Computer networking Report I need to write a report of 2 pages about the attached slides until slide number 25. Chapter 1 Introduction Computer Networking:
Computer networking Report I need to write a report of 2 pages about the attached slides until slide number 25. Chapter 1
Introduction
Computer
Networking: A Top
Down Approach
7th edition
Jim Kurose, Keith Ross
Pearson/Addison Wesley
April 2016
Introduction 1-1
Chapter 1: introduction
our goal:
▪ Have an overview of
the Internet;
introduce
terminology
▪ More in-depth
details later in course
▪ approach:
• use Internet as
example
overview:
▪ what’s the Internet? what’s a
protocol?
▪ network edge: hosts, access net,
physical media
▪ network core: packet/circuit
switching, Internet structure
▪ performance: loss, delay,
throughput
▪ protocol layers, service models
▪ security
▪ history
Introduction 1-2
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
Introduction 1-3
What’s the Internet: “nuts and bolts” view
▪ billions of connected
server
computing devices:
wireless
• hosts = end systems
laptop
• running network apps
smartphone
PC
▪ communication links
• fiber, copper, radio,
wireless
links
satellite
wired
• transmission rate:
links
bandwidth
router
mobile network
global ISP
home
network
▪ packet switches: forward
packets (chunks of data)
institutional
network
• routers (network layer)
• link-layer switches (data link layer)
regional ISP
Introduction 1-4
What’s the Internet: “nuts and bolts” view
▪ Internet: “network of networks”
mobile network
• Interconnected ISPs
global ISP
▪ protocols control sending, receiving
of messages
• e.g., TCP, IP, HTTP, Skype, 802.11
▪ Internet standards
home
network
regional ISP
• RFC: Request for Comments
▪ https://www.ietf.org/standards/rfcs/
▪ https://www.rfc-editor.org/
• IETF: Internet Engineering Task Force
institutional
network
Introduction 1-5
What’s the Internet: a service view
▪ infrastructure that provides
services to applications:
• Web, VoIP, email, games, ecommerce, social nets, …
▪ provides programming
interface to apps
mobile network
global ISP
home
network
regional ISP
• hooks that allow sending
and receiving app programs
to “connect” to Internet
• provides service options,
analogous to postal service
institutional
network
Introduction 1-6
What’s a protocol?
human protocols:
network protocols:
▪ “what’s the time?”
▪ “I have a question”
▪ introductions
▪ machines rather than
humans
▪ all communication activity
in Internet governed by
protocols
… specific messages sent
… specific actions taken
when messages
received, or other
events
protocols define format, order of
messages sent and received
among network entities, and
actions taken on message
transmission, receipt
Introduction 1-7
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
time
Introduction 1-8
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
Introduction 1-9
The network edge: a closer look
▪ End systems:
mobile network
• hosts: clients and servers
• clients: various wireless
devices, desktop computers,
etc.
• servers: often always on in
data centers
global ISP
home
network
regional ISP
▪ Access networks
• The network from the end
systems to the first ISP router
▪ Links using various physical
media: wired, wireless
communication links
institutional
network
Introduction 1-10
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 bits/sec.
• link transmission rate,
aka link capacity, aka
link bandwidth
packet
transmission
delay
=
two packets,
L bits each
2 1
R: link transmission rate
host
time needed to
transmit L-bit
packet into link
=
L (bits)
R (bits/sec)
Introduction 1-11
Access networks
Q: How to connect end systems
to edge router?
▪ residential access nets
▪
▪
▪
▪
Dial-up
DSL
Cable Internet
FTTH
▪ institutional access networks
(school, enterprise, company)
▪ mobile access networks
keep in mind:
▪ bandwidth (bits per second) of
access network?
Introduction 1-12
Access network: digital subscriber line (DSL)
central office
DSL splitter
modem
voice, data transmitted
at different frequencies over
dedicated line to central office
telephone
network
DSLAM
ISP
DSL access
multiplexer
▪ use existing telephone line to central office DSLAM (DSL Access
Multiplexer)
• data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net
▪ < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
▪ < 24 Mbps downstream transmission rate (typically < 10 Mbps)
Introduction 1-13
Access network: cable network
cable headend
…
cable splitter
modem
V
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1
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Channels
frequency division multiplexing: different channels transmitted
in different frequency bands
Introduction 1-14
Access network: cable network
cable headend
…
cable splitter
modem
data, TV transmitted at different
frequencies over shared cable
distribution network
CMTS
cable modem
termination system
ISP
▪ HFC: hybrid fiber coax
• asymmetric: up to 30Mbps downstream transmission rate, 2
Mbps upstream transmission rate
▪ network of cable, fiber attaches homes to ISP router
• homes share access network to cable headend
• unlike DSL, which has dedicated access to central office
Introduction 1-15
Access network: home network
wireless
devices
to/from headend or
central office
often combined
in single box
cable or DSL modem
wireless access
point (54 Mbps)
router, firewall, NAT
wired Ethernet (1 Gbps)
Multiple technologies can be combined to provide required services.
Introduction 1-16
Institutional access networks (Ethernet)
institutional link to
ISP (Internet)
institutional router
Ethernet
switch
institutional mail,
web servers
▪ typically used in companies, universities, etc.
▪ 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
▪ today, end systems typically connect into Ethernet switch
Introduction 1-17
Wireless access networks
▪ shared wireless access network connects end system to router
• via base station (access point in WiFi, and cell tower in cellular
networks)
wide-area wireless access
wireless LANs:
▪ within building (100 ft.)
▪ 802.11b/g/n (WiFi): 11, 54, 450
Mbps transmission rate
▪ provided by telco (cellular)
operator, 10’s km
▪ between 1 and 10 Mbps
▪ 3G, 4G: LTE
to Internet
to Internet
Introduction 1-18
Physical media
▪ bit: propagates between
transmitter/receiver pairs
▪ link: what lies between
transmitter & receiver
▪ guided media:
• signals propagate in solid
media: copper, fiber
• Copper:
twisted pair (TP)
▪ two insulated copper
wires
• Category 5: up to 1 Gbps
Ethernet
• Category 6: 10Gbps
▪ twisted pair (TP)
▪ coaxial cable
• Fiber: optical fiber cable
▪ unguided media:
• signals propagate freely,
e.g., wireless radio
Introduction 1-19
Physical media: coax, fiber
coaxial cable:
optical fiber cable:
▪ two concentric copper
conductors
▪ Bidirectional
▪ Used in cable television and
Cable internet
▪ broadband:
▪ glass fiber carrying light
pulses, each pulse a bit
▪ high-speed operation:
• multiple channels on cable
• high-speed point-to-point
transmission (e.g., 10’s-100’s
Gbps transmission rate)
▪ low error rate:
• repeaters spaced far apart
• immune to electromagnetic
noise
Introduction 1-20
Physical media: radio
▪ signal carried in
electromagnetic spectrum
▪ no physical “wire”
▪ bidirectional
▪ propagation environment
effects:
• reflection
• obstruction by objects
• interference
radio link types:
Terrestrial Radio Channels
Very short range
▪ Personal wireless devices
▪ Local-area
▪ WiFi
▪ Wide area
▪ 4G cellular: ~ 10 Mbps
▪
Satellite radio channels
▪ Geostationay satellites
▪ Low-earth orbiting (LEO)
satellites
Kbps to 45Mbps channel (or
multiple smaller channels)
270 msec end-end delay
Introduction 1-21
Side note: Numbers
▪ 1 Kilo = 10^3
▪ 1 Mega = 10^6
▪ 1 Giga = 10^9
▪ 1 Kibi = 2^10
▪ 1 Mebi = 2^20
▪ 1 Gibi = 2^30
▪ 1 millisecond = 10^(-3) seconds
▪ 1 microsecond = 10^(-6) seconds
▪ 1 nanosecond = 10^(-9) seconds
▪ File size is usually specified in Bytes.
▪ Network speed (transmission rate/bandwidth) is
usually specified in bits/sec.
▪ 1 Byte = 8 bits.
Introduction 1-22
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
Introduction 1-23
The network core
▪ The network core is a mesh of
interconnected routers
▪ The core of computer
networks (and the Internet)
uses packet-switching.
▪ 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
Introduction 1-24
Packet-switching: store-and-forward
L bits
per packet
source
3 2 1
R bps
R bps
destination
▪ takes L/R seconds to
one-hop numerical example:
transmit (push out) L-bit
▪ L = 7.5 Mbits
packet into link at R bps
▪ R = 1.5 Mbps
▪ store and forward: entire
packet must arrive at router
▪ one-hop transmission
before it can be transmitted
delay = 5 sec
on next link
▪ end-end delay (with two links) =
2L/R (assuming zero propagation more on delay shortly …
delay)
Introduction 1-25
Packet Switching: queueing delay, loss
A
C
R = 100 Mb/s
R = 1.5 Mb/s
B
queue of packets
waiting for output link
D
E
queuing and loss:
▪ if arrival rate (in bits) to link exceeds transmission rate of link
for a period of time:
• packets will queue, wait to be transmitted on link
• packets can be dropped (lost) if memory (buffer) fills up →
congestion
Introduction 1-26
Two key network-core functions
routing: determines sourcedestination route taken by
packets
▪ routing algorithms
forwarding: move packets from
router’s input to appropriate
router output
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
3 2
destination address in arriving
packet’s header
Introduction 1-27
Alternative core: circuit switching
end-end resources allocated
to, reserved for “call”
between source & dest:
▪ 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)
▪ commonly used in traditional
telephone networks
Introduction 1-28
Circuit switching: FDM versus TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
Introduction 1-29
Packet switching versus circuit switching
packet switching allows more users to use network!
example:
▪ 1 Mb/s link
▪ each user:
• 100 kb/s when “active”
• active 10% of time
▪ circuit-switching:
N
users
1 Mbps link
• 10 users (network must be nonblocking, no more than 10 users
can be active at the same time;
circuits needs to e allocated).
▪ packet switching:
• with 35 users, probability > 10
active at same time is less than
.0004 *; if total sending request is
greater than 1 Mb/s, packages can
be queued first.
Q: how did we get value 0.0004?
Q: what happens if > 35 users ?
Check out the online interactive exercises for more
examples:
http://gaia.cs.umass.edu/kurose_ross/interactive/
Introduction 1-30
Packet switching versus circuit switching
is packet switching a “slam dunk winner?”
▪ great for bursty data
• resource sharing
• simpler, no call setup
▪ Issues/problems needs to be dealt with:
▪ excessive congestion possible: 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 9)
Introduction 1-31
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