Google Global Cache (GGC) Operations for YouTube (Part 1. KT)
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Google Global Cache (GGC) Operations for
YouTube (Part 1. KT)
April 16, 2012 | By Chris (email@example.com) | Netmanias Tech-Blog | www.netmanias.com
We are going to present you workflow that shows how a YouTube video is downloaded to a subscriber
device via Google Global Caches installed in LG U+ IP network. Below, we will look at downloading over
the KT IP network, which has no Google Global Cache installed in it.
In the subsequent post, downloading procedures in the LG U+ IP network, which has Google Global
Caches installed in it, will be discussed using two different cases - on a Cache Hit and on a Cache Miss (i.e.
when a Google Global Cache has a video requested and when it does not).
YouTube Downloads over the KT IP Network
We assumed a network configured as follows for the purposes of this post:
On the grey board in the left [Google Server (USA)]: YouTube server (www.youtube.com) and
Google Global Cache (o-o.preferred.lax04t01.v1.lscache6.c.youtube.com) located in US
On the grey board in the right [KT Network (Korea)]: A KT subscriber connected to KT IP network
On the grey board in the middle [Transit]: Transit network that connects KT IP network to a IP
network in US
1 DNS Query
2 DNS Response
4 HTTP GET
3 Click “Avatar”
in YouTube page
Request Video = Avatar
6 HTTP Response
Download Server Hostname = o-o.preferred.lax04t01.v1.lscache6.c.youtube.com
5 Check User IP address:
7 DNS Query
If (User IP addr is LG U+ range)
Assign “LG U+ Google Cache”
Assign “Google Cache in USA”
8 DNS Response
9 HTTP GET
Request Video = Avatar
10 Video (Avatar) Download
RTT = 200ms
PC KT Subscriber
Google Server (USA)
KT Network (Korea)
Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 1. KT)
1. The KT subscriber enters www.youtube.com into his browser to access a YouTube server. The
subscriber device sends a DNS query to a KT DNS server (the DNS server doesn't have to be a KT
DNS server) to obtain the IP address of the YouTube server.
2. The KT DNS server gives the subscriber device the IP address of the YouTube server (i.e.
3. The subscriber accesses the YouTube server and clicks "Avatar" on YouTube.
4. The subscriber device sends a HTTP GET message to the YouTube server to request an Avatar
5. This is the most important step of the process. The YouTube server checks the IP address of the
subscriber device when it receives the HTTP GET message. This step is to check whether or not
the IP address of a device is within the range assigned to an operator who has Google Global
Caches installed in its network. In this example, KT has no Google Global Cache in its network.
6. Therefore, the YouTube server gives the hostname of a Google Global Cache located in US (i.e. oo.preferred.lax04t01.v1.lscache6.c.youtube.com) to the subscriber device.
7. The subscriber device performs a DNS query about hostname = oo.preferred.lax04t01.v1.lscache6.c.youtube.com.
8. As a result of the query, the subscriber device receives an IP address of 18.104.22.168, which is
the IP address of the Google Global Cache located in US.
9. Now, the subscriber device sends a request for the video to the server at 22.214.171.124.
10. The subscriber downloads the video from the Google Global Cache (presumably located in LA
since the hostname has "lax"). The RTT between two countries is very high - about 200 ms.
Besides, if there is heavy traffic (e.g. in the evening), buffering will be severe. Severe enough to
keep the subscriber from watching the video.