Ethernet technology refers to a packaged based network that is most suitable for LAN (local area network) Environments and includes LAN products of the IEEE 802.3ae. 10 Gigabit Ethernet standards which is an up gradation on all other earlier versions, works on an optical fibre and operates in full duplex mode (Held, 1996). The IEEE 802.3ae is an upgraded version of the IEEE 802.3 base version developed as early as 1980. Ethernet technology originated nearly 30 years ago as a least expensive high-speed LAN based option (Ferrero, 1996).
Ethernet defines the CSMA/CD protocol and is currently used in major LAN-based settings. Ethernet has the advantages of low implementation cost, simplicity and ease of installation and maintenance, reliability and compatibility with LAN based networks. Almost all Internet traffic generates and terminates with an Ethernet connection, which has been adapted for higher speeds and the volume of traffic over the Internet.
Ethernet technology is rapidly changing and the new 10 Gigabit technologies maintains certain older characteristics like package format and at the same time adapts itself to faster connections, higher speeds and more efficient handling of internet traffic. The newer versions of Ethernet like the Gigabit Ethernet and10 Gigabit technologies have wide-ranging applicability in LAN, WAN,MAN and SWAN (Axel son, 2003).
We will discuss these points in greater detail in the dissertation beginning our discussion with a brief description of Ethernet technology, its history, modes of operations, Gigabit architecture and applications and the rise of the 10 Gigabit technology in Ethernet applications. In our final analysis we will analyse the uses of Gigabit technology and the advantages involved. We would also discuss the market demands as far as setting up the new technology in business and enterprises is concerned and conclude with a final short summary giving the prospects of Ethernet and Gigabit Ethernet in this information savvy New Age.
Ethernet tends to connect computers using hardware that could be used on different linking machines and workstations. It differs from the Internet because the Internet connects remotely located computers with telephone or cable line or a software system. Ethernet uses software but connects in LAN on the basis of hardware and the Ethernet patent is referred to as the Multipoint data communication system with collision detection. Ethernet was the first technology that could connect through LAN hundreds of computers located in the same region or building(Spurgeon, 2000).
Ethernet technology can be used on optical fibre and twisted cables and it operates on a half-duplex and in recent versions, full duplex mode. There are three major varieties of Ethernet and these are Gigabit Ethernet, 10Base T Ethernet and Fast Ethernet that supports data transfer rate of 100mbps. Ethernet uses a star or bus topology and supports a data transfer rate of 10 mbps. The CSMA/CD protocols aroused to handle simultaneous demands and workloads. The newest Gigabit version supports a transfer rate of 1000 megabits per second and thus has a speed of a 1000mbps. Ethernet is the most widely used LA standards.
Ethernet specifications are used in IEEE 802.3 standard software and specify physical software layers within the system. Ethernet is used in nearly 90% of LAN workstations and LAN-connected PCs in the world (Lee and Lee 2002). Although Ethernet is the most popular physical layer of LAN technology that is in use, the other common LAN types include the Token ring, Fibre Distributed Data Interface (FDDI), Local Talk, Asynchronous Transfer Mode or ATM, Fast Ethernet, a more advanced variety of Ethernet and Gigabit technology. Ethernet helps in giving a high-speed connection along with the ease and convenience of installation and maintenance.
Ethernet applications and installation are comparatively inexpensive and it has wide applicability and compatibility with LAN and other widely used networks but LAN is the most popular compatible networking. Ethernet inacceptable in the computer market and supports all popular network protocols making Ethernet the ideal networking technology for all computers used at present. The Ethernet standard is set at IEEE 802.3,deriving its name from the Institute of Electrical and Electronic Engineers (IEEE), which defines this, standard. An adherence to the standards can ensure the efficient communication and links between the networking equipment’s and the networking protocols. The IEEE standard802.3 defines the rules for configuring an Ethernet network and also specifies how the elements in an Ethernet network can actually interact with each other.
Brief History about Ethernet:
Ethernet originated nearly 30 years ago when Xerox corporation used an experimental coaxial cable network with an original transfer rate of just 3 mbps using a CSMA/CD (carrier sense multiple access/collision detect protocol that could be used in then existing LAN and that could support some heavy traffic. This experimentation and development of the first Ethernet technology received some attention and around 1976-1980,DEC (Digital Equipment Corporation) and Intel joined Xerox Corporation to develop a LAN architecture that supported a data rate of 10 mbps.
This was the Ethernet version 1.0 specification and the original version of IEEE 802.3 was also based on this initial Ethernet version specification. The draft of IEEE 802.3 version received its approval in1983 and was specified as an official standard by the IEEE in 1985.Ethernet and IEEE 802.3 and all versions of these are ultimately compatible, derived from and improved versions of this basic version of original Ethernet technology.
A number of supplemental versions and technologically upgraded and advanced versions have been used to support higher data transfer rates. Thus Ethernet technology saw gradual development with a gradual LAN technology development in the1970s to the formation of IEEE subcommittee and approval of Ethernet version IEEE 802.3 later declared as standard in the 1980s. This was upgraded further with the development of Fast Ethernet and an associated speed of 100 mbps in 1995 with the final 1000 mbps Gigabit standards approved in the middle of June 1998.
A general description of what is Ethernet and how it works can be given as Ethernet seems to be based on the idea of a group of people within the same location and on the same network sending messages through a radio system and using a common wire or channel and this has been referred to as ether, a supposed medium that 19th century physicists believed helped in the propagation of light.
Each member in the system seems to have a 48-bit key MAC address assigned to the network-interface card and this makes sure that all systems within the Ethernet network have their own distinct addresses. As Ethernet is found and available and compatible nearly everywhere with wide ranging applicability, manufacturers tend to build the functionality of an Ethernet card directly into PC motherboards, which are printed circuit boards used in personal computers, also known as main boards.
In the initial stages of its development and discovery, Ethernet used shared coaxial cable, which was found in the building attached to every connected machine brought within the system. All computers in a building were connected to an attachment unit interface (AUI)transceiver and this in turn connected to another cable. A simple passive wire was used for small Ethernets and was considered not quite applicable to large extended networks as any damage to the wire could actually make the Ethernet segment dysfunctional.
Within the Ethernet technology, the systems are run in such a way that all communications between PCs, happen along the same wire, and information transmitted bygone computer is received by all computers in the network even if the information was meant to go only to one computer or specific destination. The interface card of the network filters out all information that is not originally addressed to the entire network and the CPU is interrupted when applicable packets are received.
This information sharing by all computers is considered one of the weaker points of the shared medium of Ethernet since any node within the entire network connected by the Ethernet can dig out information that seems to have been originally meant for a single location. Thus all traffic within the single wire used for the technology, can be intercepted and manipulated. A single cable thus has its ups and downs because not only is there an information security risk with such networking, the bandwidth is also shared so after a power failure or are start, traffic can crawl to a point that it can cause a slowing down of information transmission and data transfer due to too much crowding within a single wire.
The computers with an Ethernet connection networking share the channel using the CSMA/CD technology that stands for Carrier Sense Multiple Access with Collision Detection. The CSMA was first developed and used for ALOHA net in Hawaii and is comparable to token Ring and master controlled networks we have discussed here. An algorithm is generally followed when the computers transmits data and there can be several commands from start, transmitting, end transmission, wire busy, to wire idle and transmission stopped or maximum transmission attempts exceeded.
In this way, a medium, the Ethernet is chosen through computers try to transmit information. When there is too much traffic, there is an apparent cessation of these attempts, which renews again after a random period of time. This aid in avoiding collision and an exponential increase of back-off times are used when there is more than one failed attempt of transmission.
Depending on the type of medium used Ethernet segments can have restricted size. A 10BASE5 coax cable can only have a maximum length of500 metres. An Ethernet repeater can be used to have a bigger length cable and this device uses the signal from one Ethernet cable and repeats it into another cable. This way Ethernet repeaters can be used to connect up to five different segments with a maximum three of these devices used as attached devices. Since many segments are connected, cable breakages can be handled more efficiently. Thus when any one of the Ethernet segments breaks off, most of the devices are unable to communicate as connections are broken, however Ethernet repeaters allow the workings of different segments separately which can continue to work despite the cable breakage in one part of the network (Quinn,1997).
Ethernet segments can usually be terminated with a resistor at both its ends within the network and as for the equipment’s used, each end of the coaxial cable must have 50 ohm resistor and head sink and this is called the terminator affixed to an N or BNC connector. When resistors are not used, it is usually perceived as a cable breakage and consequences will be such that the alternating current signal transmitted will be reflected and as a reflected signal is indistinguishable from a collision, similar results as in collision will take place with complete cut-off of all communication between the units. When Ethernet repeaters are used electrically different segments can continue to function even in isolation as separate units and this helps in regenerating and retiming the signals (Field, et al 2002).
Most repeaters have an auto-partition function and this means they are capable of removing and isolating a segment from service when there are too many collisions, breakages, and traffic or when the collisions last too long. This is done to prevent the other segments from getting affected by such collisions or breakages and once there is a renewal of activities that are smooth and without collisions, the Ethernet repeaters reconnect the unattached segment to the original network.
The advantages of using cables in the star Ethernet system has been used effectively by net workers who create Ethernet repeaters with multiple ports known as Ethernet hubs or fan outs that could be connected to other hubs or coax backbones. The earlier hubs were also known as multiport transceivers and DEC’s DELNI is one such example of an Ethernet fan out. Multiport transceivers allow the sharing of single transceiver by multiple hosts having AUI connections. This also allows the working of a standalone single Ethernet segment that does not essentially require a coax cable.
Companies such as the DEC and Synoptic sold many multiport transceivers that could connect many10BASE-2 thin coaxial segments. However, coaxial Ethernet segments have been made obsolete by the development of unshielded twisted pair cables(UTP), which began with Starling and continued with 10BASE-T. The new developed of the unshielded twisted pair variety allowed Cat-3/ Cat-5cables and RJ45 telephone connectors to connect the fan outs to the ends. This further helped to replace the coaxial and AUI cables. Unshielded twisted pair Ethernet takes the termination problem into consideration and every segment is taken separately so that the termination could be built as a hardware component without requiring special and separate external resistor.
However despite the development of the star topology, Ethernet networks use a half-duplex transmission access method and also use the CSMA/With minimal cooperation from the hub that deals with packet collisions. Every packet transmitted is sent to every port and node of the hub so what really remains are bandwidth and security problems due to this open information sharing, so to speak. Since the chance of collisions is proportional to the number of transmitters and the data that have to be transmitted, implying that the larger the amount of data sent, the higher are the chances of packet collisions.
Modes of Operation:
The Ethernet network elements have interconnecting media and network nodes which basically falls into two major classes known as the Data terminal equipment (DTE) which are the PCs, workstations, servers, and are usually the destination or source of data frames often referred toast end stations; the other category of network node is the Data communication equipment (DCE) that are the standalone intermediate devices such as the repeaters, interface cards, modems, switchers or routers (Hancock, 1988). The DCEs are intermediate network devices that receive and forward data frames across the entire network.
The traditional Ethernet and IEEE 802.3 variety works in a half-duplex mode. For the other mode of operation as in Full-duplex CSMA/CD is not used. Auto-negotiation is another mode of operation for the Ethernet.
Half-Duplex Mode of Transmission/ CSMA/CD Access Method:
The Half-Duplex mode of transmission was developed in the original version of IEEE 802.3 Ethernet application and the CSMA/CD is considered as a means by which two or more stations could share common media in an environment that is switch less and does not require arbitration, or assigned time slots to indicate when workstations are ready to transmit information. This means that individual Ethernet Macias capable of determining when it can send a frame.
The CSMA/CD access rules are given in the full form of the CSMA/Protocol as it involves Carrier sense multiple access and Collision Detect. Carrier sense implies that each station continuously keeps alert for traffic on the medium to determine when gaps between frame transmissions are seen. ‘Multiple access’ refers to stations that may begin transmission any time they detect that there is no traffic and the network is relatively quiet.
Collision detect acronym implies that when there are two or more stations in the CSMA/CD network and if they begin transmitting data at the same instance the streams of bits from each of the workstations will collide with each other and both the transmissions which collide will then become unreadable (Halaby and McPherson, 2000). Each transmitting station should be able to determine and detect that a collision has taken place before the station has finished sending its frame. Each transmitting station then must stop transmitting any further data as soon as a collision is detected and then this workstation must show a state of abeyance in its activity for random length of time determined by a back-off algorithm before attempting to retransmit the frame all over again.
In certain situations when two distant stations on the network need to send a frame and the second station does not even begin transmitting until just before frame of the first station arrives. In that case, the collision is detected immediately by the second station yet the first station does not detect it until the corrupted frame signal goes all the way to the station. The time required to detect a collision can reach a twice the time required for the signal propagation between two distant stations on the network situated at farthest points (Quinn,1997).
This suggests that the maximum collision diameter and minimum frame length are directly related to the slot time and longer minimum frame lengths translate to longer slot times and larger collision diameters where the shorter the minimum frame lengths are they correspond to shorter slot times and smaller collision diameters.
There was growing understanding and need to reduce the impact of collision recovery and the need for network diameters to be large enough to accommodate networks, which are large, sized. The general consensus was to choose the maximum network diameter of around 2500metres, and to set the minimum frame length to ensure that all potentially damaging collisions are reported quickly.
This system worked for 10mbps speed of Ethernet but for higher transfer rate Ethernet connections and developers such as the Fast Ethernet, backward compatibility with earlier Ethernet networks were necessary and this involved the inclusion of the existing IEEE 802.3 frame format and error detection procedures as also all the networking software and applications which could run on the 10mbps networks (Quinn, 1997). For all transmission rates, the time required to transmit a frame is inversely related the transmission rate and at 100 mbps, a minimum length frame could be transmitted at one tenth of the defined and original slot time and so any collision that might occur at this time would go undetected. The maximum network diameters used and specified for 10 mbps could not be used for 1000mbps networks.
Fast Ethernet networks and connections help in reducing the maximum network diameter by more than 200 meters. This problem is also seen in the Gigabit Ethernet, as there is a decrease in network diameters by a factor of 10to more than 20 meters for 1000 mbps operations. This is however potential hindrance although as a solution the same maximum collision domain diameters were used to increase the minimum frame size adding an extension field to frames shorter than the minimum lengths.
The full-duplex mode allows the simultaneous two way transmission of data along the same or one link. The full-Duplex mode is an MA capability that allows the two-way transmission of information over point-to-point links. This Full-duplex transmission is functionally much simpler than half duplex transmissions as no collisions, media contentions, schedule retransmissions and extension bits on short frames ends are involved.
Since there is a reduction is the procedural complications, more time is available for transmission and there is also a doubling of link bandwidth and each width is capable of supporting full-rate, simultaneous two way transmission of data frames and each transmission begins as soon as frames are ready to send. The main restriction is inter-frame gap between two successive frames that has to be of a minimum specified length. Usually all frames conform tithe Ethernet standard frame formats.
Apart from the broad varieties of Ethernet types that transmit data at10mbps (Ethernet), 100mbps (Fast Ethernet) and 1000 mbps (Gigabit Ethernet), 10 Gigabit Ethernet and the earlier varieties such as Starling, there can be variations in the Ethernet frame types as well. We give a brief description of Ethernet types below.
The earliest and first varieties of Ethernet was the Xerox Ethernet which was the original 3m bit per second Ethernet implementation and had versions 1 and 2(Hall, 2003).The framing format version 2 is stilling use.
The other earlier Ethernet application 10BROAD36 is now no longer used although it was one of the earlier standards supporting Ethernet overlong ranges. The broadband modulation techniques are similar as founding cable modems and systems operated on coaxial cables.
Starling or 1BASE5 as the first Ethernet implementation on twisted paired wiring and operated at 1mbps speed. This was gradually replaced by the other versions.
Among the more recent versions of the 10 mbps Ethernet is the 10BASE5that uses thick net coaxial cables also called thick wire or yellow cable is the original implementation of the 10mbps Ethernet. Transceivers could be connected using a vampire tap and connecting the core and the screen with N connectors. There is a cable that could be used to connect the transceiver to the AUI or Attachment unit Interface.
This type of Ethernet can have 5 network segments with 4repeaters, with three of the segments that could be connected to the network. The bus topology is used here and the maximum segment lengths 500 meters with the overall length at 2500 metres. The minimum length between nodes is stipulated at 2.5 metres with the maximum number of nodes per segment at 100. This system is obsolete as of now.
10BASE2 uses the thin net coaxial cable, also called the Thin wire or Cheaper net, a BNC connector and bus topology with a terminator at the end of each cable. The cable specified for its purposes is RG-58 A/U orRG-58C/U with a 50 ohms resistance. the 5-4-3 rule is applicable here meaning like the 10BASE5 Ethernet there are 5 network segments, 4repeaters and 3 of these could be connected to computers.
185-200metres is the maximum length for each segment and each machine uses at-adaptor to connect with a BNC connector. Although signal quality is considerably reduced with each barrel connector, barrel connectors could be added to link the smaller cable pieces in the network. Length between nodes is given at a minimum of 0.5 meters. This is one of the more widely used Ethernet applications.
The Starling which was the first Ethernet twisted wire implementation later evolved into 10BASETwhich comprises of 4 wires and two twisted pairs with a Cat-3 or Cat-5 cable of up to 100 meters in length. At the middle of the connection is a hub or switch, which has a port for each node. The 10BASET uses star topology and as we mentioned 2 pairs of unshielded twisted wires.
This category of the Ethernet is not subject to the 5-4-3 rule and can use 3, 4 or 5 cables with the best performance given by category 5 cable. The maximum segment length here is 100 meters. Maximum number of connected segments can be nearly thousand. The minimum length between nodes is 2.5 meters. Whereas only1 node can be present in every segment using the star topology, this system uses RJ-45 connectors.
10BASEF is the generic name for 10 Ambits/s Ethernet standards using fibre optic cable extending up to 2 mms in length. The number of network nodes can be 1024 with a maximum segment length of 200 meters. Specialized connectors for fibre optic cables are used here. This has three main varieties: the 10BASEFL is an updated and more advanced version of the FOIRL standard. FOIRL is the Fibre-optic inter-repeater link and the original standard for Ethernet on fibre optic. This Ethernet type is used to connect computers in a LAN setting a task not done mainly due to the incurring costs.
This is the most widely used of the 10BASEF Ethernet type. The 10BASEFB that has never been used serves as a backbone between hubs. The 10BASEFP is a star network that does not require a repeater for its connections connect a number of computers with hubs and switches and gets cable distances up to 500metres.
The 100BASET is also known as the Fast Ethernet and is a generic term for any of the three standard varieties if Ethernet that transfers data at 100mbits/s over twisted cables up to 100 meters long. These three varieties include 100-BASETX, 100BASE-T4 and 100-BASET2. Fast Ethernet uses RJ-45 connectors and star topology. The CSMA/CD media access issued here. The minimum length between nodes is specified at 2.5 meters. With 1024 maximum number of connected segments possible, the IEEE802.3specification is used.
The 100BASETX is a star shaped configuration similar to 10BASE T and uses two pairs of wires and Cat-5 cable to achieve the 100mbit/s speed. 100BaseTX requires category 5 two pair cables and the maximum distance of these is given at 100 meters. The100BaseT4 requires a category 3 cable with 4 pair and maximum distance of these cables is 100 meters. This system uses a Cat-3 cabling and uses all four pairs in the cable limited to half-duplex access methods. As now the popular Ethernet cabling is the cat-5 cabling, his is now considered obsolete.
The final variety 100BASEFX is a 100mbit/Ethernet type that uses a multimode fibre. The maximum length specified here is 400 metres for half-duplex connections and 2 mms for full duplex connections to ensure that all collisions are detected.100BASEFX can thus use fibre optic to transmit up to 2000 meters and for this purpose it requires two strands of fibre optic cable.
100VG LAN is also another Ethernet variety that uses star topology, a series of interlinked hubs and RJ-45 connectors. In addition to Ethernet packets this implementation also supports the Token ring packets and has an IEEE 802.12 specification. It requires 4 pairs of category 3 cable wires and the maximum distance covered is 100 metres(Held, 1996). However with a category 5 cable 150 metres could be reached. Additionally the fibre optic can be used to transmit data up to 2000 metres.
We next turn to Gigabit Ethernet Technology, which being a new and improved version of Ethernet altogether requires a separate section.
Gigabit Ethernet Technology:
Also known in its abbreviated form Gibe, the Gigabit Ethernet technology describes the implementation of Ethernet networking and transmitting ate speed of one or more than one Gigabit per second. Gigabit Ethernet is supported with the use of optical fibre and twisted pair cables and the physical layer standards in this category includes 1000BASET. 1 Gaps issued over a category 5 cable with copper cabling and 1000BASE SX issued to attain for short to medium distances over fibre.
The first Gigabit Ethernet standard was set at the IEEE 802.3 standard in 1998.Its relatively recent launch suggests that the Gigabit Ethernet is the latest version of the Ethernet, which is the most popular and widely used computing network worldwide (Katsambis, 1998). The Gigabit speed of1000 mbps of raw bandwidth is 100 times faster than the original Ethernet version of 10mbps and its greatest advantages lies in the fact that it is compatible with existing Ethernets and uses the existingCSMA/CD and MAC protocols.
Gigabit Ethernet competes directly with ATMas far as market competition is concerned. It is deployed in high capacity backbone network links and for small installations Gigabitspeed is not yet necessary. Gigabit Ethernet has been used in desktop technology in apple computers, Power MacG5, Apple’s power notebook and is also being built into Pentium boards. One of its desktop features includes professional video editing. Gigabit Ethernet has been outsmarted by the 10gigabit Ethernet technology, which is the fastest Ethernet standard that became fully operational in 2002.
Introduction to Gigabit Ethernet
Our discussion on Gigabit Ethernet began by providing a brief description of the Gigabit technologies and the main characteristic of this upgraded Ethernet variety. The transceiver used for Gigabit Ethernet is the GBIC also known as the Gigabit Interface Converter. Thebe measures 8.5 mm by 13.4 mm and has a depth of about 50mm. A hot swap standard electrical interface of a one Gigabit Ethernet port can support any physical media including copper to 100 km of single mode fibre.
The standard Gigabit Ethernet system operates at 1000 Mbps speed of transfer of information (Norris, 2002). The 802.3z is the standard that describes the specifications for fibre optics for the 1000BASE-XGigabit Ethernet system. The 802.3ab standard describes specifications for the category 1000BASE-T twisted pair Gigabit Ethernet system. This rate the major two varieties of Gigabit Ethernet technologies used. The10 Gigabit Ethernet is a further up gradation and has speeds reaching10000 Mbps.
According to Frazier, the chair of the Gigabit Task Force developing the Gigabit Ethernet technology has been challenging and hard work mainly because this new technology aimed at developing a standard that scales the operation of Ethernet networks to 1000 Mbps while retaining the known characteristics that are compatible with Ethernet and that have made Ethernet the dominant-local area network (LAN) technology.
The Draft D3.1 of the P802.3z was approved in a letter ballot of thieve 802.3 working group and this was only possible when an approval rate of 75% was obtained from the working group. The protocol layers in802.3 standards are the areas that have been developed and modified in802.3z version (Riley and Braver, 1998). The 100BASE SX and 1000BASE Fibre optic transceiver specifications have already been highlighted here.
The 1000BASE-SX specifications for short wavelength laser transceivers uses 62.5 micron fibre and supports multimode fibre optic links of up to 260 meters. The 50 micron fibre can be used to support multimode fibre optic links of up to 550 metres. The 1000BASE Supports installations at longer distances and uses higher cost components with 62.5 micron fibre used for 440 meters and 50 micron fibre on 550 meters.
On a single mode fibre, up to 3 mms of fibre optic links are possible. One of the latest technologies 1000BASE-CX that supports copper cabling links of 25 metres, is included in the 802.3zspecification for transceiver technology.
Frasier goes on to describe that the Gigabit Ethernet encompasses the new full-duplex Media Access Control (MAC) and the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) MAC. The full duplex operation takes advantage of the contention free access and flexible topologies and the 802.3z used the CSMA/CD MAC to work at an extended range of 1000Mbps.
This was done with the aid of a technique known as ‘carrier extension’ which was added to the CSMA/CD to overcome certain limitations of the algorithm that was based on the rule that the roundtrip messaging time between two workstations could not be higher than that required to transmit the smallest frame. To improve the throughput of Gigabit CSMA/CD LANs, frame bursting was introduced as an optional feature.
In the early stages of deployment of the Gigabit Ethernet it is mainly being used to interconnect high performance switches, routers and servers in LAN backbones. The full duplex operating mode is suited for this type for application environment and is favoured over the CSMA/Chalk duplex mode. This also ensures that high performance desktop computers can take advantage of high peak bandwidths of repeating hubs that are cost effective. Frasier’s claim also points to the fact that gigabit technology may be more compatible with full duplex rather than half-duplex modes of Ethernet operation. The 10 Gigabit Ethernet is full-duplex technology and the half-duplex access mode cannot be used for its purposes.