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BASICS

OF

NETWORKING

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NETWORK:- When two or more communicating device connected with each other that is called network.

Eg: telephone network, computer network ,ATM network etc.

COMPUTER NETWORKING:-Its just sharing of information and services among computers. Computer networking provides communication tools to allow computers to share information and abilities.

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How computer networking is useful?

The utility of a network increases as the square of the number of systems connected to it.

Computer networking technologies are generally based on these computing models:-

Centralized computing

Distributed computing

Collaborative computing

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CENTRALIZED COMPUTING

Large centralized computers, called mainframes are used to store and organize data.

People enter data on local device called terminals.

Terminal is simply a remote input/output device. It consists of input device such as keyboard, and some communication hardware and monitor as output device.

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DISTRIBUTED COMPUTING

PCs are used with their own processing capabilities.

Application are divided into tasks and each task is assigned to a computer for processing.

Result of the processing can be sent as data to other computers.

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COLLABORATIVE COMPUTING

A type of distributed computing.

Similarity between distributed and collaborative computing:-Both use networked computers with processing capabilities, and both divide application into task.

Difference :-Collaborative computing allows tasks to be shared by computers as distributed computing assigns each task to a single computer.

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The following computing models are used to categorize the way networking services are provided:-Client/serverClient/network

CLIENT/NETWORK COMPUTING

In this computing model user log in to a network and connect to a set of services rather than to a specific server.

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CLIENT/SERVER COMPUTING

Processing capabilities are distributed across multiple machines.

Clients request services from servers.

The server performs some of the processing for the client.

Applications used in a client/server model can be split into a front end that runs on the client and back end that runs on the server

ex:-A database application that provides a client interface for requests and a search engine on the server that locates records stored on the server.

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NETWORK CLASSIFICATION

Computer networks are often classified by size, distance covered, type of media used or structure.

Following network classification are commonly used.

Local area network (LAN)

Wide area network (WAN)

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LOCAL AREA NETWORKSmall group of connected computers

LAN normally do not exceed 10 km distance

LAN transmission speed are often measured in Megabits/sec (mbps)

WIDE AREA NETWORKA WAN comprises multiple LANs.

WANs interconnect LANs located around the world

WANs often use telephone or satellite communications

Access to WAN links is leased from a WAN service provider.

Transmission speed attainable over the available bandwidthis measured in kilobits/sec

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THERE ARE TWO SPECIFIC WAN CATEGORY enterprise and global

An enterprise network connects all LANs of a single organization (extremely large organization or network that cross regional or international boundaries).

A global network is one that spans the earth. Global network might not cover the entire globe but they cross multiple national boundaries and can include the networks of several organizations. Internet is an example of global network.

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REQUIRED NETWORK ELEMENTS

Something to share---(Network services)

A pathway for contacting others---(Transmission media)

The rules for communication---(Protocols)

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NETWORK SERVICESNetwork services are the capabilities that networked

computer share.

Network services are provided by numerous combinations of computer hardware and software.

A service provider is not a computer but a subset of the computer software and hardware.

Common network services are :-File servicePrint serviceMessage serviceApplication serviceDatabase service

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Types of service providers and requesters

Servers are classified as service providers. They only provide services.

Clients are classified as service requesters. They only request services.

Peers can be classified as both a service requester or provider. They request as well as provide service.

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Computer networks are often classified as one of the following:-

Peer-to-peer

Server-centric

Peer-to-peer:- It allow any entity to both request and provide network service.

P2P network software is designed so that peers perform the same for each other.

Ex:-

Server-centric:- It involve strictly defined roles.

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Transmission media:- computer transmission media includes cable and wireless technology that allow networked devices to contact one another.

It can’t guarantee that other network devices will understand a message.

It can guarantee a message delivery.

Network Protocols:- A protocol can be a rule or a complete set of rules and standards that allow different devices to hold conversations.

Communication protocols have been standardized by ISO (international standards organization)

In a computer communication network, data exchange required among many different types of :

› application programs,› operating systems, › computers, › networking devices.

Without a standard for communication simply it would not work.

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ISO: International Standards Organization

› Members are national standards organizations.

ITU: International Telecommunication Union ::ITU-T sector responsible for networking standards.

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The goal of standardization is to achieve an open system.

The devices manufactured by different manufacturers can communicate easily.

Open system:-An open system has external interfaces through which other systems can easily communicate with it due to use of standard interface.

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All communication activity in a computer network are governed by protocols:

Protocols define the format, order of

messages sent and received among network entities, and actions taken on message transmission, and receipt.

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Protocol Layering

• Computer communication is a complex task.

• Needs to be properly segmented into layers to make it:– Flexible,

– Ease if implementation

– Interoperable.

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Protocol Layers• Each layer offers certain services to higher

layers:– Shields the details of how the services are

actually implemented.

• Layering minimizes information flow across boundaries and prevents bugs.

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ISO/OSI Architecture• ISO: International Standards Organization

• OSI: Open Systems Interconnection.

Physical

Data link

Network

Transport

Session

Presentation

Application

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

Layer 7

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Layer 7: Application Layer

• Deals with network applications such as:– File transfer, e-mail, network management,

etc.

– Example protocols: ftp, http, smtp.

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Layer 6: Presentation Layer

• Responsible for presenting data in a format that the user understands:– Two computers may use different numeric

and character formats.

– Translation of one representation to the other (not into bit streams).

– Provides security measure through encryption and decryption.

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Layer 5: Session Layer

• Responsible for establishing a session or logical connection between two applications.

• Initiates, maintains and terminates communication link between sender and receiver .

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Layer 4: Transport Layer

• Handles reliable delivery of data (message) between computers (end-to-end):– Segmentation and Reassembly: Ensures data

is sent (transported) in proper order from source to destination.

– Provides end-to-end error recovery.– End-to-end flow control.

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Layer 3: Network Layer

• Responsible for source-to-destination delivery of packets possibly across multiple networks.– Deals with routing of data from host to

destination across a network.

Provides for reliable transfer of frames across a transmission link.› Frames are organized in a specified

format.› Responsible for flow control, error

detection and correction techniques. Functions: framing, error control,

flow control, and medium access control (in shared networks).

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Layer 1: Physical Layer

• Handles sending raw bits across a transmission medium (“the wire”):– Conversion of bits into electrical signals

and their transmission.

• Issues:– What’s being transmitted.

– Transmission medium.

– How it’s being transmitted.

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COMMON NETWORK TRANSMISSION MEDIA

Cable media:-This provide a conductor for electromagnetic signal (guided media:-Signals propagate in solid media: copper, fiber.)

Wireless media (unguided media:-Signals propagate freely, e.g., radio.)

Benefits and considerations relate to following factors:-

Cost and ease of installation

Capacity

Attenuation

Immunity from interference and signal capture.

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Cable media are wires or fibers that conduct electricity or light.

Types of cable used in networking:-

1.Twisted pair cable

2.Coaxial cable

3.Fiber optic cable

Twisted pair cable

Single twisted pair

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One or more twisted pair are combined within a common jacket to form a twisted pair cable.

Twisted pair cable uses copper wire.

When two copper wires conduct electric signals in close proximity, a certain amount of electromagnetic interference occurs. This type of interference is called cross talk.

Twisting of copper wires reduces cross talk.

Two types of TP cables are:-Unshielded twisted pairShielded twisted pair

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EIA (Electronic Industries Association) has developed standards for unshielded twisted pair cable (UTP). They are:-

Cat 2

Cat 3: gently twisted

Cat 5: more twists/cm

•Better quality signals

•Higher speed communication

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Cat 2• Used in telephone

wiring.

• Rated for 1MHz

• Terminated by RJ-11.

RJ-11

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Cat 3• Commonly used for

Ethernet 10Base-T networks.

• Terminated by RJ-45 plugs (Similar to RJ-11 but has 4 pairs of wires, instead of 2 pairs).

• Rated for 16MHz.

RJ-45

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RJ-45 connector

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Cat 5• Minimum Specification

for Fast Ethernet (100Base-T).

• Most common wiring in modern LANs.

• Uses RJ45 plugs.

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Coaxial cable

Coaxial cable is made of two conductors that share a common axis, hence the name (coax)

Center of cable is a relatively solid copper wire or wire encased in insulating plastic foam.

The foam is surrounded by the second conductor.

A tough insulating plastic tube forms cover of the cable.

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Fiber optic cableFiber optic cable is made of a light

conducting glass or core surrounded by more glass , called cladding.

The center core provides the light path or wave guide.

The cladding is composed of varying layers of reflective glass, is designed to refract light back into the core.

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Fibers of fiber optic cable

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Optical FiberData is transmitted in the form of pulses of light.Very high bit rate (up to 1 Gb/s) over many miles:• Rather expensive.• Connections and splicing difficult to

make. • Often used to interconnect different

LANs.Two types of optical fibers: Single and multi-mode types.

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Optical FiberSingle mode:

– Much smaller diameter (8 to 10 microns).

– Laser light has to be used: Expensive.

– Can be used for larger distances.

Multi-mode:

– Larger diameter (50 microns).

– LEDs can be used.

– Smaller distances: buildings, campuses, etc.

Twisted

PairCoaxial

Optical fiber

Speed Fast Fast Very fast

Length Short Medium Very long

Cost Cheap Medium expensive

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Circuit switching (isochronous): › After a connection is made between

two systems, the path is dedicated and cannot be used by other systems.

Packet switching (asynchronous):› Data is sent in discrete units called

packets.45

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Differences Between Circuit & Packet Switching

Send data immediatelyBefore sending data establishes a path

More efficientCapacity is wasted if data is bursty

Packets may be reordered, delayed, or dropped

No reordering; constant delay; no pkt drops

Different packets might follow different paths

All data in a single flow follow one path

No guarantees (best effort)Guaranteed capacity

Packet-SwitchingCircuit-switching

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Circuit Switching• Assume link capacity is C bits/sec.• Each communication requires R bits/sec.• Maximum number of concurrent

communications is C/R

Reasons due to which circuit switching is not used to share computer network.

• if we have more than C/R communications? • if the a communication sends less/more than R

bits/sec?

Design is unsuitable for computer networks where transfers have variable rate (bursty)

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Packet Switching• Used in the Internet.• Data is sent in Packets (header contains control info, e.g.,

source and destination addresses)

• At each node the entire packet is received, stored, and forwarded (store-and-forward networks)

Header Data

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Bit Rate• Bit-rate = numbers of bits per second we

need to transmit:– For each second we transmit F=1/T samples – Each sample is defined with a word of B bits.– Bit-rate = F*B

• Example: if F is 10 samples/s and B=8, then the bit rate is 80 bits/s.

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Some Definitions• Interval of time between two samples:

– Sampling Interval (T)

• Sampling frequency F=1/T• E.g.: if the sampling interval is 0.1 seconds,

then the sampling frequency is 1/0.1=10– Measured in samples/second or Hertz

• Each sample is defined using a word of B bits– E.g.: we may use 8 bits (1 byte) per sample.

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Bit Rate

• Bit rate: rate at which data is transmitted:

–Unit is bits/sec or bps (applies to digital signal).

–Example: 2Mbits/sec, or 2Mbps.

–“b” stands for bits and “B” for bytes.

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Types of Communication

• Simplex: Only one party can talk.– E.g. Radio or TV

• Half-duplex: Only one party can talk at a time.– E.g., walkie-talkie.

• Full-duplex: Both parties can talk at the same time.– E.g., telephone

• Modems use full-duplex communication.

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Local area networkA LAN is popularly named after the protocol used in the data link segment of the network:

1.Ethernet2.Gbit Ethernet3.Token ring, etc.

Popularity of LANs:-Connects multiple computers across short distances (“within a building” or up to a few KM):

InexpensiveHighly reliableEasy to install and manage

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Nodes in a LAN are interconnected using one of four basic configurations:

1. Bus

2. Tree

3. Star

4. Wireless

Basic LAN Topologies

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Bus Topology

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Tree Topology

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Star Topology

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Wireless LAN• Availability of low-cost portable equipments• Advantages of WLAN

– Mobility– Installation speed and simplicity– Installation flexibility– Reduced cost of ownership– Scalability

• Why it was not popular in the past?– High cost – Low data rate – Occupational safety concerns – Licensing requirements

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Bluetooth Wireless Technology developed for

Personal Area Network (PAN) Designed to connect Computers,

Cameras, Printers, etc It is an ad hoc type network operable over

a small area such as a room

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Bluetooth Topology Two types of topology – Piconet, Scatternet Piconet: A small network of maximum 8

stations

One is called Master and the others are called SlavesAll slave stations synchronizes their clocks with the masterPossible communication - One-to-one or one-to-manyThere may be one station in parked state

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Bluetooth Topology Scatternet: By making one slave as a

master of another Piconet, Scatternet is formed by combining several Piconets

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WiMAX WiMAX is defined as Worldwide Interoperability for

Microwave Access by the WiMAX Forum, formed in June 2001 to promote conformance and interoperability of the IEEE 802.16 standard

Ability to transfer data, voice, and video at speeds of up to 70 Mbps

will support subscriber stations moving at pedestrian and vehicular speeds (speeds of 120 to 150 kmph)

Has potential to be deployed far faster, less expensively, and more flexibly than similar wireless installations.

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Ethernet Versions• 10Base2

• 10Base5

• 10BaseT

• 10BaseF

• 100BaseT (Fast Ethernet)

• 1000BaseT (Gbit Ethernet)

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10Base2• Commonly called thin Ethernet.

• Operates at 10Mbps and maximum distance of 200m.

• Uses thin coaxial cable in bus topology.

• Connectors used are BNC T-junctions.

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10Base5• Popularly called thick Ethernet.

• Uses thicker coaxial cable.

• 500m maximum distance.

• Was often used as backbone:–Thick cables are inflexible and not

suitable to connect to a computer.

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10BaseT• 10Base2 and 10Base5 were

completely abandoned since about 10 years back.

• 10BaseT became popular:– T stands for Twisted Pair.– Uses Cat3 or Cat5.– Reduced cost, increased reliability.

• Deviates substantially from 10Base2 and 10Base5 topology:– It is now a star topology.– Nodes are connected to a hub.

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10Mbps EthernetName Cable Max.

segm. Nodes adv.

10Base5 thick coax

500m 100 f or backbones

10Base2 thin coax

200m 30 cheapest

10Base-T TP 100m 1024 easy maintenance

10Base-F fiber 2000m 1024 between buildings

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Fast Ethernet (100BaseT)

• The challenge faced in creating high-speed networks:– High frequency signals do not propagate well in

many mediums.

• Manchester encoding used in 10Mbps Ethernets is not very efficient:– 100BaseT uses NRZI encoding.– Transfers at a faster rate without substantially

increasing the signalling speed.

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Gbit Ethernet• Versions for twisted pair and fiber exist.

• 1000BaseT requires Cat5 cables.

• Network cable restricted to 100m only.

• Uses 5-level pulse amplitude modulation (PAM).

• Now 10 Gbit Ethernet are becoming available.

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Wired Ethernet• Originally, Ethernet operated at 10

Mbps.

• Then 100 Mbps was introduced. – Most NICs sold today are 10/100 Mbps.

• More recently, 1000 Mbps (1 Gbps) Ethernet has been introduced.

• 10 Gbps Ethernet is now being installed in high-end applications.

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What is “internetworking”?• internetwork : interconnection of networks

– also called an “internet”.

• Subnetwork : a constituent of an internet.

• Intermediate system: a device used to connect two networks allowing hosts of the networks to correspond with each other.– Hubs, Switches, Bridges .– Routers.

• Internet is an example of an internet.

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•Also known as LAN adapter.

•Acts as an interface between the computer and the network.

•It relieves the CPU from electrical and low-level networking issues.

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NIC • It is an internal transceivers ,can receive as well

as transmit electromagnetic or electric signals.• Can directly access the computer’s memory

independent of the CPU:– “Direct Memory Access” or DMA.

• Accesses memory through the “data bus” within the computer (typically PCI bus):

• PCI: parallel communication.• NIC converts from parallel to serial and vice-

versa.• Most manufacturers nowadays build the NIC into the

motherboard.

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ETHERNET HUB

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It receive transmission from connected devices and transmit the signals to the other connected devices.

Active hubs:-which connects medium segments together ,regenerates or amplifies signal.

Passive hubs:-which connects medium segment but does not amplify or regenerate signals.

Two passive hubs cannot be connected to each other.

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•Simple, inexpensive devices.•Multi-tier arrangement provides graceful degradation:

• Portions of the LAN continue to operate if one hub malfunctions.

•Extends maximum distance between node pairs (100m per Hub).•More robust than coax-cable based Ethernet:

•Hubs detect typical problems such as excessive collisions on certain ports and disconnect them.

•Cannot connect different Ethernet types (e.g., 10BaseT and 100baseT).

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EtherswitchSwitch is a type of hub with an inbuilt ROM due to

which it only forwards the signal through the port that allow the transmission to be delivered to the device to which it is addressed.

This can significantly improve performance by optimizing bandwidth use.

If the destination port is busy:Etherswitch buffers the frame until the port becomes available.

One can use switch and hubs at different locations in a LAN according to convenience as switches are expensive than hubs.E.g:-

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BridgesIt selectively pass signals from one segment to

another based on physical location of destination device.

Physical location are referred to as addresses

Data link layer device.

It divides the network users in functional groups

Groups are usually formed according to physical location and common requirements such as services and application used etc.

User in one group one media segment and other use another segment. It improves network performance.

A network layer device. A device that connects a LAN to a WAN

or a WAN to a WAN. A router accepts an outgoing packet,

› Removes any LAN headers and trailers, › Encapsulates the necessary WAN

headers and trailers. Because a router has to make routing

decisions, › The router has to dig down into the

network layer of the packet to retrieve the network destination address.

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Gateways• Similar to a router.

• However, gateways may need to operate in all 7 protocol layers.– A gateway is a protocol converter.– A router can route across networks using

similar protocols.– A gateway can handle communication across

different protocols: it is a multi protocol router.

– Might have to adjust data rate, size, format, etc.

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Bridges vs. Routers• Both store-and-forward devices:

– routers: network layer devices (examine network layer headers)

– bridges are data Link Layer devices

• Routers maintain routing tables, implement routing algorithms.

• Bridges maintain filtering tables, implement filtering, learning and spanning tree algorithms

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Routers vs. Bridges

Bridges + and -

+ Bridge operation is simpler requiring less processing bandwidth

- Topologies are restricted with bridges: - a spanning tree must be built to avoid cycles

- Bridges do not offer protection from broadcast storms (endless broadcasting by a host will be forwarded by a bridge).

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Routers vs. BridgesRouters + and -+ arbitrary topologies can be supported, cycling

is limited by TTL counters (and good routing protocols)

+ can provide firewall protection- require IP address configuration (not plug and

play)- require higher processing bandwidth• Bridges are fine in small (few hundred hosts)

– while routers used in large networks (thousands of hosts)

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Port Numbers• The port numbers are divided

into three ranges: –Well Known Ports: 0–1023

• Opening a port in this range to receive incoming connections requires administrative privileges.

–Registered Ports: 1024–49151. –Dynamic and/or Private Ports: 49152–

65535.

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Well Known Port Numbers

Port Number Application Description

20 FTP -- Data

21 FTP -- Control

22 SSH Remote Login Protocol

23 Telnet

25 Simple Mail Transfer Protocol (SMTP)

80 HTTP

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TCP/IP – A Brief History• TCP/IP is a protocol suite:

– Developed by a US DoD (Department of Defense) research project ARPANET (1969).

– TCP/IP are the two most prominent protocols in the suite.

• Objectives Behind TCP/IP:– 1. Use packet switching technology to build

reliable communication systems.– 2. Connect networks designed by different

vendors into a network of networks.

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TCP/IP• It became very successful because it

was reliable and delivered a few basic services that every one needed:– E-mail, file transfer, remote login, etc.

• In computer domain, technologies become outdated in less than a decade:– TCP/IP is holding firm even after four

decades.

– Only some evolutionary growth occurring.

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Reference

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TCP Protocol Suite• 5. Application layer:

– DHCP, DNS, FTP, HTTP, IMAP4, MIME, POP3, SMTP, SNMP, SSH,TELNET...

• 4. Transport layer: – TCP, UDP ...

• 3. Network layer: – IP (IPv4 . IPv6), IGMP, ICMP, RSVP, IPsec,

ARP, RARP ...• 2. Data link layer:

– 802.11, ATM, Ethernet, FDDI .

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Features of TCP• Connection-oriented:

• An application requests a “connection” to destination before transferring data.

• State information is maintained at both ends:• sequence numbers • window size, etc.

• Point-to-point: – A TCP connection has two endpoints– No broadcast/multicast support.

• Reliable: – TCP guarantees that data will be delivered

without loss, duplication or transmission errors.

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Internet Applications and Transport Protocols