Computer networks Lecture#6 Date:. Computer Network Any system of interconnected computers, computer...
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Transcript of Computer networks Lecture#6 Date:. Computer Network Any system of interconnected computers, computer...
Computer Network
• Any system of interconnected computers, computer
peripheral equipments used for transmit and receive
of information.
Applications of Networks
• Resource Sharing– Hardware (computing resources, disks, printers)– Software (application software)
• Information Sharing– Easy accessibility from anywhere (files, databases)– Search Capability (WWW)
• Communication– Email– Message broadcasting
Components of a Network
A computer network typically includes four things:
1. Network interface cards (NICs)
2. Networking Software
3. Networking Media
4. Networking Devices
1) Network interface cards (NICs):
• Plugs into the back of your computers and lets them send and receive messages from other computers
• The MAC address is a 48 bit long unique value associated with a network adapter.
• MAC addresses are also known as hardware addresses or physical addresses.
IP Address
• Every machine on the Internet has a unique identifying number, called an IP Address.
• A typical IP address looks like this:
216.27.61.137
• Computers communicate in binary form. Look at the same IP address in binary:
11011000.00011011.00111101.10001001
2) Networking Software
TCP/IP • The basic communication
language or protocol of the Internet.
• The TCP/IP model has four layers.
• Each layer performs a certain role or task.
• Each layer a packet of information travels through adds what is called a header.
TCP/IP Data Communication Example
Network Header
SegmentHeader
FrameTrailerData
Segment Header Data
Data
FrameHeader
NetworkHeader
Segment Header Data
0111111010101100010101101010110001
E-mail message
Data
Segment
Packet
Frame(medium dependent)
Bits
3) Networking Devices
All networks are made up of basic hardware building blocks to interconnect network nodes, such as:
• Hubs• Switches• Routers
Building an Internetworking using Router
• An Internetwork is a collection of individual networks,
connected by intermediate networking devices, that
function as a single large network.
• A router is needed to connect individual networks.
• Router maintains routing table to keep track of individual
networks.
Routers
Networking Media
• Networking media can be defined simply as the
means by which signals (data) are sent from one
computer to another (either wired or wireless
means).
Networking MediaPhysical communications Channels
• Twisted Pair
– uses copper wire, twisted together in pairs
to form a telephone wire.
– Maximum segment length of 100 meters
• Coaxial Cable/Co-ax
– uses one or more central wire conductors
surrounded by an insulator and encased in
metal sheathing.
Networking Media• thin coaxial cable is able to transport a signal up to
around 185 meters without line loss.
• thick coaxial cable is able to carry signals over long distances: up to 500 meters without line loss
• Fiber-optic Cable– A physical communications channel that uses light and
glass fibers. – It is light-weight and tolerates data rates on the order
of 100Mbps up to 60km.
Networking MediaWireless Channels
Wireless channels transmit data through air or space
• Radio Waves– RF frequency ranges from roughly 30 kilohertz to 1 gigahertz– A radio wave is an electromagnetic wave propagated by an
antenna. – All FM radio stations transmit in a band of frequencies
between 88 megahertz and 108 megahertz.
• Microwave– Microwaves frequency ranges between 1 GH(109 Hz) to 1 TH
(1012 Hz).
Networking Media• They are the principal carriers of television, telephone, and
data transmissions between stations on Earth and between the Earth and satellites.
• Radar beams are short pulses of microwaves used to locate ships and planes etc.
• Infrared– Transmits data and information by means of an infrared
light. The signal cannot travel through objects.– commonly used in remote control of TVs, VCRs and CD
players
Network Topology
• The network topology defines the way in which computers, printers, and other devices are connected.
• LAN topologies define the manner in which network devices are organized.
Introduction to Computer Networks
Bus Topology
• Commonly referred to as a linear bus,
all the devices on a bus topology are
connected by one single cable.
• Broadcast shared media.
• Suitable for small networks.
• Single point of failure.
Introduction to Computer Networks
Star & Tree Topology
Introduction to Computer Networks
• The star topology is the most commonly used
architecture in most LANs.
• No single point-of-failure
• Larger networks use the extended star
topology also called tree topology.
• When used with network devices, like bridges,
switches, and routers, this topology
significantly reduces the traffic on the wires by
sending packets only to the wires of the
destination host.
Ring TopologyIntroduction to Computer Networks
• A frame travels around the ring, stopping at each
node. If a node wants to transmit data, it adds the
data as well as the destination address to the frame.
• The frame then continues around the ring until it
finds the destination node, which takes the data out
of the frame.
• The dual ring topology allows data to be sent in both
directions.
Mesh Topology
• The mesh topology connects all devices (nodes)
to each other for redundancy and fault
tolerance.
• Chances of connection break downs are very
minimal.
• It is used in WANs to interconnect LANs and for
mission critical networks like those used by
banks and financial institutions.
• Implementing the mesh topology is expensive
and difficult.
Introduction to Computer Networks
Network Classification• Based on their size, networks
can be classified as:
• Local Area Network (LAN)
• Metropolitan Area Network
(MAN)
• Wide Area Network (WAN)
• Internet
• A network covering a small geographic area, like a home, office, or building.
• LANs are designed to share resources between personal computers.
• The resources to be shared can include hardware (e.g., printer, Scanner), software (e.g., an application program) or data.
Local Area Network (LAN)
• A network that connects two or more LANs but does not extend
beyond the boundaries of the immediate town/city.
• In many cities under the streets, Copper and Fiber Optic cables are
run. Above ground we find Wireless, Microwave and Lasers. These
technologies are typically limited to distances under 100 miles.
These limitations define a MAN or Metropolitan Area Network.
Examples:
• A network of fire stations in a suburban area would be an example
• A newspaper/media company employ a MAN.
• A chain of community colleges could be linked by a MAN.
Metropolitan Area Network (MAN)
• A data communications network that covers a relatively
broad geographic area (i.e. one city to another and one
country to another).
• WAN often uses transmission facilities provided by
common carriers, such as telephone companies.
• Dedicated transoceanic cabling or satellite uplinks may
be used.
Wide Area Network (WAN)
• There are at least three variants of internetwork, depending on who administers and who participates in them:
• Intranet • Extranet • VPN
Modern Internetwork
What is an Intranet?
• Intranet is an internal network used strictly within the
confines of a company, university, or organization.
• Belongs to an organization, and is designed to be accessible
only by the organization's members, employees, or others
with authorization.
• An intranet's Web site looks and act just like other Web sites,
but has a firewall surrounding it to guard against
unauthorized users.
What is an Extranet?
• An “extended intranet”, uses the Internet to link selected resources of a company’s intranet with its customers, suppliers, or other business partners
• Extranet transmissions are conducted over the Internet to save money. But it offers no privacy or transmission security.
• By creating tunnels of secure data flows using cryptography and authorization algorithms, called VPNs, the security can be improved.
Virtual private network (VPN)• Provide secure connectivity between a corporation’s intranets and
intranets of its business partners, material suppliers, financial services, and customers.
• Tunneling: the process by which VPNs transfer information by encapsulating traffic in IP packets over the Internet
Layered System View
Clients, partners, customers
Intranet
Extranet
Internet
Corporate members
Global society: competitors
Common Network Attacks• Reading contents of messages is called eavesdropping• Difficult to detect• Sniffing/Snooping - Monitoring the network for sensitive
data and passwords
Common Network Attacks
• Modification or creation of messages (by attackers)
• Easy to detect but difficult to prevent
Common Network AttacksDenial-of-service Attack- Lowering or removing quality of service in a network
Security MethodsFirewalls• A firewall is a part of a network that is designed to block unauthorized
access while permitting authorized communications.
• It is a device or set of devices that is configured to permit or deny network transmissions based upon a set of rules and other criteria.
• All messages entering or leaving the intranet pass through the firewall.
• Firewalls can’t protect against malicious insiders viruses, and scans for source & destination addresses & port numbers, not details of data