1-4_参考模型
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第一章引言
参考模型
主要内容
☐为什么需要参考模型？☐ISO-OSI参考模型
☐TCP/IP参考模型
☐两者的异、同
为什么需要参考模型/分层？
☐各层工作独立，层之间通过接口联系，降低协议工作的复杂程度
☐灵活性好，任何一层的改变不影响其它层
☐每层的实现技术可以不同，减少了实现的复杂度
☐易于维护，每层可以单独进行调试
☐便于标准化
如何分层？
☐分层原则：信宿机第n层收到的对象应与信源机第n层发出的对象完全一致。
☐典型分层模型：
OSI七层模型
TCP/IP（DoD）四层模型
Network Processes to Applications Provides network services to application processes (such as electronic mail,file transfer,and terminal emulation )Application
Presentation
Session Transport Network Data Link Physical
765
4
3
2
1The 7 Layers of the OSI Model
Network Processes to Applications Insure data is readable by receiving system Format of data Data structures Negotiates data transfer syntax for application layer Application
Presentation
Session Transport Network Data Link Physical
765
4
3
2
1The 7 Layers of the OSI Model Data Representation
Network Processes to Applications Establishes,manages,and terminates sessions between applications Application
Presentation
Session Transport Network Data Link Physical
765
4
3
2
1The 7 Layers of the OSI Model Data Representation Interhost Communication
Network Processes to Applications Concerned with transportation issues between hosts Data transport reliability Establish,maintain,terminate virtual circuits Fault detection and recovery
Information flow control Application
Presentation
Session Transport Network Data Link Physical
765
4
3
2
1The 7 Layers of the OSI Model Data Representation Interhost Communication End-to-end Connections
L3：网络层
Network Processes to Applications Provides connectivity and path selection between two end systems Domain of routing Application
Presentation
Session Transport Network Data Link Physical
765
4
3
2
1The 7 Layers of the OSI Model Data Representation Interhost Communication End-to-end Connections Address and Best Path
L2：数据链路层
Network Processes to Applications Provides reliable transfer of data across media
Physical addressing,network topology,error notification,flow control Application
Presentation
Session Transport Network Data Link Physical 765
4
3
2
1The 7 Layers of the OSI Model Data Representation Interhost Communication End-to-end Connections Address and Best Path Access to Media
L1层：物理层
Network Processes to Applications Wires,connectors,voltages,data rates
Application
Presentation
Session Transport Network Data Link Physical 765
4
3
2
1The 7 Layers of the OSI Model
Data Representation Interhost Communication End-to-end Connections Address and Best Path Access to Media Binary Transmission