Networking Fundamentals: Layers and Protocols

Overview of Information Exchange and Multiplexing

  • Information can be exchanged between a source and destination through various physical mediums: electrical wires, optical links, and radio links.

  • Multiple sources and destinations can share the same physical medium independently through multiplexing methods.

Multiplexing Techniques

  • Time Division Multiplexing (TDM)

    • Sources and destinations use specific time intervals to communicate.

    • Each pair occupies the transport medium fully during its assigned time slot.

  • Frequency Division Multiplexing (FDM)

    • Communication encoded into different frequency bands.

    • Similar to radio stations on specific frequencies, this method applies to electrical wires and optical waveguides.

  • Code Division Multiplexing (CDM)

    • Bundles information from different pairs into a common code.

    • The code is encoded at the source and unraveled at the destination, facilitating rapid transmission.

  • Wavelength Division Multiplexing (WDM)

    • Used in optical communication by utilizing different light frequencies.

Information Encoding Methods in Transmission

  • Basic transmission involves binary encoding (0s and 1s).

  • Amplitude Shift Keying (ASK)

    • Changes in amplitude represent bits; for example, small amplitude (0) vs. large amplitude (1).

  • Frequency Shift Keying (FSK)

    • Uses different frequencies for encoding bits, e.g., one frequency for 0 and another for 1.

  • Phase Shift Keying (PSK)

    • Same frequency is used with phase changes representing bits.

  • Higher Bit Encoding

    • More complex methods can encode multiple bits per symbol by varying amplitude, frequency, or phase.

The Data Link Layer

  • The Data Link Layer manages data transfer between devices and includes error detection and correction.

  • It provides a structure for data packets, including source and destination MAC addresses.

Components of a Data Link Layer Frame

  • MAC Addresses

    • Each device has a unique hardware MAC address.

  • Frame Structure

    • Includes destination MAC, source MAC, protocol type, variable-length payload data, and a cyclic redundancy check (CRC).

  • Error Detection and Correction

    • Includes checks for errors using parity checks and cyclic redundancy checks, with the latter being more robust and complex.

Understanding MAC Addresses

  • MAC addresses are typically expressed as 48-bit identifiers unique to each device on a network.

  • Ensures devices are differentiated within local networks.

Error Handling

  • If a frame fails the CRC check, it is discarded, leading to a request for the source to resend the frame.

  • This prevents corrupted data from being propagated through the network.

Network Layer

  • The Network Layer establishes paths for packets across the network using unique IP addresses.

Internet Protocol (IP)

  • IPv4

    • 32-bit addressing scheme, limited to approximately 4 billion unique addresses.

    • Written in dot-decimal notation (e.g., 192.168.0.1).

  • IPv6

    • 128-bit addressing scheme, offering a vastly larger address space to accommodate more devices.

    • Written in hexadecimal notation with colons separating groups (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

Packet Structure in IPv4

  • Contains a header (20-60 bytes) with information on total length, fragmentation, and checksum for error checking.

  • Special reserved addresses exist for local networks, multicast, and loopback communication.

Routers and Packet Forwarding

  • Routers direct packets through networks using Address Resolution Protocol (ARP) to determine optimal paths.

  • Algorithms like Dijkstra's are used to manage congestion and determine the most efficient routing paths.

Transport Layer

  • Handles communication services for applications, utilizing port numbers for transferring data.

Protocols in the Transport Layer

  • User Datagram Protocol (UDP)

    • Fast and efficient for real-time applications, provides no guarantees of order or correction.

  • Transmission Control Protocol (TCP)

    • Connection-oriented, ensures reliable data transmission. Includes error checking, packets are tracked and acknowledged to maintain order and integrity.