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