NETWORKS

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NETWORKCOMPONENT

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CLIENTS AND SERVERS

Computer networks exist in many different places, from small networks that are used at homes with just a few family computers connected to it to huge networks that are used in large companies.

The client-server networks are the

smallest type of networks, in which

the computers that are attached to

the network act as either clients or

servers.

 

Servers are computers that are assigned to do certain tasks for the whole network, in addition they also provide to other computers (clients).

THERE ARE MANY DIFFERENT TYPES OF SERVERS THAT ARE RESPONSIBLE FOR DIFFERENT TASKS:

The File Server

This stores the users’ files

and data and this controls

access to the files

Application Servers

A program that handles all application operations between users and an organization's backend business applications or databases.

 

 

 

 

 

Web Server

  These are computers that deliver web pages so users can connect to them.

Print Server

This is a device that connects printers to client computers over a network.

 

 

 

 

 

Authentication Server

This server is responsible for processing login requests and the server is able to determine if a user is allowed access to networks and resources.

 

 

Server computers

These normally have higher specifications than regular desktop computers meaning that performance levels may be higher because they deal with many clients at once. These computers use multiple processors and extra RAM because it is responsible for storing lots of data.

Client computers

These are the regular desktop or laptop devices we use every day that connect to a network.

 

 

 

 

 

SHARED DEVICES

This is where many devices such as printers are connected to one network.

The advantages are that rather than buying printers for all the computers, one printer can be used by multiple computers which will reduce costs, another advantage is that having more printers to be replaced every year will contribute to the global e-waste problem and instead only one printer can be replaced.

Shared devices are connected to a network hub or switch using an Ethernet cable.

EVALUATE THE IMPACTS OF HAVING MULTIPLE DEVICES

SUCH AS PRINTERS CONNECTED TO ONE

SERVER.

(6 MARKS)

HUBS, ROUTERS AND SWITCHES

These perform a similar basic task.However, - They operate differently + has implications for network performance and cost.- They broadcast data differently.

HUBS, ROUTERS AND SWITCHES

They all have Ethernet ports.

HUBS, ROUTERS AND SWITCHES

The number of ports depends on the model: 8, 16, 32, and 64 ports are common configurations.

If a network administrator needs more ports it is easy to link two or more devices together.

Many devices have Wi-Fi capabilities to allow clients to connect wirelessly.

Feature: status light to indicate whether the cable is connected at both ends and whether data is being sent over the connection.

When is this useful?

HUBS

• Most basic• Cheapest

When it receives data, it rebroadcasts it to every connected device including the one that sent it.

Computers ignore data if it is not intended for them. This method of operation has implications for network performance because a lot of bandwidth is wasted sending unnecessary data over the network.

MONITORING NETWORKSNetwork monitoring systems are usually used by network

administrators, like Arthur!

Administrators can be automatically alerted or notified by an email or pager if any network devices fail, or the network itself starts to perform some problems.

There are 2 protocols that are commonly used to network:

• Simple network monitoring protocol (SNMP)

• Windows management instrumentation (WMI)

SWITCHES

• Smarter versions of hubs

They inspect data they receive to determine the intended destination, and then forwards it to only the intended recipient. This saves a bandwidth compared to the hub.

Hubs and switches are both used to connect

multiple computers on the same LAN.

http://www.youtube.com/

watch?v=6g523V8jcIM

ROUTERS

These connect two or more separate networks.

E.g. a switch connects the computers in a school network, while a router will connect the school network to another network (internet).

It acts as a gateway through which all data entering and leaving the network passes.

This enables a router to perform more tasks:

- Filtering information that passes through it.

BROADBAND ROUTERS

These are often supplied by Internet Service Providers (ISPs) when installing Internet

access at a home or small business.

They effectively combine the functions of a router (network to the internet), with the

features of a switch (connecting to multiple computers).

NETWORKARCHITECTU

RE

NETWORKARCHITECTURE

This refers to the way computers are logically organised on a network, and the roles each takes.

In a client / server network, one of the most common architectures: one or more computers act as servers that provide services to the rest of the network.

Having central providers many advantages:

• Files located on a server can be accessed by their owners from any client (not tied down to one computer).

• Reduces the impact on work if a client computer needs repair.

• Makes it easier to backup files regularly.

• Security can also be improved (authenticates users and control access to shared resources).

NETWORKARCHITECTURE

In a thin client network, the client computers rely heavily on a server:

• To store files and application.

• To run software on the clients behalf.

• It acts as a terminal for accepting input and displaying output.

The server can run the operating system on behalf of the thin client: the client only contains enough software to initialize the hardware and network

connection, and connect to the server. The heavy reliance on server’s bulk of their work.

MONITORING NETWORKS

Network monitoring systems are usually used by network administrators, like Arthur!

Administrators can be automatically alerted or notified by an email or pager if any network devices fail, or the network itself starts to perform some problems.

There are 2 protocols that are commonly used to network:

• Simple network monitoring protocol (SNMP)

• Windows management instrumentation (WMI)

Network monitoring software’s usually record their data into a log file, which can be checked later by the Arthur.

If Arthur gets alerted that a problem has been detected and he happen to be away from the network, re-mote access can be used to investigate the problem.

A re-mote access is a tool that allows users to login to a system as though they were actually physically present, including seeing a copy of the computers screen and user interface and interacting with it. Because a network administrator’s account is a desirable target for unauthorised users, remote access is usually restricted to particular computers and communication sent over a virtual private network (VPN)

Network monitors usually tend to perform specific tasks such as:

• Checking if pages on an organisation’s web site are accessible

• Checking that response time from a web site is within an acceptable range

• Checking email servers are receiving emails and are able to send outgoing emails

• Checking if bandwidth is being used efficientlyBandwidth: measure of a networks speed

• Performing traffic shaping- giving more bandwidth to higher priority applications or users

• Looking for unusual traffic patterns which could indicate an infection by worm or a virus.

• Checking that the network traffic is being routed correctly, for load balancing

• Monitoring of server resources (CPU utilisation, disk space memory, memory) – load balancing purposes

Load Balancing

It is an optimisation technique to make sure that bandwidth and network facilities such as servers are efficiently used. Load balancing ensures that visitors of a website are equitably distributed among the different servers, in order to help prevent individual servers being swamped by traffic, as well as to improve the response time for everyone. It can be achieved through configuration of network switches and they can take place dynamically, in case one machine is performing a CPU-intensive task, less work can be assigned to it until the task is done. The load balancer can automatically stop delegating tasks to a server if it stops responding for any reason. Therefore in this situation, the load balancer helps implement a failover system.

A failover system is designed to keep a system running if the primary system fails – perhaps due to hardware or power failure. They are usually redundant systems as they provide the same functionality as the primary system. However, they do nothing unless the primary system fails first, at which point they can be switched automatically.

Audit Trails

Individual users can also be monitored, including their long and logoff times, files and web sites accessed, emails sent and received and even key strokes made.