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CMSC691C Multimedia Networking A Course Overview. Padma Mundur CSEE, UMBC [email protected] List of Topics. Multimedia Networking: Source Representations, Networks, and Applications Multimedia Compression Fundamentals & Coding Standards Scalable Video Coding for Heterogeneous Networks

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Cmsc691c multimedia networking a course overview l.jpg

CMSC691C Multimedia NetworkingA Course Overview

Padma Mundur


[email protected]

List of topics l.jpg
List of Topics

  • Multimedia Networking: Source Representations, Networks, and Applications

  • Multimedia Compression Fundamentals & Coding Standards

  • Scalable Video Coding for Heterogeneous Networks

  • Fundamentals of IP Routing

  • IETF QoS Efforts

  • Existing Solutions for Scalable Multimedia QoS

The telephone voice network l.jpg
The Telephone (Voice) Network

  • Circuit switched network:

    • Analog (since1890): manually switching

    • Digital: voice  bit stream (64 Kbps)

    • Better channel utilization by time-divisionmultiplexing:

    • Reservation fixed for the whole transmission




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The Internet (Data) Network

  • Packet-switched network:

    • packets share resources (buffers, links)

    • reservation not fixed, but on-demand

    • multiple links (connectivity, reliability)

    • buffers (store, process, forward)

    • control information in packets (s,d,seq#)

Internet users growth l.jpg
Internet Users Growth


  • 1B mobile users by 2005 and 1B Internet users by 2005

  • 90% of all new mobile phones will have internet access by 2003 (Morgan Stanley Dean Witter, May 2000)

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Video Clip


Wireless Browsing




Information Search

Music Streaming

Digital Photos



Multimedia over IP Networks

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Multimedia Networking Applications

  • Media Broadcast: simultaneous pushing of content to multiple recipients

    • Network IP Multicast – Multicast enabled routers and switches

  • Hosted Streaming: content users initiate requests and content networks/providers push content through network

  • Interactive Conferencing: no centralized source of contents

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Multimedia Broadcast over IP

IP (internet protocol) makes it

possible to link all (global) nodes together independent of applications and terminal devices

content provider


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  • Standalone player

  • Java based player

  • Browser plug-in player

  • Appliance








Send Stream

To Clients




  • Decode

  • Buffer

  • Sync.

Send Request to Media Server

Send Request

To Servers



Hosted Multimedia Streaming

To hear or view a media file without downloading it

Interactive conferencing and meeting server l.jpg


Bandwidth concern for multipoint interaction

Interactive Conferencing and Meeting Server

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Meeting Client


How A Server Distributes the Data

Meeting Token Holder

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Meeting Client


Dynamic Token Passing

Old Token Holder

New Token Holder

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Bits per


Bit Rate

Telephone Voice

Wideband speech

Wideband audio

(2 channels)

B/W documents

Color Image


CCIR-601 (PAL)

SIF (standard)

CIF (common)

QCIF (quarter)




8000 samples/sec


44.1 Ks/sec

300 dpi (dots/inch)

















96 Kbps

224 Kbps

1.412 Mbps

(2 channels)

90 Kb/inch2

6.3 Mb/image

248.8 Mbps

248.8 Mbps

31 Mbps

37 Mbps

2.3 Mbps

Multimedia Signals and Bitrates

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IP Networks

  • IP uses packet switching

    • Suitable for unexpected burst of data without establishing an explicit connection.

    • Bandwidth is shared statistically so data can be sent at any time.

  • IP is not reliable nor delay-bounded.

    • Best effort

    • Queuing delay, especially when congested.

    • Network failures can cause temporary packet loss.

    • Time critical applications cannot operate well due to large e-mail attachments and Web surfing

    • Delay and jitter degrade voice and video performance

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Multimedia Signals

  • Text

  • Speech

  • Audio

  • Image (B/W and color)

  • Video

  • Graphics & Animation

  • Documents (various formats)

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Image & Video Coding Standards

  • Combination of lossy (transform coding) and lossless (run-length, Huffman, Arithmetic coding, LZW, etc) coding techniques along space and time.

  • JPEG - Joint Photographic Experts Group

    • Still image compression, intraframe picture technology

    • Motion JPEG (MJPEG) is sequence of images coded with JPEG

  • MPEG - Moving Picture Experts Group

    • Defined by ISO/IEC, several standards MPEG1, MPEG2, and now MPEG4

  • H.263/H.263+/H.26L - Videophone/Conferencing

    • Low to medium bit rate, quality, and computational cost defined by ITU

    • Used in H.320 and H.323 video conferencing standards

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Huffman Code

Run-length Code

A Complete JPEG Encoding


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From Image to Video Coding

  • Intra-frame compression (similar to JPEG)

    • Remove redundancy within frame (spatial)

  • Inter-frame compression (motion compensation)

    • Remove redundancy between frames (temporal)

  • Rate Control (constant bit-rate or constant SNR)

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Video Coding Standards

  • MPEG1 – VHS quality, VCD (1992)

    • CIF images, 4:2:0 sampling, 1.5 Mbs, Frame encoding

  • MPEG2 - broadcast quality, HDTV and DVD (1994)

    • CCIR 601 images, 4:2:2 sampling, 4-15 Mbs

    • Interlaced and progressive scanning, Frame and field

  • H.261 for videotelephony (p=1,2) & videoconferencing (p>= 6) (1992)

    • Improve JPEG through temporal redundancy

  • H.263 – low bitrate video coding (1995)

    • Half pixel motion compensation, 4 (optional) modes

    • Optimized VLC tables & better motion vector prediction

  • H.26L(H.264) – flexible, high quality video applications (2002)

    • 1/4 pixel accuracy for MC, 7 different block sizes for ME/MC

    • Residual coding uses 4x4 blocks & an integer transform

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MPEG-4: An Emerging Standard

  • For multimedia applications

    • Interactive natural & synthetic contents

    • Various access conditions: low bit-rate, error prone, heterogeneous (scalable)

    • Management and protection of media contents

  • Standard

    • 1st generation (1998-2000): 1st+2nd versions, frame based content creation & communication, 64-384 Kbps, mobile videophone (3G and IP) and digital camcorder

    • next generation (2001-): upto 2Mbps, frame/object based, scalable streaming, interactive set-top box

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Heterogeneous IP Networks

  • Adaptive Rate Control

  • Scalable Coding

    • Real-time bandwidth estimation

    • Receiver feedback

    • Adaptive Multicast control

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Video Scalable Coding

  • Why a scalable video codec?

    • Compression efficiency

    • Robustness with respect to packet loss

    • Adaptation to the changing bandwidth

  • Techniques of scalable video coding

    • Temporal

    • Spatial

    • Signal-to-Noise Ratio (SNR)

    • Data Partition

    • Wavelet

    • Fine Granularity Scalability (FGS)

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IP Stack: A Layered Architecture

Web (HTTP), E-mail (SMTP),

File transfer (FTP), Name resolution (DNS),

Remote terminal (TELNET), …

Reliable multi-connection bit-stream (TCP),

unreliable multi-connection (UDP).

Unreliable end-to-end delivery of

packets up to 64 KB.

Point-to-point links (PPP, SONET, …),

LANs (Ethernet, FDDI, wireless, …)

Ip packet routing delay and loss l.jpg














IP Packet Routing: Delay and Loss

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FIFO - First In First Out queuing, definitely not compatible with QoS since high priority packets can get stuck behind low priority packets

Queuing and Scheduling (1)

Queuing and scheduling 2 l.jpg

Priority Scheduling - services higher priority queue whenever there are packets present, can lead to starvation of lower priority queues

Queuing and Scheduling (2)

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Custom Queuing (or Weighted Round Robin Scheduling) - services all queues (with different service time) within a traffic class, round robin assuring that all queues get appropriate treatment

Queuing and Scheduling (3)

Queuing and scheduling 4 l.jpg

Weighted Fair Queuing (WFQ) - queue is serviced based on a weight proportional to the bandwidth dynamically allocated to it

Queuing and Scheduling (4)

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Congestion Control & Queue Discard

  • Tail Drop

    • Drops arriving packets when buffers in queue are full, can lead to network meltdown due to TCP global synchronization

  • RED = Random Early Detection

    • Queuing algorithm for congestion avoidance that randomly discards packets from queues in an attempt to prevent TCP retransmits simultaneously on all flows

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Congestion Control & Queue Discard

  • WRED = Weighted Random Early Discard

    • A variant of RED that attempts to weight queues for random early discard

  • Tri-Color Marking (deterministic)

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IP QoS and Multimedia

  • Quality of Service (QoS) methods aim at trading quality vs. resources to meet the constraints dictated by the user, the functionality and the platform.

  • QoS originally developed in network communication, and recently extended to the domain of multimedia communication.

  • QoS relevant in multimedia scalable systems, where the resources and the functionality can be controlled by a set of parameters.

Ip quality of service qos l.jpg
IP Quality of Service (QoS)

  • Techniques to intelligently match the performance needs of applications to available network resources

  • QoS Metrics

    • availability

    • delay (latency)

    • delay variation (jitter)

    • throughput (average and peak rates)

    • packet loss

Ietf ip qos efforts l.jpg
IETF IP QoS Efforts

  • Policy based IP QoS Solutions

    • Integrated Services (RSVP protocol): flow based

    • Differentiated Services (DiffServ byte settings): packet based

    • Multi-Protocol Label Switching (MPLS): flow+packet based

  • IP Multicast and Anycast

  • IPv6 QoS Support

Connection oriented qos l.jpg
Connection Oriented QoS

  • Int-Serv (Integrated Services): IETF RFC 1633

    • Defined by RSVP requires resource reservation at each hop end-to-end for each IP packet flow, and end-to-end signaling along nodes in the path

    • Reserve resources at the routers so as to provide QoS for specific user packet stream

    • This architecture does not scale well (large amount of states)

    • Many Internet flows are short lived, not worth setting up VC

Integrated services rsvp l.jpg
Integrated Services / RSVP

  • Sender sends a “PATH” message to the receiver specifying characteristics of traffic

    • every intermediate router along the path forwards the “PATH” message to the next hop determined by the routing protocol

  • Receiver responds with “RESV” message after receiving “PATH”. “RESV” requests resources for flow

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Connectionless QoS: IP Diff Serv

  • Mark IP packet to specify treatment: IETF RFC 2474, e.g., first class, business class, coach, standby

  • Per Hop Behaviors (PHBs) based on network-wide traffic classes

  • Flows are classified at the edge router based on rules, and are aggregated into traffic classes, allowing scalability

  • Diff Serv uses the IP header TOS byte (first 6 bits), which is renamed the DS field

  • Diff Serv defines code points (DSCP) for the DS field, DE (default) = 000000 = best effort, and EF (Expedited Forwarding) = 101110 = low latency, etc.

Diffserv operation l.jpg

DS Domain

DS Domain

DiffServ Operation

  • Each ISP configures its own routers to match the service that it offers, and each ISP has its own DiffServ Domain.

Customer Site









(service level agreement)



Edge Router

Interior Nodes

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MPLS Fundamentals

  • MPLS is a forwarding scheme that tags packets with labels (independent of layers 2,3) that specify routing and priority (IETF RFC 3031)

  • Enables scalability by alleviating IP over ATM problems

    • Defines a homogeneous network based upon label-switching

    • Requires all devices (i.e., ATM switches) to be capable of routing

  • Enables differentiated services via QoS-aware label switched paths (LSPs)

  • Designed to run over a wide range of media

    • ATM, frame relay, and Ethernet

Unicast multicast l.jpg








Multimedia ip multicast l.jpg
Multimedia IP Multicast

  • Why multicast?

    • When sending same data to multiple receivers

    • Better bandwidth utilization

    • Lesser host/router processing

    • Receivers’ addresses unknown

  • Applications

    • Video/audio conferencing

    • Resource discovery/service advertisement

    • Media streaming and distribution

Ip multicast service model l.jpg
IP Multicast Service Model

  • IETF RFC 1112, each multicast group is identified by a class D IP address

    • Range from through

  • Well known addresses designated by Internet Assigned Number Authority (IANA)

    • Reserved use: through

  • Members join and leave the group and indicate this to the routers

  • Multicast routers listen to all multicast addresses and use multicast routing protocols to manage groups

What ipv6 can offer l.jpg

128-n bits

who you are

where you are connected to

n bits

What IPv6 can Offer?

  • Global Addressing (128 bits):

    • 1 million networks per human

    • 20 hosts per m2 of Earth

  • Plug and play:

  • Efficient mobility (instant-on ad-hoc networking)

Ipv6 key features and advantages l.jpg
IPv6: Key Features and Advantages

  • Increased Address Space (128 bits)

  • Efficient and extensible IP datagram

  • Improved host and router discovery

  • Plug and Play

  • Enhancements for Quality of Service (QoS)

  • Improved Mobile IP support

  • Coexistence with IPv4

  • Built in security (authentication and encryption) in IP layer

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IPv6 Support of QoS

  • IPv6 Flow Labels provide support for Data Flows

    • Packet Prioritizing-- sure that high priority traffic is not interrupted by less critical data

  • IPv6 supports Multicast & Anycast

    • Multicast delivers data simultaneously to all hosts that sign up to receive it

    • Anycast allows one host initiate the efficient updating of routing tables for a group of hosts.

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Existing Scalable MulticastSolutions

  • Content Distribution Networks

  • Receiver-Driven Layer Multicast (RDLM)

  • Source Adaptive Multi-Layer Multicast (SAMM)

  • Filtering Method

  • Destination Set Grouping (DSG)

  • Multiple Description Coding (MDS) of Multimedia

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Distributing Content to the Edges

  • Adding backbone bandwidth is not the best solution, the last mile (edge) connection is even more critical.

  • How to direct traffic to the site (routing) and resolve the appropriate server (load balancing) that will perform best for a particular query (front-end content delivery).

  • How to keep content updated efficiently (back-end content delivery)

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Getting Contents to the Edge

  • Caching (on-demand “pull”)

    • Contents may be “pulled” from another proxy cache in the hierarchy or the origin of the contents.

    • Problems: stale content delivery, hit statistics loss, dynamic contents

  • Replication (changes made on the origin server)

    • Updates are “pushed” to replica using a “back-end” content delivery system.

    • The origin server is in total control (database keep track of content changes), with scalable architecture (multicast or packet-relay).

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Getting Contents to the Edge

  • Resolution Problem

    • The best site: geographic vs. network proximity (quickest service)

    • Domain Name Service (DNS) criteria: # of authoritative servers (domain) hops, # of router hops, health/load of site, round trip latency, packet loss rate, etc.

  • Hybrids of Caching/Replication

    • Reverse Proxy Cache: all queries directed to proxy caches by load balancer for front-end delivery.

    • Pre-Filling of Proxy Caches: parts of the Web site are pre-filled to the cache – i.e., replica in proxy cache form

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Content Distribution Network (CDN)

  • Service providers using proprietary caching/replication technologies to build overlay networks (internet or satellite) to deliver contents – application level multicast

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Receiver-driven Layer Multicast (RLM)

  • RLM Protocol Concepts (McCanne 1996):Source: No active role in the protocol.Receivers: On congestion, drop a layer. On spare capacity, add a layer.

  • When to drop a layer:Whenever congestion happens. Congestion is expressed explicitly in the data stream through lost packets.

  • When to add a layer:Join-experiment: To carry out active experiments by spontaneously adding layers at “well chosen” time.

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RLM Characteristics

  • A fixed number of multicast groups.

    • Lack of granularity adaptation

    • Severe quality degradation when pack loss on base layer.

  • Slow adaptation to changes of varying network bandwidth (Liu, Hwang 2002)

    • Synchronization is crucial

    • Well-developed protocol is crucial

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Source Adaptive Multi-layer Multicast

  • SAMM Protocol Concepts (Suda 1998):

    • Video is encoded into several layers and each layer has an unique discarding priority.

    • When a network link experiences congestion, packets from the lowest priority layer are discarded.

    • The video source obtains backward feedbacks from receivers to adjust the number of video layers and also the encoding rate for each layer.