Gürkan RAKANOĞLU

OutlineOverview of Wireless Mesh NetworksVideo Streaming over Wireless NetworksApplications of Video over Wireless Networks

Overview of Wireless Mesh NetworksEmerging technology to provide open access

to the Internet with high bandwidth low cost

• Similar with Ad-hoc Networks, howeverAd-hoc Networks focused on military and

specialized civillian applications,while WMNs are for fullfilling the actual user

requirements• The most prospective candidates for the

Future Internet technology

Overview of Wireless Mesh Networks• WMNs consist of two types of nodes:

mesh routersmesh clients

• Mesh Routers:usually equipped with multiple wireless interfaces

(built on either the same or different wireless access technologies)

Compared to conventional router, it consumes lower transmission power through multi-hop communications

Enhanced MAC protocol with better scalability in a multi-hop mesh environment

Overview of Wireless Mesh Networks• The architecture of WMNs can be classified into

three types:

Infrastructure/Backbone WMNsClient WMNsHybrid WMNs

Overview of Wireless Mesh NetworksInfrastructure/Backbone WMNs

• In addition to the mostly used IEEE 802.11 technologies, various types of radio technologies can be used such as:Cellular networksSensor networks

• a mesh of self-configuring, self-healing links among the mesh routers

• With gateway functionality, mesh routers can be connected to the Internet

Overview of Wireless Mesh NetworksInfrastructure/Backbone WMNs

Overview of Wireless Mesh NetworksClient WMNs

• provides peer-to-peer networks among client devices

• client nodes constitute the actual network to perform RoutingConfiguration functionalities

• usually formed using one type of radios on devices

• actually the same as a conventional ad hoc network

Overview of Wireless Mesh NetworksHybrid WMNs

• combination of infrastructure and client meshing

• the routing capabilities of clients provide improved connectivity and coverage inside WMNs

Overview of Wireless Mesh NetworksThe Advantages of WMNs

costs less to set up a network, particularly for large areas of coverage

The more nodes you install, the bigger and faster your wireless network becomes

They rely on the same WiFi standards (802.11a, b and g) already in place for most wireless networks.

They are convenient where Ethernet wall connections are lacking -- for instance, in outdoor concert venues, warehouses or transportation settings.

Overview of Wireless Mesh NetworksThe Advantages of WMNs (cont.)

They are useful for Non-Line-of-Sight (NLoS) network configurations where wireless signals are intermittently blocked.

Mesh networks are "self configuring;" the network automatically incorporates a new node into the existing structure

Mesh networks are "self healing," (since the network automatically finds the fastest and most reliable paths to send data, even if nodes are blocked or lose their signal)

Overview of Wireless Mesh NetworksThe Advantages of WMNs (cont.)

Wireless mesh configurations allow local networks to run faster (because local packets don't have to travel back to a central server)

Wireless mesh nodes are easy to install and uninstall, making the network extremely adaptable and expandable

Video Streaming over Wireless Networks

Video Streaming over Wireless Networks

Wireless Network Challenges•Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)

Listenning line if avaliable, sending dataif ACK is not received, receiving the process(this loop enhances the reliability of the WLAN network, however, this process also adds jitter and latency to the video traffic)

•Request to send/clear to send (RTS/CTS) While this mechanism increases robustness it also adds to the latency of packets

Video Streaming over Wireless Networks

Wireless Network Challenges•key for running video applications over networks:

Low, predictable and consistent latency

• large amounts of bandwidth does not guarantee high quality video (because of the packet loss and packet errors)• In many wireless networks a 20% to 40% packet loss is not uncommon• If error occurs:

the packet is retransmitted (creates additional 4ms latency) up to 16 retransmissions can be required per packet error (This leads unacceptable levels of latency, delay and jitter, which is seen as frozen, jerky, or pixilated video on the viewing screen)

Video Streaming over Wireless Networks

Factors Contributing to Packet Errors, Latency, Jitter, and Delay

•InterferenceDirect spectrum interference and noise Near-angle interference Multipath and Reflection

• Other contributing factors

Video Streaming over Wireless Networks

Factors Contributing to Packet Errors, Latency, Jitter, and Delay

•Interference predominate cause of packet errors and loss in wireless networks

•Direct spectrum interference and noise occurs when:

• other wireless elements are set up on the same• overlapping frequencies• other devices create radio frequency waves (RF) that conflict with those of the wireless device (e.g. microwave ovens, portable telephones, and bluetooth devices can produce RF waves (noise) that interfere with many wireless communications systems )

Video Streaming over Wireless Networks

Factors Contributing to Packet Errors, Latency, Jitter, and Delay

•Near-angle interference can happen when there are 2 or more point-to-point shots with two centrally located antennas arranged physically close to one another

•Multipath and Reflection usually occurs when parts of a transmission beam are refracted from objects (e.g., glass, water, furniture, metallic surfaces) causing the signals to be received a different times or severely attenuated is likely to occur

in large enclosed environments such as warehouses and manufacturing facilities when used in proximity to large reflective objects such as high-rise buildings

Video Streaming over Wireless Networks

Factors Contributing to Packet Errors, Latency, Jitter, and Delay

•Other contributing factors• congestion• bandwidth limitations

Applications of Video over Wireless Networks

•Video streaming of news and entertainment clips to mobile phones is now widely available• For surveillance applications, cameras can be flexibly and cheaply installed, if a wireless network provides connectivity• A wireless local area network (WLAN) might connect various audiovisual entertainment devices in a home• In search-and-rescue operations, real-time audiovisual communication over wireless ad-hoc networks can save lives