Video over Wireless

Sowjanya

Talasila

Topics for discussion

Introduction Issues and solution Challenges Future work Conclusion References

Video

Video – the technology of capturing, recording, processing, transmitting and reconstructing the moving pictures using celluloid film, electronic signals or digital media

Quality of the video depends on the method used for capturing and storing

Characteristics of video stream

Frame rate – number of still pictures per unit time of video

Video resolution – size of video image

Aspect ratio – dimensions of video screen and video picture elements

Bits per pixel – determines the number of distinct colors

Contd..

Video quality – in terms of PSNR (ratio of max power of the video signal to the power of the corrupting noise)

Bit rate (digital only) – rate of information content in a video stream

Higher the bit rate, better the video quality

Introduction

With the development of broadband wireless networks, attention is given to the delivery of video over wireless networks

Issues

Rate control

Handover

Security

Issue 1 : Rate control

Importance of rate control: Results in full utilization of the link

by ensuring that sending rates are not too slow

Prevents congestion collapse by ensuring that sending rates are not too aggressive

Contd..

Ensures fairness among the users sharing the common link in a given network

TCP – Friendly Rate Control (TFRC)

This solution is proposed so that the performance of TCP doesn’t deteriorate when both TCP and UDP sessions co-exist in the internet

TFRC – a non TCP connection should receive the same amount of bandwidth as a TCP connection if they traverse on the same path

TFRC contd..

TFRC regulates the data sending rate according to the network condition, expressed in terms of RTT and packet loss probability, to achieve same throughput that a TCP connection would acquire on the same path.

TFRC Contd..

The TFRC sender changes the sending rate at least once a RTT

This affects the video quality

Experimental setup

Contd..

Assumptions: No cross traffic at node1 and

node2 No congestion at node1 No congestion and queuing delay

at node2 if and only if wireless bandwidth is underutilized

Contd..

The available wireless link bandwidth Bw and packet loss rate (caused by wireless channel error) Pw is a constant

Backward path is error free and congestion free

Contd..

Based on the above mentioned scenario and the assumptions, it is proved that, one TFRC connection underutilizes the wireless link as the available bandwidth is larger than the highest sending rate

Contd..

The total throughput of the application will increase with the number of TFRC connections until it reaches the hard limit of Bw(1-Pw)

For a particular packet size, the maximum number of TFRC connections to achieve proper utilization of the link is derived

Contd..

Any connection beyond this number will result in increase in RTT or packet loss rate and hence the sending rate of each connection has to be decreased

Multiple TFRC (MULTFRC)

A practical scheme called MULTFRC is developed to determine the optimal number of connections

Measures RTT and adjusts the number of connections accordingly to utilize the wireless bandwidth efficiently and ensure fairness between the applications

Contd..

The proposed system consists of two subsystems : RTT Measurement Subsystem (RMS) and Connections Controller Subsystem (CCS)

Based on the RMS, CCS responds

Comparision (One TFRC Vs MULTFRC)

Contd..

When there is a change in the route, say change in the wireless base station, the RTT changes and the performance of MULTFRC is affected

Employing route change detection tools such as Traceroute, helps in resetting the RTT value

Analysis of MULTFRC

Issue 2 : Handover Video applications are delay

sensitive. Certain delay in handing over the mobile device to another access point leads to loss in data.

In video streaming packet loss should be as minimum as possible

Low latency and low packet loss are the critical design issues

Handover decision based on packet delay

Delay is used as an indicator of when loss is likely to occur

UDP is used in the transport layer Hard handoff not preferred as

there could be a possibility for data loss by the time the mobile device is handed over to the next suitable access point

Experimental setup

Experiment results

Contd..

The MN has two WLAN interfaces, so that it can handoff from one WLAN to another

The MN uses soft handoff in the application layer, enabling the video decoder in the MN to present an uninterrupted video stream to the user

Contd..

Experimental setup

Experimental results

USHA and VTP

Cost effective Handoff solution with minimal

changes in the current internet infrastructure

Adapts to the user mobility faster while maintaining better connectivity for established network sessions

Contd..

Contd..

Handoff network configured using IP tunneling methods

Handoff server (HS) as one end of the IP tunnel and Mobile Host (MH) as other end of the IP tunnel

IP tunnel uses two virtual IP addresses and two fixed IP addresses

Contd..

Physical connection between HS and MH made using fixed IP addresses

The handoff client is responsible for automatically switching the underlying physical connection of the virtual tunnel to new interface

Contd..

USHA provides seamless handoff environment

Video Transfer Protocol (VTP) is used to adapt video streaming rates according to eligible rate estimates

Contd..

VTP provides substantial improvements to streaming performance in terms of perceived video quality and robustness against sudden changes in link capacities

Issue 3 : Security

Transmission over wireless can be intercepted by any suitable device within the transmission radius

If a network intruder is able to attach to unsecured AP, he can get access to the

wireless network and internet connection

MAC address filtering

Limit the access to only identifiable network cards with approved MAC addresses

Not a good solution as MAC addresses are broadcasted, any intruder can figure it out

Encryption

Only authorized receivers can understand the transmitted data

WPA – encryption security standard for wireless networks

Novel secure wireless video surveillance system

Video encryption is very important in WLAN environment since everyone can receive the video content and inject faked video packets

Architecture of secure video wireless system

Contd.. The video source is capture by the

camera nodes and is compressed and stored in the processor

Authentication information and encryption key is embedded to this

Camera nodes also act as routers and route the encrypted frames to the monitoring center

Real-time key embedding and key detecting process

Contd..

New keys are embedded in I-frame (intra frame) of group of pictures (GOP) and directly modulated into the direct current component of discrete cosine transform (DST) coefficients of luminance blocks

All GOPs will be encrypted by a selective encryption algorithms

Challenges

To improve QoS (video quality, packet loss, delay etc)

High variability of network throughput

Cost

Future work Rate and quality control

mechanism under lossy conditions Single physical WLAN interface to

access multiple networks simultaneously

In novel secure system, the misbehavior detection capability is limited by the computational power of

Contd..

the camera nodes. An adaptive mechanism has to be figured out to suit the application

Monitoring center is the only non-distributed component. Some solutions must be found to scale the network size

Conclusion

Video streaming in wireless networks is one of the upcoming multimedia applications which is still in it’s developing stages.

There are many areas of research to improve it’s performance over wireless networks.

References Rate control for streaming video over wireless

by Minghua Chen, Avideh Zakhor, August 2005, IEEE http://ieeexplore.ieee.org/iel5/7742/32173/01497856.pdf?tp=&arnumber=1497856&isnumber=32173

Seamless handover of streamed video over UDP in wireless LANs by Ger Cunningham, Philip Perry, Sean Murphy, Liam Murphy http://www.eeng.dcu.ie/~perryp/pub/cunningham4.pdf

Contd.. Adaptive video streaming in vertical handoff

by Chen L-J, Guang Yang, Gerla M etc, August 2004, IEEE http://ieeexplore.ieee.org/iel5/9259/29413/01331716.pdf?tp=&arnumber=1331716&isnumber=29413

A novel secure wireless video surveillance system based on Intel IXP425 network processor by Hao Yien, Xiaowen Chu, Oxtober 2005, ACM http://delivery.acm.org/10.1145/1090000/1089748/p62-hao.pdf?key1=1089748&key2=6505163411&coll=GUIDE&dl=GUIDE&CFID=72460738&CFTOKEN=4574127