Transcript Computer Networks BITS ZC481

Computer Networks BITS ZC481
LECTURE 1
Grading Policy
 EC1 : 3 Quizes of 5% Weightage Each (Closed Book).
 EC2: Mid Sem Test 35% on Sunday 08/09/2013 at
2 PM – 4 PM (Closed Book).
 EC3: Compre Exam 50 % on Sunday 10/11/2013 at
2 PM – 5 PM (Open Book).
Required Textbook
 Text Book: Computer Networking: A Top Down Approach
Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross
Addison-Wesley, 2005.
 R1: Andrew S. Tanenbaum, Computer Networks, Fourth Edition,
Pearson Education, 2006.
 R2: William Stallings, Computer Networking with Internet
Protocols and Technology, Pearson Education, 2004
 L. Peterson and B. Davie, Computer Networks: A Systems
Approach, Fourth Edition, Elsevier, 2007 (Book From 24x7
Online Book)
Course Objectives
 Learn how communication networks are put
together

mechanisms, algorithms, technology components
 Understand fundamental challenges
 Learn about existing solutions
 typically: no single dominant solution
 What problems still need solving?
Today’s Agenda
 Introduction to Internet/computer networks
 Uses of Computer Networks
 Network Hardware: The Network Edge, The
Network Core, Access Networks
Internet :Nuts & Bolts View
 Internet is hundreds of millions of connected computing
devices (nodes). End Systems are the hosts.
 Internet applications run on end system but don’t run in
packet switches in network core.
 All the nodes are connected via Communication links
(fiber, copper, radio, satellite).
 Transmission rate to transmit the data between the
devices is measured in Bandwidth
Internet :Nuts & Bolts View(1)
 Intermediate Nodes between two hosts forwards the
packets (Packet Switching) from one node to other
towards destination host can be routers or switches.
PC
Mobile network
Global ISP
server
wireless
laptop
cellular
handheld
access
points
wired
links
router
Home network
Regional ISP
Institutional network
Internet :Nuts & Bolts View(2)
 Internet: “network of networks”
 loosely hierarchical
 public Internet versus private intranet
 Internet standards
 RFC: Request for comments
 IETF: Internet Engineering Task Force
Internet :Nuts & Bolts View(3)
 End system attached to the Internet provides an API
(Application programming interface).
 API Specifies how a software piece running on one
end system asks the internet infrastructure to deliver
data to specific destination software piece running
on other end system.
 It is set of rules the sending software piece must
follow.
Internet: a service view
 Most people know about the Internet (a computer network)
through applications like
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
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
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
World Wide Web
Email
Online Social Network
Streaming Audio Video
File Sharing
Instant Messaging
Internet: a service view(1)
 Communication infrastructure enables distributed
applications: Web, VoIP, email, games, e-commerce,
file sharing.
 Different Communication services provided to apps:
 reliable data delivery from source to destination.
 “best effort” (unreliable) data delivery.
Protocol
 All communication activity in Internet governed by
protocols.
 Define format, order of messages sent and received
among network entities, and actions taken on
messages transmission, receipt, or timeout.
eg: TCP, IP, HTTP, Skype, Ethernet
 Protocol defines the interfaces between the layers in the
same system and with the layers of peer system.
Protocol(1)
 Each protocol object has two different interfaces:


service interface: operations on this protocol
peer-to-peer interface: messages exchanged with peer
Protocol(2)
 Except at the hardware
level, where peers directly
communicate with each
other over a link, peer-topeer communication is
indirect—each
protocol
communicates with its
peer by passing messages
to some lower level
protocol, which in turn
delivers the message to its
peer.
Network Structure
 Network edge:
applications and hosts.
 Access networks, physical
media: wired, wireless
communication links
 Network core:


interconnected routers
network of networks
(Internet)
Network Edge
 End systems (hosts):
run application programs at
“edge of network e.g. Web,
email
 client/server model
 client host requests,
receives service from
always-on server e.g. Web
browser/server; email
client/server
 peer-peer model:
 minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrent
Network Edge: connection-oriented service
Goal: data transfer between
end systems
 handshaking: setup
(prepare for) data transfer
ahead of time
TCP service [RFC 793]
 reliable, in-order bytestream data transfer
Hello, hello back human
protocol
set up “state” in two
communicating hosts
 flow control:
 sender won’t overwhelm
receiver


 TCP - Transmission
Control Protocol

Internet’s connectionoriented service

loss: acknowledgements and
retransmissions
 congestion control:
 senders “slow down sending
rate” when network
congested
Network Edge: connectionless service
Goal: data transfer between
end systems
 UDP - User Datagram
Protocol [RFC 768]:
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
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connectionless
unreliable data transfer
no flow control
no congestion control
App’s using TCP:
 HTTP (Web), FTP (file
transfer), Telnet
(remote login), SMTP
(email)
App’s using UDP:
 streaming media,
teleconferencing,
DNS, Internet
telephony
Access networks
 How to connect end
systems to edge
router?
 residential access nets
 institutional access
networks (school,
company)
 mobile access
networks
Access Network: Dial Up
 User
software actually
dials a ISP Phone
Number and makes a
traditional
phone
connection with ISP.
 Home
Modem coverts
digital output from PC to
analog
format
and
Modem in ISP converts
back data from analog to
digital format.
Access Network: Dial Up(1)
Drawback:
up to 56Kbps direct access to router (often less)
 Can’t surf and phone at same time: can’t be “always
on”

Access networks: DSL
Access networks: DSL(1)
 Telephone lines carries both data and telephone
signals encoded at different frequencies.
 Splitter separates the data from telephone signals
and transfers it to DSL Modem.
 Upstream and downstream transmission rates are
different (asymmetric).
Access Network: Cable
 Cable
head end broadcast the television channels
through distribution networks of coaxial cable and
amplifiers to residence.
 Hybrid Fiber-coaxial (HFC) access network makes use of
both coaxial and fiber cables.
 Shared broadcast Medium
 asymmetric:
upstream
up to 30Mbps downstream, 2 Mbps
Access Network: Cable(1)
Access Network: Ethernet
Access Network: Ethernet(1)
 company/university local area network (LAN)
connects end system to edge router.
 Ethernet:
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
10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet
modern configuration: end systems connect into Ethernet
switch
Access Network: Wireless Access
 In wireless LAN, Wireless users transmit/receive packets
to/from access point. Eg: 802.11b/g (WiFi): 11 or 54
Mbps.
 In
wide area wireless access network, packets are
transmitted to the base station over same wireless
infrastructure used for cellular telephony.
 Wimax(10’s Mbps over wide area).
Access Network: Wireless Access(1)
router
base
station
mobile
hosts
Physical Media
 Bit: propagates between
transmitter/reciver pairs
 physical link: what lies
between transmitter &
receiver
 guided media:

signals propagate in solid
media: copper, fiber, coax
 unguided media:
 signals propagate freely, e.g.,
radio
Twisted Pair (TP)
 two insulated copper
wires


Category 3: traditional phone
wires, 10 Mbps Ethernet
Category 5:
100Mbps Ethernet
Physical Media: coax, fiber
Coaxial cable:
 two concentric copper
conductors
 bidirectional
 baseband:


single channel on cable
legacy Ethernet
 broadband:
 multiple channels on cable
 HFC
Fiber optic cable:
 glass fiber carrying light
pulses, each pulse a bit
 high-speed operation:
 high-speed point-topoint transmission
(e.g., 10’s-100’s Gps)
 low error rate: repeaters
spaced far apart ;
immune to
electromagnetic noise
Physical media: radio
 signal carried in
electromagnetic spectrum
 no physical “wire”
 bidirectional
 propagation environment
effects:
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

reflection
obstruction by objects
interference
Radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., Wifi)
 11Mbps, 54 Mbps
 wide-area (e.g., cellular)
 e.g. 3G: hundreds of kbps
 satellite
 Kbps to 45Mbps channel
(or multiple smaller
channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
Next Lecture
 Network Core
 ISP
 Delay & loss in packet-switched networks
 Protocol layers, service models
 OSI and TCP/IP reference models
Thanks!!!
Queries?