CiT Networking Essentials Notes

Data rates and data units

  • In data communications, a Kilobit is one thousand bits. Kilobits per second is shortened to kb/s, Kbps (as opposed to KBps, which is Kilobytes per second).

  • The lowercase b denotes bits; the uppercase B denotes bytes.

  • The “K” stands for 1024 i.e. 2^10; the “k” stands for 1000 i.e. 10^3.

  • 1 kb/s = 1000 bits per second.

  • 1 KB/s = 1024 bytes per second.

ISP bandwidth and download speeds

  • A common confusion arises from the similarity of KBps and kbps when considering internet bandwidth and download speeds.

    • Data transfer speeds are usually measured in kilobits per second (kbps), so an ISP connectivity of 512 kbps promises a maximum of 512 thousand bits per second.

    • File size is measured in kilobytes, so download speeds are measured in kilobytes per second (KBps).

    • KBps and kbps are not interchangeable.

  • To convert a connection speed in kbps to a maximum download speed in KBps:


    • Download KB/s=Kbps×10008×1024\text{Download KB/s} = \frac{\text{Kbps} \times 1000}{8 \times 1024}

    • Example: for 512 kbps, the maximum theoretical download speed is approximately 64 KB/s (512000 / 8 / 1024 ≈ 62.5 KB/s).

Hardware components of networks

  • Network Interface Card (NIC)

    • An add-on card plugged into a motherboard expansion slot that provides a connection between the computer and the network.

    • Typically a circuit board or chip installed on a computer to enable network connections.

  • Network medium

    • The cable that plugs into the NIC to connect the computer to the network.

    • Can also be air waves in wireless networks.

  • Interconnecting device

    • Devices that allow two or more computers to communicate on the network without needing a direct point-to-point connection.

Software components of networks

  • Network clients and servers

    • Network client software requests information stored on another network computer or device (e.g., Chrome browser).

    • Network server software allows a computer to share its resources (e.g., Apache web server).

  • Protocols

    • Define the rules and formats for sending information across the network (e.g., TCP/IP protocol stack).

  • NIC driver

    • Receives data from protocols and forwards this data to the physical NIC.

Layers of the network communication process

  • Layer 1: User application

    • An application tries to access a network resource.

  • Layer 2: Network software

    • Client software detects the attempt to access the network and passes the message on to the network protocol.

  • Layer 3: Network protocol

    • The protocol packages the message in a format suitable for the network and sends it to the NIC driver.

  • Layer 4: Network interface

    • The NIC driver sends the data in the request to the NIC card, which converts it into the necessary signals to be transmitted across the network medium.

  • Note: Each step is a layer; all layers work together to enable network communication.

How two computers communicate on a LAN: some details

  • TCP/IP is the most common protocol (language) used on networks.

  • TCP/IP uses two addresses to identify devices:

    • Logical address (IP address)

    • Physical address (MAC address)

  • Analogy: Think of the Logical address as your name and the Physical address as your postal address — both are needed to deliver data to the correct device.

CIDR IP addressing and subnetting

  • CIDR range example: 192.168.1.0/24

  • Netmask: 255.255.255.0

  • Wildcard bits: 0.0.0.255

  • First IP: 192.168.1.0

  • Last IP: 192.168.1.255

  • Total hosts: 256 addresses in the block

  • Reserved addresses within this block: 192.168.1.0 (network address) and 192.168.1.255 (broadcast address)

  • Usable hosts: 256 − 2 = 254 (i.e., 192.168.1.1 to 192.168.1.254)

Broadcast IP address

  • Broadcast addressing is designed to facilitate broadcasting a message to all devices in the network.

    • Example: For 192.168.1.0/24, the broadcast address is 192.168.1.255.

How two computers communicate on a LAN: steps for a ping example

  • Step 1: A user at Comp A types ping 10.1.1.2

  • Step 2: Network software creates a ping message

  • Step 3: The network protocol packages the message by adding the IP addresses (source and destination) and acquires the destination MAC address

  • Step 4: The network interface software adds the MAC addresses of the sending and destination computers

  • Step 5: Comp B receives the message, verifies the addresses, and then sends a reply to Comp A using Steps 2–4

Saving a file with network communication (example flow)

  • The client on a workstation saves a file to a shared folder on a server (ServerX) via network resources.

  • Steps mirror the layered model: User application, Client software, Network protocol (e.g., TCP/IPv4), NIC driver, NIC, server NIC, server OS services (e.g., File and Printer Sharing), and disk I/O on the server.

Network terminology and internetworks

  • Internetworks

    • A networked collection of LANs tied together by routers (internetworks).

    • Reasons for creation:

    • Logical separation of groups while enabling communication

    • LAN size growth makes a single LAN inefficient

    • Distances exceed LAN device capabilities

  • PANs (Personal Area Networks)

    • Private ownership and control over the local network; used for personal devices.

  • LANs (Local Area Networks)

    • Private ownership, short propagation delays, covers small areas (e.g., campus, buildings).

  • Wireless LANs

    • LANs that use wireless communication to connect devices within a local area.

  • MANs (Metropolitan Area Networks)

    • Cover larger areas (e.g., multiple sites within a city); more expensive; may not be owned by a single organization.

  • WANs (Wide Area Networks)

    • Cover large geographic areas (countries/continents); expensive; may be owned by multiple organizations; PSTN or satellite media are common WAN transports.

  • PSTN (Public Switched Telephone Network)

    • A network of switches that route calls between endpoints; used historically for data as well.

  • Internet, Intranet, Extranet

    • Internet: worldwide public internetwork using protocols such as TCP/IP and HTTP.

    • Intranet: private internetwork accessible to authorized users within an organization.

    • Extranet: controlled access to internal resources by external users.

IP addressing: private vs public and address examples

  • Private IP address ranges (reserved for private networks):

    • 192.168.0.0 to 192.168.255.255 (65,536 addresses)

    • 172.16.0.0 to 172.31.255.255 (1,048,576 addresses)

    • 10.0.0.0 to 10.255.255.255 (16,777,216 addresses)

  • Private vs public IP addresses

    • Private: used within private networks for internal communication.

    • Public: identifiable on the internet; unique globally.

  • Examples and notes:

    • Each device within the same private network has a unique private IP address (e.g., 192.168.1.1, 192.168.1.2, etc.).

    • A public IP address identifies you to the wider internet (e.g., 8.8.8.8).

    • Your public IP may be different from the private IP assigned to devices inside your home or office.

Private IP address ranges and examples

  • Example ranges shown:

    • 192.168.1.0/24 within 192.168.0.0/16 blocks

    • Private addresses are used inside LANs and do not route on the public internet by default.

  • How to determine your IP in practice:

    • You can find it via device settings or commands (e.g., ipconfig on Windows or ifconfig/ip a on Unix-like systems).

ipconfig and public vs private lookups

  • ipconfig (Windows) displays your IPv4 address, subnet mask, and default gateway.

  • Public IPs can be discovered by services like whatismyipaddress; local/private IPs are visible only within the private network.

  • The screenshots/examples show typical ipconfig outputs and how to interpret addresses.

Traceroute and network path visualization

  • Traceroute is a diagnostic tool used to determine the path packets take to a destination.

  • It reveals each hop, latency, and the route length between source and destination.

  • Example outputs show multiple hops, with each hop providing RTT measurements and sometimes hostnames or geolocation information.

  • Limited responses (denied or timeout) can appear as * * * in the output.

Packets vs Frames; encapsulation

  • Packets

    • A packet is a chunk of data with an IP header added (source and destination IP addresses).

    • Routers forward packets between networks based on the IP header.

    • Analogy: A packet is like an envelope with a street address (IP) but not a postal address (MAC).

  • Frames

    • A frame is a packet with the MAC addresses added (source and destination MAC) to traverse a local network segment.

    • Frames also include an error-checking trailer (frame check sequence) and are handled by the NIC.

  • Encapsulation

    • The process of adding IP addresses and MAC addresses to data is called encapsulation.

  • Headers vs trailers

    • Information added to the front of the data is the header.

    • Information added to the end is the trailer.

Web traffic example: HTTP over TCP/IP

  • Web browser (client) makes an HTTP request to a web server.

  • Example: HTTP request uses port 80 by default.

  • A simple stack can be summarized as:

    • HTTP application on the client

    • TCP as the transport protocol (port 80 on the server)

    • IP for addressing across networks (destination IP 164.78.252.4 in the example)

    • Ethernet as the physical/lower-layer medium

  • The path involves multiple layers, including NICs and routing devices that forward frames and packets accordingly.

Client and server concepts

  • Client

    • A computer or software that requests network resources from a server.

    • Contexts:

    • Client operating system

    • Client computer running user applications

    • Client software that requests network resources from server software

  • Server

    • A computer or software that provides network services to clients.

    • Contexts:

    • Server operating system

    • Server computer that serves client requests

    • Server software that responds to client requests

Summary and key takeaways

  • To network a stand-alone computer, you need a NIC, a network medium, usually an interconnecting device, plus client/server software, protocols, and a NIC driver.

  • The network communication process is layered: user application → network software → network protocol → network interface.

  • Network scope terms: LAN, Internetwork, WAN, MAN.

  • Units and addressing:

    • Distinguish between kbps (bits) and KBps (bytes).

    • CIDR notation (e.g., 192.168.1.0/24) defines a subnet with a specific netmask and range of usable addresses.

    • Private IP ranges provide private networking space; public IPs identify devices on the internet.

  • Data units and routing concepts:

    • Data is transmitted in packets; frames carry packets over local links with MAC addresses.

    • Encapsulation chains IP headers and MAC headers as data moves through the network.

  • Utilities like ping and traceroute help diagnose reachability and path characteristics.

  • The Internet comprises public networks (Internet) and private networks (Intranet/Extranet) depending on access controls and scope.