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Faxing Q and A


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Faxing Q and A from 2600hz (2600hertz)

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Faxing Q and A

  1. 1. Powerful, Distributed, API CommunicationsCall-in Number: 805-309-5900 Pin 705-705-141Expert Q&A: Faxing EditionMay 3rd, 2013
  2. 2. BEFORE WE BEGIN!This presentation will make absolutely no senseto you if you do not watch the following video MINUTES 00:44 through 2:50Call-in Number: 805-309-5900 Pin 705-705-141 Expert Q&A: Faxing EditionMay 3rd, 2013
  3. 3. Welcome
  4. 4. Our PanelistsJoshua GoldbardMarketing Ninja,2600hzDarren SchreiberFounder, 2600hz
  5. 5. Some background…
  6. 6. What is a Fax?• First patented in 1843• Morse was 1844• Bell was 1876• Used to send documents using the most availableinfrastructure• Preceded by flag and smoke signaling
  7. 7. • 1843: Fax Patented• 1924: First Color Fax• 1964: Xerox invents Digital Faxing• 1985: First Computer Fax BoardVery old industry, lots of standardization and lots ofweirdnessMajor Milestones
  8. 8. IP Faxing is weird…• No transport advantage when compared to other IP transit• Expensive• Slow• Kind of a painWhy do we do it? Facsimiles are legally binding; ergo regulations.Plus, people are stubborn and used to their “old” technology
  9. 9. Why IP Fax > Analog Faxing• IP Fax is cheaper• IP Fax can be centralized• IP is much easier to manipulate and integrate• Analog has a long setup time (45 days for PRI)• IP Fax can be geographically fault tolerant
  10. 10. Let’s Get Technical!
  11. 11. Trouble With Faxing• Jitter• Codec Selection / Compression• T. 38 Negotiation• PSTN Equipment Configuration• Latency
  12. 12. Trouble with Faxing:SILENCE is DEATH
  13. 13. Faxing is sort of “synchronous”• One side at a time!• One side sends a message while the other side is silent• When the sending side pauses, it means it’s time for theopposite side to respond• Fax transmission is made up of tones and silence• Tones represent signaling• “static” sound represents your data image (very fast tones)• Silence represents a hand-off of control to the other side
  14. 14. A standard fax transmissionHi!I’m readyHey! MeToo!Let’s testout thisline!Heard youperfectly! Send me apage!Here yougo!Done!OK! Whatnext?
  15. 15. Look Closely• If only one person can “speak” at a time…How do you tell the other guy you’re done and it’s his turn?SILENCE IS GOLDEN!
  16. 16. A standard fax transmissionHi!I’m readyHey! MeToo!Let’s testout thisline!Heard youperfectly! Send me apage!Here yougo!Done!OK! Whatnext?
  17. 17. This works great on the PSTN• PSTN isn’t perfect• It has cracks, pops, hisses, static• Fax machines were designed for that, so they can removethose in most cases• PSTN does have some general guarantees• The audio, even if distorted, almost always makes it• Not really a concept of “cutting out” in PSTN land• So, fax machines assume there will not be cutting out
  18. 18. PSTN call w/ NoiseThis will getcorrectedStill clear gapsof silence(end)
  19. 19. But VoIP introduces jitter…• Jitter is a slight pause when audio packets are missing• Usually because the line is too slow/congested and the datadoesn’t get there in time• Or because of packet loss on a misconfigured device• Some other reasons as well, but those are the major ones
  20. 20. VoIP Fax w/ JitterHeard youperfectly, send mea page!OK, sending!Umm, hey, you paused, Ithought you were done!Synchronization islost…
  21. 21. Dealing with Jitter• First, note that a line which sounds perfectly fine for voicecalls may still have lots of jitter• The human ear tolerates some amounts of jitter so youdon’t notice it• Faxes do not• You can deal with jitter on VoIP most of the time• Most devices have a jitter buffer. Turn it up (high)• Turn OFF adaptive jitter buffers. Faxes need the timing andsignal to be consistent
  22. 22. Dealing with Jitter• Let’s take a look at how to adjust the jitter buffer settings• It’s so easy!• Sidebar: Turn off echo cancellation while you’re at it• Since the fax is not listening to itself anyway while it’ssending, echo almost never matters• Echo cancellation just adds one more “feature” on thedevice that might screw up faxing
  23. 23. Making Fax Over IP Work:T. 38 to the Rescue
  24. 24. T. 38 Overview• Another way of dealing with Jitter is T.38• T.38 is an adaptation of faxing designed for VoIP• Modifies the transmission mechanism on the IP side• Inserts padding / white-noise on the PSTN side• Intentionally duplicates RTP packets to make sure they getthere
  25. 25. VoIP Fax w/ Jitter + T. 38Fax would havecontinued!T. 38 would havefilled this in withwhitespace
  26. 26. T. 38 Overview• T. 38 was mainly designed for converting faxes when runninglong-distances between PSTN endpoints• Began being added to endpoint devices directly• The idea was to get the T.38 conversion to happen as close aspossible to the fax machine
  27. 27. T. 38
  28. 28. T. 38Jitter isunlikely here Jitter won’t reallymatter here
  29. 29. T. 38• But people always say, T. 38 doesn’t work that well.• Why?• Different vendors implemented it slightly differently• Sometimes the ATA or device you’re using doesn’t workwith your vendor• BUT MORE LIKELY• Your vendor sometimes cheats• More on that next…
  30. 30. T. 38• Here’s a secret• When you do a PCMU call, your vendor often hasequipment that just passes the data along with minimal / noprocessing• When you do G729 or T. 38 your call must be routed tospecial equipment on the carrier side to handle that andconvert it to PCMU• That is why some carriers tell you to start fax calls as G.729
  31. 31. T. 38• This leads to the typical requirement that…• You use a carrier who supports T. 38 (has the equipment)• You start your call as something other than PCMU• You properly setup T. 38 on your side and request itproperly• Let’s look at a sample request
  32. 32. T. 38• But wait – G729 causes a problem…• Why is this a problem?FAILBACK!
  33. 33. Making Fax Over IP Work:CODECS
  34. 34. Voice “Speeds”
  35. 35. Fax Speeds
  36. 36. How do you fit a 14.4kbpsfax over a 8kbps voicesignal?ANSWER: YOU CAN’T
  37. 37. Lessons from the front lines• What codec is best?• T.38? Why or why not?• A cornucopia of telecom equipment• Fax Servers• Configuration settings• NAT Transversal
  38. 38. Let’s take some time to pontificate aboutfaxing at scale…Massive Lethal Papercuts
  39. 39. Virtualization inFaxing?
  40. 40. How toavoidExcessiveFingerPointing
  41. 41. • Faxing is hard because IPIntroduces unbounded timeUncertainty• Variation in time is unexpectedbehavior for faxing equipment• Solution: Reduce Complexity• (As much as you possibly can)Recap
  42. 42. QUESTIONS???