Proceeding of: 2018 European Conference on Networks and Communications (EuCNC), June 18-21, Ljubljana, SloveniaWe are currently observing the softwarization of communication networks, where network functions are translated from monolithic pieces of equipment to programs running over a shared pool of computational, storage, and communication resources. As the amount of this resources might vary over time, in this paper we discuss the potential benefits of introducing resource awareness to softwarized network functions. More specifically, we focus on the case of computational elasticity, namely, the ability to endure shortages of computational resources while providing an adequate (although non-ideal) service. We discuss how to enable this ability by re-designing network functions, and illustrate the potential benefits of this approach with a numerical evaluation

Banchs Roca, Albert

Bega, Dario

García Avilés, Ginés

Gramaglia, Marco

Gutiérrez-Estévez, David M.

Serrano Yáñez-Mingot, Pablo

English

Universidad Carlos III de Madrid e-Archivo

This is a postprint version of the following document: Serrano, P., et al. On the benefits of bringing cloud-awareness to network virtual functions, in 2018 European Conference on Networks and Communications (EuCNC), June 18-21, Ljubljana, Slovenia © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. On the Benefits of Bringing Cloud-Awareness toNetwork Virtual FunctionsPablo Serrano,∗ Marco Gramaglia,∗ Dario Bega,∗†David Gutierrez-Estevez,‡ Gines Garcia-Aviles,∗† and Albert Banchs∗†∗Universidad Carlos III de Madrid, Spain†Institute IMDEA Networks, Spain‡Samsung Electronics R&D Institute, UKAbstract—We are currently observing the softwarization ofcommunication networks, where network functions are translatedfrom monolithic pieces of equipment to programs running overa shared pool of computational, storage, and communicationresources. As the amount of this resources might vary over time,in this paper we discuss the potential benefits of introducingresource awareness to softwarized network functions. Morespecifically, we focus on the case of computational elasticity,namely, the ability to endure shortages of computational re-sources while providing an adequate (although non-ideal) service.We discuss how to enable this ability by re-designing networkfunctions, and illustrate the potential benefits of this approachwith a numerical evaluation.I. INTRODUCTION5G mobile networks will be characterized by a variety ofservices imposing a diversity of requirements.1 To efficientlysupport this diversity, we need a change of paradigm in theprovisioning of Network Functions (NFs), moving from thetraditional vision where Physical Network Functions (PNFs)are tightly coupled with the hardware substrate running them,to the new vision where Vertical Network Functions (VNFs)run over instantiations of a general-purpose infrastructure. Itis envisioned that this transition will introduce a tremendousimprovement in flexibility, adaptability and reconfigurability,similar to the one that happened when transitioning fromcircuit-based to packet-based networking.By softwarizing the operation of the network, VNFs (e.g.,schedulers, databases, gateways) run as software componentsover a set of shared resources (antennas, links, servers, etc.),and can be dynamically provisioned as needed. This ap-proach indeed improves the flexibility of the network: thesemonolithic programs run over shared computational resources,allowing, e.g., their re-instantiation on-demand, the reductionof development cycles and easier reconfiguration in general.Still, softwarization poses a number of challenges such asthe efficient resource assignment to VNFs. This problem hastraditionally been investigated from the network managementperspective [4], but a very little effort has been done from theVNF design point of view.1This has been repeatedly argued by now, in a number of position paperssuch as, e.g., [1], in SDOs such as 3rd Generation Partnership Project (3GPP)[2], and in industry fora such as Next Generation Mobile Networks Alliance(NGMN) [3]In this paper, we focus on the computational elasticity ofVNF, which we define as the ability to endure shortages ofthe computational resources while maintaining an adequateservice level. The current protocol stack and its composingblocks are “legacies” of the past, namely, their design approachhas not changed since early 3GPP Releases. Indeed, thenetwork functions addressed by current softwarization efforts— e.g., Serving Gateway (S-GW), Packet Data NetworkGateway (P-GW), or Radio Access Network (RAN) upperlayers — have a practically direct mapping with the onesdefined in 3GPP Release 8 [6], [7], which was publishedalmost ten years ago. If these VNFs are not designed to runover shared resources (that is, with virtualization in mind),there is the risk that any variation in these resources wouldcause service disruption: this potential sensitivity of VNFsto e.g. resource shortages, updates in the infrastructure, orcontainer migrations, may preclude their wide use in futurenetworks. Furthermore, given the indivisibility of these piecesof software, the assignment of programs to execution nodes(known as network embedding [5]) has been usually performedwith a relatively coarse level of granularity, which hinders anefficient use of the resources.For these reasons, we need a change of paradigm in thedesign of the network functions, to efficiently support all thenovel features that network softwarization and cloudificationbring. In other words, the time is ripe for a new class of cloud-aware protocol stacks, which embrace softwarization as thefundamental design criteria.II. THE QUEST FOR CLOUDIFICATIONThe advantages brought by a cloud-driven VNFs designwill fuel the research community. In fact, while researchershave devoted so far just a little attention to solve the problemsinvolved by this approach, we believe that the relative maturityof current software initiatives provides the means for researchin this area to bloom. We argue that future, fully softwarizedand cloudified mobile networks will necessarily build oncloud-aware protocol stacks. We believe that both networkmanagement and the resulting overall performance will benefitfrom making VNFs aware of being executed in environmentssuch as virtual machines or containers, running on sharedresources. One of the key challenges to implement the abovevision is to support an elastic operation, to efficiently copewith changing input loads while running in an infrastructureof resources that is not over-provisioned.While having a cloud-aware protocol stack will benefit anykind of telecommunication service, this may be particularlyrelevant for the extreme ones. For example, a mission criticalVNF can be optimized to reduce its memory footprint, whilelow latency services may exploit especially tailored orchestra-tion patterns involving edge computing facilities.An immediate and appealing advantages of a cloudifiednetwork is the possibility of reducing costs, by adaptingand re-distributing resources following (and even anticipating)temporal and spatial traffic variations. However, it is alsolikely that in certain occasions the resource assignment acrossthe cloud cannot cope with the existing traffic due to somepeaks of resource demands. This is particularly true forCloud RAN (C-RAN) deployments, that have to deal withdemand loads known to be highly variable. In this scenario,allocating resources based on peak requirements would behighly inefficient, as this design jeopardizes multiplexing gainsin particular when cloud resources may be scarce (e.g., a“flash crowd” at an edge cloud): here any temporal shortagemight result in a system failure. VNFs, instead, shall efficientlyuse the resources they are assigned with. Thus, they haveto become elastic, i.e., adapt their operation when temporalchanges in the resources available occur, in the same waythey have a long-established manner of dealing with outagessuch e.g. channel errors. Therefore, to fully exploit the benefitsof softwarizing the network operation, the network functiondesign has to take the potential scarcity into account, and beprepared to react accordingly.The concept of elasticity usually refers to a graceful perfor-mance degradation when the spectrum becomes insufficientto serve all users. However, in the framework of a cloudifiedoperation of mobile networks that has to deal with elasticityunder resource shortages, we also need to consider other kindsof resources that are native to the cloud environment such ascomputational, memory, and storage assets available to thecontainers the VNFs are bound to. In particular, we focuson the case of computational elasticity: the ability to endureshortages of computational resources while maintaining anadequate service level (although non-ideal). This has hardlybeen a problem for traditional network functions, that weredesigned to run over a given hardware substrate with exclusiveaccess to the resources, and requires the definition of novelinterfaces that will provide the amount and type of availablecloud resources at a given point in time, just like, e.g., theaccessible spectrum is a parameter for a RAN function.Elasticity has also been considered by non-VNFs cloudoperators, but our concept deviates very much from theirs:the time scales involved in RAN functions are significantlymore stringent than the ones required by e.g., a Big Dataplatform or a web server back-end. Another key differenceis that resources are way more scattered in our scenario (e.g.they are distributed across the “edge clouds”), which reducesthe possibility of damping peaks by aggregating resources.0 25 50 75 100Computational Outage probability [%]0255075100PerformanceDegradation[%]Elastic GainsMinimumFootprintElastic ApproachStandard ApproachFig. 1: Graceful performance degradation achieved by elasticcomputation: performance is not degraded by the same relativeamount as resources are reduced.A. Potential BenefitsTo better illustrate the benefits of elasticity in the cloudifiedmobile network operation context, we first consider the notionof “computational outage” [8], i.e., the unavailability of therequired resources to perform the expected operation. In atraditional, non-elastic operation, there is a 1-to-1 mappingbetween outages and performance loss, as Fig. 1 illustrates: ifthe resources are not available 20% of the time, there is a 20%performance degradation, as the function is unable to operateunder any shortage. In contrast, an elastic design supports agraceful performance degradation, which causes that the VNFstill functions under a resource shortage, this resulting in the“gains” illustrated in Fig. 1. Making a protocol stack cloud-aware through elastic VNFs requires hence a paradigm shiftin their design, moving away from the tight hardware-softwareco-design that we discussed before, to a flexible operationin which the amount of available resources is an additionalparameter.To fully take advantage of elastic VNFs, a detailed analysisof their operation is required: first, a thorough assessment ofthe resources consumed during execution, including statisticsabout temporal variations over time; second, a characterizationof the correlations between VNFs operations, to serve as inputfor the orchestration algorithm, so it could e.g. dynamicallyassign resources to resilient VNFs and quickly “rescue” themwhen outages happen.2III. A PRACTICAL SCENARIOWe next discuss the potential benefits of bringing cloud-awareness in a practical scenario. We consider a C-RANscenario where the scheduling of a number of base stationsis done by a central entity. In a traditional approach, the VNFperforming frame decoding has to be dimensioned for peakcapacity, i.e., all Physical Resource Blockss (PRBs) usingthe highest Modulation and Coding Scheme (MCS), which2Indeed, the quest for cloudification will end up with novel orchestrationalgorithms.corresponds to ideal radio conditions for all users (having aset of users with good channel conditions is a common as-sumption for schedulers that rely on Opportunistic Schedulingtechniques [9]). However, planning for peak capacity not onlyrequires prior knowledge of the users’ demand, but also resultsin resource wastage when mobile traffic falls below this peak.Thus, let us assume a C-RAN scenario where resourcesare not over-provisioned, and the scheduling function for theuplink is serving a large enough set of base stations. Underthese conditions, it will be likely that during short periods oftime a set of users (experiencing good channel quality andhence using high MCS) require more capacity than available,as a higher MCS requires more iterations to be decoded [10].A non-elastic function would fail to e.g. decode the PRBs, thisresulting in an abrupt degradation of performance.A cloud-aware MCS selection function helps to addressthis challenge more efficiently. Given that the “disruption”is caused by a relatively large set of users using high MCS,one elastic strategy is to purposely “downgrade” some of theMCS to be used in the PRBs, to find a combination that canbe supported by the available computational resources. Thisversion of the function, originally proposed in [11], mighthave better short-term fairness properties than the previousone, as users are still scheduled but at a lower rate. Also, thismight support a more “graceful degradation” in the absenceof resources.REFERENCES[1] P. Rost et al., “Cloud Technologies for Flexible 5G Radio AccessNetworks,” IEEE Communications Magazine, 2014.[2] 3GPP TR 22.891, “Feasibility Study on New Services and MarketsTechnology Enablers,” 2015.[3] NGMN Alliance, “5G white paper,” 2015. Available Online:http://www.ngmn.org/5g-white-paper.html[4] A. De La Oliva et al., “Xhaul: toward an integrated fronthaul/backhaularchitecture in 5G networks,” IEEE Wireless Communications, 2015.[5] A. Fischer et al., “Virtual network embedding: A survey,” IEEECommunications Surveys & Tutorials, 2013.[6] E. Dahlman et al., “3G evolution: HSPA and LTE for mobilebroadband,” Academic press, 2010.[7] 3GPP TS 36.300, “Evolved Universal Terrestrial Radio Access(E-UTRA) and Evolved Universal Terrestrial Radio Access Network(E-UTRAN); Overall description;” version 8, 2007.[8] M. Valenti and P. Rost, “The role of computational outage in densecloud-based centralized radio access networks,” in IEEE GLOBECOM,2014.[9] A. Asadi and V.Mancuso, “A survey on opportunistic scheduling inwireless communications,” IEEE Communications surveys & tutorials,2013.[10] S. Bhaumik et al., “CloudIQ: A framework for processing basestations in a data center,” in ACM MOBICOM, 2012.[11] P. Rost et al., “Computationally aware sum-rate optimal scheduling forcentralized radio access networks,” in IEEE GLOBECOM, 2015.

On the benefits of bringing cloud-awareness to network virtual functions

Gutiérrez-Estévez, David

Name not available

We are currently observing the softwarization of communication networks, where network functions are translated from monolithic pieces of equipment to programs running over a shared pool of computational, storage, and communication resources. As the amount of this resources might vary over time, in this paper we discuss the potential benefits of introducing resource awareness to softwarized network functions. More specifically, we focus on the case of computational elasticity, namely, the ability to endure shortages of computational resources while providing an adequate (although non-ideal) service. We discuss how to enable this ability by re-designing network functions, and illustrate the potential benefits of this approach with a numerical evaluation.© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

On the benefits of bringing cloud-awareness to network virtual functions

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