NET NET 331 331 ––Computer NetworksComputer Networks · Introduction to the Internet ... Mobile...

NET NET 331 331 –– Computer NetworksComputer Networks

Reformatted slides from textbookComputer Networking – a top-down appraoch, Fifth Edition by Kurose and Ross, (c) Pearson Education - Prentice Hall, 2011

31-Jan-12

Lecture 02

Introduction to the Internet

Dr. Anis Koubaa

Learning Outcome

� Get feeling on what the Internet is

� Understand the concept of a protocol

� Learn the basic of Networking

NET 331: Computer Networks, by Dr. Anis KoubaaTextbook: Computer Networking : a Top-Down Approach , 5/EBy Kurose and Ross – Original Slides from Authors (modified)2

Learn the basic of Networking

� Get familiar with performance metrics of networks

� Get familiar of network security issues

� Get an idea on the history of the Internet

Recommended Reading

� Chapter 1: Computer Networks and the Internet

� Textbook: Computer Networking – a top-down appraoch, 5E

� Chapter 2: Protocol Architecture, TCP/IP and Internet-Based Applications

� Textbook: Data and Computer Communications, 9E

Outline

� 1.1 What is the Internet?

� 1.2 Network edge

� end systems, access networks, links

� 1.3 Network core

1.3 Network core

� circuit switching, packet switching, network structure

� 1.4 Delay, loss and throughput in packet-switched networks

� 1.5 Protocol layers, service models

� 1.6 Networks under attack: security

� 1.7 History

What’s the Internet: “nuts and bolts” view

� millions of connected computing devices: Hosts= End Systems

� running network apps

Communication Links

server

wirelesslaptop

cellular handheld

� Communication Links

� fiber, copper, radio, satellite

� transmission rate = bandwidth

� Routers: forward packets (chunks of data)router

wiredlinks

access points

“Fun” internet appliances

IP picture framehttp://www.ceiva.com/

Web-enabled toaster +weather forecaster

Internet phonesInternet refrigerator

Slingbox: watch,control cable TV remotely

What’s the Internet: “nuts and bolts” view

� protocols control sending, receiving of msgs� e.g., TCP, IP, HTTP, Skype,

Ethernet

� Internet: “network of networks”� loosely hierarchical

Home network

Mobile network

Global ISP

Regional ISP

� loosely hierarchical

� public Internet versus private intranet

� Internet standards� RFC: Request for comments

� IETF: Internet Engineering Task Force

Institutional network

Regional ISP

A Services DescriptionA Services Description

Introduction1-8

What’s the Internet: a service view

� Communication infrastructure enables distributed applications:

� Web, VoIP, email, games, e-commerce, file sharing

� Communication services

Home network

Mobile network

Global ISP

Regional ISP

� Communication services provided to apps:

� reliable data delivery from source to destination

� “best effort” (unreliable) data delivery

Institutional network

Regional ISP

What’s a protocol?

� human protocols:

� “what’s the time?”

� “I have a question”

� introductions

… specific msgs sent

� network protocols:

� machines rather than humans

� all communication activity in Internet governed by protocols

� … specific msgs sent

� … specific actions taken when msgs received, or other events

protocols

protocols define format, order of msgs sent and received

among network entities, and actions taken on msgtransmission, receipt

What is a Protocol?What is a Protocol?

Introduction1-11

What’s a protocol?

� a human protocol and a computer network protocol:

Outline

� 1.7 History

Network EdgeNetwork Edge

�� ا��

Introduction1-14

A closer look at network structure:

� Network Edge

� applications and hosts

� Access Networks, Physical Media:

� wired, wireless communication links

communication links

� Network Core

� interconnected routers

� network of networks

The Network Edge

� End systems (hosts)� run application programs

� e.g. Web, email

� at “edge of network”

� Client/Server Model� client host requests, receives

service from always-on server

peer-peer

client host requests, receives service from always-on server

� e.g. Web browser/server; email client/server

� Peer-to-Peer (P2P) Model� minimal (or no) use of

dedicated servers

� e.g. Skype, BitTorrent

client/server

Access NetworksAccess Networks

Introduction1-17

Access Networks and Physical Media

� Q: How to connect end systems to edge router?

� residential access nets

� institutional access networks (school, company, university)

university)

� mobile access networks

� Keep in mind:

� bandwidth (bits per second) of access network?

� shared or dedicated?

Using a Telephone Network (Dial-up / DSL)

telephonenetwork Internet

homedial-upmodem

ISPmodem(e.g., AOL)

homePC

central office

Dial-up Modem

� uses existing telephony infrastructure

� home directly-connected to central office

� up to 56Kbps direct access to router (often less)

� can’t surf, phone at same time: not “always on”

telephonenetwork

homephone

Internet

Existing phone line:0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data

splitter

central

Digital Subscriber Line (DSL)

DSLmodem

homePC

centraloffice

� uses existing telephone infrastructure

� up to 1 Mbps upstream (today typically < 256 kbps)

� up to 8 Mbps downstream (today typically < 1 Mbps)

� dedicated physical line to telephone central office

Using a Television/Modem Cable

Residential Access: Cable Modems

� uses cable TV infrastructure, rather than telephone infrastructure

� HFC: hybrid fiber coax

� asymmetric: up to 30Mbps downstream, 2 Mbps upstream

� network of cable, fiber attaches homes to ISP router

� homes share access to router

� unlike DSL, which has dedicated access

Residential Access: Cable Modems

NET 331: Computer Networks, by Dr. Anis Koubaa 24Textbook: Computer Networking : a Top-Down Approach , 5/EBy Kurose and Ross – Original Slides from Authors (modified)

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Typically 500 to 5,000 homes

Cable Network Architecture: Overview

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

server(s)

cable headend

cable distributionnetwork

cable headend

cable distributionnetwork (simplified)

Channels

CONTROL

1 2 3 4 5 6 7 8 9

FDM (more shortly):

cable headend

cable distributionnetwork

Channels

Fibre to Home (FTTH)

Fiber to the Home

� Optical links from central office to the home

� Two competing optical technologies:

� Passive Optical network (PON)

� Active Optical Network (PAN)

� Much higher Internet rates; fiber also carries television and phone services

Ethernet

Ethernet Internet access

� Typically used in companies, universities, etc

� 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet

� today, end systems typically connect into Ethernet switch

Wireless Access

Wireless access networks

� shared wireless access network connects end system to router� via base station aka “access

point”

� wireless LANs:� 802.11b/g (WiFi): 11 or 54

� 802.11b/g (WiFi): 11 or 54 Mbps

� wider-area wireless access� provided by telco operator

� ~1Mbps over cellular system (EVDO, HSDPA)

� next up (?): WiMAX (10’s Mbps) over wide area http://www.home-network-help.com/wireless-network.html

Wireless access networks

� shared wireless access network connects end system to router� via base station aka “access

point”

� wireless LANs:� 802.11b/g (WiFi): 11 or 54

� 802.11b/g (WiFi): 11 or 54 Mbps

� wider-area wireless access� provided by telco operator

� ~1Mbps over cellular system (EVDO, HSDPA)

� next up (?): WiMAX (10’s Mbps) over wide area

http://www.atrexx.com/applications/WiMAX-Wireless-Access-Networks/

Home networks

� Typical home network components:

� wireless access point

� DSL or cable modem

� router/firewall/NAT

� Ethernet

Physical MediaPhysical Media

Physical Media

� Bit: propagates betweentransmitter/receiver pairs

� Physical link: what lies between transmitter & receiver

Guided media:

� Twisted Pair (TP)

� two insulated copper wires

� Category 3: traditional phone wires, 10 Mbps Ethernet

� Guided media:

� signals propagate in solid media: copper, fiber, coax

� Unguided media:

� signals propagate freely, e.g., radio

Ethernet

� Category 5: 100Mbps Ethernet

Physical Media: Coax, Fiber

� Coaxial cable

� two concentric copper conductors

� bidirectional

� baseband

� single channel on cable

� Fiber optic cable

� glass fiber carrying light pulses, each pulse a bit

� high-speed operation:

� high-speed point-to-point transmission (e.g., 10’s-100’s

� single channel on cable

� legacy Ethernet

� broadband

� multiple channels on cable

� HFC

transmission (e.g., 10’s-100’s Gpbs)

� low error rate: repeaters spaced far apart ; immune to electromagnetic noise

Physical Media: Radio (Wireless)

� signal carried in electromagnetic spectrum

� no physical “wire”

� bidirectional

� propagation environment effects:

� Radio link types:� Terrestrial microwave

� e.g. up to 45 Mbps channels

� LAN (e.g., WiFi)� 11Mbps, 54 Mbps

� wide-area (e.g., cellular)

effects:� reflection

� obstruction by objects

� interference

wide-area (e.g., cellular)� 3G cellular: ~ 1 Mbps

� Satellite� Kbps to 45Mbps channel (or

multiple smaller channels)

� 270 msec end-end delay

� geosynchronous versus low altitude

Outline

� 1.7 History

The Network Core

� Mesh of interconnected routers

� The fundamental question: how is data transferred through net?

Circuit Switching: dedicated

� Circuit Switching: dedicated circuit per call: telephone network

� Packet-Switching: data sent through the network in discrete “chunks”

Network CoreNetwork Core

Circuit Switching

Network Core: Circuit Switching

� End-to-end resources reserved for “call”

� link bandwidth, switch capacity

� dedicated resources: no sharing

sharing

� circuit-like (guaranteed) performance

� call setup required

Network Core: Circuit Switching

� Network resources (e.g., bandwidth) divided into “pieces”

� Pieces allocated to calls

� Resource piece idle if not used by owning call (no

� Dividing link bandwidth into “pieces”

� Frequency division

� Time division

used by owning call (no sharing)

Circuit Switching: FDM and TDM

Frequency

4 users

Example:

Frequency

Numerical example

� How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?

� all link speeds: 1.536 Mbps

� each link uses TDM with 24 slots/sec

� 500 msec to establish end-to-end circuit

� Let’s work it out!

Packet Switching

Network Core: Packet Switching

� Each end-end data stream divided into packets

� User A, B packets share network resources

� Each packet uses full link bandwidth

� Resource contention

� Aggregate resource demand can exceed amount available

� Congestion: packets queue, wait for link use

bandwidth

� Resources used as needed

queue, wait for link use

� Store-and-forward:packets move one hop at a time

� node receives complete packet before forwarding

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation

Packet Switching: Statistical Multiplexing

� Sequence of A & B packets has no fixed timing pattern

� bandwidth shared on demand: statistical multiplexing.

� TDM: each host gets same slot in revolving TDM frame.

Packet-switching: store-and-forward

� takes L/R seconds to transmit (push out) packet of L bits on to link at R bps

� store and forward: entire packet must arrive at

� Example:

� L = 7.5 Mbits

� R = 1.5 Mbps

� transmission delay = 15 sec

packet must arrive at router before it can be transmitted on next link

� delay = 3L/R (assuming zero propagation delay)

NET NET 331 331 ––Computer NetworksComputer Networks · Introduction to the Internet ... Mobile...

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