Lecture 2 -_understanding_networks_2013

BITS 2513 INTERNET TECHNOLOGY

LECTURE 2: UNDERSTANDING

NETWORKS

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• Network Terminology

• Network Components

• Operating Systems on the

Network

TOPICS

Network

• The OSI Model and

Networking

• Addressing on a Network

• How Data Travels on the

Network: an Example

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• Network Adapter– Usually an expansion card called NIC (Network Interface Card)

• Network Protocol – A set of rules for network communications. Examples:

Network Terminology

• OS protocols: TCP/IP, NetBEUI

• Hardware protocols: Ethernet, Token Ring

• Segments, Packets, Datagrams – Small “chunks” of data that travel on network

– In the network media, the packets travel in frames, which carry each data packet with a header and trailer to identify each packet

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Network Components

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• Hardware:

– Network Interface Card

(NIC)

– Servers

– Workstations

• Software:

– Operating Systems

– Applications

– Middleware

Network Components

– Workstations

– Hub, MAU,

Concentrator, Switch

– Connectors (RJ-45, BNC)

– Cable(UTP, coax)

– UPS (Uninterruptable

Power Supply)

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NIC

Hub

switch

UPS

MAU

RJ-45 and UTP

BNC male

Operating Systems on

the Networkthe Network

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Introduction

• Communications between computers require network OS(es) and network protocols.

• Functions of OS in a computer: – manage applications, hardware, and connection to the network.

– enabling the computers on the local area

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– enabling the computers on the local area network (LAN) to share their resources

• Protocols specify network functionality.– Using the same set of network protocols, different devices can communicate.

– The selected network protocol must be supported by every operating system on the network.

– Example : HTTP, SMTP and FTP

Introduction (continued)� How resources are shared:◦ peer-to-peer model: several computers using different operating systems in a small business or home can be connected to form a small LAN.

◦ client/server model, a.k.a. domain model, a server is used to control which resources on the LAN are shared, and who can access these resources.

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� Network OSes are used to manage resource sharing through mechanisms such as◦ user account: a collection of all of the information that pertains to a user on a computer

◦ authentication, validation, or logging on: The process of entering a correct user ID and password to gain access to a computer

• Windows 98 and Windows Me

• Windows NT Workstation, Windows

2000 Professional, Windows XP

• Linux

• Macintosh OSes e.g. Mac OS X

Client OSes

• Macintosh OSes e.g. Mac OS X

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• can be installed on a server and used to manage network resources, including user accounts, printers, and file sharing across the LAN.

• Windows NT Server, Windows NT

Network OSes

• Windows NT Server, Windows NT Enterprise Server

• Windows 2000• Windows Server 2003• Novell NetWare• UNIX, Linux

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Network Operating Systems

• Some criteria to consider when selecting a

NOS are as follows:– Reliability – stably perform in any condition

– Performance – serve the clients in a seamless way

– Adaptability – adapt request of diff. platform

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– Adaptability – adapt request of diff. platform

– Security – ability to eliminate and repel threats

– Scalability – cont. function well when size expand

– Affordability

– Ease of use and ease of installation

The OSI Model and Networking

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� Variety – OS: Apple OS X, Windows, Linux,

Unix, Sun. Hardware: Cisco, 3Com,Huawei

� In an effort to identify and standardize all

the levels of communication needed in

networking, ISO developed a networking

Understanding the OSI Model

networking, ISO developed a networking

model called the Open Systems

Interconnection (OSI) reference model.

� The OSI reference model provides a

universally accepted reference illustrating

how data is transmitted on a network or

between two or more networked devices.

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(Continued)

Physical Layer� Physical layer is responsible for: Passing data packets on

to the cabling or wireless media (whether the media be cabling or wireless).

� Data is in ‘bit’ form

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Data Link Layer� Data Link layer is responsible for: Receiving packets of

data from the Network layer and presenting them to the Physical layer for transport.

� E.g: NIC (with firmware)

� When software is permanently embedded on a hardware device, it is called firmware.

� Data is called ‘frame’

Network Layer

• Network layer is responsible for:

Dividing a block of data into

segments that are small enough to

travel over a network.


(Continued)

travel over a network.• Segments of data are called packets,

data packets, or datagrams and contain

data, along with special identifying

information in headers and trailers at the

beginning and end of the packet.

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Transport Layer

� Transport layer is responsible for: Error checking and requests retransmission of data if it detects errors.

� The Transport layer might or might not guarantee successful delivery of data (depends on the transport protocol used).


(Continued)

protocol used).� Data is called ‘segment’

Session Layer� Session layer is responsible for: Establishing and

maintaining a session between two networked

stations or hosts.

� A host is any computer or other device on a

network that has been assigned an IP address.18

Presentation Layer

• Presentation layer is responsible for: receiving requests for files from the Application layer, and presents the requests to the Session layer.

• The Presentation layer reformats, compresses, or encrypts data as necessary.


(Continued)

• The Presentation layer reformats, compresses, or encrypts data as necessary.

Application Layer

• The Application layer of the OSI model is responsible for interfacing with application software, such as Web browsers or Web servers.

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TCP/IP Protocols at Each Layer (Continued)

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The OSI Model Applied to a TCP/IP

Network

� The Web browser wants to make a request to a Web server, and processes the request using an API (Application Program Interface )call to the OS.

� The API process packages the data using HTTP format, which includes an HTTP header, and addresses it to an IP address and port 80, which is the default port for a Web server.

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Fig 5-33 An application asks the OS to do something using an API call


Network (Continued)

• HTTP delivers the package to TCP, giving the

destination IP address and port.

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Network (Continued)

• TCP hands the data off to IP, which resides in

the network layer and is also managed by

the OS.

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Network (Continued)

� The data with its header information is a long stream of bytes. IP breaks it into individual packets. IP adds its own IP header that contains its own IP address (source) and the server’s IP address (destination). IP passes the packets off to the hardware (NIC).to the hardware (NIC).

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Fig 5-36 IP divides data into packets, which are then released to the network


Network (Continued)� On the NIC, each

packet is given

information at its

beginning and end

in the form of frame.

A checksum is

calculated using a calculated using a

technique called

cyclical

redundancy check (CRC). Then each

frame is sent off to

the Ethernet cable.

� At the destination,

the checksum is

verified and passed

to the IP layer to be

regrouped.25


Network (Continued)

• IP then passes the reassembled data and

header stream on to the TCP layer who

acknowledges the TCP layer on the client.

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Network (Continued)

• The HTTP server, listening at port 80, receives

the data and passes it on to the Web server.

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TCP/IP Protocols at Each Layer

(Continued)

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• TCP/IP covers the first five layers of the OSI

model, and is included in an operating system

as a group of utilities called the TCP/IP stack.

TCP/IP Protocols at Each Layer

• Figure 5-41 shows the four major

groupings of the OSI model as

applied to TCP/IP networks.

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• The first three layers of the OSI model

are handled by the protocol specific to

the application using it and are best

treated as a single group rather than

Protocols at the Application,

Presentation, and Session

Layers

treated as a single group rather than

unique layers.

• The language or protocol each

of these applications uses is listed

at the Application, Presentation,

and Session layers.

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• A TCP/IP network has two protocols that work at the Transport layer; one protocol guarantees delivery and the other does not.

• With TCP/IP, the protocol that guarantees delivery is TCP and the

Protocols at the Transport Layer

• With TCP/IP, the protocol that guarantees delivery is TCP and the protocol that does not is UDP (User Datagram Protocol).

• TCP is used for client and server requests and responses.

• UDP ??32

• Because TCP establishes a connection, it is

called a connection-oriented protocol.

• UDP is a protocol that sends data

Protocols at the Transport

Layer (Continued)

• UDP is a protocol that sends data

without caring about whether the

data is received.

• It does not establish a connection

first; thus, it is called a connectionless

protocol.33

• TCP and UDP communicate with the Network layer, which is sometimes called the Internet layer.

• Some of the other supporting protocols include ARP (Address Resolution Protocol), responsible for locating a host on a LAN; RARP (Reverse Address

Protocols at the Network Layer

locating a host on a LAN; RARP (Reverse Address Resolution Protocol), responsible for discovering the Internet address of a host on a LAN; and ICMP (Internet Control Message Protocol), responsible for communicating problems with transmission to devices that need to know about these problems.

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• PPP (Point-to-Point Protocol) is used over

telephone lines, and allows a computer to

connect to a network using a modem.

• PPP is the most popular protocol for

Protocols at the Data Link and

Physical Layers

• PPP is the most popular protocol for

managing network transmission

from one modem to another.

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Addressing on a Network

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• MAC addresses function at the lowest (Data Link) networking level.

• If a host does not know the MAC address of another host on a local area network, it uses the operating system to discover the

MAC (Media Access Control)Addresses

uses the operating system to discover the MAC address.

• MAC-48 addresses in human-friendly form is six groups of two hexadecimal digits

• e.g. 01-23-45-67-89-ab or 01:23:45:67:89:ab

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• All the protocols of the TCP/IP suite identify a device on the Internet or an intranet by its IP address.

• An IP address is 32 bits long, made up of 4 bytes separated by periods.

• Within an IP address, each of the four

IP Addresses

• Within an IP address, each of the four numbers separated by periods is called an octet.• The first part of an IP address identifies the network, and the last part identifies the host.

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• IP addresses that can be used by companies and individuals are divided into three classes: Class A, Class B, and Class C, based on the number of possible IP addresses in each network within each class.

Classes of IP Addresses

class.

• The group of IP addresses assigned to an organization are unique to all other IP addresses on the Internet and are available for use on the Internet.

• The IP addresses available to the Internet are called public IP addresses.

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• Private IP addresses are IP addresses that

are assigned by a network administrator for

use on private intranets that are isolated

from the Internet.

• The RFC 1918 recommends that the

Private IP Addresses

• The RFC 1918 recommends that the

following IP addresses be used for private

networks:– 10.0.0.0 through 10.255.255.255

– 172.16.0.0 through 172.31.255.255

– 192.168.0.0 through 192. 168. 255.255

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• Instead of IP addresses permanently

being assigned to computers (called

static IP addresses), an IP address is

assigned for the current session only

Dynamically Assigned IP

Addresses

assigned for the current session only

(called a dynamic IP address).

• Internet service providers (ISPs) are

organizations through which individuals

and businesses connect to the Internet.

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• If the hosts on a network using private IP

addresses need to access the Internet, a

problem arises because the private IP

addresses are not allowed on the Internet.

Network Address Translation

• The solution is to use NAT (Network

Address Translation), which uses a single public IP address to access the

Internet on behalf of all hosts on the

network using other IP addresses.

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• Because of an impending shortage of IP

addresses, as well as some limitations in

the current standards for IP, a new

scheme of IP addresses called the IPv6

(IP version 6) standard is currently being

Plans for New IP Addresses

(IP version 6) standard is currently being

developed and implemented.

• Current IP addresses using the current

IPv4 (IP version 4) have 32 bits with

eight bits in each of four octets.

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• With the new system, each address

segment can have 32 bits, for a total of

128 bits for the entire address.

• A disadvantage of IPv6 is the fact that so

much software used on the Internet would

Plans for New IP Addresses

(Continued)

much software used on the Internet would

become outdated because current

software is designed to hold 32-bit IP

addresses and, with the new system,

this number would no longer be

sufficient.

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IPv6 Status April 2013

• IPv6 address allocation has

happened and is happening

very smoothly

• More work in regional and local

transit networkstransit networks

• Content providers (especially

local content) and enterprise

customers need to keep working

on enabling IPv6 in their Internet

resources

• A port is a number used to address software or services running on a computer.

• A host computer might have several services running on it.

Ports

services running on it.

• Each server running on the host is assigned a port.

• The port is written at the end of the IP address, separated from the IP address with a colon—like this: 169.49.209.19:80

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Lecture 2 -_understanding_networks_2013

Technology

Transcript of Lecture 2 -_understanding_networks_2013