Computer Networks

• Malfunctions

because networked services are shared, when a network malfunction occurs, usually some or all, of the normally accessible resources become unavailable.

• Increased productivity

because several people can work on a project simultaneously, productivity is increased when compared to just one person working on the same project. Communications between workers fosters a more productive work environment.

PAN (personal area network)

usually the interconnection of personal digital devices or electronics: • No cables/wires are used to form network • Range of about 30 feet

Disadvantages of Networks

• Malfunctions, • Unauthorized access, • LANs are vulnerable to malicious code

• LANs are vulnerable to malicious code

again, by their inherent nature, linked devices on a LAN allow for the wide scale proliferation of malcode among many nodes.

• Shared Resources

allow people to work or play together: o Using collaborative software such as groupware, wiki's, etc, several people can work together on a single document, communicate by email, use webex services,and take part in computer games.

• Wi-Fi can be less secure

than wired connections because an intruder does not need a physical connection

In general, both in industry and for personal use,

the benefits of a LAN outweigh the negatives associated with them.

• Reduce costs

through the use of software site license which is cheaper than many individual licenses. Also, sharing of networking hardware reduces costs, example shared networked printers vs. many printers.

Advantages of wired networks

• Faster than wireless networks (advantage) • More secure than wireless networks (advantage) • Limited mobility compared to wireless (disadvantage)

Network ready devices have circuitry either:

• On the system or motherboard of the device • NIC - network interface card

Advantages of Networks in general

• Shared Resources, • Reduce costs, • Increased productivity, • Shared Internet connection

Disadvantages of wireless networks

• Slower than wired networks (disadvantage) • Less secure than wired networks (disadvantage) • Greater mobility than wired networks (advantage) • Can use your own device (advantage)

Wireless Network Devices

Wireless router, Access Point, Wi-Fi

Transmission Control Protocol/Internet Protocol

Circuit Switched Networks vs. Packet Switching Networks

Ethernet

Ethernet is a wired network technology that is defined by IEEE 802.3 standards Simultaneously broadcasts data packets to all network devices Wired networked devices, such as network ready computers, printers, and scanners, are usually connected via Category 5 or Category 6 cables terminated at each end with a plastic RJ45 connector.

Network Devices - Wired

Examples of some commonly used wired networking devices: • Core network switches • End switches • Fiber optic cables • Ethernet cables

Circuit Switching -

In a circuit-switched network: • before communication can occur between two devices, a circuit is established between them • once set up, all communication between these devices takes place over this circuit, even though there are other possible ways that data could conceivably be passed over the network of devices between them.

Advantages of Networks in general

In the world today, the benefits of a LAN are significant regardless of whether the work being accomplished is for business or personal matter.

Computer network

a group of computer and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. The connections between the devices on a network are established using either cable media (Ethernet or fiber optic cables) or wireless media. Networks are classified according to their size and geographic scope.

Core network switch -

a large networking switch into which many smaller network switches are plugged or patched into. Fiber optic cable than connects this switch to an Internet Service Provider - ie: Verizon Fios.

LAN (local area network)

a network that connects personal computers within a very limited geographic area: • usually a network in a building

WAN (wide area network)

a network that covers a large geographic area: • Made up of many different networks • Involves different computer platforms • Involves different network technologies • Internet is an example of a WAN.

Packet Switched -

in a packet switched network: • no specific path is used for data transfer • instead, on the sending end, the data is chopped up into small pieces called packets and sent over the network • On the receiving end, the process is reversed—the data is read from the packets and re-assembled into the form of the original data The ability to have many devices communicate simultaneously without dedicated data paths is one reason why packet switching is becoming predominant today, although in some instances, the two types of networks are combined.

Geographic scope

is important because normally networks are built on a small scale. As business and personal demands grew, and continue to grow, the need for more computers and other electronic devices increases, meaning networks are needed to insure communications is effective and reachable in larger geographic areas.

MAN (metropolitan area network)

public high speed network: • is a larger network that usually spans several buildings in the same city or town • Range is about 50 miles • Internet service providers are an example

Communications Protocols

refers to a set of rules for efficiently transmitting data from one network to another. • Two computers on a network negotiate their communications protocols through a process called handshaking. Here's how it works: o One device transmits a signal that means it wants to communicate o It then waits for an acknowledgement from the receiving device o The two devices than negotiate a protocol that both of them can handle, and thus communications start.

These cables are also known as Ethernet cables and have:

• a maximum length of 328 feet • made of 4 pairs of shielded, twisted copper wire (reduces signal noise) • Vary in speed from 10Mbps to 100Gbps In contrast, MANs and WANs often use fiber optic cables to carry network signals. Made up of: • many strands of glass tubes • data speeds through the tubes as rays of light

Devices that are equipped with network circuitry installed from the manufacturer are known as

"network ready" meaning they can be placed on the LAN immediately.

Routers

A router is a network device that forwards, or routes, data packets along networks. • A router is connected between at least two networks • Routers are located at gateways - the place where two or more networks meet • Routers use packet headers and tables to determine the best path to forward packets • Routers use protocols to communicate with each other to determine the best route of packet travel between two nodes

Network Devices

As mentioned earlier, each device on a network is known as a node, and every node has a unique Internet Protocol or IP address that identifies it specifically on a network. More about IP addresses later.

Types of devices and how they connect to a network

Personal computers, laptops, mainframes, supercomputers, servers, printers, scanners, switches, other network peripherals, and smartphones all are capable of connecting to a LAN.

Wired vs. Wireless Networks

Wired networks are networks that use cables between the computer, printer, scanner and the network devices such as switches, routers, etc. Wireless networks also include such devices as computers (laptops), printers, routers.

• Shared Internet connection

a LAN allows all connected devices to access a single Internet connection. Savings here is that each device does not have to have its own individual Internet connection.

Access Point -

is a device that allows wireless devices to connect to a wired network using Wi-Fi.

Wireless router

is a device that performs the functions of a wired router but also includes the functions of a wireless access point. • It is commonly used to provide access to the Internet or a different computer network. • It does not require a wired link, as the connection is made wirelessly, via radio waves

Fiber optic cables -

is a network cable that contains strands of glass fibers inside an insulated casing. These cables are designed for long distance and very high bandwidth (gigabit speed) network communications.

Packet -

is a parcel of data that is sent across a computer network. It contains: • Address of its sender • The destination address • A sequence number • Some data Packets are reassembled at the destination by the TCP protocol.

Communications channel -

is a physical transmission medium, such as a wire, for signal transmissions. With respect to wireless communications, it is a frequency or channel for signal transmissions. So obviously, a larger communications channel is able to move more data than a smaller one.

Wi-Fi -

is a popular technology that allows an electronic device to exchange data or connect to the Internet wirelessly using radio waves.

The image below is an example of a catalyst or network switch. This type of network switch

is a small hardware device that joins multiple computers together within one LAN.

- Bandwidth

is the transmission capacity of a communications channel. The amount of data that can be transferred in a given period of time Measured in bits per second (bps), Kbps (thousands), Mbps (millions ), or GFbps (billions)

• Unauthorized access

networks, by their inherent nature, may be vulnerable to unauthorized access from many points (devices) and from multiple locations. Unauthorized access allows the perpetrator access to the servers and other significant resources held by the individual or organization. Often times the attacks are from foreign countries.

• Communications protocols are responsible for the following aspects of network communications:

o Dividing messages into packets o Putting addresses on packets o Starting the transmission o Regulating the flow of data o Checking for transmission errors o Acknowledging receipt of transmitted data

• Best known communications protocol is TCP/IP:

o the suite of communications protocols used to connect hosts on the Internet.