1. (20%) Briefly Describe The Seven Layers In Osi Model.

1. (20%) Briefly describe the seven layers in OSI model. (Hint: Layer names and functions) Application (Layer 7) Presentation (Layer 6)

Session (Layer 5) Transport (Layer 4)

Network(Layer 3)

Data Link(Layer 2) Physical(Layer 1)

This layer supports application and end-user processes This layer provides independence from differences in data representation by translating from application to network format, and vice versa This layer establishes, manages and terminates connections between applications This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node At this layer, data packets are encoded and decoded into bits This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level

2. (20%) Answer the following question briefly. (a) (10%) How many bites are in IPv4, IPv6 and MAC addresses, respectively? IPv4 IPv6 Mac

32bits 264bits 48bit

(b) (10%) How to differentiate class A, B, C, D IP address. IP Address consists of 32 Bits, which means it's 4 bytes long. The first octec (first 8 Bits or first byte) of an IP Address is enough for us to determine the Class to which it belongs. And, depending on the Class to which the IP Address belongs, we can determine which portion of the IP Address is the Network ID and which is the Node ID. 3. (20%) Compare the circuit switching and packet switching Networks Technology Circuit switch A circuit switching network is one that establishes a circuit (or channel) between nodes and terminals before the users may communicate, as if the nodes were physically connected with an electrical circuit. Packet switch Packet switching is a digital network communications method that groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. The network over which packets are 1

transmitted is a shared network which routes each packet independently from all others and allocates transmission resources as needed 4. (40%, 課本 HW#20) Use your web browser to access the IETF web page (currently at www.ietf.org) and learn the Interet Standards process documented in RFC 2026. a. What are the different types of Requests for Comments (RFC)s? (Hint: The status ofInternet protocol and service specifications is summarized periodically in an RFC entitled Internet Official Protocol Standards.) Some RFCs document Internet Standards. These RFCs form the 'STD' subseries of the RFC series. Some RFCs standardize the results of community deliberations about statements of principle or conclusions about what is the best way to perform some operations or IETF process function. These RFC form the BCP (Best Current Practices) subseries. Not all specifications of protocols or services for the Internet should or will become Internet Standards or BCPs. Such non-standards track specifications are not subject to the rules for Internet standardization. Non-standards track specifications may be published directly as "Experimental" or "Informational" RFCs at the discretion of the RFC Editor in consultation with the IES b. What is an Internet Draft? During the development of a specification, draft versions of the document are made available for informal review and comment by placing them in the IETF's "Internet-Drafts" directory, which is replicated on a number of Internet hosts. This makes an evolving working document readily available to a wide audience, facilitating the process of review and revision. c. What are the difference among Proposed Standard, Draft Standard, and Standard? Proposed Standard specification is the entry level for the IETF standards track. A Proposed Standard specification is generally stable, has resolved known design choices, is believed to be well-understood, has received significant community review, and appears to enjoy enough community interest to be considered valuable. However, further experience might result in a change or even retraction of the specification before it advances. A specification from which at least two independent and interoperable implementations from different code bases have been developed, and for which sufficient successful operational experience has been obtained, may be elevated to the "Draft Standard" level. Elevation to Draft Standard is a major advance in status, indicating a strong belief that the specification is mature and will be useful. A Draft Standard may still require additional or more widespread field experience. A specification for which significant implementation and successful operational experience has been obtained may be elevated to the Internet Standard level. An Internet Standard is characterized by a high degree of technical maturity and by a generally held belief that the specified protocol or service provides significant benefit to the Internet community. d. Which group in the IETF approves a certain specification for standards‐track? A "standards action" -- entering a particular specification into, advancing it within, or removing it from, the standards track -- must be approved by the the Internet Engineering Steering Group (IESG).

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