chapter 1: introduction

CSci4211: Introduction 1

Chapter 1: Introduction What is a Network? What is Internet?

Compared with postal service & telephone system Services provided “Nuts and Bolts” description

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!


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


Map of Internet

csci4211 Introduction

6

csci4211 Introduction

7

More gadgets are plugged in …• servers, desktops, laptops, …

High-tier

Low-tier

High Mobility Low MobilityWide Area

Local Area

Wireless technologies revolutionizing Internet! WiFi, bluetooth, 3/4G cellular networks, …

mobile computinglocation services

• smart mobile phones, iPads, e-readers, … • now TVs, thermostats, smart meters, etc., soon toasters, fridges, …


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 !



So what’s so special about the Internet?

But first, what is a Network?


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


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


Nuts and Bolts DescriptionNetwork 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 ?


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 …


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


Service PerspectiveBasic 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!)


Fundamental Issues in NetworkingNetwork 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”


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


Switching & Multiplexing• Network is a shared resource


• 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!


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


http://www.answers.com/main/Record2?a=NR&url=http://commons.wikimedia.org/wiki/Image:Railway%2520turnout%2520labelled.jpg

Analogy: Highway and cars


22

Circuit Switchingnetwork 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?


23

Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 users

Example:


24

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


Networks with Circuit Switchinge.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



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 SwitchingEach 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 allocationResource reservation

28CSci4211: Introduction


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

C100 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link


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 on next link: store and forward

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

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

R R RL

more on delay later …

15 sec


31

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

Nn

nMn ppn

M

1

1


32


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)?


34


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!


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

netw

ork

core

netw

ork

edge

/end

hos

ts

37

“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


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


38

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

companynetwork

regional ISP

router workstation

servermobile


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


40

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


41

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-

oriented 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


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


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?


44

On the Internet Edge …

InternetInternet home users

banking &e-commercedumb &

smart phones POTS

VoIP

musicstreaming 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

others


45

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


46

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


47

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 organizing structure or principle of network?

Or at least our discussion of networks?

Network architecture: “blue prints” (or principles) regarding

functional division and function placement


48

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


49

ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol 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


50

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


51

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


52


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

other layers– Information/complexity hiding– Similar to object oriented

methodology


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!!!)


55

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 thetime?

AliceBob

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

2:00pm


56

What’s a protocol?a human protocol and a computer network protocol:

Q: Other human protocols? (e.g., in-class interaction)

Hi

Hi

Got thetime?

2:00

TCP connection request

TCP connectionresponse

Get http://www.cnn.com

<file>time



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


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

sourceapplicatio

ntransportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hn

frame



Internet and ISO/OSI Reference Models


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


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


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?


Internet Protocol “Zoo”ap

plic

atio

n

SMTP telnet, ssh

NFS/RPC

FTP, SCP

DNSHTTP

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?



Internet Structure

LANs

International lines

Regional or local ISP local ISPs

company university

National or tier-1 ISP

National or tier-1 ISP

IXPsor private peering

Regional ISPs

company

access via WiFi hotspots

Internet: “networks of networks”!

Home users

Internet eXcangePoints

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


Tier-1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence



• “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 ISPTier-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 oftier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect at IXP



• “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

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

CSci4211: Introduction71


• a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

IXP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

traceroute www.cnn.com


Routing & forwarding:how do packets gofrom 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



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

nodalprocessing queueing

2. queueing•time waiting at output link for transmission •depends on congestion level of router



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

nodalprocessing 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

proptransqueueprocnodal ddddd



Statistical Multiplexing and Queueing

A

B

C10 MbsEthernet

1.5 Mbs

45 Mbs

D E

statistical multiplexing

queue of packetswaiting for output

link


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


“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


“Real” Internet delays and routes

Let’s Traceroute to www.bbc.com


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, withfile 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 carryfluid at rate

Rc bits/sec)

server sends bits

(fluid) into pipe


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


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


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

companynetwork

regional ISP

router workstation

servermobile



Fundamental Issues in NetworkingNetwork is a shared resource


•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


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


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/nodesGoal: to fill the gap between what applications

expect and what underlying technology provides


The Internet Network layer

routingtable

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, …)

Networklayer

Introduction: SummaryAnswers 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!



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


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


Supplementary Readings

• How big is Internet, Who pays for it?• Access Network Technologies • NAPs, Private Peering and ISPs• Internet “Governing” Bodies• History of Internet

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



Physical Media

• physical link: transmitted data bit propagates across link

• guided media: – signals propagate in

solid media: copper, fiber

• 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 TP: 100Mbps Ethernet


Physical Media: coax, fiber

Coaxial cable:• wire (signal carrier)

within a wire (shield)– baseband: single channel

on 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


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


Access networks

Q: How to connection 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?

telephonenetwork Internet

homedial-upmodem

ISPmodem(e.g., AOL)

homePC

central office

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


telephonenetwork

DSLmodem

homePC

homephone

Internet

DSLAM

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

splitter

centraloffice

Residential access: Digital Subscriber Line (DSL)

Also uses existing telephone infrastruture 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


Residential access: cable modems

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

upstream

• Network of cable and fiber attaches homes to ISP router– homes share access to router

• Deployment: available via cable TV companies– Comcast triple play: Internet, vioce and TV


Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html104CSci4211: Introduction

Physical Media used in HFC

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-to-point

transmission (e.g., 10’s-100’s Gps)

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


Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes



home

cable headend

cable distributionnetwork (simplified)



home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM:


100 Mbps

100 Mbps

100 Mbps1 Gbps

server

Ethernetswitch

Institutionalrouter

To Institution’sISP

Ethernet Internet access

• Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into Ethernet switch


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 Mbps

• wider-area wireless access– provided by telco operator– ~1Mbps over cellular system (3G)– next up (?): WiMAX (10’s Mbps) over wide

area and LTE (100’s Mbps)

• satellite– Kbps to 45Mbps channel (or multiple smaller

channels)– 270 msec end-end delay– geosynchronous versus low altitude

basestation

mobilehosts

router


Case Study: Home networks

Typical home network components: • DSL or cable modem• router/firewall/NAT• Ethernet• wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet



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


Pre-Internet Modes of Human Telecommunications

The Dark Age before the Internet: before 1960Non-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 phonographElectrical:• 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 operational

• 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


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


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


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



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, …


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– organized 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)


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– ….

chapter 1: introduction

Documents

network compare internet

networks of networks

real internet look

nodesa network

information service

types of networks

links postal

kinds of information