StreamScope™ DTV Monitor & Analyzer

StreamScope™ DTV Monitor & Analyzer
July SCTE Piedmont Rakhi Modi Copyright © 2008 Triveni Digital, Inc.

Copyright © 2008 Triveni Digital, Inc.
Overview MPEG Transport Stream Basics Packet header PSI Tables metadata PAT PMT PSIP Tables metadata Static tables Dynamic tables Elementary streams Encoding Buffering Synchronization IP monitoring & synchronization Monitoring and Troubleshooting streams StreamScope architecture Typical use case Copyright © 2008 Triveni Digital, Inc.

DTV Broadcast Stream Special case of MPEG-2 transport stream May contain multiple virtual channels Video channels A video stream One or more audio streams Possibly one or more data streams Audio channels Data-only channels One or more data streams Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Transport Stream
Made up of 188-byte transport packets, each with 4 byte header & 184 byte payload Each packet contains any ONE kind of information– audio, video, data, PSI, … One Transport (MPEG) Packet Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Transport Stream (Contd.)‏
We say transport packets have multiple interleaved elementary streams -- audio, video, data, PSI, ... Packets belonging to the same elementary stream are identified by packet id (PID) in packet header (same color in our illustrations). MPEG-2 Transport Stream These three packets are the same color. They have the same PID and belong to the same Elementary stream. Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Transport Stream – Header Fields
Noteworthy fields: Sync Byte – Find packet boundary PID – Used while demultiplexing stream Continuity Counter – Identify packet loss PCR stamp in adaptation field – Clock sync Adaptation Field Continuity Counter Sync Byte PID 188 Bytes Header (4 Bytes)‏ PES 1 (Optional)‏ PES x Or other Payload (Pat, PMT, PSIP, etc)……………………………... MPEG-2 Transport Stream Copyright © 2008 Triveni Digital, Inc.

MPEG Header Fields: Sync Byte
When a decoder first tunes, all it sees are a stream of 0’s and 1’s The decoder must first identify the beginning of packets before it can interpret the stream The decoder uses the Sync Byte field to do this MPEG Data Prior to Packet Sync Copyright © 2008 Triveni Digital, Inc.

MPEG Header Fields: Sync Byte (Contd.)‏
The Sync Byte of a packet is always 0x47 (Hexadecimal) or binary The decoder looks for strings of zeros and ones which match the pattern of the sync byte (see red below)‏ Copyright © 2008 Triveni Digital, Inc.

Once the decoder finds a 0x47 in the stream, it looks 187 bytes down the stream, and looks for another 0x47 If it finds three Sync Bytes in a row, then the Decoder has Found Sync and assumes packet boundaries from then on Each packet is tested for 0x47 as soon as it arrives. If a packet arrives with an incorrect sync byte, the decoder starts over. This is called SYNC LOSS Found Sync 0x47 187 bytes Packet 188 bytes Sync Lost 0x32 Packet 188 bytes Copyright © 2008 Triveni Digital, Inc.

If you don’t have Packet Sync, the decoder cannot find packet boundaries. You will not be able to decode at all Packet Sync problems typically occur in hardware at packet boundaries during format converters, edge devices, demodulators etc: ASI to Gig-E ASI to Microwave or QAM Satellite to ASI Copyright © 2008 Triveni Digital, Inc.

PIDs Defined PID stands for Packet ID Each Packet has a PID (indicated by color). Packets belonging to the same source of information have the same PID (same color). MPEG-2 Transport Stream These three packets are the same color. They have the same PID and belong to the same Elementary stream. Copyright © 2008 Triveni Digital, Inc.

PIDs Defined - ATSC Bitstream
Data channel PSIP Tables Video Encoder Audio Encoder Data- enhanced Audio/Video channel Audio/Video channel PAT PMT Null Video Audio Data PSIP MPEG-2 Transport Stream Data Server PSIP Generator Multi- plexer Copyright © 2008 Triveni Digital, Inc.

PIDs Defined - Digital Cable Bitstream
Audio Encoder Video/Audio channel PAT Video Audio PMT Video Encoder Video Null Audio CAT Video Audio Encoder Video/Audio channel Audio Video Video Encoder Audio Multi- plexer Audio Encoder Video/Audio channel Video Encoder Video/Audio channel Audio Encoder Video Encoder MPEG-2 Transport Stream Copyright © 2008 Triveni Digital, Inc.

Transport Stream Demultiplexing
When a set top box first receives a Transport Stream, it demultiplexes that stream based on PID. set top box Copyright © 2008 Triveni Digital, Inc.

Metadata Data about included data is metadata Metadata tells the decoder which kinds of information are contained in each PID, and which PID’s go together. There are two kinds of Metadata Program Specific Information (PSI) - Tables in the stream defined in the MPEG standards Program and System Information Protocol (PSIP) -Tables defined in ATSC A/65 Copyright © 2008 Triveni Digital, Inc.

PSI Tables (MPEG-2 Tables)‏
PAT - Program Association Table Appears in PID 0x0000 Identifies MPEG-2 programs in transport stream and gives PIDs for their PMTs The PAT is on PID 0x00. This is the first PID or ‘Base PID’ a MPEG decoder looks for PMT - Program Map Table Identifies elementary streams in program (virtual channel), and gives their PIDs. CAT - Conditional Access Table NIT - Network Information Table Copyright © 2008 Triveni Digital, Inc.

MPEG-2 PSI Tables (Contd.)‏
PMT 1 Video PID 0x31 Audio PID 0x34 Audio PID 0x35 PCR_PID 0x31 PMT 2 Video PID 0x41 Audio PID 0x44 Audio PID 0x45 PCR_PID 0x41 PMT 3 Video PID 0x51 Audio PID 0x54 Audio PID 0x55 PCR_PID 0x51 PID 0x30 PAT (always on PID 0x0)‏ Station TSID PMT 1 -> On PID 0x30 PMT 2 -> On PID 0x40 PMT 3 -> On PID 0x50 PID 0x40 PID 0x50 The PAT always appears on pid 0. This is often called the MPEG-2 Base PID; it is the first PID a set top box looks at once it has acquired sync. The PAT contains a reference for each PMT in the Transport Stream. Each service in the stream will have it’s own PMT Each PMT contains information crucial for the decoding of it’s service. It contains a list of audio and video PID’s associated with that service, as well as a value called PCR_PID The PCR_PID is usually the same as the video. The PCR_PID is the one which contains the Program Clock Reference, or time base, for the service. Copyright © 2008 Triveni Digital, Inc. 17

MPEG-2 PSI Tables (Contd.)‏
Set top Box “WXXX Channel Video” PID 0x31 “WXXX Channel Audio” PID 0x34 Program Specific Information (PSI) tells the decoder which kinds of information are contained in each PID, and which PID’s go together. For example: JRM Channel has an audio component and a video component. The audio component arrives at the decoder on packets with PID 32. The video arrives at the decoder with PID 34. These two PID’s are synchronized; they share the same Time Base. We know this because the audio and video are in sync. The PSI tells the decoder which packets to decode when a user tunes to “The HPO Movie Channel.” Namely, PID 342 and It also informs the decoder that these two PID’s are synchronized, and where to find the timing information. PSI PID assignments These PIDS go together Copyright © 2008 Triveni Digital, Inc. 18

PSIP Tables (ATSC Tables)‏
Branding – Station call letters and Channel number Signaling – V-Chip data, information about audio and Video PID’s Announcement – Program Guide PSIP stands for Program and System Information Protocol It was developed by the ATSC (American Television Systems Committee) to meet the specific needs of broadcast television. PSIP is made up of a group of tables which provide Branding, Signaling and Announcement services for broadcasters PSIP is also used by Open QAM televisions for tuning. There are special considerations for Grooming of television broadcast streams related to PSIP. Copyright © 2008 Triveni Digital, Inc. 19

ATSC PSIP Tables MGT - Master Guide Table - Appears in PID 0x1FFB. - Gives PIDs, sizes, and version numbers of other PSIP tables (except STT). STT - System Time Table - Appears in PID 0x1FFB - Gives current UTC time. VCT - Virtual Channel Table - Identifies and describes virtual channels. Copyright © 2008 Triveni Digital, Inc.

ATSC PSIP Tables (Contd.)‏
RRT - Rating Region Table - Describes content advisory system(s) being used to rate events. EIT - Event Information Table - Gives titles, start times, durations, content advisory ratings of events (TV programs). ETT - Extended Text Table - Gives extended textual descriptions of virtual channels and events. Copyright © 2008 Triveni Digital, Inc.

PSIP and PSI Link Table Information for a Television Broadcast Stream PAT (On PID 0x0)‏ Station TSID PMT 1 -> On PID 0x30 PMT 1 (On PID 0x30) Video PID 0x31 Audio PID 0x34 PCR_PID 0x31 VCT On Pid 0x1FFB 4-1 WXXX Video PID 0x31 Audio PID 0x34 The second way that PSIP can complicate Grooming occurs when the Groomer attempts to regenerate PSI, and is not aware that PSIP is also in the stream. The picture above shows how PSI and PSIP share some information. The VCT from PSIP carries some of the same information as the PMT in PSI. The Audio and Video PID’s in the PMT are the same ones found in the VCT. No matter which table the set top box or decoder looks at, it will see the same PID assignments, and will pick up the correct PID’s. The next slide shows why this creates problems when we try to groom this stream. PAT and PMT Tables PSIP table Copyright © 2008 Triveni Digital, Inc. 22

Table Intervals Metadata is transmitted periodically in the transport stream Each table in the system, MPEG or PSIP, has a defined repetition rate. e.g. the Program Association Table (PAT) must appear in the transport stream every 100ms If the table does not appear frequently enough in the stream, it can cause minor problems while decoding If the table is MISSING all together then larger decoding problems begin to occur Copyright © 2008 Triveni Digital, Inc.

Electronic Program Guide
Receiver periodically scans all channels and caches program info from EITs and ETTs. Receiver displays: Channel, program title, etc., on channel change. Detailed info on current program on request. On-screen, interactive program guide on request. Detailed info on future programs on request. Note: Closed Captioning information NOT in this location Copyright © 2008 Triveni Digital, Inc.

MPEG Header: Continuity Counter
The continuity counter is a 4 bit field in the header which increments by 1 each time a packet comes out on a specific PID: All Packets PID 0x52 1 2 3 4 5 6 7 8 … 14 15 1 When a PID ‘skips’ one value of the continuity Counter, we call it a ‘Continuity Error.’ This means one or more packets were lost. Continuity Error Here All Packets PID 0x54 1 2 3 7 8 9 10 11 … Copyright © 2008 Triveni Digital, Inc.

MPEG Header: Continuity Counter (Contd.)‏
Identifies WHEN we lose Packets, but not HOW MANY! Packet loss causes many other kinds of analysis to ‘reset’ or give bogus results. Any analysis based on an average over many packets will automatically reset when it encounters continuity problems. Since a continuity error mean ‘some packets’ have been lost, frequent continuity errors should be one of the FIRST things you look for when debugging. Copyright © 2008 Triveni Digital, Inc.

Three Things to Remember
Three main monitoring and troubleshooting lessons: Fix Continuity Problems first Continuity errors create bogus alarms in other areas. Until you resolve the continuity problems, it will be very hard to determine if you have other problems in your stream TBD Copyright © 2008 Triveni Digital, Inc.

Video Formats ATSC supports 18 different MPEG-2 video formats: HDTV 1080x1920 pixels; 60i, 30p, 24p; 16:9 aspect 720x1280 pixels; 60p, 30p, 24p; 16:9 aspect SDTV 480x704 pixels; 60p, 60i, 30p, 24p; 16:9, 4:3 aspect 480x640 pixels; 60p, 60i, 30p, 24p; 4:3 aspect SCTE supports more video formats 480x528 pixels; 60i, 24p; 4:3 aspect 480x352 Pixels; 60i, 24p; 4:3 aspect Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Video Encoding Video is sequence of frames. Each frame is encoded in one of three ways: I-picture: intra-picture encoding, similar to jpeg encoding (exploiting spatial redundancy). B-picture: bi-directional encoding, using motion adjusted deltas from a previous and a future frame (exploiting temporal redundancy). P-picture: predictive encoding, using motion adjusted deltas from a previous reference frame (exploiting temporal redundancy). Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Video Encoding (Contd.)‏
Example 1. Panning Camera I-picture B-picture I-picture Example 2. Moving Object I-picture B-picture I-picture Copyright © 2008 Triveni Digital, Inc.

MPEG-2 Video Encoding (Contd.)‏
Encoder emits sequence of encoded frames. Sizes of encoded frames vary. Encoded frames are packed into packetized elementary stream (PES) packets. PES packets are packed into MPEG-2 transport packets. (All packets for single video stream have same PID value.)‏ Overall compression ratio is 50:1 or more. Closed captioning associated with video frame is encoded here Copyright © 2008 Triveni Digital, Inc.

ATSC/SCTE Audio Formats
ATSC uses AC-3 audio encoding, with up to 6 audio channels: left, right, center, left surround, right surround, low frequency enhancement. The full set is often called 5.1 audio. The sampling rate is always 48 kHz. The encoded bit rate may be up to 384 kbps. Copyright © 2008 Triveni Digital, Inc.

AC-3 Audio Encoding Audio frames, each 32 milliseconds in length, are encoded. Encoded frame size depends only on bitrate. Encoded frames are packed into packetized elementary stream (PES) packets. PES packets are packed into MPEG-2 transport packets. (All packets for single audio stream have same PID value.)‏ Copyright © 2008 Triveni Digital, Inc.

Audio-Video Synchronization
Audio, video are encoded independently, must be synchronized during play. MPEG has to allow for great distances between the Encoder and Decoder, and still allow for Correct Decode of the transport stream Copyright © 2008 Triveni Digital, Inc.

The Encoder and Decoder Clock
The MPEG encoder and MPEG decoder use a 27Mhz ‘clock’ to encode/decode incoming audio and video The clock is actually a ‘counter’ which advances every 1/ seconds Encoder 27Mhz Clock 1,2,3,4….. Decoder 27Mhz Clock 1,2,3,4….. Copyright © 2008 Triveni Digital, Inc.

Decode Time Stamp - DTS Each Frame is marked with a DTS – “Decode Time Stamp” – a positive number The value of the DTS is set to the value of the Encoder Clock when the frame is encoded Encoder 27Mhz Clock 1,2,3,4….. MPEG Packets F1 DTS 500 F2 DTS 950 Packetizer Copyright © 2008 Triveni Digital, Inc.

Packets Assigned to Decode Buffer
As packets flow into the Decoder, a space in memory is set aside for them, one buffer for each PID. Decoder 27Mhz Clock 1,2,3,4….. MPEG Packets Buffer 1 Pid 0x31 Video Buffer 2 Pid 0x34 Audio Copyright © 2008 Triveni Digital, Inc.

Reconstruction of Frames From Buffer
Packets form Video and Audio Frames in the buffer Decoder 27Mhz Clock 1,2,3,4….. MPEG Packets Buffer 1 Pid 0x31 Video F1 DTS 500 F2 DTS 675 F3 DTS 950 Buffer 2 Pid 0x34 Audio F1 DTS 200 F2 DTS 990 Copyright © 2008 Triveni Digital, Inc.

The Magic of Decode When the value of the Decode clock MATCHES the DTS on the frame, that frame is sent to the decode hardware Decoder 27Mhz Clock = 200 Decode Hardware MPEG Packets F1 DTS 200 Buffer 1 Pid 0x31 Video F1 DTS 500 F2 DTS 675 F3 DTS 950 Buffer 2 Pid 0x34 Audio F2 DTS 990 Copyright © 2008 Triveni Digital, Inc.

Another Frame Goes to Decode Hardware
Next Frame Decoder 27Mhz Clock = 500 Decode Hardware MPEG Packets F1 DTS 500 Buffer 1 Pid 0x31 Video F2 DTS 675 F3 DTS 950 Buffer 2 Pid 0x34 Audio F2 DTS 990 Copyright © 2008 Triveni Digital, Inc.

One More Frame Heads to Decode
And the next frame… Decoder 27Mhz Clock = 675 Decode Hardware MPEG Packets F2 DTS 675 Buffer 1 Pid 0x31 Video F3 DTS 950 Buffer 2 Pid 0x34 Audio F2 DTS 990 Copyright © 2008 Triveni Digital, Inc.

Audio and Video Buffers
Receiver must buffer audio and video frame data until presentation time. If data appears too late in the transport stream, buffer underflow results. If data appears too early in the transport stream, buffer overflow results. Either condition results in garbled play or incorrect synchronization. Different set top boxes may respond differently to the same underlying buffer violations Copyright © 2008 Triveni Digital, Inc.

How to Assure Audio/Video Sync?
In order for the audio and video Elementary Streams to remain in Sync, the Encoder Clock and the Decoder Clock must remain in sync The next few slides will demonstrate how this happens and what components to check when it fails… Copyright © 2008 Triveni Digital, Inc.

Encoder Inserts PCR When the encoder streams creates packets, it embeds the current value of it’s 27 MHz clock into the stream This time reference is called the PCR: Program Clock Reference MPEG demands that one PCR packet appear in the stream every 100ms MPEG Packets Encoder 27Mhz Clock MPEG Packet with PCR Stamp Copyright © 2008 Triveni Digital, Inc.

Decoder Consumes PCR When the decoder gets a packet containing a PCR timestamp, it adjusts it’s 27Mhz clock accordingly Decoder 27Mhz Clock Adjusts value of counter based on incoming PCR Packet MPEG Packets Copyright © 2008 Triveni Digital, Inc.

PCR Timestamp Issue What could conceptually cause PCR timestamps to go awry? Encoder possibly time stamped incorrectly Decoder possibly failed to consume time stamps PCR packet was accidentally lost in transmission When PCR time stamps go awry, we have “PCR jitter” Copyright © 2008 Triveni Digital, Inc.

PCR Jitter PCR Jitter is: Difference between the Actual Value of the PCR time stamped by encoder and the expected value of the PCR as calculated by decoder based on the clock rate and the time at which the PCR value is received. Copyright © 2008 Triveni Digital, Inc.

PCR Rate (Frequency) Offset
PCR Frequency Offset is: Difference between the clock frequency calculated at decoder based on actual PCR values received and an “ideal” 27 MHz clock, which is the clock rate dictated by the MPEG-2 standard Copyright © 2008 Triveni Digital, Inc.

PCR Intervals, Jitter and Rate
Transmit interval: 100 ms Jitter: no more than 500 ns Rate: 27 MHz +/- 810 Hz Most streams seen in the field are compliant, but every now and then extreme jitter shows up. Copyright © 2008 Triveni Digital, Inc.

PCR Timestamp Issue (Contd.)‏
What in your network facility could cause PCR timestamps to go awry? Three of the most common are:  It can happen any time you MUX streams It can happen at the source encoding (rare except for broadcast streams!)‏ It can happen on any IP link – due to network lag Copyright © 2008 Triveni Digital, Inc.

PCR Packet Spacing Before Muxing
Note the Number of Packets between each PCR packet in each Input Stream Video 0x31 Transport Stream Multiplexer PID Packet Spacing 0x31 2 Packets 0x41 1 Packet 0x51 0 Packets Video 0x41 Video 0x51 Copyright © 2008 Triveni Digital, Inc.

PCR Packet Spacing After Muxing
Note that the PCR packet spacing has changed! Video 0x31 Transport Stream Multiplexer Video 0x41 PID Old Spacing New Spacing 0x31 2 Packets 8 Packets 0x41 1 Packet 5 Packets 0x51 0 Packets 2 Packets Video 0x51 Copyright © 2008 Triveni Digital, Inc.

Muxing Causes PCR Jitter
When we MUX multiple streams together, the spacing between the PCR packets in each stream CHANGES The physical shift results in a TEMPORAL shift as well, throwing the time stamps off The TEMPORAL shift in PCR values is referred to as “PCR jitter” Copyright © 2008 Triveni Digital, Inc.

Muxing Causes PCR Jitter (Contd.)‏
The MUX has to RESTAMP all the PCR values to correct for the change in the packet spacing – THIS IS VERY HARD TO DO The more services on the output, the harder it is to restamp The fewer ‘null’ packets at the output, the harder it is to restamp Copyright © 2008 Triveni Digital, Inc.

What in your network facility could cause PCR timestamps to go awry? Three of the most common are: It can happen any time you MUX streams  It can happen at the source encoding (rare except for broadcast streams!)‏ It can happen on any IP link – due to network lag Copyright © 2008 Triveni Digital, Inc.

PCR Jitter From Incorrect Encoding
If the MPEG encoder’s parameters are set up incorrectly, you can introduce jitter at the source This is relatively rare If HBO sent it’s stream up to the bird with jitter in it, a LOT of people would complain! Local broadcast streams are more likely to have this problem Copyright © 2008 Triveni Digital, Inc.

What in your network facility could cause PCR timestamps to go awry? Three of the most common are: It can happen any time you MUX streams It can happen at the source encoding (rare except for broadcast streams!)‏  It can happen on any IP link – due to network lag Copyright © 2008 Triveni Digital, Inc.

PCR Jitter Due to IP Carriage
Network lag can conceal MPEG jitter problems on an IP link. The network jitter is usually so much larger than the PCR jitter that the PCR jitter is ‘lost in the noise.’ Hopefully, the IP-ASI or IP-QAM edge device will provide buffering and use ‘high level math’ to smooth out the network lag. MT-40 provides a way to separate the Network Lag from PCR Jitter. Copyright © 2008 Triveni Digital, Inc.

IP Encapsulation of MPEG Packets
When MPEG packets are carried over Gig-E, they are ‘Encapsulated’ inside IP packets. An IP header is wrapped around the MPEG packets, so that the MPEG data can be routed through an IP network Typically, other intermediate encapsulations involved are UDP, RTP, VLAN tags An IP packet Up to 7 MPEG packets IP Packet Header IP data section Copyright © 2008 Triveni Digital, Inc.

Multicast IP Basics Network edge devices forward packets to hosts based on the packet’s IP address Packets with destination Address of Enter the network here NETWORK Packets routed to Host with matching IP Host 1 IP Host 2 IP Host 3 IP Copyright © 2008 Triveni Digital, Inc.

Multicast IP Basics (Contd.)‏
There is a reserved range of IP addresses which go to ALL hosts on the network! 224.x.x.x to 239.x.x.x NETWORK Packets with destination Address of Enter the network here Packets routed to ALL hosts! Host 1 IP Host 2 IP Host 3 IP Copyright © 2008 Triveni Digital, Inc.

Sending packets to all hosts on a network is NOT desirable. Not appropriate for services such as VOD Requires MASSIVE amounts of network resources and bandwidth. That’s why most cable networks only route multicast packets when they are REQUESTED with IGMP (Internet Group Management Protocol) message! Copyright © 2008 Triveni Digital, Inc.

In this case, the multicast packet comes into the network, but doesn’t go out to a host until an IGMP ‘join’ request comes in Packets with destination Address of Enter the network here NETWORK IGMP Join From Host IGMP Join From Host Packets To Host Packets To Host Host 1 IP Host 2 IP Host 3 IP Copyright © 2008 Triveni Digital, Inc.

In order to monitor multicast Gig-E packets at an edge switch, one must first generate IGMP requests from the Host. In this case, the analyzer is the host. NETWORK Stream Scope IGMP Message Packets for Analysis Copyright © 2008 Triveni Digital, Inc.

GigE Monitoring Point-to-Point (Non-IGMP)‏
This method is much simpler. Plug the Monitor card directly into the Switch under test. MT-40 Analyzer Switch under test Monitor GIG-E Card Copyright © 2008 Triveni Digital, Inc.

Overall Jitter versus MPEG Jitter
Use ‘Overall’ or ‘MPEG’ jitter settings when measuring from constant bit rate sources like ASI Use ‘MPEG’ jitter setting when measuring jitter on ‘Gig- E’ links to exclude the network associated jitter from the jitter calculation. Use ‘Overall’ jitter setting when measuring jitter on ‘Gig-E’ links if you want to see the total jitter due to network lag AND MPEG issues (requires Gig-E w/PCR option)‏ Copyright © 2008 Triveni Digital, Inc.

Overall Jitter versus MPEG Jitter (Contd.)‏
Gigabyte Ethernet offers specific difficulties when monitoring PCR related issues The network delay on a typical UDP network is usually orders of magnitude greater than the PCR Jitter detected on the network Be sure to use the appropriate setting for ‘MPEG’ or ‘Overall’ jitter when measuring PCR on Gigabyte Ethernet networks (see previous slide)‏ Copyright © 2008 Triveni Digital, Inc.

How to Assure Audio/Video Sync? (Contd.)‏
PCR values help the Encoder Clock and the Decoder Clock to remain in sync PCR jitter can cause synchronization problems for elementary streams Ensure PCR jitter and frequency offsets are within standard limits Elementary stream buffers limits are NOT violated Large PCR jitter values can cause “Lip sync” error Buffer over- or underflow problems may cause “tiling”, “pixelization”/”macroblocking” errors Copyright © 2008 Triveni Digital, Inc.

Three main monitoring and troubleshooting lessons: Fix Continuity Problems first Continuity errors create bogus alarms in other areas Until you resolve the continuity problems, it will be very hard to determine if you have other problems in your stream Check for PCR jitter PCR jitter can cause packet over- or underflow problems Lip synch errors may also be result of PCR jitter TBD Copyright © 2008 Triveni Digital, Inc.

Why Transport Stream Analyzer?
With analog transmission, if audio/video did not have any anomalies on a TV set up in the studio, it would show up intact on the end user’s TV For digital transmission, this assumption is NOT valid as digital signals rely on the decoder’s Firmware implementation Buffer sizes Software decoding capability Copyright © 2008 Triveni Digital, Inc.

Why Transport Stream Analyzer? (Contd.)‏
The transition to digital has introduced some specific challenges for broadcast engineers Not all Set top boxes will respond the same way to the same underlying problem Standards violations in digital Transport Streams may show up on a receiver only intermittently The only streams which will consistently decode are those which are compliant The best way to assure compliance is with a Transport stream Analyzer/Monitor Copyright © 2008 Triveni Digital, Inc.

MT-40: Collaborative Mode Debugging
Two or more technicians use MT-40 to examine the same input. Customers leverage subject matter experts from many different geographical locations Equipment Room LAN MT-40 MUX Encoder IRD Modulator Head End Tech Operations Center LAN WAN Copyright © 2008 Triveni Digital, Inc.

MT-40: Multi- Channel Fleet Monitoring
Local DTV Station or Headend Remote location with MT-40 Chief Engineer’s Office MT-40 Visualization Client viewing all sources, all channels simultaneously Network Equipment Room Remote location with MT-40 MT-40 Monitoring local channel Copyright © 2008 Triveni Digital, Inc.

Troubleshooting Example – Audio Outage
Customer calls into station – audio dropping out on their set In station set top boxes do not have any problems How serious is this problem? Are other Customers seeing it? PSIP Generator MUX ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB Here’s an example of a problem, and how it might be solved using the methodology from the previous slide. This picture represents a very simple cable head end. Video is received ‘off the bird,’ groomed into a QAM, and then sent to the customer. ASI Satellite Dish Copyright © 2008 Triveni Digital, Inc. 75

Standards violation has occurred In this case, Audio Buffer Underflow is reported by the Analyzer. This explains why the audio and video elementary streams are out of sync with one another. But where does the problem originate in the system? Copyright © 2008 Triveni Digital, Inc. 77

Move backwards in your set up PSIP Generator MUX ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB ASI Satellite Dish Let’s take a look at the output of the groomer’s Gig-E interface. Does the MPEG Analyzer indicate that there is an Audio Buffer problem here? Transport Stream Analyzer Copyright © 2008 Triveni Digital, Inc. 78

Standards violation is still present In this case, Audio Buffer Underflow is reported by the Analyzer. This explains why the audio and video elementary streams are out of sync with one another. But where does the problem originate in the system? Copyright © 2008 Triveni Digital, Inc. 79

Move backwards further in your set up PSIP Generator MUX ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB ASI Satellite Dish Now connect to the output of the Satellite Receiver. Does the program under test still show Audio Buffer alarms? In this case, the Audio buffer errors do not show up when the MPEG analyzer is plugged into the Output of the Satellite receiver. Clearly the buffer problems are introduced in the Groomer/Splicer component of the system. Transport Stream Analyzer Copyright © 2008 Triveni Digital, Inc. 80

And further… PSIP Generator MUX ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB ASI Satellite Dish QPSK Now connect to the output of the Satellite Receiver. Does the program under test still show Audio Buffer alarms? In this case, the Audio buffer errors do not show up when the MPEG analyzer is plugged into the Output of the Satellite receiver. Clearly the buffer problems are introduced in the Groomer/Splicer component of the system. Transport Stream Analyzer Copyright © 2008 Triveni Digital, Inc. 81

Using recording capability to collect data Groomer and/or Splicer Modulator and Upconverter (RF or Fiber)‏ Gig-E Or ASI QPSK Satellite Receiver QAM Satellite Dish Record from These points The source of the underlying standards violation has been identified. Engineers on site can now troubleshoot that device themselves. Settings in the Groomer/Splicer should be altered, or perhaps a software upgrade is in order… They could also forward the problem to a subject matter expert; someone intimately familiar with the device under test. Finally, it is possible to contact the support organization for the manufacturer of the device under test for help. Be sure to have the information that the support engineer needs when you call: 1) The type of standards violation detected on the analyzer 2) A recording of the ENTIRE transport stream at the input and the output of the device under test. Most errors can be diagnosed with a 30 second recording of stream. Transport Stream Analyzer Copyright © 2008 Triveni Digital, Inc. 82

MPEG Monitoring Over the Long Term
PSIP Generator MUX ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB ASI Satellite Dish QPSK MPEG analyzers can help enormously with fault isolation. However, they are often too expensive to realistically use to monitor all transport streams leaving a Head end all the time. Fault Transport Stream Analyzer Copyright © 2008 Triveni Digital, Inc. 83

On Error – Do something! PSIP Generator MUX QPSK Transmitter 8VSB
ASI QPSK SMPTE 310 Transmitter Satellite Receiver 8VSB ASI Satellite Dish QPSK Transport Stream Analyzer Error Detected! , SNMP, Contact Closure etc. Copyright © 2008 Triveni Digital, Inc.

Three main monitoring and troubleshooting lessons: Fix Continuity Problems first Continuity errors create bogus alarms in other areas Until you resolve the continuity problems, it will be very hard to determine if you have other problems in your stream Check for PCR jitter PCR jitter can cause packet over- or underflow problems Lip synch errors may also be result of PCR jitter Move Backward through your network as you debug Isolate the offending device first, then go for detailed problem solving steps (recording a file, etc.)‏ Copyright © 2008 Triveni Digital, Inc.

References Information Technology -- Generic Coding of Moving Pictures and Associated Audio Information: Systems (MPEG-2 Systems standard), ISO/IEC ATSC Digital Television Standard, ATSC Doc. A/53. Program and System Information Protocol for Terrestrial Broadcast and Cable, ATSC Doc. A/65 (with corrigenda and amendments). ATSC Data Broadcast Standard, ATSC Doc. A/90. Measurement Guidelines for DVB Systems, ETSI Technical Report ETR 290. Copyright © 2008 Triveni Digital, Inc.

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