Subnetting and VLSM

Splitting Up an IP Allocation into Different-Sized Blocks

• Subnetting and VLSM (Variable Length Subnet Masking) are used when organizations need to divide an IP block into smaller subnets for departments like HR, IT, and Finance.
• The steps to split an IP block are:
  • Determine Subnet Requirements (e.g., HR needs 60 hosts, IT needs 30, Finance needs 10).
  • Calculate Subnet Sizes: HR needs 60 hosts, use /26 (64 addresses, 62 usable).
  • IT needs 30 hosts, use /27 (32 addresses, 30 usable).
  • Finance needs 10 hosts, use /28 (16 addresses, 14 usable).
  • Allocate Subnets Sequentially: 192.168.0.0/26 goes to HR (192.168.0.1 - 192.168.0.62).
  • 192.168.0.64/27 goes to IT (192.168.0.65 - 192.168.0.94).
  • 192.168.0.96/28 goes to Finance (192.168.0.97 - 192.168.0.110).
  • Verify No Overlaps and assign remaining space (192.168.0.112/28) for future use.
• Example: Given 10.0.0.0/24, split for Sales (50 hosts) using /26 (10.0.0.0/26). For Marketing (25 hosts) use /27 (10.0.0.64/27) and for Admin (10 hosts) use /28 (10.0.0.96/28).

Determining Next-Hop Router Based on IP

• Longest Prefix Match is used in Routing Tables to determine the next hop.
• Routers use routing tables to forward packets. Each entry has a Destination Network (e.g., 192.168.1.0/24), Next-Hop IP (e.g., 10.0.0.1), and Interface (e.g., eth0).
• The process involves:
  • Extracting Destination IP from packet (e.g., 192.168.1.5). Comparing with Routing Table Entries: 192.168.1.0/24 → Next-hop: 10.0.0.1.
  • 192.168.0.0/16 → Next-hop: 10.0.0.2.
  • 0.0.0.0/0 (Default route) → Next-hop: 10.0.0.254. Applying Longest Prefix Match: 192.168.1.5 matches 192.168.1.0/24 (24 bits) better than 192.168.0.0/16 (16 bits).
  • Packet is forwarded to 10.0.0.1.
• Example: A packet to 172.16.3.2 has a routing table with 172.16.0.0/16 → Next-hop: 192.168.1.1 and 172.16.3.0/24 → Next-hop: 192.168.1.2 and forwards to 192.168.1.2 due to the longer prefix.

Calculating Attenuation

• Attenuation measures signal loss over distance.
• Attenuation (dB) = 10 × log10(P1 / P2) where P1 = Input power and P2 = Output power.
• For instance, with a signal starting at 100 mW and dropping to 10 mW after 5 km, the Attenuation = 10 dB.

Calculating Bits per Baud

• Baud Rate (Symbol Rate) measures the number of signal changes per second.
• Bit Rate (bps) is Baud Rate multiplied by Bits per Symbol.
• The formula for Bit Rate is Baud Rate × log2(M), where M is the modulation levels.
• If bit rate = 2400 bps and frequency (baud rate) = 600 Hz, then 2400 = 600 × log2(M) → M = 16 (16-QAM, which is 4 bits per symbol).

Two Types of Addresses in Data-Link Layer

• MAC Address (Physical Address) is unique to each NIC (e.g., 00:1A:2B:3C:4D:5E) and used in Ethernet frames for local delivery.
• Logical Address (IP Address) is used for network-layer routing (e.g., 192.168.1.1).

Datagram Routing in Network Layer

• A Source Host sends a packet with a destination IP.
• Each Router checks its routing table for the next hop and forwards the packet using the longest prefix match.
• The Final Router delivers the packet to the destination host.
• Example: Sending from 192.168.1.1 to 10.0.0.5 happens via multiple hops.

Four Network Topologies

• Bus is the least secure, with a single point of failure.
• Star is centralized, depending on a hub/switch.
• Ring has moderate security and unidirectional flow.
• Mesh is the most secure, with redundant paths, and is hard to intercept.

Shannon Data Capacity

• Formula: C = B × log2(1 + SNR), where C = Max capacity (bps), B = Bandwidth (Hz), and SNR = Signal-to-Noise Ratio.
• If B = 3000 Hz and SNR = 1000, then C ≈ 30 kbps.

Fields of IP & Ethernet Frames

• IP Header Fields: Version, TTL, Protocol, Source/Dest IP, Checksum.
• Ethernet Frame Fields: Preamble, Dest/Src MAC, Type, Data, FCS.

Why VLANs Save Time & Money

• VLANs reduce broadcast traffic by isolating domains.
• They simplify network management through logical grouping.
• They eliminate the need for physical reconfiguration, saving cabling costs.

Shortest Path Between Nodes (Dijkstra’s Algorithm)

• Steps: Assign 0 to the source, ∞ to others, visit the nearest unvisited node, update distances, and repeat until all nodes are visited.

Final Notes

• Use VLSM for efficient subnetting.
• The longest prefix match decides the next hop.
• Higher dB means more signal loss.
• Mesh topology is most secure.
• VLANs cut costs by reducing physical changes.

Chapter 1: Network Fundamentals

• Three Criteria for an Effective Network are Performance, Reliability, and Security.
  • Performance measures data transfer speed and reliability and includes metrics like Throughput (amount of data transferred) and Latency (delay in data transfer).
  • Reliability includes minimal network downtime, quick recovery from failures, and consistent data transmission.
  • Security involves protecting data from unauthorized access, ensuring data privacy and integrity, and preventing potential breaches.

Transmission Modes

• Half-Duplex involves communication in both directions, but not simultaneously, like walkie-talkies, where only one party can communicate at a time.
• Full-Duplex denotes simultaneous communication in both directions, allowing both parties to talk and listen simultaneously, like phone calls.

Network Topologies and Failure Consequences

• Mesh Topology features maximum connectivity but needs a high number of cables, calculated by the formula n(n-1)/2, where n is the number of devices and the number of ports per device is (n-1).
  • If a connection fails, only that connection is affected.
• Star Topology connects all devices to a central hub, and if a connection fails, the isolated device is disconnected. However, other devices remain connected.
• Bus Topology connects all devices via a single cable and if the cable breaks, the entire network fails.
• Ring Topology connects devices in a circular chain, and if the ring breaks, the network may fail completely, unless a dual-ring setup provides redundancy.

Addressing in TCP/IP Protocol Suite

• Network Layer uses IP addresses with two addresses for source and destination in examples such as IPv4: 192.168.1.1 and IPv6: 2001:0db8::1.
• Data Link Layer uses MAC addresses with two addresses for source and destination, for example: 00:1A:2B:3C:4D:5E.

Chapter 2: Signal Transmission and Impairments

• Three Transmission Impairments are Attenuation, Noise, and Distortion.

Transmission Impairments

• Attenuation measures signal strength loss over distance and is calculated as Attenuation (dB) = 10 * log10(Power at A / Power at B). For example, if power at A is 100 W and power at B is 90 W, the Attenuation is approximately 0.46 dB.
• Noise is unwanted signals interfering with the original signal and reduces signal quality.
• Distortion involves changes in signal shape or form and affects signal integrity.

Bandwidth and Data Rate Calculations

• Bandwidth is calculated as the difference between the highest and lowest frequencies, expressed as: Bandwidth = Highest frequency - Lowest frequency and for frequencies of 20, 50, 100, 200 Hz, the Bandwidth = 200 Hz - 20 Hz = 180 Hz.

Data Rate calculations

• Transmission Time calculation is Time = Number of bits / Transmission Rate where sending with network data at 5 kbps a transmission of 100 bits will be 100/5000=0.02 seconds; 100,000 Unicode characters will be (100,000 * 16bits) /5000 = 320 seconds.
• Bit Rate calculation is Bit rate = Sampling rate * Bits per sample, for example, with 8000 samples/second and 16 bits/sample, Bit rate = 8000 * 16 = 128 kbps.

Signal Levels and Data Rate

• Nyquist Formula: C = 2B * log2(L), where C measures Channel capacity, B is the Bandwidth, and L counts Number of signal levels and when sending 300 kbps over 40 kHz channel it has around 8 number of signal levels.

Modulation Techniques

• Formula: log2(Number of levels) is used to calculate Bits per baud. Examples are ASK (4 amplitudes): 2 bits per baud; FSK (8 frequencies): 3 bits per baud; PSK (4 phases): 2 bits per baud; and QAM (128 points): 7 bits per baud.

Multiplexing Techniques

• FDM (Frequency Division Multiplexing) combines analog signals and shares bandwidth (frequency channels).
• TDM (Time Division Multiplexing) combines digital signals and shares time slots.
• WDM (Wavelength Division Multiplexing) combines optical signals and shares wavelengths (light frequencies).

Chapter 3: Error Detection and Correction

• Three examples of Error Detection Methods are Checksum, Parity Bit, and CRC (Cyclic Redundancy Check).

Error Detection Methods

• Checksum has limitations, and cannot detect swapped data items as the total sum remains unchanged if items are swapped.
• Parity Bit ensures an odd or even number of 1s, doing so by counting the number of 1s in the data and adding/removing a bit to maintain parity.
• CRC (Cyclic Redundancy Check) adds redundant bits for error detection.

Bit Stuffing

• Cannot be used in character-oriented framing or byte-level flags and would corrupt data integrity.

Chapter 4: Network Access Layer

• Wireless and Physical Layer Technologies include Bluetooth Radio Layer, IEEE 802.11 Wireless LAN Station Types, and Data Link Layer Protocols in HDLC Frame Addressing.

Bluetooth Radio Layer

• Handles physical transmission, frequency hopping, and modulation in the 2.4 GHz band.

IEEE 802.11 Wireless LAN Station Types

• Three types are: No-transition: Fixed stations, BSS-transition: Moves within the same Basic Service Set, and ESS-transition: Moves between Extended Service Sets.

Data Link Layer Protocols

• HDLC Frame Addressing uses a single address field in point-to-point links and only one destination address is needed.

Chapter 5: Network Access Technologies

• DSL Technology uses telephone lines for high-speed data. Its components ar a DSL Modem (User-end data conversion) and DSLAM (Provider-end connection aggregation).
• Cable TV Data Transfer uses coaxial cable, frequency-division multiplexing (FDM), and DOCSIS standard for data transmission.
• Satellite Communications use GEO (Geostationary Earth Orbit) at 35,786 km altitude, which is stationary relative to Earth.

Chapter 6: Network Switching

• VLAN Grouping Characteristics include port number, MAC address, IP address, and protocol type.
• Switch is less complex and Router is more complex relating overhead.
• Switches process Layer 2 (MAC) headers while routers Layer 3 (IP) headers.

Chapter 7: Network Layer

• Auxiliary TCP/IP Network Layer Protocols include ICMP for Error reporting, IGMP for Multicast management, and ARP for MAC address resolution.
• IP Address Block Calculations include determining the network range and calculating first and last addresses, for example:
  • 14.12.72.8/24
  • First address: 14.12.72.0
  • Last address: 14.12.72.255

IPv6 Address Abbreviation

• Remove leading zeros and use :: to compress consecutive zero segments. Examples:
  • 0000:FFFF:FFFF:0000:0000:0000:0000:0000 → ::FFFF:FFFF:0:0:0:0
  • 1234:2346:3456:0000:0000:0000:0000:FFFF → 1234:2346:3456::FFFF

Routing Considerations

• Packet Forwarding:Datagram uses destination IP address and Virtual-circuit uses Virtual Circuit Identifier (VCI).

Packet Delays

• There are four types, Transmission delay, Propagation delay, Processing delay, and Queuing delay.

Chapter 8: Routing Algorithms

• Shortest Path Routing combines the shortest subpaths into A → B → H → G → N.
• Routing Information Protocol (RIP) uses UDP for lightweight communication, Tolerates packet loss, Periodic updates with a multicast address of 224.0.0.9.
• An example of IP Multicast to Ethernet Address Conversion is: 224.18.72.8 → 01-00-5E-12-48-08.

Chapter 1 Study Guide: Introduction to Data Communications and Networking; 1.1 Data Communication

• Key Components of Data Communication: Message, Sender, Receiver, and Transmission.
  • Message is the information being transmitted and can be in various forms such as text, numbers, images, audio, video
  • Sender is the device that initiates the communication by creating and transmitting the message.
  • Receiver is the device meant to receive the message which interprets and processes the incoming data
  • Transmission Medium is the pysical path through which data must travel through and is done through cables or wireless (airwaves),
    • Protocol specifies a defined set of rules which dictate how data is transmited and received

Data Flow Types

• Simplex is a one way communication where only one device can be sending and the other can only receive an example is TV broadcasting
• Half-Duplex is a two way communication where both parties take turns sending and receiving like a walkie talkie
• Full-Duplex is a two way communication where both devices can send and receive simultaneously, like a telephone conversion

1.2 - Networks, Network Critera

• Performance is measured by transit and response time
• Reliability is the rate of success with recovery time and if it can handle failures
• Security entails protecting data from damage or illegal access

Network Structures

• Point to Point is a direct connection between devices
• Multi-point is multiple devices connected to each other
• Physical Topologies include:
  • Mesh contains every device connected to one another offering redundancy and high secure
  • Star contains devices that are connected to a centrall hup/switch with easy installation
  • Bus contains every device connected through a single line of connection, is simple in design
  • Ring structure connects devices through a circular chain for predicatble performance

1.3 Network Types

• Local Area Network (LAN)
  • Privately managed
  • Connects devices that are small such as an office campus
  • Connects using high speed communication
• Wide Area Network (WAN)
  • Covers a far wider area such as towns
  • Connect devices using multiple LANs
• Internetwork
  • Connects multiple networks to allow communication between various network types

1.4 - Protocol Layering

• First Principle: objects under each layer should be identical
• Second Principle: Each layer must perform opposite tasks

1.5 TCP/IP Protocol Suite

• Physical Layer:
  • Carries individual bits and ensures the connection is at its lowest communication level
• Data Link Layer:
  • Moves data from adjacent networks/connections
  • Handles routing between connections
• Network Layer:
  • Creates host-to-host connections
  • Determines best packet routes through router

Transport Layer

• End-to-End communication
• Encapsulates messages that are sourced from the App layer
• Transports messages to app connections

Application Layer

• Process to Process communication
• Exchanges messages between apps

1.6 - OSI Model

• The OSI model has additional layers such as sessions and presentations
• The TCP/IP model combines these extra feature into the APplication layer instead

Transmission Media

• Guided transmission:

  • Twisted Pair cable:
    • Contains two insulated copper wires where Categories include (Cat 3 to Cat 8) which have different bandwidths
  • Coaxial cable:
    • Central conductor, braided shielded housing with higher bandwidths
  • Fiber optic cable:
    • Glass coated cladding encased in glass for high bandwidths, low insulation

• Unguided/Wireless transmission:

  • Radio waves:

    • 3 KHz to 1GHz
    • Omnidirectional range

  • Microwaves:

    • 1GHz to 300GHz
      • Unidirectional when alignment is correct

  • Infrared:

    • 300GHZ to 400THz
      • Short range with inability to penetrate through walls

• The nyquist relation is tied to the sampling theorem

2.1 - Signal Characteristics

Analog signals:

• Continuous & infinite in range of values
• Sine wave has components such as:
  • Peak amplitude: Maximum signal strength in Volts
  • Frequency(f): cycles per second using Hertz
  • Period(t): time of full cycle (t = 1/f)
  • Phase: Wave form relative to origin
  • Wavelength: distance signal travels using lambda where (λ = c/f -propagation speed from source)
• Composite makes multiple since waves which are then processed with a bandwidth diff where highest to lowest levels

Digital Signals: Discrete and limited in terms of values Rate of transmission (bits in bps)

• Bit length: Distance one bit can maintain (propagation speed * bit duration)
• Transmission types
  • Baseband: Digital signal sent over a media
  • Broadband Digital signal: Conversions to analogs

2.2 - Signalling Impairments

Attenuation:

• Signal degrades over time
  • Loss as distance goes on as well - measurement is in decibels
  • To be exact in Decibels (db):
    • Db = 10 logo10(p2/p10
  • Solved by using amplifiers
• Noise
  • Signal shape has diff properties
    • Thermal noise
      • Caused by electron fluctuations
    • Intermodulation Noise
    • Mixe signals
    • Cross talk
      • One line affects another -Implus noise(sudden spikes/lightning)
• Signal to Noise Ratio

Data Rate Limits

• Nyquist:
  • For all noiceless Channels/Maximum bitrates -Bitrate = 2 X B X log2L)
  • B: Bandwidth | L: Number of Signal Levels Shannon Capacity:
• bit rate = B X log2(1 +Snr)

Performance Metrics

Bandwidth: Link speed

• Throughput: actual
• Latency: time it takes(transmission,queue and processing)
• Jitter: Packet variance

2.3 Digital transmedia

Conversion:

• Line coding: convert to digital/digital -Unipolar,multilevel etrc or -Self sync/correcting -Characteristics: -Block: add redundancy -Scrambling: modify long streams of Os (B8Zs, HDB3)

Chapter Three - Error correction

Check Sum limitation:

• cannot detect swapped Parity: add/remove bit Crc: Adds bits for error detection, polynimal divison -Add Os to data word Stuffing
• used for char/corrutpi data

Chapter 4: Addressing and Ethernet

4.1 Ethernet

• The most used wired lan, evolves fast

4. Standard bits (10 mgbs)

• connecelss, frames sent.

4. Formate

• synched/receiver bit Destination AddrHardware
• Length-type

Fast/Gig Ethernet

• Negotiate the speed as well auto Wi-fi and bluetooth ad hoc networks tech

5. Networking Data Lan

• Data layer is responsible for logical, routing and forwarding packets Key responsbility is : Packetizing for a to b
• Routing and determining the data
• error corrections

6. Packets & Network Protocols

ipv4

• 3 bits/addres

6 - Network & MIB

• What is network management - Monitoring, configuring.
• Key protocols work together - The snmp which defines the formats, SmI, mib, to gather objects