lec01 02 introduction
TRANSCRIPT
-
8/8/2019 Lec01 02 Introduction
1/43
Computer Networks-FallComputer Networks-Fall
0909Lec-IntroductionLec-Introduction
Prepared byPrepared by
Zia QureshiZia Qureshi
Fatima Jinnah Women UniversityFatima Jinnah Women University
-
8/8/2019 Lec01 02 Introduction
2/43
A non technical look at networksA non technical look at networks Let us look at a few examples of networks from
our day to day lives and try to learn a fewconcepts.
What are examples of networks we use in life?
Power distribution network
Water distribution network
Network of city roadsThe good old surface mail network
-
8/8/2019 Lec01 02 Introduction
3/43
IssuesIssuesHow is the content delivered?
Are the links between source and receiver one-way or both-ways?
Do we need identifiers (or addresses) for
delivering the service?Is the content provided by the network to each
receiver the same?
Is the content given to the network by each sourcethe same?
Can we keep adding sinks indefinitely?
Can we keep adding sources indefinitely?
-
8/8/2019 Lec01 02 Introduction
4/43
Motivation for NetworksMotivation for Networks Information Access
Sharing of Resources
Facilitate Communications
-
8/8/2019 Lec01 02 Introduction
5/43
What a Network IncludesWhat a Network Includes Hardware: Talk just a bit about how you can configure
a bunch of computers into a network:
Local Area Networks (LAN)
Metropolitan Area Networks (MAN)
Wide Area Networks (WAN)
Software: This is what actually makes computernetworks not the hardware!
Protocols: describe howtwo communicating partiesexchange information.
encodes and formats data
detects and corrects problems
Reference models: Describe how the OSI andInternet networks are organized.
-
8/8/2019 Lec01 02 Introduction
6/43
What a Network DoesWhat a Network Does Provides communication that is
Reliable
Fair
Efficient
From one application to another
-
8/8/2019 Lec01 02 Introduction
7/43
What a Network DoesWhat a Network Does Automatically detects and corrects
Data corruption
Data loss
Duplication
Out-of-order delivery
Automatically finds optimal path from source to
destination
-
8/8/2019 Lec01 02 Introduction
8/43
Data Communication versus NetworkingData Communication versus Networking
With only two nodes, mostly EE issues.
With more than two nodes, lot more issues!
-
8/8/2019 Lec01 02 Introduction
9/43
Direction of TransmissionDirection of Transmission
Broadcast Point to Point
-
8/8/2019 Lec01 02 Introduction
10/43
Broadcast NetworksBroadcast Networks Single Communication channel shared by all
the machines on the network.
Any machine can send short messages(packets).
Each packet contains the address of intendedrecipient.
All machines receive the messages, only theaddressed machine processes the message.
-
8/8/2019 Lec01 02 Introduction
11/43
Broadcast NetworksBroadcast Networks Example of a person shouting in a corridor
Calling name of some other person
What is one key issue with Broadcast
Networks? Packet Collisions.
-
8/8/2019 Lec01 02 Introduction
12/43
Point-to-point NetworksPoint-to-point Networks Individual pairs of machines are physically
connected.
To go from a source to a destination a packettypically goes through intermediate nodes.
What is a key issue in point-to-point networks?
How do you optimally connect pairs of
machines?
-
8/8/2019 Lec01 02 Introduction
13/43
Network ScopeNetwork Scope Local Area Network (LAN)
Wide Area Network (WAN)
Metropolitan Area Network (MAN)
-
8/8/2019 Lec01 02 Introduction
14/43
Local Area Networks (LANs)Local Area Networks (LANs) Mostly used to connect PCs, shared resources
like printers, file servers etc. in a building. LANs are broadcast networks
Their size is limited:
Maximum distance between two nodes.
Number of nodes connected.
-
8/8/2019 Lec01 02 Introduction
15/43
Local Area Networks (LANs)Local Area Networks (LANs) Traditionally the common media was a cable
that all nodes were attached to.
We will study bridges etc. later.
Wireless LANs are available now.
-
8/8/2019 Lec01 02 Introduction
16/43
Local Area Networks (LANs)Local Area Networks (LANs)
-
8/8/2019 Lec01 02 Introduction
17/43
Local Area Networks (LANs)Local Area Networks (LANs)LANs generally dont have any switching
elements
The wire does all the work.
This makes them extremely efficient
But harder to scale.
-
8/8/2019 Lec01 02 Introduction
18/43
Wide Area Network (WAN)Wide Area Network (WAN) WANs cover large geographic areas (country or
continent). Two key components of a WAN are:
Transmission lines
also called channels, circuits, trunks etc.
Move bits from one node to the other
Switching elements
also called packet switching nodes, routers etc.
select outgoing transmission lines for data coming onincoming lines.
-
8/8/2019 Lec01 02 Introduction
19/43
Wide Area Networks (WANs)Wide Area Networks (WANs)
In a WAN, hosts are connected to a subnet
Subnet Consists of routers and transmissionlines
Routers are switching elements
-
8/8/2019 Lec01 02 Introduction
20/43
Wide Area Networks (WANs)Wide Area Networks (WANs)Routers generally adhere to a store-and-
forward principle
Each router first receives a complete packetover some link
Stores the packet in its internal memory
Forwards the packet across the selected output
line.
-
8/8/2019 Lec01 02 Introduction
21/43
MANMANMetropolitan area Network covers a city.
Examples include Cable TV Network.
Cable modem for internet access.
-
8/8/2019 Lec01 02 Introduction
22/43
Wireless NetworksWireless NetworksDivided into 3 Main Catagories
System Interconnection Interconnecting components of a computer using short
range radio. E.g. Bluetooth to connect KB,Mouse,Printer.
Wireless LANs
Every Computer has a radio modem and antenna withwhich it can communicate with other systems (IEEE 802.11)
Wireless WANs
Radio Network for cellular phones. Operate below 1Mpbs over many KM.
High bandwidth WANs are being developed for highspeed wireless internet access. Standard developed for it iscalled IEEE802.16
-
8/8/2019 Lec01 02 Introduction
23/43
Bigger NetworksBigger Networks
Or, two or morenetworksconnected by two
or more nodes
A network can be defined recursively
as...two or morenodes connectedby a link
-
8/8/2019 Lec01 02 Introduction
24/43
Switched NetworksSwitched NetworksSwitching nodes:
Sole purpose is store and forward
Host nodes:
Use the networkRun application programs
SwitchSwitch
HostHost
-
8/8/2019 Lec01 02 Introduction
25/43
Interconnection of NetworksInterconnection of NetworksIndependent networks are interconnected to
form an internetworkor internetfor shortNode connected to two or more networks is
called a Router or Gateway
RouterRouter
-
8/8/2019 Lec01 02 Introduction
26/43
Network ComponentsNetwork Components
Network Core Network Edge
-
8/8/2019 Lec01 02 Introduction
27/43
The Network Core: StrategiesThe Network Core: Strategies Mesh of interconnected routers
Fundamental question: how is datatransferred through net?
Circuit switching:
dedicated circuit per call
telephone net
Packet-switching:data sent through net in discrete chunks
-
8/8/2019 Lec01 02 Introduction
28/43
Network Core: Circuit SwitchingNetwork Core: Circuit Switching
End-to-End resources
reserved for call link bandwidth, switch
capacity
dedicated resources: nosharing
circuit-like (guaranteed)performance
call setup required
-
8/8/2019 Lec01 02 Introduction
29/43
Network Core: Circuit SwitchingNetwork Core: Circuit Switching
Network resources (e.g., bandwidth)
divided into pieces Pieces allocated to calls
Resource piece idleif not used by owning call
(no sharing)
Dividing link bandwidth into pieces
Frequency division
Time division
-
8/8/2019 Lec01 02 Introduction
30/43
Circuit Switching: FDMA and TDMACircuit Switching: FDMA and TDMA
FDMA
frequency
time
TDMA
frequency
time
4 usersExample:
-
8/8/2019 Lec01 02 Introduction
31/43
Network Core: Packet SwitchingNetwork Core: Packet Switching Instead of having a continuous stream of data, divide it into
chunks; Packet
Each packet uses full link bandwidth
Resources used as needed
Resource Contention:
Aggregate resource demand can exceed amount available
Congestion: packets queue, wait for link use
Store and forward: packets move one hop at a time
Bandwidth division intopieces
Dedicated allocation
Resource reservation
N t k Ed
-
8/8/2019 Lec01 02 Introduction
32/43
Network Edge:Network Edge:
End systems (hosts):
Run application programs
e.g. Web, email
at edge of network
Client/Server modelClient host requests, receives
service from always-on server
e.g. Web browser/server; emailclient/server
How do end systemscommunicate?
Through Protocols
?Wh t t l?
-
8/8/2019 Lec01 02 Introduction
33/43
Whats a protocol?Whats a protocol?Human protocols:
whats the time? I have a question
Introductions
specific msgs sent
specific actions takenwhen msgs received,or other events
Network protocols:
Machines rather thanhumans
All communicationactivity in Internet
governed by protocolsProtocols define:
Msg format
Order of msgs sent andreceived among networkentities
Actions taken on msgtransmission, receipt
Wh l?Wh t t l?
-
8/8/2019 Lec01 02 Introduction
34/43
Whats a protocol?Whats a protocol?
A human protocol
Hi
Hi
Got thetime?
2:00
Connection
requiredConnectionresponsed
Get http://www.awl.com/kurose-ross
time
A computer network protocol:
P t l L P t l L
-
8/8/2019 Lec01 02 Introduction
35/43
Protocol LayersProtocol Layers
Networks are complex! Many pieces:
hosts
routers
links of variousmedia
applications
protocols
hardware, software
Question:
Is there any hope of
organizingstructure ofnetwork?
O i i f i lO i ti f i t l
-
8/8/2019 Lec01 02 Introduction
36/43
Organization of air travelOrganization of air travel
a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
A Diff t ViA Diff t Vi
-
8/8/2019 Lec01 02 Introduction
37/43
Layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
A Different ViewA Different View
L d i t l iL d i t l i
-
8/8/2019 Lec01 02 Introduction
38/43
Layered air travel: servicesLayered air travel: services
Counter-to-counter delivery of person+bags
baggage-checkin-to-baggage-claim delivery
people transfer: loading gate to arrival gate
runway-to-runway delivery of plane
airplane routing from source to destination
Di ib dDi t ib t d i l i f l f i lii l t ti f l f ti lit
-
8/8/2019 Lec01 02 Introduction
39/43
DistributedDistributed implementation of layer functionalityimplementation of layer functionality
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
Departing
air
port
arrivinga
irport
intermediate air traffic sites
airplane routing airplane routing
Wh l i ?Wh l i ?
-
8/8/2019 Lec01 02 Introduction
40/43
Why layering?Why layering?
Modularization eases maintenance, updating
of system
Change of implementation of layers servicetransparent to rest of system
e.g., change in gate procedure doesntaffect rest of system
I t t t l t kI t t t l t k
-
8/8/2019 Lec01 02 Introduction
41/43
Internet protocol stackInternet protocol stack Application: supporting network applications
FTP, SMTP, STTP
Transport: host-host data transfer
TCP, UDP
Network: routing of datagrams from source todestination
IP, routing protocols
Link: data transfer between neighboringnetwork elements
PPP, Ethernet
Physical: bits on the wire
application
transport
network
link
physical
I t t P t l l i d d tI t t P t l l i d d t
-
8/8/2019 Lec01 02 Introduction
42/43
Internet Protocol layering and dataInternet Protocol layering and data
Each layer takes data from above
Adds header information to create new data unit
Passes new data unit to layer below
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
Physical View
I t t P t l l i d d tI t t P t l l i d d t
-
8/8/2019 Lec01 02 Introduction
43/43
Internet Protocol layering and dataInternet Protocol layering and data
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
Each layer takes data from above
Adds header information to create new dataunit
Passes new data unit to layer below
Layer 4 ProtocolLayer 4 Protocol
Layer 3 ProtocolLayer 3 Protocol
Layer 2 ProtocolLayer 2 Protocol
Layer 1 ProtocolLayer 1 Protocol