Ch 10. Multimedia Communications over WMNs

Ch 10. Multimedia Communications over WMNs

Myungchul Kim

[email protected]

– WMN

• high number of traversed hops

• Wireless channels

• Dynamic behavior of network nodes

Introduction

• Communication requirements– Dealy and bandwidth

– Multimedia applications: interactive and streaming

– Voice: max dealy constraint ~150ms : forward error correction

– Streaming: a few seconds: automatic repeat request

Multimedia characteristics and QoS requirements

• Robustness issues– MPEG


• Perceived quality evaluation– Throughput and packet loss rate?

– Subjective experiments

• Mean opinion score (MOS)

– Objective quality measures

• Perceptual evaluation of speech quality (PESQ)

• Perceptual evaluation of audio quality (PEAQ)

• The mean squared error (MSE)

• Peak signal-to-noise ratio (PSNR)


• Perceived quality evaluation• Peak signal-to-noise ratio (PSNR)


– Multimedia: bandwidth degradation, network latency, and radio interference

– 802.11: speeds up to 100Mb/s, QoS support, fast handoff, and mesh functionalities,…

• Network capacity– 802.11n: MIMO

– Multiple nodes

Protocols and open issues

• Network latency– Single-radio: half-duplex

– Multiradio mesh networks

– UCSB MeshNet result


• Handoff– Max allowed delay during handoff cannot exceed 50ms

– 802.11r: IP-based telephony over 802.11-enabled phones by speeding up handoffs between APs

– Layer 2 roaming delay: scanning, reassociation, and re-authentication

– Passive scanning: 100ms

– Active scanning: 20 – 300 ms

– Peremptive scanning

– A mobile device cannot know if necessary QoS resources are available at a new AP until after the handoff

– 802.11e: admission control


• Network routing– Proactive routing

– Reactive routing

– Routing metrics

– As the sender and receiver move, link quality metrics cannot quickly track the change in the link quality.

– No perfect protocol for QoS

– Adv of Multipath multimedia streaming

• High aggregate bandwidth to realtime multimedia applications

• Data partitioning

• Reduce the chance of interrupting the service due to node mobility.


– Satisfactory QoS level in WMNs?

– Multiple paths

• Streaming services– Routing?

– Multiple transmission paths

– Multiple Description Coding (MDC)

Innovative multimedia applications

• Streaming services– Layered coding

– How to optimally subdivide multimedia traffic over different paths

• Interactive voice services– Issues related with network congestion, delay and link quality

– The capacity is related to the channel bandwidth, voice codec, packetization interval and data traffic in the system

– VoIP over 802.11b using G.711 codec -> 800kb/s and 6 calls

– Node congestion depends more on the number of packets that need to be processed than on the actual bandwith

– Put more than one voice frame into the same packet -> delay increases -> end-to-end dealy increase

– Number of hops: from ten (with a single hop) to one when four hops


• Interactive voice services– Traffic delay variations

– QoS mechanism

• Prioritization of voice

• Changes to the 802.11 to reduce the jitter and delay by changing the transmission scheme

– Multiple description speech coding

– Roaming

– Dejitter buffers

– Adaptively adjust the dejitter buffer size to the network conditions so that the end-to-end delay is always kept as small as possible.

– Handoff-prediction with audio time-scaling


• Intervehicle communications– 802.11p

– Applications: road information, obstacle avoidance and automatic driving, virutal meeting,

– Different from generic MANET

• Driver behavior

• Mobility constraints

• High speeds


• Intervehicle communications– Routing layer

• Rapid changes in intervehicle networks

• Network fragmentation

• Effective network diameter is small

• The presence of redundant paths is often limited

• The number of nodes within the communications range grows linearly with the increase in the radio range.

• Roadside APs: the time interval in which the link is available is limited to a few seconds -> fast handoffs


• Intervehicle communications– Cross-layer design

– 97% communication for the urban and less than 50% for the rural

– High-speed mobility of network nodes and multihop communications.


• Real-time multiplayer games– Movement of the game characters

– The highest demand on QoS requirements and round-trip delays up to 150 ms with minimum jitter and low packet loss rate

– Bandwidth is not so important

– Players’ perception of jitter

– Routing protocols and QoS techniques

• End-to-end communications delay and jitter

– Cross-layer design• AODV: desabling its local repair property and implementing

a backup route mechanism

– Traffic menagment level• Priority queueing, timeouts, and real-time neighbor-aware

rate control


• Real-time multiplayer games– Movement of the game characters

– The highest demand on QoS requirements and round-trip delays up to 150 ms with minimum jitter and low packet loss rate

– Bandwidth is not so important

– Players’ perception of jitter

– Routing protocols and QoS techniques

• End-to-end communications delay and jitter

– Cross-layer design• AODV: desabling its local repair property and implementing

a backup route mechanism

– Traffic menagment level• Priority queueing, timeouts, and real-time neighbor-aware

rate control


Documents

Ch 10. Multimedia Communications over WMNs