Improving Ethernet Performance Ethernet has moved computer data at high speeds across local areas for more than twenty years. This article extols the impressive Ethernet performance increases during the last ten years. 1. The original Ethernet used a wirespeed of 10,000,000 bits per second. Because an entire LAN shares the same data bus, each user only gets part of the entire transmission capacity. Specifically, if there were 100 active computers on the same Ethernet, all constantly trying to send data, the theoretical maximum throughput any one computer could ever attain would be 10,000,000/100, or 100,000 bits/second. Practically, one computer might get a good deal less due to longer transmissions by other computers, timing accidents, etc. Or that one computer might get a good deal more if the other computers don't happen to send data for a long time (for instance, if the users of those computers are looking at data and not using the network in the meantime. 2. If there were 100 active computers sharing the LAN, each one gets a maximum of only 100,000 bits/second. The next enormous performance improvement was the switching hub, In fact, while the old shared media hub can handle only one 10-Megabit-per-second (10 Mb/s) stream at a time, the switching hub can handle several such streams simultaneously. An organization can replace only the hub, and so doesn't have to spend money to replace all the network cards in their computers. 3. If a switching hub can handle eight streams simultaneously, its effective speed now becomes 8 * 10 = 80 Mb/s. Although this breakthrough is very impressive, the network performance will usually not reflect it unless the computer connections are adjusted to the switch. This is because most networks use dedicated-server operating systems, which means that the desktop computers never send data to each other. Each user's desktop computer communicates exclusively with the server. Hence, although the switching hub could handle more data, a server can only transmit to or receive from one desktop ("client") computer at a time if it has only one network interface. 4. If all communication is between one of the desktop computers and the single server with a single network interface, then even a switching hub still supports a practical maximum of only 10 Mb/s. Adding more interfaces to the server will enable several clients to simultaneously access it through the switch, thus taking better advantage of the switch's capacity. In this case the maximum effective throughput of the switch and therefore of the LAN will approach the previous improved value, but only if each computer can generate network traffic as fast as the LAN can carry it. 5. If the server has eight NICs (Network Interface Cards), it can carry on eight (or more) separate conversations with the user (client) computers simulaneously, thus actually achieving again the theoretical 80 Mb/s. Another possible throughput increase can be achieved by installing a switch that works at Fast Ethernet speeds. This 100 Base T system will carry separate streams at 100 Mb/s. Unfortunately, this means that the standard Ethernet NICs in the connected computers must be replaced with Fast Ethernet NICs, so upgrading 100 computers will not be as inexpensive as in step 3 above. Standard production Fast Ethernet NICs and switches can be purchased today. In fact, many Ethernet products today are labelled 10/100 which means that they can run either (traditional) Ethernet or Fast Ethernet. This simplifies inventories and spares, an economic and logistics benefit for the customer. 6. If the same switch is upgraded to Fast Ethernet, then the aggregate data throughput can approach 8 * 100 Mb/s = 800 Mb/s. The vast majority of Ethernet devices installed today operate in half duplex mode. At any moment a particular NIC in some computer is either sending or receiving data, but not both simultaneously. Another improvement offerred by some products is Full Duplex Ethernet, so that throughout can be doubled again. 7. Since these products can both send and receive on each switching port at 100 Mb/s, their total data transfer capacity can approach 2 * 8 * 100 Mb/s = 1600 Mb/s. Looming as a tantalizingly close alternative to speed data still faster is Gigabit Ethernet. This scheme will continue to move bits in exactly the same formats as old traditional Ethernet but at wirespeeds of 1000 Mb/s. The IEEE 802 standard for Gigabit Ethernet is rumored to be eminent, and prestandard products (NICs and switches) are already available on the market. Although these products are currently expensive, one can expect that prices will drop when volume production starts. 8. If a full-duplex, switching, Gigabit LAN were constructed, it might come close to achieving an aggregate throughput of 2 * 8 * 1000 Mb/s = 16,000 Mb/s. One might wonder what applications could be found to fill, let alone to challenge, such an awesome bandwidth. Next time, I will discuss some of these applications, like imaging, and how they do challenge our network technologies today. -------- 30 -------- Author Note: Carl Shinn is the principal at compuTutor Consulting, a Denver-based computer networking and training firm. Please contact him at cshinn@compututor.com or at 303.467.2888.