Business Data Communications

Primary Learning Objectives • Differentiate between clients and servers • Describe five server physical components • Identify major server types • Understand the concept of well-known ports • Explain server clustering • Define “system area network” Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Clients and Servers • Networks commonly make use of both clients and servers: • Clients request networked resources from servers • Servers manage and distribute networked resources to clients • Clients and servers both have operating systems that differentiate them from each other • Modern client operating systems are network-aware • Server operating systems are specialized Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Server Physical Components • A server has a variety of physical components • Five physical components particularly important to a server’s performance are: • Physical case • Memory • Processor • Drive interface • Network Interface Card Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Physical Case • A client desktop’s physical case is usually kept to a minimal size as it occupies and shares space in a user’s work environment • The case occupies a “footprint” • Servers are typically secured and locked away, with infrequent physical access by staff: • Therefore, a server’s footprint can be larger than a client’s • The server’s physical case is often more rugged • The server’s physical case is referred to as its chassis Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Physical Case • A larger server physical chassis: • Allows technicians more room for working within the chassis • Facilitates upgrading the server • Provides more bays for expansion • Offers more space for additional components • Allows for a larger and more robust power supply • A server may require a redundant power supply, as well as its own internal power surge protector Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Intel Server Chassis SC5250-E: Has four fixed-drive bays and supports up to five hot-swap SCSI or four hot-swap SATA hard-drive bays. This chassis allows adding more storage without having to take the server offline. Expansion cards can be easily added due to the tool-free access enabled by thumb screws on side panels. Physical Case Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Memory • Memory is also called RAM, for random access memory • RAM “sticks” plug into slots housed on a server computer’s motherboard • Servers generally support much higher capacities of RAM than do clients • A server’s RAM slots are often able to support higher capacity RAM sticks than a client’s Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Processor • A server’s processor is also called a CPU, for central processing unit • The CPU is the workhorse of the server and is critical for processing of instructions and data • Server motherboards often support multiple CPUs • If a server has multiple CPUs, its server operating system (SOS) must be able to support the number configured • If multiple CPUs are used, the SOS must be capable of managing the CPUs that reference each other’s cache Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Drive Interface • Servers usually support more drives than does a typical client device • Drives include: • Floppy • Tape • CD • Hard drive • Hard drives, in particular, are a key server component • Drives require an interface to the server’s CPU Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Drive Interface • Two common drive interfaces are: • IDE – Integrated Drive Electronics • Is used mostly by clients • Requires a controller • SCSI – Small Computer System Interface • Is used mostly by servers • Requires a controller • The SCSI controller is often an adapter card that plugs into a motherboard’s expansion slot • The SCSI adapter card uses a parallel bus to communicate with devices connected to the parallel bus • The SCSI adapter can support up to 15 internal and/or external devices Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Network Interface Card – NIC • Critical server NIC considerations include: • Throughput capacity • Half- or full-duplex communications • Direct memory access (DMA) • Bus mastering • Buffers • On-board processor Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Major Types of Servers • If a resource needs to be shared or managed, a server can likely be configured to do it • Many types of servers are possible, including: • File and application • Database • Web, e-mail, and FTP • Domain Name System (DNS) • Dynamic Host Configuration Protocol (DHCP) Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

File and Application Servers • Having duplicate files and applications on multiple devices raises numerous questions, including: • Who has the most current version of the file or application? • How can multiple copies be adequately secured? • How many copies have been distributed? • Who maintains these multiple copies? • File and application servers allow for centralized management, control, and distribution • Users are typically authenticated before being given access to networked file and application resources Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

File and Application Servers • Must be fast and reliable • Require sufficient storage to accommodate user needs • Are often implemented in software • File servers transmit the entire file from the server to the client: • For small files this may be suitable • For large files this may result in a server bottleneck • Application servers control applications, using two components: • The client front-end • The server back-end Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

File and Application Servers • Licensing is an additional legal and ethical consideration when sharing files and applications across the network • Three forms of licensing are: • Individual • Metered • Site • For a file or application to be distributed across a network, it must be network-compatible • Not all applications, nor other resources, can be shared Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Database Servers • Provide management access control software that makes database records available to users across the network • In most implementations, perform much of the processing, with only the result being transmitted to the client • As with application servers, require a client front-end process and a server back-end process • Allow for distributed databases Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Web, E-mail, and FTP Servers • A Web server runs application layer TCP/IP protocols • A client accessing a Web server utilizes a browser • Web pages hosted on a Web server are expressed using HTML – HyperText Markup Language • Two popular Web server programs are: • Apache – an open system program • Internet Information Server (IIS) – a Microsoft program Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Web, E-mail, and FTP Servers – Well-known Ports • Requests come to a Web server through “ports” • These ports are logical designations that represent a particular type of requested service • Port values are also called “well-known ports” • The most common port used by a client Web browser is well-known port 80 • Well-known ports are primary targets by hackers • Many application layer server requests have been standardized to use particular well-known ports Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Web, E-mail, and FTP Servers • A client request is initiated through a Uniform Resource Locator, or URL • For most users of a Web server the URL takes the form of a World Wide Web (WWW) address: • www.woodbury.edu • A URL has four parts: • The protocol (HTTP or FTP, for example) • The server’s IP or Domain Name System address • An optional port number • The directory or file being requested Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Web, E-mail, and FTP Servers • Popular e-mail Web server protocols include: • SMTP – Simple Mail Transfer Protocol • POP3 – Post Office Protocol version 3 • IMAP – Internet Message Access Protocol • A single physical mail server might be running multiple logical mail services • FTP provides for transfer of files from a server to a client, and vice-versa • Whether Web, e-mail, or FTP, a client component and a server component must both be configured Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Domain Name System (DNS) Servers • DNS servers are critical in a TCP/IP network • DNS servers resolve logical IP network layer addresses to logical application layer domain name addresses • The DNS system is designed around a hierarchy of domains: • There are top- and second-level domains • A domain can have subdomains • A domain name is resolved when the DNS server matches a host’s IP address to a domain name address Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Domain Name System (DNS) Servers Clients must be configured to know who their DNS server is. A redundant DNS server can be specified. Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Dynamic Host Configuration Protocol (DHCP) Servers • Clients in a TCP/IP network must be configured to know their logical network layer IP address • This IP address can be manually configured or automatically configured using software: • In a small enterprise, manual configuration is often practical • In a large enterprise, with hundreds or thousands of clients, manual configuration is not practical • DHCP servers are used primarily to automate a client IP addressing configuration Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Dynamic Host Configuration Protocol (DHCP) Servers This Windows client has been configured so that DHCP has been automatically enabled. Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Proxy Servers • Are used primarily to provide increased security: • A “proxy” literally means authorization to act on behalf of another • A proxy server: • Intercepts an internal networked client’s request • Attaches its own IP address to that request • Hands the request out to the external world, so that the external world sees the address of the proxy, not the address of the originating client • Reverses the above process when requested resources are returned • Maintains an address list of which internal client is making what request • Is often used in conjunction with a firewall Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Server Clusters • Connect multiple physical servers into a single logical group: • To clients accessing the server cluster, the servers in the cluster appear to be one single server • Servers in the cluster can share their workload, resulting in load balancing of network traffic • Should one of the servers in the cluster fail, other servers in the cluster can take over its duties • This is called failover capability • Servers in a cluster must have a server operating system that supports clustering • Server clusters are highly scalable Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

System Area Networks • Are a local network designed for high-speed interconnection in cluster environments • Almost exclusively use a “switched fabric” technology: • A switched fabric refers to the way that physical ports within a switch are linked, allowing the ports to communicate and transfer data amongst themselves • Fibre Channel, a switching fabric implementation, is particularly associated with System Area Networks Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

In summary • Servers play a critical role in the enterprise • Important server components typically include: case, memory, processors, drive interface, and Network Interface Cards • Common types of servers include: file, application, database, Web, e-mail, FTP, DNS, and DCHP • Server clustering allows the grouping of multiple physical servers into a single logical group • System Area Networks are one way in which server clusters are being implemented Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall

Business Data Communications