Wireless Networks

XORs in The Air: Practical Wireless Network Coding
   Network has been encapsulated in the world of point-to-point abstraction all this time. To this point-to-point convention, the introduction of network coding is an idea that brings new aspect to the nature of the wireless network. Network coding is set out to reduce number of transmitted packets in the network to increase the throughput, efficiency, and the congestion. This paper is worth noting from other papers on network coding because it presents practical algorithms that are implemented and simulated in a wireless network.
   The main idea is that an XORed packet can be recovered if a router has all the packets the XORed packet was encoded with. With this, you only need to broadcast one packet compared to sending packets to each end-point. As number of gadgets that use wireless network increase, reduction in number of packets sent can significantly help in the common problems as interference and waiting time for transmission.
   One problem I see with this protocol is that the transmission success becomes even more non-deterministic because each hop needs to have proper packet information to decode the packet. In light of performance, the protocol determines how many packets to weave with XOR based on probability that the destination hop can decode it.
   Also, the protocol does not account for the usage of memory. Network coding cannot be done without a survey of information from the neighboring routers. Gathering and storing all these information can be almost impractical if there are thousands of routers in the network. As more hops are introduced to the system, the memory usage will grow exponentially. It is not scalable in my opinion.
   Even then, the idea of broadcasting an encoded packet to reduce the number of packets flowing in the network is a noble idea in the network field. With more engineering, this network coding can become more practical and ultimately cut down the amount of packets that need to be queued.

ExOR: Opportunistic Multi-Hop Routing for Wireless Networks
   Traditional transmission mechanism was designed back when survivability of the network outweighed almost all other design principles. Now the way Internet is being used is much different than the times the Internet was designed. Nowadays, the internet line is maintained by profit-motivate companies that can keep the Internet backbone at a stable condition. Recent emergence of mobile devices that can connect to internet brought more traffic to Internet. Traditional transmission mechanism cared about sending each packet to the destination on per packet basis but ExOR presents a protocol that can transmit packets in batch. Sending multiple packets at a time can increase the throughput of the connection because the overhead of sending a packet between each hop get reduced.
   ExOR is moving the transmission mechanism from per packet basis to batch mode, and on top of that the transmission is done via broadcasting which is also different from traditional unicast. By broadcasting the packets, transmission becomes shot-gun method in which whatever gets through goes to the destination. This protocol has been tested for packets over 100 Bytes and found to be more effective than the traditional mechanism. As packet sizes become bigger, batch mode becomes more efficient in reducing the number of communications. The key importance in this protocol is that the messages are broadcast in batch. When the number of communications get smaller, wireless network gets a huge improvement because the wireless network receives less interference from other signal sources in the network.
   The benefits of ExOR is not so sure at this point because it has not been tested in the open wireless network with variable environments, but it is worth a shot to examine this new way of transmitting packets. Current wireless transmission protocol does not scale well with many signal sources. ExOR helps in solving interference problem that occurs often if implemented for web applications that stream large data. It is one optimization the current wireless network can take to improve the scalability.