Shulou(Shulou.com)11/24 Report--

Nowadays, both the fixed network (broadband) used at home and the mobile network (mobile phone) that can be used at home and outdoors have become an indispensable part of daily life as well as water, electricity and gas.

Watching TV dramas, playing games, online shopping, long-distance online classes, video conferencing and so on, while enjoying the convenience of life brought by the network, have you ever thought about how we get these services anytime and anywhere?

All this should start with the access network which is closest to us and accessible to us.

What is access network? to put it simply, it is a network composed of all communication devices from user terminals (such as mobile phones, computers, tablets, network television, etc.) to the metropolitan area network of operators.

The transmission distance of the access network generally ranges from a few hundred meters to a few kilometers, so it is often vividly called "the last kilometer".

Through this "last kilometer" service, our mobile phones, computers and other terminals can access the metro backbone network of operators until they are connected to the Internet.

There are many classification methods of access network. At present, the most widely used access network is divided into wired access network and wireless access network according to the access mode.

According to the different cables used, the wired access network is mainly divided into three categories:

Copper access uses xDSL (x Digital Subscriber Line,x Digital subscriber Line) technology, which used to be the kind of dial-up Internet access using telephone lines.

Fiber coaxial hybrid access is a flexible mix of optical fiber and coaxial cable technology, which is used in cable television at home.

Optical fiber access, using all-optical fiber access PON (Passive Optical Network, passive optical network) technology, is the mainstream technology of cable access network. FTTH (Fiber to the Home) allows everyone to enjoy the convenience brought by ultra-high network speed.

According to the mobility of access terminals, wireless access networks are mainly divided into two categories:

Fixed wireless access serves fixed-location users or small-scale mobile users. The main technologies include Bluetooth, Wi-Fi, WiMAX and so on.

Mobile wireless access serves a large number of users who use mobile terminals (such as mobile phones). The main technologies are cellular mobile technology 4G, 5G and so on.

Let's take the optical fiber access PON network technology and wireless access 5G mobile technology which are closest to everyone's life as an example, let's understand what kind of network wired access network and wireless access network are.

PON network technology since the advent of the Internet service, people's efforts to pursue network speed have never stopped.

From the early telephone line dial-up to today's FTTH optical fiber home, the technology is improving and the network is constantly increasing speed.

FTTH, which is often referred to as fiber-to-the-home, refers to the installation of optical fiber directly into the user's home, bringing users enough bandwidth to meet various network needs, such as voice, high-definition video, large-scale games and so on.

The convenience of FTTH benefits from the development of PON network technology, so what does PON network look like?

What is connected behind each household's optical fiber broadband is the PON network. Let's go back to the source along the optical fiber and take a look at what the PON network is made of.

The PON network connects up to the networks of various service providers (such as Internet, IPTV, telephone / video services, etc.) through the metropolitan area network, and downwards connects users' home telephones, IPTV televisions, computers and other terminals and provides network services.

From the distance from the user, the PON network is mainly composed of three parts.

ONU (Optical Network Unit, Optical Network Unit): closest to the user, ONU devices are generally installed and deployed directly to the user's home. There are two common types: SFU (Single family Unit, single home subscriber unit) and HGU (Home Gateway Unit, home gateway unit). One end of the ONU is connected to the splitter through optical fiber, and the other end is connected to the home terminal device by wired or wireless means.

A little knowledge

SFU (can be understood as light cat) generally needs to be used with HGW (Home Gateway, home gateway, can be understood as home router). HGU is more powerful, integrating the functions of optical cats and routers.

ODN (Optical Distribution Network, Optical Distribution Network): ONU and OLT are provided with "transmission channels" through optical fibers and splitters, which can divide one optical signal into multiple channels in a certain proportion.

OLT (Optical Line Terminal, Optical Line Terminal): farthest from the user, OLT equipment is the core equipment of PON, which is generally installed and deployed in the operator's computer room to collect user data and send it to the metropolitan area network for transmission.

What is mentioned above is the composition of PON network, but it is PON network technology that plays a decisive role in network speed in practical application. In the process of continuous evolution for many years, technologies such as EPON, GPON, 10G-EPON and XG (S)-PON have come into being.

Students who are interested in the relationships and differences between these technologies can click on the extended reading at the end of the article to continue to understand.

5G mobile access technology in the mobile communication network, the wireless access network is the nearest link to us, connecting users and business core network. The base station (iron tower) that can be seen everywhere is the symbol of the wireless access network.

When we call or surf the Internet through the mobile phone, the base station will access the signal of the mobile phone, and the signal will be transmitted to the core network through the carrier network, and then the signal will be processed by the core network and transmitted to the network application on the destination city or the Internet.

The core of the wireless access network is the base station. The traditional base station is composed of BBU (Base Band Unit, baseband unit, mainly responsible for baseband signal modulation), RRU (Remote Radio Unit, remote radio frequency module, mainly responsible for RF processing) and antenna (responsible for transmitting or receiving electromagnetic waves). Although the structure of wireless access network is constantly upgrading in the 2G ~ 4G era, the function allocation of these three modules is basically unchanged.

In the 4G era, wireless access network provides users with unprecedented user experience (such as short video, distance education, etc.), but with the emergence of 5G services such as self-driving, Internet of things, ultra-high-definition video, wireless access network requires higher spectrum, larger bandwidth and lower delay.

In the 5G era, wireless access network needs a brand-new change from architecture to technology. Compared with the 4G era, 5G wireless access network has undergone two subversive upgrades:

The baseband unit (BBU) is reconstructed into CU and DU

In order to deal with the multi-application scenarios under the 5G network slice, the BBU function is reconstructed into CU and DU. CU (Centralized Unit) is the central unit, which is responsible for handling high-level protocols and non-real-time services, and can control and coordinate multiple cells within the access network; DU (Distributed Unit) is a distributed access point, which is responsible for handling physical layer protocols and real-time services.

At the same time, the functions of RRU and antenna are merged in AAU.

This method of splitting functions reduces the burden of network transmission on the one hand, and makes the network deployment more flexible on the other hand.

Develop in the direction of virtualization

In the era of 2G~4G, one BBU can complete the communication processing of multiple antenna ranges, while 5G uses higher frequency band for communication, and more base stations are needed to cover the same size area, so it is not practical to solve the problem simply by increasing the number of CU and DU.

5G wireless access network solves this problem with the help of virtualization technology. Virtualization technology realizes the ability to run multiple different operating systems on the same physical server. For the access network, the hardware equipment that used to be dedicated to CU is more expensive. After virtualization, running software with CU function on the virtual machine can realize the function of the original CU.

5G wireless access network can aggregate a large number of underlying resources through virtualization technology, and these resources will be dynamically and real-time allocated according to business needs, user distribution and other actual conditions.

In the future, not only the wireless access network will evolve towards virtualization, the entire 5G mobile network will virtualize multiple virtual networks, realize the sharing and isolation of resources, and make the end-to-end network slice into reality. Provide operators with lower-cost solutions.

In summary, the future development trend of access network, whether wired access or wireless access, are constantly moving forward with the needs of users for larger bandwidth.

In fact, in the future, the network will also provide services for users based on services, rather than access methods, users will not care about wireless access or wired access, and the core network providing services will also be gradually clouded and unified. Service convergence will accelerate network convergence, and the existing independent access networks, such as fixed access, mobile bearer, government-enterprise access, will become the focus of network convergence.

As the last kilometer of user access, the optical access network (PON network) also plays an important role in the fixed-mobile convergence in the 5G era. Based on the unified ODN network, the flexible application of WDM-PON, 10GPON, Combo PON and other technologies according to different application scenarios (wired and wireless) can not only provide fixed broadband access, but also realize the forward service of 5G base stations. The unified optical access network can adopt unified construction and unified management, which greatly saves the investment cost of the network and improves the utilization rate of the network.

In the 5G era, based on the ubiquitous ODN optical fiber resources, and combined with the evolving PON technology and SDN&NFV technology, the integrated access of wired and wireless services can be realized. Resource sharing can also simplify business deployment and operation and maintenance, which will bring better network services for users.

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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