1. Joint Topology Design and Mapping of Service Function Chains for Efficient, Scalable, and Reliable Network Functions Virtualization
By,
Z – jie meng
Z – Zaid Ahmed Khan
Z – Yixin Liu
Z – yue cao

2. Summary
Introduction to Virtual network functions and software defined networking topology design and mapping in a telecom cloud. Mapping problems
To solve the JTDM problem, there is an algorithm called CCMF which can leverage the feedback from mapping the critical sub-topologies.
For the scalable and reliable of the JTDM system, two algorithms are mentioned in this presentation and three major protection types a discussed based on their total bandwidth consumption and system reliability
There are still many open challenges in order to make JTDM fit for optical network. In real-world telecommunication, we still need to think more about security and availability of JTDM.

3. Introduction
Software Defined Networking (SDN) is an architecture that is manageable, cost-effective, and adaptable, making it ideal for the high-bandwidth nature of today’s applications.
Network Function Virtualisation (NFV) offers a new way to design, deploy and manage networking services. NFV focuses on optimizing the network services themselves.
With new advancements in NFV’s, traditional hardware-based network appliances are replaced by software-based Virtual Network Functions (VFN) which can run in Telecom Clouds (TC) to yield lower cost and faster deployment
Network Forwarding Path (NFP) shows the path for the actual traffic flow in the virtual links of a network
We address scalable and reliable Joint Topology Design and Mapping (JTDM) strategies to reduce network reconfigurations and enhance service reliability.

4. Topology design and mapping
The figure shows us the layout of the Topology design and mapping in Telecom Clouds.
Many initiatives have been taken by telecom companies such as Europe Telecommunications Standard Institute (ETSI), International Telecommunications Union (ITU) and so on but were not able to address the optimization problem of service function chains which we refer to Joint Topology Design and Mapping (JTDM) problem.
MRF: multimedia resource function
CS: Call session
CF: Control function
HSS: Home Server
MME: mobile mgmt. entity

5. Mapping problems
Virtual Network Mapping includes two important processes :
Virtual Node Mapping: Different virtual nodes are mapped to different substrate nodes.
Virtual Link Mapping: Requires a virtual link between two virtual nodes to be mapped onto a physical path in the substrate network.
As virtual network functions differ from each other in terms of their functionality and resource requirements, the provider needs to determine how to solve the following sub-problems :
Design an appropriate topology for each SFC where the function of an original VNF may be combined with another VFN into one virtual node.
Map the designed topology to the substrate Telecom Cloud (TC) network.

6. Joint Topology Design and Mapping problems are very different and much more challenging than the traditional Virtual network mapping problem primarily due to the two following factors :
JTDM allows many to one VNF mapping which is also called VNF combination. As Telecom Clouds are designed to support distinct network functions, some VFNs in the initial service function chain topology may be mapped to the same telecom cloud but not all VFNs can be combined and mapped due to a function restriction or conflict.
JTDM involves trade-offs due to VNF virtualization. For example, if two VNFs are combined we need to find out a way that less bandwidth is used in the telecom cloud for greater efficiency.
New advancements are being proposed such as Closed Loop with Critical Mapping Feedback (CCMF) to solve the JTDM problem with the objective of minimizing the total bandwidth consumption (TBC). Advancements in reconfiguring and improving the service reliability will reduce the TBC.

7. Joint topology design and mapping problems1
Distributed and Heterogeneous Telecom Clouds: A telecom cloud has a certain computing capacity and is equipped with a set of network functions. Each link in the TC has to be checked for the bandwidth capacity it is occupying. 2
SFC Requests: Each VNF requests some network functionality and computing resources and is also associated with a set of combinable partners that are VNFs from the same SFC request. 3
JTDM Process: The process consists of SFC topology design and SFC mapping. 4
VNF Combination Process: Each VNF may be combined with one or more of its partners and the combined VNF are the sum of computing requirements of each VNF. 5
SFC Mapping Process: Includes VNF mapping and virtual link mapping process

8. The Closed-Loop with Critical Mapping Feedback Algorithm

9. CCMF Purpose： To solve the JTDM problem. Basic idea：
To solve the JTDM problem. The basic idea is to leverage the feedback from mapping the critical sub-topologies (CSs) of an SFC to coordinate and jointly optimize VNF combination and SFC mapping.

10. Steps of CCMF algorithm:1
First, we find a set of CSs that can accurately estimate the cost of mapping the entire SFC
topology.
WHY？: the VNF combination may significantly affect SFC mapping.
HOW？: select the combined VNFs, the attached virtual links, and neighboring VNFs as the components of the CSs.

11. Steps of CCMF algorithm:2
Second, optimal VNF combination can be determined through feedback from CS mapping.
HOW？: a decision tree can be constructed according to the descending order of bandwidth saving.
NOTE:
“&” specifies combination and “|” specifies the absence of combination.
The one with the smallest mapping cost is selected.

12. Steps of CCMF algorithm:3
Finally, once the CSs have been mapped, the remaining non-critical components of the SFC topology are mapped.

13. Comparison with OMC OMC Algorithm
Who is this？: Open-Loop with Maximum Combination(OMC).
Basic idea: enumerate all the combination strategies and select the one with the maximum bandwidth saving to construct the SFC topology.
TBC increases with
the number of SFC requests for both CCMF and OMC.
The CCMF algorithm consistently outperforms the OMC algorithm,
particularly when the number of SFC requests is larger.

14. Scalable JTDM Requirement
Real-world network requirement
Computing and bandwidth demand a time varying SFC request
The reconfiguration of VNF combination and SFC mapping assignments
Two algorithms:
Periodically Re-Optimize (PRO)
Incremental Reconfiguration (IR)
Consider the Total Bandwidth Consumption and the number of network reconfigurations over time.

15. Periodically Re-Optimize (PRO)
Basic Concept:
Run the same JTDM algorithm at the beginning of each time slot.
Trade Off:
May achieve the minimum TBC over time
Cause a large amount of reconfigurations.
Frequent service interruption
Overhead problem

16. Incremental RECONFIGURATION (ir)
Aim:
To balance the performance between the TBC optimization and constant reconfiguration.
Scheme Steps:
Identify the SFC set which may increase the virtual bandwidth links and the physical links.
Design a strategy to reassign the VNF combination and SFC mapping which has been sorted out in step 1.
Reconfiguration these SFC requests and keep other (usually the majority) JTDM assignments unchanged.
Do not perform at each time slot or request individually.

17. Fig. 1. TBC and Configuration performance for each scheme
Comparison
Fig. 1. TBC and Configuration performance for each scheme

18. Reliable jtdm
In a real-world communication network, data-intensive and mission-critical network services request a high reliability performance. It is essential for the network operator to provide a reliable JTDM.
Three reliability schemes:
No Protection (NP)
Dedicated Protection (DP)
Shared Protection (SP)
Evaluation criteria:
TBC
Service reliability

19. 𝑎 𝑖 = 𝑛 𝑖 𝑝 ∈𝑁 𝑎 𝑛 𝑖 𝑝 . 𝑙 𝑖 𝑝 ∈𝐿 𝑎 𝑙 𝑖 𝑝 (1)
No protection scheme
Nothing to do about the system reliability
Reliability Equation:
𝑎 𝑖 = 𝑛 𝑖 𝑝 ∈𝑁 𝑎 𝑛 𝑖 𝑝 𝑙 𝑖 𝑝 ∈𝐿 𝑎 𝑙 𝑖 𝑝 (1)
N: TC sets;
L : Physical Link sets;
𝑎 𝑛 𝑖 𝑝 : Reliability of TC 𝑛 𝑖 𝑝 that host the VFNs 𝑛 𝑖 ;
𝑎 𝑙 𝑖 𝑝 : Reliability of physical link 𝑙 𝑖 𝑝 that the virtual link 𝑙 𝑖 route.

20. DEDICATED PROTECTION SCHEME
Concept:
For a given SFC request, pre-computing and reserve the backup resources. Thus, the backup resource will be disjoint from the primary resources.
Guarantee the node-disjoint between the primary and backup SFCs and the no-sharing backup physical resources.
Reliability Equation:
𝑎 𝑖 =1− 1− 𝑎 𝑖 𝑝 ∙(1− 𝑎 𝑖 𝑏 ) (2)
𝑎 𝑖 𝑝 : Primary SFC reliability;
𝑎 𝑖 𝑏 : Backup SFC reliability;
Algorithm Steps:
Provision the primary SFC;
Remove the assigned TCs and physical links;
Remove the computing and bandwidth resources assigned to other primary and backup SFCs;
The backup SFC would be provisioned.

21. Shared protection scheme
Concept:
To balance the performance trade-off between the optimal TBC and high reliability.
Reliability Equation:
𝑎 𝑖 = 𝑎 𝑖 𝑝 + 1− 𝑎 𝑖 𝑝 ∙ 𝑎 𝑖 𝑏 ∙ 𝜙 𝑖 (3)
𝜙 𝑖 =1− 𝑗≠𝑖 𝑀𝑇𝑇𝑅 𝑗 𝑀𝑇𝑇𝑅 𝑖 + 𝑀𝑇𝑇𝑅 𝑗 ∙(1− 𝑎 𝑗 ) (4)
𝑎 𝑖 𝑝 : Reliability of the primary SFC;
𝑎 𝑖 𝑏 : Reliability of the backup SFC;
𝜙 𝑖 : The probability that the shared backup resources can be assigned to the request 𝑖.

22. Shared protection scheme
Algorithm Steps:
Assign the primary SFC request using CCMF;
Remove all the primary SFC used physical TCs and links;
Remove the backup resources with primary SFCs which overlap the given SFC request;
Provision the backup SFC using CCMF.
Expected Results:
Backup infrastructure is node-disjoint with its primary infrastructure.
Backup resources can be shared with other backup infrastructures.

23. Fig. 2. TBC performance and reliability performance
SCHEME comparison
Fig. 2. TBC performance and reliability performance

24. Challenges JTDM in OFDM-based flexible grid optical networks
Upgrade-aware JTDM
Multicast service-oriented JTDM
Security-aware JTDM
SLA-based high availability JTDM

25. JTDM in OFDM-based flexible grid optical Network
Optical communication
Low latency and high bandwidth data transmission
More challenging to provision JTDM
Modulation format selection and spectrum allocation
Trade-off between efficiency, transmission reach and optical layer constraints

26. Upgrade-aware JTDM
Expand services by requesting one or more additional VNFs and virtual links
When reconfiguration is not allowed, avoid mapping an SFC request to a remote region
When reconfiguration is allowed, find the best way to reconfiguration

27. Multicast service-oriented JTDM
Big data application and large scale distributed file systems
Multicast tree topology design will highly affect total bandwidth consumption
Security Aware JTDM
Present a risk of information leakage whenever SFCs share disk and I/O resources

28. SLA-based high availability JTDM
Availability of JTDM assignment
Develop to meet a client’s SLA requirement

29. Conclusion
NFV enables an efficient way to manage the infrastructure resources.
CCMF algorithm adopts feedback from mapping and efficiently solve the JTDM problem
Efficient strategies for scalability and reliable JTDM
There are still many open challenges

30. Q&A

31. Reference
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Ye, Z. (2017). Efficient, Scalable and Reliable Network (Function) Virtualization in Software-Defined Optical Networks. [online] Ubir.buffalo.edu. Available at: [Accessed 19 Oct. 2017].
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