Behind the Curtain: The importance of replica selection in next generation cellular networks

John P. Rula, and Fabián E. Bustamante
Poster in ACM Sigcomm, August 2014.

EECS Department
Northwestern University
Evanston, IL 60201, USA
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WINNER SIGCOMM 2014 Student Research Competition - Graduate


Smartdevices are becoming the primary or only Internet point of access for an ever larger fraction of the population. Nearly a quarter of current web traffic is mobile, and recent industry studies have estimated a fourfold increase on global mobile data traffic by 2018, mainly driven by the content demands and growing number of smart phones and tablets [2]. The most recent CISCO VNI report estimates that by 2018, the majority of North America devices and connections will have 4G capability and, while 4G will be 15% of world-wide connections then, these connections will be responsible for 51% of traffic.

Cellular networks pose a challenge to content delivery networks (CDNs) given their opaque network structure, limited number of ingress points, and obfuscated DNS infrastructure. Previously, large cellular radio latencies meant CDN replica selection had little impact on the total end-to-end latency. However, the advancement of 4G networks such as LTE has lowered mobile device access latency to make it comparable with many existing broadband services, making the choice of content replica server a significant contributor to end-to-end performance. In general, but particularly in cellular networks, CDNs have limited signals for locating clients. Mobile IPs have been shown to be dynamic for mobile end hosts [1], and external entities such as CDNs are prevented from probing their mobile clients or their infrastructure by NAT and firewall policies implemented by cellular operators.

In this poster, we present preliminary work looking at the impact of replica selection in next generation cellular networks. Using a collection of over 250 mobile end-hosts over a two-month period, we explore CDN replica selection in cellular networks measuring the latency to content replicas for a selection of popular mobile websites. We find that clients in next generation radio technologies can see up to 400% differences in latency to selected replicas. We discover that, in large part, these poor selections are due to current localization approaches employed by CDNs such as DNS redirection which, while fairly effective in wired hosts, performs rather poorly within cellular networks mainly due to cellular DNS behavior.