Advanced Computer Networks: Lecture 43. This lecture will cover the following: headers and header format; distributed services; HTTP and TCP connections; dynamic document; multimedia applications; streaming stored audio/video: using a web server with a metafile; real-time transport protocol (RTP);...
CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 43 Headers and Header Format HTTP Example 1 HTTP Example 2 Distributed Services 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 Hypertext Static Document Dynamic Document 10 Realtime Transport Protocol (RTP) • ApplicationLevel Framing • Data Packets – Sequence number – Timestamp (app defines “tick”) • Control Packets (send periodically) – Loss rate (fraction of packets received since last report) – Measured jitter 17 Protocol Stack for Applications Using RTP Application RTP UDP IP Subnet 18 RTP Header Format V=2 P X CC M PT Sequence number Timestamp Synchronization source (SSRC) identifier Contributing source (CSRC) identifiers Extension header RTP Payload 19 Padding of RTP Packet Length as carried in UDP header UDP header RTP header RTP payload Padding Pad count Pad count bytes 20 Time Relationship 21 Jitter • Jitter is introduced in real time data by the delay between packets 22 Timestamps 23 Playback Buffer • To prevent jitter, we can timestamp the packets and separate arrival time from the playback time 24 Realtime Traffic Issues • A playback buffer is required for real time traffic • A sequence number on each packet is required for realtime traffic • Realtime traffic needs the support of multicasting • Mixing means combining several streams of traffic into one stream 25 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 26 Transport Protocol for RTP • RTP uses a temporary evennumbered UDP port • RTCP uses an oddnumbered UDP port number that follows the port number selected for RTP 27 RTCP Message Types 28 Communication Through SIP Proxies cisco.com proxy bsd-pc.cisco com bruc e@cisco.com princet on.edu proxy llp-ph cs.princeton.edu larry@princeton.edu 29 Message Flow for a SIP Session bsdpc.cisco.com cisco.com provxy princeton.e du proxy llpph.cs.princeton.edu invite 100 trying invite 100 trying invite 180 ringing ringin g 180 ringing ringin g 180 ringing ringin g 200 OK 200 OK 200 OK ACK Media BY E 200 OK 30 Devices in H.323 Network Conventional telephone network H.323 gatekeeper H.323 terminal H.323 gateway H.323 terminal 31 .. .Lecture? ?No.? ?43 Headers and Header Format HTTP Example 1 HTTP Example 2 Distributed Services HTTP and TCP Connections... RTCP Message Types 28 Communication Through SIP Proxies cisco.com proxy bsd-pc.cisco com bruc e@cisco.com princet on.edu proxy llp-ph cs.princeton.edu larry@princeton.edu 29 Message Flow for a SIP Session