Transcript Computer Networking From LANs to WANs: Hardware, Software

Computer Networking From LANs
to WANs: Hardware, Software, and
Security
Chapter 14
Multimedia Networking
Objectives
• Explain the basic properties of GIF, JPG, and PNG
image files
• Discuss the various sound file formats, such as
WAV, MID, and MP3
• Describe MPEG, Voice-over-IP, and multicasting
Computer Networking From LANs to WANs: Hardware, Software, and Security
2
Image Files
• Web browser image types
– Graphics Interchange Format (GIF)
– Joint Photographic Experts Group (JPEG)
– Portable Network Graphics (PNG)
• Image file types and their properties
– Affect Web page application development and
performance
Computer Networking From LANs to WANs: Hardware, Software, and Security
3
GIF images
• 256 colors possible (maximum)
– Eight bits needed to store pixel color
– Not photographic quality
– Suitable for buttons, banner ads, or other Web page
graphics
• Lossless compression
– Uses LZW (Lempel-Ziv-Welch) algorithm
• No original image data lost during compression
Computer Networking From LANs to WANs: Hardware, Software, and Security
4
GIF Images (cont’d.)
• Animation and transparency support built-in
– Animation images stored in a single GIF image file
– Appropriate time delays inserted between each stored
image display
• Transparency
– Accomplished by assigning one of the 256 color
values to be the transparent color
Computer Networking From LANs to WANs: Hardware, Software, and Security
5
JPG Images
• 24-bit color (16,777,216 colors possible)
– Provides high quality photographic-quality color
• Lossy compression
– Using the DCT (Discrete Cosine Transform) algorithm
on 8-by-8 blocks of pixels
– Superior to lossless GIF compression
• No animation or transparency features available
Computer Networking From LANs to WANs: Hardware, Software, and Security
6
Table 14-1 Comparing EARTH.JPG
and EARTH.GIF files
Figure 14-1 Sample image and
the effect of compression on text
Computer Networking From LANs to WANs: Hardware, Software, and Security
7
PNG Images
• PNG-8:
– Supports 8-bit color palette (256 colors), 1-bit
transparency
– Better compression than equivalent GIF image
• PNG-24
– Supports 24-bit color palette (16 M colors)
– Similar to JPG image except lossless compression
method used
• Animation
– Provided by the Multiple-image Network Graphic
(MNG) image format
Computer Networking From LANs to WANs: Hardware, Software, and Security
8
PNG Images (cont’d.)
• Pixel transparency
– Value between 0 (full transparency) and 255 (no
transparency
– Called alpha channels
– More realistic blending of images with backgrounds
Computer Networking From LANs to WANs: Hardware, Software, and Security
9
Sound Files
• Three types of sound files are popular on the Web
– WAV files
– MID
– MP3
Computer Networking From LANs to WANs: Hardware, Software, and Security
10
WAV Files
• Standard Windows audio file format
Figure 14-2(b) Windows Vista Sound
Recorder ready to record
Figure 14-2(a) Windows XP Sound
Recorder displaying a portion of BLAST.WAV
Computer Networking From LANs to WANs: Hardware, Software, and Security
11
WAV Files (cont’d.)
Figure 14-4 Changing the sampling
properties
Figure 14-3 BLAST.WAV properties
Computer Networking From LANs to WANs: Hardware, Software, and Security
12
MID Files
• File extension
– Used on Musical Instrument Digital Interface (MIDI)
files
• Contains information (MIDI sequencer commands)
– What notes to play, how to play them
• 128 pitched instruments can generate 24 notes in
16 channels
– PC sound card uses MIDI information to reproduce
notes
• Produces very complex sounds
– With small amount of data
Computer Networking From LANs to WANs: Hardware, Software, and Security
13
MP3 Files
• MPEG Audio Layer 3 files
• Moving Picture Experts Group (MPEG) audio, video
– Encoding methods for creating high quality, low-bit
rate multimedia files
– Three audio layers
• Use perceptual audio coding and psychoacoustic
compression for encoding audio, compressing data
Table 14-2 MPEG audio layer differences
Computer Networking From LANs to WANs: Hardware, Software, and Security
14
MP3 Files (cont’d.)
• Benefit: smaller file size, identical sound quality
• Used to burn audio CD-ROM
• Downloadable into a portable MP3 player
Table 14-3 Comparing WAV and MP3 file sizes
Computer Networking From LANs to WANs: Hardware, Software, and Security
15
The Digital Conversation
Figure 14-5 Analog and Digital conversions
Computer Networking From LANs to WANs: Hardware, Software, and Security
16
Transmitting Data over a Network
• Network overhead
– 26 bytes of Ethernet framing
– 24 bytes of IP header
– 24 bytes of TCP header
Figure 14-6 Network overhead in an Ethernet frame
Computer Networking From LANs to WANs: Hardware, Software, and Security
17
Transmitting Data over a Network
(cont’d.)
• Network overhead (cont’d.)
– Affects bandwidth requirements
– 74 bytes of overhead
• 5.28% of a 1400 data byte message
• 92.5% of a 80-byte data message
Computer Networking From LANs to WANs: Hardware, Software, and Security
18
Transmitting Data over a Network
(cont’d.)
Table 14-4 Transmitting 8000 bytes (64,000 bits) of data
using multiple packets
Computer Networking From LANs to WANs: Hardware, Software, and Security
19
Voice-over-IP
• Method for sending voice and fax data
– Uses the IP protocol
• Interfaces with the public switched telephone
network (PSTN)
– Attempts to provide same service quality
• Several different IP protocols used
– Real-Time Transfer Protocol (RTP)
– Real-Time Control Protocol (RTCP)
– Resource Reservation Protocol (RSVP)
Computer Networking From LANs to WANs: Hardware, Software, and Security
20
Figure 14-7 VoIP architecture
Computer Networking From LANs to WANs: Hardware, Software, and Security
21
Voice-over-IP (cont’d.)
• H.323 standard
– Specifies voice processing, gateway/terminal
operation
• Factors impacting conversations
–
–
–
–
End-to-end delay
Jitter
Packet loss
Out-of-order arrivals
Computer Networking From LANs to WANs: Hardware, Software, and Security
22
Voice-over-IP (cont’d.)
• Standards exist for rating VoIP conversation quality
• Lacks security
– Can extract entire conversation from packet capture
Table 14-5 Voice Quality Test Scores
Table 14-5 Voice Quality Test Scores
Computer Networking From LANs to WANs: Hardware, Software, and Security
23
Voice-over-IP (cont’d.)
• VoIP services becoming more common
– Residential, business communities
• VoIP service providers
– Offer all traditional phone company features
• Many VoIP network devices on the market today
Figure 14-10(a) Linksys PAP2 indicator lights
Computer Networking From LANs to WANs: Hardware, Software, and Security
24
Video
• Great bandwidth required
• User can easily spot problems with video stream
• Real-time video requirements
– Powerful processor, fast network connection
• Protocols used to manage information stream
– RTP, RTCP, RSVP
• Video cameras now affordable for PCs
Computer Networking From LANs to WANs: Hardware, Software, and Security
25
MPEG Files
• Defines set of digital video parameters
– Bit rate, resolution, compression techniques
• Video compression: lossy
– Uses Discrete Cosine Transform
• Three frame types:
– I (Intra): stand-alone video frame
– P (Predicted): generated using most recent I or P
frame
– B (Bidirectional): generated based on past, future
frames
Computer Networking From LANs to WANs: Hardware, Software, and Security
26
Multicasting
• Eliminates large portion of duplicated information
– Server sends one copy of video data to a
multicasting-enabled switch
– Switch forwards single copy to other multicastingenabled switches
• They replicate video data, forward copies to each client
• IP multicasting
– Uses Internet Group Management Protocol (IGMP)
• MBone
– Experimental multicasting backbone
• Supports multicasting over the Internet
Computer Networking From LANs to WANs: Hardware, Software, and Security
27
Figure 14-14 Unicasting versus multicasting
Computer Networking From LANs to WANs: Hardware, Software, and Security
28
Games
• Network computer games growing in popularity
• One machine runs game in server mode
– Multiple game client machines connect to it
• Factors developers consider for real-time
environments
– Available bandwidth, communication delay,
processing speed
• Packet problems affect game play
– Dead reckoning
• Combats effect of packet loss on player position
Computer Networking From LANs to WANs: Hardware, Software, and Security
29
Troubleshooting Techniques
• Bandwidth issues
– Streaming music and video are high bandwidth
applications
• CODEC issues
– Video file must be played with the same CODEC
used to create the video file
• Quality of Service
– Affects users ability to use audio, video, VoIP phone
services
• May be necessary to prioritize network traffic
Computer Networking From LANs to WANs: Hardware, Software, and Security
30
Summary
• Web browsers accept
– GIF, JPG (or JPEG) or PNG images
• Audio file types
– Wave, MIDI, MP3
• Streaming media describes any media type (audio,
video, animations ,etc.) that may be streamed
• Voice-over-IP (VoIP)
– Method for sending voice and fax data using IP
Computer Networking From LANs to WANs: Hardware, Software, and Security
31