IEEE 802.3: Ethernet
Design decisions
CSMA/CD
To manage wire access.
Ethernet Frame
| Field | Content |
|---|---|
| Destination | MAC address of the frame's recipient. |
| Source | MAC address of the sending system. |
| Type | Type of data (e.g., IPv4). It does not tell you about higher-level data such as en email. |
| Data | The actual payload. |
| Frame Check Secuence (FCS) | Data goes through a cyclic redundancy check (CRC) formula and its result is attached to the frame. The receiving NIC will perform the same calculation and compare it with this answer to check data is correct. |
| Pad (optional) | The minimum frame is 64 bytes in size. If the frame has fewer data to haul, the sending NIC will automatically add extra data. |
Preamble
Transmission of a frame starts with a preamble, a 7-byte series of alternating ones and zeroes followed by a 1-byte _start frame delimiter. This always preceds a frame. The preamble is added by the sending NIC.
The preamble gives a receiving NIC time to realize a frame is coming and to know exactly where the frame starts.
Variants
Standards
| Name | Speed | Distance between switch and node | Cable type |
|---|---|---|---|
| 10BaseT | 10Mbps | 100m | Cat 3 UTP w/RJ-45 |
| 10BaseFL | 10Mbps | 2000m | Multimode fiber-optic cabling w/ST|SC |
| 100BaseT/TX (i.e., "Fast Ethernet") | 100Mbps | 100mts | Cat 5 UTP|STP w/RJ-45|8P8C |
| 100BaseFX | 100Mbps | 2km | Multimode fiber-optic w/ST|SC |
| 1000BaseT (i.e., "Gigabit Ethernet") | 1Gbps | 100mts | Cat 5e/6 UTP w/RJ-45 |
| 1000BaseSX | 1Gbps | 220-500m | Multimode fiber 850nm w/LC commonly |
| 1000BaseLX | 1Gbps | 5km | Single-mode fiber 1300nm w/LC|SC commonly |
| 10GBaseSR | 10Gbps | 26-300m | Multimode 850nm LAN |
| 10GBaseSW | 10Gbps | 26-300m | Multimode 850nm SONET/WAN |
| 10GBaseLR | 10Gbps | 10km | Single-mode 1310nm LAN |
| 10GBaseLW | 10Gbps | 10km | Single-mode 1310nm SONET/WAN |
| 10GBaseER | 10Gbps | 40km | Single-mode 1550nm LAN |
| 10GBaseEW | 10Gbps | 40km | Single-mode 1550nm SONET/WAN |
| 10GBaseT | 10Gbps | 55/100m | Cat6/6a UTP four-pair/full-duplex w/RJ-45 |
Subcommittees
The original Ethernet used a single piece of coaxial cable to connect several computers, enabling them to transfer data at a rate of up to 3 million bits per second (3 Mbps).
| Standard | Area of jurisdiction |
|---|---|
| 802.3i | 10 Mbps using twisted pair cabling (1990) |
| 802.3ab | 1 Gigabit over twisted pair (1999) |
| 802.3by | 25Gb over fiber (2016) |