(China Unicom Network Research Institute,Beijing 100048,China)

SDN⁃Based Broadband Network for Cloud Services

Xiongyan Tang,Pei Zhang,and Chang Cao

(China Unicom Network Research Institute,Beijing 100048,China)

Over⁃the⁃top services and cloud services have created great challenges for telecom operators.To better meet the requirements of cloud services,we propose a decoupled network architecture.Software⁃defined networking/network function virtualization(SDN/ NFV)will be vital in the construction of cloud⁃oriented broadband infrastructure,especially within data centers and for intercon⁃nection between data centers.We also propose introducing SDN/NFV in the broadband access network in order to realize a virtu⁃alized residential gateway(VRG).We discuss the deployment modes of VRG.

SDN;NFV;Cloud Services;Broadband Network

1 Introduction

The rapid growth of internet⁃based IT services has had an unprecedented influence on traditional tele⁃com business models.Over the top(OTT)business⁃es are replacing traditional telecom businesses. OTT services erode the profitability of an operator’s tradition⁃al voice and SMS services and force the operator to fall back on more fundamental network businesses for revenue growth. From January to September 2013,the revenue of China’s big three operators grew by only 0.7%year⁃on⁃year whereas in⁃come from non⁃voice business,dominated by mobile traffic and fixed broadband access,rose 16.6%year⁃on⁃year.These three operators were responsible for 95.7%of revenue growth in China’s domestic telecom industry[1].The number of point⁃to⁃point SMS sent by mobile users declined sharply in 2013, down by 13.7%year⁃on⁃year.

From the perspective of the ICT industry,the industry value chain has significantly changed.The basic network,i.e.,the pipe,it the operator’s core and lifeline,but its value is con⁃stantly declining.Concurrently,the value of terminals and the cloud is rising fast.Industry profit continues to be captured by IT enterprises such as Apple,Google,Facebook,and Amazon as well as China’s Tencent,Baidu,and Alibaba.

If operator revenue increased in line with traffic growth, then basic network operation would still be a good business. However,nowadays there are also huge challenges and costs associated with providing basic network service.The end re⁃sult is that more traffic does not generate more revenue.On the one hand,users and applications are demanding more in terms of network bandwidth,and network resources are being rapidly consumed.On the other hand,network unit bandwidth is get⁃ting cheaper,which means that network traffic is being decou⁃pled from revenue.Telecom operators have two paths to sus⁃tainable development:increase income or reduce costs.With the former,a plateau in user numbers and the difficulty of inno⁃vating in the application business mean that operators have to rely more on innovation in areas such as traffic operation,open networks,and collaborative cloud⁃network terminals in order to increase network value.With the latter,the key is to continu⁃ously reduce equipment,construction,and OAM costs as well as improve resource utilization by innovating with technology and optimizing architecture.

OTT services have created great challenges for telecom oper⁃ators,and both service model and network architecture need to be transformed in order to overcome these challenges.Here, we propose a decoupled network for cloud services,which greatly depend on a broadband network based on software⁃de⁃fined networking(SDN)in order to provide flexible,dynamic connection for customers and cloud data centers.

The rest of the paper is organized as follows:In section 2, we explain the decoupled network architecture that supports current cloud services;in section 3,we describe the role of SDN in a cloud⁃oriented broadband network as well as some typical SDN applications;in section 4,we discuss SDN⁃based broadband access network;and in section 5,we conclude the paper.

2 Decoupled Network Architecture for Cloud Services

A network supports and serves various services and applica⁃

tions and evolves constantly in response to service demand. There are two main trends in ICT business development:user mobility and service end on cloud.In terms of user mobility, smart terminals have become the main tool that people use to access ICT services and are driving the development of mobile Internet and the Internet of Things(IOT).In terms of service end on cloud,ICT services are fully embracing cloud service modes and are the impetus behind changes in network traffic models and system architecture.Although cloud computing on⁃ly appeared at the end of 2007,its philosophy and modes have quickly penetrated all aspects of ICT service.

Cloud service is a new technological concept and also a kind of new business thinking.Cloud services create new op⁃portunities for telecom operators because they basically ex⁃change computing and storage resources for network resources. Cloud services require data infrastructure such as cloud data centers as well as highly reliable,flexible,smart,ubiquitous broadband networks.Operators should play a leading role in providing cloud service infrastructure,such as data centers and broadband networks,in order to open up new space for growth.According to Gartner Research,in 2013,global cloud service markets were worth$131.7 billion and grew at an annu⁃al rate of 18%.This figure is estimated to rise to$244.2 billion in 2017,with growth remaining at 15%or higher.

In the telephony era,network traffic was primarily person⁃to⁃person traffic.In the cloud service era,network traffic is pri⁃marily communication between smart terminals and the cloud and communication between clouds.From 2000 to 2008,end⁃to⁃end file sharing was the main source of internet traffic;howev⁃er,since 2008,internet traffic has primarily been generated or terminated by data centers.Globally,cloud computing traffic is expected to increase 12⁃fold between 2010 and 2015,with average annual compounding growth of 66%[2].Global cloud data traffic first reached the zettabyte level in 2012.In 2015, one⁃third of data center traffic will be cloud traffic,and in 2016,two⁃thirds of data center traffic will be cloud traffic[2].

Cloud services rely heavily on Internet data centers(IDCs), which are similar to telephone switches in the telephony age. Future cloud data centers will be centers of data infrastructure, such as server and memory,and also basic network centers. Traditional data centers are mostly located in big cities where there is a concentration of users and good network conditions. However,when selecting the location of new cloud data cen⁃ters,factors such as land,energy consumption,and climate will be major considerations.The underdeveloped regions of north and west China will become home to future cloud data centers.That is to say,the focus when choosing IDC locations has moved from towards energy efficiency.This will lead to a decoupling of the user center,which encompasses information generators and users,from the data center,which encompasses information storage and processors.In the past,data and net⁃work followed users,and the three were tightly bound.In the traditional telephony era,networks mainly served as vehicles for communication between people.In the cloud service era, user centers and data centers are separate,and a“double cen⁃ter”pattern for users and data is formed.Thus,networks serve more as vehicles for communication between users and data ap⁃plications and are used for delivery of data itself.In the cloud era,basic network services will need to take into account net⁃working between virtual machines(VMs);IDC internal net⁃working,including front⁃end service networking and back⁃end storage networking;inter⁃networking between multiple IDCs,e.g., super IDC networking and edge IDC networking;and connec⁃tion between users and IDCs.Flexible,dynamic,open net⁃works and quick access to resources are particularly important for cloud services.To better support cloud service develop⁃ment,there must be a transformation from cloud⁃follows⁃net⁃work to network⁃follows⁃cloud.

Newly decoupled network architecture contains the data cen⁃ter domain and data user domain.Fig.1 shows the connections within and between these domains.

Here,we define the data center domain and data user do⁃main and related connections.

The data center domain includes super data centers and their connections.The main service in the data center domain is data resource transfer and scheduling between servers and their VMs.The data center domain usually crosses the back⁃bone network.The direction of the traffic flow is fixed and cen⁃tralized,and the volume of traffic can be predicted.The con⁃nection between data centers can be full⁃mesh,ring,or star.

The user domain contains a huge number of end users.The main service in the data user domain is web⁃browsing,on⁃de⁃mand gaming and video,instant messages,and various applica⁃tion services.These services have high requirement in terms of user experience,i.e.,in terms of latency,jitter,and response/ backup time.

The first type of connection is between super data centers (super DCs),which are connected to each other via full⁃mesh, ring,or star topology and high⁃speed fiber channels.

The second type of connection uses the operator’s broad⁃band network to deliver data or content from super DCs to smaller data centers at the edge side of a metro network(edge

DC).The edge DCs usually store part of the content that local users have often accessed.

▲Figure 1.Decoupled network architecture.

The third type of connection facilitates data transfer be⁃tween edge DCs and end users.The traffic in this domain is random,dispersive,and bursty.All data users first visit the nearest edge DC in order to access commonly used content.If this data is not in edge DCs,one edge DC requests data need⁃ed by users via the second type of connection.

3 SDN in a Cloud-Oriented Broadband Network

The proposed decoupled architecture lays the foundation for constructing next⁃generation broadband infrastructure.In cloud services,frequent migration of virtual resources depends on flexible broadband network support.SDN is one of the hot⁃test topics in ICT in recent years[3]-[5].It is also an important technical concept for building flexible broadband network sys⁃tems.The concept of SDN originated in the OpenFlow project conducted by Stanford University.The initial motivation for SDN was to break the monopoly of integrated network hard⁃ware and software and to enable network equipment to follow computer open industry chain by separating hardware from software[3].SDN is a new type of network architecture that en⁃ables programmable network control by separating the network control plane from the transfer plane and virtualizing the bot⁃tom network.SDN,as defined by the Open Network Founda⁃tion(ONF),decouples network control and forwarding so that network control becomes programmable,and the underlying in⁃frastructure is abstracted for applications and network services [6].Narrowly defined,SDN refers to SDN based on OpenFlow standard protocols released by the ONF.More generally de⁃fined,SDN refers to various open⁃interface,software⁃program⁃mable network architectures,including related standards and technology systems proposed by the IETF,ETSI and other stan⁃dardization organizations.Network function virtualization (NFV)proposed by ETSI is another important concept support⁃ed by many telecom operators.NFV uses software to imple⁃ment network functions.It can run on industry⁃standard server hardware and can be moved to or instantiated in various loca⁃tions in the network without the need to install new equipment. NFV is designed to break up the current network infrastructure model,where building blocks are black boxes vertically inte⁃grated by each vendor.NFV complements SDN,and the two concepts and technologies can be combined.In short,SDN/ NFV has broken the closed,rigid network system originally formed by proprietary network elements and reduces the cost of network equipment.It has also simplified network OAM and made network services more flexible.

SDN/NFV technology can be used in all layers of the broad⁃band network,including for routing switch,transport,access, and home network[7],[8],and is vital for constructing a cloud⁃oriented next⁃generation broadband network.SDN will soon be used for data center internal networks,data center interconnec⁃tion,virtual residential gateways,IP intelligent edges,mobile backhaul,mobile core network,and more.SDN has broad pros⁃pects and has given a profound influence on network develop⁃ment.

At the current stage of technological development,the main application of SDN is in data center networks.Cloud services have imposed higher requirements in terms of the flexibility, automation,and scalability of a data center network.Because traditional data centers have a large number of internal switch⁃es,network deployment strategies are complex,cross⁃domain migration of virtual resources is difficult,and security is diffi⁃cult to guarantee.SDN meets satisfies the requirements of data center networks.It can also be conveniently deployed in data centers,and the internal network environment is relatively in⁃dependent.SDN switches in a data center network are good for rapid,synchronized migration of virtual resources and are a good network strategy.SDN switches enable closer collabora⁃tion between the network and computing and storage resourc⁃es,and it facilitates greater control of overall resources.SDN may be further used for wide⁃area data center interconnection. Google has successfully used SDN in this way and has set the standard for this within the industry.Using SDN to intercon⁃nect data centers significantly improves bandwidth utilization, improves link availability,improves network scalability,and lowers network costs.It also simplifies OAM and makes cloud services smoother and more efficient.

More and more internet enterprises and OTT/cloud service providers are using SDN/NFV and other emerging network technologies to build their cloud service infrastructures.The use of SDN/NFV and other technologies enables closer collabo⁃ration between networks and cloud services.If telecom opera⁃tors fail to provide flexible network services that are adaptable to cloud services,providers of these services will rely more on their own network facilities,and this may result in a decrease of data traffic on the operator’s network.Operators should be aware that OTT is significantly affecting their application ser⁃vices.The threat of OTTs to an operator’s basic network ser⁃vices should not be underestimated.For example,Google cur⁃rently owns huge data centers in many countries.It has built its own data center network and has also cooperated with opera⁃tors to jointly invest in the rollout of submarine fiber cables in the Pacific Ocean.In addition,Google has entered the US broadband service market and launched 1 Gbps fiber access, which has a very high price⁃performance ratio in numerous cit⁃ies in the United States.Apple has also begun to deploy cloud broadband infrastructure.With the expectation of catching up with Google,Apple is preparing network infrastructure to han⁃dle more cloud services and distribute more digital content.In China,major internet companies are also arranging and build⁃ing cloud service infrastructures,including cloud data centers, content delivery networks(CDN),and related networks.In the current environment,telecom operators have to be open and in⁃

novative,hasten network transformation through the introduc⁃tion of new technologies,provide better network services to meet OTT cloud service requirements,and come to a win⁃win arrangement with OTT providers.

4 SDN in the Broadband Access Network

Broadband access networks are the most important part of a broadband infrastructure.They determine customer experience over last one mile and are also critical for the end⁃to⁃end QoE of cloud services.Residential gateways in broadband access are a potential area where SDN/NFV could be applied.There are a number of issues with current fixed⁃access networks,in⁃cluding high capes,difficulty in introducing new services,and complex OAM.By introducing SDN technology,forwarding and controlling planes can be separated in the access network so that access equipment and services are decoupled.SDN ar⁃chitecture can help a telecom operator build a simple,swift, flexible,value⁃added access network.In future architecture, the network access point can be simplified as a programmable device.A unified access network control and management plat⁃form can be used to realize a simple access point that does not require configuration,that has no faults,and that is not costly in terms of OAM.Clouding service and residential gateways en⁃ables flexible service deployment and network evolution.In a word,SDN represents a great step forward for access networks, especially residential networks.

4.1 Residential Gateway Virtualization

Residential gateways are broadband access network interfac⁃es provided by operators.Residential gateways are also the core communication equipment between an internal home net⁃work and external public network.A residential gateway is a data processing center inside the home and connects to the ex⁃ternal operator networks,where there are devices for broad⁃band access and VoIP services.Operators use these devices to administrate and maintain their residential networks.

In current multiservice network architectures,the user de⁃vice has complex functions.The access network and metro net⁃work are usually designed as a layer⁃2⁃based Ethernet trans⁃parent network.The benefit of this architecture is that it is highly scalable and low⁃cost.Functions of the upper two lay⁃ers,e.g.,IP protocol and application/service processing,have to be enabled in residential gateway devices.In such architec⁃ture,flexible adjustment and evolution of IP layer functions is sacrificed.Many layer⁃3 functions and service functions have to be deployed at the residential gateway,which is tightly cou⁃pled and restricted by the gateway.

With SDN,most layer⁃3 network functions are moved from the home network to provider network and hosted in a pool of resources.This is the function of the virtualized residential gateway(VRG).In the provider network,the VRG realizes third(higher)layer functionality that is usually tightly coupled with the physical residential gateway.At the same time,the residential gateway can be simplified to a bridge device with only layer 1 and layer2 functionality(Fig.2).

A simplified residential gateway makes installation,altera⁃tion,troubleshooting and replacement of residential gateway devices easier and more cost⁃effective.

The VRG has had a profound influence on access and home networks.The main advantages of VRG are standardized hard⁃ware,differentiated services,automated network,simplified terminal maintenance,quick service deployment,network re⁃source savings,operator control of the home network,and inno⁃vation with terminals and services.

4.2 Realizing the Virtualized Residential Gateway

4.2.1 VRG at the Access Point

VRG is deployed at the optical line terminal(OLT)with a passive optical network(PON)upstream residential gateway (Fig.3).The first scheme involves adding a VRG service⁃pro⁃cessing card on the OLT.The second scheme involves realiz⁃ing VRG functions on the main control panel of the OLT.

4.2.2 VRG Deployed at the Broadband Network Gateway

Fig.4 shows VRG deployed at broadband network gateway (BNG).BNG nodes are less than access network points,and the broadband remote access server(BRAS)supports the main functions of VRG,e.g.,network address transition(NAT)for⁃warding.Therefore,we only need to estimate the impact on BRAS after VRG functions are added.This scheme also simpli⁃fies service procedures;for example,it cancels point⁃to⁃point

protocol over Ethernet(PPPoE)function and procedure.Be⁃cause VRG functions are maintained by a data network mainte⁃nance team rather than an access network maintenance team, this scheme affects the maintenance system.

▲Figure 2.Network functions in a virtualized residential gateway.

▲Figure 3.VRG deployed at an access point.

4.2.3 VRG Independent Deployment

Fig.5 shows VRG deployed in a metro network.The deploy⁃ment location can be flexibly chosen according to require⁃ments in terms of VRG processing.

This scheme does not require other equipment to be signifi⁃cantly altered and supports smooth migration according to ser⁃vice requirements.However,some functions,such as NAT, may be deployed redundantly,and service processing should be redefined.

4.2.4 VRG Distributed Deployment

Because some network nodes already have some VRG func⁃tions,it is better to deploy different functions,e.g.,voice over IP(VoIP),NAT,application layer gateway service(ALG),dy⁃namic host configuration protocol(DHCP),IP over Ethernet (IPoE)and PPPoE,on different equipment.This scheme in⁃volves more network devices and more complex service pro⁃cessing,but risk of upgrading legacy devices can be reduced.

VRG has many advantages over traditional residential gate⁃ways;however,several QoS and security issues require atten⁃tion.On the one hand,some network protocols only run inside the home network,and some services are highly sensitive to timing and need special a QoS guarantee mechanism.On the other hand,some local,private information may be exposed to public network sites,and security in relation to virtualization needs to be taken into account.

5 Conclusion

▲Figure 4.VRG deployed at BNG point.

▲Figure 5.VRG independent deployment.

Cloud service is the future direction of ICT services.Broad⁃band networks have to be transformed in order to better meet the requirements of cloud services.In this paper,we have pro⁃ posed decoupled network architecture for cloud services.SDN/ NFV is vital in the construction of a cloud⁃oriented broadband network and can be applied in all layers of broadband network for routing switch,transport,access,home network,and more. Currently,SDN is mainly used within data center networks and for interconnection between data center networks.SDN can be introduced into a broadband access network to realize a virtual⁃ized residential gateway,and this enables a more flexible,cost⁃effective broadband infrastructure.

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Manuscript received:2014⁃03⁃24

Biograpphhiieess

Xiongyan Tang(tangxy@chinaunicom.cn)is now the chief engineer at China Uni⁃com Network Technology Research Institute.He is also the vice⁃chairman of China Communication Standardization Association TC10.He received his PhD degree in telecom engineering from Beijing University of Posts and Telecommunications in 1994.From 1994 to 1997,he researched high⁃speed optical communications in Sin⁃gapore and Germany.Since 1998,he has been working on technology management in telecom operators in China.His research interests include broadband communica⁃tions,optical fiber networks,next generation networks,and Internet of things.

Pei Zhang(Zhangp7@chinaunicom.cn)received his PhD degree from the Next⁃Gen⁃eration Optical Network Laboratory,Beijing University of Posts and Telecommunica⁃tion,in 2008.He has been researching next⁃generation high⁃speed optical transmis⁃sion,optical access system technology,assessment testing,standard tracking,and other related areas for many years.Over the past few years,he has participated in re⁃search on PON,OTN,and packet transport technology with China Unicom.He has published more than 20 papers,applied for seven patents of invention,submitted more than 30 standards documents at ITU⁃T/FSAN,and written three academic books.

Chang Cao(ccao_bupt@126.com)received his PhD degree from Beijing University of Posts and Telecommunications in 2012.From 2010 to 2011,he was a visiting scholar in the Department of Computer Science,North Carolina State University, US.His main research interests include optical network design and high⁃speed transmission system evaluation.He has published more than 20 papers and holds five patents.