week6 final
TRANSCRIPT
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Lecture 6Communication Networks
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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
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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]
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BenefitsResource sharing (cost savings)
Personal communication
Data backups
Reliability (reduced errors/inconsistencies)
Greater performance (distributed computing)
Personalized/ contextualized services
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Network Design Issues
Media; Topology; Protocol;
Addressing; Naming;
Example networking application.
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Transmission mediaWired (or Guided) Media
1) Copper pair:• Unshielded Twisted Pair (UTP)
• Shielded Twisted Pair (STP)
2) Coaxial Cable
3) Optical Fiber
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Transmission mediaWireless (or Unguided) Media
1. Infrared
2. Radio
3. Microwave
4. Satellite
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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
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Network Topology (cont)
Point to Point Star
Partial Mesh
Tree
Bus
Ring
Fully Connected
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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]
‘‘ ’
’
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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.
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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.
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Physical Addressing: MACMAC Address: 48 bits (Ethernet)Flat addressing
Usually non-configurable
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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
???
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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
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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
???
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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:
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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)
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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
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Example applicationhttp://www.niit.edu.pk
Other browsers include Firefox, Opera.
Browser acts as:
a client of webserver
fetches and displays user requested documents
12
This is an example of a browser (Internet Explorer)
Address Bar
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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
1
2
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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
???
Example application (contd.)
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WWW
DNS
Example application (contd.)
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DNS Client/Server Exchange
WWW
DNS
Request
Tell me the IP address of www.niit.edu.pk?
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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
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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 |
Example application (contd.)
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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)
Example application (contd.)
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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
??
Example application (contd.)
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ARP Client/Server Exchange
WWW
DNS
Request
Any one knows the MAC (physical) address of 202.125.157.196 ?
Request
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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
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Now that the physical (MAC) addresses are known, communication can take placeThe destination MAC address is 12:34:aa:bb:cc:dd
The source MAC address (let’s assume) is 23:34:aa:bb:cc:dd
IP packet containing the data
MAC frame
Source IP | Destination IP | Source Port | Destination Port | GET / HTML/1.1202.125.157.150 | 202.125.157.196 | > 1024 | 80 |
PayloadSource MAC address | Destination MAC address FCS
Example application (contd.)
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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
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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
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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
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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
.
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InternetworkingInterconnecting multiple networks
Hierarchical addressing; Routing; Encapsulation/ layered communication
Next
Lecture
References (today’s and next lecture): “Networking basics” and “Data Communications”
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???Questions/
Confusions?
Credits/ Acknowledgement can be found
at the course website:
http://tinyurl.com/5hb8pp