Fading Channels

As far as channel is concerned, wired networks are affected only by the attenuation of the signal. But for a wireless network there is yet another factor that is to be considered, called as fading. The signal that is transmitted by the transmitting antenna undergoes attenuation, reflection and travels through multiple paths before reaching the receiver. Hence the effect of all these on the signal strength has to be taken into consideration and hence there is a necessary to model the channel.

Order of execution

Previous schemes for fair queuing that achieved nearly perfect fairness were expensive to implement; specifically, the work required to process a packet in these schemes was O(log(1) ), where O(1). is the number of active flows. This is expensive at high speeds. DRR achieves nearly perfect fairness in terms of throughput, requires only O(1) work to process a packet, and is simple enough to implement in hardware

Wired Networks

Wired networks' equipments are generally connected to each other with the help of wires and cables. Generally the cables that are being used to connect this type of networks are category 5 or category 6 cables. The connection is usually then established with the help of some easy to use physical devices like Switches and Hubs in between to increase the strength of the connection. These networks are usually more efficient and much faster than wireless networks. Once the connection is set there is a very little chance of getting disconnected. There are several protocols and standards which can be readily used in the wired network. The major advantage is the reliability of the connection in a wired network.

Advantages

1. A wired network offer connection speeds of 100Mbps to 1000Mbps
2. Physical, fixed wired connections are not prone to interference and fluctuations in available bandwidth, which can affect some wireless networking connections.

Disadvantages

1. Expensive to maintain the network due to many cables between computer systems and even if a failure in the cables occur then it will be very hard to replace that particular cable as it involved more and more costs.
2. When using a laptop which is required to be connected to the network, a wired network will limit the logical reason of purchasing a laptop in the first place.

CSWFQ

CSWFQ tries to achieve both short-term fairness in the rate proportional guarantee sense and a reasonable system throughput. In wireless systems, the situation is different notably with respect to the amount of bandwidth seen by the different flows at any given time. A flow might be anything like real time or non-real time traffic and many more. Scheduling is done for each and every flow based on several criteria

Inference

In a wireless packet network, a number of mobile hosts transmit or receive data from base station. Transmission of data from mobile host to base station is called uplink and reception of data from base station is called downlink. Since the scheduler has no access to uplink packets tagging mechanisms that are often used in wire line oriented scheduling discipline such as WFQ, SCFQ and their variants cannot be used

Fair Queueing

Previous schemes for fair queuing that achieved nearly perfect fairness were expensive to implement; specifically, the work required to process a packet in these schemes was O(log(1) ), where O(1). is the number of active flows. This is expensive at high speeds. DRR achieves nearly perfect fairness in terms of throughput, requires only O(1) work to process a packet, and is simple enough to implement in hardware

Opportunity based deficit round robin

It is based on the premise that fairness has to be ensured only in the opportunity given to the flow to transmit data and not in the actual result achieved by the flows. The more the node utilizes the network resource effectively, the more it is given the opportunity to transmit the data. While the nodes that utilizing the network resources inefficiently are given less opportunity and hence the algorithm reduces the chances of packet loss, thereby increasing the throughput.

Overview of networks

Wired network like ethernet and hiperlan saw a great acceptance among the users. Now it is the era of the wireless technology. Mobility offered by the wireless technology has been the most sought after feature. With the development of WiFi and WiMAX it becomes necessary to standardize and optimize the protocols used for the wireless networks.

Packet scheduling

With the development of multimedia applications, the network is now required to carry huge traffic. During the periods of maximum usage, the buffers at each of the nodes get filled and hence dropping becomes inevitable. In such a scenario there must be a procedure that allows fair buffer allocation to each of the flows. This is where the scheduling discipline comes into picture. The schedulers decide which flow has to be served first.

Scheduling intro

So far we have discussed a mere definition of Scheduling. It would be appropriate and intriguing for the readers, if we kick off with the actual concept. For understanding the scheduling concept In computer science, a scheduling algorithm is the method by which threads or processes are given access to system resources, usually processor time. This is usually done to load balance a system effectively. The need for a scheduling algorithm arises from the requirement for most modern systems to perform multitasking, or execute more than one process at a time. Scheduling algorithms are generally only used in a time slice multiplexing kernel. The reason is that in order to effectively load balance a system, the kernel must be able to suspend execution of threads forcibly in order to begin execution of the next thread.

The algorithm used may be as simple as round-robin in which each process is given equal time (for instance 1 ms, usually between 1 ms and 100 ms) in a cycling list. So, process A executes for 1 ms, then process B, then process C, then back to process A.

More advanced algorithms take into account process priority, or the importance of the process. This allows some processes to use more time than other processes. It should be noted that the kernel always uses whatever resources it needs to ensure proper functioning of the system, and so can be said to have infinite priority. In SMP systems, processor affinity is considered to increase overall system performance, even if it may cause a process itself to run more slowly. This generally improves performance by reducing cache thrashing.

Zidane

He is a legend. He played as a mid fielder for France. He captained France to the World Cup finals at 2006. He head-butted Marco Materadzi during the final match of the World Cup. Unfortunately France lost the match and it was a dismal end to his international career too. He played for Real Madrid in Spanish Premiera.