3.1.1 Application layer
The real-time multimedia service over wireless network is the major application of our proposed scheme. How to provide the smooth and live voice or video streaming in this wireless application is our main challenge. In general, the good quality of network can improve the playback smoothness. However, quality of service (QoS) usua lly reflects the network condition, while the users may prefer better quality of experience (QoE). QoS is consisted of network parameters, which are measured objectively, such as throughput, packet loss, and latency, but QoE is evaluated subjectively by real humans. To make the application perform easily and smoothly in wireless network, QoE is more important than QoS. To ensure acceptable of QoE when transmitting real- time data in wire network is easy whereas it is difficult in wireless network. As a result, transmitting the data in our scheme would be the bottleneck due to applying the application in wireless network.
With considerations mentioned above, a real-time streaming transmitted smoothly over wireless network is the major concern of our application. Users can hold the devices with our application to speak with each other whenever they move. Since the movement of the users is unpredictable, making a progress in such application is extremely difficult. The major challenge for P2P streaming is to offer users satisfactory QoE in terms of playback smoothness and average packet delay. In the proposed scheme, we keep the acceptable QoE instead of QoS.
3.1.2 Session layer
As we introduced above, P2P overlay management is quite suitable for streaming
12
application. With scalability there is no limitation for the number of users in the network, because the more the user, the more peers able to forward data. As the number of peers grows, the messages sent or received by the peers grows significantly, decentralizing the messages is a strong point of P2P. Thanks to mobile devices that make inter-person communication more convenient, wireless network is getting more and more poplar in recent years. As a result, we use ad hoc mode instead of infrastructure mode in Wi-Fi or Wi-Max (we’ll mention soon), and self-organization is one of the characteristic in P2P that really takes a good advantage of ad hoc mode. A reliable P2P overlay is created by a set of good peers so as to reduce the number of messages sent in the network and the number of request by peers. A load balanced P2P application equally divides the overhead of the network. Owing to these characteristic of P2P, we design a Ring overlay that tries to feature these good points every minute of dripping.
The main idea of our scheme is simple and efficient. The characteristic of the scheme we proposed is that all peers only keep the information of two peers, the front peer and the rear peer, in the P2P overlay. The streaming data can be forwarded in a short time, and the management of peers joining and leaving is performed as usual. In general, the simpler protocol is suitable for Internet. The complexity of maintenance for every peer is O(1) approximately in our scheme so the complexity of the system is O(n) approximately, while n peers are in the system. Since the real- time streaming application is applied on MANET, the number of users is limited by the size of network topology in MANET. On the other hand, the distance of every user in MANET is only several microsecond, the end-to-end delay won’t be long and can be acceptable by users for real- time applications. Therefore, the P2P overlay we proposed can be deployed on the ad hoc network that we will explain later.
13
3.1.3 Transport layer
In our scheme, UDP and RTP are more suitable than TCP for forwarding streaming data immediately. In UDP and RTP packet loss happens more often than in TCP, consequently out-of-date information is not the issue we concern of in the live streaming.
Using UDP and RTP not only shortens the transmission time, but also reduces the overhead of the traffic in routing. Though UDP and RTP provides real-time data transmission, sometimes TCP can be applied owing to the rate of packet loss in wireless network is higher than in wired network.
3.1.4 MAC (network) layer
As previously stated in the session layer, the ring overlay based on P2P structure we proposed is quite simple and easy to maintain and create. Because of these advantages, the routing in the ad hoc as well as the routing table of the nodes that involved in the Ring overlay in the network layer can be simply constructed. Hence, the routing of the data can be speeded up, and the routing table will be easily managed in the whole topology. To save costs, every node broadcasts once instead of floods recursively the data to other nodes. As a result, the cost of network traffic, system overhead, and the message loading is significantly low.
The scheme we proposed is robust and available because it makes no t too much difference to deal with the MAC layer whether it is in WiFi ad hoc mode or WiMAX ad hoc mode. The two possible differences in these two modes may be transmission speed and transmission range. Nevertheless, our routing is in ad hoc mode, the transmission range of WiFi is limited; the data forwarding of the voice streaming doesn’t need too much bandwidth, hence the speed of WiMAX (802.16e offers 128/56 Mbit/s) in ad hoc mode
14
wouldn’t be the bottleneck.
Both 802.11 (which includes WiFi) and 802.16 (which includes WiMAX) define Peer-to-Peer (P2P) and ad hoc networks, where an end user communicates to users or servers on another Local Area Network (LAN) through its access point or base station.
Though there is just a little difference between using WiFi and using WiMAX, adapting different IP address schemes to the Ring overlay is quite different, such as IPv4 and IPv6.
VoIPv6 provides better QoS, scalability, reachability, end-to-end interworking, and security than VoIPv4. Implementing QoS with the assistance of classification and marking, IPv6 provides a reliable VoIP infrastructure. IPv6 prioritizes packets better than IPv4 and scales up the network topology. IPv6 with the redesigned header can speed up their path through the router therefore it performs the real “end to end” delivery. Due to these advantages in IPv6, traffic flow of live real-time application is more efficient and system overhead is reduced for VoIP.