Mobile communication plays a vital role to support interactive multimedia services such as wireless Internet, teleconferencing and etc. As the demand gets more complex, need for portability, wider bandwidth with higher data dates are needed to support the intricate file transfer, live video streaming or even voice over IP. The popularity of P2P has generated tremendous interest worldwide and radically changes the future of networking as anyone could access and share their files online. Generally, a P2P network is a network made up of computers/mobile devices which are connected to each other through the Internet.
Files of all type can be shared between computers on the P2P network. This allows Internet users to transfer files directly, rather than through the use of a website or server. In this paper, we will be summarizing about the various data transfer forms such as live video streaming, VoIP and file sharing over wireless mesh networks and network security. Since wireless data transfer can be risky and privacy is highly valued, network security plays an essential role to prevent the sensitive data from being stolen. II. VoIP The scalable VoIP routing architecture is the base for P2P communication system.
A good and efficient architecture is a key word in the next generation of global IP networks. A scalable VoIP architecture based on the control layer focuses on the following features: Efficient voice gateway allocation techniques. When voice routing fails, it can automatically go back to PSTN. This gives backup capability to the peer to peer network and tolerance of routing failures. Peer-to-Peer VoIP routing architecture. In this system, a routing forward and routing update protocol can supply a multi-routing algorithm to achieve a good QoS service.
There are three main methods for routing which are discussed in the following sections . A. CENTRALIZED APPROACH. It has a control node in the network that contains all the routing information of all agents in the networks. This control node is the bottle neck of the whole system. When this node is down, it will seriously harm the performance of the whole network . B. PURE DISRIBUTED APPROACH All the agents are connected with other agents and only one hop for any routing. It is a simple and quick routing technique, but it is not scalable and it is too expensive in huge networks.
C. OVERLAY APPROACH Each agent in this approach is just connected with the neighbor node and the routing takes place from one node to another. In order to improve the efficiency and QoS, Routing Request Forwarding Protocol is used. This protocol selects the route by weight of the neighbor nodes. Each node weight depicts the possibility to be selected . Ci has relationship with distance and load of the node. For this method to run smoothly, the weight information of each node has to be updated because the links between nodes change from time to time.
Thus the weight of nodes has to be modified to reflect the real information of the networks. Fig. 1. RD performance of Routing Algorithm Figure 1 is the result of test between static routing and dynamic weight-based routing . From Figure 1, benefits of dynamic weight-based routing method are apparent. The average routing delay is dramatically decreased in dynamic weight-based routing method. Dynamic weight-based routing technique shows its great efficiency and QoS in Peer-to-Peer approach for global Voice over IP. III. VIDEO STREAMING
Usages of handheld devices have been increasing exponentially each year and the need for internet mobility has to be improved in order to cope with the demands. Live video streaming has become a popular tool due to its convenience and versatility. Applications such as YouTube and BitTorrent are some of the popular Peer-to-Peer tools which provide video streaming. A hybrid approach is implemented where low-resolution multimedia content is streamed directly on mobile devices, while providing built-in metadata to retrieve the full resolution video file offline .
The core functions that deals with the video content delivery are the seed and bootstrap. Tree or mesh is used for the topology construction to determine which set of peer devices that a user can exchange content with. A Linux PC is used as a server along with the core functions at the server side. The seed is responsible to provide streaming content to the overlay where the source of the content can be a standard streaming server such as a window server . Next, the bootstrap entity is similar to the tracker in BitTorrent where end user device can request an initial peer list from the bootstrap.
This establishment will choose the appropriate partners and start receiving streaming video for playing out. Fig. 2. The Basic Components Fig. 2 demonstrate the basic components where the player is responsible for video decoding and playing, which in either window media format or real network player . The stream manager is responsible for the packetization when sending out a video stream and processing the data when receiving video packets . In order, for the device to locate the content from other devices, it needs to perform handshake with other devices known as membership relationship.
When the membership and partnership are initiated, the device successfully joins the overlay. Content related messages are exchange periodically with other devices. Based on the information, the device can determine from which set of end users to request and retrieve video content. The video content adopt a push-pull mechanism where it is divided into fixed size blocks and a video stream is divided into multiple sub-streams . Each end device can call for a sub-stream independently from a peer device instead of a single video block.
The device will continue to push all appropriate data blocks currently in its buffer to the requested device. The overall streaming performance is heavily dependent on the capability and stability of the internet connection. This might cause potential problems as it will drain the handheld device performance especially the battery life, a variety of interferences such as unstable wireless networks and the limited computation capability. As the handheld device moves, the IP address can change which will disrupt the video connection.
Although P2P live video streaming is popular, it is essential that video streaming applications should be less demanding especially for the handheld devices because of their performance limitations. IV. FILE SHARING FOR WIRELESS NETWORKS Wireless mesh networks (WMNs), which provides low-cost access to the Internet, has been widely used in computer networks for constructing large-scale distributed network applications. However, the same method is not suitable for direct use in mobile and wireless environment. Thus duel–layer mesh network architecture is introduced to support peer-to-peer file sharing over wireless mesh routers .
To achieve dual-layer WMNs, two-tier architecture is introduced for linking end-user computing terminals to mesh nodes. The mesh nodes generate a multi-hop wireless backhaul tier that routes data packets to and from gateway nodes that are connected to the Internet. Structured P2P protocols developed to transport large files by locating information in the P2P systems mainly depended on the performance of virtual topologies and distributed hash tables (DHTs). The function of the DHTs is to let a node to generate a query with a key and also give permits to the node to reset the value allocated to the key.
By this way, peer-to-peer file sharing becomes possible. Foreign agent is used to solve the problems introduced by Mobile IP (MIP), which gives a changeable IP address when a node moves from its home agent and connecting to other agents. P2P applications over a WMN is challenging because noise is introduced in the wireless medium which limits capacity and data transfer rates at the end nodes. Therefore, simple two-layer architecture for P2P file-sharing in wireless mesh networks and protocol for efficient file dissemination in a WMN is developed.
It helps in achieving more bandwidth efficient communication, reducing fail probability, and increasing peers throughput. V. CHALLENGES IN PEER-TO-PEER COMMUNICATIONS The development of file sharing P2P systems has opened a new page in area of internet technology as well as data management problems. The main problems are due to the quality of service and data security which has resulted in the phenomenon of free riding in many P2P file sharing systems. A. FREE RIDING Free riding phenomena occur when an individual utilizes the system resources without contributing anything to the system.
There are 70% of users of P2P file sharing systems don’t share any files and 63% of peers who do share some files but never answer and query . Only a few users share popular files and other users all try to connect these users and made them hot spots. This will overload their machines and also cause congestion problems on their networks. There are two solutions suggested to deal with the problem of free riding. These are explained below: Replication based scheme: It replicate file at every peer that downloaded them. Utility Function Based Schemes:
Three utility-based schemes have been introduced for controlling free riding in P2P systems to encourage users to share files on the systems. The three important factors related to user’s usefulness into account; the number of files shared by the users, total size of the data and the popularity of the files shared by the user . B. SECURITY Peer to peer networks, with distributed and decentralized peer devices are having major impact on mobile communications. Multiple new scenarios like multiplayer gaming, file hosting and social networks are using the peer to peer communication networks.
These communications are susceptible to security breaches due to lack of centralized point of control, highly dynamic network topology and vulnerability of wireless links. We characterize threats in two basic domains. In availability threats, a system is denied access to resources or is prevented from accomplishing a task. In a peer to peer environment, the topology of the network is not fixed. It is essential for all peers to collaborate with each other to make the communication network work efficiently. These devices are vulnerable to denial of service attacks because failure of peers can affect the overall system performance .
In integrity threat, the integrity of the system is compromised when a third party modifies the information sent to other device. A peer to peer network doesn’t really have a fixed central infrastructure. Mobile devices in peer to peer communication network make the process of authentication very complicated thus making the task of finding a malicious device even harder. Identification and authentication of the connected peers can resolve many of the problems discussed above but it is difficult to perform authentication and identification procedures in a decentralized and distributed network.
There are multiple solutions suggested by researcher to handle this situation. One of them is resurrecting duckling security policy . In this method the two devices are connected in master-slave relationship. The relationship is established through a secret key. The slave will always follow the master device thus forming a hierarchical secure chain of connections by every interaction with a new device. Some other methods are password-authenticated key exchange and self-organized public key infrastructure.
In a peer to peer network, routers are essential for the network to function properly therefore they are more vulnerable to attacks. These attacks can be classified in two categories, active attacks and passive attacks. In active attack, the attacker can drop, modify or fabricate false packets while in passive attack, the attacker eavesdrops the routing traffic to gather information which it can use in future attacks. To counter these threats, several secure routing protocols are designed. SAR protocol uses a trust hierarchy to protect the routes from untruthful devices .
The SRP protocol, the route discovery through security association, differentiates between legitimate and non-legitimate replies  while ARAN introduces a authentication, message integrity and non-repudiation environment to detect malicious activities of third parties . After verification, a relation of trust is very important between two peers. Reputation of peers is also taken into consideration but trust and reputation are two different things. Trust between two peers depends upon honesty, reliability and belief in each other capabilities while reputation is built with the help of recommendation from other peers.
The solutions discussed in above section enhance the security of the system but these measures do have their own costs. All the security measure comes down to the user who is operating the end system. For small mobile systems, these security measures can carry performance penalties as all handheld devices have limited battery life and computational capabilities. Similarly the use of security measure should be made efficient such that the user may not get annoyed with such measure and turn that security feature off instead of following it.
It is essential for the users to understand the reasons behind the security procedures.