软件定义网络：历史、现状与未来编程网络综述

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软件定义网络（Software-Defined Networking, SDN）是近年来云计算和网络架构领域的重要革新，它通过将网络控制平面与数据平面分离，实现了网络功能的程序化和灵活性。本篇综述文章《软件定义网络：过去、现在与未来——可编程网络的演变》由Bruno Nunes Astuto、Marc Mendonça、Xuan Nam Nguyen、Katia Obraczka和Thierry Turletti合作撰写，发表于2014年的IEEE Communications Surveys & Tutorials期刊上，卷16，第3期，页码1617-1634。文章回顾了SDN的历史背景，始于早期的网络虚拟化概念，如OpenFlow，它标志着SDN作为一个独立技术的诞生。OpenFlow协议使得网络设备能够接收外部控制器的指令，实现了网络配置的集中管理和自动化。作者讨论了SDN在早期如何通过简化网络操作、提高效率和降低复杂性，促进了数据中心和云计算环境的快速发展。文章深入分析了SDN的核心组件，包括集中式控制器、开放的南向接口和北向接口，以及网络编程模型，如NetConf和RESTful API。这些技术使得网络管理员可以利用标准API来定制和调整网络行为，从而实现灵活的服务链部署和网络功能切片。此外，文章还探讨了SDN在现代网络中的应用，包括网络功能虚拟化（NFV）、边缘计算和物联网（IoT）等场景。随着网络流量的增长和多样性，SDN被用于优化流量路由、安全策略的自动化以及提供更好的服务质量保证。对于未来发展，作者预测了SDN将进一步与其他新兴技术融合，如人工智能、机器学习和区块链，以实现更智能、安全且可扩展的网络。同时，SDN将继续推动网络架构朝着更加开放、动态和自动化方向发展，以适应不断变化的业务需求和网络环境。《软件定义网络：过去、现在与未来——可编程网络的演变》是一篇深入研究了SDN技术发展历程、现状和潜力的论文，为理解这一关键技术及其在云计算和未来网络中的作用提供了宝贵的参考。

networks and decoupled control logic has been around for

many years. In this section, we provide an overview of early

programmable networking efforts, precursors to the current

SDN paradigm that laid the foundation for many of the ideas

we are seeing today.

a) Open Signaling: The Open Signaling (OPENSIG)

working group began in 1995 with a series of workshops

dedicated to “making ATM, Internet and mobile networks

more open, extensible, and programmable” [6]. They believed

that a separation between the communication hardware and

control software was necessary but challenging to realize; this

is mainly due to vertically integrated switches and routers,

whose closed nature made the rapid deployment of new

network services and environments impossible. The core of

their proposal was to provide access to the network hardware

via open, programmable network interfaces; this would allow

the deployment of new services through a distributed program-

ming environment.

Motivated by these ideas, an IETF working group was

created, which led to the speciﬁcation of the General Switch

Management Protocol (GSMP) [7], a general purpose pro-

tocol to control a label switch. GSMP allows a controller

to establish and release connections across the switch, add

and delete leaves on a multicast connection, manage switch

ports, request conﬁguration information, request and delete

reservation of switch resources, and request statistics. The

working group is ofﬁcially concluded and the latest standards

proposal, GSMPv3, was published in June 2002.

b) Active Networking: Also in the mid 1990s, the

Active Networking [8], [9] initiative proposed the idea of

a network infrastructure that would be programmable for

customized services. There were two main approaches being

considered, namely: (1) user-programmable switches, with in-

band data transfer and out-of-band management channels;

and (2) capsules, which were program fragments that could

be carried in user messages; program fragments would then

be interpreted and executed by routers. Despite considerable

activity it motivated, Active Networking never gathered crit-

ical mass and transferred to widespread use and industry

deployment, mainly due to practical security and performance

concerns [10].

c) DCAN: Another initiative that took place in the

mid 1990s is the Devolved Control of ATM Networks

(DCAN) [11]. The aim of this project was to design and

develop the necessary infrastructure for scalable control and

management of ATM networks. The premise is that control and

management functions of the many devices (ATM switches in

the case of DCAN) should be decoupled from the devices

themselves and delegated to external entities dedicated to that

purpose, which is basically the concept behind SDNs. DCAN

assumes a minimalist protocol between the manager and the

network, in the lines of what happens today in proposals such

as OpenFlow. More on the DCAN project can be found at [12].

Still in the lines of SDNs and the proposed decoupling of

control and data plane over ATM networks, amongst others,

in the work proposed in [13] multiple heterogeneous control

architectures are allowed to run simultaneously over single

physical ATM network by partitioning the resources of that

switch between those controllers.

d) 4D Project: Starting in 2004, the 4D project [14],

[15], [16] advocated a clean slate design that emphasized

separation between the routing decision logic and the pro-

tocols governing the interaction between network elements.

It proposed giving the “decision” plane a global view of the

network, serviced by a “dissemination” and “discovery” plane,

for control of a “data” plane for forwarding trafﬁc. These ideas

provided direct inspiration for later works such as NOX [17],

which proposed an “operating system for networks” in the

context of an OpenFlow-enabled network.

e) NETCONF: In 2006, the IETF Network Conﬁgu-

ration Working Group proposed NETCONF [18] as a man-

agement protocol for modifying the conﬁguration of network

devices. The protocol allowed network devices to expose an

API through which extensible conﬁguration data could be sent

and retrieved.

Another management protocol, widely deployed in the past

and used until today, is the SNMP [19]. SNMP was proposed

in the late 80’s and proved to be a very popular network

management protocol, which uses the Structured Management

Interface (SMI) to fetch data contained in the Management

Information Base (MIB). It could be used as well to change

variables in the MIB in order to modify conﬁguration settings.

It later became apparent that in spite of what it was originally

intended for, SNMP was not being used to conﬁgure network

equipment, but rather as a performance and fault monitoring

tool. Moreover, multiple shortcomings were detected in the

conception of SNMP, the most notable of which was its lack

of strong security. This was addressed in a later version of the

protocol.

NETCONF, at the time it was proposed by IETF, was

seen by many as a new approach for network management

that would ﬁx the aforementioned shortcomings in SNMP.

Although the NETCONF protocol accomplishes the goal of

simplifying device (re)conﬁguration and acts as a building

block for management, there is no separation between data

and control planes. The same can be stated about SNMP.

A network with NETCONF should not be regarded as fully

programmable as any new functionality would have to be

implemented at both the network device and the manager so

that any new functionality can be provided; furthermore, it is

designed primarily to aid automated conﬁguration and not for

enabling direct control of state nor enabling quick deployment

of innovative services and applications. Nevertheless, both

NETCONF and SNMP are useful management tools that

may be used in parallel on hybrid switches supporting other

solutions that enable programmable networking.

The NETCONF working group is currently active and the

latest proposed standard was published in June 2011.

f) Ethane: The immediate predecessor to OpenFlow was

the SANE / Ethane project [20], which, in 2006, deﬁned

a new architecture for enterprise networks. Ethane’s focus

was on using a centralized controller to manage policy and

security in a network. A notable example is providing identity-

based access control. Similar to SDN, Ethane employed two

components: a controller to decide if a packet should be

forwarded, and an Ethane switch consisting of a ﬂow table

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