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Ethernet

lastmod 2024-09-25created 2015-04-2221 edits

(Same as IEEE 802.3)

Ethernet is a computer networking technology developed for LANs. The name 'Ethernet' comes from ether, once thought to be the medium of light. Ethernet defines signaling and wiring at the physical layer of the OSI model, and the format of MAC (media access control) packets and protocols at the data link layer. Ethernet technology has mostly been standardized as the IEEE 802.3 specification. It is currently the most widely used, and has largely replaced other standards such as token ring and FDDI.

Ethernet frame

In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload.

An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer. Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.

Structure

A data packet on the wire and the frame as its payload consist of binary data. Ethernet transmits data with the most-significant octet (byte) first; within each octet, however, the least-significant bit is transmitted first.

The internal structure of an Ethernet frame is specified in IEEE 802.3. The table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets. Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, known as jumbo frames.

802.3 Ethernet packet and frame structure

Layer

Preamble

Start of frame delimiter

MAC destination

MAC source

802.1Q tag (optional)

Ethertype (Ethernet II) or length (IEEE 802.3)

Payload

Frame check sequence (32‑bit CRC)

Interpacket gap

7 octets

1 octet

6 octets

6 octets

(4 octets)

2 octets

46‑1500 octets

4 octets

12 octets

Layer 2 Ethernet frame

← 64–1522 octets →

Layer 1 Ethernet packet & IPG

← 72–1530 octets →

← 12 octets →

Gigabit Ethernet 

규격상으로는 CAT.6부터 기가비트를 정식으로 지원하지만 
CAT.5이상케이블이면 

8가닥 모두 1:1로 연결되어있으면 기가비트로 연결될수도 있습니다. 
(케이블이 차폐나 주파수가 규격에 미달되어 속도는 다소 줄어들지만 그래도 95%이상 속도는 나옵니다.) 
...

Gigabit Ethernet vs. ATM

Gigabit Ethernet

Gigabit Ethernet was proposed as IEEE 802.3z, and the standard is planned for mid-1998. Gigabit Ethernet provides 1Gbps of bandwidth in Full and Half duplex, and uses CSMA/CD for Collision detection. Gigabit Ethernet also uses the same Physical Layer Technology as Fiber Channel for Fiber transmission. In the near term, shielded and unshielded twisted pair (UTP) will be developed using ASICs incorporating 0.35 micron transistors. The main advantages of using Gigabit Ethernet are its similarity to existing technology and its price. Because it is used without changes to the Protocol, it can be adopted without retraining existing network administrators, and many Vendors expect Gigabit Ethernet to be a very cost-effective technology.

ATM

ATM is a cell-based technology with theoretically no limit on bandwidth capacity.

It supports T1 (1.544Mbps), E1, T3, and E3, commonly used in WANs; 25Mbps and OC-3 for LAN Desktop environments; and OC-12 and OC-48, used for most backbone connections. Based on a 53 Byte Cell structure, ATM technology combines the advantages of frame- and channelized-based transmission, so ATM can be used effectively at any bandwidth and supports Multimedia Traffic. ATM uses LAN Emulation (LANE) to connect to existing Ethernet and Token ring, and MPOA (Multi-Protocol Over ATM) will be adopted for layer 3 switching.

In summary, ATM was designed to support end-to-end Multimedia Traffic across LAN and WAN networks, and will be standardized as the infrastructure for many enterprise and carrier backbones.

Conclusion

Gigabit Ethernet and ATM have similarities and differences in many respects, and they can be seen as complementary rather than competing technologies. Both Gigabit Ethernet and ATM operate at High Speed with the aim of eliminating or reducing backbone congestion, the bottleneck of the network. In addition, ATM using LANE can run over existing Ethernet, just like Gigabit Ethernet.

There are two major differences between Gigabit Ethernet and ATM in terms of Applications. Gigabit Ethernet, which supports 1Gbps, does not yet support priority or Qos (quality of service). However, Gigabit Ethernet is excellent at accommodating existing Ethernet or Fast Ethernet data traffic, and if applications running on 100Mbps or 1Gbps networks can be used without setting Qos parameters, there is nothing to discuss. Conversely, if a network administrator wants to use time-sensitive Voice or Video Applications, the network must be carefully designed to support them regardless of traffic load. ATM was designed from the start to support multimedia traffic. It is in practice the best technology for supporting time-sensitive data, Voice, and Video, and in terms of scalability, ATM users can increase speed simply by replacing the interface module. The Term of VLAN use is the Forum standards LANE 1.0 and LANE 2.0, which provide ELAN compatibility between Vendors.

In conclusion, ATM has advantages in Qos and congestion control for multimedia transmission, but has the disadvantage of being more expensive than Gigabit Ethernet while offering similar speeds.

Ultimately, Gigabit Ethernet and ATM are not competing technologies but technologies that make up for each other's weaknesses, and the choice of technology should focus more on the applications being designed for.

MGMT

If you look at a server-grade PC with several Ethernet ports, you can see one labeled MGMT.

An Ethernet port labeled "MGMT" stands for "Management". Ethernet ports are generally used to exchange data between network equipment and devices, but some equipment has an MGMT port for additional management functions.

This MGMT port is used for configuring, monitoring, diagnosing, and remotely managing the equipment, separate from the regular data flow. Network administrators and system administrators can remotely manage and configure equipment through this MGMT port, and can also perform diagnostics when problems occur.

Typically, such MGMT ports are assigned a specific IP address and port number so they can be accessed remotely, and security features such as encryption or access control may also be provided to protect the equipment. This allows the equipment to be managed and maintained effectively from a remote location.

Ethernet Physical Layer Standards

10BASE-T, 100BASE-TX, 1000BASE-T: Various physical layer technologies defined in the Ethernet standard. They support transmission speeds of 10Mbps, 100Mbps, and 1Gbps respectively, and use twisted pair cables.

Fiber Optic Ethernet (e.g., 1000BASE-LX, 10GBASE-SR): Ethernet standards that use fiber optic cables to support gigabit and 10-gigabit speeds.

See also

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