Network Cabling Types and Data Frame Structure Explained

Networking Fundamentals: Media and Frame Structure

Network Transmission Media (Layer 1 Components)

Unshielded Twisted Pair (UTP) Cable

Unshielded Twisted Pair (UTP) cable is a medium composed of four pairs of wires, used in diverse types of networks. Each wire pair is isolated from the rest.

Coaxial Cable

Coaxial cable is composed of a hollow outer cylindrical conductor that surrounds a single inner wire. This structure is composed of two conductive elements. One of these elements (located in the center of the cable) is a copper conductor.

Fiber Optics

Optical fiber cable is a networking medium that transmits data using modulated light. Compared to other networking media, it is more expensive; however, it is not susceptible to electromagnetic interference and offers significantly higher data speeds.

RJ-45 Connector

The RJ-45 connector reduces noise, reflection, and mechanical stability problems. It is similar to a phone jack, but it has eight wires instead of four, making it suitable for Ethernet connections.

Generic Network Frame Format (Layer 2)

Understanding the structure of a network frame is crucial for data transmission across the physical medium.

• Start of Frame Fields

  When computers are connected to a physical medium, there must be a way for them to draw the attention of other computers to send a broadcast message, signaling: "Here is a frame!" Different technologies handle this differently, but all frames, regardless of technology, have a sequence of bytes for starting and signaling the transmission.

• Address Fields

  All frames contain addressing information, specifically the name of the source computer (MAC address) and the name of the destination computer (MAC address).

• Length/Type Fields

  Most frames include specialized fields. In some technologies, the "length" field specifies the exact length of a frame. Others use a "type" field, which specifies the Layer 3 protocol (e.g., IP) that makes the request being sent. Note that some technologies do not utilize these fields.

• Data Fields

  The primary reason for sending frames is to ensure that data from the upper layers—ultimately the user's application data—arrives from the source computer to the destination computer. The data packet being sent is composed of two parts:

  1. The message to send.
  2. The encapsulated bytes intended to reach the destination computer.
  Along with this data, a few extra bytes, known as padding bytes, must sometimes be sent. These padding bytes are added so that the frames meet a minimum required length, often for purposes related to delay and timing.