Chapter 1 : Explore The Network

       This chapter introduces the platform of data networks upon which our social and business relationships increasingly depend. The material lays the groundwork for exploring the services, technologies, and issues encountered by network professionals as they design, build, and maintain the modern network.

How Networks Support we communicate?

Some forms of communication include:

• Texting –  Texting enables instant real-time communication between two or more people.
• Social Media – Social media consists of interactive websites where people and communities create and share user-generated content with friends, family, peers, and the world.
• Collaboration Tools – tools that allow individuals to work together as a team on a project, no matter where they are located.
• Blogs – web pages easily updated and edited by a person who wants to express his or her opinions about any subject.
• Wikis – a web page that can be created and edited by a group of people.
• Podcasting – a technology that allows people to access a website and download an audio recording delivered by someone.
• Peer-to-Peer (P2P) File Sharing – Peer-to-Peer file sharing allows people to share files with each other without having to store and download them from a central server. the user joins P2P network by simply installing the P2P software. P2P file sharing has not been embraced by everyone. Many people are concerned about violating the laws of copyrighted materials.

Intermediary Network Devices

       Intermediary devices connect the individual end devices connect the individual end devices to the network and can connect multiple individual networks to form an internetwork. These intermediary devices provide connectivity and ensure that data flows across the network.

Network Media

       Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are:

Copper – data is encoded into electrical impulses

Glass or Plastic Fibers (Fiber Optic Cable) – data is encoded as pulses of light

Wireless Transmission – data is encoded using wavelengths from the electromagnetic spectrum

Network Representations

       Diagrams of networks often use symbols, like those shown in Figure, to represent the different devices and connections that make up a network. A diagram provides an easy way to understand how devices in a large network are connected. This type of “picture” of a network is known as a topology diagram. The ability to recognize the logical representations of the physical networking components is critical to being able to visualize the organization and operation of a network.

Topology Diagrams

Topology diagrams are mandatory for anyone working with a network. They provide a visual map of how the network is connected.

There are two types of topology diagrams:

1. Physical Topology Diagrams – identify the physical location of intermediary devices and cable installation.
2. Logical Topology Diagrams – identify devices, ports, and addressing scheme.

Types of Networks

• Local Area Network (LAN) – A network infrastructure that provides access to users and end devices in a small geographical area, which is typically an enterprise, home, or small business network owned and managed by an individual or IT department.
• Wide Area Network (WAN) – A network infrastructure that provides access to other networks over a wide geographical area, which is typically owned and managed by a telecommunications service provider.

Other Type of Networks Include:

• Metropolitan Area Network (MAN) – A network infrastructure that spans a physical area larger than a LAN but smaller than a WAN (e.g., a city). MANs are typically operated by a single entity such as a large organization.
• Wireless LAN (WLAN) – Similar to a LAN but wirelessly interconnects users and end points in a small geographical area.
• Storage Area Network (SAN) – A network infrastructure designed to support file servers and provide data storage, retrieval, and replication.

The Internet

Internet the collection of globally interconnected networks.

There are two other terms which are similar to the term Internet:

• Extranet a network that provides safe and secure access to an organization’s data to authorized people who work outside that organization
• Intranet a private interconnection of LANs and WANs inside an organization that can only be accessed by organization members or by non-members with authorization

Home and Small Office Internet Connections

• DSL – Digital Subscriber Lines provide a high bandwidth, always on, connection to the Internet. DSL runs over a telephone line. In general, small office and home office users connect using Asymmetrical DSL (ADSL), which means that the download speed is faster than the upload speed.
• Cable – Typically offered by cable television service providers, the Internet data signal is carried on the same cable that delivers cable television. It provides a high bandwidth, always on, connection to the Internet.
• Cellular – Cellular Internet access uses a cell phone network to connect. Wherever you can get a cellular signal, you can get cellular Internet access. Performance will be limited by the capabilities of the phone and the cell tower to which it is connected.
• Satellite – The availability of satellite Internet access is a real benefit in those areas that would otherwise have no Internet connectivity at all. Satellite dishes require a clear line of sight to the satellite.
• Dial-up Telephone– An inexpensive option that uses any phone line and a modem. The low-bandwidth provided by a dial-up modem connection is usually not sufficient for large data transfer, although it is useful for mobile access while traveling.

Network Architecture

• Fault Tolerance – A network characteristic that restricts the impact of a failure on network access and allows a network to recover quickly from the failure.
• Scalability – A scalable network can expand quickly to support new users and applications without impacting the performance of the service being delivered to existing users
• Security – A network infrastructure includes the physical securing of devices that provide network connectivity, and preventing unauthorized access to the management software that resides on them
• Quality of Service (QoS) – A mechanism to manage the flow of traffic based on different requirements to ensure reliable delivery of each type of traffic

Security Threats

The most common external threats to networks include:

• Viruses, worms, and Trojan horses– malicious software and arbitrary code running on a user device
• Spyware and adware– software installed on a user device that secretly collects information about the user
• Zero-day attacks, also called zero-hour attacks– an attack that occurs on the first day that a vulnerability becomes known
• Hacker attacks– an attack by a knowledgeable person to user devices or network resources
• Denial of service attacks– attacks designed to slow or crash applications and processes on a network device
• Data interception and theft– an attack to capture private information from an organization’s network
• Identity theft– an attack to steal the login credentials of a user in order to access private data

it is equally important to consider internal threats.

Security Solutions

Network security components for a home or small office network should include, at a minimum:

• Antivirus and antispyware– These are used to protect end devices from becoming infected with malicious software.
• Firewall filtering – This is used to block unauthorized access to the network. This may include a host-based firewall system that is implemented to prevent unauthorized access to the end device, or a basic filtering service on the home router to prevent unauthorized access from the outside world into the network.

In addition to the above, larger networks and corporate networks often have other security requirements:

• Dedicated firewall systems– These are used to provide more advanced firewall capabilities that can filter large amounts of traffic with more granularity.
• Access control lists (ACL)– These are used to further filter access and traffic forwarding.
• Intrusion prevention systems (IPS)– These are used to identify fast-spreading threats, such as zero-day or zero-hour attacks.
• Virtual private networks (VPN)– These are used to provide secure access to remote workers.