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

PowerPoint Presentation

Introduction
All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved
George Parisis
School of Engineering and Informatics
University of Sussex

Introduction
Roadmap
what is the Internet?
delay, loss, throughput in networks
network edge
end systems, access networks, links
network core
packet switching, circuit switching, network structure
protocol layers, service models
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Introduction
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Introduction
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
The network core
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Introduction
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Introduction
Packet-switching: store-and-forward
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
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source
R bps
destination
1
2
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L bits
per packet
R bps
end-end delay = 2L/R (assuming zero propagation delay)

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Network Layer
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Two key network-core functions
forwarding: move packets from router’s input to appropriate router output
routing: determines source-destination route taken by packets
routing algorithms

routing algorithm

local forwarding table
header value
output link

0100
0101
0111
1001
3
2
2
1

0111

1
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dest address in arriving
packet’s header

Network Layer

Introduction
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

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Introduction
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Introduction
Circuit switching: FDM versus TDM

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frequency

time

FDM
TDM

frequency

time

4 users

Example:

Introduction
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Two simple multiple access control techniques.

Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.

As we will see, used in AMPS, GSM, IS-54/136

Introduction
Packet switching versus circuit switching
example:
1 Mbps link
each user:
100 kbps 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
packet switching allows more users to use network!
N
users
1 Mbps link
…..
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Introduction
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Introduction
great for bursty data
resource sharing
simpler, no call setup
excessive congestion possible: packet delay and loss
protocols needed for reliable data transfer, congestion control
is packet switching a clear winner?
Packet switching versus circuit switching
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Internet structure: network of networks
End systems connect to Internet via access ISPs (Internet Service Providers)
Residential, company and university 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

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

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Internet structure: network of networks
Option: connect each access ISP to every other access ISP?
connecting each access ISP to each other directly doesn’t scale: O(N2) connections.

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

global
ISP

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Internet structure: network of networks
But if one global ISP is viable business, there will be competitors ….

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ISP B

ISP A

ISP C

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Internet structure: network of networks
But if one global ISP is viable business, there will be competitors …. which must be interconnected

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ISP B

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ISP C

IXP

IXP

peering link

Internet exchange point

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Internet structure: network of networks
… and regional networks may arise to connect access nets to ISPs

regional net

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ISP B

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IXP

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Internet structure: 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

regional net

Content provider network

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Introduction
Internet structure: network of networks
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 network (e.g, Google): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs
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access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
Regional ISP
Regional ISP
IXP
IXP
Tier 1 ISP
Tier 1 ISP
Google

IXP

Introduction
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Introduction
Roadmap
what is the Internet?
delay, loss, throughput in networks
network edge
end systems, access networks, links
network core
packet switching, circuit switching, network structure
protocol layers, service models
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Introduction
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Introduction
Protocol “layers”
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?

…. or at least our discussion of networks?
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Introduction
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Introduction
Why layering?
dealing with complex systems:

explicit structure allows identification, relationship of complex system’s pieces

modularization eases maintenance, updating of system
change of implementation of layer’s service transparent to rest of system
Top-Down approach vs Bottom-Up

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Introduction
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Introduction

Internet protocol stack
application: supporting network applications
FTP, SMTP, HTTP
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”

application

transport

network

link

physical
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Introduction
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Introduction
source

application
transport
network
link
physical
segment
datagram
destination

application
transport
network
link
physical
router
switch
Encapsulation
message
frame
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Ht
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Ht

Ht
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M

network
link
physical

link
physical

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Introduction
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
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Introduction
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
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
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Introduction
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
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Introduction
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
1990, 2000’s: commercialization, the Web, new apps
Internet history
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Introduction
2005-present
~750 million hosts
Smartphones and tablets
Aggressive deployment of broadband access
Increasing ubiquity of high-speed wireless access
Emergence of online social networks:

Facebook: soon one billion users
Service providers (Google, Microsoft) create their own networks

Bypass Internet, providing “instantaneous” access to search, email, etc.
E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2)

Internet history
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Introduction
Globally, there will be 3.9 billion total Internet users (51% of population) in 2019, up from 2.8 billion (39% of population) in 2014

By 2020, forecasts suggest that there will be around 6.58 network connected devices per person around the globe. With a total world population of over 7.5 billion people, this means that there could be nearly 50 billion network connected devices by 2020.

The Internet of Things (IoT)
The Future
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Introduction
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Introduction
Introduction: summary
Internet overview
what’s a protocol?
network edge, core, access network
packet-switching versus circuit-switching
Internet structure
performance: loss, delay, throughput
layering, service models
security
history
you now have:
context, overview, “feel” of networking
more depth, detail to follow!
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