This paper looks at CDN networks and, in particular, suggests Provider-aided Distance Information System (PaDIS), which is a mechanism to rank client-host pairs based upon information such as RTT, bandwidth or number of hops. Headline figure, 70% of http traffic from a major european ISP can be accessed via multiple different locations. “Hyper giants” are defined as the large content providers such as google, yahoo and CDN providers which effectively build their own network and have content in multiple places. Quote: “more than half of the total traffic, including the dominant HTTP traffic, can be delivered in principle from multiple servers at diverse network locations based on obser- vations from passive packet-level monitoring” also “there is choice between at least two subnets over 40% of the time”.
Data: 1 day anonymised packet trace from large European ISP, 2 weeks of http data and 5 days of DNS data from same ISP. “HTTP alone contributes almost 60% of the overall traffic at our vantage point, BitTorrent and eDonkey contribute more than 10%.” Popularity of requests has a Zipfian distribution.
Figure 3 shows how a particular DNS resolver returns different results according to the type of content – in particular, a media server does load balancing using the DNS resolver. Two techniques can be used to map a DNS request to many IP addresses, either Multquery (one query returns several addresses) or Crossquery (repeated queries return different addresses).
A table is given which attempts to assess the proportion of http requests which could potentially be served within the ISPs own network depending on which DNS server the user uses (ISPs own, OpenDNS or GoogleDNS). The table has columns for “observed” (amount of content served which is within ISP network) and “potential” (amount which could be if DNS were more clever about addresses returned).
PaDIS allows optimisation based on delay (for small volume websites) or bandwidth (for bulk transfers) and it can be used as an ALTO server for localising P2P. PaDIS can reorder DNS responses according to these preferences for better use of network resources.
Experiments are performed from ten “vantage points” (presumably researchers and machines owned by them?). The PaDIS recommended server is compared with the CDN recommended one for speed of download at given times of day. PaDIS is shown to select servers with better download speeds.
Analysis is performed on One Click Hosts (OCH) and Video Streaming Providers as well. “Video streaming via HTTP is popular and accounts for more than 20% of the HTTP traffic.” “the most popular OCH… is responsi- ble for roughly 15% of all HTTP traffic” The conclusion is that OCH and VSP traffic could potentially be served from several servers.
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