課程名稱︰ 網際網路電話系統
課程性質︰ 選修
課程教師︰ 逄愛君
開課系所︰ 資訊所、網媒所
考試時間︰ 2006 Nov 7
是否需發放獎勵金：是
試題 :
IP Telephony (Midterm Exam)
November 7, 2006
1. What does ``carrier grade'' mean for VoIP services? (6%)
2. Please briefly descirbe and compare two evaluation tools for voice
quality for VoIP. (6%)
3. How does a VoIP system provide low-bandwidth voice transmission?
Is it applicable to PSTN? Why or Why not? (12%)
4. Why is voice carried over UDP, not TCP? (8%)
5. Please compare the ``Timestamp'' and ``Sequence Number'' fields
in an RTP packet. (6%)
6. Why do we need a separate signaling protocol from RTP for VoIP
systems? (8%)
7. How to use LSR (Last Sender Report Timestamp) and DLSR (Delay
since Last Sender Report) to compute the round-trip time? (8%)
8. Please compare between the mixer and translator defined in RTP
based on SSRC (Synchronization Source) and CSRC (Contributing
Source). (6%)
9. Elaborate on the advantages of SIP (3%) Also describe the funcitons
of SIP network entities: UAC, UAS, Proxy Server, Redirect Server,
Registrar. (12%)
10.Please compare between the stateful and stateless proxies (10%)
11.SIP Messages
(a) Describe the functions of the following SIP headers: To, From,
Contact, Via, CSeq, Expires, Retry-After, Content-Type,
Record-Route and Route. (10%)
(b) What is the difference between Request-URI and From, To
headers in SIP REGISTER? (5%)
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