Presenter: Dongsu Han
Introduction/Motivation
The talk was about the flexible framework for network resource
allocation, called FCP, that accommodates diversity by exposing a simple
abstraction for resource allocation.
Congestion control is concerned about resource allocation,
which requires coordination among all participants to ensure high utilization
and fairness. Two different styles of
congestion control cannot co-exist as they interfere with each other’s resource
allocation. There are two congestion
control policies: end-to-end based (TCP) and router-assisted (XCP, RCP). End-point based systems like TCP provides
flexibility to deploy different algorithms and the notion of TCP friendliness
provides a mechanism for co-existence between different algorithms and
behaviors. But router-assisted
congestion control is more efficient than TCP in achieving high utilization, small delays and faster flow completion times.
So, the presenter presents the congestion control protocol – FTP, which
combines the best of both the worlds.
System
They designed a protocol, which allows each domain to
allocate resources (budget) to a host and make networks explicitly signal the
congestion price. To ensure safe co-existence of different end-point resource
allocation strategies, the system maintains a key invariant that the amount of
traffic a sender can generate is limited by its budget, which is the maximum
amount it can spend per unit time.
Each sender (host) is assigned a budget ($/sec), the amount,
which it can spend per unit time. At the start of the flow, sender allocates
part of its budget to the flow taking into account the traffic demands and
application objectives. The rate of each
flow generated by the sender is equal to the budget allocated to it divided by
the price for the path that the flow is traversing. The network determines the congestion price
($/bit) for the each flow in the form of the feedback. The price of the path
traversed by a flow is the sum of link prices.
The also talked about preloading which helps in increasing
or decreasing the budget amount per flow on a packet-by-packet basis.
Evaluation
They compared FCP with other schemes (XCP and RCP) using
packet level simulations. FCP convergence is faster than the other two for long
running flows. Average bottleneck link
utilization was 99% with FCP, 93% with XCP and 97% in case of RCP. FCP handles
mixed flow sizes much more gracefully and efficiently than RCP.
Conclusion
FCP accommodates diverse behaviors in resource allocation
while utilizing explicit feedback. FCP maximizes end-point flexibility by
simplifying the mechanism of coexistence. FCP’s explicit feed-back and
feed-forward provides a generic interface for efficient resource allocation.
Q: How do you allocate budget to a new flow?
A: We take from
the existing flows and allocate to the new flow.
Q: If you are aware of RUCN? And how is your
approach different than them?
A: We use the
similar idea where we attach the previous price to the packet header and the
routers extract the price. But the
difference is that they are allocating budget over a long period of times like
a month or billion periods but we allocate it for shorter duration. And here
the unit is $/sec, with every second you get this budget, the constant
streaming rate of budget, that’s the difference!
Q: Why can’t you
achieve coexistence using multiple queues?
A: Because that
is not scalable.
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