LA CRUZ
Network storage
BY: ALBERTO DE LA CRUZ
Network user applications
• The most common network user applications include the following:
• E-mail: very valuable application for most users, users can communicate information (messages
and files) electronically in a timely manner, to not only users in the same network but also outside
the network.
• Web browser: allows access to the Internet through a common interface. The Internet provides a
wealth of information and it is vital to the productivity of both home and business users. Browsers
allows to communicate with suppliers, customer, handling orders, and locating information saving
time and increasing overall productivity.
• Instant messaging: started as personal user-to-user space; however provided considerable
benefit in the corporate world. There are many instant messaging applications that provide data
encryption and logging, which are essential for corporate use.
• Collaboration: working together as individuals or groups is greatly facilitated when
collaborators are on the network. Users creating separate parts of an annual report or business
plan, for example data files can be sent to a central resource for later compilation.
• Database: this type of application allows users on a network to store information in central
location (file servers) so that other users on the network can easily retrieve selected information
in the format that are most useful to them.
BY: ALBERTO DE LA CRUZ
Impact of users applications on the network
• Batch application: FTP and TFTP, inventory updates would be initiated by the user
then there is no further direct human interaction. Bandwidth is important but no critical
as long as the time it took the application to complete does not become excessive
• Interactive applications: Inventories queries, updates required human interaction,
the user will request some type of information from the server and wait for a reply.
Bandwidth become more important as uses become impatient with slow responses but
still is not critical. In most cases QoS (Quality of Service) could overcome bandwidth
limitation by giving priority over batch applications
BY: ALBERTO DE LA CRUZ
Impact of users applications on the network
• Real-time application: VoIP and video application involve human interaction and
because the amount of information that is transmitted, bandwidth has become critical.
In addition because this application are time-critical, latency (delay through the
network) has become critical, even variations in the amount of delay can affect the
network and not only bandwidth is mandatory but QoS is mandatory as well. VoIP and
video must be given the highest priority. With the proper network design issues as
poor QoS and latency can be resolved.
BY: ALBERTO DE LA CRUZ
Characteristics of a Network
• Network can be described and compared according to network performance and structure
as follows:
• Speed: Measure of how fast data is transmitted over the network. A more precise
term would be data rate.
• Cost: Indicates the general cost of component, installation and maintenance of the
network.
• Security: Indicates how secure the network is, including the data is transmitted
over the network. The subject of security is important and constantly evolving. You
should consider security whenever you take actions that affect the network
• Scalability: Indicates how well the network can accommodate more users and
data transmission requirements. If a network is design and optimized for just the
current requirement, it can be very difficult and expensive to meet new needs
when the network grows.
• Reliability: Indicates the dependability of the components (routers, switches, PCs,
etc.) that make up the network. This is measure as probability of failure, or mean
time between failures (MTBF)
BY: ALBERTO DE LA CRUZ
Characteristics of a Network – cont.
• Availability: Measure of the probability that the network will be available for use when it
is required. For networks to be used 24 hours a day, 7 days a week, 365 days a year, the
availability is calculated by dividing the time is actually available by the total time in a
year and the multiplying by 100 to get a percentage.
For example: if a network is unavailable for 15 minutes a year because of network outages its percentage
availability can be calculated as follows:
([number of minutes in year – downtime] / [number of minutes in year]) * 100 = Percentage availability
([525600 – 15] / [525600]) * 100 = 99.9971
BY: ALBERTO DE LA CRUZ
Characteristics of a Network – cont.
• Topology: In networks, there are two types of
topologies
• Physical: which is the arrangement of cables, network devices and end
systems (PCs and servers)
• Logical: which is the path the data signals take through the physical
topology
These characteristics and attributes will provide a means to compare
different networking solutions
BY: ALBERTO DE LA CRUZ
Logical Topology
• Refers to the logical path that the signal use to travel from one point
on the network to another, that is, the way in which data accesses the
network media and transmits packets across it.
• Physical and logical topologies could be same but at the same time
could have different topologies
• Star topology is by far the most common implementation of LAN,
Ethernet uses logical bus topology in either a physical bus or
physical star.
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Logical Topology
BY: ALBERTO DE LA CRUZ
Physical Topologies
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Physical Topology – cont.
• Refers to the physical layout of the devices and cabling.
• You must match the appropriate physical topology to the type of
cabling (twisted pair, coaxial, fiber, and so on) that will be
installed.
• You must understand the type of cabling used is important in
understanding each type of physical topology
• Three primary physical categories
• Bus
• Ring
• Star
BY: ALBERTO DE LA CRUZ
Physical Topology – Bus Topology
• Consist of cables connecting PCs or file servers together like a
chain
• Terminator attached to each end of bus cable segment
• There is a beginning and an end to each segment
• The main cable segment must end with a terminator that
absorbs the signal when it reaches the end of the line of the wire
• If there is no terminator the electrical signal representing the data
bounces back at the end of the wire, causing errors in the network.
• When transmitting a packet across a bus:
• It is detected by all nodes on the segment
• Given time limit to reach destination or it is considered late
• IEEE (Institute of Electrical and Electronics Engineers)
• Develops standards for network cabling, transmission
BY: ALBERTO DE LA CRUZ
Physical Topology – Bus Topology
• Early bus topologies were cable together in line using coaxial
cable
• Modern bus topologies establish the bus in a hardware device
and connect the host devices to the bus using twisted-pair
wiring
Advantages:
• Requires less cable than other topologies
• Easy to extend bus with a workstation
Disadvantages:
• High management costs
• Single defective node can take down entire network
• Can become quickly congested with network traffic
BY: ALBERTO DE LA CRUZ
Physical Topology – Bus Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Star Topology
• Multiple nodes attached to central device (hub, switch, router)
• Cable segments radiate from center like a star
• Example: Workstations/Servers connected to a switch
• Most common physical topology in Ethernet LAN
Advantages:
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Start-up costs are much lower than other topologies
Easier to manage, defective nodes quickly isolated
Easier to expand by connecting nodes or networks
Offers better equipment and high-speed options
Cabling and connector are less expensive
Disadvantages:
• Failure of central device may cause network failure
• Requires more cable than bus
BY: ALBERTO DE LA CRUZ
Physical Topology – Star Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Extended-Star Topology
• When a star network is expanded to include an additional
network device that is connected to the main network devices
Disadvantage:
• The problem with a pure extended-star topology is that if the central
node point fails, large portions of the network can be isolated
BY: ALBERTO DE LA CRUZ
Physical Topology – Extended-Star Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Ring Topology
• Continues data path with no beginning or ending point
• Workstations attached to cable at points around ring
• Transmitting data across ring topology
• Goes around ring to reach destination
• Continues until ends at source node
Advantages:
• Easier to manage than bus
• Suited to transmitting signal over long distances
Disadvantages:
• More expensive to implement than bus
• Has become outdated so there are fewer equipment options
BY: ALBERTO DE LA CRUZ
Physical Topology – Ring Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Dual-Ring Topology
• In dual-ring topology two rings allow data to be sent in both
directions.
• This setup creates redundancy (fault tolerance), meaning that if
one ring fails, data can be transmitted on the other ring
BY: ALBERTO DE LA CRUZ
Physical Topology – Dual-Ring Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Full Mesh Topology
• Every node is connected to every other node in the network
• Provides fault tolerance
• Fault tolerance: built-in protection against failure
• If link breaks, nodes can still communicate
• Alternate communication path increases as number of nodes
increases
• Mesh is used less on cabled LANs
• Expensive and difficult to implement
• Often used in MANs and WANs due to reliability
• How to calculate the number of connections in a mesh
n(n-1)
2
BY: ALBERTO DE LA CRUZ
Physical Topology – Full Mesh Topology
BY: ALBERTO DE LA CRUZ
Physical Topology – Partial Mesh Topology
• At least one device maintains multiple connections to all other
devices, without being fully mesh
• This methods trades off the cost of meshing all devices by allowing the
network designer to choose which nodes are the most critical and properly
interconnect them
BY: ALBERTO DE LA CRUZ
Physical Topology – Partial Mesh Topology
BY: ALBERTO DE LA CRUZ
Connection to the Internet
• Three common methods of connecting the small office to the
internet
• DSL (Digital Subscriber Line)
• Uses the existing telephone lines and a DSL modem
• Modem is a device that convert the incoming digital encoding into Ethernet
format
• Cable
• Uses cable television (CATV) infrastructure and a Cable modem
• Serial
• Uses the classic digital local loop and a CSU/DSU (Channel service unit/Data
service unit)
• CSU/DSU is a device that converts a digital data frame from the LAN
technology to a frame appropriate to the WAN technology or vise versa
• All three methods the Ethernet output is sent to a router that is
part of the customer premises equipment (CPE)
BY: ALBERTO DE LA CRUZ
Connection to the Internet
BY: ALBERTO DE LA CRUZ
Network Design Introduction
• Step 1: Understand protocols, access methods, topologies
• Example: Telecommunications-based WAN vs satellite-based WAN
• Step 2: Understand physical equipment used
• Example: Different media is used for backbone and internal network
nodes
• Step 3: Understanding basic network design principles
• Structured wiring and networking techniques
• Designing for multimedia and client/server applications
• Taking advantage of LAN and WAN characteristic
BY: ALBERTO DE LA CRUZ
Network Design Introduction
• Step 4: Assess characteristics of the planned network
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Types of computers used as well as location
Software applications used and resources required
Pattern in organization relative to network use
High and low network use periods
How simplify troubleshooting and maintenance
Determine security need for the network
Anticipate how growth will affect network resources
BY: ALBERTO DE LA CRUZ
Designing a simple LAN
Scenario:
Small law office with 4 attorneys & 1 secretary
• Four components of solid design
• Star topology
• Switch connecting computes in middle of star layout using
network cable
• Ability to share certain information on network
• Ability to share printers on network
BY: ALBERTO DE LA CRUZ
Designing a simple LAN
• Rationale for the design:
• Star economical to implement and maintain
• Using cable instead of wireless due to sources of interference
and building construction
• Use of switch satisfies need for fast communication
• Resource sharing using peer-to-peer network instead of using a
server
• Clients decide which files to share
• Printers can be shared
• Network will be simple and easy to maintain
• Internet access easily added
BY: ALBERTO DE LA CRUZ
Designing a simple LAN
BY: ALBERTO DE LA CRUZ