Networking Notes

LAN, WAN, Intranet, and Internet Structure

Characteristics of Effective Data Communications

Delivery – Information must be delivered to the correct destination; only the intended user should receive the data.
Accuracy – Data must be delivered without errors.
Timeliness – Data must be delivered on time (must not be late).
Jitter – Variation in packet arrival time should be minimized.

Main Components of Data Communication

Message – Information to be conveyed.
Sender – Device that sends the message.
Receiver – Intended recipient of the message.
Medium – The physical path by which the message travels.
Protocol – A set of rules dictating how data is communicated between devices.

Networks

A network is two or more computers connected together for communication.
A stand-alone refers to an isolated computer.

Advantages

File sharing
Hardware sharing (e.g., printers)
Communication between devices
Roaming access – access files on any device
Centralized maintenance and updates
Centralized security (antivirus, firewalls)
User monitoring
Access level differentiation (different rights for users)

Disadvantages

Cost (equipment/resources required)
Malware spread (if poorly secured)
Hacking (unauthorized access to files)

Types of Networks

Local Area Network (LAN) – Geographically constrained to one site/building.
Wide Area Network (WAN) – Covers more than one site.
internet * /Internetwork – When two or more networks are connected.
Internet – Global system of connected networks that use TCP/IP protocols; includes private, public, academic, business, and government networks.
Intranet – Private network limited to an organization for internal communications and collaboration (restricted to organization members).
* - small letter i

OSI Reference Model

Host Layers

Each layer provides services to the layer above it and does not know where data from the previous layers came from.

Application / Presentation / Session → Data
Connect directly with applications.
Transport → Segment (TCP) / Datagram (UDP)
Translates formats between systems; handles compression and encoding.
Network → Packet
Routing of packets across networks.
Data Link → Frame
Ensures data transfer across physical links, framing, error detection, and MAC addressing.
Physical → Bits
Transmission and reception of bitstream over the medium.

Physical Layer

Represented in 1s and 0s.
Decides rate and duration of transmission.
Synchronizes bit-rate to prevent loss.
Concerned with device connections and modes of transmission:
- Simplex – One-way communication.
- Half-duplex – Two-way communication, but one device transmits at a time.
- Full-duplex – Both devices communicate simultaneously.

Transmission Media

Wired
- Twisted Pair Cable – Ethernet LANs (Cat5, Cat6).
- Coaxial Cable – Used in cable TV and older networks.
- Fiber Optic Cable – High-speed, long-distance, minimal interference.
Wireless
- Radio Waves – Wi-Fi, mobile networks.
- Microwaves – Satellite and long-distance comms.
- Infrared – Short-range comms (e.g., TV remotes).

Physical Connections

Multipoint / Multidrop
- Time-shared: Devices take turns.
- Spatially shared: Devices use link simultaneously.

Topologies

Multipoint/Multi drop - all devices connected to one link, devices take turns and use the link simultaneously
Bus – Multi point, Single cable shared by all devices.
Mesh – Every device has a dedicated connection with all others.
Point to point - Every device has two dedicated connections to the devices around it
- sorry i dont have the images but i guess you can imagine it
Star – Central controller; all traffic passes through it.
Ring – Each connected to two neighbors; signals passed until reaching destination.

Data Link Layer

Represented in frames.
Responsible for direct connection between two devices on the same local network.
Functions:
- Oversees packet delivery.
- Packages data into frames (Header – Source/Destination MAC, Payload, Trailer – error info).
- Error/Duplicate detection (checksums, parity bits, CRC).
  - devices can ask for re-transmissions
- Flow control (preventing overflow).
- Access control (who can transmit).

Access Control

Manage which device have control over the link when two or more devices are connected to the same link.

MAC protocol (Ethernet) – Listens before transmitting, detects collisions.
CSMA/CA (Wireless) – Avoids collisions by waiting for a “go” signal.

Components

LLC (Logical Link Control) – Interface with network layer; error/flow control.
MAC (Media Access Control) – Physical addressing, channel access.

Frame Structure

Preamble – Synchronization.
SFD – Start of frame delimiter.
Destination – Destination MAC.
Source – Source MAC.
Type – Type of packet.
Data – Payload.
FCS – Error check.

MAC Addresses

$00 : 1 A : 2 B : 3 C : 4 D : 5 E$

48-bit hardware address (6 groups of 2 hex digits).
Formats: 00:1A:2B:3C:4D:5E, 00-1A-2B-3C-4D-5E, or 001A2B3C4D5E.
First 3 bytes = manufacturer; last 3 bytes = device ID.
Unique and fixed to the NIC.
Used for local addressing.

Network Layer

Responsible for source-to-destination packet delivery across multiple networks.
Data link same network only.
treats all packages independently
Logical addressing – Packets crossing boundaries are made to carry source/destination addresses(logical addressing).
Routing – Routers switching packets to the correct destination.(Internetworks and large networks)
Important to note!:

if the two hosts are connected to the same network, network layer is still needed to accomplish source to destination,
no routing needed

Transport Layer

Responsible for process-to-process delivery (application to application).
Ensures the whole message arrives intact and in order.
Provides both error control and flow control from source to destination.
- Service Point Addressing(ports)
  - Ensures data is delivered to the correct process.
  - Works at two levels:
    - One device to another.
    - One program (process) to another.
  - Uses a service point address (port number) to direct the packet to the correct process
Segmentation and Reassembly
- Messages are divided into smaller units called segments.
- Each segment contains a sequence number
- At the destination, segments are reassembled according to sequence numbers.
- If a packet is lost, a request is made for re-transmission of the missing data.
connection control
- segments are treated as independent packets
- connection oriented transport layer establishes a connection with the destination transport layer before delivering said packets, before the connection terminates upon completion(tcp requires a connection, udp doesnt need a prior connection to work)
- flow control
  - flow control of end to end rather than a single link
- error control
  - process to process errors
  - makes sure message arrives at receiving end without loss / error
  - else the data is re transmitted(correction)
Flow Control
- Provides end-to-end flow control (not just on a single link like the data link layer).
- Prevents the sender from overwhelming the receiver.
Error Control
- Provides process-to-process error control.
- Ensures that the entire message arrives at the receiving end without loss or error.
- If errors are detected, the affected data is re transmitted (correction).

Session Layer

Manages concurrent sessions.
Session initiation/tear-down – Starts and terminates sessions.
Token management – Controls which device can transmit (important for simplex/half/full duplex).

Presentation Layer

Ensures proper format for application data.
Handles compression, encryption, translation.

Application Layer

Provides end-user services.
Identifies available services.
Manages QoS parameters, security mechanisms, and synchronization of communication apps.

OSI Model Summary

Each layer adds/removes its own header and trailer.

Transport adds sequence numbers and acknowledgements (TCP).

Routers

Routers are network devices.
They partially unpack packets up to the network layer.
Read routing info, select best path, repackage, and forward.
Repeat until reaching the destination.
At the transport layer, segments are reassembled based on sequence numbers.

(from here its networking 2 stuff)
Networks 2

TCP/IP(transmission control protocol / internet protocol)

A protocol suite - set of protocols organised in different layers

same concept as the OSI layers, but as a predecessor to it

Layering - the layer recieves same object sent by corresponding layer at source

Benefits of layering:

Molecularity: grouping of specific functions into layers makes it easier to design, understand and troubleshoot.
Interoperability: standardize layers and functions
- cross compatibily for software as long as they follow the same protocols for each layer
Flexibility and abstraction: Changes made to one layer shouldn’t affect functionality of other layers
Simplified troubleshooting - network issues can be diagnosed by layers
standardization - common language and framework for implementing network protocols.

protocols of each layer in the TCPIP

encapsulation process in TCPIP

Kety characterists of the TCPIP suite:

It is designed to work over any underlying network infrastructure
runs over any sort of hardware
- flexible

Physical

supports all standard and proprietary protocols
communication between two nodes(computer or router)
communicates in bits

Data link

supports all standard and proprietary protocols
communication between two nodes
communicates in frames - packet that encapsulates data recieved from above and optional trailer

Network layer

selects the best path for data to travel
mainly uses Internet Protocol
includes various supporting protocols for IP

Transport

responsible for source to destination and end to end conversations
Transmission Control protocol(TCP)
- connection based
User data-gram Protocol(UDP)
- connection less communication

Application layer:

in charge of exchange information between transport and application layers
- source to destination
- contains many “high level” protocols that cover wide uses
  - HTTP, FTP, SMTP, Post office protocol, Telnet Domain name service

Modes of data transfer:

Circuit switching:

connection established before the start of data transfer(between network layers)
Data moves through the same path defined by the connection
eg: early telephone systems

Packet switching:

connectionless
data fragmented into manageable packets
individually addressed and sent to recipient
- takes the best route
Network layer in charge
- Network layer waits for all packets to arrive before reassembly and delivery
- routing - selection of best path to destination for a packet
  - IP is responsible for packet sending
  - Host A:
    - Packet is encapsulated with IP header, with addresses of hosts A and B
    - consults routing table:
      - if B is on the same network, it is directly sent to B
      - else: it sends to a default gateway(no need to worry about this its just another device that’s set as the default IP to send to)
    - packets will be fragmented if it exceeds the Maximum transmission unit(MTU)
  - Router:
    - router receives and validates the packet(check for corruptions and destination issues)
    - Checks the destination IP
    - consults the routing table for the next hop to send the packet towards B(same process as host A)
    - fragments packets into smaller units and passes it to data link
    - repeat until destination
  - B:
    - validates packet for errors, extract data and caches it
    - reassembles and sent to transport when all info is received
    - cached info has a reassembly timer
      - if expiry, destroys caches and sends an error for re-transmission.

Main differences:

circuit switching is a connection based data transfer method that relies on a pre established connection
- all data will take same path 
circuit switching is a connectionless based data transfer method that breaks data upp into smaller packets that travel independently

Advantages and disadvantages of circuit switching

- garenteed data rate
- reliable
- quality of service
- securityease management
- compatibility

However it is:
- limited in scalibility
- resource intensive
- prone to failure
- there somewhat is latency
Switching uses MAC addresses and MAC address tables

Protocols

Features of a Protocol

Ensures compatibility and interoperability between systems, software, and devices.
Defines how data is formatted and organized in transmission.
Defines how devices initiate, maintain, and terminate connections.
Defines how errors are handled.

Network Protocols

IPv4 – Packetizing, forwarding, and delivery.
ICMPv4 (Internet Control Message Protocol v4) – Handles errors that may occur during delivery.
IGMP (Internet Group Management Protocol) – Supports multicasting.
ARP (Address Resolution Protocol) – Connects the network and data link layers by mapping IP addresses to MAC addresses.

Internet Protocol (IP)

Unreliable
- Best-effort delivery.
- Packets can be corrupted, lost, out of order, delayed, or cause network congestion.
Connectionless – No prior connection is established.
Independent packet handling – Each packet can follow a different route to the destination.
Responsible for source-to-destination delivery.

IP Host-to-Source Delivery

An IP header is added with source and destination IP addresses before passing down the stack.
If destination is on the same network:
- (Same subnet mask) → Sent directly to destination.
If destination is on a different network:
- Sent to the default gateway or router (indirect delivery).
Packet may be fragmented according to the MTU (Maximum Transmission Unit).
Before passing to the data link layer, the MAC address of the next hop (host or router) is required.
The MAC is resolved from the destination IP using ARP.

Address Resolution Protocol (ARP)

Maps IP addresses to MAC (hardware) addresses.

Resolves IP → hardware address.
Process:
1. Looks in the ARP cache.
  - If found → entry is used (stored for 2–10 mins).
  - If not found → request broadcast is sent.
2. All nodes in the local network receive the ARP request.
3. The node with the matching IP responds with its hardware (MAC) address.

Internet Control Message Protocol (ICMP)

Used for:
- Sending error messages.
- Performing diagnostics.
- Controlling data flow.
ICMP source-quench – Router tells a source host to slow down due to overload.
PING – Sends ICMP echo request packets to test connectivity.

Internet Group Management Protocol (IGMP)

Allows one host to send one stream of data to many hosts simultaneously.
Supports multicast communication – delivers streams to multiple hosts concurrently.

IP Addresses (Networking)

Every host in TCP/IP networks needs a unique address for host-to-host delivery.

Packets carry addressing information in their headers for routing.

IPv4 (Logical Address)

32-bit address uniquely identifies each host.
Characteristics:
- Software-assigned (not permanent).
- Prefix (n bits) = network.
- Suffix (32-n bits) = host.
Example: 192.168.2.100
Written in dotted decimal notation.

IPv6

128-bit address, allowing up to 2^128 unique addresses.
Written in hexadecimal form (32 hex digits).
- Example:

Quartz 5

Explorer

Networks 1