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Efficient big link allocation scheme in virtualized software-defined networking

2017 13th International Conference on Network and Service Management (CNSM) IEEE, Tokyo, Japan, 2017, pp. 1-7, doi: 10.23919/CNSM.2017.8256020.

Wontae Jeong, Gyeongsik Yang, Seong-Mun Kim, Chuck Yoo

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Abstract

We propose an efficient resource allocation scheme for big links in virtualized software-defined networking. Network virtualization based on software-defined networking provides big link concept to facilitate simple network management - big link maps a set of switches and links into a single virtual link. However, this paper reports an issue of the big link in that there is a severe performance degradation in virtualized SDN environments. We find the cause: the existing network hypervisors do not consider the network traffic when allocating physical resources to a big link. To address this issue, we present big link allocation scheme (BAS) that considers network traffic when allocating and reallocating resources to a big link. A prototype implementation is done with OpenVirteX, and experiments demonstrate that the big link with BAS achieves four times greater throughput than that of the big link without BAS. Moreover, by including a timer in OpenVirteX, the BAS decreases unnecessary resource reallocations, which reduces overhead.

Paper summary

Allocate virtual links against current physical traffic

A virtual link’s physical route should account for topology and available capacity.

A big link abstracts several physical links into one virtual connection. BAS postpones physical allocation until traffic arrives and revisits the allocation when other tenants change the load.

Delay allocation until traffic arrives, then revise it

Initialization creates the virtual link endpoints without fixing a physical route. When traffic arrives, BAS selects resources using monitored physical-link load. Soft reallocation handles opportunities between flows, while hard reallocation revisits active assignments. The implementation installs a new forwarding policy before removing the old one and orders rule changes to limit packet loss. It also evaluates an asynchronous alternative that handles packets arriving during rule replacement.

When BAS assigns or revisits a big link’s physical route.
OperationTiming
Initial allocationWhen traffic arrives
Soft reallocationBetween flows
Hard reallocationWhile assignments are active

Adapt the big link when another tenant adds traffic

The OpenVirteX prototype is evaluated with two virtual networks in Mininet: one adds competing load and the other uses the big link. Under the heavier initial bottleneck loads, BAS achieves 2.7–3.8 times the throughput of OpenVirteX in the reported test; at lighter loads, the results are similar. When competing traffic starts later, reallocation restores much of the big link’s throughput. The experiments also assess packet loss and throughput fluctuation during route changes. A guaranteed bandwidth or latency service is left for future work.

Big-link throughput over time for OpenVirteX and BAS when competing traffic begins.View full-size figure
Competing traffic starts at 30 seconds. BAS reallocates the big link and restores throughput, while the unchanged OpenVirteX allocation remains constrained.

Key takeaways

  1. A virtual link’s best physical allocation depends on current contention. BAS delays allocation until traffic arrives and revisits it as other tenants change the load.
  2. Reallocation is part of maintaining the abstraction. Coordinated rule replacement lets the big link recover throughput when the original route becomes constrained.