Download Data Communications and Networking

Data Communications and
Networking
Chapter 1
Data Communications, Data Networks,
and the Internet
Reading:
Book Chapter 1
Data and Computer Communications, 8th edition
By William Stallings
1
Outline
• Section 1: Data Communications and
Networking for Today’s Enterprise
• Section 2: A Communications Model
• Section 3: Data Communications
• Section 4: Networks
• Section 5: The Internet
• Summary: Key Points
• Appendix: History of Communications
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Section 1
Data Communications and Networking
for Today’s Enterprise
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What are the trends?
•
Three forces are driving the evolution of data communications and
networking
1. Growth of communication traffic
— Voice traffic
•
telephone
•
Internet access, video conferencing
•
how to maximize the capacity and minimize the cost?
— Data traffic
— Challenges (to the network service providers):
2. Development of new services
— Refer to the figure on the next page
3. Advances in technology
—
—
—
—
Faster and cheaper computing and communications
Networks are more intelligent: quality of service (QoS)
Internet, Web, intranets, extranets, etc.
Pervasive computing/ubiquitous computing
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Figure 1: Service versus Throughput Rates
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Case Studies:
• What networking services do we use today?
— Phone service (mainly for voice)
— Internet service (mainly for data)
• Example of Mobile Phone Service: THREE.com
— http://www.three.com.hk/website/template?pageid=35200&lang=chi
• Example of Broadband Internet Access: HKBN
— http://www.hkbn.com.hk/bb1000/offer_no_contract.html
• Questions
— Why mobile phone service is charged based on time (i.e., number of
minutes)?
— why Internet access service is charged based on the data rate (i.e.,
number of MB/s)?
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How is our life without Internet?
• Time: Dec. 26, 2006
• Event: An earthquake at Taiwan
• Consequence:
—香港《新报》28日头条报道称，台湾大地震除了在当
地造成伤亡，亦令互联网世界出现前所未有的大灾难
。多条经台湾传送互联网数据的海底电缆在地震中受
破坏，由于台湾是香港以至东南亚互联网用户接驳至
外地的主要“出口”，电缆受损令香港等多个地区的
互联网一度“与世隔绝”，香港网民未能登入外国网
站，电邮服务亦几乎全部中断，长途电话及国际漫游
服务同受影响。
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(Cont.)
华声报旧金山消息：
12月26日台湾的一场强震不仅给台湾百姓造成了严重的损失，也给在美
华人带来了程度不同的经济影响。由于地震毁掉了6条海底电缆，导
致中美之间的网络中断，南加华商生意遭受挫折抱怨连连。
Case 1:
吴老板说，“在美国雇一个员工的钱在中国可以雇10个，网上销售
为我带来了无限商机。”可是26日他突然发现上不去网了。
“网络销售占本公司全部销售额的一半，如果要两个星期才能修复
海底光缆的话，仅网上eBay销售这一块我的损失就超过28万元，加
上国内网站的管理费和员工工资等，这场地震给我造成的直接损失至
少在30万元以上”。
Case 2:
工业市华裔商人石小姐在经营运输公司之余，还在香港做些股票生
意，27日她发现无法登陆香港股市网站，当得知是地震的原因时，她
心急如焚地表示，“完了，这几天上不了网，我的几百万股票恐怕凶
多吉少。”
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What lessons can we learn?
• Internet is an important infrastructure of our
society.
• Reliability is a critical factor, especially for
businesses that rely on networking technology.
• Question: If you are a network manager for a
company, how will you increase the reliability of
your company’s network connection?
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Section 2
A Communications Model
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Human Communications
• A transmitter: mouth
• A receiver: ear
• The media: air
— Question: Can you talk at outer space?
• The protocol: a common human language
— Question: why do we learn English?
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A Communications Model
• What is the purpose of communications?
— Exchange of information between two parties
• Key elements
• Source: Generates data to be transmitted. E.g., telephones, PCs.
• Transmitter: A transmitter transforms and encodes the information
in such a way as to produce electromagnetic signals that can be
transmitted across some sort of transmission system.
• Transmission System
− It can be a single transmission line or a complex network
connecting source and destination.
• Destination: Takes incoming data from the receiver
• Receiver: The receiver accepts the signal from the transmission
system and converts it into a form that can be handled by the
destination device.
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Simplified Communications Model
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Section 3
Data Communications
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Simplified Data
Communications Model
Assume the source and destination are PCs.
The source wishes to send a message m to the destination.
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Transmission of Information
• One basic choice facing a business user is the
selection of transmission medium.
—Within the business premise
• Completely up to the business
—Long-distance communications
• Up to the long-distance carrier
—New technologies
• Optical fiber transmission
• Wireless transmission
• How to improve the efficiency of the use of
network facilities?
—Multiplexing and compression
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Section 4
Networks
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Why do we need a network?
• Point to point
communication is not
always practical
— Devices are too far
apart
— Large set of devices
would need impractical
number of connections
Telegraph wires in late 19th century
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Networking
• Solution is to use a communications network
A telephone switch in 1960s
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Today’s network switches
Cisco Catalyst 6500 Series Switches
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At Ancient Time
• How to achieve long-distance communications?
• Solution 1
— Signal fires
— Example
• See the movie segment in “The Lord Of The Rings –
Return Of The King” directed by Peter Jackson.
• Solution 2
— Messengers, horses, post houses (驛站)
— How efficient is it?
• 56 days from 北京 to 廣州
• In both solutions, the concept of “relay” is very
important, and it forms the basic principle of
today’s Internet.
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Wide Area Networks
• Cover a large geographical area
—Consists of a set of interconnected switching nodes
• Alternative technologies
—I. Circuit switching
• Telephone network
—II. Packet switching
• X.25: popular in 1980s
• Frame relay: to replace X.25
• Asynchronous Transfer Mode (ATM): an evolution from frame
relay
• Internet: the dominant global network today
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(I) Circuit Switching
•
•
Dedicated communications path established for
the duration of the conversation
Three steps:
1. Setup the circuit: allocate dedicated resources.
2. Transmit the data: utilize resources.
3. Terminate the circuit: release resources.
•
E.g. telephone network
— Now, can you answer the question on Slide 6?
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(II) Packet Switching
• Data are sent out in a sequence of small
chunks, called packets.
• Each Packet is passed through the network from
node to node along some path leading from
source to destination
• At each node, the entire packet is received,
stored, and then transmitted to the next node
—Store-and-forward: buffering
• What’s the impact?
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Local Area Networks
• Smaller scope
—Office, Building, Campus
• Usually owned by the same organization that
owns the attached devices
• Internal data rates are high
—10Mbps  100Mbps  1Gbps  10Gbps
• Wireless LANs become more and more popular
—Data rates of wireless LANs are increasing: 11Mbps
 54Mbps  hundreds of Mbps
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Section 5
The Internet
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Internet Elements
• The purpose of the Internet is to interconnect end systems, called
hosts
— Such as PCs, servers, notebooks, PDAs, smart phones, etc.
• Most hosts that use the Internet are connected to a network, such
as a LAN or a WAN
• Networks are in turn connected by routers. Each router attaches
to two or more networks.
• A host may send data to another host anywhere on the Internet:
— The source host breaks the data into a sequence of packets, called IP
packets, or IP datagrams.
— Each packet includes the unique numeric addresses of the source host
and destination host, called IP addresses.
— Based on the destination IP address, each packet travels through a
series of routers and networks from source to destination.
• Each router, upon receiving an IP packet, makes a routing decision and
forwards the packet along its way to the destination.
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Internet Elements
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Internet Architecture
• Today’s Internet is made up of thousands of overlapping
hierarchical networks.
• Individual hosts and LANs are connected to an Internet
Service Provider (ISP) through a Point of Presence
(POP).
— Customer Premises Equipment (CPE): the communications
equipment located onsite with the host, such as the modem.
• Different levels of ISPs
— Local ISP, Regional ISP, Backbone ISP
• Backbone ISPs may be connected through the Network
Access Point (NAP).
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Internet Architecture
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KEY POINTS
• Data communications deals with the
transmission of signals in a reliable and efficient
manner. Topics covered include signal
transmission, transmission media, signal
encoding, interfacing, and data link control.
• Networking deals with the technology and
architecture of the communications networks
used to interconnect communicating devices.
This field is generally divided into the topics of
local area networks (LANs) and wide area
networks (WANs).
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Appendix:
A brief history of communications
• 1830-1840s, Samuel Morse
— Morse code
— Telegraph
• 1850s
— European and US are connected by submarine telegraphy
cables.
• 1870s, Alexander Bell
— Telephone
— Bell labs was setup in 1925, three years after Bell’s death.
• 1956
— US and UK are connected by telephone cables.
• Question: why is it more difficult to make long-distance
telephones work, as compared with long-distance
telegraph?
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Morse Code
.B -...
C -.-.
D -..
E .
F ..-.
G --.
H ....
I ..
J .--K -.L .-..
M -A
-.
O --P .--.
Q --.R .-.
S ...
T U ..V ...W .-X -..Y -.-Z --..
N
0
1
2
3
4
5
6
7
8
9
----.---..--...-.........
-....
--...
---..
----.
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(Cont.)
•
1960s
•
Late 1960s and early 1970s
•
Late 1960s, K. C. Kao
— Digital data communications occurred
— ARPANET: the first computer network, the beginning of the Internet
— Optical Fiber
— K.C. Kao: Father of the fiber
•
•
Served as the president of CUHK from 1987 to 1996.
Nobel prize in Physics 2009
— http://www.youtube.com/watch?v=9l_0QDIM60o
•
•
Digital transmission and switching begins
1973, Robert Metcalfe
•
1981
•
1991, Tim Berners-Lee
— Ethernet
— Founded 3Com Corp. in 1979
— Cellular mobile telephone
— World-Wide Web
— Explosion of Internet
Charles Kuen Kao 高錕
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