Q2. What sources are used to build the IXP list?
The IXP list is comprised of prefix lists collected from Packet Clearing House (PCH) [1], PeeringDB [2] and additional manually collected sources.
Q3. What is the main reason why content providers are becoming more dominant?
In addition to saving transit costs, content providers increase their offerings to customers by providing Software as a Service (SaaS), such as hosting, cloud services, collaboration tools and others, without worrying for network neutrality violations or other traffic shaping that can interfere with the service grade they provide.
Q4. How many months of active traceroutes did the authors create?
In this paper the authors create a snapshot of the AS-level graph every 3 months, using a month of active traceroutes, from late 2006 till early 2011.
Q5. What are the connectivity trends of content providers?
The connectivity trends indicate that content providers increase the number of neighbors and diversify their types and geographical spread.
Q6. What is the definition of the nucleus?
The nucleus (or core) is the shell with the highest index, which is considered to contain top level providers, mostly tier-1 transit networks.
Q7. What is the effect of being close to the nucleus?
For a content provider, being close to the nucleus has direct capital effect, because the higher the shell a network is located in, the less it needs to be a paying customer of transit networks [11], mainly since it does not need transit services in order to reach most other customer networks.
Q8. What is the CC of a vertex in a graph?
More formally, the CC of a vertex in a graph is the number of triangles it forms with its immediate neighbors out of the potential number of triangles.
Q9. What is the recent study of the inter-domain traffic?
Most recently, Labovitz et al. [16] performed a large-scale two-year study of the inter-domain traffic, showing that the amount of traffic originated from content providers is rising, and most of it is routed outside of the traditional Internet core.
Q10. What is the trend of the assortativity coefficient?
Analysis of the trend of the assortativity coefficient indicates that the AS-graph becomes slightly less disassortative, partly indicating that ASes increase their connections with other similar-degree ASes.
Q11. What is the density of the graph?
Given a graph G = (V,E), the density D of the graph is defined as the number of existing links out of the number of potential links, i.e., D =2|E| |V |(|V |−1) .
Q12. What is the role of the key Internet players?
The appearance and rapid growth of large content providers, such as Google, Yahoo! and others, is gradually changing the roles of key Internet players to accommodate their needs.
Q13. What can be the reason for the decrease in the neighbor degree of the transit networks?
This can be an indication that small customers are disconnecting from the transit networks, or alternatively, that the tier-1 neighbors are becoming better connected, hence increase their degree.
Q14. Why does iPlane suffer from vantage point churn?
Although DIMES, due to its diverse distribution, uncovers more links than iPlane [25], it suffers from vantage point churn, making its observed topology more “noisy” and susceptible to measurement artifacts.
Q15. What is the effect of measurement errors on the AS graph?
the effect of measurement errors [3], errors in the IP to AS translation [21, 22], and similar inaccuracies, which are discussed in the measurement literature, are not significant for this study since they can not affect trends.
Q16. How many IXPs are used by content providers?
Although both transit and content providers exhibit a rising trend, the percentage of IXP links used by content providers is significantly higher, reaching almost 40% of their links, indicating that content providers indeed embrace IXPs as method for increasing connectivity.
Q17. What is the difference between ASes in the first and kth shells?
In the AS graph, ASes in the first shell are those who have only one link leading to the ‘center’ ofthe graph, whereas ASes in the kth shell have k-connectivity towards the center.
Q18. What is the significance of the potential load on an AS?
Approximating the potential load on an AS is an estimate of its importance, since it indicates that an AS serves many other ASes for routing packets [19].