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20100718.144024
website is now in archive mode. visit blog.subnova.com for information.
20080730.144615
i added amazon context links... just because i can... if they're not too obtrusive... i'll leave them
20080114.231544
enabled mod_deflate on andromeda. the site is now seeing an estimated 80% reduction in overall size for clients to download
20080109.022443
added an rss 2.0 feed for the news at http://www.subnova.com/news/rss/. it will show the 14 most recent posts
20070823.031056
updated cq calculations so that if a member doesn't login to the website in the past 77 days, the contribution points start vanishing in a hurry... tanking the irank
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There are seven layers in the OSI network model, and each has different tasks in the process of transmitting data between computers. There are also network devices (such as hubs, switches, and routers) that operate at specific layers.
Layer 1: Hubs and Repeaters. These "dumb" devices do nothing more than retransmit the electrical signals from the wire out the other port(s). A repeater allows you to extend the length of wiring and reduce any errors that might be incurred through signal degradation. A hub accomplishes the same task, but is more commonly used to connect several devices and retransmits any signal received on one port to all ports except the one it received the signal on.
Note: All devices connected to a hub or a repeater are on the same collision domain, and the same broadcast domain.
Layer 2: Switches and Bridges. A bridge is the "two port" version of a switch, the purpose of which is to seperate two collision domains and allow traffic to be sent between them. A switch is a multiport bridge. A switch/bridge analyzes every packet it recieves and has a table of MAC addresses (the layer 2 ID for network communication) of which addresses are on which ports. It then forwards the packet to the appropriate port. If it doesn't have an entry for the destination MAC address, it forwards it out every port except for the one it received the packet from. When a switch is first turned on, the table is empty and so it operates in this mode (which reduces it to the functionality of a hub, for the most part), but then can quickly build the table.
Note: All devices connected to a switch or a bridge are on the same broadcast domain, but different collision domains. Connecting individual computers to the ports on a switch is known as microsegmentation, to give each device its own collision domain. Also, switches allow the use of full duplex communication, instead of half duplex.
Half duplex communication (the speed when you connect to a hub) is when 2 of the 8 wires in your network cable are used for communication. This requires your network interface to enable CMSA/CD (Carrier Sense Multiple Access / Collision Detect) and prevent collisions in your network segment. This (obviously) slows transmission. When full duplex communication is used, 4 of the 8 wires are utilized. All upstream transmissions are conducted over one pair, and all downstream communications across the other, effectively "doubling" your bandwidth from 10 or 100 MBit to 20 or 200MBit.
Layer 3: Routers. Routers are intelligent devices that route packets from one broadcast domain to the next. They build tables of IP addresses (layer 3 addresses) and use one of several different routing protocols (such as RIP, IGRP, OSPF, EIGRP, etc.) to determine how best to get your packet from point A to point B.
Miscellaneous Notes:
Collision Domain: All devices connected to the same hub are in what is known as a collision domain. They "share" the same theoretical wire to transmit data across, and thus if two of them transmit at the same time, a collision occurs. When this happens, the devices "back off", wait a random period of time, and try to transmit again. Intuitively, the more devices you connect to the same theoretical wire, the harder it becomes to transmit without a collision occuring.
Broadcast Domain: All devices connected to the same subnet (under normal circumstances) are part of the same broadcast domain. That means that if your IP address is 192.168.1.1 and you ping 192.168.1.255 (your subnet's broadcast IP), everyone in the subnet will receive the ping. Before subnets were invented, IP addresses were broken down into "classes". One Class A block, for example, was in the format of: 10.0.0.0 - 10.255.255.255. This meant that if anyone in that range sent a broadcast, everyone else would get it. This is obviously a bad thing for large networks. As such, routers do not forward broadcasts, and everything on one port of a router is considered to be in the same "broadcast domain".
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