Chapter 1: Introduction What is a Network? What is Internet? - - PowerPoint PPT Presentation

CSci4211: Introduction 1

Chapter 1: Introduction

 What is a Network? What is Internet?

Compared with postal service & telephone system



“Nuts and Bolts” description



Services provided

 Packet Switching vs. Circuit Switching  Fundamental Issues in Computer Networking  Protocol and Layered Architecture  Internet Protocols, Architecture & History

Readings: Chapter 1, Lecture Notes

Goal and Motivating Questions

Our goal:

• get “feel” and

terminology

• more depth, detail

later in course

• approach:

– use Internet as example

Motivating Questions:

• What is internet? What’s so

special about it?

• What’s a protocol?
• How do I build a network?
• How do I deal with the

complexity?

• What does real Internet look like

now?

• Why I download slowly?

CSci4211: Introduction 2

Internet is the network!

• It’s big!
• It’s diverse!
• It’s complex!
• It’s everywhere (almost)!
• … and it keeps growing and changing!

CSci4211: Introduction 3

Inter-networking

– two or more nodes connected by a link, or

 two or more networks

connected by two or more nodes

 A network can be defined recursively as...

Internet: networks of networks

• started as ARPAnet with only 4 nodes

CSci4211: Introduction 4

Map of Internet

csci4211 Introduction

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Internet Usage Statistics

source: http://www.internetworldstats.com/stats.htm

csci4211 Introduction

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• servers, desktops, laptops, …

High-tier Low-tier High Mobility Low Mobility Wide Area Local Area

Wireless technologies revolutionizing Internet!

• WiFi, bluetooth, NFC, Zigbee, 3/4G (soon 5G) cellular networks

mobile computing location services

• smart mobile phones, iPads, e-readers, …
• now TVs, lightbulbs, thermostats, cars,

etc., soon fridges, … everything

CSci4211: Introduction 8

More gadgets are plugged in …

New Era of Internet of Things (IoT)

IoT & Smart Cities

1: Introduction

9

Why VIA –Hardware structure

CPU CPU

Memory

Controller

PCI Bridge

Memory

PCI Bus SCSI

Ethernet

FC

SAN LAN

Disk Disk Disk

1: Introduction

10

A Case for Data and Control Flow between Host and NIC

Internet:

a huge transformative & disruptive force! What has become of the Internet:

• Information Service and E-Commerce Platform

– deliver all kinds of information, news, music, video, shopping – web, spotify, iTune, youtube, Netflix, Hulu, …

• Global Information Repository

– store and search for all kinds of information – google, flickr, dropbox, icloud, …

• Cyberspace and Virtual Communities

– keep in touch with friends and strangers – email, facebook, twitter, …

• Enormous Super-Computer

– mobile, cloud computing and services

We’re increasingly depending on it !

CSci4211: Introduction 11

CSci4211: Introduction 12

So what’s so special about the Internet?

But first, what is a Network?

CSci4211: Introduction 13

What is a Network?

 There are many types of networks!  Key Features of Networks



Providing certain services

• transport goods, mail, information or data



Shared resources

 used by many users, often concurrently



Basic building blocks

• nodes (active entities): process and transfer goods/data
• links (passive medium): passive “carrier” of goods/data



Typically distributed & “multi-hop”:

 two “end points” cannot directly reach each other  need other nodes/entities to relay

CSci4211: Introduction 14

What is a Network …

Compare Internet with Postal Service and Telephone System

 Services Provided  Various Key Pieces and Their Functions  How the pieces work together to provide

services

• Internet: “network of

networks”

– Interconnected ISPs

• protocols control sending,

receiving of messages

– e.g., TCP, IP, HTTP, Skype, 802.11

• Internet standards

– RFC: Request for comments – IETF: Internet Engineering Task Force

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

mobile network global ISP regional ISP home network institutional network

CSci4211: Introduction 13

What’s the Internet: a service view

• infrastructure that

provides services to applications:

– Web, VoIP, email, games, e- commerce, social nets, …

• provides programming

interface to apps

– hooks that allow sending and receiving app programs to “connect” to Internet – provides service options, analogous to postal service

mobile network global ISP regional ISP home network institutional network

CSci4211: Introduction 14

CSci4211: Introduction 17

Nuts and Bolts Description

Network is fundamentally distributed in nature: a collection of distinct entities: “nodes” and “links”

Postal:



Mailboxes



Local/Branch Postal Offices, Regional, Central Postal Offices



Mail Sorting Machines



Postmen, Delivery Trucks/Trains/Planes, Roads, … Telephone:



Phones



Local Switching Office, Central Switching Offices, …



Telephone Switches



Wires Internet ?

CSci4211: Introduction 18

Internet: Building Blocks

• Nodes: PCs, special-purpose hardware, …

– Hosts (or end systems): servers, PCs, laptops, mobile devices, smart meters, …… – Switches: routers, switches, …

• Links: coax cable, optical fiber, wireless, …

– point-to-point – multiple access

…

CSci4211: Introduction 19

Inter-networking

– two or more nodes connected by a link, or – two or more networks connected by two or more nodes

• A network can be defined recursively as...
• Internet: networks of networks

1: Introduction

20

Physical Media

• physical link:

transmitted data bit propagates across link

• guided media:

– signals propagate in solid media: copper, fiber

• unguided media:

– signals propagate freelye.g., radio

Twisted Pair (TP)

• two insulated copper

wires

– Category 3: traditional phone wires, 10 Mbps ethernet – Category 5 TP: 100Mbps ethernet

1: Introduction

21

Physical Media: coax, fiber

Coaxial cable:

• wire (signal carrier)

within a wire (shield)

– baseband: single channel

• n cable

– broadband: multiple channel on cable

• bidirectional
• common use in 10Mbs

Ethernet

Fiber optic cable:

 glass fiber carrying

light pulses

 high-speed operation:

 100Mbps Ethernet  high-speed point-to-point

transmission (e.g., 5 Gps)  low error rate

1: Introduction

22

Physical media: radio

• signal carried in

electromagnetic spectrum

• no physical “wire”
• bidirectional
• propagation

environment effects:

– reflection – obstruction by objects – interference

Radio link types:

 microwave

 e.g. up to 45 Mbps channels

 LAN (e.g., waveLAN)

 2Mbps, 11Mbps

 wide-area (e.g., cellular)

 e.g. CDPD, 10’s Kbps

 satellite

 up to 50Mbps channel (or

multiple smaller channels)

 270 Msec end-end delay  geosynchronous versus

LEOS

CSci4211: Introduction 23

Service Perspective

Basic Services Provided



Postal: deliver mail/package from people to people



First class, express mail, bulk rate, certified, registered, … 

Telephone: connect people for talking



You may get a busy dial tone



Once connected, consistently good quality, unless using cell phones 

Internet: transfer information between people/machines



Reliable connection-oriented or unreliably connectionless services!



You never get a busy dial tone, but things can be very slow!



You can’t ask for express delivery (not at the moment at least!)

CSci4211: Introduction 24

Fundamental Issues in Networking

Network is a shared resource

– Provide services for many people at same time – Carry bits/information for many people at same time

• Switching and Multiplexing

– How to share resources among multiple users, and transfer data from one node to another node

• Naming and Addressing

– How to find name/address of the party (or parties) you would like to communicate with – Address: byte-string that identifies a node

• unicast, multicast and broadcast addresses
• Routing and (end-to-end) Forwarding:

– Routing: process of determining how to send packets towards the destination based on its address

• find out neighbors, build “maps” (routing tables), …

– transfer data from source to destination “hop-by-hop”

CSci4211: Introduction 25

What’s so special about the Internet?

• Internet is based on the notion of “packet switching”

– enables statistical multiplexing

– better utilization of network resources for transfer of

“bursty” data traffic

CSci4211: Introduction 26

Switching & Multiplexing

• Network is a shared resource

– Provide services for many people at same time – Carry bits/information for many people at same time

• How do we do it?

– Switching: how to deliver information from point A to point B? – Multiplexing: how to share resources among many users Think about postal service and telephone system!

Switching and multiplexing are closely related!

CSci4211: Introduction 27

Switching Strategies

• Circuit switching

– set up a dedicated route (“circuit”) first – carry all bits of a “conversation” on one circuit

• original telephone network
• Analogy: railroads and trains/subways
• Packet switching

– divide information into small chunks (“packets”) – each packet delivered independently – “store-and-forward” packets

• Internet

(also Postal Service, but they don’t tear your mail into pieces first!)

• Analogy: highways and cars
• Pros and Cons?
• think taking subways vs. driving cars, during off-peak vs. rush hours!

Analogy: railroad and train

CSci4211: Introduction 28

Analogy: Highway and cars

CSci4211: Introduction 29

Circuit Switching

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

• pieces allocated to calls
• resource piece idle if

not used by owning call (no sharing)

 dividing link bandwidth

into “pieces”

 frequency division  time division  code division

 Trivia Q: You must have heard of the term “CDMA” (think the company Qualcom, for which it is most associated with), what does “CD” in CDMA stands for?

CSci4211: Introduction 30

Circuit Switching: FDM and TDM

FDM frequency time TDM frequency time 4 users Example:

CSci4211: Introduction 31

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 links are 1.536 Mbps – Each link uses TDM with 24 slots/sec – 500 msec to establish end-to-end circuit

Let’s work it out!

10.5 seconds

CSci4211: Introduction 32

Networks with Circuit Switching

e.g., conventional (fixed-line) telephone networks

End-end resources reserved for “call”

• link bandwidth, switch

capacity

• dedicated resources:

no sharing

• circuit-like

(guaranteed) performance

• call setup required

CSci4211: Introduction 33

CSci4211: Introduction 34

Circuit Switched Networks

• All resources (e.g. communication links) needed by

a call dedicated to that call for its duration

– Example: telephone network – Call blocking when all resources are used

Packet Switching

Each end-end “data stream” divided into packets

• users A, B packets share

network resources

• 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

 Node receives complete

packet before forwarding

 Packets may suffer delay or

losses!

Bandwidth division into “pieces” Dedicated allocation Resource reservation

35 CSci4211: Introduction

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Statistical Multiplexing

• Time division, but on demand rather than fixed
• Reschedule link on a per-packet basis
• Packets from different sources interleaved on the link
• Buffer packets that are contending for the link
• Buffer buildup is called congestion
• This is packet switching, used in computer networks

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. A B C

100 Mb/s Ethernet 1.5 Mb/s

D E

statistical multiplexing

queue of packets waiting for output link

37 CSci4211: Introduction

Packet-switching: store-and-forward

• Takes L/R seconds to

transmit (push out) packet of L bits on to link or R bps

• Entire packet must

arrive at router before it can be transmitted

• n next link: store and

forward

• delay = 3L/R (assuming

zero propagation delay) Example:

• L = 7.5 Mbits
• R = 1.5 Mbps
• delay = ?

R R R L more on delay later …

15 sec

CSci4211: Introduction 38

Packet switching versus circuit switching

• 1 Mb/s link
• each user:

– 100 kb/s when “active” – active 10% of time

• circuit-switching:

– 10 users

• packet switching:

– with 35 users, probability > 10 active less than .0004

Packet switching allows more users to use network! N users 1 Mbps link

Q: how did we get value 0.0004?

 



  

        

M N n n M n

p p n M

1

1

CSci4211: Introduction 39

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Circuit Switching vs Packet Switching

Item Circuit-switched Packet-switched

Dedicated “copper” path Yes No Bandwidth available Fixed Dynamic Potentially wasted bandwidth Yes No (not really!) Store-and-forward transmission No Yes Each packet/bit always follows the same route Yes Not necessarily Call setup Required Not Needed When can congestion occur At setup time On every packet Effect of congestion Call blocking Queuing delay

Packet switching vs. circuit switching

• Great for bursty data

– resource sharing – simpler, no call setup

• Excessive congestion: packet delay and loss

– protocols needed for reliable data transfer, congestion control

• Q: How to provide circuit-like behavior?

– bandwidth guarantees needed for audio/video apps – still an unsolved problem (chapter 7)

Is packet switching a “slam dunk winner?”

Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

CSci4211: Introduction 41

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What’s so special about the Internet?

• Internet is based on the notion of “packet switching”

– enables statistical multiplexing

– better utilization of network resources for transfer of

“bursty” data traffic

• Internet’s key organizational/architectural principle:

“smart” end systems + “dumb” networks

– architecture: functional division & function placement – hourglass Internet architecture: enables diverse

applications and accommodates evolving technologies

– “dumb” network (core): simple packet-switched, store-

forward, connectionless “datagram” service, with core functions: global addressing, routing & forwarding

– “smart” end systems/edges: servers, PCs, mobile devices, …;

diverse and ever-emerging new applications!

CSci4211: Introduction 43

Internet Hourglass Architecture

WiFi, Bluetooth, Docsis, gMPLS, DWDM/fiber, …, 3G/4G cellular, …. p2p file sharing, skype, YouTube, Netflix, Cloud Computing bitTorrent, DHT, SIP, DASH, ….

enabling diverse applications & new types of end devices accommodating evolving & new technologies network core network edge/end hosts

44

“Dumb” Networks & “Smart” End Systems

• Five Layer Architecture:

– Lower three layers are implemented everywhere – Top two layers are implemented only at hosts Network Datalink Physical Network Datalink Physical Network Datalink Physical Physical medium Application Transport

Host A

Application Transport

Host B Router

CSci4211: Introduction

An Overview of Network Structure:

a “horizontal view”

• network edge:

applications and hosts

• network core:

– routers – network of networks

• access networks,

physical media: communication links

CSci4211: Introduction 45

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

• millions of connected

computing devices: hosts = end systems

• running network apps
• communication links

– fiber, copper, radio, satellite – transmission rate = bandwidth

• routers: forward packets

(chunks of data)

local ISP company network regional ISP router workstation server mobile

46 CSci4211: Introduction

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

• peer-peer model:

– minimal (or no) use of dedicated servers – e.g. Skype, BitTorrent, KaZaA

CSci4211: Introduction 47

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

– Cloud & Mobile Computing

• peer-peer model:

– minimal (or no) use of dedicated servers – e.g. Skype, BitTorrent, KaZaA cloud computing

CSci4211: Introduction 48

Network edge: connection-oriented service

Goal: data transfer

between end systems

• handshaking: setup

(prepare for) data transfer ahead of time

– Hello, hello back human protocol – set up “state” in two communicating hosts

• TCP - Transmission

Control Protocol

– Internet’s connection-

• riented service

TCP service [RFC 793]

• reliable, in-order byte-

stream data transfer

– loss: acknowledgements and retransmissions

• flow control:

– sender won’t overwhelm receiver

• congestion control:

– senders “slow down sending rate” when network congested

CSci4211: Introduction 49

Network edge: connectionless service

Goal: data transfer

between end systems

– same as before!

• UDP - User Datagram

Protocol [RFC 768]:

– connectionless – unreliable data transfer – no flow control – no congestion control

App’s using TCP:

• HTTP (Web), FTP (file

transfer), Telnet (remote login), SMTP (email), Flash videos, DASH stream videos

App’s using UDP:

• streaming media,

teleconferencing, DNS, Internet telephony

CSci4211: Introduction 50

The Network Core

• mesh of interconnected

routers shared by many users

• the fundamental questions:

– how network is shared – how to find the other party (person, website, …) you want – how is data transferred through net?

CSci4211: Introduction 51

On the Internet Edge …

Internet

home users banking & e-commerce dumb & smart phones POTS VoIP music streaming games surveillance & security

video streaming & IPTV

web

• Large # of (mobile &

stationary) users

• Large # of “dumb” or

smart devices & appliances

• Some “always-on,” high-

speed connection

• Others intermittent

connectivity with varying bandwidth

• Diverse applications

and services

• Heterogeneous

technologies

smart pads & e-readers

social networks sensors & smart home

• thers

CSci4211: Introduction 52

Within the Internet “Cloud”

Network Core:

• big ISPs (& cellular

providers) with large geographical span

• As well as medium & smaller

ISPs

And the “other end/edge”:

• big content providers with

huge data centers

• High bandwidth, dense and

rich topology

• Enormous computing &

storage capacities to support cloud, mobile computing/services

CSci4211: Introduction 53

Well, Internet is too complex for me to learn. How can they even build it? And what’s a protocol & why do we need protocols?

Motivating Questions 3-5

CSci4211: Introduction 54

Network Architecture

(or organizational principles)

Networks are complex!

• many “pieces”:

– hosts – routers – links of various media – hardware, software – applications – protocols – …..

Question:

Is there any hope of

• rganizing structure or

principle of network? Or at least our discussion of networks?

Network architecture:

“blue prints” (or principles) regarding functional division and function placement

CSci4211: Introduction 55

Organization 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

CSci4211: Introduction 56

ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing

departure airport arrival airport intermediate air-traffic control centers

airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing

ticket baggage gate takeoff/landing airplane routing

Layering of airline functionality

Layers: each layer implements a service

– via its own internal-layer actions – relying on services provided by layer below

CSci4211: Introduction 57

Why Layering?

Dealing with complex systems:

• explicit structure allows identification,

relationship of complex system’s pieces

– layered reference model for discussion

• modularization eases maintenance, updating of

system

– change of implementation of layer’s service transparent to rest of system – e.g., change in gate procedure doesn’t affect rest of system

CSci4211: Introduction 58

Internet Protocol Stack

• application: supporting network

applications

– FTP, SMTP, HTTP, DASH, …

• transport: process-process data

transfer

– TCP, UDP

• network: routing of datagrams from

source to destination

– IP, routing protocols

• link: data transfer between

neighboring network elements

– PPP, Ethernet

• physical: bits “on the wire”

application transport network link physical

CSci4211: Introduction 59

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Layered Architecture

• Layering simplifies the architecture of

complex system

• Layer N relies on services from layer

N-1 to provide a service to layer N+1

• Interfaces define the services offered
• Service required from a lower layer is

independent of its implementation – Layer N change doesn’t affect

• ther layers

– Information/complexity hiding – Similar to object oriented methodology

CSci4211: Introduction 61

Protocols and Services

• Protocols are used to implement services

– Peering entities in layer N provide service by communicating with each other using the service provided by layer N-1

• Logical vs physical communication

What’s a protocol?

human protocols:

• “what’s the time?”
• “I have a question”
• introductions

network protocols:

• machines rather than

humans

• all communication

activity in Internet governed by protocols (why this concept is so important!!!)

CSci4211: Introduction 62

Make sure Bob is awake Bob can speak English Bob can understand English Bob is willing to talk

1. 3 2 4

Human protocol

• protocols define:

– Format. – Order of msgs sent and received among network entities (two or more) – Actions taken on msg transmission, receipt

Hi Hi

Got the time?

Alice Bob

Q: What are the purposes of first hi-hi exchange

2:00pm

CSci4211: Introduction 63

What’s a protocol?

a human protocol and a computer network protocol: Q: Other human protocols? (e.g., in-class interaction) Hi Hi

Got the time?

2:00

TCP connection request TCP connection response

Get http://www.cnn.com

<file> time

CSci4211: Introduction 64

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Protocols

• Protocol: rules by which network elements communicate
• Protocols define the agreement between peering entities

– The format and the meaning of messages exchanged

• Protocols in everyday life

– Examples: traffic control, open round-table discussion etc

CSci4211: Introduction 66

Protocol Packets

• Protocol data units (PDUs):

– packets exchanged between peer entities

• Service data units (SDUs):

– packets handed to a layer by an upper layer

• Data at one layer is encapsulated in packet at a lower layer

– Envelope within envelope: PDU = SDU + (optional) header or trailer

source

application transport network link physical

Ht Hn M

segment

Ht

datagram

destination

application transport network link physical

Ht Hn Hl M Ht Hn M Ht M M

network link physical link physical

Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M

router switch

Encapsulation

message

M Ht M Hn

frame

CSci4211: Introduction 67

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Internet and ISO/OSI Reference Models

CSci4211: Introduction 69

ISO/OSI Reference Model

• Application layer
• Examples: smtp, http, ftp, dash, etc

– process-to-process communication – all layers exist to support this layer

• Presentation layer (OSI only)

– conversion of data to common format

• Example: “little endian” vs. “big endian” byte orders

– multimedia streaming presentation (e.g., mpeg-dash)

• Session layer (OSI only)

– session setup (and authentication) – recovery from failure (broken session)

• Internet applications perform presentation/session

layer functions, e.g., “little” & “big” endian conversions

CSci4211: Introduction 70

ISO/OSI Reference Model (cont’d)

• Transport layer: end-to-end data delivery, e.g.,

– connection-oriented (TCP) or connection-less (UDP) services – error control, flow/congestion control, …

• Network layer: examples: IP, X.25

– (global) naming and addressing, routing (build routing tables) – forwarding packets hop-by-hop across networks – avoidance of congested/failed links, traffic engineering, …

• Data link layer: data transfer between “neighboring”

elements – Examples: Ethernet, 802.11 WiFi, PPP – framing and error/flow control – media access control

• Physical layer (EE stuff)

– encoding/decoding information (bits) into physical media – modulating & transmitting raw bits (0/1) over wire

CSci4211: Introduction 71

Comments on Layering

• Layering simplifies the architecture of complex system
• Advantages

– modularization eases maintenance and updating – hide lower layer complexity/implementation details from higher layers

• Layering considered harmful?

– Q: which layer should implement what functionality?

• e.g., reliability, hop-by-hop basis or end-to-end basis?
• Possible Drawbacks?

– possible duplication of functionality between layers

• error recovery at link layer and transport layer

– Other possible drawbacks?

CSci4211: Introduction 72

Internet Protocol “Zoo”

applicatio n

SMTP

telnet, ssh

NFS/RPC

FTP, SCP

DNS HTTP

RealAudio RealVideo

802.11 WiFi

Flash DASH SOAP

….. …..

VoIP IPTV

2.5G/3G/4G (GPRS,UMTS, WiMAX, LTE, …) Cellular Radio Networks DWDM MPLS/gMPLS

DSL or DOCSIS PPP

ICMP, OSPF, RIP, BGP, …

P2P

What real Internet looks like now?

CSci4211: Introduction 73

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Internet Structure

LANs International lines

Regional or local ISP

local ISPs

company university

National or tier-1 ISP National or tier-1 ISP IXPs

• r private peering

Regional ISPs

company

access via WiFi hotspots

Internet: “networks of networks”!

Home users

Internet eXcange Points

Home users

Internet structure: network of networks

• Roughly hierarchical
• At center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,

L3, Cable and Wireless), national/international coverage

– treat each other as equals

Tier 1 ISP Tier 1 ISP Tier 1 ISP

Tier-1 providers interconnect (peer) privately

IXP

Tier-1 providers also interconnect at Internet Exchange Point

CSci4211: Introduction 75

Tier-1 ISP: e.g., Sprint

…

to/from customers peering to/from backbone

… . … … …

POP: point-of-presence

CSci4211: Introduction 76

Internet structure: network of networks

• “Tier-2” ISPs: smaller (often regional) ISPs

– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP Tier 1 ISP Tier 1 ISP

IXP

Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet

 tier-2 ISP is

customer of tier-1 provider Tier-2 ISPs also peer privately with each other, interconnect at IXP

CSci4211: Introduction 77

Internet structure: network of networks

• “Tier-3” ISPs and local ISPs

– last hop (“access”) network (closest to end systems)

Tier 1 ISP Tier 1 ISP Tier 1 ISP

IXP

Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest

• f Internet

CSci4211: Introduction 78

Internet structure: network of networks

• a packet passes through many networks!

Tier 1 ISP Tier 1 ISP Tier 1 ISP

IXP

Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

traceroute www.cnn.com

CSci4211: Introduction 79

Routing & forwarding: how do packets go from A to B?

B A

Map of Internet

Why it takes so long to download my friends’ pictures from web? Or why $#@! can’t I access the Internet now?

Motivating Question 6

CSci4211: Introduction 81

CSci4211: Introduction 82

Fundamental Problems in Networking …

Or what can go wrong?

• Bit-level errors: due to electrical interferences
• “Frame-level” errors: media access delay or frame

collision due to contention/collision/interference

• Packet-level errors: packet delay or loss due to

network congestion/buffer overflow

• Out of order delivery: packets may takes

different paths

• Link/node failures: cable is cut or system crash

Four sources of packet delay

• 1. nodal processing:
• check bit errors
• determine output link

A B

propagation transmission nodal processing queueing

• 2. queueing
• time waiting at output link

for transmission

• depends on congestion level
• f router

CSci4211: Introduction 83

CSci4211: Introduction 84

Delay in packet-switched networks

• 3. Transmission delay:
• R=link bandwidth (bps)
• L=packet length (bits)
• time to send bits into

link = L/R

• 4. Propagation delay:
• d = length of physical link
• s = propagation speed in

medium (~2x108 m/sec)

• propagation delay = d/s

A B

propagation transmission nodal processing queueing

Note: s and R are very different quantitites!

Nodal delay

• dproc = processing delay

– typically a few microsecs or less

• dqueue = queuing delay

– depends on congestion

• dtrans = transmission delay

– = L/R, significant for low-speed links

• dprop = propagation delay

– a few microsecs to hundreds of msecs

prop trans queue proc nodal

d d d d d    

CSci4211: Introduction 85

CSci4211: Introduction 86

Statistical Multiplexing and Queueing

A B C

10 Mbs Ethernet 1.5 Mbs 45 Mbs

D E

statistical multiplexing

queue of packets waiting for output link

CSci4211: Introduction 87

Queueing delay (revisited)

• R=link bandwidth (bps)
• L=packet length (bits)
• a=average packet

arrival rate traffic intensity = La/R

• La/R ~ 0: average queueing delay small
• La/R -> 1: delays become large
• La/R > 1: more “work” arriving than can be

serviced, average delay infinite!

Queueing delay and Packet loss

• Queue (aka buffer) preceding link in

buffer has finite capacity

• When packet arrives to full queue, packet

is dropped (aka lost)

• lost packet may be retransmitted by

previous node, by source end system, or not retransmitted at all

CSci4211: Introduction 88

“Real” Internet delays and routes

• What do “real” Internet delay & loss look like?
• Traceroute program: provides delay

measurement from source to router along end-end Internet path towards destination. For all i:

– sends three packets that will reach router i on path towards destination – router i will return packets to sender – sender times interval between transmission and reply.

3 probes 3 probes 3 probes

CSci4211: Introduction 89

“Real” Internet delays and routes

Let’s Traceroute to www.bbc.com

CSci4211: Introduction 90

Throughput

• throughput: rate (bits/time unit) at which

bits transferred between sender/receiver

– instantaneous: rate at given point in time – average: rate over longer period of time server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec pipe that can carry fluid at rate Rs bits/sec) pipe that can carry fluid at rate Rc bits/sec) server sends bits (fluid) into pipe

CSci4211: Introduction 91

Throughput (cont’d)

• Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

 Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

link on end-end path that constrains end-end throughput bottleneck link

CSci4211: Introduction 92

Throughput: Internet scenario

10 connections (fairly) share backbone bottleneck link R bits/sec Rs Rs Rs Rc Rc Rc R

• per-connection

end-end throughput: min(Rc,Rs,R/10)

• in practice: Rc or

Rs is often bottleneck

CSci4211: Introduction 93

What’s the Internet: Recap

• protocols control sending,

receiving of messages

– e.g., TCP, IP, HTTP, FTP, PPP

• Internet: “network of

networks”

– loosely hierarchical – public Internet versus private intranet

• Internet standards

– RFC: Request for comments – IETF: Internet Engineering Task Force – IEEE local ISP company network regional ISP router workstation server mobile

CSci4211: Introduction 94

CSci4211: Introduction 95

Fundamental Issues in Networking

Network is a shared resource

– Provide services for many people at same time – Carry bits/information for many people at same time

• Switching and Multiplexing

– How to share resources among multiple users, and transfer data from one node to another node

• Naming and Addressing

– How to find name/address of the party (or parties) you would like to communicate with – Address: byte-string that identifies a node

• unicast, multicast and broadcast addresses
• Routing and Switching/Forwarding:

– process of determining how to send packets towards the destination based on its address: finding out neighbors, building routing tables – transferring data from source to destination

CSci4211: Introduction 96

Fundamental Problems in Networking …

Or what can go wrong?

• Bit-level errors: due to electrical interferences
• “Frame-level” errors: media access delay or frame

collision due to contention/collision/interference

• Packet-level errors: packet delay or loss due to

network congestion/buffer overflow

• Out of order delivery: packets may takes

different paths

• Link/node failures: cable is cut or system crash

CSci4211: Introduction 97

Fundamental Problems in Networking

What can be done?

• Add redundancy to detect and correct erroneous

packets

• Acknowledge received packets and retransmit lost

packets

• Assign sequence numbers and reorder packets at

the receiver

• Sense link/node failures and route around failed

links/nodes Goal: to fill the gap between what applications expect and what underlying technology provides

CSci4211: Introduction 98

The Internet Network layer

routing table

Routing protocols

• path selection
• RIP, OSPF, BGP

IP protocol

• addressing conventions
• packet handling conventions

ICMP protocol

• error reporting
• router “signaling”

Transport layer: TCP, UDP Data Link layer (Ethernet, WiFi, PPP, …) Physical Layer (fiber optics, radio, …)

Network layer

Introduction: Summary

Answers to 6 motivating questions

• What is internet? What so

special about it?

• What internet looks like now?
• How I deal with the complexity?
• What’s a protocol?
• How I build a network?
• Why do I suffer delays?

You now have:

• context, overview,

“feel” of networking

• more depth, detail

to follow!

CSci4211: Introduction 99

CSci4211: Introduction 100

Internet Summary

• Computer networks/Internet use packet switching
• Layered architecture for handling complexity &

attaining maintainability

– Key notions: protocols, services and interfaces

• Internet is based on TCP/IP protocol suite

– Networks of networks! – Shared, distributed and complex system in global scale – No centralized authority

• Fundamental issues in networking

– addressing/naming – routing/forwarding – error/flow/congestion control, media access control

CSci4211: Introduction 101

Readings for Next Week

• Read Chapter 1
• Review these lecture notes

– Read the supplementary notes that follow these one if you have time

• Read Chapter 2: sections 2.1 –2.6

– Learn how web works – Learn how email works – Understand what Domain Name System does for us – P2P File Sharing – Glance through Chapter 7: sections 7.1-7.2

CSci4211: Introduction 102

Supplementary Readings

• Physical Media
• Access Network Technologies
• History of Internet
• Internet “Governing” Bodies
• Network Security: Cyber Attacks

Access networks and physical media

Q: How to connect end systems to edge router?

• residential access nets
• institutional access

networks (school, company)

• mobile access networks

keep in mind:

• bandwidth (bits per

second) of access network?

• shared or dedicated?

CSci4211: Introduction 98

Physical media

• bit: propagates between

transmitter/receiver 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 5: 100 Mbps, 1

Gbps Ethernet

• Category 6: 10Gbps

CSci4211: Introduction 99

Host: sends packets of data

host sending function:

• takes application message
• breaks into smaller chunks,

known as packets, of length L bits

• transmits packet into

access network at transmission rate R

• link transmission rate,

aka link capacity, aka link bandwidth

R: link transmission rate

host

1 2

two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link

L (bits) R (bits/sec) = =

CSci4211: Introduction 100

Physical media: coax, fiber

coaxial cable:

• two concentric copper

conductors

• bidirectional
• broadband:
• multiple channels on cable
• HFC

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 Gbps transmission rate)

• low error rate:
• repeaters spaced far apart
• immune to electromagnetic

noise

CSci4211: Introduction 101

CSci4211: Introduction 107

Physical media: radio

• signal carried in

electromagnetic spectrum

• no physical “wire”
• bidirectional
• propagation

environment effects:

– reflection –

• bstruction by objects

– interference

Radio link types:

• microwave

– e.g. up to 45 Mbps channels

• LAN (e.g., waveLAN)

– 2Mbps, 11Mbps

• wide-area (e.g., cellular)

– e.g. CDPD, 10’s Kbps

• satellite

– up to 50Mbps channel (or multiple smaller channels) – 270 Msec end-end delay – geosynchronous versus LEOS

1: Introduction

108

1: Introduction

109

1: Introduction

110

1: Introduction

111

1: Introduction

112

1: Introduction

113

1: Introduction

114

A closer look at network structure:

• network edge:
• hosts: clients and servers
• servers often in data

centers

• access networks, physical

media: wired, wireless communication links

• network core:
• interconnected routers
• network of networks

mobile network global ISP regional ISP home network institutional network

CSci4211: Introduction 103

telephone network Internet home dial-up modem ISP modem (e.g., AOL) home PC central

• ffice

 Uses existing telephony infrastructure  Home is connected to central office  up to 56Kbps direct access to router (often less)  Can’t surf and phone at same time: not “always on”

Residential access: Dial-up Modem

CSci4211: Introduction 116

ISP

Access network: digital subscriber line (DSL)

central office telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office

• use existing telephone line to central office DSLAM
• data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net
• < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
• < 24 Mbps downstream transmission rate (typically < 10 Mbps)

DSL modem splitter

DSL access multiplexer

CSci4211: Introduction 105

Access Network: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 118 CSci4211: Introduction

Access network: cable network

cable modem splitter

…

cable headend Channels

V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9

frequency division multiplexing: different channels transmitted in different frequency bands

CSci4211: Introduction 107

ISP

data, TV transmitted at different frequencies over shared cable distribution network

cable modem splitter

…

cable headend CMTS cable modem termination system

• HFC: hybrid fiber coax
• asymmetric: up to 30Mbps downstream transmission rate, 2

Mbps upstream transmission rate

• network of cable, fiber attaches homes to ISP router
• homes share access network to cable headend
• unlike DSL, which has dedicated access to central office

Access network: cable network

CSci4211: Introduction 108

Access network: home network

to/from headend or central office

cable or DSL modem router, firewall, NAT wired Ethernet (1 Gbps) wireless access point (54 Mbps)

wireless devices

• ften combined

in single box

CSci4211: Introduction 109

Enterprise access networks (Ethernet)

• typically used in companies, universities, etc.
• 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
• today, end systems typically connect into Ethernet switch

Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet)

CSci4211: Introduction 110

Wireless access networks

• shared wireless access network connects end system

to router

– via base station aka “access point”

wireless LANs:

• within building (100 ft.)
• 802.11b/g/n (WiFi): 11, 54, 450

Mbps transmission rate

wide-area wireless access

• provided by telco (cellular)
• perator, 10’s km
• between 1 and 10 Mbps
• 3G, 4G: LTE

to Internet to Internet

CSci4211: Introduction 111

• mesh of

interconnected routers

• packet-switching:

hosts break application-layer messages into packets

– forward packets from one router to the next, across links on path from source to destination – each packet transmitted at full link capacity

The network core

CSci4211: Introduction 112

CSci4211: Introduction 125

Origin of Internet?

Started by U.S. research/military organizations:

• Three Major Actors:

– DARPA: Defense Advanced Research Projects Agency

• funds technology with military goals

– DoD: U.S. Department of Defense

• early adaptor of Internet technology for

production use

– NSF: National Science Foundation

• funds university research

CSci4211: Introduction 126

Pre-Internet Modes of Human Telecommunications

The Dark Age before the Internet: before 1960

Non-electrical (source: wikipedia)

• Prehistoric: Fires, Beacons, Smoke signals, drums, Horns
• 6th century BCE: (snail) mail (e.g., delivered by human couriers on horse)
• 5th century BCE: Pigeon post
• 4th century BCE: Hydraulic semaphores, heliographs (shield signals)
• 15th century CE: Maritime flag semaphores
• 1672: First experimental acoustic (mechanical) telephone
• 1790: Semaphore lines (optical telegraphs)
• 1867: Signal lamps; 1877: Acoustic phonograph

Electrical:

• 1830: telegraph
• 1876: circuit-switching (telephone)
• 1896: radio
• TV (1940?) , and later cable TV (1970s)

Internet History

• 1961: Kleinrock - queueing

theory shows effectiveness of packet- switching

• 1964: Baran - packet-

switching in military nets

• 1967: ARPAnet conceived

by Advanced Research Projects Agency

• 1969: first ARPAnet node
• perational
• 1972:

– ARPAnet public demonstration – NCP (Network Control Protocol) first host-host protocol – first e-mail program – ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

CSci4211: Introduction 127

Internet History

• 1970: ALOHAnet satellite

network in Hawaii

• 1974: Cerf and Kahn -

architecture for interconnecting networks

• 1976: Ethernet at Xerox

PARC

• ate70’s: proprietary

architectures: DECnet, SNA, XNA

• late 70’s: switching fixed

length packets (ATM precursor)

• 1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles: – minimalism, autonomy - no internal changes required to interconnect networks – best effort service model – stateless routers – decentralized control define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets

CSci4211: Introduction 128

Internet History

• 1983: deployment of

TCP/IP

• 1982: smtp e-mail

protocol defined

• 1983: DNS defined

for name-to-IP- address translation

• 1985: ftp protocol

defined

• 1988: TCP congestion

control

• new national networks:

Csnet, BITnet, NSFnet, Minitel

• 100,000 hosts

connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

CSci4211: Introduction 129

Internet History

• Early 1990’s: ARPAnet

decommissioned

• 1991: NSF lifts restrictions on

commercial use of NSFnet (decommissioned, 1995)

• early 1990s: Web

– hypertext [Bush 1945, Nelson 1960’s] – HTML, HTTP: Berners-Lee – 1994: Mosaic, later Netscape – late 1990’s: commercialization of the Web

Late 1990’s – 2000’s:

• more killer apps: instant

messaging, P2P file sharing

• network security to forefront
• est. 50 million host, 100

million+ users

• backbone links running at

Gbps

• Napster, BitTorrent, …
• Myspace, Facebook, twitter,..
• YouTube, Netflix, Hulu, …

Now to the future:

• … (your invention here!)

1990, 2000’s: commercialization, the Web, new apps

CSci4211: Introduction 130

CSci4211: Introduction 131

Who Runs the Internet

“nobody” really!

• standards: Internet Engineering Task Force (IETF)
• names/numbers: The Internet Corporation for

Assigned Names and Numbers (ICANN)

• DNS root server operators, domain name registrars
• networks: ISPs (Internet Service Providers), IXPs

(Internet Exchange Points), ……

• fibers: telephone companies (mostly)
• content: companies, universities, governments,

individuals, …;

• content distribution networks, …

CSci4211: Introduction 132

Internet “Governing” Bodies

• Internet Society (ISOC): membership organization

– raise funds for IAB, IETF& IESG, elect IAB

• Internet Engineering Task Force (IETF):

– a body of several thousands or more volunteers –

• rganized in working groups (WGs)

– meet three times a year + email

• Internet Architecture Board

– architectural oversight, elected by ISOC

• Steering Group (IESG): approves standards,

– Internet standards, subset of RFC

• RFC: “Request For Comments”, since 1969

– most are not standards, also

• experimental, informational and historic(al)

CSci4211: Introduction 133

Internet Names and Addresses

• Internet Corporation for Assigned Names and

Numbers (ICAAN):

– coordinate IPv4 & IPv6 address spaces, keep track of numbers (e.g., protocol identifiers), delegates Internet address assignment to regional Internet registries – manage top-level domain names & operations of root name servers – designate authority for each top-level domain; create new TLDs

• Regional Internet Registries: AfriNIC, APNIC, ARIN,

LACMIC, RIPE NCC:

– manage the allocation and registration of Internet number resources

– e.g., hand out blocks of addresses to ISPs; assign AS numbers – maintain WHOIS registries – ….

Network security

• field of network security:

– how bad guys can attack computer networks – how we can defend networks against attacks – how to design architectures that are immune to attacks

• Internet not originally designed with

(much) security in mind

– original vision: “a group of mutually trusting users attached to a transparent network”  – Internet protocol designers playing “catch-up” – security considerations in all layers!

134

Bad guys: put malware into hosts via Internet

• malware can get in host from:

– virus: self-replicating infection by receiving/executing

• bject (e.g., e-mail attachment)

– worm: self-replicating infection by passively receiving

• bject that gets itself executed
• spyware malware can record keystrokes,

web sites visited, upload info to collection site

• infected host can be enrolled in botnet,

used for spam. DDoS attacks

135

target

Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic

• 1. select target
• 2. break into hosts around

the network (see botnet)

• 3. send packets to target from

compromised hosts

Bad guys: attack server, network infrastructure

136

Bad guys can sniff packets

packet “sniffing”:

• broadcast media (shared Ethernet, wireless)
• promiscuous network interface reads/records all packets

(e.g., including passwords!) passing by

A B C

src:B dest:A payload

• wireshark software used for end-of-chapter labs is a

(free) packet-sniffer

137

Bad guys can use fake addresses

IP spoofing: send packet with false source

address

A B C

src:B dest:A payload

138

… lots more on security (throughout, Chapter 8)