netmanias.2012.04.18.ggc operation for youtube (part 2. lg u+) (en)

7/18/2019 Netmanias.2012.04.18.GGC operation for YouTube (Part 2. LG U+) (en)

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NETMANIAS TECH-BLOG Please visit www.netmanias.com to view more posts

Google Global Cache (GGC) Operations for

YouTube (Part 2. LG U+)

April 18, 2012 | By Chris ([email protected]) | Netmanias Tech-Blog | www.netmanias.com

As noted in our previous post, we will present you workflow that shows how a YouTube video is

downloaded to an LG U+ subscriber device via Google Global Caches installed in the LG U+ Internet. First,

we will discuss the case when LG U+ Google servers have a video that has been requested by a subscriber

(Cache Hit). Then, we will discuss the case when none of the servers have it (Cache Miss).

YouTube Downloads over the LG U+ IP Network

(1) If an LG U+ Google Global Cache has a video requested (Cache Hit)

Except the fact the LG U+ network has Google Global Caches installed in its Internet Data Center (IDC),

the network is configured the same as in KT's case.

1. The LG U+ subscriber enters www.youtube.com into his browser to access a YouTube server. The

subscriber device sends a DNS query to an LG U+ DNS server (the DNS server doesn't have to be

an LG U+ DNS server) to obtain the IP address of the YouTube server.

2.

The LG U+ DNS gives the subscriber device the IP address of the YouTube server (i.e.

74.125.71.136).

Google Server (USA)

www.youtube.com

4 HTTP GET

6 HTTP Response

Request Video = Avatar

Transit LG U+ Network (Korea)

o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com

Google Global Cache

LG U+ DNS

PC LG U+ Subscriber

1 DNS Query

www.youtube.com

2 DNS Response

74.125.71.136

7 DNS Query


8 DNS Response

61.36.166.12

12 Video (Avatar) Download

...RTT < 10ms

3 Click “Avatar”in YouTube page

Download Server Hostname = o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com

10 Check User IP address:

If (User IP address is LG U+ range) go to step 11 (Check Cache Hit)else HTTP 302 Redirect to Google Server in USA

11 Check Cache Hit:

If (User request Video is stored in Cache) Download Video to User

else HTTP 302 Redirect to Google Server in USA

C a c h e

H i t !

9 HTTP GET



If (User IP addr is LG U+ range) Assign “LG U+ Google Cache”else Assign “Google Cache in USA”

http://www.netmanias.com/en/?m=view&id=blog&no=6001





Netmanias Tech-Blog

Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+)

2

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

video.

5.

This is an important step in the process. The YouTube server checks the IP address of thesubscriber device when it receives the HTTP GET message. In this example, the IP address of the

subscriber device is within the IP address blocks allocated for LG U+, who again has installed

Google Global Caches in its IDC. So, the YouTube server selects a Google Global Cache located in

LG U+.

6. The YouTube server gives the hostname of the Google Global Cache (i.e. o-

o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com) to the subscriber device.

7.

The subscriber device performs a DNS query about the hostname (again, the DNS server doesn't

have to an LG U+ DNS server).

8.

As a result of the query, the subscriber device receives an IP address of 61.36.166.12, which is

the IP address of the Google Global Cache in LG U+.

9.

Now, the subscriber device sends a request for an Avatar video to the LG U+ Google Global Cache.

10.

This is another important step in the process. The LG U+ Google Global Cache checks again the

IP address of the device that sent the HTTP GET. If the IP address is not within the IP address

blocks allocated for LG U+, the cache will send a HTTP 302 Found message to the device to

redirect to another Google Global Cache in US (HTTP Redirect). This way, the cache makes it clear

that only LG U+ subscribers are welcome. In this example, since the subscriber is an LG U+

subscriber, the process will move on to the step 11.11. The LG U+ Google Global Cache checks whether it has the video requested (e.g. Avatar here) in

its storage and finds it (Cache Hit).

12. So, the LG U+ Google Global Cache sends the video to the device. Since RTT is lower than 10 ms,

the subscriber will be able to watch it shortly.

(2) If an LG U+ Google Global Cache does not have a video requested (Cache Miss)

In the figure below, the DNS flow is excluded for more simplified illustration.

1.

The LG U+ subscriber clicks "Avatar" on YouTube.

2. The subscriber device sends a HTTP GET message to the YouTube server to request an Avatar

video.

3. The YouTube server checks the IP address of the device and recognizes it as an LG U+ subscriber.

4.

The YouTube server gives the hostname of an LG U+ Google Global Cache (i.e. o-

o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com) to the subscriber device.



Netmanias Tech-Blog


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5. The device sends a request for an Avatar video to the LG U+ Google Global Cache.

6. The LG U+ Google Global Cache checks the IP address of the device and confirms that it belongs

to an LG U+ subscriber.

7. The cache then checks to see if it has any Avatar video previously cached, and finds none (Cache

Miss).

8. Based on our actual test findings, we can presume the following: probably, the LG U+ Google

Global Cache has no idea which Google Global Cache in US has the Avatar video, so it will redirectthe message to a pre-configured parent Google Global Cache server (HTTP Redirection). In our

test, we noticed a certain mapping rule has been applied in the number values of the hostnames

as follows:

The parent server of the LG U+ Google Global Cache "o-o.preferred.lgupluswireline-

gmp1.v9.lscache5.c.youtube.com" was "v9.nonxt5.c.youtube.com" in US

The parent server of the LG U+ Google Global Cache "o-o.preferred.lgupluswireline-

gmp1.v12.lscache6.c.youtube.com" was "v12.nonxt6.c.youtube.com" in US

9. The subscriber device sends a request message for an Avatar video to v9.nonxt5.c.youtube.com

as instructed by the LG U+ Google Global Cache.

Google Server (USA)

www.youtube.com

Transit LG U+ Network (Korea)


LG U+ DNS

PC

Google Global Cache

LG U+ Subscriber

4 HTTP Response

5 HTTP GET

7 Check Cache Hit:

If (User request Video is stored in Cache) Download Video to Userelse HTTP 302 Redirect to Google Server in USA


If (User IP address is LG U+ range) go to step 11 (Check Cache Hit)else HTTP 302 Redirect to Google Server in USA

C a c h e

M i s s

!8 HTTP 302 Found

Location = v9.nonxt5.c.youtube.com

13 HTTP GET


14 Video (Avatar) Download

...RTT = 200ms

1 Click “Avatar”in YouTube page

2 HTTP GET


Download Server Hostname = o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com



If (User IP addr is LG U+ range) Assign “LG U+ Google Cache”else Assign “Google Cache in USA”

v9.nonxt5.c.youtube.com

9 HTTP GET


o-o.preferred.lax04t01.v1.lscache6.c.youtube.com

Google Cache

redirector.c.youtube.com

10 HTTP 302 Found

Location = redirector.c.youtube.com

11 HTTP GET


12 HTTP 302 Found

Location = o-o.preferred.lax04t01.v1.lscache6.c.youtube.com

C a c h e

F i l l L o

g i c ? ? ?



Netmanias Tech-Blog


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10.

If this server does not have the video either, it redirects the message again to

redirector.c.youtube.com (HTTP Redirection). We assume redirector.c.youtube.com is the top-

level server which manages the locations of all video files (i.e. which cache has what videos).

11.

The subscriber device sends a request for an Avatar video to redirector.c.youtube.com.12.

Finally, the subscriber device receives the hostname of a Google Global Cache that has the Avatar

video (i.e. o-o.preferred.lax04t01.v1.lscache6.c.youtube.com).

13. Now, the subscriber device sends a request for the Avatar video to the hostname.

14. Then, the subscriber device downloads the video from the Google Global Cache in US.

At this point, you may wonder "Then, when does the LG U+ Google Global Cache perform Cache Fill?" In

our test, when we requested the same video again after a Cache Miss, the video was downloaded again

from a Google Global Cache in US. Given that, it can be assumed that Google has certain policies set

regarding cache filling, for instance, "Cache Fill is performed for a content requested more than a

specified number of times".

Closing

As seen above, the YouTube servers in US and the LG U+ Google Global Caches check the IP address of a

device that sent a HTTP GET message. Then based on the findings, they decide through which Google

Global Cache (i.e. one in US or one in Korea) to download the video requested by the device. KT

subscribers use IP addresses that are within the IP address blocks allocated for KT, and thus they cannotaccess the LG U+ Google Global Caches simply by switching their DNS server to an LG U+ DNS server (If KT

subscribers switch the IP addresses of their device into ones within the IP address blocks allocated for LG

U+, then routing will fail, providing no Internet connection at all). This means, an LG U+ subscriber will be

able to download videos through the LG U+ Google Global Caches with no problem even when the

subscriber uses a KT DNS server.

One last thing to note...

Netmanias is currently using LG U+ Enterprise Internet service. Our measurement confirmed that, for

those who use LG U+ Enterprise Internet service, videos are not downloaded from the LG U+ Google

Global Caches in Korea, but from the Google Global Caches in Hong Kong (e.g. o-

o.preferred.hkg05s01.v20.lscache7.c.youtube.com), which have a relatively shorter RTT (about 100 ms).

In conclusion, the YouTube server in US redirects a subscriber to:

1) a LG U+ Google Global Cache if the IP address of a subscriber device is within the IP address

blocks allocated for LG U+ Home subscribers

2) a Google Global Cache in Hong Kong if the IP address is within the IP address blocks allocated

for LG U+ Enterprise subscribers3) Google Global Cache in US if the IP address is not within one of the two IP address blocks

above (e.g. ones within the IP address blocks allocated for KT)



Netmanias Tech-Blog


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About NMC Consulting Group (www.netmanias.com)

NMC Consulting Group is an advanced and professional network consulting company, specializing in IP network areas (e.g., FTTH, Metro Ethernet and IP/MPLS), service

areas (e.g., IPTV, IMS and CDN), and wireless network areas (e.g., Mobile WiMAX, LTE and Wi-Fi) since 2002.

Copyright © 2002-2013 NMC Consulting Group. All rights reserved.

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