3,190 research outputs found
On the Feasible Scenarios at the Output of a FIFO Server
We consider the case of a FIFO multiplexer fed by flows that are individually constrained by piecewise linear concave arrival curves. We show that, contrary to what happens at the input, at the output not all valid scenarios in accordance with the worst case arrival curves can occur. This implies that taking an iterative approach to characterize the arrival curves at the output when flows pass throughout several FIFO nodes is suboptimal (in the sense that, although valid, they do not necessarily have to be the best arrival curves that can be found)
Revisiting Size-Based Scheduling with Estimated Job Sizes
We study size-based schedulers, and focus on the impact of inaccurate job
size information on response time and fairness. Our intent is to revisit
previous results, which allude to performance degradation for even small errors
on job size estimates, thus limiting the applicability of size-based
schedulers.
We show that scheduling performance is tightly connected to workload
characteristics: in the absence of large skew in the job size distribution,
even extremely imprecise estimates suffice to outperform size-oblivious
disciplines. Instead, when job sizes are heavily skewed, known size-based
disciplines suffer.
In this context, we show -- for the first time -- the dichotomy of
over-estimation versus under-estimation. The former is, in general, less
problematic than the latter, as its effects are localized to individual jobs.
Instead, under-estimation leads to severe problems that may affect a large
number of jobs.
We present an approach to mitigate these problems: our technique requires no
complex modifications to original scheduling policies and performs very well.
To support our claim, we proceed with a simulation-based evaluation that covers
an unprecedented large parameter space, which takes into account a variety of
synthetic and real workloads.
As a consequence, we show that size-based scheduling is practical and
outperforms alternatives in a wide array of use-cases, even in presence of
inaccurate size information.Comment: To be published in the proceedings of IEEE MASCOTS 201
Sprinklers: A Randomized Variable-Size Striping Approach to Reordering-Free Load-Balanced Switching
Internet traffic continues to grow exponentially, calling for switches that
can scale well in both size and speed. While load-balanced switches can achieve
such scalability, they suffer from a fundamental packet reordering problem.
Existing proposals either suffer from poor worst-case packet delays or require
sophisticated matching mechanisms. In this paper, we propose a new family of
stable load-balanced switches called "Sprinklers" that has comparable
implementation cost and performance as the baseline load-balanced switch, but
yet can guarantee packet ordering. The main idea is to force all packets within
the same virtual output queue (VOQ) to traverse the same "fat path" through the
switch, so that packet reordering cannot occur. At the core of Sprinklers are
two key innovations: a randomized way to determine the "fat path" for each VOQ,
and a way to determine its "fatness" roughly in proportion to the rate of the
VOQ. These innovations enable Sprinklers to achieve near-perfect load-balancing
under arbitrary admissible traffic. Proving this property rigorously using
novel worst-case large deviation techniques is another key contribution of this
work
Tight arrival curve at the output of a work-conserving blind multiplexing serve
As a means of supporting quality of service guarantees, aggregate multiplexing has attracted a lot of attention in the networking community, since it requires less complexity than flow-based scheduling. However, contrary to what happens in the case of flow-based multiplexing, few results are available for aggregate-based multiplexing. In this paper, we consider a server multiplexer fed by several flows and analyze the impact caused by traffic aggregation on the flows at the output of the server. No restriction is imposed on the server multiplexer other than the fact that it must operate in a work- conserving fashion. We characterize the best arrival curves that constrain the number of bits that leave the server, in any time interval, for each individual flow. These curves can be used to obtain the delays suffered by packets in complex scenarios where multiplexers are interconnected, as well as to determine the maximum size of the buffers in the different servers. Previous results provide tight delay bounds for networks where servers are of the FIFO type. Here, we provide tight bounds for any work-conserving scheduling policy, so that our results can be applied to heterogeneous networks where the servers (routers) can use different work-conserving scheduling policies such as First-In First-Out (FIFO), Earliest Deadline First (EDF), Strict Priority (SP), Guaranteed Rate scheduling (GR), etc
Cross-Layer Optimization of Fast Video Delivery in Cache-Enabled Relaying Networks
This paper investigates the cross-layer optimization of fast video delivery
and caching for minimization of the overall video delivery time in a two-hop
relaying network. The half-duplex relay nodes are equipped with both a cache
and a buffer which facilitate joint scheduling of fetching and delivery to
exploit the channel diversity for improving the overall delivery performance.
The fast delivery control is formulated as a two-stage functional non-convex
optimization problem. By exploiting the underlying convex and quasi-convex
structures, the problem can be solved exactly and efficiently by the developed
algorithm. Simulation results show that significant caching and buffering gains
can be achieved with the proposed framework, which translates into a reduction
of the overall video delivery time. Besides, a trade-off between caching and
buffering gains is unveiled.Comment: 7 pages, 4 figures; accepted for presentation at IEEE Globecom, San
Diego, CA, Dec. 201
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