Advanced Computer Networks: Lecture 43 - Dr. Amir Qayyum
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CS716
Advanced Computer Networks
By Dr. Amir Qayyum
1
Lecture No. 43
2
Headers and Header Format
3
HTTP Example 1
4
HTTP Example 2
5
Distributed Services
6
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
7
Hypertext
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Static Document
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Dynamic Document
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Active Document
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Multimedia Applications
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Streaming Stored Audio/Video:
Using a Web Server
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Streaming Stored Audio/Video:
Using a Web Server with a Metafile
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Streaming Stored Audio/Video:
Using a Media Server
15
Streaming Stored Audio/Video:
Using a Media Server and RTSP
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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
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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
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Jitter
• Jitter is introduced in real time data by the delay
between packets
22
Timestamps
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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
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