The have to buffer in an elastic store to be able to do this. Similar to pseudowire for T1.
Then he has to sync the output of his buffer with GPS or colorburst or WWVB or some other external sync on his end. Nobody can sync that tight over the internet, not even dedicated ethernet is good enough for that tight. From: Adam Moffett Sent: Tuesday, December 10, 2019 2:32 PM To: [email protected] Subject: [AFMUG] Testing ridiculous jitter constraints I was discussing with a TV station engineer some sort of disturbance he's seeing in a video feed which crosses a section of our network. This is crossing a blend of fiber and part 101 microwave, and it's been working fine for several years until suddenly their problem cropped up about a month ago. His words, emphasis mine: "We are seeing PCR clocking intolerance in our television data streams (~19.392685 Mbps, plus overhead; PCR is sent at a defined interval, at least once every 40ms, for each of five embedded streams with a drift tolerance of <10mHz and a jitter error of <25us per ETSI TR 101 290), " I know jack-all about TV broadcasting, but I discussed packet to packet delay variation of less than 1 millisecond being considered perfect in my world, and "do I understand you correctly that you really need clock signals transmitted across the network with less than 25 micro seconds of jitter?" He seems to feel that yes, that is the case. Is this guy mistaken? I can't believe whatever converts the TV signal to ethernet and back wouldn't have at least some minimal jitter buffer. Even if he's right....how do you even test that? A wireshark capture will have a time attached to each packet, and that is displayed in microseconds, but how precise could that be in real life? I mean hypothetically, by the time a frame gets copied to a mirrored switch port, hits my ethernet card, passes through the whole software stack to get into Wireshark couldn't that have introduced 25us worth of new variance? What about MEF OAM statistics? Would that be precise enough? More than anything I'm shocked at the assertion about the required precision. I feel like on a one-way transmission like TV they could add a half second delay to accommodate jitter or retransmissions and nobody watching at home would ever know the difference. But I'm also curious about how you would check that assuming you had to. -Adam -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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