In: Computer Science
MACs
Question 3:
3a.) Why should a MAC be configurable?
3b.) What are the effects of RF radio realities on the MAC
layer?
Answer 3a.)MAC Addresses are unique 48-bits hardware number of a computer, which is embedded into network card (known as Network Interface Card) during the time of manufacturing. MAC Address is also known as Physical Address of a network device. In IEEE 802 standard, Data Link Layer is divided into two sublayers –
MAC address is used by Media Access Control (MAC) sublayer of Data-Link Layer. MAC Address is word wide unique, since millions of network devices exists and we need to uniquely identify each.
1. Unicast – A Unicast addressed frame is only sent out to the interface leading to specific NIC. If the LSB (least significant bit) of first octet of an address is set to zero, the frame is meant to reach only one receiving NIC. MAC Address of source machine is always Unicast.
2.Multicast – Multicast address allow the
source to send a frame to group of devices. In Layer-2 (Ethernet)
Multicast address, LSB (least significant bit) of first octet of an
address is set to one. IEEE has allocated the address block
01-80-C2-xx-xx-xx (01-80-C2-00-00-00 to 01-80-C2-FF-FF-FF) for
group addresses for use by standard protocols.
3.Broadcast – Similar to Network Layer, Broadcast is also possible on underlying layer( Data Link Layer). Ethernet frames with ones in all bits of the destination address (FF-FF-FF-FF-FF-FF) are referred as broadcast address. Frames which are destined with MAC address FF-FF-FF-FF-FF-FF will reach to every computer belong to that LAN segment.
Answer 3b.)The main objective of the cognitive radio is to obtain the best available spectrum through cognitive capability and reconfigurable ability. the key component of dynamic spectrum access in Cognitive radio network is dynamic spectrum sharing, which is responsible for providing efficient and fair spectrum allocation or scheduling solutions among primary and secondary users. Spectrum sharing was generally regarded as similar to generic medium access control (MAC) problems in existing wireless systems. The function of MAC is to coordinate the access among the competing nodes in an orderly and efficient manner to maximize throughput, guarantee an acceptable delay and fair access which consider as a big challenge in CR networks with a dynamic environment. The purpose of this paper is to provide the essential concepts and background related to MAC layer for Cognitive Radio networks, classification of cognitive MAC protocols, advantages, drawbacks and design challenges of cognitive MAC protocols.