냐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� +-+-+-+-+-+-+-+-+ 栢栢栢栢昉께께굇굇굅같�|O|u|t|b|r|e|a|k|臍같굇굇굉께께栢栢栢� +-+-+-+-+-+-+-+-+ Issue #3 - Page 4 of 12 냐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� TCP/IP Part 2 ------------- By: antimatt3r Shout outs to the whole Outbreakzine crew, this is TCP/IP continuation. LAN stands for Local Area Network. The devices and computers that make up a LAN communicate over small geographical areas such as offices, homes, and bulidings to name just a few. LANs can run over various network architectures, such as Ethernet and token ring. (Specified by IEEE standards 802.3 and 802.5 respectively) These standardized network architectures are ways for data to move across wires and cabels. Using Ethernet, any device on the network can send data in a packet to whereever it wants whenever it wants. When two or more devices are sending data at the same, the packets collide. When packets collide, Ethernet makes the devices stop transmitting, waits a little while, then begins again. The wait time is different and random each time a collision occors. Ethernet architecture is called CSMA/CD (Carrier Sense Multiple Access / Collision Detection). This means that the devices realize when a collision occors, so they wait and retry. All of the devices on the Ethernet network are peers. In token ring networks, the devices are connected using a circle, or ring, and a token is passed among the devices around the ring. When a device has data to send, it must wait for the token to come around to it. When the device has the token, it ensures that no other device can send data, thus, making it impossible for a collision to occor. If a device has nothing to send, or when it finishes sending its data, it passed the token and the next device sends or passes. In token ring architecture, each device gets an equal turn to send data. No matter if your network runs token ring or Ethernet, your data gets to where it needs to go. The advantage to token ring is that Ethernet style collisions don't happen. On the other hand, all devices need to take a turn with the token, so on a computer that has high priority information to send has to wait for a computer that has not much or nothing to send to pass the token around until it reaches the computer. TCP/IP runs on both token ring and Ethernet network styles. Ethernet and token ring are all about hardware, but TCP/IP is mostly about software and works on mostly all hardware. Information moves at a theoretical rate of 10 Mbps (mega, or million bits per second) on Ethernet. Each character you type is 8 or 16 bits, so do the math, 10,000,000 / 8 and it seems like you have a lot of information speeding across your network. I use the term theoretical because many things can happen on Ethernet to slow your data down on the way. Fast Ethernet (IEEE standard 802.3aa-1998) moves data at 100 Mbps. This is 10 times the rate of normal Ethernet, so collisions act as friction, but at 100 Mbps, your data is still crusin pretty fast. There is also Gigabit Ethernet (IEEE standard 802.3z-1998). Imagine your data moving at one billion bits per second - 1 Gbps. Be prepared to spend giga-units of money if you need this kind of speed. An IEEE task force is now in the process of making a new, faster Ethernet that would run at 10 Gbps. Ten billion bits per second. 10,000 times faster then normal Ethernet. It should be complete by March 2002. By contrast, the early token ring networks ran at just 4 Mbps, while 16 Mbps is the most common speed. The new IEEE 802.5t standard specifies high-speed token ring networks running at 100 Mbps and work further goes on to 1 Gbps. Wide area networks span geographical areas too large for local area networks, LAN's can be joined with hardware such as routers, hubs and gateways to form a WAN. Network services in general have 3 levels, as follows. Low: Connection services determine how information gets from one computer, on to the connection medium, then to the next computer. They don't guarentee the information will arrive in the right order, or even at all. Medium: Transport services augment the low connection service to provide completely reliable communications between computers. Packets are numbed, even when they arrive out of order, computers perform error checking to be sure no packets are lost or damaged. High: Application services lets an application on one computer talk to the application on the remote computer in order to perform tasks, such as copying files. Application depends on Transport services to provide for reliable, efficient communications. An example of these network levels in motion would be sending an e-mail. Connection services start out by translating the sender's name to a TCP/IP format address. Next, is transport services create the packets and mark them with numbers. Connection services then send the packets across the network. Transport makes sure the message reaches the destination ungarbled and in one piece. Finally the application services deliver the message to the reciever theirself. To be continued in the next issue of OUTBREAK!