CS计算机代考程序代写 dns Java FTP algorithm PowerPoint Presentation

PowerPoint Presentation

Introduction: 1-1
Chapter 1
Introduction
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All material copyright 1996-2020
J.F Kurose and K.W. Ross, All Rights Reserved
Computer Networking: A Top-Down Approach
8th edition
Jim Kurose, Keith Ross
Pearson, 2020

Version History

7.2 (January 2020)
All slides reformatted for 16:9 aspect ratio
Use of Calibri font, rather that Gill Sans MT
Updated slide content for 2020 link technologies and applications
Add more animation throughout
New Master slide
Feb. 2020 (8.0)
a few updates suggest by Catherine Rosenberg (thanks!)
titles in a lighter font
Sept 2020 (8.1)
Added ~7 new slides, in particular: data center slide; routing versus forwarding; security line of defense; several on encapsulation and layers (this section is a lot better now). Other relative minor changes throughout

Chapter 1: introduction
Chapter goal:
Get “feel,” “big picture,” introduction to terminology
more depth, detail later in course
Overview/roadmap:
What is the Internet? What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Protocol layers, service models
Security
History

Introduction: 1-2

Internet

The Internet: a “nuts and bolts” view

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network
Packet switches: forward packets (chunks of data)
routers, switches

Communication links
fiber, copper, radio, satellite
transmission rate: bandwidth

Billions of connected computing devices:
hosts = end systems
running network apps at Internet’s “edge”

Networks
collection of devices, routers, links: managed by an organization

Introduction: 1-3

“Fun” Internet-connected devices

Web-enabled toaster +
weather forecaster

Internet phones

Slingbox: remote
control cable TV
Security Camera

IP picture frame

Internet
refrigerator

Tweet-a-watt:
monitor energy use

sensorized,
bed
mattress

Amazon Echo
Others?

Pacemaker & Monitor

AR devices

Fitbit

Gaming devices

cars
scooters
bikes
Introduction: 1-4

Internet: “network of networks”
Interconnected ISPs

The Internet: a “nuts and bolts” view

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

protocols are everywhere
control sending, receiving of messages
e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet

Ethernet
HTTP
Skype
IP
WiFi
4G
TCP
Streaming
video
Internet standards
RFC: Request for Comments
IETF: Internet Engineering Task Force

Introduction: 1-5

Infrastructure that provides services to applications:
Web, streaming video, multimedia teleconferencing, email, games, e-commerce, social media, inter-connected appliances, …

The Internet: a “services” view

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

HTTP
Skype
Streaming
video
provides programming interface to distributed applications:
“hooks” allowing sending/receiving apps to “connect” to, use Internet transport service
provides service options, analogous to postal service

Introduction: 1-6

What’s a protocol?
Human protocols:
“what’s the time?”
“I have a question”
introductions
Network protocols:
computers (devices) rather than humans
all communication activity in Internet governed by protocols
Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

Rules for:
… specific messages sent
… specific actions taken when message received, or other events
Introduction: 1-7

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

Q: other human protocols?

Got the
time?

2:00

time

TCP connection
response

TCP connection
request

GET http://gaia.cs.umass.edu/kurose_ross
Introduction: 1-8

Explain important points
distributed entities, exchanging messages (governed by protocols)
Time going down
go over definition of protocol (showing format, order of messages sent and received, and actions taken)
We’ll see these kinds of diagrams a lot

Chapter 1: roadmap
Introduction: 1-9
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

A closer look at Internet structure

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Network edge:
hosts: clients and servers
servers often in data centers

Introduction: 1-10

A closer look at Internet structure

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Network edge:
hosts: clients and servers
servers often in data centers
Access networks, physical media:
wired, wireless communication links

Introduction: 1-11

A closer look at Internet 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
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Introduction: 1-12

Access networks and physical media

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Q: How to connect end systems to edge router?
residential access nets
institutional access networks (school, company)
mobile access networks (WiFi, 4G/5G)

Introduction: 1-13

Access networks: cable-based access

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

C
O
N
T
R
O
L

1
2
3
4
5
6
7
8
9

frequency division multiplexing (FDM): different channels transmitted in different frequency bands

Introduction: 1-14

Access networks: cable-based access

cable
modem
splitter

…

cable headend

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

HFC: hybrid fiber coax
asymmetric: up to 40 Mbps – 1.2 Gbps downstream transmission rate, 30-100 Mbps upstream transmission rate
network of cable, fiber attaches homes to ISP router
homes share access network to cable headend

cable modem
termination system
CMTS

ISP

Introduction: 1-15

ISP

Access networks: 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
24-52 Mbps dedicated downstream transmission rate
3.5-16 Mbps dedicated upstream transmission rate

DSL
modem
splitter

DSL access
multiplexer

Introduction: 1-16

Access networks: home networks

to/from headend or central office

cable or DSL modem

router, firewall, NAT

wired Ethernet (1 Gbps)

WiFi wireless access
point (54, 450 Mbps)
Wireless and wired
devices

often combined
in single box

Introduction: 1-17

Wireless access networks
Shared wireless access network connects end system to router
via base station aka “access point”
Wireless local area networks (WLANs)
typically within or around building (~100 ft)
802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate

to Internet

Wide-area cellular access networks
provided by mobile, cellular network operator (10’s km)
10’s Mbps
4G cellular networks (5G coming)

Introduction: 1-18

Access networks: enterprise networks
companies, universities, etc.
mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly)
Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps
WiFi: wireless access points at 11, 54, 450 Mbps

Ethernet
switch

institutional mail,
web servers
institutional router

Enterprise link to
ISP (Internet)

Introduction: 1-19

Access networks: data center networks
high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org)
Introduction: 1-20

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)
=
=
Introduction: 1-21

Links: 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 Ethernet

Introduction: 1-22

Links: physical media
Coaxial cable:
two concentric copper conductors
bidirectional
broadband:
multiple frequency channels on cable
100’s Mbps per channel

Fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point transmission (10’s-100’s Gbps)
low error rate:
repeaters spaced far apart
immune to electromagnetic noise

Introduction: 1-23

Links: physical media
Wireless radio
signal carried in various “bands” in electromagnetic spectrum
no physical “wire”
broadcast, “half-duplex” (sender to receiver)
propagation environment effects:
reflection
obstruction by objects
Interference/noise
Radio link types:
Wireless LAN (WiFi)
10-100’s Mbps; 10’s of meters
wide-area (e.g., 4G cellular)
10’s Mbps over ~10 Km
Bluetooth: cable replacement
short distances, limited rates
terrestrial microwave
point-to-point; 45 Mbps channels
satellite
up to 45 Mbps per channel
270 msec end-end delay
Introduction: 1-24

Chapter 1: roadmap
Introduction: 1-25
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

The network core
mesh of interconnected routers
packet-switching: hosts break application-layer messages into packets
network forwards packets from one router to the next, across links on path from source to destination

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Introduction: 1-26

Two key network-core functions

1
2
3

0111
destination address in arriving
packet’s header

routing algorithm

header value
output link

0100
0101
0111
1001
3
2
2
1

local forwarding table

Forwarding:
aka “switching”
local action: move arriving packets from router’s input link to appropriate router output link

local forwarding table

Routing:
global action: determine source-destination paths taken by packets
routing algorithms

routing algorithm

Introduction: 1-27

routing
Introduction: 1-28

forwarding

forwarding
Introduction: 1-29

Packet-switching: store-and-forward
packet transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps
store and forward: entire packet must arrive at router before it can be transmitted on next link

source

R bps

destination
1
2
3

L bits
per packet
R bps

One-hop numerical example:
L = 10 Kbits
R = 100 Mbps
one-hop transmission delay = 0.1 msec
Introduction: 1-30

Packet-switching: queueing

A
B
C
R = 100 Mb/s
R = 1.5 Mb/s

D
E
queue of packets
waiting for transmission over output link

Queueing occurs when work arrives faster than it can be serviced:

Introduction: 1-31

Packet-switching: queueing

A
B
C
R = 100 Mb/s
R = 1.5 Mb/s

D
E
queue of packets
waiting for transmission over output link

Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:
packets will queue, waiting to be transmitted on output link
packets can be dropped (lost) if memory (buffer) in router fills up

Introduction: 1-32

Alternative to packet switching: circuit switching
end-end resources allocated to, reserved for “call” between source and destination
in diagram, each link has four circuits.
call gets 2nd circuit in top link and 1st circuit in right link.
dedicated resources: no sharing
circuit-like (guaranteed) performance
circuit segment idle if not used by call (no sharing)

* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive
commonly used in traditional telephone networks

Introduction: 1-33

Circuit switching: FDM and TDM

frequency

time

frequency

time

4 users

Frequency Division Multiplexing (FDM)
optical, electromagnetic frequencies divided into (narrow) frequency bands

Time Division Multiplexing (TDM)
time divided into slots
each call allocated its own band, can transmit at max rate of that narrow band

each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s)
Introduction: 1-34

Packet switching versus circuit switching
example:
1 Gb/s link
each user:
100 Mb/s when “active”
active 10% of time

Q: how many users can use this network under circuit-switching and packet switching?
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive

N
users
1 Gbps link

…..

circuit-switching: 10 users

Q: how did we get value 0.0004?
A: HW problem (for those with course in probability only)

packet switching: with 35 users, probability > 10 active at same time is less than .0004 *

Introduction: 1-35

Packet switching versus circuit switching
great for “bursty” data – sometimes has data to send, but at other times not
resource sharing
simpler, no call setup
excessive congestion possible: packet delay and loss due to buffer overflow
protocols needed for reliable data transfer, congestion control
Q: How to provide circuit-like behavior with packet-switching?
“It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible.
Is packet switching a “slam dunk winner”?
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)?
Introduction: 1-36

Internet structure: a “network of networks”
hosts connect to Internet via access Internet Service Providers (ISPs)
access ISPs in turn must be interconnected
so that any two hosts (anywhere!) can send packets to each other
resulting network of networks is very complex
evolution driven by economics, national policies

Let’s take a stepwise approach to describe current Internet structure

mobile network
home network
enterprise
network

national or global ISP

local or regional ISP
datacenter
network
content
provider
network

Internet structure: a “network of networks”
Question: given millions of access ISPs, how to connect them together?

access
net

access
net
…
…
…
…
…
…
Introduction: 1-38

…
…
…
…
…
Internet structure: a “network of networks”
Question: given millions of access ISPs, how to connect them together?

access
net

access
net
…
…
…
…
…
…
connecting each access ISP to each other directly doesn’t scale: O(N2) connections.
Introduction: 1-39

Internet structure: a “network of networks”
Option: connect each access ISP to one global transit ISP?
Customer and provider ISPs have economic agreement.

global
ISP

access
net

access
net
…
…
…
…
…
…
Introduction: 1-40

ISP A

ISP C

ISP B

Internet structure: a “network of networks”

access
net

access
net
…
…
…
…
…
…
But if one global ISP is viable business, there will be competitors ….

Introduction: 1-41

ISP A

ISP C

ISP B

Internet structure: a “network of networks”

access
net

access
net
…
…
…
…
…
…
But if one global ISP is viable business, there will be competitors …. who will want to be connected

IXP
peering link
Internet exchange point

IXP

Introduction: 1-42

ISP A

ISP C

ISP B

Internet structure: a “network of networks”

access
net

access
net
…
…
…
…
…
…
… and regional networks may arise to connect access nets to ISPs

IXP

access
net

regional ISP

access
net

Introduction: 1-43

ISP A

ISP C

ISP B

Internet structure: a “network of networks”

access
net

access
net
…
…
…
…
…
…
… and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users

IXP

access
net

Content provider network

regional ISP

Introduction: 1-44

Internet structure: a “network of networks”
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
At “center”: small # of well-connected large networks
“tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage
content provider networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs

Regional ISP
Regional ISP

Tier 1 ISP
Tier 1 ISP

IXP

Google

IXP

IXP
Introduction: 1-45

Chapter 1: roadmap
Introduction: 1-46
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

How do packet delay and loss occur?
packets queue in router buffers, waiting for turn for transmission
queue length grows when arrival rate to link (temporarily) exceeds output link capacity
packet loss occurs when memory to hold queued packets fills up

A
B

packet being transmitted (transmission delay)

packets in buffers (queueing delay)

free (available) buffers: arriving packets
dropped (loss) if no free buffers

Introduction: 1-47

Packet delay: four sources
dproc: nodal processing
check bit errors
determine output link
typically < microsecs dqueue: queueing delay time waiting at output link for transmission depends on congestion level of router propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission Introduction: 1-48 48 Packet delay: four sources propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission dtrans: transmission delay: L: packet length (bits) R: link transmission rate (bps) dtrans = L/R dprop: propagation delay: d: length of physical link s: propagation speed (~2x108 m/sec) dprop = d/s dtrans and dprop very different Introduction: 1-49 49 Caravan analogy car ~ bit; caravan ~ packet; toll service ~ link transmission toll booth takes 12 sec to service car (bit transmission time) “propagate” at 100 km/hr Q: How long until caravan is lined up before 2nd toll booth? time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr) = 1 hr A: 62 minutes toll booth toll booth (aka link) ten-car caravan (aka 10-bit packet) 100 km 100 km toll booth toll booth (aka link) toll booth Introduction: 1-50 50 Caravan analogy toll booth toll booth (aka router) ten-car caravan (aka 10-bit packet) 100 km 100 km suppose cars now “propagate” at 1000 km/hr and suppose toll booth now takes one min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at first booth? A: Yes! after 7 min, first car arrives at second booth; three cars still at first booth Introduction: 1-51 51 Packet queueing delay (revisited) a: average packet arrival rate L: packet length (bits) R: link bandwidth (bit transmission rate) La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large
La/R > 1: more “work” arriving is more than can be serviced – average delay infinite!

La/R ~ 0
La/R -> 1
traffic intensity = La/R
average queueing delay

1
service rate of bits
R
arrival rate of bits
L
a
.
:
“traffic
intensity”
Introduction: 1-52

“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:

3 probes
3 probes
3 probes

sends three packets that will reach router i on path towards destination (with time-to-live field value of i)
router i will return packets to sender
sender measures time interval between transmission and reply
Introduction: 1-53

Real Internet delays and routes
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.fr
* Do some traceroutes from exotic countries at www.traceroute.org
* means no response (probe lost, router not replying)
3 delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu

3 delay measurements
to border1-rt-fa5-1-0.gw.umass.edu

looks like delays decrease! Why?

trans-oceanic link

Introduction: 1-54

Packet loss
queue (aka buffer) preceding link in buffer has finite capacity

A
B
packet being transmitted

buffer
(waiting area)

* Check out the Java applet for an interactive animation (on publisher’s website) of queuing and loss

packet arriving to
full buffer is lost
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous node, by source end system, or not at all
Introduction: 1-55

Throughput
throughput: rate (bits/time unit) at which bits are being sent from sender to 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
server sends bits
(fluid) into pipe

pipe that can carry
fluid at rate
(Rs bits/sec)
pipe that can carry
fluid at rate
(Rc bits/sec)

Introduction: 1-56

Throughput

Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput?

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

Rs bits/sec

Rc bits/sec

Introduction: 1-57

Throughput: network scenario
10 connections (fairly) share backbone bottleneck link R bits/sec

Rs
Rs

Rc
Rc
R

per-connection end-end throughput: min(Rc,Rs,R/10)
in practice: Rc or Rs is often bottleneck
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/
Introduction: 1-58

Chapter 1: roadmap
Introduction: 1-59
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

Segue: from performance to security
59

Network security
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!
We now need to think about:
how bad guys can attack computer networks
how we can defend networks against attacks
how to design architectures that are immune to attacks
Introduction: 1-60

Bad guys: packet interception
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 our end-of-chapter labs is a (free) packet-sniffer

Introduction: 1-62

Bad guys: fake identity
IP spoofing: injection of packet with false source address

A
B
C

src:B dest:A payload
Introduction: 1-63

Bad guys: denial of service

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

Introduction: 1-64

Lines of defense:
authentication: proving you are who you say you are
cellular networks provides hardware identity via SIM card; no such hardware assist in traditional Internet
confidentiality: via encryption
integrity checks: digital signatures prevent/detect tampering
access restrictions: password-protected VPNs
firewalls: specialized “middleboxes” in access and core networks:
off-by-default: filter incoming packets to restrict senders, receivers, applications
detecting/reacting to DOS attacks

… lots more on security (throughout, Chapter 8)
Introduction: 1-65

Chapter 1: roadmap
Introduction: 1-66
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

Protocol “layers” and reference models
Networks are complex,
with many “pieces”:
hosts
routers
links of various media
applications
protocols
hardware, software

Question: is there any hope of organizing structure of network?
and/or our discussion of networks?
Introduction: 1-67

Example: organization of air travel
a series of steps, involving many services
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing

How would you define/discuss the system of airline travel?
end-to-end transfer of person plus baggage

Introduction: 1-68

Example: organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing

airplane routing
ticketing service
baggage service
gate service
runway service

routing service
layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below

Introduction: 1-69

Why layering?
Approach to designing/discussing complex systems:
explicit structure allows identification, relationship of system’s pieces
layered reference model for discussion
modularization eases maintenance, updating of system
change in layer’s service implementation: transparent to rest of system
e.g., change in gate procedure doesn’t affect rest of system
Introduction: 1-70

Layered Internet protocol stack
application: supporting network applications
HTTP, IMAP, SMTP, DNS
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
Ethernet, 802.11 (WiFi), PPP
physical: bits “on the wire”

link

application
network
transport
physical

application

transport

network

link

physical
Introduction: 1-71

Services, Layering and Encapsulation
source

transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header Ht to create a transport-layer segment
Ht used by transport layer protocol to implement its service

application
transport
network
link
physical

destination

application
transport
network
link
physical
Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer

M
Application exchanges messages to implement some application service using services of transport layer

Introduction: 1-72

Services, Layering and Encapsulation
source

Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer

M
network-layer protocol encapsulates transport-layer segment [Ht | M] with network layer-layer header Hn to create a network-layer datagram
Hn used by network layer protocol to implement its service

application
transport
network
link
physical

destination

application
transport
network
link
physical

M
Ht
Hn
Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services
Introduction: 1-73

Services, Layering and Encapsulation
source

M
link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header Hl to create a link-layer frame

application
transport
network
link
physical

destination

application
transport
network
link
physical

M
Ht
Hn
Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services

M
Ht
Hn
Hl

M
Ht
Hn
Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services
Introduction: 1-74

Services, Layering and Encapsulation
source

application
transport
network
link
physical

destination

application
transport
network
link
physical

M
Ht
Hn

M
Ht
Hn
Hl

M
Ht
Hn

message
segment
datagram
frame

M
Ht
Hn
Hl
Introduction: 1-75

network
link
physical

application
transport
network
link
physical

Encapsulation: an end-end view

source

Ht
Hn
M

segment

Ht
datagram
destination

Ht
Hn
Hl
M

Ht
Hn
M

Ht
M

Ht
Hn
Hl
M

Ht
Hn
M

Ht
Hn
Hl
M

router
switch
message

Hn
frame

link
physical
Introduction: 1-76

Chapter 1: roadmap
Introduction: 1-77
What is the Internet?
What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure
Performance: loss, delay, throughput
Security
Protocol layers, service models
History

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 demo
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
late70’s: proprietary architectures: DECnet, SNA, XNA
1979: ARPAnet has 200 nodes
1972-1980: Internetworking, new and proprietary networks
Cerf and Kahn’s internetworking principles:
minimalism, autonomy – no internal changes required to interconnect networks
best-effort service model
stateless routing
decentralized control
define today’s Internet architecture

Introduction: 1-79

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

Introduction: 1-80

Internet history
early 1990s: 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 1990s: commercialization of the Web
late 1990s – 2000s:
more killer apps: instant messaging, P2P file sharing
network security to forefront
est. 50 million host, 100 million+ users
backbone links running at Gbps

1990, 2000s: commercialization, the Web, new applications
Introduction: 1-81

Internet history
aggressive deployment of broadband home access (10-100’s Mbps)
2008: software-defined networking (SDN)
increasing ubiquity of high-speed wireless access: 4G/5G, WiFi
service providers (Google, FB, Microsoft) create their own networks
bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to social media, search, video content, …
enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure)
rise of smartphones: more mobile than fixed devices on Internet (2017)
~18B devices attached to Internet (2017)

2005-present: scale, SDN, mobility, cloud
Introduction: 1-82

Chapter 1: summary
Introduction: 1-83
We’ve covered a “ton” of material!
Internet overview
what’s a protocol?
network edge, access network, core
packet-switching versus circuit-switching
Internet structure
performance: loss, delay, throughput
layering, service models
security
history
You now have:
context, overview, vocabulary, “feel” of networking
more depth, detail, and fun to follow!

Additional Chapter 1 slides
Introduction: 1-84

ISO/OSI reference model
Introduction: 1-85
Two layers not found in Internet protocol stack!
presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers!
these services, if needed, must be implemented in application
needed?

application

presentation

session

transport

network

link

physical

The seven layer OSI/ISO
reference model

Wireshark
Introduction: 1-86

Transport (TCP/UDP)
Network (IP)
Link (Ethernet)
Physical

application
(www browser,
email client)
application
OS

packet
capture
(pcap)

packet
analyzer

copy of all Ethernet frames sent/received

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