The Application Layer

1
The Application Layer

• Chapter 7

2
DNS The Domain Name System

• The DNS Name Space
• Resource Records
• Name Servers

3
Domain Name System
Goal Convert host names to IP addresses. Provide
s a hierarchical naming system of domains. There
are currently about 200 top-level-domains. Each
domain is managed by a registrar. netlab.cis.temp
le.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.
4
The DNS Name Space

• A portion of the Internet domain name space.

5
Resource Records
Mapping 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.
6
Resource Records

• The principal DNS resource records types.

7
Resource Records (2)

• A portion of a possible DNS database for cs.vu.nl.

8
Name Servers
Having one big DNS server will all records is not
a good idea

• Part of the DNS name space showing the division
  into zones.

9
Name Servers (2)
flits.cs.vu.nl looking for IP address of
linda.cs.yale.edu

• How a resolver looks up a remote name in eight
  steps.

10
Multimedia

1. Introduction to Audio
2. Audio Compression
3. Voice over IP
4. Video over IP

11
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.
12
Audio compression
Waveform coding Fourier transform audio and
minimally encode components. Perceptual
coding Exploit 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.
13
Audio Compression

• (a) The threshold of audibility as a function of
  frequency.
• (b) The masking effect.

14
Streaming Audio

• A straightforward way to implement clickable
  music on a Web page.

15
Streaming Audio (2)
When packets carry alternate samples, the loss of
a packet reduces the temporal resolution rather
than creating a gap in time.
16
Streaming Audio (3)

• The media player buffers input from the media
  server and plays from the buffer rather than
  directly from the network.

17
Streaming Audio (4)

• RTSP commands from the player to the server.

18
Internet Radio

• A student radio station.

19
Voice over IP

• The H323 architectural model for Internet
  telephony.

20
Voice over IP (2)

• The H323 protocol stack.

21
Voice over IP (3)

• Logical channels between the caller and callee
  during a call.

22
SIP The Session Initiation Protocol

• The SIP methods defined in the core specification.

23
SIP (2)

• Use a proxy and redirection servers with SIP.

24
Comparison of H.323 and SIP
25
Video Analog Systems

• The scanning pattern used for NTSC video and
  television.

26
The JPEG Standard

• The operation of JPEG in lossy sequential mode.

27
The JPEG Standard (2)

• (a) RGB input data.
• (b) After block preparation.

28
The JPEG Standard (3)
(b)
(a)

• (a) One block of the Y matrix.
• (b) The DTC coefficients.

29
The JPEG Standard (4)

• Computation of the quantized DTC coefficients.

30
The JPEG Standard (5)

• The order in which the quantized values are
  transmitted.

31
The MPEG Standard

• Synchronization of the audio and video streams in
  MPEG-1.

32
The MPEG Standard (2)

• Three consecutive frames.

33
Video on Demand

• Overview of a video-on-demand system.

34
Video Servers

• A video server storage hierarchy.

35
Video Servers (2)

• The hardware architecture of a typical video
  server.

36
The MBone The Multicast Backbone

• MBone consists of multicast islands connected by
  tunnels.