思科认证考试：CCNA考试第七十九题

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1.What is the correct order for the OSI model？
P=Presentation， S=Session， D=Datalink， Ph=Physical， T=Transport， A= Application，
N=Network
9 D4 E1 h; `! dA. P S A PH D N T B. A P S T N D PH
; L1 c5 G$ [, U7 N1 E) b" vC. PH D N T A S P D. P S A T N D PH
& a. T1 a: W. CAnswer B. It is crucial you not only memorize this and know what each layer does.
2. What is encapsulation？
A. Putting the header on an incoming frame
B. Putting a header on an incoming segment
C. Putting a header on an outgoing frame
1 S, ?0 i. q! `/ @: ^: q. aD. Putting a header on an outgoing bit

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</p>Answer C. This also includes trailers and can be put on segments， packets， and frames.
! {1 W! F  u7 m6 T3. Which layer is most concerned with user applications？
A. Application B. Presentation C. Network D. Physical
Answer A.
4. Which of the following is de-encapsulation？
/ F8 J+ ?) I9 V) J. uA. Stripping the header from a frame
B. Putting a header on a segment
; r; O) j3 @: \% w3 R6 QC. Putting a header on a frame
  t! W9 o  C7 F: {' JD. Stripping a frame from a link
' n/ _+ ?/ s- {. O- ^Answer A. This also includes trailers as in question 2.
% D, a( ^: {7 y. t3 l! G6 A) ^5. What layer converts data into segments？
$ {2 X4 Y9 i! n$ U3 WA. Application B. Presentation C. Transport D. Physical
( \0 q! b6 N1 F2 W, {/ F2 z3 Y8 nAnswer C.
6. What layer converts data into Packets？
; i2 w! S( D' A0 ?4 n2 H) L; kA. Network B. Application C. Physical D. Data Link
Answer A.
7 R: I3 ?$ g$ b; N$ o& I, ?7. What layer converts data into Frames？
A. Application B. Physical C. Data Link D. Transport
Answer C.
, a, J5 _3 I0 M& j  ]4 D7 c8. What layer converts data into bits？
+ X( o9 J! I; h/ D$ v3 ~& j
' C/ s2 f* ]7 ^# NA. Application B. Session C. Data Link D. Physical

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</p>Answer D. All of the layers need to convert data into something that they can pass
. D, F# A/ A6 i9 I, z7 y: ~8 tdown to the next level， with the exception of the Application layer which hands
data to the Presentation layer. The Presentation layer encrypts， and compresses
before sending it to the Session layer for it s first conversion.
9. Which layer is most concerned with getting data from the beginning to the final
destination？
6 Y: f, A' |1 L& a! l- H8 t- xA. Application B. Presentation C. Session D. Transport
Answer D. The transport layer is most concerned with reliable transportation from
one end to the other.
10. Which of the following is not a part of the Session layer？
A. Establishing a session
B. Ensuring error free segments
C. Ending a session
, W9 F# h' r: i: q7 N- ~) u9 M' DD. Keeping the sender and receiver from sending a message at the same time
Answer B. That is the job of the Transport layer.