# Introduction

## TERMINOLOGY

### Topology

There are two types of Topologies:

* Physical:
  * The ACTUAL physical arrangement or how they are connected by use of cabling)  of the components of a network such as cables, network devices and endpoints
    * Bus Topology - Cabled in a ***line*** like co-ax cable 10 Base 2. Nowadays, the bus is established in a hardware device and connect the host device to the bus using twisted pair wiring 
    * Ring Topology was used by Token Ring and FDDI , whereby the last device was connected back to the 1at device thus forming a "ring"
    * Star Topology, one of the most common typologies, a central device had other devices connected to it
    * Mesh Topology - redundant links and reliability.
* Logical
  * This can be very different to the physical topology and describes the PATH over which DATA is transferred in a network. 
    * For example a 'hub" is physically a  star topology but logically acts as a bus topology
    *

![The hub is physically a star topology but logically acts as a BUS topology ](https://4011257951-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LtfmTuncdFr6DnNyt_b%2F-M-q1xUdcH1nf4-PWlJD%2F-M-qAJL-koZ4X9xWNiFH%2Fimage.png?alt=media\&token=29b52a19-c96d-4716-b809-ec8799f23ee0)

### Speed

* Speed is the measure of the data rate over a given kink and id measured in bits per second (bps). Don't get confused with Bytes (8 bits = 1 Byte)

### Cost, Security and Availability

* Cost is the expense for purchasing the network components as well as the cost for installing and maintaining the equipment
* Security - how well a network is protected from both inside and outside threats. Security is very important especially because of the number of attacks on companies by hackers etc
* Availability is the measure of probability that a network will be available for use when it is required .Its represented as a percentage of time that the network is available and its represented by the UPTIME. To calculate the uptime:
*  **Availability = (No of min per year - down time)/ (no min per year)\*100**
* Example 15 min of outage therefore
  * Availability = \[(24\*365\*60 - 15)] / (24\*365\*60) \*100 = 525585/52560 \* 100  = **99.9971%**

## Scalability

* Scalability indicates how easily the network can grow and accommodate more users and transmission requirements. Must be designed with growth in mind

### Reliability

* Indicates the dependability of the components that make up the network and is often measured as a probability of failure or Mean Time Before Failure (MTBF)

### Network Diagram

![](https://4011257951-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LtfmTuncdFr6DnNyt_b%2F-M-q1xUdcH1nf4-PWlJD%2F-M-qB2gSycswGn__nFHp%2Fimage.png?alt=media\&token=e3c3708d-1d56-4429-bcc0-c1ee3ffc2dcf)

* A network diagram captures network related information and the amount of information varies between different organisations
* A network diagram is essentially a "map" of a network and illustrates the logical representation of the devices in the network and helps clarify how the devices are interconnected
* In addition, a well designed network diagram provides information such as the:
  * interface id's of devices
  * device identifiers as well as,
  * network addressing
  * network icons such as lane switches, routers , wireless access points, servers, end points, Ethernet links, serial links, wireless links and networks (cloud symbol) which could indicate the cloud, different networks, internet network or lab network etc.

### Application Types and Network Performance

Different types of applications can affect network performance, and network performance can affect user experience of applications. Some application types and points to consider:

* FTP and TFTP are considered "batch" applications. Other types of applications include Inventory updates, file copies (within Windows) and Software downloads require no or little human intervention.
* "Interactive" applications like Inventory inquiries and database updates require a lot more human intervention. In these instances a user will usually "wait" for a response etc.
* Real Time applications (like Voice and Video), require very good quality of service and little or no delay. These applications are used for human-to-human interaction and any delay or latency will degrade the user experience.

### Initial Setup Commands

#### Enable Password

![](https://4011257951-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LtfmTuncdFr6DnNyt_b%2F-MKaADzztV3K96uFQcxp%2F-MKaCiyHAn2XJMPvMoBa%2Fimage.png?alt=media\&token=b167d70b-9dbd-430b-ba04-78f7a2a2fa53)