問題：
Which layer of the 7 layer model provides services to the application layer over the Session layer connection?
A.Network
B.Transport
C.Session
D.Presentation
E.Application
F.Datalink
Select the 1 best answer(選擇一個(gè)答案)
在7層OSI模型中為應(yīng)用層連接會(huì)話層及提供服務(wù)的是那一層？
解答：
在7層模型中分部情況是：物理層－數(shù)據(jù)鏈路層－網(wǎng)絡(luò)層－傳輸層－會(huì)話層－表示層－應(yīng)用層，在會(huì)話層和應(yīng)用層之間是表示層，表示層提供的服務(wù)是：為異種機(jī)通信提供一種公共語(yǔ)言，以便能進(jìn)行互操作。這種類型的服務(wù)之所以需要，是因?yàn)椴煌挠?jì)算機(jī)體系結(jié)構(gòu)使用的數(shù)據(jù)表示法不同。對(duì)于用戶數(shù)據(jù)來說,可以從兩個(gè)側(cè)面來分析：一個(gè)是數(shù)據(jù)含義被稱為語(yǔ)義同，另一個(gè)是數(shù)據(jù)的表示形式，稱做語(yǔ)法，像文字，圖形，聲音，文種，壓縮，加密等都屬于語(yǔ)法范疇。
例如：ASCⅡ，EBCDIC，JPEG，GIF，PICT，MIDI，MPEG
本題是講在會(huì)話層和應(yīng)用層之間的層是什么層：就是表示層。
記憶7層模型的方法：物－數(shù)－網(wǎng)絡(luò)－傳－會(huì)－表－應(yīng)。
正確答案：D
參考資料：
Sybex CCNA 4.0 - Chapter 1 ：Internetworking - The OSI Reference Model
The Presentation Layer
The Presentation layer gets its name from its purpose: It presents data to the Application layer and is responsible for data translation and code formatting.
This layer is essentially a translator and provides coding and conversion functions. A successful data-transfer technique is to adapt the data into a standard format before transmission. Computers are configured to receive this generically formatted data and then convert the data back into its native format for actual reading (for example, EBCDIC to ASCII). By providing translation services, the Presentation layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another one.
The OSI has protocol standards that define how standard data should be formatted. Tasks like data compression, decompression, encryption, and decryption are associated with this layer. Some Presentation layer standards are involved in multimedia operations too. The following serve to direct graphic and visual image presentation:
PICT A picture format used by Macintosh programs for transferring QuickDraw graphics.
TIFF Tagged Image File Format; a standard graphics format for high-resolution, bitmapped images。
JPEG Photo standards brought to us by The Joint Photographic Experts Group。
Other standards guide movies and sound:
MIDI Musical Instrument Digital Interface (sometimes called Musical Instrument Device Interface), used for digitized music.
MPEG Increasingly popular Moving Picture Experts Group standard for the compression and coding of motion vdeo for CDs. It provides digital storage and bit rates up to 1.5Mbps.
QuickTime For use with Macintosh programs; manages audio and video applications.
RTF Rich Text Format, a file format that lets you exchange text files between different word processors, even in different operating systems.
