TYPES OF NETWORKS

Organizations of different sizes, structures, and budgets need different types of networks. A local newspaper company has needs for its network that would be different from the needs of a multinational company. Networks can be divided into one of two categories: peer-to-peer or server-based networks.

PEER-TO-PEER NETWORK:

A peer-to-peer network has no dedicated servers; instead, a number of workstations are connected together for the purpose of sharing information or devices. When there is no dedicated server, all workstations are considered equal; any one of them can participate as the client or the server. Peer-to-peer networks are designed to satisfy the networking needs of home networks or of small companies that do not want to spend a lot of money on a dedicated server but still want to have the capability to share information or devices. For example, a small accounting firm with three employees that needs to access customer data from any of the three systems or print to one printer from any of the three systems may not want to spend a lot of money on a dedicated server. A small peer-to-peer network will allow these three computers to share the printer and the customer information with one another. The extra cost of a server was not incurred because the existing client systems were networked together to create the peer-to-peer network. The Microsoft term for a peer-to-peer network is a workgroup. Be aware that peer-to-peer networks typically consist of fewer than 10 systems. Most of the modern operating systems such as Windows XP and Windows Vista already have built-in peer-to-peer networking capabilities, which is why building a peer-to-peer network would be a “cheap” network solution. The disadvantage of a peer-to-peer network is the lack of centralized administration—with peer-to-peer networks, you need to build user accounts and configure security on each system.

Figure: Peer-To-Peer Network

It is important to note that peer-to-peer networks are designed for fewer than 10 systems, and with Microsoft client operating systems such as Windows XP Professional, only 10 concurrent network connections to those clients are allowed. This means that if you have 15 or 20 employees, you eventually will need to implement a server-based network.

SERVER-BASED NETWORKS:
A big disadvantage of peer-to-peer networking is that you can’t do your day-today administration in a single place. With peer-to-peer networking, user accounts typically are created on all the systems, and data files are stored throughout all the systems. This leads to a more complicated environment and makes your job harder as a network administrator. Usually after four or five systems have been networked, the need for a dedicated server to store all of the user accounts and data files becomes apparent this is a server-based network.

The advantage of a server-based network is that the data files that will be used by all of the users are stored on the one server. This will help you by giving you a central point to set up permissions on the data files, and it will give you a central point from which to back up all of the data in case data loss should occur. With a server-based network, the network server stores a list of users who may use network resources and usually holds the resources as well.

Figure: Server-Based-Network

The server in a server-based network may provide a number of different services. The services it will offer to the network usually are decided by the server’s role.

There are a number of different roles that a server could play on a network:

• File and print servers 
• Application servers 
• Web servers 
• Directory servers 

File and print servers control and share printers and files among clients on the network. File and print servers were the original reason to have a network; a large number of users needed access to the same files, so the files were placed on a server, and all clients were connected to the server when they needed to work with the files.

File servers often have the following characteristics:

• Large amounts of memory 
• Fast hard disks 
• Multiple CPUs 
• Fast I/O buses 
• High-capacity tape drives 
• Fast network adapters 
• Redundant power supplies 
• Hot-swappable hard disks and power supplies 

File and print servers also check the access control list (ACL) of each resource before allowing a user to access a file or use a printer. If the user or a group to which the user belongs is not listed in the ACL, the user is not allowed to use the resource, and an “access denied” message appears on the user’s screen. Application servers are servers that run some form of special program on the server. A good example of an application server is a server that runs the company’s e-mail server. The e-mail server software is special software that can be run on a server operating system. Another example of software that would run on an application server is a database server product such as Microsoft SQL Server. A database server is a server that holds the company’s core business data and typically gives this data to custom applications that run on the workstations. These are some applications that you might find on an application server:

• Microsoft SQL Server 
• Oracle 
• Microsoft Exchange Server 
• IBM Lotus Domino 

Web servers are servers that run the Hypertext Transfer Protocol (HTTP) and are designed to publish information on the Internet or the corporate intranet. Web servers are popular in today’s businesses because they host web applications (web sites) for the organization. These web applications could be designed for internal use, or they could be used to publish information to the rest of the world on the Internet. Examples of web server software are Microsoft’s Internet Information Services that runs on Windows or Apache web server software that runs on UNIX/Linux, Novell NetWare, and Windows. Directory servers hold a list of the user accounts that are allowed to log on to the network. This list of user accounts is stored in a database (known as the directory database) and can store information about these user accounts such as address, city, phone number, and fax number. A directory service is designed to be a central database that can be used to store everything about such objects as users and printers. In a server-based network environment, the centralized administration comes from the fact that the directory server stores all user accounts in its directory database. When a user sits at a client machine to log on to the network, the logon request is sent to this directory server. If the username and password exist in the directory database, the client is allowed to access network resources. It is important to note that a server can have numerous roles at the same time. A server can be a file and print server, as well as an application server, or it can be a file, print, and directory server all at the same time. Because a single server can perform multiple roles, a company will not need to purchase an additional server every time a new product (or feature) is implemented on the network, and this fact reduces the cost of a server-based network.