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Google Global Cache (GGC) Operations for
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Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+)

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Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+)

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Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+)

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Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+)

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

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

  1. 1. 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 (tech@netmanias.com) | 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 DNS Query www.youtube.com 2 DNS Response 74.125.71.136 4 HTTP GET 3 Click “Avatar” in YouTube page Request Video = Avatar 6 HTTP Response Download Server Hostname = o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com 5 Check User IP address: 7 DNS Query If (User IP addr is LG U+ range) Assign “LG U+ Google Cache” else Assign “Google Cache in USA” 10 Check User IP address: o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com 8 DNS Response If (User IP address is LG U+ range) go to step 11 (Check Cache Hit) else HTTP 302 Redirect to Google Server in USA 9 HTTP GET 11 Check Cache Hit: Request Video = Avatar it ! If (User request Video is stored in Cache) eH Download Video to User ach C else HTTP 302 Redirect to Google Server in USA www.youtube.com 61.36.166.12 12 Video (Avatar) Download RTT < 10ms ... LG U+ DNS o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com PC LG U+ Subscriber Google Global Cache Google Server (USA) Transit LG U+ Network (Korea) 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). 1
  2. 2. Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+) 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 the subscriber 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. oo.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. oo.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com) to the subscriber device. 2
  3. 3. Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+) 2 HTTP GET 1 Click “Avatar” in YouTube page Request Video = Avatar 4 HTTP Response Download Server Hostname = o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com 3 Check User IP address: 6 Check User IP address: If (User IP addr is LG U+ range) Assign “LG U+ Google Cache” else Assign “Google Cache 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 5 HTTP GET 7 Check Cache Hit: Request Video = Avatar C 8 HTTP 302 Found If (User request Video is stored in Cache) ! Download Video to User iss else M HTTP 302 Redirect to Google Server in USA che a Location = v9.nonxt5.c.youtube.com 9 HTTP GET Request Video = Avatar 10 HTTP 302 Found Location = redirector.c.youtube.com 11 HTTP GET Request Video = Avatar 12 HTTP 302 Found Location = o-o.preferred.lax04t01.v1.lscache6.c.youtube.com 13 HTTP GET Request Video = Avatar 14 Video (Avatar) Download RTT = 200ms ... www.youtube.com v9.nonxt5.c.youtube.com redirector.c.youtube.com C ic og ill L eF ach LG U+ DNS o-o.preferred.lgupluswireline-gmp1.v9.lscache5.c.youtube.com o-o.preferred.lax04t01.v1.lscache6.c.youtube.com PC LG U+ Subscriber Google Global Cache Google Cache Google Server (USA) ??? Transit LG U+ Network (Korea) 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 redirect the 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.lgupluswirelinegmp1.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.lgupluswirelinegmp1.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. 3
  4. 4. Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+) 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 toplevel 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 cannot access 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. oo.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 subscribers 3) 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) 4
  5. 5. Netmanias Tech-Blog Google Global Cache (GGC) Operations for YouTube (Part 2. LG U+) 5
  6. 6. Netmanias Research and Consulting Scope 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 eMBMS/Mobile IPTV CDN/Mobile CDN Transparent Caching BSS/OSS Services Cable TPS Voice/Video Quality IMS Policy Control/PCRF IPTV/TPS LTE Mobile Network Mobile WiMAX Carrier WiFi LTE Backaul Data Center Migration Carrier Ethernet FTTH Wireline Network Data Center Metro Ethernet MPLS IP Routing CDN Transparent Caching Analysis Networks eMBMS LTE IMS Infrastructure Services Analyze trends, technologies and market Report Technical documents Blog One-Shot gallery Concept Design DRM POC Training Wi-Fi We design the future protocols IP/MPLS We design the future Carrier Ethernet We design the future Consulting Visit http://www.netmanias.com to view and download more technical documents. Future 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. 6

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