LG U+'s IPTV service
►1. Live TV 
         1.1 Basic channel 
         1.2 Multiview: operator-selected channels
         1.3 Personalized Multiview: user-selected channels
   2. VoD   
         2.1 UHD VoD: Encoding rate and streaming of 4K UHD VoD content

LG U+, with its competitors KT and SK Broadband, presented Live TV service (real-time retransmission of broadcast channels over IP network, linear TV channels service) to the nation back in January 2009. Initially, the service was available only in SD and HD resolution. But later in August 2013, the company switched a whopping 33 channels into Full HD (1920x1080), opening a Full HD era for the first time in Korea.
 
And a year later in August 2014, all of its 122 HD channels to Full HD. As of May 2015, LG U+ is offering 163 channels, and 126 of them are Full HD. No channel is available for 4K UHD (3840x2160) yet, and 4K UHD videos can be viewed only through VoD.
 
Of all IPTV services currently offered by LG U+ (Service: U+ tv G 4K UHD, UHD STB: LG's ST9401-UP), this post will particularly discuss Live TV service.
 
LG U+'s IPTV Live TV service consists of roughly the following three services:

1. basic channel service: channels from Over-The-Air (OTA) broadcasters are merely retransmitted in real time through LG U+'s its IP network  
2. Multiview: Multiple (4~5) live channels are transmitted as one multicast stream, so that users can watch the channels on one screen.
3. Personalized multiview: This service allows a user to select 4 channels to display on one screen.

 
Table 1. LG U+'s Live TV Service

		1. Basic channel	2. Multiview (operator-selected channels)	3. Personalized Multiview (user-selected channels)
	Service description	Mere relaying of broadcast channel	A set of operator selected-channels are displayed on one screen.	A set of user selected-channels are displayed on one screen
	No. of IP multicast  streams	1 stream (1 channel through 1 multicast stream)	1 stream (4~5 channels through 1 multicast stream)	4 streams (4 channels through 4 multicast streams)
	Resolution	Full HD (1920x1080)	Full HD (1920x1080)	Main channel: Full HD (1920x1080) Sub channels: SD(720x480)
	Codec	H.264	H.264	Main: H.264, Sub: H.264
	Encoding rate	8.5Mbps	8.6Mbps	Main: 8.5Mbps, Sub: 1.34Mbps
	Streaming rate	11.3Mbps	11.1Mbps	Main: 11.3Mbps, Sub: 1.86Mbps
	Network BW	11.7Mbps	11.5Mbps	Main: 11.7Mbps, Sub: 1.96Mbps
	Multicast IP (In this test)	233.18.145.194(MBC)	233.18.145.88 (Multiview)	Main: 233.18.145.194 Sub 233.69.194.192(kbs1) 233.68.194.237(sbs) 233.69.194.199(kbs2)
	Transport Protocol	UDP	UDP	UDP
	Request for IP multicast stream	IGMPv2	IGMPv2	IGMPv2
	Service launch	Full HD: August 2013 SD/HD: Jan. 2009	May 2013	Sep. 2014

* Streaming rate: Refers to the UDP payload rate which can be obtained by subtracting the network overhead (including Ethernet, IP, UDP headers) from the network bandwidth of a multicast stream measured by Wireshark. In general, streaming data includes not only video data, but also other data including encryption information, FEC data, etc. So, the actual encoding rate of a video is lower than its streaming rate.

* Encoding rate: Refers to the Content Bitrate value measured in VLC.

1. Basic channel service
 
This service is the basic service that displays one channel on one screen. All high-quality channels provided by LG U+ are in Full HD (with resolution of 1920x1080). Let's learn how the company's Full HD channels are transmitted through its IP network.

• request for IP multicast stream: IGMPv2
• Multicast IP addresses by channel: MBC(233.18.145.194), KBS1(233.18.145.192), KBS2(233.18.145.120), SBS(233.18.145.195), ...​
• Consumed Network BW: 11.7Mbps
• Video streaming rate excluding overhead (Ethernet header, IP header and UDP header): 11.3Mbps
• QoS marking: DiffServ EF

♦ Screenshot of basic channel traffic: MBC multicast stream (233.18.145.194) 

 
Channel switch: If a channel is switched, messages are sent from STB: IGMP Leave message for the channel watched, and IGMP Join message for the selected channel.
 
♦ Screenshot of basic channel traffic (Channel switching)

 
LG U+ offers several ways of watching multiple channels on one screen. You can watch the channels pre-selected by LG U+, as originally offered. Or you can go for customization service, which began in September 2014. This allows you to choose four channels you want.    
 
2. Multiview: Operator-selected channels
 
Operator-selected multiview service offers the following options of display:
1. 4 OTA channels
2. 4 home shopping channels
3. 5 sports channels
4. 4 golf and economy channels
5. 4 movie channels 
 
        
       1. 4 OTA channels           2. 4 home shopping channels         3. 5 sports channels
 
We conducted a test to check, for multiview service, whether all the channels are transmitted to STB in individual multicast streams, or they are mixed/encoded into one stream at LG U+'s IPTV headend first, and then transmitted in one multicast stream.  When an option of watching 4 OTA channels (by clicking 4CH on U+ tv G 4K UHD screen) is selected, STB sends out IGMP Join message (233.18.145.88) and receives Multicast UDP Stream. Then this single IP multicast stream (11.5Mbps, UDP, CBR) alone takes charge of transmitting all 4 OTA channels (MBC, SBS, KBS1 and KBS2). The channel configuration cannot be changed by users.  
 
♦ Screenshot of multiview traffic: 4 channels are displayed, but only one IP multicast stream is used (233.18.145.88)

When one channel is selected in 4-channel multiview mode, STB stops the multicast stream carrying all 4 channels by sending out IGMP Leave message (233.18.145.88). Then it sends out IGMP Join message (233.18.145.194) for MBC channel right away and get MBC multicast stream.  
 
♦ Screenshot of multiview traffic: Click the MBC screen in multiview mode

3. Personalized Multiview: User-selected 4 channels
 
User selects 4 channels (in this test, MBC, SBS, KBS1 and KBS2) by clicking 'my 4 channel' button on the remote control and saved. In the test scenario, a user, while watching in 4-channel multiview, clicks SBS to watch it on the main screen still in multiview mode, and then finally watches it in full screen.
 
❶ When the user clicks 'my 4channel' button, STB sends out IGMP Join messages (all 4 of them) for the 4 channels he selected to the network. Then 4 multicast streams are received from the network, and 4 channels are displayed on the screen soon. In the test, MBC stream was received at 11.3Mbps (Full HD) while other 3 channels were transmitted at 1.86Mbps (SD). ❷ When the user selects SBS, the screen displays SBS channel in the main screen in Full HD and the rest 3 in SD (1.86Mbps). ❸ Then when the user clicks SBS again, the screen shows only SBS in Full HD (11.3Mbps), the multicast streams for the rest 3  channels disappear(IGMP Leave).
 
♦ Screenshot of personalized multiview (my 4 channel): 4 channels are transmitted in individual multicast streams independently

We have so far learned about LG U+'s real-time channel service. In the next post, we will study VoD service including UHD VOD.