Week6 final

Lecture 6Communication Networks

1. Definition and benefits of networks

2. Network design issues:

• Media

• Topology

• Protocol

• Addressing

• Naming

3. Clarifying example:

Data transfer between a

browser and a

webserver

Today’s

lecture Lecture Outline

Networking

‘‘

’’

Networks is a set of technologies – including hardware, software and media – that can be used to connect computers together, enabling them to communicate, exchange information and share resources in real time

[Peter Norton]

BenefitsResource sharing (cost savings)

Personal communication

Data backups

Reliability (reduced errors/inconsistencies)

Greater performance (distributed computing)

Personalized/ contextualized services

Network Design Issues

Media; Topology; Protocol;

Addressing; Naming;

Example networking application.

Transmission mediaWired (or Guided) Media

1) Copper pair:• Unshielded Twisted Pair (UTP)

• Shielded Twisted Pair (STP)

2) Coaxial Cable

3) Optical Fiber

Transmission mediaWireless (or Unguided) Media

1. Infrared

2. Radio

3. Microwave

4. Satellite

Network TopologyNetwork topology is the study of the physical (real) and logical (virtual) interconnections between nodes [Wikipedia]

Topology types:Point to Point; Bus; Star; Ring; Mesh and Hybrid

Network Topology (cont)

Point to Point Star

Partial Mesh

Tree

Bus

Ring

Fully Connected

Protocol

‘‘

’’

The rules governing the syntax, semantics, and synchronization of communication.

[Wikipedia]Protocol defines 1) format and 2) order of messages sent and received among network entities and 3) action(s) taken on transmission and receipt of message

[Kurose and Ross]

‘‘ ’

’

ProtocolIn this course, we will focus on protocols for data traffic only.

TCP/IP is the most dominant suite of protocols and is used on the Internet.

TCP/IP suite of protocols is often organized in a hierarchy of layers (OSI layers; to be covered next week)

Some other protocol suites (no where as popular) include: NetBIOS/ NetBEUI and IPX/ SPX.

AddressingEach station must be addressableTwo kinds of addresses:1) Physical addressing (MAC addresses)2) Logical addressing (IP addresses)

The communicating applications (source/ destination applications) must also be identifiableIdentified through TCP ports

A socket (IP address + TCP port) identifies both an application and the machine it’s on.

Physical Addressing: MACMAC Address: 48 bits (Ethernet)Flat addressing

Usually non-configurable

Logical Addressing: IPIP Version 4; Address: 32 bitsIP Version 6; Address: 128 bits

Hierarchical addressing2 parts: a network part and a host part.Machines in a LAN have the same network part; they differ in host partsHow is the network part of an IP address defined Subnet mask

4,294,967,296 possible addresses = 232

???

IP (Internet Protocol)IP Address192.168.15.2 (decimal)

11000000 10101000 00001111 00000010 (binary)

Subnet Mask:255.255.255.0 (decimal)

11111111 11111111 11111111 00000000 (binary)

IP Address192.168.15.2 (decimal)

11000000 10101000 00001111 00000010 (binary)

Subnet Mask:255.255.255.0 (decimal)

11111111 11111111 11111111 00000000 (binary)

Network part Host part

Applications IdentificationHow to identify source/ destination application communicating

The source/ destination applications are identified through TCP ports

Common TCP Ports:

HTTP: 80; SMTP:25; DNS: 53

???

NamingMachine addresses are difficult to memorize

Solution: Provide recognizable names to numerically addressed Internet resources.

google.com; stanford.edu; niit.edu.pkgoogle.com; stanford.edu; niit.edu.pk…, Third level domain, Second level domain; Top level domain (TLD);

List of TLDs: http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains

Examples:

http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains

NamingHow to manage address to name mapping?1) A hosts file on each machine

Unix/ Linux: /etc/hosts fileWindows: %SystemRoot%\system32\drivers\etc

2) A decentralized domain name server systemScalable solutionThe name to IP mapping is available at a DNS server

DNS servers are of two typesa) DNS Authoritative server (each domain has at least two

authoritative servers)b) DNS Caching server (each LAN can have one)

Example application

Let’s assume that a student (in the niit.edu.pk LAN) wishes to access NUST-SEECS website hosted at www.niit.edu.pk

WWWP

C

To clarify concepts, let us assume a greatly simplified

model of the LAN of NUST-SEECS

Network’s domain name: niit.edu.pk

Example applicationhttp://www.niit.edu.pk

Other browsers include Firefox, Opera.

Browser acts as:

a client of webserver

fetches and displays user requested documents

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This is an example of a browser (Internet Explorer)

Address Bar

Example application (contd.)

The HTTP request sent by the student PC (the machine pc.niit.edu.pk) to the webserver (the machine www.niit.edu.pk) would be something like “GET / HTML/1.1”

Packet so far:

Outstanding issues: How to send this request to Webserver?

Which application at webserver must process this packet?

GET / HTML/1.1

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http://www.pc.niit.edu.pk/

http://www.niit.edu.pk/

But how to send this request to Webserver?

To communicate with www.niit.edu.pk (hostname), its IP address must be known

How to resolve hostnames to IP addresses

Domain Name Service (DNS)

1

???



WWW

DNS


DNS Client/Server Exchange

WWW

DNS

Request

Tell me the IP address of www.niit.edu.pk?


WWW

DNSReply

The IP address of www.niit.edu.pk is 202.125.157.196

DNS Client/Server Exchange

The IP address of www.niit.edu.pk is 202.125.157.196



Which application at webserver must process this packet?

In TCP/IP, each well-known application is identified using ports.

The port of DNS is 53; HTTP is 80; SMTP is 25.

In our considered example, HTTP server application (port 80) would process the packet.

Packet so far:

2

Source Port | Destination Port | GET / HTML/1.1> 1024 | 80 |


The destination IP address (found through DNS)is 202.125.157.196.

Let’s assume the source IP address is 202.125.157.150 (network must be same; to be explained later)

Packet so far: Source IP | Destination IP | Source Port | Destination Port | GET / HTML/1.1202.125.157.150 | 202.125.157.196 | > 1024 | 80 |

Logical addressing: network and host parts*Assuming /24 subnet mask (to be explained later)


How to send the created packet to Webserver?

To communicate with any host, its physical address (called MAC address) must be known.

How to resolve IP addresses to MAC addresses

Address Resolution Protocol (ARP)

3

??


ARP Client/Server Exchange

WWW

DNS

Request

Any one knows the MAC (physical) address of 202.125.157.196 ?

Request

WWW

DNS

Reply

The MAC address of 202.125.157.196 is

12:34:aa:bb:cc:dd

ARP Client/Server Exchange

The MAC address of 202.125.157.196 is

12:34:aa:bb:cc:dd

EncapsulationThis topic is to be studied in more depth next lecture

GET / HTML/1.1

Source MAC address | Destination MAC address 23:34:aa:bb:cc:dd | 12:34:aa:bb:cc:dd

FCSPayload

Payload

Source Port | Destination Port> 1024 | 80

Payload

Payload

Source IP | Destination IP 202.125.157.150 | 202.125.157.196

Payload

Application data

TCP Segment

MAC Frame

IP Packet

HTTP Client/Server Exchange

WWW

DNS

Send me the index.html page for the host www.niit.edu.pk

using HTTP version 1.1

Request

Send me the index.html page for the host www.niit.edu.pk

using HTTP version 1.1



WWW

DNS

Reply

The index.html page in the wwwroot directory configured for the www.niit.edu.pk webserver

is sent back to the browser for display

HTTP Client/Server Exchange


Lecture’s

Summary

a) We’ve discussed basic types of

1) network

media; 2) network topologies;

3) addressing

schemes; 4) name resolution techniques.

b) We’ve studied an example of data transfer

between a browser

and a webserver

.

InternetworkingInterconnecting multiple networks

Hierarchical addressing; Routing; Encapsulation/ layered communication

Next

Lecture

References (today’s and next lecture): “Networking basics” and “Data Communications”

???Questions/

Confusions?

Credits/ Acknowledgement can be found

at the course website:

http://tinyurl.com/5hb8pp

http://tinyurl.com/5hb8pp

Week6 final

Technology

Transcript of Week6 final