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Since the MIT Review selected 10 major technological advances in 2009, SDN has maintained considerable popularity during the decade.
SDN is an abbreviation of software-defined networking. Its essence is to realize flexible control of network traffic through the separation of control plane and forwarding plane of network equipment.
So how does "software" define "network" and what effect does it have on "5G network"?
Origin of SDN: distributed or centralized?
When it comes to SDN, people in the industry will mention "transfer, control separation."
The essence of SDN can be broken: SDN has no other stove, just refactoring the traditional network.
Beginning with ARPANET, the originator of the Internet, traditional networks use a distributed architecture to deliver reachable information through a series of network protocols.
One pass ten, ten passes hundred, to achieve interconnection.
The most prominent feature of this structure is that the forwarding and control are combined into one: each node determines its own forwarding rules; once a node is damaged or a new node joins, each node re-learns and converges through the network protocol, and realizes interworking again.
ARP: Address resolution protocol, obtaining the host MAC address by IP address.
OSPF: Open Shortest Path First, used in a link state-based routing protocol in an autonomous domain.
RIP: Routing information protocol for a distance vector-based routing protocol in an autonomous domain
BGP: Border Gateway Protocol, used to exchange routing information between different autonomous domains.
Traditional network
This "individual" approach seems to be good, both to withstand the risk of failure of some nodes, but also has some scalability.
However, with the rapid development of the Internet, especially the emergence of emerging technologies such as cloud computing and big data, the bottleneck of traditional networks has gradually emerged.
For example, each node decides its own forwarding rules, lacks an overall concept; it takes too long to develop a new network protocol.
In response to these problems, some companies have tried to separate forwarding and control since the 1990s.
The creation and popularity of the word SDN are attributed to Professor Nick McKeown of Stanford University, whose OpenFlow has almost become the actual southbound interface standard.
The network architecture of SDN is divided into three layers, from the bottom to the top, the forwarding plane, the control plane, and the application layer.
The control-oriented interface is the southbound interface, which is responsible for configuring and modifying the forwarding rules. The mainstream standard is the OpenFlow mentioned above.
The control is oriented upwards to the northbound interface, providing APIs for network applications and realizing network customization. Currently, there is no open standardized interface.
SDN network
The status quo of SDN: intensive cultivation or flowering everywhere?
Since ONF (Open Networking Foundation, which promotes standardization of SDN and OpenFlow) was established in 2011, SDN has evolved in two dimensions: one dimension is the key components of SDN, including the evolution of forwarding, control, and southbound interfaces. The other is an extension to other application areas.
Forwarding surface
Because it is a reconstruction of the traditional network, the original form of the forwarding surface is naturally similar to the traditional network equipment.
With the rise of data center and network virtualization, the software has emerged as a new forwarding surface. One of the representatives is the Open vSwitch of the open-source community.
It is worth mentioning that, in combination with the DPDK (a data plane development kit from Intel's third-party software development company), Open vSwitch demonstrates excellent linear switching capabilities in some applications, approaching hardware performance. The potential of software in reconfigurability and scalability is unmatched by hardware and has a very broad application prospect.
Control surface
As the central brain of SDN, the control plane configures the network topology and forwarding rules according to the policies defined by the network operator.
The more well-known controllers are OpenDayLight (the most mature open-source platform) and ONOS (for operators, with enhancements in clustering, reliability, and performance).
Southbound interface
The development of the southbound interface presents the situation that OpenFlow stands out. OpenFlow uses a flow table as a configuration object. The flow table defines the basic processing of packets, including matches, counters, and actions.
High abstraction and ease of implementation are key to the success of OpenFlow.
Application area extension
After the success of the data center, SDN began to be applied to other areas.
Being adopted by the 5G network architecture is another important milestone in the history of SDN development (although 3GPP will define a new southbound interface).
At the beginning of 4G/LTE design, due to the lack of business and the low data requirements of users, the packet core network was designed into the following architecture.
The data influx from the access network is unified into the Serving Gateway (S-GW) and the Packet Data Gateway (P-GW).
4G/LTE network architecture
With the emergence of new applications and new services such as VR/AR, driverless, and drone clusters, users are demanding more data (not only bandwidth), but also on quality (time delay). Requirements.
This architecture of LTE has hindered the adoption of new applications and services.
To meet these challenges, 3GPP follows the basic principle of SDN "transfer, control separation", making major changes in the design of 5G network architecture: data sinking + control plane concentration.
5G network architecture
In the LTE era, the number of packet core gateways is very small, while 5G uses a large number of distributed gateways (that is, the UPF in the above figure).
At the time, based on the software switch Open vSwitch, Intel added the encapsulation, decapsulation, forwarding and other gateway functions of wireless packet data (mainly GTP-U tunnel), and completed the industry's first SDN software supporting 5G distributed gateway. The switch is designed to cover traffic export and offload, mobile edge computing, high reliability, low latency communication, and other services.
The future of SDN: Evolution or rebirth?
The golden rule of "forwarding and controlling separation" is difficult to shake, but in the key components of SDN, the change seems difficult to avoid.
Take the southbound interface OpenFlow as an example. The 1.0 version has only 12 matching domains, and the latest version 1.4 has surged to 41.
With the addition of new protocols, this number will continue to increase if only patched evolution is made.
In terms of forwarding, the SDN software switch supporting the 5G distributed gateway mentioned in the previous example is only an example. To support the processing of wireless packet data, the Open vSwitch is modified to involve more than 20 files, for a total of more than 300.
The cost of upgrading a feature is not small.
As one of the evolution directions of SDN, P4 (Programming protocol-independent Packet Processors) has become one of the hot spots after 2016.
The change that P4 brings to us is no longer stick to MAC/IP/TCP (UDP), you can define the message encapsulation format on your own, and use the compiler to automatically generate hardware or software forwarding surfaces.
Personally, feel that the development of SDN is a technological opportunity
The emergence of SDN technology has changed the production mode of software and hardware integration in the traditional network industry and gradually transformed into the architecture of the underlying high-performance storage/forwarding + upper layer intelligent and flexible scheduling.
This is also the case. Many small vendors in network equipment have always intended to actively follow the SDN technology, and hope to use technology changes to shorten the gap between giants such as Huawei and Cisco.
At the same time, Huawei, Cisco, and other network equipment giants are also actively deploying the R&D and technology reserves of SDN technology, waiting for opportunities based on changes in market conditions.
It can also be seen from some of Cisco’s actions over the years.
SDN is originally an important part of DC
SD-WAN is placed in the direction of EI Enterprise Network in 2020.
It means that Cisco has begun to promote SDN on the global stage.
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