Evolution of the Wired Access Network Standard

Based on cost-effective twisted pairs and the need for power over Ethernet (PoE), the wired access layer on a traditional campus network typically uses copper media for transmission. Legacy category 5 enhanced (CAT5e) twisted pairs can directly support 2.5GE, or even 5GE, transmission without re-cabling. Therefore, copper is still used for transmission on the wired access layer on an intent-driven campus network.

Twisted pairs are the most commonly used copper transmission cables on campus networks, formed by winding two thin copper wires wrapped with insulation materials in a certain proportion. Twisted pairs are classified into two types: unshielded twisted pairs (UTPs) and shielded twisted pairs (STPs).

STPs are wrapped with a layer of metal, which reduces leakage of radiation and prevent interception of data. In addition, STPs support a high transmission rate of data but are high cost and require complex installation. UTPs, however, are wrapped with only a layer of insulation tape without metal shielding material.

Compared with STPs, UTPs are lower in cost and support more flexible networking. In most cases, UTPs are preferentially used, except in some special scenarios (for example, scenarios where interference from electromagnetic radiation is strong or the requirement for transmission quality is high). Table 4.1 lists the frequency bandwidth, transmission rate, and typical application scenarios of common twisted pairs.

The evolution of the transmission rate at the access layer of a campus network complies with the evolution of Ethernet standards defined by the IEEE 802.3 Working Group, including physical layer connections,

TABLE 4.1 Frequency Bandwidth, Transmission Rate, and Typical Application Scenarios of Common Twisted Pairs

TABLE 4.2 Data Transmission Rates Defined in Different IEEE 802.3 Ethernet Standards

electrical signals, and MAC layer protocols. Table 4.2 shows the evolution phases of Ethernet standards in chronological order.

1. Standard Ethernet (IEEE 802.3)

Formulated in 1983, IEEE 802.3 is the first formal Ethernet standard, which defines a method for LAN access using carrier sense multiple access with collision detection (CSMA/CD) technology, with a maximum data rate of 10 Mbit/s. This early Ethernet is called standard Ethernet that enables connections through various types of transmission media, such as thick coaxial cables, thin coaxial cables, UTPs, STPs, and optical fibers.

2. Fast Ethernet (IEEE 802.3u)

Fast Ethernet was introduced in 1995 as the IEEE 802.3u standard that raised the maximum data rate to 100 Mbit/s. Compared with the IEEE 802.3 standard, IEEE 802.3u provides a higher network bandwidth for desktop users and servers (or server clusters). IEEE 802.3u signifies that LANs are embracing the Fast Ethernet era.

3. Gigabit Ethernet (IEEE 802.3ab)

The IEEE 802.3ab standard came into use in 1999. It supports a maximum data rate of 1 Gbit/s, 10 times the rate of Fast Ethernet. On this Ethernet, data can be transmitted through optical fibers, twisted pairs, and twinax cables. IEEE 802.3ab signifies the beginning of the Gigabit Ethernet era.

4. 10GE (IEEE 802.3ae)

The IEEE 802.3ae standard was ratified in 2002, defining 10GE with a maximum data rate of 10 Gbit/s. Data can be transmitted through optical fibers, twisted pairs, and coaxial cables. IEEE

• 802.3ae signifies the beginning of the 10 Gbit/s Ethernet era and lays a foundation for end-to-end Ethernet transmission.
• 5. Multi-GE (IEEE 802.3bz)

Initially released in 2016, the IEEE 802.3bz standard comes with 2.5GBASE-T and 5GBASE-T, which reach transmission rates of 2.5 and 5 Gbit/s, respectively, at a distance of 100 m. Physical layer (PHY) transmission technology of IEEE 802.3bz is based on 10GBASE-T but operates at a lower signal rate. Specifically, IEEE 802.3bz reduces the transmission rate to 25% or 50% that of 10GBASE-T, to achieve a rate of 2.5 Gbit/s (2.5GBASE-T) or 5 Gbit/s (5GBASE-T). This lowers the requirements on cabling, enabling 2.5GBASE-T and 5GBASE-T to be deployed over 100 m long unshielded CAT5e and CAT6 cables, respectively.

The IEEE 802.3bz standard is intended to support the improvement in air interface forwarding performance of wireless APs.

In January 2014, the IEEE 802.11ac standard was officially released. It uses signals on the 5 GHz frequency band for communication and provides a theoretical transmission rate of higher than 1 Gbit/s for multistation WLAN communication. With IEEE 802.11ac, an uplink rate of 1 Gbit/s on the backbone network can hardly meet the requirements of next-generation APs, as it is impossible to carry 10 Gbit/s traffic over CAT5e cables that have been routed alongside existing network devices. The 10GE can provide the rate required by APs, but the need for re-cabling using CAT6 or higher-specifications cables or optical fibers to implement this rate results in high costs and complex construction.

Against this backdrop, there is an immediate solution. Specifically, an Ethernet standard that supports intermediate speeds between 1 and 10 Gbit/s while eliminating the need for re-cabling is gaining wide recognition from users and network vendors. This technology is also known in the industry as multi-GE technology.

Two technology alliances have been established in the world to promote the development of 2.5GE and 5GE technologies on enterprise networks. In October 2014, the NBASE-T Alliance was jointly founded by Aquantia, Cisco, Freescale Semiconductor, and Xilinx, with its members now including most network hardware manufacturers. In December 2014, the MGBASE-T Alliance was founded by Broadcom, Aruba, Avaya, Brocade, and Ruijie Networks. Finally, the multi-GE technology promoted by the NBASE-T Alliance became a standard supported by IEEE.

Currently, campus networks use a wired access transmission rate of 1 or 2.5 Gbit/s; however, with the popularity of Wi-Fi 6, the uplink transmission rate of APs needs to reach 5 Gbit/s, or even 10 Gbit/s. Therefore, during network construction or capacity expansion, it is recommended that twisted pairs of CAT6 or higher specifications be used for the wired access network, as these cables deliver a transmission rate of 10 Gbit/s, protecting customer investment.