OSI Model Layers

• A numbering system represents numbers using specific symbols or digits.
• Common numbering systems include decimal (base 10), binary (base 2), hexadecimal (base 16), and octal (base 8).
• A bit is the smallest unit of data (0 or 1), and eight bits form a byte.

Networking Examples

• The letter 'A' is stored as 01000001 (65 in decimal).
• IPv4 Addresses consist of 4 bytes (e.g., 192.168.1.1).

ASCII

• The American Standard Code for Information Interchange, ASCII is a standardized character encoding scheme.
• ASCII is used in computers and electronic devices to represent text and control characters.
• ASCII is fundamental in data communication, programming, and text processing and is widely used in protocols like HTTP, FTP, and email, and in programming languages and file formats.

Convert IP Address in Decimal Octet to Binary

• To convert the IP address 192.168.1.3 to binary, convert each decimal octet separately:
  • 192 = 11000000
  • 168 = 10101000
  • 1 = 00000001
  • 3 = 00000011
• The full binary representation is 11000000.10101000.00000001.00000011

Binary to Decimal Conversion

• Start with the binary number, such as 1011.
• Write the powers of 2 from right to left (2^0, 2^1, 2^2, 2^3).
• Multiply each binary digit by its corresponding power of 2:
  • 1 × 2^3 = 8
  • 0 × 2^2 = 0
  • 1 × 2^1 = 2
  • 1 × 2^0 = 1
• Add the results to get the decimal equivalent: 8 + 0 + 2 + 1 = 11.

Hexadecimal to Binary Conversion

• Start with the hexadecimal number, such as 2F3.
• Convert each hexadecimal digit to its 4-bit binary equivalent:
  • 2 (hex) = 0010 (binary)
  • F (hex) = 1111 (binary)
  • 3 (hex) = 0011 (binary)
• Combine the binary equivalents: 001011110011.

Decimal to Hex Conversion

• Divide the decimal number by 16.
• Note the quotient and remainder.
• Continue dividing the quotient by 16 until it reaches 0.
• Convert the remainders to hexadecimal.
• Reverse the order of the remainders.
• Example: Convert 473 to hexadecimal:
  • 473 ÷ 16 = 29, remainder 9 (9 in hex)
  • 29 ÷ 16 = 1, remainder 13 (D in hex)
  • 1 ÷ 16 = 0, remainder 1 (1 in hex)
• Result: 1D9.

Decimal to Octal Conversion

• Divide the decimal number by 8.
• Note the quotient and remainder.
• Continue dividing the quotient by 8 until it reaches 0.
• Write the remainders in reverse order.
• Example: Convert 473 to octal:
  • 473 ÷ 8 = 59, remainder 1
  • 59 ÷ 8 = 7, remainder 3
  • 7 ÷ 8 = 0, remainder 7
• Result: 731 (base 8).

Subnet Mask to Determine the Network Portion of an IP Address

• Given IP address 192.168.1.3 and subnet mask 255.255.255.0, convert to binary:
• IP Address: 11000000.10101000.00000001.00000011
• Subnet Mask: 11111111.11111111.11111111.00000000
• Perform a bitwise AND operation:
  • 11000000 AND 11111111 = 11000000
  • 10101000 AND 11111111 = 10101000
  • 00000001 AND 11111111 = 00000001
  • 00000011 AND 00000000 = 00000000
• Convert the result back to decimal: 192.168.1.0.
• Therefore, the network portion is 192.168.1.0.

Binary AND Operation

• 1 AND 1 = 1: Both bits are 1, the result is 1.
• 1 AND 0 = 0: One bit is 1 and the other is 0, the result is 0.
• 0 AND 1 = 0: One bit is 0 and the other is 1, the result is 0.
• 0 AND 0 = 0: Both bits are 0, the result is 0.

The Transport Layer

• The fourth layer of the OSI model, it provides reliable data transfer services to upper layers.
• It manages end-to-end communication, error recovery, and flow control.

Key Functions

• Segmentation and Reassembly: Divides large messages into smaller segments and reassembles them.
• Connection Control: Establishes, maintains, and terminates connections.
• Flow Control: Prevents overwhelming the receiver.
• Error Detection and Correction: Detects and corrects errors during transmission.
• Multiplexing: Manages multiple connections through ports.

Protocols

• TCP (Transmission Control Protocol): Provides reliable, connection-oriented data transmission.
• UDP (User Datagram Protocol): Provides connectionless, best-effort data transmission.

Examples

• TCP: Web browsing (HTTP/HTTPS), email (SMTP), file transfer (FTP).
• UDP: Streaming media, online gaming.

Ports

• Web Browsing (HTTP): TCP Port 80
• Secure Web Browsing (HTTPS): TCP Port 443
• Domain Name System (DNS): UDP Port 53
• File Transfer Protocol (FTP): TCP Ports 20 and 21

The Session Layer

• The fifth layer of the OSI model and manages sessions between applications.
• A session is an interactive information interchange between communicating devices.

Key Functions

• Session Management: Establishes, maintains, and terminates sessions.
• Synchronization: Provides synchronization points for recovery.
• Dialog Control: Manages the dialog between devices.
• Authentication: Handles authentication for secure sessions.
• NetBIOS works on this layer.

Examples

• Remote Procedure Calls (RPC): Executes a procedure in another address space.
• SQL Session: Manages sessions between SQL clients and SQL servers.
• Network File System (NFS): Manages sessions for file sharing.

The Presentation Layer

• The sixth layer of the OSI model and handles translation, encryption, and compression of data.
• Ensures data is readable between different systems' application layers.

Key Functions

• Translation: Converts data formats.
• Encryption/Decryption: Ensures data security.
• Compression/Decompression: Reduces data size for efficient transmission.

Examples

• Translation: ASCII to EBCDIC conversion.
• Encryption/Decryption: SSL/TLS protocols.
• Compression/Decompression: JPEG and MPEG.

The Application Layer

• The seventh and topmost layer of the OSI model and provides network services to end-user applications.
• Facilitates communication between software applications and lower network layers.

Key Functions

• Network Services: Provides services like email, file transfer, and web browsing.
• Resource Sharing: Allows applications to share resources.
• Remote Access: Facilitates remote access to applications.
• Service Advertisement: Advertises available network services.

Examples

• HTTP/HTTPS: Web browsing.
• FTP: File transfer.
• SMTP: Email.
• DNS: Domain name resolution.

OSI Highlights

• OSI has seven layers.
• OSI is a theoretical model.
• The Data link layer is responsible for encapsulation and framing.
• The transportation layer manages end to end communication and controls the flow between host and systems.
• The network layer is responsible for routing packets between networks.
• Intrusion Detection System (IDS) and Intrusion Prevention System (IPS) happens mainly on network, transport and application layers.
• The layer responsible for security is the application layer in collaboration with transport and network layer.

The TCP/IP Model

• The foundational protocol suite for the internet, consisting of four layers.
• Each layer in the TCP/IP model corresponds to one or more layers in the OSI model.

Layers of the TCP/IP Model:

Application Layer:

• Function: Represents data to the user, manages encoding, and dialog control. -Protocols: HTTP, FTP, SMTP, DNS, etc. -Key Features: Combines the OSI model's Application, Presentation, and Session layers. Transport Layer:
• Function: Ensures reliable communication between devices on different networks, handles error recovery, and flow control.
• Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
• Key Features: Provides end-to-end communication services and data integrity.
• IDS/IPS monitor transport layer traffic for anomalies and potential threats. Internet Layer:
• Function: Determines the best path through the network, handles packet routing and addressing.
• Protocols: IP (Internet Protocol), ICMP (Internet Control Message Protocol), ARP (Address Resolution Protocol).
• Key Features: Corresponds to the OSI Network layer and handles logical addressing and routing. Network Access Layer:
• Function: Manages hardware devices, media access control, and physical data transmission.
• Protocols: Ethernet, Wi-Fi, PPP (Point-to-Point Protocol).
• Key Features: Combines the OSI model's Data Link and Physical layers.
• Like the Network Layer in the OSI model, IDS/IPS analyze IP packets and routing information.

Key Points of TCP/IP Model

• Protocol Suite: TCP/IP includes many protocols such as HTTP, FTP, SMTP, TCP, UDP, IP, etc. Open Standard: TCP/IP is freely available and can be implemented by any vendor.
• Interoperability: Endorsed by the networking industry and approved by standards organizations to ensure interoperability.
• IDS/IPS Functions are crucial at the Network, Transport, and Application layers of both the OSI and TCP/IP models.

Application in Networking

• Application Layer: Manages protocols for user applications (e.g., web browsers, email clients).
• Transport Layer: Ensures data is delivered error-free and in sequence.
• Internet Layer: Routes data packets to their destination IP address.
• Network Access Layer: Interfaces with physical network hardware and manages the transmission of data.

TCP (Transmission Control Protocol)

• Connection-Oriented: Establishes a connection before data transfer.
• Reliability: Provides error-checking and ensures data delivery in the correct order.
• Flow Control: Manages data transmission rate to prevent congestion.
• Use Cases: Web browsing, email, file transfers (HTTP, SMTP, FTP).

UDP (User Datagram Protocol)

• Connectionless: Sends data packets without establishing a connection.
• Speed: Minimal error-checking, resulting in lower latency.
• Broadcasting: Supports broadcasting and multicasting.
• Use Cases: Video streaming, online gaming, VoIP (DNS, VoIP).

Summary:

• TCP ensures reliable, ordered delivery of data with error-checking, suitable for applications needing high reliability.
• UDP offers faster, connectionless communication with lower overhead, appropriate for applications where speed is critical, and some data loss is acceptable.

This quiz covers the layers of the OSI model. It tests knowledge of the functions of each layer, including the application, presentation, and session layers. It also covers related concepts like secure web browsing and application layer protocols.