1. 11 CS716 Advanced Computer Networks By Dr. Amir Qayyum

2. 2 Lecture No. 43

3. 3 Headers and Header Format

4. 4 HTTP Example 1

5. 5 HTTP Example 2

6. 6 Distributed Services

7. 7 HTTP and TCP Connections HTTP 1.0 establishes a separate TCP connection for each data item retrieved –Inefficient mechanism with connection setup/teardown HTTP 1.1 allows persistent connections –Client and server exchange multiple request/response messages over the same TCP connection –Reduced load on server, lesser delay, etc. With persistent connections, neither the client nor the server knows how long to keep the connection open

8. 8 Hypertext

9. 9 Static Document

10. 10 Dynamic Document

11. 11 Active Document

12. 12 Multimedia Applications

13. 13 Streaming Stored Audio/Video: Using a Web Server

14. 14 Streaming Stored Audio/Video: Using a Web Server with a Metafile

15. 15 Streaming Stored Audio/Video: Using a Media Server

16. 16 Streaming Stored Audio/Video: Using a Media Server and RTSP

17. 17 Real-time Transport Protocol (RTP) Application-Level Framing Data Packets –Sequence number –Timestamp (app defines “tick”) Control Packets (send periodically) –Loss rate (fraction of packets received since last report) –Measured jitter

18. 18 Protocol Stack for Applications Using RTP

19. 19 RTP Header Format PTMCCXPV = 2Sequence number Timestamp Synchronization source (SSRC) identifier Contributing source (CSRC) identifiers Extension header RTP Payload

20. 20 Padding of RTP Packet Pad count bytes UDP headerRTP headerRTP payloadPaddingPad count Length as carried in UDP header

21. 21 Time Relationship

22. 22 Jitter Jitter is introduced in real time data by the delay between packets

23. 23 Timestamps

24. 24 Playback Buffer To prevent jitter, we can timestamp the packets and separate arrival time from the playback time

25. 25 Real-time Traffic Issues A playback buffer is required for real- time traffic A sequence number on each packet is required for real-time traffic Real-time traffic needs the support of multicasting Mixing means combining several streams of traffic into one stream

26. 26 Transport Protocol for RTP TCP, with all its sophistication, is not suitable for interactive multimedia traffic because we cannot allow retransmission of packets UDP is more suitable than TCP for interactive traffic. However, we need the services of RTP, another transport layer protocol, to make up for the deficiencies of UDP

27. 27 Transport Protocol for RTP RTP uses a temporary even-numbered UDP port RTCP uses an odd-numbered UDP port number that follows the port number selected for RTP

28. 28 RTCP Message Types

29. 29 Communication Through SIP Proxies

30. 30 Message Flow for a SIP Session princeton.edu proxy bsd-pc.cis co.com invite 100 180ringing 180ringing 180ringing 200OK 200OK 200OK ACK 200OK BYE cisco.com provxy llp-ph.cs.princeton.edu invite ringing trying Media ringing

31. 31 Devices in H.323 Network H.323 terminal H.323 gatekeeper H.323 terminal H.323 gateway Conventional telephone network