ELECTROCARIAN

The standards are divided into parts. The 802.1 standard gives an introduction to the set of standards & defines the interface primitives. The 802.2 standard describes the upper part of the data link layer. The parts 802.3 through 802.5 describes the 3 lan standards,the CSMA/CD,token bus & token ring standards respectively. Each standard covers the physical layer & MAC sublayer protocol. IEEE Standard 802.3 This standard is for a 1-persistant CSMA/CD lan. E.g: when a station wants to transmit,it listen to the cable.if the cable is busy,the station waits until it goes idle;otherwise it transmits immediately. If two or more stations simultaneously begin transmitting on an idle cable,they will collide. All colliding stations then terminate their transmission,wait a random time,& repeat the whole process all over again. The real beginning of 802.3 was the  ALOHA system constructed to allow radio communication. Later,carrier sensing was added,& Xerox PARC built a 2

Introduction —   In a VPN, private communication between two or more devices is achieved through a public network the Internet. Therefore, the communication is virtually but not physically there.   Although those two devices are communicating with each other in a public environment, there is no third party who can interrupt this communication or receive any data that is exchanged between them.   A VPN is a network which can transmit information over long distances effectively and efficiently. —   With VPNs businesses can securely connect remote offices and remote users using cost-effective, third-party Internet access rather than expensive dedicated WAN links or long-distance remote dial links. —   Organizations can reduce WAN bandwidth costs while increasing connectivity speeds by using high-bandwidth Internet connectivity, such as  Ethernet, and cable, and securing it with VPN tunnels . —   VPNs provide the highest possible level of security through encryption and authentication. —