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The OSI model
In case you see a question on the OSI model on the exam, the layers from top to bottom are
* Application (7)
* Presentation (6)
* Session (5)
* Transport (4)
* Network (3)
* Datalink (2)
* Physical (1)
The interfaces between each layer are published and standardized, so that you can use, say, a transport protocol from one vendor with a network card driver from another vendor, if both vendors follow the model.
Time Shaver For the exam, you probably won't need to know exactly what each layer does, but I suggest that you remember the layer order. Use a memory aid. The phrases 'Please Do Not Throw Sausage Pizza Away' (bottom to top) or 'All People Seem To Need Data Processing' (top to bottom) can jog your memory by providing the first letter of each layer.
Microsoft designed Windows XP in a modular fashion, including the networking bits, which correlate fairly closely to the OSI model. Some of the OSI layers are fixed in Windows XP, such as the Win32 network API (Application Program Interface) that programmers use when writing applications. Some other OSI layers combine to form a single software component that you can add, replace, or delete in Windows XP. The end result is that in Windows XP, user-installable networking modules fall into the following four categories:
* Adapter: The network interface card (NIC) adapter requires a software device driver so that the upper layers of network software can communicate across the physical medium (copper cable, fiber optic cable, and so on). You must have at least one adapter to participate in a network.
* Protocol: The 'network language,' or transport protocol, defines how Windows XP packages information. Two computers must speak the same protocol to communicate across a network. You must have at least one protocol to participate in a network.
* Client: The network client allows Windows XP to communicate with specific network operating systems, such as Windows 2000 Server and Novell NetWare. You must have at least one client to participate in a network.
* Service: Network services provide specialized capabilities, such as resource sharing (File and Printer Sharing for Microsoft Networks). You don't necessarily have to have any services loaded to participate in a network, but services are necessary to perform certain network functions.
You can see evidence of this four-level structure when you right-click a local area connection in the Network Connections folder and choose Properties, displaying a screen like what you see in Figure 6-1.
Figure 6-1: The LAN link's property sheet.
* The adapter for the specific LAN connection appears at the top in its own little area.
* Clients, protocols, and services are in the main list of 'connection items.'
This layout differs from that in Windows 9x, where all adapter drivers appear in the same list with all the other connection items, in the Network control panel.
The fact that these four modular pieces are separately installable means that you can mix and match pieces to some extent. For example, a single adapter can support two protocols; you can run two or more clients over a single protocol; you can run a specific client over one protocol, or over a different one; and so on. You can also get modules from manufacturers other than Microsoft. The freedom to mix and match components provides flexibility, but it also begets a certain amount of complexity for the system designer.
Network adapters, also known as network interface cards or NICs, typically plug into a bus slot of the PC on one end and into a network cable on the other end. Windows XP comes with a wide variety of network adapter drivers, the software components that allow Windows to communicate with the devices. Windows XP supports traditional Ethernet and Fast Ethernet NICs, as well as newer wireless and HPNA (Home Phoneline Network Adapter) devices. You can have as many NICs as your hardware can support.
Installing a network adapter
You can install a network adapter driver two ways:
* If it's Plug and Play compatible, pop it into a bus slot and start the computer. Windows XP may ask for the installation CD-ROM or for a third-party diskette. An icon automatically appears for the network card in the Network Connections folder.
* If it's not Plug and Play, run the Add New Hardware Wizard from the control panel and follow the prompts to select the adapter's make and model.
NDIS (Network Device Interface Specification) Version 5.0 is Microsoft's preferred adapter driver type. It permits several different protocols and networks to run on a single adapter, and it supports Plug and Play hardware detection.
Configuring and troubleshooting a network adapter
You can configure network adapter properties in two places:
* Device Manager tab of the System control panel
* Configure button in the network connection's property sheet
You generally won't need to change the resource settings that Windows XP assigns automatically (see Figure 6-2), and indeed you may not be able to change them depending on your PC and network card. But check the Resources tab for any reports of a conflict with another device's interrupt or memory requirements.