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Ethernet frame format in data link layer | IEEE 802.3

frame format

  • Ethernet frame format, also known as IEEE 802.3, is the standard for organizing data in Ethernet networks.

  • IEEE stands for the Institute of Electrical and Electronics Engineers and is responsible for creating these standards.

"The standard for Ethernet frame format is known as IEEE 802.3"

Speed and cable types

  • Ethernet protocol was designed to operate at a speed of 10 megabits per second (Mbps).

  • Different types of cables can be used with Ethernet frame format, depending on the network requirements.

  • For example, for 10BASE5, a thick coaxial cable is used, while 10BASE2 utilizes a thin coaxial cable.

  • Twisted pair cables are used for 10BASE-T, and optical fibers are used for 10BASE-F.

"Ethernet protocol was designed to operate at 10 Mbps, and different cable types are used for different Ethernet frame formats."

Maximum lengths and topologies

  • Each cable type has a maximum length or segment that it can support in Ethernet networks.

  • 10BASE5 has a maximum segment length of 500 meters, while 10BASE2 has a maximum length of 200 meters.

  • Twisted pair cables (10BASE-T) can have a maximum segment length of 100 meters, and optical fibers (10BASE-F) support up to 2 kilometers.

  • The topology or network layout differs depending on the cable type: 10BASE5 and 10BASE2 use a bus topology, 10BASE-T uses a star topology, and 10BASE-F also uses a star topology.

"Different cable types have different maximum segment lengths and network topologies."

Advantages of different cables

  • Thick coaxial cables (10BASE5) allow connecting workstations with taps on cables, enabling multiple workstations to be connected to a single cable.

  • Thin coaxial cables (10BASE2) are cost-effective for Ethernet networks.

  • Twisted pair cables (10BASE-T) can be easily used in existing environments by connecting stations through hubs.

  • Optical fibers (10BASE-F) have good noise immunity, leading to better signal quality and reduced disturbances.

"Different cables used in Ethernet networks have advantages like connecting multiple workstations or providing good noise immunity."

Frame structure and fields

  • IEEE 802.3 or Ethernet frame format utilizes the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) method.

  • The frame structure consists of eight fields: Preamble, Start Delimiter (SD), Destination Address (DA), Source Address (SA), Length of Data Field (LF), Data, Pad, and Frame Checksum (FCS).

"Ethernet frame structure consists of eight fields, including Preamble, Start Delimiter, Destination Address, Source Address, and Data."

Node Field and Destination Address

  • The node field in the Ethernet frame format identifies the particular node that is checking the frame. If the frame is for that node, it will keep it; otherwise, the remaining nodes will discard it.

  • The destination address in the Ethernet frame allows the receiving nodes to determine whether the frame is intended for them or for another node. If it is for them, they will keep it; if not, they will discard it.

"The node field in the Ethernet frame format is used to identify the specific node checking the frame, determining whether it should be kept or discarded. The destination address provides information to receiving nodes about whether the frame is meant for them or another node."

Source Address and Length of Data Field

  • The source address, also known as the essay, is the physical address of the sender. It contains the address of the node that initiated or transmitted the frame.

  • The length of the data field indicates the number of bytes in the actual data being transmitted. It tells how many bytes of actual data will be included in the frame, with a maximum allowable value of 1518 bytes.

"The source address field in the Ethernet frame format contains the physical address of the sender, while the length of the data field indicates the number of bytes in the actual data being transmitted."

Data Field and Pad Field

  • The data field in the Ethernet frame format is where the actual data to be transmitted is located. It can be a minimum of 46 bytes and a maximum of 1500 bytes.

  • The pad field is used when the data size is less than 46 bytes. It ensures that the frame meets the minimum required length by filling the remaining space. It can be 0 to 46 bytes in length.

"The data field in the Ethernet frame format contains the actual data that is transmitted, with a minimum length of 46 bytes. The pad field is utilized when the data size is less than 46 bytes, filling the remaining space to meet the minimum length requirement."

Frame Checksum or FCS

  • The frame checksum, or FCS, is the last field in the Ethernet frame format. It is four bytes long (32 bits) and is used for error detection. It allows the receiver to identify errors in the transmitted data by comparing the received frame with the original data.

"The frame checksum field in the Ethernet frame format is used for error detection, helping to identify errors in the transmitted data."

Length of the Frame and Padding

  • The minimum frame length for normal operation in CSMA/CD (a Carrier Sense Multiple Access with Collision Detection) is 64 bytes (512 bits). This minimum length ensures that the receiver receives at least the first bit of the frame before it is fully transmitted, reducing the chances of collision.

  • The maximum frame length for Ethernet frames is 1518 bytes (12,144 bits), excluding the Preamble and Start Delimiter. This maximum length can be achieved by subtracting the 18 bytes of header and trailer from the total frame length.

"The minimum frame length in CSMA/CD is 64 bytes, ensuring that the receiver receives the first bit before the entire frame is transmitted. The maximum frame length for Ethernet frames is 1518 bytes, excluding the Preamble and Start Delimiter."

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