ARP = Address Resolution Protocol VLSI = Very Large Scale Integration, referring to IC (Integrated Circuits of miniaturized transistors) Integrated Circuits were the THIRD generation key building block or electronic component for computers. From IC, to LSIC, to VLSI, to ULSIC for Large Scale Integration (LSI), and then very large scale integration, and then ULTRA LARGE SCALE INTEGRATION, etc. MEDIA ACCESS CONTROL = MAC CSMA/CD Carrier Sense Multilple Access / Collision Detection NIC listens to the cable (sense the carrier, "listen" for signals, "listen" for collisions if this computer just put something on the cable, on the LAN, on the Local Area Network media (ethernet twisted pair cable wires or coaxial cable, etc) sense the carrier, NIC, it is your PCs connection to the rest of the LAN and to the rest of the internet through that. Do you sense it is a quiet cable? Carrier sense it is quiet, then you can put a packet or two or 203 on the cable. Do you sense it is having traffic, i.e. a packet is "driving" by? You better read the packet's HW address, the 48 bit destination address to see if it is your address, NIC/NAC? If it is YOUR MAC address, Network Interface Card (NIC), then you grab that packet and deliver it up to the higher level protocols, cause it is for your computer. Carrier sense, listen to the wire, listen to the carrier of packets. Make sure the carrier is quiet before you put something on the cable!!!! Make sure there is no car or bike or jogger or walker in the road before I pull out of my driveway in the morning, or there will be a collision. Multiple Access (CSMA/CD) means there are -- many different computers SHARING this one media, this one cable. That is why the Network Adapter Card (NIC/NAC) has to "listen" to the wire and make sure it is quiet BEFORE letting the packet pull out of the PC driveway and get on the shared road (Ethernet cable). Otherwise, your packet can CRASH INTO another packet on the MULTIPLE ACCESS Local Area Network media. If the cable is quiet, your computer sends out a packet on the cable. Sometimes another computer has the same idea and sends out a packet on the same LAN media cable at almost the exact same time. These packets collide!!!!! That is why all ethernet networks use the last part of the CSMA/CD protocol, which is: -- Collision Detection.... - - After a packet has been sent out, by the NIC, for your PC, it has to listen for a certain amount of time to make sure the cable goes from a pattern of transmitting bits signal to quiet again. If two packets collide, the cable makes and transmits a garbage pattern, kind of like when you hear a crash, and know to look over toward the road where it came from, because you know that is NOT the normal noise pattern of typical successfully getting from one place to another traffic. CD = Collision Detection That packet did NOT get sent and arrive at its destination, or even get off this LAN to other LAN's in this great land of ours or other lands across the seas of this wide world that is a web of interconnected LANs. So the CD means your NIC "knows" there was a collision detected, and has held a copy of the packet, and will send it out again. CSMA/CD Carrier Sense Multiple Access / Collision Detection - - - - - - Ethernet networks. CSMA/CD is just one of the large set of protocols needed to allow you to sit at your computer and get to your email or browse the web, etc.