Transcript network - 广西医科大学

Computer Networking
网络课件
双语教学
模拟实验
计算机网络教研室
CHAPTER 3
Network Architetures and Standarts
1
The first section
2
Exercises
3
Online lecture
Department of Computer
Networking Application
Chapter 3 Network
Architetures and Standarts
3-1
Introduction
3-8
Communication Architecture
ISO Reference Model
3-2
Definition Architecture
3-9
3-3
Why have Architecture
3-10
3-4
Standards making org
3-11
3-5
Definition Architecture
3-12
Manufactures Architecture
3-6
The V.and X.standards
3-13
A caveat about
3-7
Advs and disadvs of standards
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3-14
TCP/IP Architecture
Internet Architecture
Layered architecture
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OBJECTIVES
Explain the difference between architectures and standards.
Explain the need for network architecture and standards.
Identify a number of communications standards-making org.
Describe the OSI model architecture.
Describe TCP/IP architecture.
Describe the architecture of the Internet.
Discuss the ADV and DISADV of layered architecture.
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3.1 Introduction
Definitions of architectures and standards.
The difference among them.
The need of them
Specific example of them
Examine adv & disadv
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3.2 DEFINITION OF ARCHITECTURES AND STANDARDS
Architecture: is a plan or direction that is oriented
toward the needs of the user.
Network architecture is a set of principles used as
the basic for the design and implementation of a
communications network.
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It includes the organization of functions that must
be performed by the network and the description of
data formats and procedures.
Network architecture=layer + protocols
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Network architecture features
May or may not conform to standards.
Don’t provides enough detail how network to
be implemented.
Provides a set of generic concepts .
Most architecture (plan) are designed for the
long term use.
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Single Layer Model
First Communication Between Computer Devices
The communication and application software be
intermingled (To mix).
The early networks were not flexible.
Single specification for all aspects of communication
Hardware
&
Software
Hardware
&
Software
DEVICE A
DEVICE B 1
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IBM SNA(System Network Architecture)
IBM : 1974 by the first computer network architecture
IBM’s SNA is a proprietary architecture
NOTE:Not SNA(storage area network)
Most network architectures developed since use a
layered approach.
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Communication standard
The rules that are established to ensure compatibility
among similar communications products and services.
Communications standards are the flesh on the
architectural skeleton.
They specify how a particular communications product,
service,or interface will operate.
V.90 modem
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3.3 why have network architectures?
1.Communication system were becoming too
complex.
2. wanted to be isolated from the complexities of the
network.
3.Wanted to connect different types of devices to the
network.
4.Distributed processing and client-server processing
became practical.
5.Network needed to be managed.
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3.4 TWO VIEWPOINTS ABOUT STANDARDS
Background:
Communications vendors realized early standards.
computer manufacturers were slower to recognize
the need for standards.
Customers demanded that product was
standardization.
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One
People who have a strong networking background
see the computer as a tool to enhance a network`s
capability.
Tend to wait for standards and follow them closely.
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Two
Those who have a strong computer background
tend to focus on what can be done with software
or specially designed circuit chips for computers.
They Two
forge
ahead
ofrelative
therolesstandards-making
process
different
views of the
of networks and computers.
Figure 3-1
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Purport
While neither viewpoint is wrong ,it leads to
differing philosophies.
Both are legitimate and have their place.
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3.5 STANDS AND STANDS-MAKING ORGANIZATIONS
Because of the recognized need for common
international standards, there is a great deal of
cooperation among communications standards
making organizations.
Data communication standards are more
complicated than Voice communication standards.
Early standards were mostly electrical in nature.
The standards-setting process is slow.
Writing standards is difficult work.
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ITU (The International Telecommunication Union)
1865 in the U S was established in Paris,
1947 as part of the United Nations, members from
188 countries, headquartered in Geneva, Switzerland.
The most important telecommunications standardssetting organization in the world is the ITU .
ITU-T has created two sets of standards for the
electrical connection of terminals to communications
networks.
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ISO:International Standards Organization
Don’t confuse the OSI with ISO and IOS,.
ISO :means the international organization for
standardization.
IOS :(internet operation system) is used in
CISCO system’s routers and switches.
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Figure of the organizations involved in setting telecommunications
standards or in passing input to the standards-setting bodies.
The American National Standards Institute (ANSI) is not involved in setting
communications standards.
The official TCP/IP model is now maintained by the IETF.
All communications standards are developed by one organization, the ISO.F
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3.6Ｖ.STANDARD X.STANDARD
The ITU-T has created two sets of standards
for the electrical connection of terminals to
communications networks.
They are called the V. and X. standards
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V.standards :
define the connection of digital equipment to the
PSTN`s analog lines
V.32, V.33, V.42 standard for the use of telephone
transmission of data made a clear statement .
X.standards:
Define the connection of digital equipment to
digital lines.
E.G X.25, X.400, X.500
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3.7 ADVANTAGES AND DISADVANTAGES
OF STANDARDS
Adv Standards allow products from multiple
vendors to be connected to one another and
to communicate.
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disadvance
The standards-setting process is slow.
Standards tend to freeze technology.
Multiple conflicting standards.
The standards-setting process can occur
quickly(Writing standards is relatively easy )，
when an architecture is in place.F
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3.8 COMMUNICATIONS ARCHITECTURES
ISO and ITU-T developed OSI reference model in
1978.
OSI-RM: Open Systems Interconnection reference
model.
The standards development process took so long that
the osi model never came into widespread use.
It is the standard reference point by which data
communications networks are described
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3.9 THE ISO`S OSI REFERENCE MODEL
3.9.1 Objective
Provide a basis for interconnecting dissimilar
systems for the purpose of information exchange.
Define communications rules.
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OSI and most network architecture use a layered approach.
A layer in the OSI RM represents a component of the total
process of communicating.
Each one layer requests services from the layer below it.
N layer Provide services to N+1 layer
The same network, any two-system must have the same
level.
The actual physical communication completed only in the
bottom layer.
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Why layering?
1) Layering forces the modularization of function .
Dealing with complex systems.
The output of laying definition process is standards.
eases maintenance, updating of system.
One layer can be changed without affecting other layers
Different implementations can be substituted relatively
Transparently。
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Layer
Layer requires reasonably sophisticated software
and hardware at each end of the connection.
前置处
理机
中央主机
中央主机
前置处
理机CCP
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前置处
理机
中央主机
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The philosopher-translator-Secretary architecture.
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Example :Scientific exchange layered
Scientific opinion
CN scientists
JP scientists
protocol
English
CN Translate
protocol
JP Translate
Letters
CNTelegrafisten
protocol
JPTelegrafisten
Telegraph code
Telex machine
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protocol
Telex machine
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Network Architecture Layered principle
Basic concept ：
Entity：Can send or receive any information of hardware
/ software process
Peer layer ：Two different systems the same level 。
Interface：Interaction between the two neighboring layer
SERVE：for the upper classes a capacity to provide
services through the interface
Protocol：Communication both in communication must
comply with the rules.
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Layered network Architecture
SYSA
SYS
entityA
serve
r
interfact
Pee
r
lay
peer
er
entit
y
SYS
B
N+1
N
N-1
Pn+1
Pn
Pn-1
3
2
1
P3
P2
P1
SYSB
N+1
N
N-1
3
2
1
Physical communication
Physical
line
communication line
The way that the interaction between the layers actually takes place is that each
one requests services from the layer above it.
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Services
The way that the interaction between the layers
actually takes place is that each one requests
services from the layer above it.
Each layer provides services to the next higher
layer
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Service Primitives
Primitive
Meaning
Request
An Entity wants the service to do some work
Indication
An Entity is to be informed about an event
Response
An Entity wants to respond to an event
Confirm
The Response to an eariler request has come
back
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Relations
among Service Primitives
服务用户 服务提供者
服务提供者 服务用户
系统A
（N+1）
系统B
（N）
Request
需证实
（N）
PDU
（N+1）
Indication
Response
无需证实
Confirm
Request
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Indication
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电话系统工作示例
例如：张三打电话请李四吃饭，服务提供者为电话局
① CONNECT.request
 张三拨李四的电话号码
② CONNECT.indication
 李四的电话振铃
③ CONNECT.response
 李四摘机
④ CONNECT.confirm
 张三听到振铃停止，知道有人应答
⑤ DATA.request
 张三说话，发出邀请
⑥ DATA.indication
 李四听到张三的邀请
⑦ DATA.request
 李四说话，接受邀请
⑧ DATA.indication
 张三听到李四的答复
⑨ DISCONNECT.request
 李四挂机
⑩ DISCONNECT.indication  张三听到李四挂机，也挂机。
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Services, interface protocols and functions
Protocols can provide a service for upper
layer .
Protocols is “level”，
But Services is “Vertical ”，
Service is adopted by the lower layer of
interface.
Functions is the internal activities 。
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Services to Protocols Relationship
The relationship between a service and a
protocol.
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A layer in the OSI model represents a component of the total process of communicating. T
Layers of the ISO’s OSI reference model.
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The layers of the OSI model on each node
communicate with each other.
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Actual communication passes down through the layers on
the sending node and then up through the layers on the
receiving node.
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X.25
The first three layers of the OSI model have been
standardized, and together are called the X.25
standard for data transmission.
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GOSIP
government open system Interconnetion Protocol.
a subset of the OSI model that vendors must support
if they want to sell network services or equipment to
the U.S. government.
GOSIP is neither a new architecture nor a New
standard.It is a more precise specification of what
parts of the OSI model the government will use.
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3.9.2The Function Of Each Layer
LAYER 1 THE PHYSICAL LINK LAYER
It specifies the electrical characteristics
between the communications line and the
terminal or computer .
Cabling
Interconnect methods (topology / devices)
Data encoding (bits to waves)
Electrical properties
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What are the Physical Layer components on my
computer?
Typical equipment
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Physical Layer
This is the only layer at which actual bits pass.
The only layer that is implemented strictly in hardware.
The only layer that actually communicates across the transmission line to the
other node.
Layer1 only knows about a strem of bits.
Data transmission unit is bits.
Transmission media does not belong to the physical layer.
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LAYER2 THE DATA LINK LAYER
Function
Framing（成帧）
Line discipline
Flow control
Error control
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Data link layer
It is responsible for establishing a link between two
points on a network and ensuring that data are
successfully transferred between the two points .
Divide the data into smaller units for transmission.
（FRAME）
Detecting transmission errors and correcting errors.
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Network Interface Card Bridge
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LAYER 3 THE NETWORK LAYER
It is responsible for routing a message all the way
through the network from the transmitter to the
receiver is the network layer.
Transmission units is package.
Point-to-point
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LAYER4 THE TRANSPORT LAYER
Identifies actual address .but don’t know route.
Determine if the entire message was received
correctly.
is responsible for end-to-end (source to
destination) packet delivery
Task
…
两端点间可靠的透明数据传输
（应用进程间的逻辑通信）
…
network
end-to-end
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Also calculates a check sum for the entire
message.which is recalculated by layer4 at
The receiving end and compared.
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LAYER 5 THE SEEION LAYER
It is responsible for establishing the
communications rules between specific machines
or applications.
provides the mechanism for opening, closing
and managing a session between end-user
application processes.
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Session Layer Dialog
Pacing the rate of transmission so data are not
sent faster than the receiver can handle it.
Certain accounting function.
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LAYER 6 THE PRESENTATION LAYER
Provides common data formatting between
communicating devices.
Components make sure the receiving station can
read the transferred data
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Direct and Indirect Methods of Translation
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Concept of Encryption and Decryption
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Data Compression Methods
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Run-Length Encoding
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LAYER 7 THE APPLICATION LAYER
It is “where” the user works at a terminal with computer
software.
It provides a set of interfaces for applications to obtain access to
networked services as well as access to the kinds of network
services that support applications directly.
OSI
- FTAM,VT,MHS,DS,CMIP
TCP/IP - FTP,SMTP,TELNET,DNS,SNMP
Although the notion of an application process is common to both,
their approaches to constructing application entities is different.
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Five common application of OSI
OSI application
TCP/IP application
CMIP（通用管理信息协议）
SNMP、NETVIEW
DS（目录服务）
NDS、NTDS
FTAM（文件的传输、存取和管理）
NETWARE、 NFS
MHS（报文处理系统）
VTP（虚拟终端协议）
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TELNET
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Typical equipment
Gateway proxy firewall
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Summary of Layer Functions
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OSI模型是协助网络检修人员识别网络问题一种理想的框架
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3.10 TCP/IP ARCHITECTURE
TCP/IP ：
Transmission Control Protocol/Internet Protocol
The official TCP/IP model is now maintained by the IETF(ITU-T).
Because progress on setting standards for the OSI model was slow,
DARPA developed a set of protocols called TCP/IP.
TCP/IP has become the de facto standard protocol for internets.
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TCP/IP and the Internet
The acronym of the U.S. government's version of the open system
interconnection protocol is Internet.
In 1969
ARPA funded and created the “ARPAnet” network
In 1975
Convert from experimental to operational network
TCP/IP begun to be developed
In 1983
The TCP/IP is adopted as Military Standards
ARPnet  MILNET + ARPnet = Internet
In 1985
The NSF created the NSFnet to connect to Internet
NSF = National Science Foundation
In 1990
ARPA passed out of existence, and in 1995, the NSFnet became t
he primary Internet backbone network
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TCP/IP 4-layer or 5-layer
Application
Layer
Transport
Layer
Internet
Layer
Network Interface
Application
Layer
Transport
Layer
Internet
Layer
Network
Interface
Physical
CISCO and IBM use the four-layer model.
We use the five-layer model .
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A comparison of the layers of the OSI reference
model and the implementation of TCP/IP.
Network Interface
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PROTOCOLS
Each layer has several
protocols.
A layer define a data
communication function that
may be performed by certain
protocols.
A protocol provides a service
suitable to the function of
that layer.
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TCP/IP and the OSI Model
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Application layer
Provide services that can be used by other applications.
Incorporate the functions of top 3 OSI layers
Contains the programming required to support the user`s
application.
Different module are required for each application：
OSI application
TCP/IP application
CMIP（通用管理信息协议）
SNMP、NETVIEW
DS（目录服务）
NDS、NTDS
FTAM（文件的传输、存取和管
NETWARE、 NFS
理）
MHS（报文处理系统）
VTP（虚拟终端协议）
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TELNET
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Transport layer
Application layer directly run over the transport layer, corresponding
to OSI transport layer.
Two kinds of services: TCP & UDP.
TCP—Transmission Control Protocol,
reliable connect-oriented transfer of a byte stream.
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UDP—(User Datagram Protocol)
best-effort connectionless transfer of individual
messages.
The advantage of a connectionless protocol is
that there is no setup time at the beginning of the
communication.
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Internet layer
The internet layer of TCP/IP routes data between networks when
necessary using the IP protocol.
Machine A
Application
Transport
Internet
Router/Gateway
Internet
Network Interface
Network Interface
Network 1
Machine B
Application
Transport
Internet
Network Interface
Network 2
1. Transfer of information across networks through gateways/routers
2. Global unique IP address and IP packets
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Figure 2.11
Chapter 3 Network
Architetures and Standarts
Network interface layer
Handles the connection between the end system and the network to
which it is attached.
IP
packet
Machine A
Application
Transport
Internet
Network Interface
Packet
of network1
Router/Gateway
IP
IP
Internet
packet Network
packet
Packet InterfaceS
of network1
Network 1
Machine B
Application
Transport
Internet
Network Interface
Packet
of network2
IP
packet
Packet
of network2
Network 2
1. Corresponding to part of OSI network layer and data link layer
2. Different network interfaces: X.25, ATM, frame relay, Ethernet, etc
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Figure 2.11
Chapter 3 Network
Architetures and Standarts
Some Protocols in TCP/IP Suite
App.
Transport
Internet
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A Critique of the TCP/IP Reference Model
Problems:Service, interface, and protocol not distinguished.
Not a general model.does not require strict layering.
Application
ayer
Application
Layer
Transport
Layer
Transport
Layer
Internet
Layer
Internet
Layer
Network
Interface
Network
Interface
(a)
(b)
TCP/IP network architecture
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3.11 Architecture of the Internet
Guide: Informal architectural，it was not formalized until later.
The Internet is a network of networks.
The architects of the Internet don't insist on
documenting every detail of Internet operation
before implementation work began.
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Design Guidelines
The four initial requirements confronting the
Internet’s architects were :
Multiplexing Survivability service generality
supporting diverse network technologies
The primary initial requirement that the architects
of the Internet addressed were diverse network
technologies.
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Designer
What entities
security
Naming addressing routing
Concerned with
Modularized
Resources are allocated
It wasn`t until 1991 that the Word Wide Web was introducee and
Internet began to move from being an academic and military tool
to being the tool it now os for research,sales,and communication.
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3.12 MANUFACTURERS`ARCHITECTURES
Before OSI RM
IBM SNA
DEC DNA
Burroughs BNS
It is a proprietary architecture.
Manufacturers that developed network architectures
were primarily interested in developing proprietary
architectures on which to base their future products.
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SNA DNA ARCHITECTURES
IBM SNA
IBM SNA
DEC DNA
Because of customer and market pressures,the situation
changed and computer manufacturers became fully
supportive of the international communications standards.
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OTHER ARCHITECTURE
The ATM Reference Model
Novell NetWare RM
Windows NT RM
A Proposed Reference Model
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The ATM reference model.
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Chapter 3 Network
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NOVELL NETWARE RM
OSI
Novell NetWare
应用层
表示层
各种应用服务
会话层
传输层
SPX
网络层
IPX
数据链路层
物理层
网络接口卡与
网卡驱动程序
IPX/SPX （internetwork packet exchange /sequences packet exchange)
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Windows NT RM
层
7
6
5
4
OSI模型
客户机
应用层
文件I/O、命名管道邮
件槽mailslots
表示层
环境子系统
SMB
协议
重定向器
会话层
服务器
TDI
传输层
3
网络层
Windows NT 网络体系与模型
数据链路层
2
1
服务器
物理层
NetBEUI
TCP/IP
NDIS3.0接口
NDIS环境和驱动
以太网、令牌环
或其他
传输协议
NDIS
协议
NetBEUI NWLink
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A Proposed Reference Model
Andrew S.Tanenbaum:
5 layers of RM；
No presentation layer session； 应
用
层
传
输
层
网
络
层
数据链路层
物
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Chapter 3 Network
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3-13 A CAVEAT
It is important to understand that writing the
specifications for communications architectures
and the related standards is difficult work.
As actual communications systems have been
implemented over the years, most have not
strictly followed the OSI model.
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3-14 ADVS AND DISADVS
OF LAYERED ARCHITECTURES
1.Layering forces the modularization of function.
2. Good flexibility
3. Easy to achieve and maintain
4. Scalability
5.Standardization
A protocol stack is software that implements the
layers of a protocol
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OSI vs. TCP/IP Reference Models
OSI introduced concept of services, interface,
protocols These were force-fitted to TCP later .
In OSI, reference model was done before
protocols. In TCP, protocols were done before
the model
OSI: Standardize first, build later
TCP: Build first, standardize later
As actual communications systems have
been implemented over the years, most have
notstrictly followed the OSI model.
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课后习题
Exercises
1. The first three layers of the OSI model have been
standardized, and together are called the（ A ）.
√
A、 X.25 standard for data transmission
× B、 V. standard
× C、 consolidated transmission standard
× D、 Consolidated Transmission Protocol
Redo
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Answer
Chapter 3 Network
Architetures and Standarts
课后习题
Exercises
2. The ITU-T has created two sets of standards for the electrical
connection of terminals to communications networks. They are
called （ D ）.
× A、 the ISO and OSI standards
× B、 the TCP and IP standards
× C、 the PC and modem standards
√
D、 the V. and X. standards
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Chapter 3 Network
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课后习题
Exercises
3. IBM’s SNA （ C ）.
× A、 was never widely implemented
× B、 is a data link protocol
√
C、is a proprietary architecture
× D、 was an advanced mainframe computer for its time
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Answer
Chapter 3 Network
Architetures and Standarts
课后习题
Exercises
4. A network architecture is （ C ）.
× A、 the plan for the Internet’s evolution
× B、 a description of how a network is to be implemented
√
C、 a set of principles used as the basis for the design and implementation of a
communications network
× D、 None of the above
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Chapter 3 Network
Architetures and Standarts
课后习题
Exercises
5. The Interne （ D ）.
× A、 is implemented using the TCP/IP protocol
× B、 has the attribute of service generality
× C、 allows for diverse network technologies
√
D、 All of the above.
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Answer
Chapter 3 Network
Architetures and Standarts
课后习题
Exercises
1. A set of principles used as the basis for the design and
implementation of a communications network is called a
network architecture
________________
Answer
2.The_____________
OSI
reference model is the standard reference
point by which data communications networks are described and
measured.
Answer
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课后习题
Exercises
3.Two telephone callers may be connected but they will not be
communicate and exchange information if they speak
able to ___________
different languages.
Answer
4.The________
Physical _________
link
layer specifies the electrical
characteristics between the communications line and the terminal or
computer system.
Answer
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课后习题
Exercises
5.When data are received, the OSI presentation layer is
responsible for formatting
___________the data to meet the needs of the
application layer.
Answer
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