Computer Networks · free preview
Layered Architecture and the Hourglass
A network architecture is a set of blueprints that tame complexity by organizing protocols into layers, where each protocol offers a service interface to local software and a peer interface to its counterpart on another machine, messages are encapsulated with a header at every layer down and stripped at every layer up, and the two great architectures are the seven layer OSI model and the Internet's four layer hourglass whose narrow waist is 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.
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