CS457/557 - Computer Networks: Chapter 15 - Networking Aspects of Videoconferencing, Imaging, and Multimedia

Introduction

VideoConferencing

Basic Components

Input - camera, microphone
Output - video monitor, speaker
processor - CODEC = video digitization

Frame - number of rows and columns of pixels
Bandwidth required (NTSC) = 640 pixels / line * 8 bits / pixel * 525 lines / frame * 30 frames /sec = 80.64 megabits/sec = 2 T-3 circuits

Reducing bandwidth

reduce amount of video data
video compression

H.261 Standard

defines two video resolution formats:
CIF(common interface format) 352x288
QCIF176x144
and defines video compression algorithms (reduces bandwidth requirements to 128K - 1.544 MB)

Video Compression

interframe coding - sends only information on parts of the frame that has changed
motion compensation - sends information on how to move an image

Wide Area Network services for Videoconferencing
Videoconference	Data Communications Interface Device	Wide Area Network Service
	CSU/DSU	Leased digital services 56K, 64K, T-1
	Switched services CSU/DSU	Switched digital services 56K,128K, 384K
	T-1 MUX	Leased T-1
	ISDN BRI interface	ISDN BRI (144 K)
	Inverse multiplexer (biplexer)	Bandwidth on demand ((multiple switched 56K or 64K)
	PBX	Leased or switched digital service

MCUs (multipoint control units) - videoconferencing wide area router (used for multipoint conferences)
H.243 - standardized interface between MCUs and CODECs
virtual bridges - integrating MCUs with inverse MUXs for bandwidth on demand access
video-hub - combines functionality of multiple inverse MUXs, central video wiring hub and a video switch or bridge
standalone desktop videoconferncing - CUSeeMe
LAN-based videoconferencing
IEEE 802.9 - standard for LAN-based videoconferencing

Available bandwidth the Determining Factor

Videoconferencing technology characteristics
Characteristic	Options/Implications
Desktop components	CODEC; Camera; Microphones;Monitor; Audio/Visual Processing Card Management Software; WAN/LAN Interface What are the bandwidth requirements?
LAN Issues	How well is the videoconferencing system integrated with the PC? How well can PC software be incorporated into the videoconference? Is the videoconferencing system LAN-enabled or LAN-based?
Performance issues?	Audio - What is the compression rate? How much bandwidth is required? Video - What is the minimum as wel as maximum frame refresh rate? Full color video? Added Features - FAX, electronic blackboard, data exchange, graphics capabilities?
Standards compliance	Support H.261, H.243?

video dialtone - video-on-demand requires much higher bandwidth

Local Loop Implications of Video Dialtone

HDSL - high bit rate digital subscriber loop = offers 1.544Mbps full duplex over 2 twisted pair (doesn't require repeaters)
ADSL - asymmetrical digital subscriber loop = only offers 16Kbps uplink
FITL - fiber in the loop = fiber to the curb (up to 135 Mbps)
VHDSL - full duplex over two twisted pairs = 3-6 Mbps
ISDN-PRI - 23B+D (1.5Mbps)
Wireless

Imaging: Productivity Improvement or Financial Burden?

Top-down analysis of imaging systems

Business

Business Process:	Business reengineering
Business Objectives:	Improved customer service Increased worker productivity Increased competitive advantage Reduced paper handling

Application

Workflow or document-flow application software
Must offer both user-oriented and inter-user effective retrieval and manipulation
Often custom written on a company-by-company basis at significant expense

Data

Image compression, data distribution analysis, and dynamic image indexing help to minimize transmission requirements

Network

Imaging network bandwidth

Technology

Processing Platforms	mainframe, mincomputer, LAN, client-server
Image Storage	proprietary image databases; image aware SQL databases
Storage Devices	magnetic disk drives; optical jukeboxes
NOS	image-enabled software
DBMS	image optimized or capable databases: ORACLE, INFOMIX, SYBASE, GUPTA
Front-end tools	image-enabled Lotus NOTES

User-oriented performance

locating and retrieving a folder
locating and retrieving a document within a folder
viewing multiple documents simultaneously on one's desktop

Inter-user effectiveness

Length of time required to fully process a particular document
Backlog of documents to be processed
Level of customer complaints due to slow and ineffective processing of paperwork

Data Requirements

one page scanned document = 30-50K
5 page folder = 250K
scanned photographs = 1 MB (with compression 25-30K)
images can be stored in databases as BLOB (binary large objects)

Technology: Image Platform Evolution

HCSS - High Capacity Storage Services
DMS - Document Management Services
IMS - Image Management Services

Putting it all Together: Multimedia Networking

Business Demand as a Driving Force

When multimedia can deliver true user-location transparency at a reasonable cost, then the demand side of the equation should be satisfied

Applications Must Meet the Business Demand

distributed multimedia groupware
virtual meeting room:

A shared on-screen chalkboard on which documents can be posted
Any conference participant may annotate or point on the chalkboard and have those notes and points appear on all conference attendees' workstations
Chat utilities allow conference participants to exchange text messages

Server-Based Multimedia Applications

authoring software - software to produce multimedia presentations

Client-Server-Based Multimedia Applications

Client-server-based multimedia application architecture

Clients

Multimedia-Enabled Applications
Client OS

Network

Multimedia middleware (Enterprise Networking) Quicktime -Microsoft Video for Windows

Multimedia API - Quicktime - Microsoft Audio Visual Kernel (AVK)

Servers

Server-Based Multimedia Systems
NOS
HArdware

Data Layer Implications of Multimedia

optical juke boxes containing multiple WORM
RAID technology

Network Implications of Multimedia

multimedia requires constant, guaranteed bandwidth = isochronous transmission
LAN Switches
Fast Ethernet
IEEE 802.9 - ISONET (Isochronous Ethernet) 16Mbps; sends video in reserved 6 Mbps channels via TDM

Multimedia on the WAN

requires compression - best done with a special-purpose chipset; i.e. DVI (digital video interactive)