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SDN system method | 9 Access network

2022-06-25 17:47:00 【yuff100】

With the explosive growth of Internet and data center traffic ,SDN It has gradually replaced the static route switching equipment as the mainstream way to build the network , This series is a free ebook 《Software-Defined Networks: A Systems Approach》 The Chinese version of , A complete introduction to SDN The concept of 、 principle 、 Architecture and implementation . original text : Software-Defined Networks: A Systems Approach^[1]

The first 9 Chapter Access network

Now we turn our attention to SDN The latest use cases : Access network , Including fiber home and mobile cellular networks . Although it is still in its early stage ( Just launched product deployment ), But there is a huge opportunity . This chapter describes two examples : Passive optical network (PON, Passive Optical Networks) and Wireless access network (RAN, Radio Access Networks) , They are the core of optical fiber home and mobile cellular networks .

9.1 background

It is used to realize the family 、 The network technology that enterprises and mobile devices connect to the last mile of the Internet has a history of development independent of other parts of the Internet . This development has been going on for decades , It started with the support of circuit based voice communication , And then gradually increased on the basis of IP Data communication support . The end result is a baroque collection of specialized equipment , For those who know how to L2/L3 For those who build networks on a collection of Ethernet switches , These devices look very strange .

But this makes the access network SDN Fertile soil , To understand what this means , We need to start with a brief overview of the legacy systems that will be replaced . We will introduce two specific access technologies (PON/RAN) Start in the context of . Fortunately, , Look down from the top , Their architecture is strikingly similar . Of course , The details vary greatly , But hide ( Even eliminate ) The unnecessary details are SDN One of the main values .

Before we discuss the details , Need a little more background knowledge . Providing broadband services ISP( Such as telecom companies or cable TV companies ) It usually operates the national backbone network , Connected to the periphery of the backbone are hundreds of edge sites . In the field of Telecommunications , These edge sites are often referred to as Central machine room (Central Offices) , In the field of wired communication , Usually called Head end (Head Ends) . Although these names imply " Centralization " and " The root of the hierarchy ", But they are all located in ISP The edge of the network , yes ISP The end of the last mile connecting customers . be based on PON and RAN Our access network is deployed in these facilities .

9.1.1 Passive optical network (Passive Optical Network)

PON It is a tree structure optical fiber network , from ISP A device at the edge site starts , It can be extended to 1024 A family .PON The name comes from passive shunt , These shunts turn the luminous signals upstream and downstream , Without the ability to actively store and forward frames . The end point completes the splicing of frames , Corresponding ISP The device is called Optical terminal (OLT, Optical Line Terminal) , Devices deployed in the home are called Optical network unit (ONU, Optical Network Unit) .

chart 51 It's a PON An example of , Reduced to just one ONU And a OLT. In actual deployment , A central computer room will have multiple OLT, Connect thousands of customer homes . chart 51 Another detail is highlighted , One connects the access network to Internet Of BNG(Broadband Network Gateway) .BNG It is a kind of equipment of telecommunication company , In addition to forwarding packets , Also authenticate users , Differentiate the level of service provided to each customer , And charge the traffic .

chart 51. Connect the central machine room OLT To families and businesses ONU Of PON Example .

Since the splitter is passive ,PON Multi access protocol is implemented . Simply speaking , Upstream and downstream services transmit on two different wavelengths of light , So it is completely independent . The downstream flow is from OLT Start , The signal follows PON Every link of the network propagates , Every frame can be reached ONU. then ONU View unique identifiers in frames , And receive the frame ( If the identifier is itself ) Or discard ( If not myself ). Prevent... By encryption ONU Eavesdropping on neighbors' communications . Upstream traffic is time-division multiplexed at upstream wavelength , Every ONU Periodically obtain the transmission period .

PON Similar to Ethernet , A sharing algorithm is defined , After years of development , The algorithm can adapt to higher and higher bandwidth . At present, the most widely deployed is G-PON(Gigabit-PON), Support 2.25 Gbps bandwidth .XGS-PON(10 Gigabit-PON) In deployment .

9.1.2 Wireless access network (Radio Access Network)

RAN The last hop is achieved by encoding and transmitting data on different bandwidths of the radio spectrum . for example , Traditional cellular technologies range from 700 MHz To 2400 MHz, Now in the 6 GHz A new if spectrum is allocated to the range , Millimeter wave (mmWave) The spectrum of technology is 24 GHz above .

Pictured 52 Shown , Given geographical area ( For example, the subway station ) A group of base stations in are connected to each other , And with the mobile core network running in the central computer room (Mobile Core) signal communication . The mobile core network is similar to BNG( In terms of high-level architecture ), Act as a connection to the access network Internet Of IP gateway , Also responsible for certification 、QoS And billing . And BNG Different , The mobile core network is also responsible for managing mobility ( for example , Record which active equipment the current BTS is serving , Manage handoff between base stations , wait ).

chart 52. Wireless access network (RAN), A group of cellular devices (User Equipment, UE) The mobile core network connected to the central machine room .

The figure shows the mobile core network and a group of retransmissions (backhaul) Network connected base station . The implementation of the backhaul network depends on the choice of technology , It can be based on Ethernet or on PON, But for our purposes , It's important to understand RAN In fact, it is a local packet switching network built on the backhaul network , The base station is the overlay Online " node ". Packets pass through this network " route " Arrive at the most appropriate base station , And at a given time for each mobile device ( User equipment or UE) Provide services ^[1]. The forwarding decision is realized by the base station , The base station is responsible for making the following decisions : Switch (handover, Switch the traffic of a given terminal from one base station to another )、 Load balancing (load balancing, A group of base stations decide which one should serve a terminal according to its current load ) and Link aggregation (link aggregation, Multiple base stations decide to jointly transmit data to a given terminal ).

[1] Reason why " route ", The reason is that based on the comprehensive consideration of mobile tracking and monitoring, it decides how to make the most effective use of the wireless spectrum , Instead of the shortest path standard commonly used in wired networks . It is important to , Base station cooperates to implement a distributed decision algorithm , Then forward packets to each other according to these decisions .

9.1.3 Key conclusions (Key Takeaways)

In discussing how to apply SDN Before principle , There are three conclusions about these two network technologies . First of all " Access network " and "IP gateway " The difference between . for example , Fiber optic home (Fiber-to-the-Home) By PON and BNG Combined realized , Again ,5G Cellular mobile network (5G Cellular Mobile Network) By RAN And mobile core network (Mobile Core) Combined realized . This chapter focuses on how to SDN Applied to the PON and RAN On , But as we are 7.4 Already seen in section ,SDN It can also be applied to BNG And mobile core network . Both are enhanced IP Router , Its new features are for those running in the switch fabric P4 Program extension . We will return to this topic in the last section , Introduce SD-Fabric And access network .

secondly , because PON It's passive , There is no opportunity for software control within the network . take SDN be applied to PON It involves the opposite end point ( namely OLT and ONU) Software control of , And think of everything between these endpoints as a passive backplane . Besides , because ONU It's a response OLT The directive " dumb " equipment , This actually boils down to decomposition OLT.

Last , because RAN A packet switching network that connects a group of base stations ( As a backhaul network overlay), Therefore, there is an opportunity to realize software control . This requires the decomposition of the base station , As we will see later in this chapter , The base station has historically run a multi-layer protocol stack , Once decomposed , These components will be distributed throughout the network , Some components are put together with the radio antenna , Some components are connected with the mobile core network of the central computer room (Mobile Core) Put together . let me put it another way , The final plan is " Division " and " distribution "RAN function .

For a broader understanding of decomposition 5G What is involved in mobile networks , In order to realize , The following supporting books are recommended .

Extended reading :
L. Peterson and O. Sunay. 5G Mobile Networks: A Systems Approach^[2]. June 2020.

9.2 SD-PON

take SDN be applied to PON The opportunity lies in ,OLT Is essentially enhanced L2 Switch , Equipped with different... Running on each switch port MAC Layer frame protocol . It's like you can buy something based on OCP Standard bare metal L2 Like a switch , Now you can also buy OLT. But in the actual implementation of the software definition PON(SD-PON) Before , There are still three problems to be solved ^[2].

[2] In order to be consistent with the naming of other use cases in this book , Let's call this SD-PON, But actually ONF Open source software projects are called SEBA: SDN-Enabled Broadband Access.

First , In order to know what level of service the network should support ,PON A large number of configurations need to be loaded into each OLT in . secondly , Deployed to the home ONU The capacity of the equipment is limited , Upstream of the connection is required OLT Indirect control . Last , Network operators may not only use bare metal hardware , Instead, it has to deal with a variety of traditional devices .

To solve these problems , Figure appears 53 Described in the SD-PON Architecture . The production network based on this architecture has been deployed by telecom companies all over the world . For the sake of simplicity , Only one... Is shown in the figure OLT, Connect to two fabric Switch . In practice , This architecture is useful for aggregation OLT It is necessary to , We will be in 9.4 Section explains the details , At present, you can think that these switches are in the 7 This chapter introduces SD-Fabric Under the control of . Next we will introduce SD-PON Other parts of the architecture .

The first is the hardware abstraction layer , be called VOLTHA( fictitious OLT Hardware abstraction , Virtual OLT Hardware Abstraction) Located on the network operating system ( for example ONOS) And single OLT Between .VOLTHA Provide northbound OpenFlow Interface , send ONOS Can be like any other SDN Control as equipment OLT, Vendor specific adapters are available in OpenFlow and OLT Between . In principle, , This conversion can be done in ONOS Internal processing ,ONOS There is already a robust southbound adapter framework , but VOLTHA Designed to be network operating system independent , So most of the mechanisms are copied .

VOLTHA Many details must be handled correctly , But there is nothing new in the concept , It mainly controls the state flow ( for example , Assign specific to subscribers QoS class ) And monitoring state flow ( for example , distinguish ONU When to connect or separate ). The main difference is the need to put Traffic Profile file ( In the figure, it is shown as TP) Load into OLT in . This configuration file specifies what the O & M personnel expect PON Supported by QoS class , Usually in OLT Load this configuration state at startup , In principle, , Also can be ONOS adopt gNMI/gNOI Conduct management .OLT Currently, such as gNMI This kind of universal API, So it is handled in this one-time way .

Last , And the most interesting thing is , because ONOS Need to know ONU, But not directly OpenFlow Or any other API Control , So the architecture is in OLT And its connected ONU An exchange abstraction layer is built on the collection , In the figure 53 Is represented by an outer gray box . We can think of this network model as a switch , Has a set of network oriented ports ( It is called in the communication industry NNI) And a set of user oriented ports ( It is called in the communication industry UNI).ONOS Think of this converged network as a logical switch , Whenever a user opens a home ONU when ,ONOS You will see the corresponding UNI There's one on "port active" event , And take corresponding actions , These operations are performed by SD-PON Control suite implementation .

So what needs to be done ？ The main task is to securely connect users to Internet. for example , When one ONU go online ( Corresponds to a port on the logical switch becoming active ) when , Will start 802.1X Authorization process , Verify the ONU Whether it is a registered customer . The result of successful authorization is ,SD-PON Program instructions ONOS adopt fabric( Use the specified QoS The configuration file ) Build a path , Connect users to L2 The Internet . Next , Connect to ONU Your home router will send a DHCP request , Trigger IP Address assignment , And trigger ONOS Establish a routing , Connect your home router upstream BNG( And the Internet ).

9.3 SD-RAN

About 5G The early publicity of is mainly about more bandwidth , but 5G Our commitment is mainly about accessing services from a single ( broadband connection ) Expand to a richer set of edge services and devices , Including support for immersive user interfaces ( Such as AR/VR)、 Mission critical applications ( Like public safety 、 Autopilot ) And the Internet of things (IoT). Only when SDN Principles apply to RAN when , These new applications are feasible , To support the rapid introduction of new features . Because of this , Mobile network operators are trying to implement software definition RAN(SD-RAN).

Extended reading :
SD-RAN Project^[3]. Open Networking Foundation. August 2020.

To understand SD-RAN The technical basis of , It's important to realize that , form RAN The base station is a dedicated packet switch . A group of base stations in a given geographical area coordinate with each other , To allocate and share scarce radio spectrum . They make switching decisions , Serve a given user together ( Think of this as link aggregation RAN variant ), The packet scheduling decision is made according to the continuously measured signal quality . Today these are purely local decisions , But turning it into a global optimization problem is SDN The specialty of .

SD-RAN The idea is to make each base station to SDN The central controller reports locally collected statistical data about radio transmission quality ,SDN The central controller combines information from a group of base stations , Build a global view of how the radio spectrum is used . A set of control procedures ( for example , One focuses on switching , One focuses on link aggregation , One focuses on load balancing , Another one focuses on frequency management ) Based on this information, a global optimal decision can be made , And push the control command back to each base station . These control instructions are not at the scheduling granularity of a single segment of transmission ( namely , There are still real-time schedulers on each base station , It's like SDN The Ethernet switch under control still has the same local packet scheduler ), But I can't get through 10 Millisecond measurement loop , It does exert near real-time control over the base station .

9.3.1 Separate type RAN(Split RAN)

To better understand how this works , Let's go from the picture 54 The fine-grained view of the base station packet processing pipeline shown begins . Please note that , This figure describes the base station as a pipeline ( Send from left to right to UE Data packets are processed ), But it can also be regarded as a protocol stack .

chart 54. RAN Processing line , It includes two components: user plane and control plane .

The key stages are as follows .

RRC( Wireless resource control , Radio Resource Control): Responsible for coarse-grained configuration and policy related aspects in the pipeline .RRC Running on the RAN On the control plane of , Do not process user plane messages .
PDCP( Packet data aggregation protocol , Packet Data Convergence Protocol): Responsible for IP The header is compressed and decompressed 、 Encryption and integrity protection , And make " In the early " Forward decision ( That is, whether the packets are sent to the terminal through the pipeline or forwarded to another base station ).
RLC( Wireless link control , Radio Link Control): Responsible for segmentation and reorganization , By implementing some form of ARQ( Automatic repeat request , automatic repeat request) Realize reliable transmission / receive .
MAC( Media access control , Media Access Control): Responsible for buffering 、 Multiplexing and demultiplexing , Including the real-time scheduling decision of when to transmit and which slices . Can also make " Delay " Forward decision ( That is, forward to include WiFi Alternative carrier frequencies including ).
PHY( The physical layer , Physical Layer): Responsible for coding and modulation , Including forward error correction (FEC).

chart 54 The last two stages of (D/A Conversion and RF front end ) Not within the scope of this book .

The next step is to understand how the functions outlined above are divided between physical components , So as to realize centralized and distributed deployment " Division ". The mainstream realization in history is " Undivided ", Pictured 54 The entire pipeline shown is running in a base station . Looking forward to the future ,3GPP The standard has been extended to allow multiple split points , chart 55 The split shown is being led by the operator O-RAN (Open RAN) The alliance actively promotes , This is also the method used in the rest of this chapter .

chart 55. Split-RAN The processing pipeline is divided into central units (CU), Distributed units (DU) And radio unit (RU).

The result is something like a graph 56 Shown RAN Configuration of scope , There is one running on the cloud Central unit (CU, Central Unit) Serve multiple Distributed units (DU, Distributed Unit) , Every DU It also serves many Radio unit (RU, Radio Unit) . The key is ,RRC( Focused on the CU in ) Only responsible for near real-time configuration and control decisions , and MAC The phase scheduler is responsible for all real-time scheduling decisions .

chart 56. Split-RAN framework , One CU Serve multiple DU, Every DU Serve multiple RU.

Because the scheduling decision of wireless transmission is made by MAC Layer in real time , Scheduling decisions cannot be made based on outdated channel information , therefore DU Need to be managed RU" near "( stay 1ms Within the time delay ), Common configurations are deployed on the same tower DU and RU. But be a RU Corresponding to a small sector , many RU It is distributed in a medium-sized geographical area ( for example , The mall 、 Campus or factory ), So one DU May serve more than one RU.5G The adoption of millimeter wave technology may make the latter more common .

9.3.2 RAN Intelligent controller (RAN Intelligent Controller)

RRC In the figure 54 As part of the base station , In the figure 55 Shown in CU Part of , representative RAN Control plane of . Because control decisions are made centrally , therefore CU The configuration of can be naturally mapped to SDN, But the goal is not just to recreate RRC A traditional collection of functions , It also wants to pave the way for the introduction of additional control functions . So ,SD-RAN It adopts a network operating system which is used in other fields / Control the parallel design of the application architecture ( And described in this book ).

The result is figure 57 The design shown , among RAN Intelligent controller (RIC, RAN Intelligent Controller) yes O-RAN The architecture document is called centralized SDN controller ( So we use this term in the following discussion )." Near real time " The qualifier indicates RIC yes CU Implemented in 10-100 Part of the millisecond control loop , Instead of running on DU Medium MAC Required by the scheduler 1 Millisecond control loop .

chart 57. RIC Centralized control separate type RAN Components in the hierarchy .

If you go further , chart 58 Show based on ONOS Of SD-RAN Example . The most remarkable thing is , be based on ONOS Of RIC Supports a set of specific RAN The north and South interfaces of , In principle, ( But not in detail ) Similar to the interface described in the previous chapter ( for example ,gNMI, gNOI, OpenFlow). We will discuss these interfaces in the next section .

chart 58. By adjusting and expanding ONOS Achieve compatibility O-RAN Of RIC.

be based on ONOS Of RIC Used the second 6 Topology services described in chapter , But two new services have also been introduced : Control and Telemetry. Based on the Atomix key / Based on value storage Control Service Manage the control status of all base stations and user equipment , Including which base station serves each user equipment , And a device that can be connected " Potential links " Set .Telemetry Service Based on the Time series database (TSDB, Time Series Database) On the basis of , track RAN Link quality information for component reports . Various control applications analyze this data , And then RAN How to best meet their data delivery goals and make informed decisions .

chart 58 Example in Control Apps (xApps) Contains a range of possibilities , But this is not an exhaustive list . These functions ( Link aggregation control 、 Interference management 、 Load balancing and switching control ) Currently, it is implemented by a single base station with only local visibility , But they have a global impact .SDN The solution is to collect available input data centrally , Make the global optimal decision , Then push the respective control parameters back to the base station for execution .

O-RAN union
since 3G since , Always by 3GPP (3rd Generation Partnership Project) Responsible for the standardization of mobile cellular networks ,O-RAN (Open-RAN Alliance) It is an alliance of mobile network operators , The definition is based on SDN Of 5G Implementing the strategy .
in consideration of 3GPP It is already the standardization organization responsible for global cellular network interoperability , Why would there be O-RAN union ？ The answer is , as time goes on ,3GPP Has become a supplier led organization .O-RAN It was founded by network operators (AT&T And China Mobile are founding members ), The goal is to drive software - based implementation , To break the monopoly of suppliers in today's market .
More specifically ,3GPP Defines the possible RAN Decoupling point , and O-RAN Appoint ( And compile ) The corresponding interface . especially E2 Interface , It is built around the idea of supporting different service models , Is the core of this strategy . It remains to be seen whether operators can successfully achieve their ultimate goals .

9.3.3 RIC Interface

Back to the picture 58 The three interfaces mentioned in , The purpose of each interface is similar to the interface described in the previous chapter . The first two ,A1 and E2, Is facing O-RAN The direction of standardization is developing . The third is the graph 58 Shown in xApp SDK, Even though O-RAN The long-term goal is to converge in a unified API( And corresponding SDK) On , But the current is based on ONOS Realized ( Conceptually similar to Flow Objectives).

A1 The interface is the management plane of the mobile operator ( Usually called OSS/BSS( Operation support system / Business support system )) Provides configuration RAN Methods . up to now , We haven't discussed communications yet OSS/BSS, But one thing is for sure , Such components are at the top of any communication software stack , It is the source of all configuration settings and business logic required to operate the network , Think of it as gNMI/gNOI stay RAN Corresponding components in .

Near-RT RIC Use E2 Interface to control the underlying RAN Components ( Include CU、DU and RU), You can think of it as OpenFlow stay RAN Corresponding components in .E2 The interface is required to be able to Near-RT RIC Connect different types of... From different suppliers RAN Components . This requirement is reflected around Service model (Service Model) In the abstract API in , The idea is that every RAN Components publish a service model , Define what the component can support RAN Feature set ,RIC Issue a combination of the following four operations on this service model .

The report (Report): RIC Require components to report configuration values for specific functions .
Insert (Insert): RIC Instructs the component to activate a user plane function .
control (Control): RIC Indicates that the component activates a control plane function .
Strategy (Policy): RIC Set the policy parameters of an activated function .

Of course , Related functions that can be activated 、 The variables that can be reported and the measurements that can be set are RAN A component is defined by its published service model .

in summary ,A1 and E2 Interface complete RAN Two of the three main control loops of : external ( Not in real time ) Loop with Non-RT RIC For the control point , middle ( Near real time ) Loop with Near-RT RIC For the control point . Third ( Inside ) Control loop , In the figure 58 It doesn't show , It runs in DU Inside , Including real-time scheduler , Embedded in the RAN Assembly line MAC Stage . The approximate time boundaries of the two external control loops are >> 1s and >10 ms, And assume that the real-time control loop <1 ms.

Near-RT RIC Opens the introduction of policy based RAN The possibility of control , therefore , If the policy defined by the operator is interrupted ( abnormal ), Indicates that the participation of external circuits is required . for example , You can imagine developing learning based controls , The inference engine for these controls will run as an application in Near-RT RIC, Non real-time learning engines can run elsewhere . then ,Non-RT RIC And Near-RT RIC Interaction , adopt A1 The interface moves from the management plane to Near-RT RIC Deliver relevant operational strategies .

Last ,xApp SDK In principle Flow Objectives stay RAN Corresponding components in , Is based on ONOS Realized , At present, it is only used as E2 Interface " transparent transmission ", It means xApps You must know the available service models . There's a problem , Because the application is implicitly coupled to the device , But defining a device independent version is still in progress .

9.4 SD-Fabric Role

As outlined earlier in this chapter ,PON and RAN All equipped with IP gateway , The gateway enhances specific access features . The gateway located at the edge of the operator's network is responsible for authorizing user access , Differentiate service levels provided to users , And charge users . When a user moves from one base station to another , The mobile core network also assumes additional responsibility for tracking mobility .

Most of these additional functions run on the control plane ( Even manage the plane ) in , The data plane behaves like any other L3 The network is very similar , This means that the data plane can be implemented through the mechanisms seen in the previous chapter , Or more specifically , Pass the first 7 What is described in this chapter SD-Fabric Solution implementation , However, these two specific access technologies need to be considered , And right SD-Fabric Influence .

take PON Connect to Internet Of BNG There are supplier defined controls / Management plane , Therefore, there is no need for industry wide standards . The data plane needs to support Q-in-Q Tags serve as a mechanism for differentiating subscriber services , This is a SD-Fabric One of the reasons for providing this functionality . This means that figure 53 Shown in fabric Switch and diagram 13( From 2 Chapter ) Sum graph 39( From 7 Chapter ) Shown in fabric The switches are identical . let me put it another way ,SD-Fabric Both will OLT Connect to the Internet , Another group is loaded BNG Control and management functions ( And any other that the operator wants to run on the edge VNF) Connect to your server .

take RAN The mobile core network connected to the Internet is composed of 3GPP standardized , This makes it a well-defined example ( Only in high-level architecture , complete 3GPP Specifications go far beyond the scope of this book ). chart 59 Gives an overview of the architecture , The composition is determined 5G Function block of mobile core network .

chart 59. 5G Overview of mobile core network architecture .

You can see from this picture ,UPF( User plane function , User Plane Function) The data plane is realized (3GPP be called User plane ). All other functions are control plane functions , among AMF Responsible for mobility management ,SMF Responsible for session management ,AUSF Responsible for authentication . All other function blocks correspond to low-level processes ,AMF、SMF and AUSF Call these processes to complete the work , But for our purposes , You can think of the entire function block as a microservice running on a commercial server . More details about the mobile core network control plane , And examples of specific implementation choices , We recommend Magma and SD-Core Open source project .

Extended reading :
Magma Core Project^[4]. Linux Foundation. 2021.
SD-Core Project^[5]. Open Networking Foundation. 2021.

For our discussion , It is important to UPF It can also be implemented as a micro service hosted by the server , Just like any software based router . With access to the programmable switching network , This function can be transferred to the switch . That's exactly what it is. 7.4 In the festival fabric.p4 Of upf Extend what you do .

But besides forwarding IP Outside the packet , What additional features are there ？UPF Perform three additional tasks . First , encapsulation / Unpack the data packets communicating with the base station , These are GTP-over-UDP/IP Encapsulated packets . secondly , Depending on what the operator wants to offer QoS Level queues packets . Both of these tasks can be done in P4 And the underlying programmable switch . The third task is " preservation " A packet sent to the terminal that has recently moved , So that no packets are dropped during the corresponding session state transition . This is not now P4 What the switch can support . therefore , The switch will temporarily redirect these packets to the server for saving and playback , Or redirect to those connected to these servers SmartNIC On .MacDavid And his colleagues introduced the mechanism in more detail .

Extended reading :
R. MacDavid, et al. A P4-based 5G User Plane Function^[6]. ACM SOSR. September 2021.

The main conclusion we draw from the discussion is , Access network and switching network are SDN Complementary use cases , Can work together . The switching network will not only carry the server of the access network control plane function ( Include RIC and xApps) Connect , It also runs some data plane functions on behalf of the access network . When all these use cases are combined , The end result is Edge access to the cloud (access-edge cloud) : A medium-sized cluster of commercial servers and switches , Deployed in enterprises and other edge sites , It can carry access network workload and edge service workload .Aether This is an open source example of the edge cloud , It will SD-Fabric、SD-RAN and SD-Core Combined in a self-contained package , Can be deployed in the enterprise , And manage it as a cloud service .

Extended reading :
Aether: 5G-Connected Edge^[7]. Open Networking Foundation. 2021.

Hello , I'm Yu fan , stay Motorola Have done research and development , Now in Mavenir Do technical work , Pair communication 、 The Internet 、 Back end architecture 、 Cloud native 、DevOps、CICD、 Blockchain 、AI And other technologies have always maintained a strong interest , I usually like reading 、 reflection , Believe in continuous learning 、 Lifelong growth , Welcome to exchange and study together .
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