1 Network as a Service: The New Vista of Opportunities Junaid Qadir1, Nadeem Ahmed1, Faqir Zarrar Yousaf2, Ali Taqweem1 1School of Electrical Engineering and Computer Science, National University of Sciences and Technology (NUST), Pakistan 2NEC Laboratories Europe, Heidelberg, Germany Email: fjunaid.qadir, nadeem.ahmed, [email protected], [email protected] Abstract—The networking industry, compared to the compute provider affording users and operators the same benefits of industry, has been slow in evolving from a closed ecosystem cloud computing. with limited abstractions to a more open ecosystem with well- The viability of NaaS is bolstered by the increasing role defined sophisticated high level abstractions. This has resulted in an ossified Internet architecture that inhibits innovation and is of modern warehouse-sized datacenters (DCs) as well as unnecessarily complex. Fortunately, there has been an exciting advancement in virtualization technology in terms of security, flux of rapid developments in networking in recent times with isolation and performance. In a DC, hundreds of thousands of prominent trends emerging that have brought us to the cusp of powerful commodity servers are placed in racks connected a major paradigm shift. In particular, the emergence of tech- by commodity switches. Virtualization technology enables nologies such as cloud computing, software defined networking (SDN), and network virtualization are driving a new vision of the instantiation of multiple virtual machines (VMs) on a ‘networking as a service’ (NaaS) in which networks are managed single server within a DC with the VMs being managed flexibly and efficiently cloud computing style. These technologies by the VM manager also known as a hypervisor. The VMs promise to both facilitate architectural and technological inno- provide a faithful imitation of the original server’s interface, vation while also simplifying commissioning, orchestration, and while ensuring inter-VM isolation, to the applications run- composition of network services. In this article, we introduce our readers to these technologies. In the coming few years, the trends ning on the VM. This enables a network operator to host of cloud computing, SDN, and network virtualization will further network service/functions on VMs while taking advantage of strengthen each other’s value proposition symbiotically and NaaS the programmability features of VM cloning and mobility will increasingly become the dominant mode of commissioning (allowing transport of VM snapshots from a busy server to any new networks. underutilized physical server). More importantly, NaaS enables Index Terms—Cloud computing; software-defined networks; the operator to virtualize the networking components in a Network-as-a-service. manner analogous to the server virtualization and to provide a ‘virtual network’ (VN) abstraction that is akin to the VM abstraction. This decoupling is essential for VNs to afford the I. INTRODUCTION same operational benefits that we have come to expect from With the proliferation of smart devices and high band- VMs. width applications, there has been a great upsurge in data The aim of this article is to provide a tutorial overview of the traffic in recent times motivating the development of novel various technologies that enable NaaS. According to the best network architectures that allow greater flexibility while re- of our knowledge, no such article exists in literature, and filling stricting the increased capital and operational expenditure this void is the main contribution of this work. The remainder (CAPEX/OPEX). The traditional network architecture—which of this article is organized as follows: The notion of NaaS, and arXiv:1606.03060v2 [cs.NI] 10 Jun 2016 is based mainly on interconnections of vertically integrated its main motivations, is described in section II. We discuss the proprietary hardware with coupled control and data planes— deficiencies of traditional network virtualization techniques in offers little in terms of high-level sophisticated abstractions to section III, before introducing the enabling technologies of program the network. This has limited operators in rolling out NaaS in section IV. Finally, we conclude this article in section new services and in adapting to changing load demands and VI. application requirements. In order to address the shortcomings of the traditional II. WHAT IS NETWORK AS A SERVICE (NAAS)? networks, the emerging concept of ‘network as a service’ (NaaS) aims at leveraging the concepts of cloud computing NaaS is in essence the ‘cloudification’ of traditional net- and virtualization to provide pluggable, scalable and applica- working. While VMs have unshackled applications from being tion programmer interface (API) driven network management tied to particular physical servers, traditional network virtual- where the users can deploy and manage their networks as ization techniques—such as virtual LANs (VLANs), virtual virtual logical networks decoupled from their physical instan- private networks (VPNs)—do not offer an analogous VN tiation on the underlying network. NaaS provides a network- abstraction that decouples the network from the physical in- ing framework that extends cloud computing’s on-demand frastructure (refer to figure 1). NaaS is the vision of providing and self-service provisioning model to the network service the VN abstraction as a service such that this VN abstraction 2 configurations as a result of tight coupling of services and infrastructure. Traditional DC networking solutions do not scale since they require manual configuration (which can increase commissioning time to days and weeks). In line with cloud computing convention, it is desirable to have instant self- service provisioning. NaaS is also motivated by the desire to avoid the expensive process of application rewriting which can result with limitations of traditional networking (such as the lack of broadcast domain abstraction, or the lack of support for custom assigned IPs to the virtual servers). The advancements of virtualization technology, the rise of high-level APIs for automated provisioning and service orchestration, and the economy of operating at cloud scale makes NaaS a very attrac- tive proposition for both the CSPs and the service consumsers. Fig. 1. In NaaS, virtual networks are logically decoupled from the underlying NaaS is also motivated by the desire to utilize the available physical infrastructure substrate. compute capacity in DCs to implement networking functions typically implemented on middleboxes1 as virtualized cloud instances to offset the expensive proposition of conventional can be instantiated, operated, cloned, moved, and repurposed proprietary middleboxes. as desired by the user in cloud computing style. C. Benefits of NaaS A. Virtual Network (VN) Abstraction The prime benefit of NaaS is the i) agility in deployment The VN abstraction implies that the virtualized network be with which networks can be provisioned in a matter of minutes managed sans any manual interaction with physical assets by and the ii) scalability and elasticity of service using which the network manager. Just like a VM is a software-container the network can be upgraded as and when desired with the (encapsulating logical CPU, memory, storage, and networking) convenient pricing model of pay-as-you-use. The users of providing an interface identical to a physical machine to an NaaS have the benefit of iii) full automation using which application, a VN is also a software container encapsulating the consumer can program, manage, and orchestrate the net- logical components (such as routers, switches, firewalls, etc.) work with programmatic control at convenient granular utility which presents an interface identical to a physical network pricing leading to iv) savings and productivity. The consumer to network applications. Implementing this VN abstraction can support v) custom policies in its own virtual network requires detachment of the virtual network from the physical which leads to vi) enterprise network innovation. This can infrastructure as well as isolation between multiple tenants mean orchestration of several networking functions as desired sharing the same infrastructure. The VN abstraction allows by the user such as custom routing, load balancing, network great flexibility to IT managers as the physical network isolation, firewalling, custom addressing, etc. In addition, can now be managed as a ‘fabric’ offering some transport the consumers can vii) work with any hardware, or even a capacity that can be used, programmed, and repurposed as mixed vendor hardware, without worrying about the burden needed without requiring any change to the existing physical of configuration and management and thereby avoid vendor network or IP addresses, the networking workload, or the lock-in. The CSPs also gain a lot from offering NaaS: e.g., by server virtualization technique. utilizing the features of viii) VM mobility, the DC resources Since VNs have the same operational model as VMs, can be effectively utilized by moving the VMs from loaded VNs should support dynamic creation, resizing, and mobility servers to idle servers without disrupting the VNs. The NaaS (within and between DCs). This is challenging in multi-tenant model has full support for ix) multi-tenancy with isolation DCs where a tenant’s VMs may reside in different servers, or which leads to better economics for CSPs while satisfying even in different DCs [1]. To allow agile operations of cloud the isolation