Ethernet

Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility.

Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.

[6] It was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation[7][8] and was originally called the Alto Aloha Network.

The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the luminiferous aether once postulated to exist as an "omnipresent, completely passive medium for the propagation of electromagnetic waves.

"[4][9][10] In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, and Butler Lampson as inventors.

[4][16] He convinced Digital Equipment Corporation (DEC), Intel, and Xerox to work together to promote Ethernet as a standard.

This so-called DIX standard (Digital Intel Xerox)[18] specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field.

3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, and that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers.

This process was greatly sped up with the introduction of 10BASE-T and its relatively small modular connector, at which point Ethernet ports appeared even on low-end motherboards.

[26] In February 1980, the Institute of Electrical and Electronics Engineers (IEEE) started project 802 to standardize local area networks (LAN).

[16] Delays in the standards process put at risk the market introduction of the Xerox Star workstation and 3Com's Ethernet LAN products.

With such business implications in mind, David Liddle (General Manager, Xerox Office Systems) and Metcalfe (3Com) strongly supported a proposal of Fritz Röscheisen (Siemens Private Networks) for an alliance in the emerging office communication market, including Siemens' support for the international standardization of Ethernet (April 10, 1981).

[29] Ethernet has evolved to include higher bandwidth, improved medium access control methods, and different physical media.

The multidrop coaxial cable was replaced with physical point-to-point links connected by Ethernet repeaters or switches.

[34] Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium.

The method used was similar to those used in radio systems,[e] with the common cable providing the communication channel likened to the Luminiferous aether in 19th-century physics, and it was from this reference that the name Ethernet was derived.

In the worst case, where multiple active hosts connected with maximum allowed cable length attempt to transmit many short frames, excessive collisions can reduce throughput dramatically.

However, a Xerox report in 1980 studied performance of an existing Ethernet installation under both normal and artificially generated heavy load.

This report was controversial, as modeling showed that collision-based networks theoretically became unstable under loads as low as 37% of nominal capacity.

In full duplex, switch and station can send and receive simultaneously, and therefore modern Ethernets are completely collision-free.

[citation needed] Despite the physical star topology and the presence of separate transmit and receive channels in the twisted pair and fiber media, repeater-based Ethernet networks still use half-duplex and CSMA/CD, with only minimal activity by the repeater, primarily generation of the jam signal in dealing with packet collisions.

Bridges also overcome the limits on total segments between two hosts and allow the mixing of speeds, both of which are critical to the incremental deployment of faster Ethernet variants.

[43] In modern network equipment, this process is typically done using application-specific integrated circuits allowing packets to be forwarded at wire speed.

Advanced networking features also ensure port security, provide protection features such as MAC lockdown[47] and broadcast radiation filtering, use VLANs to keep different classes of users separate while using the same physical infrastructure, employ multilayer switching to route between different classes, and use link aggregation to add bandwidth to overloaded links and to provide some redundancy.

[51][52][53] Fiber optic variants of Ethernet (that commonly use SFP modules) are also very popular in larger networks, offering high performance, better electrical isolation and longer distance (tens of kilometers with some versions).

Packet is used to describe the overall transmission unit and includes the preamble, start frame delimiter (SFD) and carrier extension (if present).

[55]: sections 3.1.1 and 3.2  Notably, Ethernet packets have no time-to-live field, leading to possible problems in the presence of a switching loop.

Autonegotiation is the procedure by which two connected devices choose common transmission parameters, e.g. speed and duplex mode.

The solution is to allow physical loops, but create a loop-free logical topology using the SPB protocol or the older STP on the network switches.

[citation needed] A node that is sending longer than the maximum transmission window for an Ethernet packet is considered to be jabbering.