[SOLVED] Chapter 1: introduction

Chapter 1: introduction
Chapter goal: Overview/roadmap:
Get feel, big picture, introduction to terminology
more depth, detail later in course

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Approach:
use Internet as example
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
Introduction: 1-1

The Internet: a nuts and bolts view
Billions of connected computing devices:
hosts = end systems
running network apps at Internets edge
Packet switches: forward packets (chunks of data)
routers, switches Communication links
fiber, copper, radio, satellite transmission rate: bandwidth
collection of devices, routers, links: managed by an organization
mobile network
home network
enterprise network
national or global ISP
local or regional ISP
content provider network
datacenter network
Introduction: 1-2

Fun Internet-connected devices
Pacemaker & Monitor
sensorized, bed mattress
Amazon Echo
Internet refrigerator
Security Camera
Internet phones
IP picture frame
Slingbox: remote control cable TV
Tweet-a-watt: monitor energy use
Web-enabled toaster + weather forecaster
AR devices
Introduction: 1-3

The Internet: a nuts and bolts view
Internet: network of networks Interconnected ISPs
protocols are everywhere
control sending, receiving of
e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet
Internet standards
RFC: Request for Comments
IETF: Internet Engineering Task Force
mobile network 4G
national or global ISP
local or regional ISP
Streaming video
datacenter network
home network
content provider network
enterprise network
Introduction: 1-4

The Internet: a service view
Infrastructure that provides services to applications:
Web, streaming video, multimedia teleconferencing, email, games, e- commerce, social media, inter- connected appliances,
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
mobile network
national or global ISP
Streaming video
datacenter network
local or regional ISP
home network
enterprise network
content provider network
Introduction: 1-5

Whats a protocol?
Human protocols:
whats the time? I have a question introductions
specific messages sent
specific actions taken when message received, or other events
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 msg transmission, receipt
Introduction: 1-6

Whats a protocol?
A human protocol and a computer network protocol:
Got the time?
TCP connection request
TCP connection response
GET http://gaia.cs.umass.edu/kurose_ross
Q: other human protocols?
Introduction: 1-7

Chapter 1: 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
Security
Protocol layers, service models
Introduction: 1-8

A closer look at Internet structure
mobile network
Network edge:
hosts: clients and servers servers often in data centers
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-9

A closer look at Internet structure
mobile network
Network edge:
hosts: clients and servers servers often in data centers
Access networks, physical media:
wired, wireless communication links
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-10

A closer look at Internet structure
mobile network
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
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-11

Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets
institutional access networks (school,
mobile access networks (WiFi, 4G/5G)
What to look for:
transmission rate (bits per second) of access network?
shared or dedicated access among users?
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-12

Access networks: cable-based access
cable headend
cable splitter
O VVVVVV N IIIIIIDDT DDDDDDAAR EEEEEETTO OOOOOOAAL
123456789 Channels
frequency division multiplexing (FDM): different channels transmitted in different frequency bands
Introduction: 1-13

Access networks: cable-based access
cable splitter
data, TV transmitted at different frequencies over shared cable
distribution network
cable headend
cable modem termination system
HFC: hybrid fiber coax
asymmetric: up to 40 Mbps 1.2 Gbs 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
Introduction: 1-14

Access networks: digital subscriber line (DSL)
DSL splitte modem
voice, data transmitted at different frequencies over dedicated line to central office
central office
DSL access multiplexer
telephone network
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
Introduction: 1-15

Access networks: home networks
wireless devices
often combined in single box
WiFi wireless access point (54, 450 Mbps)
to/from headend or central office
cable or DSL modem
router, firewall, NAT wired Ethernet (1 Gbps)
Introduction: 1-16

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 (10s km)
10s Mbps
4G cellular networks (5G coming)
to Internet
Introduction: 1-17

Access networks: enterprise networks
Ethernet switch
Enterprise link to
ISP (Internet) institutional router
institutional mail, web servers
companies, universities, etc.
mix of wired, wireless link technologies, connecting a mix of switches
and routers (well cover differences shortly)
Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps WiFi: wireless access points at 11, 54, 450 Mbps
Introduction: 1-18

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
two packets, L bits each
R: link transmission rate = L (bits)
R (bits/sec)
21 link transmission rate, aka link host
capacity, aka link bandwidth
packet = transmission
time needed to transmit L-bit packet into link
Introduction: 1-19

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 Category6:10GbpsEthernet
Introduction: 1-20

Links: physical media
Coaxial cable:
two concentric copper conductors
bidirectional
broadband:
multiple frequency channels on cable 100sMbpsperchannel
Fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point
transmission (10s-100s Gbps) low error rate:
repeaters spaced far apart
immune to electromagnetic noise
Introduction: 1-21

Links: physical media
Wireless radio
signal carried in electromagnetic spectrum
no physical wire broadcast and half-duplex
(sender to receiver)
propagation environment effects:
reflection
obstruction by objects interference
Radio link types:
terrestrial microwave up to 45 Mbps channels
Wireless LAN (WiFi) Up to 100s Mbps
wide-area (e.g., cellular) 4G cellular: ~ 10s Mbps
satellite
up to 45 Mbps per channel 270 msec end-end delay
geosynchronous versus low- earth-orbit
Introduction: 1-22

Chapter 1: 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
Security
Protocol layers, service models
Introduction: 1-23

The network core
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
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-24

Packet-switching: store-and-forward
per packet
source 3 2 1 destination R bps R bps
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
End-end delay: 2L/R (above), assuming zero propagation delay (more on delay shortly)
One-hop numerical example:
L = 10 Kbits
R = 100 Mbps
one-hop transmission delay = 0.1 msec
Introduction: 1-25

Packet-switching: queueing delay, loss
R = 100 Mb/s A
R = 1.5 Mb/s queue of packets
waiting for output link
Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for a 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: 1-26

Two key network-core functions
routing algorithm
locall forwarding table
header value
output link
0100 0101 0111 1001
Forwarding:
local action: move arriving packets from routers input link to appropriate router output link
destination address in arriving packets header
global action: determine source- destination paths taken by packets
routing algorithms
Introduction: 1-27

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
commonly used in traditional telephone networks
Introduction: 1-28

Circuit switching: FDM and TDM
Frequency Division Multiplexing (FDM)
optical, electromagnetic frequencies divided into (narrow) frequency bands
each call allocated its own band, can transmit at max rate of that narrow band
Time Division Multiplexing (TDM)
time divided into slots
each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s)
Introduction: 1-29

Packet switching versus circuit switching
packet switching allows more users to use network!
1 Gb/s link
each user:
100 Mb/s when active active 10% of time
circuit-switching: 10 users
packet switching: with 35 users, probability > 10 active at same time is less than .0004 *
1 Gbps link
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive
Q: how did we get value 0.0004? Q: what happens if > 35 users ?
Introduction: 1-30

Packet switching versus circuit switching
Is packet switching a slam dunk winner?
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?
bandwidth guarantees traditionally used for audio/video applications
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)?
Introduction: 1-31

Internet structure: a network of networks
Hosts connect to Internet via access Internet Service Providers (ISPs)
residential, enterprise (company, university, commercial) ISPs Access ISPs in turn must be interconnected
so that any two hosts can send packets to each other Resulting network of networks is very complex
evolution was driven by economics and national policies
Lets take a stepwise approach to describe current Internet structure
Introduction: 1-32

Internet structure: a network of networks
Question: given millions of access ISPs, how to connect them together?
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
Introduction: 1-33

Internet structure: a network of networks
Question: given millions of access ISPs, how to connect them together?
access net
access net
access net
access net
access net
access net
access net
access net
access net
connecting each access ISP to each other directly doesnt scale: O(N2) connections.
access net
access net
access net
access net
access net
access access net
Introduction: 1-34

Internet structure: a network of networks
Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement.
access net
access net
access net
access net
access net
access net
access net
access net
access net
global ISP
access net
access net
access net
access net
access net
access net
access net
Introduction: 1-35

Internet structure: a network of networks
But if one global ISP is viable business, there will be competitors .
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
Introduction: 1-36

Internet structure: a network of networks
But if one global ISP is viable business, there will be competitors . who will
want to be connected
access net
access net
Internet exchange point
access net
access net
access net
access net
access net
access net
peering link
access net
access net
access net
access net
access net
access net
access net
access net
Introduction: 1-37

Internet structure: a network of networks
and regional networks may arise to connect access nets to ISPs
access net
access net
access net
access net
access net
access net
access net
access net
regional ISP
access net
access net
access net
access net
access net
access access net
access net
Introduction: 1-38

Internet structure: a network of networks
and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users
access net
access net
access net
access net
access net
access net
access net
access net
Content provider network
regional ISP
access net
access net
access net
access net
access net
access access net
access net
Introduction: 1-39

Internet structure: a network of networks
Tier 1 ISP Tier 1 ISP
Regional ISP
access access access
ISP ISP ISP ISP
Regional ISP
access access access ISP ISP 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
Introduction: 1-40

Tier-1 ISP Network map: Sprint (2019)
POP: point-of-presence
to/from other Sprint PoPS
links to peering networks
links to/from Sprint customer networks
Introduction: 1-41

Chapter 1: 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
Security
Protocol layers, service models
Introduction: 1-42

How do packet loss and delay occur?
packets queue in router buffers
packets queue, wait for turn
arrival rate to link (temporarily) exceeds output link capacity: packet loss
packet being transmitted (transmission delay)
packets in buffers (queueing delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction: 1-43

Packet delay: four sources
transmission
propagation
processing queueing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing check bit errors
determine output link typically < msecdqueue: queueing delay time waiting at output link for transmission depends on congestion level of routerIntroduction: 1-44 Packet delay: four sourcespropagationprocessing queueingtransmission dnodal = dproc + dqueue + dtrans + dpropdtrans: transmission delay: L: packet length (bits) R: link transmission rate (bps)dtrans = L/R d and d transdprop: propagation delay: d: length of physical link s: propagation speed (~2×108 m/sec) dprop = d/s* Check out the online interactive exercises: http://gaia.cs.umass.edu/kurose_ross very differentIntroduction: 1-45 Caravan analogy100 km (aka 10-bit packet) (aka router) cars propagate at 100 km/hr toll booth takes 12 sec to servicecar (bit transmission time) car ~ bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? ten-car caravan toll boothtoll 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 minutesIntroduction: 1-46 Caravan ana CS: assignmentchef QQ: 1823890830 Email: [email protected]