In real situation, one or multiple pairs of nodes may need load moving. According to collected load information, a node will decide which pair of nodes (sending node and receiving node) needs load moving. (2) Make decision based on collected load information. There are 3 methods to collect information: periodical collection strategy, command driven strategy, and changing status driven strategy. The dynamic balancing algorithm usually contains 3 parts: By doing this, the system resource usage is improved and average task response time is shortened. It works in this way: according to the current load distribution situation, the algorithm can dynamically adjust tasks among nodes so that some tasks, having been allocated to an overload node, are moved to light-load nodes through communication equipment. However, the load status correlated balancing algorithm is based on the current state of a system.
Sometimes, opposite consequence may happen than expected, which makes the system more unbalanced, even deteriorating system performance. Because decision is made blindly without considering the current state of a system, this algorithm has very low accuracy and poor generality. The load status independent balancing algorithm is based on previous experience or system collected information to distribute external tasks among nodes or to reallocate the existing tasks on some nodes. However, the dynamic algorithm of load balancing is intelligent, which properly allocates the requests according to real load situations of servers. The static algorithm of load balancing mechanically allocates requests from clients according to the fixed and regular mode without considering the running state of servers. The former is called static balancing, and the latter is called dynamic balancing. In general, it may be divided into load status independent balancing and load status correlated balancing, according to the relation between balancing algorithm and load status. There are different ways to classify the load balancing algorithms. In a wired network, currently the load balancing technology is mainly applied to service servers such as Web server, mail server, and E-business server.ġ.2 Classification of Load Balancing Algorithms Nodes are configured differently from the view of hardware or software.Avoid the case of load jitter, that is, a task is frequently moved among nodes without being executed.The extra processing capability brings more network and host overhead, therefore, system performance is impaired. Load balancing requires extra processing capability, for example, to collect and save load information of nodes, make decisions, and move tasks.Precisely evaluate the load situation of a system.To implement load balancing, the difficulties are explained from the following aspects:
The load balancing has to solve two main problems: when to move tasks how to move tasks. Since load balancing plays an important role in wireless resource management, IEEE 802.11 Working Group-Task Group v (TGv) is especially focusing on the solution of load balancing problems in a WLAN system.ġ Load Balancing in a Wired Distribution Systemġ.1 Technical Difficulties of Load Balancing The purpose of load balancing technology is to balance the load difference among APs so that network resources can be efficiently utilized. Due to mobility of STAs (stations) and time-variability of wireless channels in an Extended Service Set (ESS) of Wireless Local Area Network (WLAN) system, the Access Point (AP) load may be different from each other.
The load balancing technology encounters more problems than in a wired system. However, when the technology of load balancing is applied to a wireless system, several new features appear. In fact, the problem that is faced by load balancing is an issue of combinatorial optimization of tasks.
The basic approach is to collect load information, make decisions with relevant algorithms, and reschedule allocated tasks by means of moving processes or tasks. In a wired distribution system, a task is the operation object adopted in a load balancing method. How to avoid the situation that busy nodes and idling nodes coexist in order to effectively improve resources usage and shorten average task response time? Load balancing is the answer to the problem. For over-load nodes, how to finish the tasks as soon as possible is an urgent affair however, for light-load nodes it is actually a waste of resources. Since tasks arrive randomly and node processing capability may be various from each other in a distribution system, some nodes may have too many tasks to be processed (called over-load), while others may be idling (called light-load). In a wired distribution system, load balancing refers to a method used to uniformly distribute external service requests to multiple back-end servers to improve the quality of network services.