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The Application Layer
Chapter 7
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DNS – The Domain Name System
a) The DNS Name Spaceb) Resource Recordsc) Name Servers
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Domain Name System
Goal: Convert host names to IP addresses.
Provides a hierarchical naming system of domains. There are currently about 200 top-level-domains.
Each domain is managed by a registrar.
netlab.cis.temple.edu has edu as the top-level domain, temple and cis are subdomains and netlab is the host.
So Temple University registered the temple domain name with the edu registrar. Then network services created a subdomain for CIS called cis. Finally we chose netlab as the name within cis.
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The DNS Name Space
A portion of the Internet domain name space.
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Resource RecordsMapping from host or domain name to IP addresses is stored as resource record in the DNS.
Resource records also store other information about a host or domain
A resolver is one that given a name queries the DNS server and returns the resource records associated with that name.
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Resource Records
The principal DNS resource records types.
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Resource Records (2)
A portion of a possible DNS database for cs.vu.nl.
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Name Servers
Part of the DNS name space showing the division into zones.
Having one big DNS server will all records is not a good idea
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Name Servers (2)
How a resolver looks up a remote name in eight steps.
flits.cs.vu.nl looking for IP address of linda.cs.yale.edu
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Multimediaa) Introduction to Audiob) Audio Compressionc) Voice over IPd) Video over IP
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Introduction to Audio
(a) A sine wave. (b) Sampling the sine wave. (c) Quantizing the samples to 4 bits.
CD quality audio requires 44,100 samples/sec with 16 bits per sample. That is a bit rate of 1.411 Mbps for stereo transmission. Clearly compression is required.
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Audio compressionWaveform codingFourier transform audio and minimally encode components.
Perceptual codingExploit flaws in human hearing. Based on psychoacoustics.MP3 (MPEG audio layer 3) is the most popular example.
Key property is: Some sounds can mask other sounds.
Frequency masking: Loud Jackhammers will mask a soft flute.Temporal masking: After a loud masking sound stops, the ear will take some time to recover and tune into the soft sound.
Idea is then to encoding only sounds that are not masked.
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Audio Compression
(a) The threshold of audibility as a function of frequency.(b) The masking effect.
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Streaming Audio
A straightforward way to implement clickable music on a Web page.
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Streaming Audio (2)
When packets carry alternate samples, the loss of a packet reduces the temporal resolution rather than creating a gap in time.
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Streaming Audio (3)
The media player buffers input from the media server and plays from the buffer rather than directly from the network.
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Streaming Audio (4)
RTSP commands from the player to the server.
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Internet Radio
A student radio station.
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Voice over IP
The H323 architectural model for Internet telephony.
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Voice over IP (2)
The H323 protocol stack.
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Voice over IP (3)
Logical channels between the caller and callee during a call.
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SIP – The Session Initiation Protocol
The SIP methods defined in the core specification.
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SIP (2)
Use a proxy and redirection servers with SIP.
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Comparison of H.323 and SIP
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Video Analog Systems
The scanning pattern used for NTSC video and television.
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The JPEG Standard
The operation of JPEG in lossy sequential mode.
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The JPEG Standard (2)
(a) RGB input data.(b) After block preparation.
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The JPEG Standard (3)
(a) One block of the Y matrix.(b) The DTC coefficients.
(a) (b)
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The JPEG Standard (4)
Computation of the quantized DTC coefficients.
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The JPEG Standard (5)
The order in which the quantized values are transmitted.
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The MPEG Standard
Synchronization of the audio and video streams in MPEG-1.
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The MPEG Standard (2)
Three consecutive frames.
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Video on Demand
Overview of a video-on-demand system.
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Video Servers
A video server storage hierarchy.
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Video Servers (2)
The hardware architecture of a typical video server.
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The MBone – The Multicast Backbone
MBone consists of multicast islands connected by tunnels.