Ch 10. Multimedia Communications over WMNs

Myungchul Kimmckim@cs.kaist.ac.kr

– WMN issues• high number of traversed hops• Wireless channels• Dynamic behavior of network nodes

Introduction

• Communication requirements– Delay and bandwidth

– Multimedia applications: interactive and streaming– Voice: max delay constraint ~150ms : forward error

correction– Streaming: a few seconds: automatic repeat request

Multimedia characteristics and QoS requirements

• Robustness issues– MPEG

Multimedia characteristics and QoS requirements

• 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)

Multimedia characteristics and QoS requirements

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

Multimedia characteristics and QoS requirements

– 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

Protocols and open issues

• 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 not feasible for VoIP: 100ms– Active scanning: 20 – 300 ms– Preemptive scanning– A mobile device cannot know if necessary QoS resources are

available at a new AP until after the handoff– 802.11e: admission control

Protocols and open issues

• 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.

Protocols and open issues

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

Innovative multimedia applications

• 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

Innovative multimedia applications

• Intervehicle communications– 802.11p– Applications: road information, obstacle avoidance and

automatic driving, virutal meeting,…– Different from generic MANET

• Driver behavior• Mobility constraints• High speeds

Innovative multimedia applications

• 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

Innovative multimedia applications

• Intervehicle communications– Cross-layer design– Link availability: 97% communication for the urban and

less than 50% for the highway scenario– High-speed mobility of network nodes and multihop

communications.

Innovative multimedia applications

• Real-time multiplayer games– Support the 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 [78]

• AODV: disabling its local repair property and implementing a backup route mechanism

• Traffic management level: priority queuing, timeouts, and real-time neighbor-aware rate control

Innovative multimedia applications