A brief history of broadband Internet technology

In today's digital age, broadband has become a necessity for each of us and every family. Without it, we would be restless and restless.

So, do you know the technical principles behind broadband? From the earliest 56k "cat" dial-up to the current Gigabit cities and Gigabit homes, what kind of changes has our broadband technology experienced? In today’s article, let’s take a closer look at the “Broadband Story”.

█ xDSL and ISDN

Have you seen the following interface? I believe that many friends born in the 70s and 80s must have seen it and are very familiar with it. Yes, this is the interface for "dial-up Internet access" when we first came into contact with the Internet. That was more than 20 years ago, when Xiao Zaojun was still in college. In order to access the Internet, I need to buy a modem card (Modem, commonly known as "cat") and plug it into the computer. Then plug the only phone line in the dormitory into the "cat". Only after the settings are completed can you start dialing. After a "heartbreaking" creaking sound, it showed that the dial-up was successful, that is, it was connected to the Internet. What is the speed of dial-up Internet access? 5KB/s... (It is claimed to be 56K dial-up, but the actual rate is 45Kbps. When actually used, it is often 1~2KB/s...) Yes, you read that right, it’s that slow . At the beginning, our entire dormitory relied on this "trickle" to connect us to the school system to select courses. Please feel for yourself how you felt at that time...With this primitive method, once you dial up to access the Internet, the phone cannot be connected and is in a "busy" state. Moreover, the cost of dial-up Internet access is also very expensive. Just like making a phone call, it is charged by the minute (about 3 cents a minute). The speed is inherently slow, but watching the money flow away can drive you to death. If you feel that the Internet speed in the dormitory is slow, you can also choose to go to the Internet cafe. The earliest Internet cafes also had dial-up Internet access. Later, some Internet cafes began to upgrade. On the door of these Internet cafes, there are often a few big words written - "ISDN dedicated line, high-speed surfing". ISDN is the Integrated Services Digital Network. It is still a technology developed based on the existing telephone network (PSTN, Public Switched Telephone Network), which can realize the transmission of multiple signals such as voice, data and video on the same line. The cost of ISDN is relatively high, and the network speed is not much faster. At that time, China Telecom provided a narrowband ISDN standard with a rate of only 128Kbps, which was a little more than 2 times faster than dial-up. A few years later, the situation finally changed. The telecommunications master brought a device to the door and said that as long as this device is used, the Internet speed will "skyrocket." After asking around, I found out that this device is called ADSL Modem. Plug the phone line into the ADSL modem, and then use the network cable to connect the ADSL modem and the computer to dial-up the Internet. After adopting ADSL, the network speed has indeed been significantly improved, from 56Kbps to 1Mbps. Later, it became 2Mbps again. This speed increase has brought about a huge improvement in experience - accessing web pages and so on is very smooth. Chatting on QQ is faster. Downloading software, movies and TV series has also become feasible (previously, 56K was simply unthinkable). As a college student majoring in communications engineering, Xiao Zaojun didn’t know at the time that the full name of ADSL is Asymmetric Digital Subscriber Line, which is a type of DSL technology. DSL technology was invented by Bell Communications Research Institute in the United States in 1989. When ADSL technology first appeared, I was very curious: it was still a telephone line, not a twisted pair of network cables, so why did the speed suddenly increase? It turns out that in the early days (56K), we only occupied the low-frequency part of the copper wire (the part below 4KHz) and did not fully utilize its full potential. ADSL technology uses frequency division multiplexing to divide ordinary telephone lines into three relatively independent channels: telephone, uplink and downlink, which not only avoids interference, but also increases the speed. Note: Specifically, ADSL uses DMT (Discrete Multi-Tone) technology to divide the original telephone line 4KHz to 1.1MHz frequency band into 256 sub-bands with a bandwidth of 4.3125KHz. Among them, the frequency band below 4KHz is still used to transmit POTS (traditional telephone service), the frequency band from 20KHz to 138KHz is used to transmit uplink signals, and the frequency band from 138KHz to 1.1MHZ is used to transmit downlink signals. Compared with the original method, ADSL not only has a significantly higher speed, but also has a significantly lower price. When surfing the Internet, there is no need to "race against time" anymore. Moreover, surfing the Internet and making phone calls no longer conflict and can be done at the same time. Later, on the basis of ADSL, ADSL2 and ADSL2 were upgraded, and the rate could reach 20Mbps for a time. Later, there were a series of technologies such as VDSL and VDSL2. These technologies are often collectively referred to as xDSL technologies. Until now, xDSL technology is still used in some places abroad. Based on G.Fast evolved from VDSL2, the maximum theoretical speed can reach 1Gbps. We mentioned earlier that some domestic Internet cafes use ISDN technology. In fact, the life cycle of this ISDN technology is relatively short. ADSL technology has developed before it has been developed. At that time, some Internet cafes upgraded to ADSL, and some changed to other dedicated lines, such as DDN (Digital Data Network, Digital Data Network), but that is a story later. In addition to ADSL, there are also radio and television broadband (cable access) and other Internet access methods around us. Radio and Television Broadband, I believe everyone who has used it will be impressed . In fact, it is a way to provide broadband access through the coaxial cable of cable television (CATV).

█ EPON and GPON

ADSL brings a significant improvement in the network experience. While we were immersed in this improvement, a new and more awesome technology came to us. This technology is, of course, fiber optic broadband. ADSL and ISDN are both based on metal cables and copper media. In the 1960s, the British-Chinese scientist Kao Kun published a paper proposing the theoretical basis for using optical fibers (optical fibers) for data communications. Not long after, the American company Corning actually pulled out the world's first optical fiber with attenuation that met the requirements, and this magical invention was introduced to the world. In the 1970s and 1980s, optical fiber technology developed rapidly. In addition to using optical fiber for backbone networks, communication manufacturers have also begun research on using optical fiber for access networks to replace copper cables. So, there was the idea of ​​optical fiber access network. The optical fiber access network is a typical P2MP (point-to-multipoint) architecture. In fact, to put it bluntly, it is a tree structure that continuously splits light to achieve optical connections for a large number of users. The early optical communication technology was relatively weak (PDH/SDH stage), and the optical fiber transmission signal had a large attenuation. Therefore, all active optical networks (Active Optical Network, AON) are developed, which require the introduction of external energy (power supply) to strengthen (relay) the light. The equipment is more complex and the cost is higher. Later, the technology gradually matured, light could be transmitted farther, and Passive Optical Network (PON) began to appear. Passive optical network is divided into OLT, ODN, ONT/ONU. OLT (Optical Line Terminal) is the office-side equipment, and ONT/ONU (Optical Network Unit/Terminal) is the user-side equipment (such as optical modem). ODN is an optical distribution network (Optical Distribution Network), which can be understood as the trunk of PON. The passivity of PON mainly refers to this part of passivity, which will greatly reduce construction and maintenance costs. In the early stages of PON (the late 1980s), manufacturers basically introduced narrowband PON technology. The speed of this technology is very low, no more than 2Mbps. Moreover, because manufacturers are working on their own, there has been no unified norms and standards. In 1995, seven network operators including BELLSOUTH, BT, and France Telecom jointly initiated the establishment of the Full Service Access Network Alliance (FSAN), hoping to propose a unified optical access network equipment standard. Soon after, in 1997, based on the recommendations of FSAN, ITU-T (Telecommunications Standards Bureau of the International Telecommunications Union) launched the APON technology system, which is the G.983.1 standard. APON is ATM PON. ATM is not an automatic teller machine, it is the abbreviation of Asynchronous Transfer Mode. The essence of ATM is a transmission protocol. The older generation of communicators must be familiar with ATM. It was once a competitor of the IP protocol and was once very popular. In 2001, FSAN and ITU-T upgraded and revised the APON specification, and changed the name to BPON (Broadband PON, broadband passive optical network). The reason for changing the name was that they did not want APON to be misunderstood as only providing ATM services. In order to further improve the rate standard of PON, in 2002, FSAN launched a new work to standardize PON networks above 1Gbps. In March 2003, based on FSAN's recommendations, ITU-T promulgated the G.984 standard, which is GPON (Gigabit-capable PON, Gigabit Passive Optical Network). While FSAN and ITU-T were working in full swing, another standardization organization was not idle and began to tinker with PON technology. It is the equally famous IEEE (Institute of Electrical and Electronics Engineers). IEEE is the developer and backer of Ethernet standards. After the IEEE released the Gigabit Ethernet standard in 1998, it was thinking about developing a PON standard based on Ethernet. In 2000, IEEE established the EFM working group and officially launched related standardization work. The full name of the EFM working group is interesting, called Ethernet for the First Mile, and it belongs to the IEEE 802.3 group that develops Ethernet standards. In April 2004, the EFM working group was completed and officially launched the IEEE 802.3ah standard, which is EPON (Ethernet PON, PON based on Ethernet Ethernet). Later, as time passed, ATM gradually lost ground in the competition with IP. APON (BPON) has also been abandoned by operators due to cost, efficiency and other reasons, and has withdrawn from the stage of history. Therefore, I won’t introduce much about APON (BPON), and you don’t need to know too much about it. Anyway, everyone remembers that the mainstream industry at that time was EPON and GPON. They are different technical systems launched by different standards organizations. There is no upgrading, evolution or substitution relationship between the two, and they can be regarded as parallel developments. There is a lot of information online about the specific technical differences between the two, so you can study it separately. In short, EPON and GPON each have their own advantages and disadvantages. Simply put, GPON has larger bandwidth, can carry more users, and is more efficient, but it is also more complex to implement, so the cost is higher. Judging from the domestic market share, EPON was widely adopted by China Telecom at that time, while GPON was more popular with China Unicom and China Mobile. Overseas, most countries and regions use GPON except Japan and a few countries that use EPON. If you have any impressions, around 2010, telecommunications technicians began to come to your home to replace equipment and no longer used telephone lines to access the Internet. Instead, it is a network cable connected to the weak current box. The inner core of the network cable is often separated. There are 8 wire cores, 2 of which are connected to the RJ11 port to connect to the phone; the other 6 wires are connected to the computer to access the Internet. At that time, Wi-Fi wireless routers gradually began to appear, and network cables could be connected to the wireless routers, allowing more desktop computers and laptops to access the Internet. After the emergence of smart phones around 2008, mobile phones can also access the Internet through Wi-Fi. Our internet access has taken another leap forward. With the emergence of 3G/4G at that time, the prosperous mobile Internet era officially began. The network cable connected to the weak current box mentioned just now basically belongs to FTTB (Fiber to the Building) or FTTC (Fiber to the Curb) technology. Taking FTTB as an example, the optical fiber from the operator is connected to the ONU in the weak power room of the building, and then converted into LAN and connected to the user's home. During that period, there was another characteristic of the times: After the third round of restructuring of domestic telecom operators in 2008, China Mobile acquired China Tietong and began to build on Tietong’s foundation. , vigorously enter the home broadband market. Later, China Unicom also joined the fray. This directly led to fierce competition in the home broadband market, and broadband costs began to drop significantly. Within a few years, FTTB began to become FTTH. It is no longer the network cable that enters the home, but the optical fiber. We have an optical modem. The optical fiber is plugged into the optical modem (ONT). The network is exclusive, and the speed becomes faster and more stable.

█ 10G PON and 10G EPON

EPON and GPON are both PONs at the 1Gbps level. Note that this 1Gbps is not the rate on the user side. EPON and GPON can only provide users with a rate of 100Mbps. Obviously, with the development of the times, this rate cannot meet the needs of home and enterprise users. As a result, PON began to evolve to the 10Gbps level. In 2006, IEEE began to establish a project to formulate a 10Gbit/s rate EPON system standard, which was later IEEE 802.3av, 10G-EPON. In this standard, 10G EPON is divided into 2 types: one is asymmetric mode, that is, the downlink rate is 10Gbps, and the uplink rate is 1Gbps; the other is symmetric mode, that is, the uplink and downlink rates are both 10Gbps. ITU-T’s GPON is also evolving. In 2008, the ITU launched research on the next generation GPON standard. In 2010, the XG-PON standard was born, which is the ITU-T G.987 series. At the beginning, there were two modes of XG-PON. One was the asymmetric mode XG-PON1, with a downlink rate of 10Gbps and an uplink rate of 2.5Gbps; the other was a symmetric mode XG-PON2, with both uplink and downlink rates. to 10Gbps. Later, around 2013, it was recommended to cancel the XG-PON2 symmetry solution because it was difficult to implement. XG-PON1 was directly renamed to XG-PON. Later, in 2015, the symmetric scheme was restarted and adopted a new name, called XGS-PON (S stands for symmetric, symmetric). In 2017, ITU officially adopted the G.9807 XGS-PON international standard. Now, the industry will collectively refer to XG-PON and XGS-PON as XG (S)-PON. XG (S)-PON and 10G-EPON are both 10Gbps level. On the user side, the rate achieved is 1Gbps, or gigabit. The Gigabit cities and Gigabit homes that many places in China have been promoting in recent years are mainly based on these two technologies. Everyone should have noticed that starting from 2018, the broadband at our homes has gradually increased from 100M to 200M, 500M, and 1000M. Telecommunications technicians will contact you every three days and come to your door to replace equipment "for free". Operators also often hold activities, offering various 199 yuan and 299 yuan packages to upgrade home broadband. But in fact, most users may feel that there is no experience in upgrading the so-called broadband network package starting from 100M. difference. This is actually not surprising. The bandwidth of 100-200M is really enough for us to play games, follow TV series, and watch high-definition videos. Unless there are many family members or enthusiasts, there is no rigid demand for high Internet speed. In contrast, the quality experience of Wi-Fi is a bottleneck. It often happens that even with 100M broadband at home, the mobile phone still "turns in circles". Based on this, the solution proposed by the operator is "whole house gigabit", which is FTTR, fiber optic entering the room. Pull fiber optics to every room and then use Wi-Fi to improve the experience. Xiao Zaojun personally believes that FTTR is indeed a good choice for large households and high-end users. . However, for most households, FTTR seems a bit “ahead of its time.” FTTR is also divided into FTTR-H and FTTR-B. The former is oriented to families, and the latter is oriented to enterprise (shopping malls, parks, hospitals, schools, etc.) scenarios. From this perspective, the market is very broad. Okay, so far, this is basically our current broadband situation. So, has our broadband technology reached its peak? Next, will we have more powerful technology? Please see the next issue - the grand debut of 50G PON! This article comes from the WeChat public account: Xian Zao Classroom (ID: xzclasscom), author: Xiao Zaojun

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