With the Ethernet network development, there are kinds of cables that have been used for the data transmission. In this post, we are going to talk about some widely used cables.
Coaxial
Beyond many people's expectations, coaxial was widely used in the Ethernet network. Coaxial cable consists inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric (insulating material). The coaxial cable is used to carry high-frequency electrical signals with low losses.
Figure 1: Coaxial wire structure
In the early Ethernet, the standard 10Base-5, 10Base-2, and 10Broad-36 were designed to normalize the Ethernet over the coaxial cable. In the latest IEEE 802.3z, the full-duplex Ethernet over coaxial cable and fiber realize the 1000Mbps transmission.
In the current live network, the coaxial cable is almost eliminated by the twisted pair and optical fiber.
Twisted pair (TP)
Twisted pair, the most widely used cable in Ethernet network, includes two types, the unshielded twisted pair (UTP) and the shielded twisted pair (STP). STP also includes two types, STP and FTP (foil twisted pair)
Figure 2: Twisted pairs
The shield layer can reduce radiation, prevent information from being eavesdropped on, and can also prevent the entry of external electromagnetic interference. So, compared with the UTP, STP, including the FTP, could transfer a higher bandwidth.
According to the rate of the twisted pair, the twisted pairs are marked with CAT. For example, in the LAN network, CAT5 and CAT5e are widely used. Though both CAT5 and CAT5e cables are used in 1Gbps Ethernet network, CAT5e has a better SNR than CAT5, which helps CAT5e provide a better service than CAT5. CAT5e even provides up to 2.5G of bandwidth in short distances
The table below lists the specifications of CAT5e, CAT6, CAT6A, CAT7, and the latest CAT8.
Table 1: Specifications for CAT5e, CAT6, CAT6A, CAT7, and CAT8
Though the bandwidth of twisted pairs is increasing as technology develops, there is still a serious problem, the transmission distance. Almost all the twisted pairs are not recommended to use in the situation that transmission distance is over 100 meters. In addition, the twisted pairs cost too much in long-distance transmission, because the twisted pair uses copper to transfer the electric signal. That comes to the latest cable material, optical fiber.
Optical fiber
In the 1840s, Daniel Colladon, a Swiss physicist, and Jacques Babinet, a French physicist, demonstrate that light by refraction in Paris makes fiber optics possible. That demonstration shows the light path could be bent in the same shape as the transmission medium.
In 1960, Kapany proposed the term fiber optics in the article Scientific American. That introduced this topic to a wide audience.
It is 1965, Charles K. Kao and George A. Hockham promote the idea that the attenuation in optical fibers could be reduced below 20dB/km. And until 1977, The Italian research center CSELT worked with Corning to develop practical optical fiber cables, resulting in the first metropolitan fiber optic cable being deployed in Turin.
Fiber usually consists of four parts, fiber core, cladding, coating, and jacket.
Figure 3: Optical fiber structure
Fiber core: high refractive index glass core, it is used to transmit the optical signal.
Cladding: a transparent material that packs the fiber core, the refractive index of the cladding is lower than the core so that the optical could total internal reflection in the fiber core.
Coating: a protective layer that is used to strengthen the mechanical behavior of optical fiber.
Jacket: plastic protective shield.
Based on the number of optical modes, optical could be divided into single-mode fiber (SMF) and multi-mode fiber (MMF).
The so-called "mode" refers to an optical signal entering the optical fiber at a certain angular velocity.
Multi-mode fiber allows multiple beams of light to propagate in the fiber at the same time, thereby forming mode dispersion (because each "mode" light enters the fiber at a different angle, their time to reach the other end is also different. This feature is called mode dispersion.), Mode dispersion limits the bandwidth and distance of multi-mode fiber. Therefore, the fiber core of the multi-mode fiber is thick, the transmission speed is low, the distance is short, and the overall transmission performance is poor, but its cost is relatively low. It is generally used in buildings or geographical areas.
Single-mode fiber can only allow one beam of light to propagate, so single-mode fiber has no mode dispersion characteristics. Therefore, the core of the single-mode fiber is correspondingly thin, transmission frequency bandwidth, large capacity, and long transmission distance. Correspondingly, the cost of single-mode fiber is higher.
Figure 4: SMF and MMF
Unlike the twisted pair that have the same RJ45 interface, optical fiber has dozens of form factors, such as SFP, SFP28, QSFP+, QSFP28, and so on. Besides the form factor, the connector type is also variant, LC, SC, MPO24, and so on.
As the mainstay of high-capacity communications, optical fiber is widely used in the data center, and submarine cable communication.
Figure 5: Submarine cable map
Due to the characteristics of the SMF and MMF, the SMF is usually used in long-distance transmissions, such as submarine cable, while the MMF servers are in the datacenters between the servers and network equipment.
That's all for this brief introduction. If you have any further questions, please comment below.
Thank you!
