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

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Faxing Q and A from 2600hz (2600hertz)

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Page 1: Faxing Q and A

Powerful, Distributed, API Communications

Call-in Number: 805-309-5900 Pin 705-705-141

Expert Q&A: Faxing EditionMay 3rd, 2013

Page 2: Faxing Q and A

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

Page 3: Faxing Q and A

Welcome

Page 4: Faxing Q and A

Our Panelists

Joshua Goldbard

Marketing Ninja, 2600hz

Darren Schreiber

Founder, 2600hz

Page 5: Faxing Q and A
Page 6: Faxing Q and A

Some background…

Page 7: Faxing Q and A

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

Page 8: Faxing Q and A

• 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

Page 9: Faxing Q and A

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

Page 10: Faxing Q and A

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

Page 11: Faxing Q and A

Let’s Get Technical!

Page 12: Faxing Q and A

Trouble With Faxing• Jitter

• Codec Selection / Compression

• T. 38 Negotiation

• PSTN Equipment Configuration

• Latency

Page 13: Faxing Q and A

Trouble with Faxing:

SILENCE is DEATH

Page 14: Faxing Q and A

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

Page 15: Faxing Q and A

A standard fax transmissionHi!

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?

Page 16: Faxing Q and A

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!

Page 17: Faxing Q and A

A standard fax transmissionHi!

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?

Page 18: Faxing Q and A

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

Page 19: Faxing Q and A

PSTN call w/ Noise

This will get corrected

Still clear gaps of silence

(end)

Page 20: Faxing Q and A

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

Page 21: Faxing Q and A

VoIP Fax w/ JitterHeard you

perfectly, send me a page!

OK, sending!

Umm, hey, you paused, I thought you were done!

Synchronization is lost…

Page 22: Faxing Q and A

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

Page 23: Faxing Q and A

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

Page 24: Faxing Q and A

Making Fax Over IP Work:

T. 38 to the Rescue

Page 25: Faxing Q and A

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

Page 26: Faxing Q and A

VoIP Fax w/ Jitter + T. 38

Fax would have continued!

T. 38 would have filled this in with

whitespace

Page 27: Faxing Q and A

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

Page 28: Faxing Q and A

T. 38

Page 29: Faxing Q and A

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

matter here

Page 30: Faxing Q and A

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…

Page 31: Faxing Q and A

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

Page 32: Faxing Q and A

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

Page 33: Faxing Q and A

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

FAILBACK!

Page 34: Faxing Q and A

Making Fax Over IP Work:

CODECS

Page 35: Faxing Q and A

Voice “Speeds”

Page 36: Faxing Q and A

Fax Speeds

Page 37: Faxing Q and A

How do you fit a 14.4kbps

fax over a 8kbps voice

signal?

ANSWER: YOU CAN’T

Page 38: Faxing Q and A

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

Page 39: Faxing Q and A

Let’s take some time to pontificate about

faxing at scale…

Massive Lethal Papercuts

Page 40: Faxing Q and A

Virtualization in Faxing?

Page 41: Faxing Q and A
Page 42: Faxing Q and A

How to avoid

Excessive Finger

Pointing

Page 43: Faxing Q and A

• 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

Page 44: Faxing Q and A

QUESTIONS???