How many pairs uses gigabit ethernet

Gigabit Ethernet / 1GBase-T / 1000Base-T / IEEE 802.3z / IEEE 802.3ab

Gigabit Ethernet belongs to a family of network technologies that are mainly used in local networks. Gigabit Ethernet is also suitable for connecting large networks. Gigabit Ethernet was first developed and specified for fiber optic cables and later also for twisted pair cables. Both variants allow data to be transferred at 1,000 Mbit / s or 1 Gbit / s. This is an increase by a factor of 10 compared to Fast Ethernet with 100 Mbit / s.

Fast Ethernet has long been considered "the" standard for local networking. But if you think that Fast Ethernet with 100 Mbit / s is completely sufficient, you are wrong. When data is stored in the network, the 100 Mbit network is a bottleneck. 1 GBit / s is a must if you want to integrate servers and storage devices into a network and have many network participants access them.
Many different applications (e.g. Internet, multimedia, electronic document exchange) cause a high network load. It is therefore necessary to use the central network stations, such as B. to connect routers, servers and switches with more bandwidth than is necessary for most hosts.

IEEE 802.3z / Gigabit Ethernet on fiber optics and twinax cables

  • 1000Base-SX: glass fiber with a wavelength of 850 nm (singlemode or multimode glass fiber)
  • 1000Base-LX: glass fiber with a wavelength of 1300 nm (singlemode or multimode glass fiber)
  • 1000Base-CX: Twinax cable up to a maximum of 25 meters (interim solution)

IEEE 802.3ab / Gigabit Ethernet over twisted pair cable

1000Base-T is an extension of IEEE 802.3z. On the physical layer of the OSI layer model, the standard describes how and in what form data is transmitted on the cable. All other functions of Ethernet, including the access method, are defined on the MAC layer.
Gigabit Ethernet is backwards compatible to 100 Mbit / s and 10 Mbit / s. In addition, Gigabit Ethernet supports Auto-MDI / X. This means that gigabit ports automatically detect an uplink connection. Gigabit switches therefore no longer have an uplink port. Cross-over patch cables are no longer necessary.

Cabling plays an important role in the network area. In addition to the coupling elements, it is the most expensive and complex part of the entire installation. One is reluctant to exchange network cabling. Especially when it is not urgently needed. A new transmission system can be introduced more easily in this area if the entire cabling does not have to be replaced immediately. The advantage is that when Gigabit Ethernet is introduced, the existing structured cabling (twisted pair cable) can be used. Provided that the cables are specified for this.
1000Base-T was designed from the start so that it can be used with RJ45 connectors. In contrast to Fast Ethernet, Gigabit Ethernet needs all four pairs of wires in a cable.

In principle, Gigabit Ethernet is designed for use with CAT5 cables. But CAT5 is not just CAT5. 1000Base-T places high demands on the cable installation. 1000Base-T fails on CAT5 in individual cases. If the requirements of 1000Base-T have not yet been taken into account during the acceptance measurement of the cabling, then you can only determine whether a CAT5 cabling is suitable for Gigabit Ethernet by performing a subsequent measurement.
For short distances of up to 10 meters, normal CAT5 cables can be used in any case. From 10 meters it should be at least CAT5e in order to be able to establish a stable and interference-free connection. Otherwise it can happen that the gigabit connections fall back to Fast Ethernet with 100 Mbit / s.

Transmission technology from 1000Base-T

CAT5 cables were originally only designed for a transmission frequency of up to 100 MHz. Before the Gigabit Ethernet era, this corresponded to a transmission speed of 100 Mbit / s with conventional technology. A transmission speed of over 1 Gbit / s on twisted pair cables is therefore only possible with sophisticated tricks. Especially when you want to cover the usual distances of up to 100 meters.

From the beginning, the development goal of 1000Base-T was to limit the transmission frequency. First of all, the usual 8B / 10B coding was dispensed with, which reduced the bit rate from 1,250 Mbit / s (gross) to 1,000 Mbit / s (net). In addition, the transmission technology uses all four wire pairs of the twisted pair cable. This technology was already used with VG-AnyLAN and 100Base-T4 (Fast Ethernet via TP cable of category 3). The usual Ethernet standards, such as 10Base-T and 100Base-T, only use two wire pairs. Only 250 Mbit / s or 250 MHz is transmitted per wire pair. In order to be able to reduce the transmission frequency even further, a five-level coding of PAM5 is used. Instead of the usual two (0 and 1) or three (-1, 0, +1) logic states, five (-1V, -0.5V, 0V, + 0.5V, + 1V) logic states are transmitted.
The PAM5 coding reduces the speed per pair of wires to 125 Mbit / s (at 100 MHz). This corresponds to the gross transmission rate of Fast Ethernet.
So that the full duplex mode is possible, echo cancelation (echo compensation) is used to be able to separate the received signal from the transmitted signal that is sent on the same wire pair.

Overview: Ethernet technology

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