virtual network embedding (vne): current research issues and challenges...

Virtual Network Embedding (VNE):Current Research Issues and Challenges

Junling LiSupervisor: Xuemin (Sherman) Shen

Broadband Communication Group(BBCR)Electrical and Computer Engineering

2016/11/16 1

Outline

Background Network virtualization (NV) in wired networks VNE in wired networks VNE in wireless networks

1) IEEE 802.11‐based wireless networks

2) Cellular‐based wireless networks

VNE in software‐defined networks

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3

Future Internet business model[1]

• Infrastructure Providers (InPs): deploy and maintain the network equipment

• Service Providers (SPs): deploy network protocols and offer end‐to‐end services

Main change:NV decouples the role of current Internet Service Providers (ISPs) into two new roles:

(1) VN generation(2) Resource allocation: VNE(3) End‐to‐end transmission protocol

What can we do?

Background

[1] Fischer, Andreas, et al. "Virtual network embedding: A survey." IEEE Communications Surveys & Tutorials 15.4 (2013): 1888-1906.

Background

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Network Virtualization (NV) vs. Network Function Virtualization (NFV)

• NV can be viewed as a tunnel connecting any two domains in a network;

• NFV deploys services on NV;

• NFV virtualizes the function from layer 4 till layer 7 such as load balancing and firewalls;

• Both NV and NFV may run on high performance x86 platforms.

NFV

NV

Seven‐layer OSI model

Background

5

NV and NFV vs. Software Defined Network(SDN)

• NV creates virtual tunnelsNFV creates virtual functions SDN modifies the physical network

• NV and NFV can reside on the servers of the existing network

• SDN requires the construction of new network where the control and data layers are decoupled.

VNE in software‐defined wireless networks emerges as hot topic recently.

VNE in wired networks has been fully investigated.

VNE in wireless networks gains increasing attention these years.

[2]

[2] Chiosi, M. "Network Functions Virtualisation–Introductory White Paper. SDN and OpenFlow World Congress. October 22–24, 2012, Darmstadt, Germany."

NFV relationship with SDN

Background

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Network virtualization environment [3]

Substrate Network

(SN)

Network Virtualization Illustration

Virtual Network

(VN)

Virtual Nodes

Virtual Links

Virtual Topology

Mapping

[3] Chowdhury, NM Mosharaf Kabir, and Raouf Boutaba. "Network virtualization: state of the art and research challenges." IEEE Communications magazine 47.7 (2009): 20-26.

VNE in Wired networks

Virtual network operator (VNO) uses embedding algorithms to • decide which virtual resources to request from the VNPs• allocate virtual resources on a physical infrastructure in an optimal way

Allocating virtual resources using embedding algorithms

Resource allocation in future Internet[1]

5


VNE In Wired Networks

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Parameters to consider

Two virtual networks mapped onto one substrate network

Two sub‐problems: • Virtual Node Mapping (VNoM)• Virtual Link Mapping (VLiM)

• Node parameters:CPU capacityLocation, etc.

• Link parameters:Bandwidth

[1]



9

Notations

The substrate network:A virtual network request:

The substrate network and a virtual network request are usually denoted by undirected graphs.

[4]

[4] M. Yu, Y. Yi, J. Rexford, and M. Chiang, “Rethinking virtual network embedding: Substrate support for path splitting and migration,” ACM SIGCOMM CCR, vol. 38, no. 2, pp. 17–29, Apr. 2008.


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Metrics The Revenue per virtual network

Acceptance ratio, which measures the percentage of VN request accepted by an algorithm;

10

The revenue‐to‐cost ratio, which provides a metric relating both revenue and cost; a high revenue‐to‐cost ratio indicates an efficient embedding.

Baseline VNE Algorithm

11

• Node mapping algorithm

A group of incoming requests are collected during a time window; Some requests may be deferred due to lack of bandwidth or CPU resources and

returned to the request queue. The requests in the queue are dropped if they cannot be served within some delay.

[4]


Baseline VNE Algorithm

12

• Link mapping algorithm

Finding an optimal mapping from a virtual link to a single substrate path with fixed node mapping reduces to the Unsplittable Flow Problem (UFP), which is NP-hard；

The k-shortest path algorithm is used as an approximation approach to minimize bandwidth consumption by the virtual network.

[4]


Summary of VNE in Wired NV

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Parameters: CPU capacity for nodes and bandwidth for links

Node mapping: usually uses greedy strategyLink mapping: shortest path algorithms for unsplittable flows

multi‐commodity flow algorithms for splittable flows

Coordinated mapping exists which can make link mapping more efficient

Classification:Centralized vs. DistributedStatic vs. DynamicConcise vs. RedundantCoordinated vs. Uncoordinated

Accepting and rejecting VN requests can be implemented by admission control mechanisms.

Wireless VNE Compared with Wired VNE

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Research Challenges

• Interference • Mobility• Distribution• Embedding quality comparison• Feasibility checking• Link reliability

These problems are not easy to solve since the bandwidth resource of a wireless link is hard to calculate

II. Challenge 1

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Interference and Isolation

Due to the broadcast nature of wireless links Activities of one VN should not affect any other VNs Strict isolation of virtual networks (or slices) is quite challenging

Current Solutions Space division multiplexing (SDM) Time division multiplexing (TDM) Frequency division multiplexing (FDM) Code division multiplexing (CDM)

II. Challenge 2

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Node Mobility

May invalidate the operations of virtual networks May change the connectivity of the substrate nodes May cause wireless links’ time‐varying characteristics

Current Solutions

Adopt mobility model to model the substrate node mobility Remap (migrate) invalid virtual networks to other substrate nodes and paths (drawback: incur a significant overhead)

Minimize the overhead associated with migrating invalid VNs

II. Challenge 3

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Handling online VN requests

VN request arrivals and departures are not known in advance Requires the statistical properties of VN requests Mapped VNs need to be reconfigured to optimize the utilization of SN resources

Also exists in wired networks

Current Solutions Admission control mechanism Dynamic programming

II. Other Challenges

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Embedding quality comparisonThe available (or remaining) bandwidth resource of a wireless link is hard to measure.

Feasibility checkingIndividual resource check at nodes and links is insufficient due to the interference between wireless links.

DistributionSome wireless network environments are lack of a centralized management entity, e.g. ad‐hoc networks.

Link ReliabilityWireless links suffer from interference and fading.

Wireless Network Categories

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• IEEE 802.11‐based networks(WMNs, multi‐hop networks)

• Cellular‐based networks (e.g. LTE systems)

• IEEE 802.16‐based networks (WiMAX)

• Heterogeneous networks

• Others

our focus

Depend on radio access technologies, wireless networks can be classified into the following four categories:[5]


VNE in WMN: Case 1

20

Virtual networks in WMNs

Characteristics of WMN Consists of a set of mesh routers

Each mesh router is equipped with multiple radios

Mesh routers are inter‐connected by wireless links

Data packets are forwarded through multi‐hop routing paths

Viewed as a promising technology for rapid deployment and expanded coverage with low cost

MAP: mesh access pointIGW: Internet gateway

[6]


VNE in WMN

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Question1: Node and link parameters?

Paper Node constraints Link constraints

[7] none (multicast) reliability

[8] CPU, desired location, how far virtual nodes can be placed from their desired position(each VN has 2‐10 nodes)

bandwidth

[6] The virtual MAP is mapped to the physical MAP with the same locationthe client, the virtual IGW is to be determined)

Up‐link and down‐link bandwidths

[7] L. Pin, C. Zhiping, X. Jia and X. Ming, “Multicast service-oriented virtual network embedding in wireless mesh networks,” IEEE Commun. Lett., vol. 16, no. 3, pp. 375-377, Mar. 2012.[8] D. S. Giovanni, S. Avallone, and R. Canonico. "Virtual network embedding in wireless mesh networks through reconfiguration of channels." WiMob. 2013.

VNE in WMN

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Question2: How to enforce isolation between each of VN?or what is the multiple access mechanism of the WMN?

Paper Methods Comments

[7] TDM Different VNs are activated during distinct periods in a round‐robin manner to avoid mutual interference

[8] TDM

[6] OFDM Through subcarrier allocation on each link virtual networks are gracefully separated from each other.

VNE in WMN

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Question3: How to take interference into consideration?

Paper Methods Comments

[7] Mesh nodes are equipped with dual radios operating on non‐interferingchannels.

Focus on link reliability constraint, bandwidth constraint are not considered

[8] By defining the concept of collision domain, a physical model of interference was adopted.

the available bandwidth of a link depends on the composition of its collision domain, and can be changed by changing the channels used to transmit

[6] (1)Mesh nodes are equipped with two channels in different bands: one for transmission, the other for receiving;(2)Different IGW‐trees were assigned with various channels to avoid interference.

A channel assignment schemeexploiting both non‐overlappingchannels and partially‐overlapped channels was developed for IGW‐trees.

Summary of VNE in WMN

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Parameters: Nodes: CPU, desired location,

how far virtual nodes can be placed from their desired positionLinks: Up‐link and down‐link bandwidths, reliability

Isolation:TDM, OFDM

Interference:equip nodes with dual radios or mulltiple radios suitable channel assignment algorithmsubcarrier allocation scheme

The link mapping of VNE needs to consider the specific multiple access mechanism of a WMN, then it determines resource allocation for each VN accordingly to guarantee the independence of each VN.

LTE Virtualization

25

Example of LTE Virtualization

Basic idea To virtualize the LTE base station

(eNodeB) An entity called “Hypervisor” is

added on top of the physical resources

“Hypervisor” is responsible for allocating the physical resources between the different virtual instances

Spectrum configuration and band width estimation (SCBE)

Spectrum allocation unit (SAU)

Two critical entities

[5]


Summary of VNE in wireless NV

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For IEEE 802.11‐based networks Link virtualization is the major challenge; FDM and TDM are usually used to enable wireless link virtualization

embedding; Interference and link reliability need to be considered; VNE algorithms can be developed based on those designed for wired

networks.

For cellular networks In the case of LTE, the InP can divide the available Physical radio resource

blocks (PRBs) into several parts and allocate them to each MVNO separately; In the case of CDMA, the air interface can be sliced in the domain of time or

frequency for the purpose of isolation; In addition to interference and link reliability, user mobility, coverage,

roaming, etc. need to be considered.

NV in Software Defined Networking

2016/11/16 27

Conventional SDN

(a) Conventional (non-virtualized) SDN network

How to virtualize SDN networks?

By inserting a hypervisor between the physical SDN network and the SDN control plane

The hypervisor views and interacts with the entire physical SDN network through the D‐CPI interface (south bound API)

The hypervisor abstracts (virtualizes) the physical SDN network and creates isolated virtual SDN networks that are controlled by the respective virtual SDN controllers[9]

[9] A. Blenk, A. Basta, M. Reisslein and W. Kellerer, “Survey on network virtualization hypervisors for software defined networking,” IEEE Commun. Surveys Tuts., vol. 18, no. 1, pp. 655–685, 1st Quart. 2016.


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Combining Network Virtualization and Software Defined Networking

(a) Conventional (non-virtualized) SDN network(b) and (c) The virtualization of the SDN network

[9]


2016/11/16 29

Hypervisor classification

FlowVisor was the first hypervisor for virtualizing and sharing SDNs based on the OF protocol, it is in widespread use and available in Mininet.

CellVisor, RadioVisor and MobileVisor are hypervisors that are investigated for wireless and mobile networks.

[9]

2016/11/16 30

VNE in Software Defined Networking

vSDN Embedding Considerations

(1) Node resources include CPU resources and flow table resources;

(2) SDN data plane elements relies on the use of the TCAM space(for flow table processing), the assignment of TCAM space has to be taken into account when embedding vSDNs;

(3) The hypervisor design has to be taken into account during the embedding process.

2016/11/16 31

Summary of VNE in SDN

• Existing VNE approaches have to be further extended to virtual SDN networks.

• Although some first studies exist, they neglect the impact of the hypervisor realization on the resources required to accept a vSDN.

• The number of papers focusing on VNE in SDN‐enabled wireless and mobile networks is limited.

• How to model different hypervisors and how to integrate them into embedding algorithms remains an open research question.

References[1] Fischer, Andreas, et al. "Virtual network embedding: A survey." IEEE Communications Surveys & Tutorials 15.4 (2013): 1888-1906.[2] http://network.51cto.com/art/201306/398240.htm[3] Chowdhury, NM Mosharaf Kabir, and Raouf Boutaba. "Network virtualization: state of the art and research challenges." IEEE Communications magazine 47.7 (2009): 20-26.[4] M. Yu, Y. Yi, J. Rexford, and M. Chiang, “Rethinking virtual network embedding: Substrate support for path splitting and migration,” ACM SIGCOMM CCR, vol. 38, no. 2, pp. 17–29, Apr. 2008.[5] C. Liang and F. R. Yu, “Wireless network virtualization: A survey, some research issues and challenges,” IEEE Commun. Surveys Tuts., vol. 17, no. 1, pp. 358–380, 1st Quart. 2015.[6] P. Lv, X. Wang, and M. Xu, “Virtual access network embedding in wireless mesh networks,” Ad Hoc Networks, no. 0, pp. –, 2012.[7] P. Lv, Z. Cai, J. Xu, and M. Xu, “Multicast service-oriented virtual network embedding in wireless mesh networks,” Communications Letters, IEEE, vol. 16, no. 3, pp. 375 –377, march 2012.[8] D. S. Giovanni, S. Avallone, and R. Canonico. "Virtual network embedding in wireless mesh networks through reconfiguration of channels." WiMob. 2013.

[9] A. Blenk, A. Basta, M. Reisslein and W. Kellerer, “Survey on network virtualization hypervisors for software defined networking,” IEEE Commun. Surveys Tuts., vol. 18, no. 1, pp. 655–685, 1st Quart. 2016.[10] N. M. M. K. Chowdhury, M. R. Rahman, and R. Boutaba, “Virtual network embedding with coordinated node and link mapping,” in Proc. IEEE INFOCOM. IEEE Infocom, Apr. 2009.[11] Singhal, Shruti, et al. Evaluation of UML based wireless network virtualization. IEEE, 2008.[12] D. Yun, J. Ok, B. Shin, S. Park, and Y. Yi, “Embedding of virtual network requests over static wireless multihop networks,” CoRR, vol. abs/1207.1878, 2012.[13] Y. Zaki, Z. Liang, C. Goerg, and A. Timm-Giel, “LTE wireless virtualization and spectrum management,” in Proc. 3rd Joint IFIP WMNC, Budapest, Hungary, Oct. 2010, pp. 1–6.[14] Y. Zaki, L. Zhao, C. Goerg, and A. Timm-Giel, “LTE mobile network virtualization,” Mobile Netw. Appl., vol. 16, no. 4, pp. 424–432, Aug. 2011.[15] G. Bhanage, I. Seskar, Y. Zhang, and D. Raychaudhuri, “Evaluation of openvz based wireless testbed virtualization,” Rutgers University, Piscataway, NJ, USA, Tech. Rep. WINLAB-TR-331, 2008.

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