A Novel Distributed VNet Mapping Algorithm

Xingui Shi, Xiangming Wen, Yong Sun, Linyan Li, Wenmin Ma School of Information and Communication Engineering

Beijing University of Posts and Telecommunications Beijing, China

Email:shixingui@gmail.com

Abstract—Network virtualization is seen as the key paradigms for future networks. Many initiatives had been proposed to solve how to implement Network virtualization. This article briefly describes the approaches taken in the 4WARD project to establish VNet, and proposes a novel distributed VNet Mapping algorithm which achieved by substrate nodes and the domain server automatically. The novel Mapping algorithm support different virtual nodes mapping to the same substrate node. We also modified VNet Mapping Protocol for effectively message exchange between substrate nodes and domain server. Through the simulation of results, it is shown that the proposed VNet Mapping algorithm can effectively reduce the number of packets which is needed to exchange information between domain server and substrate node without reducing the delay.

Keywords-Network virtualization; 4WARD; Distributed VNet Mapping Algorithm

I. INTRODUCTION

Nowadays, the Internet has become integral part of daily life, people become increasingly dependent on the Internet and require a variety of services. However, the existing Internet architecture is ill-suited and is difficult for deploying new architecture. Network virtualization is considered as a promising approach to overcome the “Internet impasse” and bring innovation back to the Internet. The concept of Network Virtualization is a potential solution for diversity the Future Internet architecture into separate Virtual Networks (VNet). The VNs can support simultaneous network experiments, services, and architectures over a shared substrate network. Although telecommunication networks have implemented some virtualization techniques, such as Virtual Local Area Networks (VLANs) and Virtual private Networks (VPNs), the full fledged virtualized solution is yet be accomplish. VPNs use public networks for enhanced security and compatible execution environments for shared and legacy applications. VPNs are limited to providing simple virtual links or IP forwarding, are not used for end-to-end deployments or full virtualization of the underlying infrastructure. VLANs allow workstations in different broadcast domains to be dynamical grouped into virtual segments. Each virtual segment enjoys common broadcast domains regardless of the physical segments of the participating nodes. VLANs are not suitable for inter-network virtualization. A fully fledged virtualized solution would be extremely flexible, by allowing multiple networks to run simultaneously, while supporting different

technologies, protocols, topologies, and Quality of Service (QoS) requirements. Many Future-Internet initiatives, such as, GENI and 4WARD, have regarded it as a feasible and non-disruptive solution for implementing future network architectures.

In 4WARD, the provider roles are divide into Infrastructure Provider (InP), Virtual Network Provider (VNP) and Virtual Network Operator (VNO), are depicted in Fig.1. Such way of division is easy for providers to occupy different parts of the value chain and develop their own business strategies [1].

� The InP is responsible for maintaining physical networking resources, such as routers, links, wireless infrastructure, etc, and enabling the virtualization of these resources. The InP also offers a resource control interface for the virtualized resources. Through this interface, InPs can make virtual resources and partial virtual topologies available to virtual network providers, which are the customers of the InP.

� The VNP is responsible for constructing virtual networks using virtual resources and partial topologies provided by one or more InPs or other VNPs. The VNP uses the interface offered by InP to constructed the VNet, which can be provided to VNO or another VNP, who can recursively use it to construct an even larger VNet.

� The VNO is responsible for operating, controlling and managing the VNet in order to offer services. Once the VNet is constructed by VPN, the VNO gets the permission to configure and manage the virtual resource from VPN.

The main goal of such VNet Architecture is to enable on-demand provision of custom-tailored virtual networks, and the provision process can be automatic. As shown in Fig.2, this process can be accomplished by VNO, VNPs and InPs cooperatively as follows:

� The VNO come up with a description of the desired virtual network topology using Resource Description Language, and pass the description to a management node of the selected VNP.

� The VNP contacts one or more InPs with whom it has contractual relationships for resources. The virtual nodes and virtual links interconnecting virtual nodes inside of

___________________________________ 978-1-4673-2101-3/12/$31.00 ©2012 IEEE

each single InP match the required virtual network topology are pre-reserved. After all required resources are pre-reserved, the VNP notifies all participating InPs about his choices.

Figure 1. VNet Provider Roles

� After approval notification from VNP, the InP create the requested virtual Network.

� If the virtual nodes and virtual links are successfully established, the Virtual Control Node send a confirm

� The InP management node then inform the Out-of-VNet Management about successful creation of the virtual node and the corresponding substrate node.

� The Out-of-VNet management creates a unique local identifier for the virtual node. For example, InP1 generates ID’.1 for the substrate node which is mapped to virtual node 1, and InP2 generates ID’’.2 for the substrate node which is mapped to virtual node2.

� InP pass the corresponding substrate node identifier of virtual node to the VNP. In order to provide a unified view of his network, VNP unifies the namespace by mapping ID’.1 to ID.1 and ID’’.2 to ID.2, which allow for moving virtual nodes between InP is transparent to VNO. Then the unified view of virtual network topology is handed over to the VNO.

The key issue of set up a VNet is selecting the best substrate nodes and links which match virtual nodes and links. The research about the issue can be classified into two categories, centralized and distributed. (1) The centralized manner needs a central entity which is responsible for the mapping algorithms. This entity assigns substrate nodes and links which interconnect the nodes to corresponding virtual nodes and virtual links based on the up to date information about the substrate network. However maintain up to date information about will cause many problems especially in dynamic network environment, like low flexibility and high latency [2], [3], [4]. (2) In distributed manner, every substrate node runs intelligence agent which can exchange messages

The rest of this paper is arranged as follows: Sectionpresents VNet and Substrate Network topology model and describe the distributed VNet Mapping problem. Section

describes the proposed distributed VNet Mapping Algorithm. Section evaluation the proposed algorithm and compare to other distributed algorithm. Conclusions and possible future work are described in Section .

Figure 2. Creation of a VNet

II. VNET MAPPING PROBLEM DESCRIPTION

A. Substrate Network model and VNet model Fig 3 depicts a VNet is mapped to a Substrate Network,

where two virtual nodes are assigned to a substrate node. The set of virtual nodes and virtual link are assigned to a specific set of substrate nodes and substrate path. A substrate path maybe a substrate link or a sequence of substrate link or even not a real substrate link when two virtual nodes locate in the same substrate node.

Both Substrate Network and Virtual Network are consist of nodes and links, so then can be expressed as weighted unsigned graph ( , )s s sG N L� and ( , )v v vG N L� , where sNand vN represent the set of Substrate nodes and Virtual nodes,

sL represents the set of substrate link between nodes of the set

Figure 3. VNet and VNet model

sN , and vL represents the set of virtual link between nodes of the set vN .

Substrate Network performance can be described by substrate node available capacity and substrate link available capacity. ( )sC n indicates the available capacity of the node

s sn N� . ( ( , ))sC l i j indicates the available bandwidth capacity of the link ( , )s vl i j L� , where ,i j means the link is between

substrate node in and substrate node jn . If i j� , which means two virtual node map to the same substrate node in , the available capacity of that link ( ( , ))sC l i j � � . And another important parameter in algorithm is link weight ( ( , ))sw l i j ,which indicates a set of parameters including cost and delay of the substrate link.

The requirements of Virtual Network also can be described by virtual node capacity and virtual link capacity. ( )vC ndenotes the minimum required capacity of virtual node

v vn N� , and ( )vC l denotes the minimum required bandwidth capacity of virtual link v vl L� . Suppose virtual link vl is mapped to substrate path P, the minimum residual bandwidth of substrate path ( )C P and weight of substrate path ( )w P can be calculated as follows:

( , )( ) min ( ( , ))

ssl i j P

C P C l i j�

� (1)

( , )( ) ( ( , ))

s

sl i j P

w P w l i j�

� � (2)

B. VNet Mapping description Upon receipt of the request to set up a VNet from VNP,

InP will choose a suitable domain and sends a Req message to the domain server. The Req message describes VNet topology and their minimum required capacity. Req= ( , , )v v vG V M where

vV and vM denote a set of node capacity vector and a link capacity matrix, respectively. [ ( )]i

v sV C n� is the minimum required capacity vector for virtual nodes i

sn , where 0 | |vi N� � and [ ( ( , )]v vM C l i j� , where 0 , | |vi j N� � .Then substrate nodes and a domain server will cooperate to complete the mapping from virtual network to substrate network. The objective of the mapping problem is to find the best mapping between the virtual graph vG and the substrate graph sG , which with minimum path weight, while satisfy the constraint of the capacity.

The mapping problem mainly is consisting of node mapping and link mapping:

� The node mapping problem can be described as :N s vMAP n n� , v vn N� and c

s sn N� , where csN

denotes the set of substrate nodes at least capable of supporting the virtual node with minimum capacity . i.e. { | ( ) min ( ( ))

v v

cs s s s n N vN n N C n C n�� �

� The link mapping problem can be described as :L vMAP l P� , v vl L� and P T� where T denotes

the set of paths which can capable of support any virtual link i.e. { | ( ) ( ), }v v vT P C P C l l L� � , so

the situation, which already assigned ivn and j

vn to isn

and jsn , but the path between that two substrate are

below the minimum requirement of the virtual link, i.e. ( ( , )) ( )vC P i j C l� , will not happen.

This article assumes link capacity is unlimited for simplify the complexity of the problem.

III. DISTRIBUTED VNET MAPPING ALGORITHM

As VNet may be quite large, completing the mapping algorithm at once may lead to high complexity and high latency. This article choose a feasible way, which is to divide the VNet topology into clusters and map each cluster separately and then interconnect them into the complete VNet topology. Such a way can reduce the complexity of mapping the whole VNet into substrate network, while delay within an acceptable range.

The VNet topology can be dividing into many hub-and-spoke clusters. Each hub-and-spoke cluster is consisting of a central node called hub and a set of nodes which are adjacent to the central node called spoke. The division process is described as follows:

1. Select virtual node which with highest required capacity as the hub node.

2. Select virtual nodes, which are directly connect to the hub, as spoke nodes

3. Remove the hub and spoke nodes as well as their corresponding links from the VNet topology.

4. Select the next hub-and-spoke cluster: Go to 1 After selection of a hub-and-spoke cluster, the domain

server send a HSM message to the node with maximum capacity, which is called root node, and the root node will take over the completion of hub-and-spoke mapping. The root node mapping process is described as follows:

1. The root node maps itself to hub node and update its availabe capacity.

2. Determine the set of candidate substrate nodes which is able to support the spoke nodes based on shortest path Tree (SPT) algorithm, then sort the candidate nodes and spokes.

3. Assign head of the set of candidate nodes to the head of spokes until all spokes are mapped and update the available capacity of substrate nodes which are assigned to hub-and-spoke nodes. Eg. Substrate node sn are

assigned to virtual node vn , the available capacity of snbecome available capacity of sn minus the minimum required capacity of vn , i.e ( ) ( ) ( )s s vC n C n C n� � .

4. Send HSMR to domain server to inform completion of

the hub-and-spoke mapping. The algorithm for selecting and mapping the hub-and-

spoke clusters is distributed but different from literature [6]. In [6], each node runs all distributed algorithm, this lead to a large number of redundant calculation and also will cause confusion if the results are inconsistent. The novel distributed VNet runs repeated algorithm while mapping process are handle by substrate node.

In this paper, the distributed VN mapping algorithm is mainly composed of three algorithm: a Node-capacity-sorting which runs in a domain server for providing up to date node available capacity information, a SPT algorithm is mainly for grasping up to date information of link available capacity, and a main VN mapping algorithm achieve mapping VNet to substrate network. The communication between substrate nodes and domain server using message defined in improved Virtual Network Mapping Protocol. The protocol has seven types of messages:

� MSG is used to report substrate node available capacity information to domain server,

� START is used to start a VNet mapping � HSM is used for inform a substrate node is chosen as

root node and start hub-and-spoke mapping algorithm, � HSMR is used for root node to confirm the success of

hub-and-spoke mapping to the domain server and inform the domain server to update the resided unmatched VNet topology, there maybe some virtual link interconnect hub-and-spoke clusters remain unmatched,

� VLM is used for mapping remain unmatched virtual link, the domain server send VLM message to the substrate node which is one vertex of the virtual link is mapped to, to inform the node to map the virtual link.

� VLMR message will send to domain server to inform the complete of virtual link mapping.

� FINISH is used for notifying InP of the VNet has been set up.

The Node-Capacity-Sorting algorithm: the algorithm runs on server at a certain time interval, to get the up to date sorted node capacity information. Each substrate send MSGmessage to the domain server, the server gathers the message and sort available capacity information from highest to lowest. The node available capacity information is stored in a capacity vector sV .

The Shortest Path Tree algorithm: the algorithm is real-time runs on substrate node to calculate the minimum cost path from the node i

sn to each node jsn . If i j� , the cost is 0.

In this paper, SPT algorithm is chosen for SPT algorithm is the fastest distributed algorithm for compute shortest path problem in general network topology. The output of the algorithm runs on substrate node i

sn is {( , ( ))}j jT P w P� ,

where jP is the shortest path between substrate node isn and

substrate node jsn , and ( )jw P is the cost of path jP .

The main Distributed Mapping algorithm: This algorithm

{ | ( ) min { ( )}}

Sort(N )( )

v v

i is s S s n N v

s

s

N n N C n C n

root Head N

�� �

�

( )( )

{ | ( , ) }

v

v

v v v v v

Sort Nhub Head Nspokes n N l hub n L

�� � � �

HSM(hub,spokes,L ) to root nodevsend

/wait for HSMR(hub,spokes,L ) messagev

/

/ { , }v v

v v

L LN N hub spokes��

Nvif ��

Lvif ��

FINISH to InPsend

/

/

receiving VLMR(L )v

v v

uponL L�

( ) ( ) to M[hub]

v v v

v

hub End l l Lsend VLM L

� �

for(req)

message

waitSTART

Figure 4. Main mapping algorithm of server side

is consist of three parts: one is to deal with messages running on server, another is hub-and-spoke mapping algorithm which implement mapping a hub-and-spoke into substrate topology and runs on root substrate node, the third is mapping a virtual link to substrate link which is responsible for mapping the remaining unmatched link.

As Fig.4 depicts the server side mainly process improved Virtual Network Mapping Protocol and update VNet topology. Upon receiving START message, the server will select a set of alternative substrate node that match VNet minimum required capacity, and decide the first hub-and-spoke cluster and the root node. Then send this information through HSMmessage to root node. Once receiving response message HSMR , the server update the alternative nodes sN ,the virtual nodes vN and virtual link vL . The domain server will choose the next hub-and-spoke cluster and root node until all nodes are mapped, and send HSM message to root node., and if all virtual nodes are mapped, the server will check if there are any virtual link remaining unmapped, the domain server send VLM message to the substrate node which is mapped to one vertex of a unmapped virtual link and wait for response information VLMR from the substrate. When all VNet topology have been mapped, the domain server will

send FINISH message to all nodes to notify the InP of the VNet mapping is complete.

/

/ /

/

( )( )

( )= { (P , ( )) | ( )> C ( ), sp o k es}

=

= { | ( ) T }

S o rt(S )

jj j s v v

K kj

s j K

S o r t sp o kesK len g th sp o kesT S P T ro o tT w P T C n n n

T M in TS n w P

��

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if spokes ��

( )

MAP ( ( )) ( )( , ( ))

/{( , ( )}/{ ( )}

_ ( ( ))/{ ( )}

N

L Head S

v v

Head spokes Head SMAP hub Head spokes PL L hub Head spokesspokes spokes Head spokesupdate capacity Head SS S Head S

��

�

�

�

/ HSMR(hub,spokes,L ) to domain servervsend

forHSM(hub,spoke, ,N )message

v s

waitL

MAP: root hub�

Figure 5. Main mapping algorithm of root node

As Fig.5 depicts the hub-and-spoke-mapping algorithm runs on root nodes, which is responsible for assign hub-and-spoke cluster to substrate node. When receiving the HSMmessage, the node will first map itself to hub node and choose the set of candidate nodes S which satisfy both minimum path cost and node capacity constraint. Then the root node will map the head of spokes to the head S according to order of their node capacity, and map corresponding Path to the virtual link ( , )hub spoke , meantime update the vL and the available capacity of substrate node which are assigned to host a virtual node so the node may appeared in the set of candidate nodes S in the next round. After all spokes are mapped, the root node will send HSMR message to the domain server. vL is the set of virtual links which interconnect hub-and-spoke clusters and are not mapped, the domain server choose a virtual vl from vL , and send a VLM message to the substrate

node lsn which is mapped to an vertex of the virtual link vl .

The substrate node will find the shortest path to the node ksn

which is mapped to another vertex of the virtual link, and map the path ( , )l k

s sP n n to the virtual link vl then send the updated to the domain server.

A. Simulation description A Multi-Agent system (MAS) is a system composed of

multiple interacting intelligent agents with an environment, the benefits of MAS is flexibility, since the system can be added to, modified and reconstruct without detailed rewrite of

the application. The MAS system also tends to rapidsly self-recovering and self-organized. So the distributed VNet mapping algorithm can be evaluated on MAS system. Java Agent Development Environment (JADE) [8] can be used to implement the MAS system to evaluate the distributed VNet Mapping algoritm.

20 25 30 35 40 45 504

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

Number of substrate nodesTi

me(

S)

traditional VNet mappingnovel VNet mapping

Fig.6 Time delay: traditional vs novel

20 25 30 35 40 45 500

500

1000

1500

2000

2500

3000

Number of substrate nodes

Num

ber o

f mes

sage

s

traditional VNet mappingnovel VNet mapping

Fig.7 Number of message:traditional vs novel

IV. SIMULATION RESULTS AND ANALYSIS

A. Simulation description A Multi-Agent system (MAS) is a system composed of

multiple interacting intelligent agents with an environment, the benefits of MAS is flexibility, since the system can be added to, modified and reconstruct without detailed rewrite of the application. The MAS system also tends to rapidsly self-recovering and self-organized. So the distributed VNet mapping algorithm can be evaluated on MAS system. Java Agent Development Environment (JADE) [8] can be used to implement the MAS system to evaluate the distributed VNet Mapping algoritm.

This article evaluates the distributed VNet mapping algorithm on time delay and number of messages of main Distributed Mapping algorithm. And compare the result with [6], which implements the VNet Mapping algorithm on each substrate node.

B. Simulation result and discussion The fig6 depicts the time delay taken by the novel

distributed VNet Mapping algorithm are little better than the traditional distributed algorithm described in [5]. This is due to the traditional algorithm wastes too much time in repetitive work and consume more time when encountering confliction of many node map to a same virtual node. The fig7 depict the number of message need to exchange for mapping a VNet to a Substrate Network. With the help of domain server, the novel algorithm can remarkably decrease the number of messages.

V. CONCLUSION This article presented a distributed VNet mapping

algorithm for mapping Virtual Network topology into substrate network topology in a MAS system. Each node communicates with domain server employing an improved VNet Mapping protocol. The evaluation result proved the proposed distributed VNet Mapping Algorithm can effectively reduce the number of packets which is needed to exchange information between server and substrate node without reducing the delay. The novel distributed VNet Mapping algorithm possess the high scalability and low latency of distributed mapping algorithm , while also have the low redundancy of centralized mapping algorithm.

As future work we intended to research how to map a VNet to a substrate network across multiple domains and multiple InPs, and how to map several VNets into substrate network parallel. This may be implemented by modify the Virtual Mapping Protocol to support different domain server communication. In [5] the author propose label each VNet Request with a Reqid to support parallel mapping VNet to

substrate network, however this is not a fine scheme for may appearing situation like a substrate node may chosen by two virtual node of different Reqid but can’t support two virtual node.

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