January 30, 2003 Week 4: Day 2
Welcome to Lesson 4- Network Interface Cards
After you have matched a network adapter to a slot in the PC or plugged it into a serial bus, the next step is to configure it to work with your computer:
Plug and Play is Microsoft's attempt (originally introduced with Windows 95) to make configuring your NIC as easy as turning on your computer. Once it boots up, the network is available - the ideal configuration strategy. However, it often does not work - particularly in the case of NICs some network admins will tell you it's more like "Plug and Pray" than "Plug and Play"! The more devices in your computer, the less likely it is that Plug and Play will work. If this is the case, you may have to configure the card manually.
Many cards are software configurable, but some cards, especially older cards, require setting be made via jumpers or DIP switches.
NIC configuration typically involves working with three types of PC settings:
Interrupt request line (IRQ) - used by devices (such as NICs) in a computer to get the attention of the CPU. Each device must have its own IRQ or problems occur with devices conflicting. Depending on the conflict, the machine may not even boot.
Base I/O Port -assigned to a device and defines an area of memory the CPU and the device can use to move messages back and forth between them. Acts like a mailbox where the CPU can leave a message for the device, and vice versa.
Base Memory Address (membase) - the starting address for the NIC's buffer space (the area in memory established by the NIC in which to store incoming and outgoing data temporarily before transferring it elsewhere for transmission over the network or delivering it some application.
Attaching to the Network
Remember that the network card must match the medium. Some cards, like Ethernet, are able to accommodate a number of media, whereas the more advanced and specialized cards are only able to support one media.
Criteria for Purchasing Network Adapters
Two primary criteria exist for selecting a network adapter: 1) the type of network technology in use and 2) the kind of connector or physical attachment the adapter must accommodate. Once you determine these basic characteristics, you should also consider other options available for purchase that can increase a card's speed and data-handling capabilities. These include Direct Memory Access (DMA), shared adapter memory, shared system memory, bus mastering, RAM buffering, on-board co-processors, security features, traffic management or grooming, and improved fault tolerance. See Page 131-132 of your text for an overview of each of these features.
3Com has a neat website for determining which of their NIC cards is appropriate for a particular computer need. Click here and use the Connection Finder to see which NIC would be appropriate to use in a desktop computer running at 10-100 Mbps, with a RJ-45 connector type. You can choose different options like management or security features and see what kind of cards are recommended.
Special-Purpose NICs
Wireless Adapters
As mentioned in Chapter 3, network adapters for wireless communication are different
than those for wired communication. These are available for most operating systems.
Check out this link to see a sample of some wireless adapters offered by Cisco
Systems.
Remote Boot Adapters
Remote boot adapters satisfy the need for specialized network adapters to be
used in diskless computers. Often, for security reasons, computers are installed
without disk drives of any nature. The network adapters in these computers use
a Boot PROM to connect to the network to load the operating system.
Network Adapter Driver Software
The device driver in network communications is used by the computer to control the NIC.
In the early days of networking, a driver was compiled for each variation of the network card. For example, a driver was created for a card using IRQ 5 and I/O port 300h. Then, if the card was moved to another machine or reconfigured for any reason, a new driver was compiled with the new settings. As you can image, this was an exceptionally tedious task.
Today, three major vendor standards apply to drivers, and these standards allow more than one protocol to run on a NIC and, in the case of ODI, simplify driver development, not only for NICs but for other devices such as printers, tape drives and disk controllers.
Network Device Interface Specification (NDIS) - allows NICs to use multiple protocols simultaneously.
Win32 Driver Model (WDM) - interfaces with the Plug and Play manager in Windows allowing maximum automation for most devices and drivers.
Open Data-link Interface (ODI) - allows a NIC to use multiple protocols, but also simplifies driver development for NIC manufacturers.
Remember to keep up with your on-line lessons and quizzes!
mdm