Assumptions for Dynamic Channel Allocation

Dynamic channel allocation are schemes for allotting shared network channels to competing users in a dynamic manner as per their requirements. The users may be base stations, access points or terminal equipment which are allotted channels from a central pool. There are a number of methods for dynamic channel allocation. The key assumptions of these methods are −

• Independent Traffic − It is assumed that the users are independent of each other, i.e. each user has to send or receive data which is independent of the data transmission of the other users in the network system. Each user has a program for generating frames for transmission. Once the user generates a frame for transmission, it is blocked until the frame has been successfully transmitted.

• Single Channel − The algorithms assume that all contending stations request for transmission via a single channel. All stations are considered to be equally capable of transmission. However, the algorithm may assign different priorities to them for contention.

• Detectable Collisions − If two frames from different stations are simultaneously transmitted, the resulting signal is distorted, and a collision is said to occur. If a collision occurs, all stations should be able to detect the collision. The frames lost due to collisions are retransmitted.

• Continuous Time or Slotted Time − Depending upon the allocation scheme, time may be considered as continuous or slotted. In continuous time, frame transmission can start at any instant. In slotted time, time is divided into discrete slots. If a slot does not contain any frame, it is called an idle slot; if it contains a single frame, then the transmission is successful; if it contains more than one frames, then a collision is said to occur.

• Carrier Sense or No Carrier Sense − The stations may or may not be capable of detecting whether the channel is in use before sending the frames. In algorithms which are based upon carrier sense, a station sends frame only when it senses that the channel is not busy. On the other hand, in algorithms based upon no carrier sense, the stations transmit a frame when it is available and later are informed whether successful transmission had occurred or not.