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The client-server paradigm operates largely on client requests for server services. Such requests require server and client hardware and compatible software, which are necessary to facilitate network functionality between the two. At the most basic level, a client must have a network connection available to transmit a request. Likewise, the client must have the correct software installed to formulate an intelligible request and pass it to the network, where a server can notice and respond to such a request.
Servers respond to client requests through a listener process represented by application services such as File Transfer Protocol (FTP) and Telnet. This process runs continuously, dispatching inbound client connections as they arrive and managing transitional connection states through the native TCP/IP stack implementation.
On the software side, servers require the following elements to make services available across the network:
- Network drivers let the server communicate with its network interface. This software lurks in the background and exists only to tie the computer to the network interface.
- Protocol stacks send and receive messages across the network. This software also lurks in the background and provides a common language shared with clients used to ferry information across the network.
- Service applications respond to requests for service and formulate replies to those requests. This software runs in the foreground and does the useful work. The service application includes the listener process, the temporary execution threads, and some type of configuration or management console.
Most software that resides on a server is network-aware because delivery of information via network is a server's primary function. Some application and protocol services that are performed on behalf of a server computer include Active Directory, SQL Server database engines, Exchange e-mail servers, and Quality of Service networking.
Three improvements to existing services and one additional service in Windows Server 2008 include:
- Failover clustering: Improvements to failover clusters (previously called server clusters) simplify setup and management and better secure cluster deployment and enhance operational stability. In addition, both networking and communication to storage devices are improved to increase availability of applications and services.
 | You won't encounter failover and clustering with only casual computing experiences, so don't feel threatened by these terms. A cluster is a set of servers running one or several applications and services. A failover cluster is one in which several server computers operate cohesively so that, in the event that one fails, another takes over processing of applications and data. |
- Network load-balancing: Network load-balancing redistributes the load for networked client/server application requests across a set of cluster servers. Advances include support for IPv6 and Network Driver Interface Specification (NDIS) 6.0, Windows Management Instrumentation (WMI) enhancements, and improved functionality with Internet Security and Acceleration (ISA) Server.
- 802.1X authenticated wired and wireless access: Authenticated access for both networking technologies relies on 802.1X-compatible Ethernet switches and access points (APs) to provide port-based network access control. This prevents unauthenticated or unauthorized accesses and packet transmission to user and computer resources.
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