System Area Network Cards
As processing needs become ever greater and demands on server availability increase, single-server systems are giving way to server clusters. In a server cluster, systems can share storage and processing power and are fault tolerant; that is, if a system in the cluster fails, one of the other systems in the cluster can take over for it and continue processing.
This level of functionality requires many things. It needs operating systems that are capable of being clustered and applications that can do the same. It also requires that the systems in the cluster be able to talk to each other. That's where system area network cards come in.
System area network cards are used in clustered systems to facilitate communication between the devices in the cluster. Figure 3.27 shows how system area network cards are used.
If only two systems are in the cluster, they can be connected directly by a cable. If the cluster has more than two systems, a specialized hub is required.
REVIEW BREAK: Network Devices Summary
The information in this chapter is very important for the Network+ exam. To summarize our coverage of network devices, we have placed some of the key points about each device in Table 3.3. You should learn this information well.
Table 3.3. Network Devices Summary| Device
| Function/Purpose
| Key Points
|
|---|
| Hub
| Connects devices on a twisted-pair network.
| A hub does not perform any tasks besides signal regeneration.
|
| Switch
| Connects devices on a twisted-pair network.
| A switch forwards data to its destination by using the MAC address embedded in each packet.
|
| Bridge
| Divides networks to reduce overall network traffic.
| A bridge allows or prevents data from passing through it by reading the MAC address.
|
| Router
| Connects networks together.
| A router uses the software-configured network address to make forwarding decisions.
|
| Gateway
| Translates from one data format to another.
| Gateways can be hardware or software based. Any device that translates data formats is called a gateway.
|
| CSU/DSU
| Translates digital signals used on a LAN to those used on a WAN.
| CSU/DSU functionality is sometimes incorporated into other devices, such as a router with a WAN connection.
|
| Network card
| Enables systems to connect to the network.
| Network interfaces can be add-in expansion cards, PCMCIA cards, or built-in interfaces.
|
| ISDN terminal adapter
| Connects devices to ISDN lines.
| ISDN is a digital WAN technology often used in place of slower modem links. ISDN terminal adapters are required to reformat the data format for transmission on ISDN links.
|
| System area network card
| Used in server clusters to provide connectivity between nodes.
| System area network cards are high-performance devices capable of coping with the demands of clustering applications.
|
| WAP
| Provides network capabilities to wireless network devices.
| A WAP is often used to connect to a wired network, thereby acting as a link between wired and wireless portions of the network.
|
| Modem
| Provides serial communication capabilities across phone lines.
| Modems modulate the digital signal into analog at the sending end and perform the reverse function at the receiving end.
|
