data comm prelim

Local Area Network (LAN)

is a network that links devices within a confined geographical region like a home, classroom, office, lab, or campus

• sharing an Internet connection

• sharing files and folders

• sharing printers and other resources

• accessing servers and applications

• supporting communication among users

• connecting IoT and other smart devices

Common purposes of a LAN

End devices

are the source or destination of network communication. They are also commonly called hosts

Intermediary device

Connects devices/networks and forwards traffic

Network media

Carries signals between devices

Protocol

Provides communication protocols

Intermediary Network Devices

connect end devices and networks and help move data toward its destination.

Switch

connects devices within a LAN. It forwards Ethernet frames based mainly on MAC-address information

Router

connects different IP networks and forwards packets using network-layer addressing.

Wireless Access Point

helps devices get on a network without any cable going into them. It then routes what those devices send over to the wired part of your local network.

Firewall

looks at data moving across a network and applies set security rules. It lets safe, expected traffic through. Meanwhile, it also blocks requests that have not been approved. It stops items that should not be on the system.

Modem / ISP Gateway

connects your local network to the provider’s network. In a lot of homes, you get one device that handles everything. It works as a modem and a router, and it may include a switch, Wi-Fi access, and a simple firewall too

Network Media

are the pathways used to carry signals from one device to another.

types of network media

Copper media

Fiber-optic media

Wireless media

Copper media

carries electrical signals through copper conductors.

Fiber-optic media

carries pulses of light through glass or plastic fiber.

Wireless media

carries information using electromagnetic radio signals.

Wireless Devices

send data through the air. So, you do not need a cable for that link. Many people pick Wi‑Fi when they build a small network. You see it in apartments, in schools, and at work. For longer distances and wider reach, cellular networks are the common choice. They can keep you connected while you are away, out of your usual area, and on the move.

Wireless Router

It moves information between the private network at home and the wider internet. Often the router also sends out a Wi-Fi signal. Then phones, tablets, and laptops can join and send data. In most setups this is done with DHCP. You may see basic firewall tools as well. NAT is commonly enabled too, and it helps with traffic as it goes between different networks.

Important wireless terms

SSID

Wi-Fi password/passphrase

WPA2/WPA3

Channel

Access point

SSID

The name used to identify a Wi-Fi network.

Wi-Fi password/passphrase

A credential used to authenticate a device to a protected wireless network.

WPA2/WPA3

Wireless security standards used to protect Wi-Fi communication.

Channel

A portion of the radio spectrum used by a wireless network.

Access point

A device/function that provides wireless access to a network.

IP address

a logical address assigned to a network interface. It helps identify the source and destination of IP communication.

IPv4

is built on 32 bits. People usually show it as four numbers, split into octets, like this in decimal form.

Default Gateway

normally the router interface a host uses when it needs to communicate with a destination outside its local IP network.

DNS

translates domain names into IP addresses and supports other namerelated functions.

DHCP

can automatically provide a host with an IP address, subnet mask, default gateway, and DNS server information.

simplified DHCP process DORA

Discover

Offer

Request

Acknowledge

Discover

client looks for a DHCP server

Offer

server offers configuration.

Request

client requests the offered configuration.

Acknowledge

server confirms the assignment.

Private IPv4 address ranges

• 10.0.0.0 – 10.255.255.255

• 172.16.0.0 – 172.31.255.255

• 192.168.0.0 – 192.168.255.255

Verify Connectivity

Configuration testing for the network needs to be done once the network is either installed or troubleshooted. Configuration testing will help us figure out whether the problem lies with the machine, the local network, the gateway, DNS, or any other portion of the route.

ipconfig (Windows)

Displays IP configuration information.

ipconfig

ping

Ping sends test messages to a destination and reports whether replies are received. It is useful for testing basic reachability.

ping 192.168.1.1

Computer Network Protocols

is a defined set of rules that devices use to communicate

Protocols

provide common expectations for how messages are formatted, addressed, transmitted, received, and interpreted.

IP (Internet Protocol)

Logical addressing and packet forwarding between networks.

TCP (Transmission Control Protocol)

Reliable, ordered transport with error recovery and flow control.

UDP (User Datagram Protocol)

Connectionless transport with low overhead; does not provide TCP-style delivery guarantees.

HTTP (Hypertext Transfer Protocol)

Web application communication.

HTTPS (Hypertext Transfer Protocol Secure)

HTTP protected using TLS.

DNS (Domain Name System)

Name resolution and other DNS services.

DHCP (Dynamic Host Configuration Protocol)

Automatic host network configuration.

FTP (File Transfer Protocol)

File transfer; other modern secure filetransfer methods are often preferred.

SMTP (Simple Mail Transfer Protocol)

Email delivery and forwarding.

Communication Rules

Message encoding

Message formatting

Message size

Timing

Addressing

Delivery method

Message encoding

data must be represented in a form the receiving system can understand.

Message formatting

messages need an expected structure, such as headers and data fields.

Message size

large data may be divided into smaller units for transmission

Timing

devices need rules about when data is sent and how quickly it is handled.

Addressing

source and destination information identifies where data comes from and where it should go.

Delivery method

communication may be unicast, broadcast, or multicast depending on the situation.

Common delivery types

Unicast

Broadcast

Multicast

Unicast

One sender communicates with one destination.

Broadcast

One sender sends to all applicable devices in a broadcast domain.

Multicast

One sender sends to a selected group of receivers.

Latency

Delay in communication. High latency can cause slow response or lag.

Packet loss

The packets do not make it to their destinations due to congestion, interference, bad links, and bad devices.

Bandwidth limitations

A link may not have enough capacity for the amount of traffic being generated.

Interference

Electrical or wireless interference may decrease signal quality.

Congestion

Excessive traffic can lead to queuing, delay, and loss of packets.

Configuration errors

Incorrect IP addresses, subnet mask, gateway, DNS, VLAN, and routing can hinder communication.

Hardware/cabling faults

Cables, ports, and network hardware malfunctions can cause disruptions in communications.

Security problems

Unauthorized access, malicious software, weak credentials, or unsafe configurations can compromise network communication.

Copper Media

copper conductors to carry electrical signals. Copper Ethernet cabling is widely used in LANs because it is relatively affordable, flexible, easy to terminate, and widely supported.

Twisted-Pair Cable

comprises insulated copper wires that are twisted in pairs.

Pair 1 → 2 conductors

Pair 2 → 2 conductors

Pair 3 → 2 conductors

Pair 4 → 2 conductors

Total → 8 conductors

UTP (Unshielded Twisted Pair)

used extensively in Ethernet networks in office settings, classrooms, and even in domestic use. It lacks any extra metallic shielding on the cable pairs.

STP / Shielded Twisted Pair

cables have been manufactured with shields meant to reduce electromagnetic interference. This is achieved through proper selection of cables, connectors, patch panels, and installation procedures.

Coaxial Cable

have inner conductor, insulating material, shield, and jacket. They are most often found in cable television systems, broadband Internet access, and close circuit television systems.

White/Green

T568A PIN 1

green

T568A pin 2

white/orange

T568A pin3

blue

T568A pin4

white/blue

T568A pin5

orange

T568A pin6

white/brown

T568A pin7

brown

T568A pin8

White/Orange

T568B pin 1

Orange

T568B pin 2

White/Green

T568B pin3

Blue

T568B pin 4

White/Blue

T568B pin 5

Green

T568B pin 6

White/Brown

T568B pin 7

Brown

T568B pin 8

Twisted-pair cable categories

describe performance characteristics such as frequency capability and transmission performance. The actual speed and distance supported depend on the cable category, Ethernet standard, installation quality, and environmental conditions.

Cat5e cable

Common enhanced Category 5 cable; widely used for Gigabit Ethernet

Cat6 cable

Higher-performance twisted pair with improved specifications

Cat6a cable

Category 6A Suitable for use in 10 Gigabit appropriate for 100 m channels

Cat8

High-performance copper cabling designed for short, high-speed datacenter links

10BASE-T

10 Mbps Ethernet over twisted pair

100BASE-TX

100 Mbps Fast Etherne

1000BASE-T

1 Gbps Gigabit Ethernet over twisted pair

10GBASE-T

10 Gbps Ethernet over twisted pair under specified conditions

IEEE 802.3

the major family of Ethernet standards.