ANT : A System for Audio Signaling Based NAT Traversal

Jan 8, 2011 COMSNETS 2011

ANT : A System for Audio Signaling Based NAT

Traversal

Ashish Patro Yadi Ma Fatemah Panahi Jordan Walker

Suman Banerjee

Department of Computer SciencesDepartment of Computer Sciences

University of Wisconsin-MadisonUniversity of Wisconsin-Madison

Outline

Problem

Overview of ANT

Component Details

Evaluation

Summary


Typical NAT scenario


Typical NAT scenario


Problem : Setting up a direct connection between NATed clients across different LANs.

Problem : Setting up a direct connection between NATed clients across different LANs.

Scenario


Client A Client B

Laptop

Cellular Phones

Goal

Create a direct end to end connection between any 2 NATed clients.

Use no third party intermediate node.

Can be used as a building block by applications.

e.g. : Direct Transfer of Large Files, Chat etc.


Issues

Identify internal and external IP/port information.

Common Solutions : Modify router configuration (Port Mapping), use external relay servers etc.

Cumbersome for lay users to deal with NAT traversal


Solution??

ANT….

A system for Audio signaling based NAT Traversal.

Uses an ordinary phone connection as an “out of band” mechanism for NAT traversal.


Outline

Problem

Overview of ANT

Component Details

Evaluation

Summary


ANT in action


Step 1 : Setup a phone connection.Step 1 : Setup a phone connection.

Client A Client B

ANT in action


Step 2 : A obtains configuration information for NAT traversal from its UPnP enabled router.

Step 2 : A obtains configuration information for NAT traversal from its UPnP enabled router.

Client A Client B

NAT Router

Internal IP:Port : 10.0.0.3:6000

Configuration Info :-External IP:Mapped port : 128.32.12.3:54678

ANT in action


Step 3 : A encodes configuration data into audio signals.

Step 3 : A encodes configuration data into audio signals.

Client A Client B

NAT Router

10101001……

ANT in action


Step 4 : Sound is transferred from A’s laptop to A’s phone,

then from B’s phone to B’s laptop.

Step 4 : Sound is transferred from A’s laptop to A’s phone,

then from B’s phone to B’s laptop.

Client A Client B

NAT Router

ANT in action


Step 5 : B decodes audio, corrects errors and gets the data back.

Step 5 : B decodes audio, corrects errors and gets the data back.

Client A Client B

NAT Router

10101001……

ANT in action


Step 6 : Setup a direct Peer to Peer (P2P) connection.Step 6 : Setup a direct Peer to Peer (P2P) connection.

Client A Client B

NAT Router

NAT Router

Outline

Problem

Overview of ANT

Component Details

Evaluation

Summary


ANT Components

Port Mapping at Client A.

Encoding/decoding audio signals.

Synchronizing encoder/decoder.

Noise filtering.

Error Correction.


NAT Traversal

NATed machines can only make outgoing connections directly.

NAT traversal requires internal-external IP/Port Mapping.

UPnP helps here.


UPnP for NAT traversal

Standard interface and widely available in Internet Gateway Devices (IGD) for the purpose of mapping ports to clients.

Retrieves the external IP address device.

Can add/remove port mappings.

We use Java Library for UPnP to create a port mapping for ANT.


Data to Audio Conversion

Modulate binary data to audio signals.

Keying techniques ASK : Amplitude Shift Keying PSK : Pulse Shift Keying FSK : Frequency Shift Keying

We use a technique analogous to FSK.


Audio Frequencies

Human audible frequency range : 20Hz to 20,000Hz.

Laptop soundcards work well between 800Hz to 9000Hz.

Phone soundcards work well between 1000Hz to 4000Hz.

We used the range 1200Hz – 3100Hz.


Encoding Scheme

We group consecutive bits into symbols.

Use 1 unique frequency per symbol.

Symbol Size = N bits.

Unique frequencies required = 2N.


Encoding Scheme


Symbol Size : 8 bits

e.g. : 1001011

------- 1200Hz------- 1230Hz

.

.

.------- 8820Hz------- 8850Hz

256 frequencies

Encoding Scheme



e.g. : 1001011

------- 1200Hz------- 1230Hz

.

.

.------- 8820Hz------- 8850Hz

256 frequencies

Requires a band of 7650 Hz for 256 unique frequencies separated by 30 Hz.

Requires a band of 7650 Hz for 256 unique frequencies separated by 30 Hz.

Encoding Scheme



e.g. : 1001

------- 1200Hz------- 1250Hz

.

.

.------- 1900Hz------- 1950Hz

16 frequencies

Easily fits within the frequency band available.Easily fits within the frequency band available.

Synchronization


Problem :-Detect start and end of the audio transmission.


Synchronization




Solution :-Use a preamble/postamble for each transmission.

Solution :-Use a preamble/postamble for each transmission.

Synchronization

Detect start of transmission.

Similar to “preamble” in wireless networks.

Also used to infer timing information.

2 synchronization frequencies for start.

1 synchronization frequency for end.Jan 8, 2011 COMSNETS 2011

Synchronization


Distinguish Consecutive Symbols Consecutive symbols can be same.

Need to distinguish between them.

One solution : Use a separation beep.

Problem : Halves the data rate.


Distinguish Consecutive Symbols Our Solution : Use two non-

overlapping frequency bands.

Transmit consecutive symbols in alternating bands.

Much easier to decode symbols.

ANT uses two separate bands of 16 frequencies (< 2000 Hz).


Decoding Audio Symbols

Synchronization to detect start of transmission.

Fast Fourier Transform (FFT) on captured audio samples.

Noise Filtering : Discard noise away from relevant frequencies (F – 15Hz to F + 15Hz) and below certain amplitude.


Error Correction

Handle errors/erasures during transmission/reception.

ANT uses Forward Error Correction (FEC).

FEC avoids a back-channel.

ANT uses Reed-Solomon codes in GF(16).


Putting the pieces together…

Use UPnP to setup a port mapping at Client A.

Client A transmits mapping via the out-of-band audio channel to Client B.

Client B decodes audio signals to obtain mapping.

Client B connects to Client A.


Putting the pieces together…


Client A Client B

NAT Router

NAT Router

Other applications of ANT

Password Transfer.

Product Key exchange.


Outline

Problem

Overview of ANT

Component Details

Evaluation

Summary


Evaluation

Tested ANT with a variety of devices (laptops, phones).

Environments No or Light Noise : Quiet Conference Room.

Medium Noise : Offices, homes.

Heavy Noise : Compute Lab (Background noise).


Experiment 1

Clients A and B are in quiet environments.

Used different combinations of phones.

Tested ANT 4-6 times for each combination.

Reported the overall success rate.


Results : Experiment 1




- ANT performed really well in the presence of little or no noise.

- Failures occurred due to a bad speaker in the Sony phone.

- ANT performed really well in the presence of little or no noise.

- Failures occurred due to a bad speaker in the Sony phone.

Experiment 2

First client is a heavy noise environment.

Second client in a light/medium noise environment.




- Errors/erasures caused by noise cause a few failures.- Success rate still above 66% in all cases.- Errors/erasures caused by noise cause a few failures.- Success rate still above 66% in all cases.

Experiment 3 (Speak Test)

Human speakers present near laptop with 4 scenarios :


Scenario Client A Client B

Scenario 1 (S1) Speaking with soft voice

Quiet, no/light background

noise

Scenario 2 (S2) Speaking with loud voice

Quiet, no/light background

noise

Scenario 3 (S3) Speaking with soft voice

Quiet, heavy background

noise

Scenario 4 (S4) Speaking with loud voice

Quiet, heavy background

noise



- Human voice causes some problems for ANT.- 2-3 attempts enough to establish a connection in

most cases.

- Human voice causes some problems for ANT.- 2-3 attempts enough to establish a connection in

most cases.

Playing Background Music…

Cause major problems to ANT.

Music generates a vast range of frequencies.

Interferes with ANT by inserting spurious symbols into audio transmissions.

Causes problems for the decoder.


Outline

Problem

Overview of ANT

Component Details

Evaluation

Summary


Summary

UPnP is easily available and provides a standard interface for port mapping.

Short Audio transmission (few seconds).

Out-of-band audio mechanism for NAT traversal works well is most scenarios.

Can also use audio mechanism for short, robust and secure data transmissions.


ANT Demo.

A demo video demonstrating ANT is available at :-

http://www.cs.wisc.edu/wings/projects/ant

Link also available in the paper.


Thank you.

Questions ?


ANT : A System for Audio Signaling Based NAT Traversal

Documents

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