Design and analysis of techniques for mapping VN to SDN … · 2014-05-26 · Introduction...
Transcript of Design and analysis of techniques for mapping VN to SDN … · 2014-05-26 · Introduction...
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DESIGN AND ANALYSIS OF TECHNIQUES FOR
MAPPING VIRTUAL NETWORKS TO SOFTWARE-
DEFINED NETWORK SUBSTRATES
Tran Song Dat Phuc - Uyanga
Department of Computer Science and Engineering
SeoulTech 2014
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Table of Contents
• Introduction
•Related work
•Model and problem statement
•Conclusion
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Introduction
• Software-defined networking (SDN) has emerged as a powerful
approach to improve the customizability and flexibility of
networks.
• By separating the control plane from the data plane, SDN
facilitates network experimentation and allows for optimizing
switching/routing policies.
• The forwarding planes in SDN are managed by remote
processes called controllers.
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Introduction
• There are some solutions for virtualization in SDN infrastructure, the
most popular are OpenFlow, FlowVisor and FlowN.
• With virtualization, slices represent for networks in SDN. Each slice
has a slice policy defining its resources and the controller associated
with it.
• Slices of the network can be used for many different purposes
depending on what the owners are trying to accomplish. Services or
experiments that run on these slices may display a wide variety of
resource requirements.
• A slice along with its controller as a virtual network (VN) in SDN. As
VNs get bigger and the number of VNs increases, resource contention
may become a problem.
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Introduction
• Embedding VNs within a network virtualization environment is an
important problem (substrate network providers are decoupled from
VN providers that deploy and operate the VNs), because suboptimal
mappings can cause bad performance and/or higher operating cost.
• Solutions that strive for well-balanced and resource-efficient VN
mappings have been proposed by researchers.
• This study designs embedding techniques for VNs in the SDN
environment along with two goals : balancing the load on substrate
nodes and links, and maintaining low delay between controllers and
switches in all VNs.
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Related work
• SDN is a suitable platform for network virtualization and researchers
have been working on ways to provide virtualization to enable the
coexistence of multiple VNs in the SDN environment.
• OpenFlow has been extensively used as a uniform interface between
the control and data planes in SDN.
• FlowVisor, a special purpose OpenFlow controller that can create
slices of network resources and place each slice under the control of a
different OpenFlow controller.
• FlowN utilizes virtualization to run a modified version of the
controller and also maps API calls between the physical and virtual
networks, but it does not employ a separate controller for each VN.
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Related work
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Related work
• VN embedding with node and link constraints is a complex problems.
• Each VN on an SDN-based substrate possesses its own controller, and
there are requirements and considerations that come with the
existence of this controller.
• The controller is responsible for organizing the operation of the VN
by sending routing updates, traffic engineering policies etc. and needs
to react quickly to faults in the network.
• The controller also must be able to communicate effectively to all the
switches that are part of the VN, so any VN embedding effort needs
to make sure all controller-to-switch channels avoid congestion and
high delays.
• The ease of customizing packet routes in SDN presents an additional
degree of freedom in VN embedding.
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Related work
• The distinctions of the SDN environment (such as the centrality and the importance of the controller, and differences in the virtualization technology) make VN embedding become a new challenge.
• The mapping of the virtual components to substrate components and the placement of the controllers are both important variables influencing the performance of the VNs in such a system. Efficient utilization of networks resources, low risk of congestion, reliability and fast response are all desirable properties.
• With those problems, this study designs a stress-balancing VN assignment algorithm to consider the stress-balancing on the substrate network, one of two VN embedding objectives.
• Another is minimizing the average and maximum delays from the controller to the switches.
• The placement of controllers at predetermined location or free, the topology of each VN, as well as the mapping of that topology to the SDN substrate is also determined.
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Model and problem statement
• SDN Resources
• Virtualization in SDNs requires a mechanism to share network
resources among multiple slices.
• FlowVisor presents some essential network resources:
• Switch CPU: Sharing power between slices at switches is considering by
two main tasks performed for each slice: generating new flow messages to
be sent to the corresponding controller, and handling controller requests
regarding the slice. CPU power demands at a switch increase with the
number of VNs and links at mapped to it/traversing it.
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Model and problem statement
• Bandwidth: Each slice has its own queue at each port, and these queues are
serviced according to the resource allocation policy. Balancing the
numbers (the number of virtual links that share a substrate link and the
number of controller-to-switch connections that must go over this link)
across the substrate is useful to avoid potential hot spots and reduce the
possibility of congestion.
• Flow entry space: The number of flow entries that can be used by each
slice is also limited at each switch. When a controller is over its limit, it is
not allowed to insert any new rules at the switch. Consider the number of
virtual links traversing a substrate node as part of the load on that node.
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Model and problem statement • VN embedding problem
• Assume underlying SDN infrastructure as the network substrate and model it as a graph (V, E), where V is set of substrate nodes and E is set of substrate links.
• While there are many VNs sharing the underlying SDN infrastructure, the two important problems are determined:
(a) deciding which switches to include in a slice.
(b) how to configure the routing within the slice.
• Focus on controller placement and VN embedding.
• Consider two options for each VN: the VN embedding with fixed-location controller (VNE-F) and the VN embedding with adjustable-location controller (VNE-A).
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Model and problem statement • With a substrate node (the number of virtual nodes) and a substrate link
(the number of virtual links), we concentrate on the stress (as a measure of VN embedding load) through two definitions : node stress and link stress.
• For node stress, we take into account the additional CPU power and flow entry space load that comes from virtual links that traverse a node.
• Assume SN (v) be the stress of a substrate node v V, then:
where nN (v) is the number of virtual nodes assigned to it,
nL (v) is the number of virtual links traversing it,
α and β are two positive parameters.
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Model and problem statement
• For link stress, we add a component for the total load due to all the
controller-to-switch communications going over a particular link.
• Total link stress is the sum of data traffic stress and control traffic
stress.
• Assume SL (e) be the stress of substrate link e E, then:
where Ci (e): the number of controller-to-switch connections traversing
link e in the ith VN out of numV - total VNs in the system,
0 ≤ γi ≤ 1: each controller-to-switch connection contributes γi to the
stress of each link on the path.
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Model and problem statement
• Let Slidei be the ith slice sharing a network of switches. The virtual topology
of this slice, VTi , defines the nodes and links included in this slice. VTi is
described as a graph (V’i , E’i), where V’i is the set of virtual nodes, and E’i is
the set of virtual links. This slice, along with its controller Ci , constitute
virtual network Ni .
• Assume the virtual topology of all numV VNs, and the location of each Ci is
fixed or adjustable, the VN embedding must be designed to organize all VNs
in such a way that:
(a) minimize the maximum stress on a switch or link while keeping all
controller-to-switch delays under a threshold R
(b) minimize the average controller-to-switch delay for each Ni while
keeping the maximum stress under a threshold T.
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Conclusion
• This research presented the virtual network (VN) embebding
problems in SDN environment. Thus, it proposed a design of
new embedding techniques in an effort to consider VN
embebding and SDN controller placement together, that focus
on two main objectives:
• Minimizing the controller-to-switch delay
• Balancing the load on substrate nodes and links.
• From this research, the further study can be developed related to
the VN reconfiguration in SDN, the controller placement,
virtual node mapping and virtual link mapping stages.
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References
• Mehmet Demirci, Mostafa Ammar, “Design and analysis
of techniques for mapping virtual networks to software-
defined network substrates”, Comput. Commun. (2014).