Communicating over the
Network
Network Fundamentals – Lecture 2 (CCNA1 – Chapter 2)
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
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Objectives

Describe the structure 結構 of a network, including
the devices and media that are necessary for
successful communications.

Explain the function 功能 of protocols 協定in
network communications.

Explain the advantages 好處 of using a layered
model to describe network functionality.

Describe the role 角色 of each layer in two
recognized network models: The TCP/IP model and
the OSI model.

Describe the importance of addressing 編址 and
naming schemes 方案 in network communications.
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Network Structure
 What is a network?
Data or information networks capable of carrying many
different types of communications
 3 common elements of communication
•
message信息 source 來源 , the channel/media 媒介 ,
message destination 目的地
信息
來源
訊號
加密
傳送媒介
傳送器
接受器
解碼器
目的地
渠道
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How messages are communicated
 Data is sent across a network in small “chunks” called
segments (段落)
插入
Segmentation: Breaking communication into pieces
Multiplexing: Interleaving the pieces as they transverse the media
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Network components 成分
 Hardware
device; media
 Software/service
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Basic Network Components
 Network devices / Intermediary 中間的 devices
provide connectivity 連接 and ensure data flows in the network
e.g. Router 路由器, Switch 交換器, Hub 中轉站, Wireless device,
etc.
 End devices
provide services directly to end users
is the interface between human and network
e.g. PC, server, networked printers, etc.
 Network media (medium)
Network cable, wireless media
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Role (作用) of end devices
 Act as client or server or both
流動
來自
通過
到達
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Basic Network Components
 Network media
Channel over which a message travels
 Factors 要素 to choose the media
Speed, Cost,
Network Media
Mobility流動性
Copper
Distance
-electrical signal
Environment
Fiber Optics
Data Amount
-light pulse
Wireless
-infra-red, radio frequency
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Software/Services
 Services and processes are the communication programs,
called software, that run on the networked devices.
A network service provides information in response to a request.
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Network Types
 Local Area Networks (LANs)
- A network serving a home, building or campus is
considered a Local Area Network (LAN)
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Network Types
 Wide Area Networks (WANs)
- LANs separated by geographic distance are connected by
a network known as a Wide Area Network (WAN)
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Network Types
 Internet is defined as
A global mesh of interconnected networks
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Network Symbols
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Protocols (協定)
 The importance of protocols and how they are used to
facilitate communication over data networks
A protocol is a set of predetermined (預先決定) rules (規則) to
govern communications
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Protocols
Network protocols
Message format
are used
to allow devices to
communicate
Sharing method
successfully
Error handling
Set up and
Termination
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Technology independent Protocols
 Different types of network devices can communicate using the
same sets of protocols.
 This is because protocols specify (詳細指明) network functionality (
功能), not the technology (技術) of devices
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Protocols in Network Communication
 Protocol suites and industry standards
A protocol suite 協議系列 is
A group of inter-related protocols that are necessary to
perform a communication function.
They are implemented in software and hardware that is
loaded on each host and network device.
For example: TCP/IP suite
A standard 標準 is
A process or protocol that has been endorsed 認可 by
the networking industry and ratified 批准 by a
standards organization.
For example:The Institute of Electrical and Electronics
Engineers (IEEE); Internet Engineering Task Force
(IETF)
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Example of protocol suites
 The interaction between a Web server and a Web
browser as an example to explain the protocol suites
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Layered Network Model
 Benefits of using a layered model
– include
• assists in protocol design
• fosters competition
• changes in one layer do not affect other layers
• provides a common language
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Networking Models
Two basic types of networking models:
 Protocol model
It provides a model that closely matches the structure of a
particular protocol suite.
For example:
TCP/IP model is a protocol model because it describes the
functions that occur at each layer of protocols within the TCP/IP
suite.
 Reference model參考模型
It provides a common reference for maintaining 保持 consistency 一致
within all types of network protocols and services. I
ts primary purpose is to aid in clearer understanding of the
functions and process involved.
For example:
Open Systems Interconnection (OSI) model
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TCP/IP Model
 Created in the early 1970s and is referred to as the
Internet model
 Open Standard
描述
譯成密碼
對話
控制
不同的
決定
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Communication Process
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Protocol Data Unit
 Protocol data units 協議數據單元 (PDU) and
encapsulation 封裝
Encapsulation
process
Protocol
Data Unit
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Process of sending and receiving messages
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OSI Model
 It provides a framework架構 on
which to build a suite of open
systems protocols.
 Unfortunately, the speed at which
the TCP/IP based Internet was
adopted, and the rate at which it
expanded, caused the OSI Protocol
Suite development and acceptance
to lag behind.
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Layers with TCP/IP and OSI Model
 Compare OSI and TCP/IP model
應用層
展示層
應用層
會談層
傳輸層
網路層
傳輸層
網際網路層
資料鏈結層
網絡接達層
實體層
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Addressing and Naming Schemes
 Encapsulation 封裝 headers 表頭 are used to manage
communication in data networks
 Using the OSI model as a guide, we can see the
different addresses and identifiers 識別號 that are
necessary at each layer
MAC Address
IP Address
Port
number
TCP Segment
IP Packet
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Addressing and Naming Schemes
 Destination and source physical addresses is
concerned with the delivery of messages on a single
local network.
 For example: In an Ethernet LAN, this address is called
the Media Access Control (MAC) address.
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Addressing and Naming Schemes
 Destination and source logical network addresses
are used to manage communication in different data
networks.
 For example: IP address
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IP Address and MAC address
 Use “ipconfig /all” to show the IP address and MAC address (Physical Address) of
a PC
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Addressing and Naming Schemes
 Destination and Source port numbers are used to
identify the source and destination processes for
data communication.
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Key Concepts of Chapter 2
 Data Network Structures and Types
End Devices, Intermediary Devices, Media,
Software/Service
LAN, WAN, Internet, Intranet
 Message Transfer using Layers
Benefits, Protocol Model and Reference Model
(TCP/IP and OSI)
 Addressing Schemes
Encapsulation and PDUs
Data, Segments, Packets, Frames and Bits
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