I’m working hard to speed up communication every day, but it can be amazing how late I go through when access from Japan to China is slow! Moreover, sometimes it is said that the route via Korea is early or sometimes the route does not match with the geography. So, I lowered the layer considerably this time and examined it from the submarine cable level.
Submarine cable situation in Japan
Below is a diagram of the seabed cable around Japan.
As you can see from this alone, many cables are laid in the East China Sea. There are several routes from Japan to China, but one example is EAC-C2C cable that passes through Shima and Chikura, which are heavily looped considering redundancy, and one as much as possible considering recent delay values. There are SJC etc.
<EAC-C2C Cable Diagram>
<SJC cable diagram>
The starting point of the submarine cable on the Japanese side is approximately threefold Shima LS or Chikura or Maruyama LS on the Kujukuri side of Chiba.
The reason for this is that Japanese ISP communication is concentrated on Osaka Dojima or Tokyo Otemachi and then headed to each LS, so it inevitably becomes the nearest Mie or Chiba from there. Kyushu and Okinawa are geographically closer to China, but the route is to go to Osaka once and head to Mie, or go to Tokyo and head to Chiba, then finally enter the submarine cable and turn back to China. It’s back and forth traffic.
Moreover, on each carrier side, there are interconnections and communication is allocated to various submarine cables, so there are cases where it can not only go along the shortest route, but sometimes it makes a big turn.
About Chinese transmission conditions – Why latency occurs.
In China, because there are territories where their carriers are strong, one has to consider that this creates latency in areas between northern and southern China. (see the diagram below). In addition, the “great firewall” on the LS on the Chinese side creates further difficulties.
This is the main reason for transmission latency in China.
<National carrier power relationships in China>
If you struggle to imagine the transmission route to China, it is easier to think about the route on this level. The situation can change drastically with your reciprocal ISP connection and whether it is goes around the Osaka or Tokyo route, or takes the shortest route, and lastly which carrier territory in China you are in.
Next, we calculate the degree of performance improvement if we use the shortest route and set a specific bypass route in each city in China to prevent transmission limits.
Here is the result of the calculation. The latency decreases roughly 1/3 with stabilization.
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