This document provides an overview and discussion of faxing over IP networks. It discusses some key challenges with IP faxing including jitter, codec selection, T.38 negotiation, and latency. T.38 is presented as a way to help deal with jitter by modifying the transmission mechanism and duplicating packets. The importance of carrier support for T.38 is highlighted. Questions from an expert panel discuss virtualization opportunities and best practices for avoiding issues when faxing at scale over IP networks.

1. Powerful, Distributed, API Communications
Call-in Number: 805-309-5900 Pin 705-705-
141
Expert Q&A: Faxing Edition
May 3rd
, 2013

2. BEFORE WE BEGIN!
This presentation will make absolutely no sense
to you if you do not watch the following video
http://bit.ly/15980DW
FROM MINUTES 00:44 through 2:50
Call-in Number: 805-309-5900 Pin 705-705-
141 Expert Q&A: Faxing Edition
May 3rd
, 2013

3. Welcome

4. Our Panelists
Joshua Goldbard
Marketing Ninja,
2600hz
Darren Schreiber
Founder, 2600hz

6. Some background…

7. What is a Fax?
• First patented in 1843
• Morse was 1844
• Bell was 1876
• Used to send documents using the most available
infrastructure
• Preceded by flag and smoke signaling

8. • 1843: Fax Patented
• 1924: First Color Fax
• 1964: Xerox invents Digital Faxing
• 1985: First Computer Fax Board
Very old industry, lots of standardization and lots of
weirdness
Major Milestones

9. IP Faxing is weird…
• No transport advantage when compared to other IP transit
• Expensive
• Slow
• Kind of a pain
Why do we do it? Facsimiles are legally binding; ergo regulations.
Plus, people are stubborn and used to their “old” technology

10. 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

11. Let’s Get Technical!

12. Trouble With Faxing
• Jitter
• Codec Selection / Compression
• T. 38 Negotiation
• PSTN Equipment Configuration
• Latency

13. Trouble with Faxing:
SILENCE is DEATH

14. 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 the
opposite 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

15. A standard fax transmission
Hi!
I’m ready
Hey! Me
Too!
Let’s test
out this
line!
Heard you
perfectly! Send me a
page!
Here you
go!
Done!
OK! What
next?

16. 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!

17. A standard fax transmission
Hi!
I’m ready
Hey! Me
Too!
Let’s test
out this
line!
Heard you
perfectly! Send me a
page!
Here you
go!
Done!
OK! What
next?

18. 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 remove
those 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

19. PSTN call w/ Noise
This will get
corrected
Still clear gaps
of silence
(end)

20. But VoIP introduces jitter…
• Jitter is a slight pause when audio packets are missing
• Usually because the line is too slow/congested and the data
doesn’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

21. VoIP Fax w/ Jitter
Heard you
perfectly, send me
a page!
OK, sending!
Umm, hey, you paused, I
thought you were done!
Synchronization is
lost…

22. Dealing with Jitter
• First, note that a line which sounds perfectly fine for voice
calls may still have lots of jitter
• The human ear tolerates some amounts of jitter so you
don’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 and
signal to be consistent

23. 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’s
sending, echo almost never matters
• Echo cancellation just adds one more “feature” on the
device that might screw up faxing

24. Making Fax Over IP Work:
T. 38 to the Rescue

25. 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 get
there

26. VoIP Fax w/ Jitter + T. 38
Fax would have
continued!
T. 38 would have
filled this in with
whitespace

27. T. 38 Overview
• T. 38 was mainly designed for converting faxes when running
long-distances between PSTN endpoints
• Began being added to endpoint devices directly
• The idea was to get the T.38 conversion to happen as close as
possible to the fax machine

28. T. 38

29. T. 38Jitter is
unlikely here Jitter won’t really
matter here

30. 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 work
with your vendor
• BUT MORE LIKELY
• Your vendor sometimes cheats
• More on that next…

31. T. 38
• Here’s a secret
• When you do a PCMU call, your vendor often has
equipment that just passes the data along with minimal / no
processing
• When you do G729 or T. 38 your call must be routed to
special equipment on the carrier side to handle that and
convert it to PCMU
• That is why some carriers tell you to start fax calls as G.
729

32. 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 it
properly
• Let’s look at a sample request

33. T. 38
• But wait – G729 causes a problem…
• Why is this a problem?
FAILBACK!

34. Making Fax Over IP Work:
CODECS

35. Voice “Speeds”

36. Fax Speeds

37. How do you fit a 14.4kbps
fax over a 8kbps voice
signal?
ANSWER: YOU CAN’T

38. 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

39. Let’s take some time to pontificate about
faxing at scale…
Massive Lethal Papercuts

40. Virtualization in
Faxing?

42. How to
avoid
Excessive
Finger
Pointing

43. • Faxing is hard because IP
Introduces unbounded time
Uncertainty
• Variation in time is unexpected
behavior for faxing equipment
• Solution: Reduce Complexity
• (As much as you possibly can)
Recap

44. QUESTIONS???