Analysis of Inter-regional Relationship among Regional Tier-1 ASes in the Internet

The ASes on the Internet are considered to be in a hierarchical structure and are called Tier 1, Tier 2 and Tier 3 from the upper level. ASes ranked at the same Tier are believed to be in an equal relationship (a peering relationship). A subset of Tier 2 is generally regarded as Regional Tier 1 which can obtain almost all route information in a specific region without receiving them from Tier-1 ASes. The scale and the target customers of Regional Tier-1 ASes are different by the region, and such factors may result in an unequal relationship when Regional Tier-1 ASes in two countries are connected. In this paper, we analyze the connection between ASes considered as Regional Tier 1 in two countries, assuming that the target region of Regional Tier 1 is one country. Firstly, we proposed the method to identify the Regional Tier-1 ASes in each country. Next, we examined the relationships between Regional Tier-1 ASes in six countries, the top five countries with the largest number of ASes and Japan, and we confirmed that there were some connections in the transit relationships. We also found that an AS becomes a provider of many foreign Regional Tier-1 ASes, and that an AS peers with small ASes but provides transit to larger ASes in foreign countries.