1. 1 TAC2000/2000.7 802.16 IP Telephony Lab Midterm Exam November 9th, 2008

2. 2 TAC2000/2000.7 802.16 IP Telephony Lab 1. According to the characteristics of TCP, explain why most multimedia applications choose UDP as the transport protocol.  Speech Small packets, 10 – 40 ms Small packets, 10 – 40 ms Occasional packet loss is not a catastrophe Occasional packet loss is not a catastrophe Delay-sensitive Delay-sensitive  TCP: connection set-up, ack, retransmit → delays 5 % packet loss is acceptable if evenly spaced 5 % packet loss is acceptable if evenly spaced  Resource management and reservation techniques  A managed IP network In-sequence delivery In-sequence delivery  Mostly yes 王筱婷

3. 3 TAC2000/2000.7 802.16 IP Telephony Lab 2. STUN vs. Symmetric NAT 陳韋霖

4. 4 TAC2000/2000.7 802.16 IP Telephony Lab Full Cone NAT  Client send a packet to public address A.  NAT allocate a public port (12345) for private port (21) on the client.  Any incoming packet (from A or B) to public port (12345) will dispatch to private port (21) on the client. Client IP: 192.168.0.1 Port: 21 NAT Port: 12345 Mapping Table Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 IP: 123.123.123.123 192.168.0.1:21 12345

5. 5 TAC2000/2000.7 802.16 IP Telephony Lab Use STUN for SIP Registration  Use port 5060 to send a packet to STUN Server  Receive public address & port mapped to client:5060 from STUN Server  Fill the SIP register message with client’s public address & port, send to proxy server IP: 123.123.123.123 Port: 12345 STUN Server IP: 222.111.99.1 Port: 20202 NAT Proxy Server IP: 140.128.10.129 Port: 5060 REGISTER sip:222.111.33.1 SIP/2.0 Via: SIP/2.0/UDP 123.123.123.123:12345 From: Bob To: Bob … Contact: Bob … Client IP: 192.168.0.1 Port: 5060

6. 6 TAC2000/2000.7 802.16 IP Telephony Lab Symmetric NAT  NAT allocate a public port each time the client send a packet to different public address and port  Only incoming packet from the original mapped public address and port will dispatch to private port on client Client IP: 192.168.0.1 Port: 21 NAT IP: 123.123.123.123 Port: 12345 Mapping Table 192.168.0.1:21 12345 (for A : 20202) 192.168.0.1:21 45678 ( for B : 10101) Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 IP: 123.123.123.123 Port: 45678

7. 7 TAC2000/2000.7 802.16 IP Telephony Lab 3. TCP Connection Establishment/Termination  Basic 3-Way Handshaking  Seq:X, SYN  Seq:Y, SYN, ACK: X+1  Seq:X+1, ACK: Y+1 黃培愷

8. 8 TAC2000/2000.7 802.16 IP Telephony Lab  結束 TCP 連線的 4 個步驟  Seq:X, ACK: Y. ACK..FIN  Seq:Y, ACK: X+1, ACK  Seq:Y, ACK: X+1, ACK..FIN  Seq:X+1, ACK: Y+1, ACK

9. 9 TAC2000/2000.7 802.16 IP Telephony Lab 4. 183 Session Progress  From the textbook: Enable the callee to indicate to the caller that a one-way media path should be opened to provide in-band call progress information, such as “Please hold while we attempt to connect your call”. Enable the callee to indicate to the caller that a one-way media path should be opened to provide in-band call progress information, such as “Please hold while we attempt to connect your call”.  From RFC 3261 Section 21.1.5 Convey information about the progress of the call that is not otherwise classified. The Reason-Phrase, header fields, or message body MAY be used to convey more details about the call progress. Convey information about the progress of the call that is not otherwise classified. The Reason-Phrase, header fields, or message body MAY be used to convey more details about the call progress.  Resource reservation?

10. 10 TAC2000/2000.7 802.16 IP Telephony Lab PSTN Interworking  PSTN Interworking A SIP URL to a telephone number A SIP URL to a telephone number A network gateway A network gateway  PSTN – SIP – PSTN MIME media types MIME media types For ISUP For ISUP  SIP for Telephony (SIP-T)  The whole issue of interworking with SS7 is fundamental to the success of VoIP in the real world. 潘韋勳

11. 11 TAC2000/2000.7 802.16 IP Telephony Lab Interne t Draft RFC Proposed Standard RFC Draft Standard RFC Internet Standard Technically complete Multiple Interoperable Implementations Significant Operational Experience Yes No 5 The Internet Standards Process 林易瑋

12. 12 TAC2000/2000.7 802.16 IP Telephony Lab 6. Un-register  Registration Via: Via: From: and To: From: and To: Call-ID: Call-ID:  host-specific Contact: (not empty) Contact: (not empty) Content-Length: Content-Length:  Zero, no msg body CSeq: CSeq:  A response to any request must use the same value of CSeq as used in the request. Expires: Expires:  TTL (Time to live)  0, un-register 唐瑋勵

13. 13 TAC2000/2000.7 802.16 IP Telephony Lab 7. Redundant Payload Original 1 234 1 12 2334 1 12 34 1 234 Redundancy Packet Loss Reconstructe d Stream 李霓雅

14. 14 TAC2000/2000.7 802.16 IP Telephony Lab Presentation  10/28 Internet Protocol 林易瑋 TCP/UDP 黃驛翔 Internet ProtocolTCP/UDPInternet ProtocolTCP/UDP  12/23 Audio I/O - 潘韋勳 Audio I/OAudio I/O  12/30 oRTP - 陳韋霖  1/6 eXosip - 賴韋立  1/13 Final Report