Estimating Minimum Sum-rate for Cooperative Data Exchange

This paper considers how to accurately estimate the minimum sum-rate so as to reduce the complexity of solving cooperative data exchange (CDE) problems. The CDE system contains a number of geographically close clients who send packets to help the others recover an entire packet set. The minimum sum-rate is the minimum value of total number of transmissions that achieves universal recovery (the situation when all the clients recover the whole packet set). Based on a necessary and sufficient condition for a supermodular base polyhedron to be nonempty, we show that the minimum sum-rate for a CDE system can be determined by a maximization over all possible partitions of the client set. Due to the high complexity of solving this maximization problem, we propose a deterministic algorithm to approximate a lower bound on the minimum sum-rate. We show by experiments that this lower bound is much tighter than those lower bounds derived in the existing literature. We also show that the deterministic algorithm prevents from repetitively running the existing algorithms for solving CDE problems so that the overall complexity can be reduced accordingly.Comment: 6 pages, 6 figure

Iterative Merging Algorithm for Cooperative Data Exchange

We consider the problem of finding the minimum sum-rate strategy in cooperative data exchange systems that do not allow packet-splitting (NPS-CDE). In an NPS-CDE system, there are a number of geographically close cooperative clients who send packets to help the others recover a packet set. A minimum sum-rate strategy is the strategy that achieves universal recovery (the situation when all the clients recover the whole packet set) with the the minimal sum-rate (the total number of transmissions). We propose an iterative merging (IM) algorithm that recursively merges client sets based on a lower estimate of the minimum sum-rate and updates to the value of the minimum sum-rate. We also show that a minimum sum-rate strategy can be learned by allocating rates for the local recovery in each merged client set in the IM algorithm. We run an experiment to show that the complexity of the IM algorithm is lower than that of the existing deterministic algorithm when the number of clients is lower than $94$.Comment: 9 pages, 3 figure

Using Tuangou to reduce IP transit costs

A majority of ISPs (Internet Service Providers) support connectivity to the entire Internet by transiting their traffic via other providers. Although the transit prices per Mbps decline steadily, the overall transit costs of these ISPs remain high or even increase, due to the traffic growth. The discontent of the ISPs with the high transit costs has yielded notable innovations such as peering, content distribution networks, multicast, and peer-to-peer localization. While the above solutions tackle the problem by reducing the transit traffic, this paper explores a novel approach that reduces the transit costs without altering the traffic. In the proposed CIPT (Cooperative IP Transit), multiple ISPs cooperate to jointly purchase IP (Internet Protocol) transit in bulk. The aggregate transit costs decrease due to the economies-of-scale effect of typical subadditive pricing as well as burstable billing: not all ISPs transit their peak traffic during the same period. To distribute the aggregate savings among the CIPT partners, we propose Shapley-value sharing of the CIPT transit costs. Using public data about IP traffic of 264 ISPs and transit prices, we quantitatively evaluate CIPT and show that significant savings can be achieved, both in relative and absolute terms. We also discuss the organizational embodiment, relationship with transit providers, traffic confidentiality, and other aspects of CIPT

Self-enforcing trade agreements: evidence from antidumping policy

This paper empirically examines how governments make trade policy adjustments under a self-enforcing trade agreement in the presence of economic shocks. Using data on US antidumping (AD) policy formation between 1997-2006, we find that US antidumping policy is often consistent with the time-varying “cooperative” tariff increases modeled in the self-enforcing trade agreement of Bagwell and Staiger (1990). Estimates of an empirical model of US antidumping indicate that the likelihood of a US antidumping duty is increasing in the size of the unexpected import surge, decreasing in the volatility of imports and decreasing in the elasticities of import demand and export supply. This suggests that time-varying increases in US tariff rates under antidumping policy could be interpreted as “cooperative” tariff increases that support a self-enforcing trade agreement facing an unexpected import surge.Antidumping duties ; Tariff

Which interest rate scenario is the worst one for a bank? Evidence from a tracking bank approach for German savings and cooperative banks

Interest income is the most important source of revenue for most of the banks. The aim of this paper is to assess the impact of different interest rate scenarios on the banks' interest income. As we do not know the interest rate sensitivity of real banks, we construct for each bank a portfolio with a similar composition of its assets and liabilities, called 'tracking bank'. We evaluate the effect of 260 historical interest rate shocks on the tracking banks of German savings banks and cooperative banks. It turns out that a sharp decrease in the steepness of the yield curve has the most negative impact on the banks' interest income. -- Der Zinsüberschuss ist für die meisten Banken die wichtigste Ertragsquelle. Stresstests in Bezug auf den Zinsüberschuss sind daher von wesentlicher Bedeutung. Die einzelnen Banken können solche Stresstests relativ einfach durchführen, weil ihnen die notwendigen Informationen (zukünftige Zahlungsströme und die Laufzeitstruktur der Forderungen und Verbindlichkeiten) vorliegen. Au?enstehende dagegen müssen die Laufzeitstruktur der Forderungen und Verbindlichkeiten auf Grundlage von Aktienkursänderungen oder Jahresabschlüssen schätzen.Interest Rate Risk,Stress Testing