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分层体系结构与沙漏
网络体系结构是一套通过将协议组织成层来驯服复杂性的蓝图：每层协议向本地软件提供服务接口，向另一台机器上的对等方提供对等接口；报文每向下一层就增加一个首部进行封装，每向上一层就剥去一个首部；两大著名体系结构分别是七层OSI模型和因特网的四层沙漏，其窄腰为IP。
1. Abstraction and layering
Abstraction and layering
2. Protocols and their interfaces
Protocols and their interfaces
3. Encapsulation
Encapsulation
4. The OSI model and the hourglass
The OSI model and the hourglass
5. Two interfaces of a protocol
A protocol defines two distinct interfaces. Which pair correctly names them and states where each one faces?
6. Reading the encapsulation order
A web application's bytes travel down an Internet stack of UDP over IP over Ethernet. In what order are headers attached as the message descends?
7. The narrow waist
Why is the Internet architecture drawn as an hourglass, and what sits at the waist?
8. When a new service is easy to add
A designer wants to add a new communication service to a layered network without disturbing existing software. Layering makes this practical for which reason?
9. The protocol graph
In a protocol graph, the nodes are protocols and the edges connect a protocol to the services it uses. What does an edge mean exactly?
10. OSI against the Internet
Which statement correctly contrasts the OSI architecture with the Internet architecture?
11. The wrapper at each layer
Each protocol attaches a small data structure holding peer-to-peer control information to the front of the message it is given. Complete the sentence with the name of this structure. The control structure is called a
12. The Internet's waist
The Internet architecture is drawn as an hourglass with a single network layer protocol at its narrow waist. Name that protocol.
13. Seven layer vocabulary
The OSI reference model from the International Organization for Standardization organizes a network into a fixed number of layers that networking vocabulary still uses. How many layers does the OSI model have? Give the number as a word or digit.
14. The process named
When a protocol wraps the message handed down from above inside a new message of its own, attaching its header around both the original data and any headers already present, the data is said to be what? One word.