Serval Project, October 2014
These notes accompany the release in October 2014 of version 0.92 of the Serval Mesh app for Android 2.2 “Froyo” and above.
Serval Mesh is an app for Android 2.2 “Froyo” and above. It provides free, secure phone-to-phone voice calling, SMS and file sharing over Wi-Fi, without the need for a SIM card or a commercial mobile telephone carrier. In other words, it lets your Android phone call other Android phones running Serval Mesh within Wi-Fi range.
The Serval Mesh Privacy Policy describes how Serval Mesh handles your personal and other sensitive information.
Serval Mesh is EXPERIMENTAL SOFTWARE. It has not yet reached version 1.0, and is intended for pre-production, demonstration purposes only. It may not work as advertised, it may lose or alter messages and files that it carries, it may consume a lot of space, speed and battery, and it may crash unexpectedly.
On the Serval Mesh "Connect" screen, connecting to "Ad Hoc Mesh" will request root permission (super-user) on your Android device in order to put Wi-Fi into Ad-Hoc mode. If you grant super-user permission to Serval Mesh, it will attempt to reinstall the Wi-Fi driver software on your device, which could result in YOUR DEVICE BECOMING PERMANENTLY DISABLED ("BRICKED").
On the Serval Mesh "Connect" screen, selecting "Portable Wi-Fi Hotspot" will put your device's Wi-Fi into Access Point mode. If you have a mobile data plan, this will give nearby devices access to your mobile data plan, and COULD COST YOU MONEY.
The Serval Mesh "Connect" screen allows you to connect to other Serval Mesh devices that act as Access Points (Hotspots) or Ad Hoc peers. If you do so, this will cut off normal Wi-Fi network access while Serval Mesh is running, and services like Google Updates, E-mail, social media and other notifications may not work.
Serval Mesh telephony is a “best effort” service, primarily intended for when conventional telephony is not possible or cost effective, and MUST NOT BE RELIED UPON for emergencies in place of carrier-grade communications systems. The Serval Project cannot be held responsible for any performance or non-performance of the technologies that they provide in good will, and if you use these technologies you must agree to indemnify the Serval Project from any such claims.
The Serval Mesh software copies all files shared using the Rhizome file distribution service to other phones and devices running the Serval Mesh software, regardless of size, content or intended recipient. The Serval Project cannot be held responsible for the legality or propriety of any files received via Rhizome, nor for any loss, damage or offence caused by the transmission or receipt of any content via Rhizome.
See the disclaimers below.
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The "Connect" screen has been simplified and made more usable. It no longer lists all available Wi-Fi networks, but can open the Android Wi-Fi settings screen to allow you to choose a network. It also supports the Commotion MeshTether app, if installed.
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The Serval mesh routing protocol now sends unicast packets whenever necessary, instead of only on single-hop links. Most devices cease responding to broadcast packets when their screen is off (to save power), so this improvement means that MeshMS messages are now delivered more rapidly, all devices now show their phone number and name on peer list screens at all times, and multi-hop voice calls are now possible, even when intermediate nodes have their screen off.
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The MeshMS protocol and implementation have been completely overhauled. MeshMS messages are encrypted end-to-end, and only decrypted when displayed. No copies of the clear text of messages will be stored. When new messages are sent, only the new data will be copied across the network. When the other party receives a message, it is acknowledged and a "delivered" label will be displayed indicating that all messages before this marker have arrived. Content is encrypted using Rhizome's default payload encryption: the Salsa20 stream cypher with key agreement using the Curve25519 elliptic curve Diffie-Hellman scheme by Daniel J. Bernstein, implemented by the NaCl library.
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MeshMS in release 0.92 is incompatible with earlier releases. A MeshMS message created using release 0.92 cannot be read on 0.91 or earlier, and vice versa. The internal format we use for storing messages, and the way we encrypt them has changed. Furthermore, due to an upgrade of the Rhizome sync protocol (see below), messages created by one release will not be carried to a device with the same release unless all intermediate nodes (hops) have the same release. This means that in order to preserve MeshMS coverage, all nodes in the network must be upgraded to 0.92. (The auto-upgrade feature makes this very easy.)
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The peer list screen is much more responsive. It now resolves phone numbers (DID) and names of peers in parallel, not sequentially, and is no longer starved by other operations that make heavy use of the internal serval-dna interface (for example the high volumes of incoming Rhizome bundles that tends to occur when starting a freshly installed app for the first time in an active mesh network). Peers dim to grey within seconds of becoming unreachable; leaving and re-entering the peer list screen will remove unreachable peers altogether. If peers fail to appear, it can now only be because they remain unreachable due to network conditions (eg, poor signal, congestion or Wi-Fi incompatibility).
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The Rhizome synchronisation protocol has been upgraded and is backward compatible but not forward compatible, ie, release 0.92 can receive content from 0.91 and earlier, but not vice versa. The new protocol uses less CPU and network to detect updates after synchronisation is complete, so conserves power and bandwidth.
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The Rhizome storage layer will attempt to preserve a minimum of 100MB of free space. While internally there are two settings to control this behaviour, no user interface has been built to set them. Old content will be discarded to make room for new content, with a bias towards discarding large files first. This check will be performed whenever new content arrives, and every 30 minutes while the application is running.
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The impact of Rhizome operations and transfers on voice call latency has been reduced but not eliminated (see Known Issues below).
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Multi-hop voice calls have been tested and are more reliable than they were in 0.90 “Shiny”, but there are still issues (see below).
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If there is no built in dialler, we now provide our own simple activity to search for a phone number and initiate a phone call.
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The Rhizome File Detail dialog now displays the "Open" and "Save" buttons together instead of just "Save" initially, which changed to "Open" after the file was saved.
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There is a new setting to change the MeshMS notification tone -- see batphone issue #86.
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The "Help" screen has been updated to include these Release Notes and Credits.
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We no longer display scary warnings on install. Instead we only display warnings if you attempt to test Adhoc Wi-Fi.
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Code quality has improved, closing various memory leaks and potential SQL injection vulnerabilities.
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Fixed batphone issue #53 -- the "Unshare" button on the Rhizome "Find" list did not remove the name from the list.
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Fixed batphone issue #68 -- application crash when the remote party hung up a voice call.
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Fixed batphone issue #71 -- application crash when opening the peer list, observed on Samsung Galaxy S running CyanogenMod 10 nightly build.
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Fixed -- application crash if there are nearby Access Points with hidden SSIDs.
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Fixed -- application crash if the phone has an incompatible library for the Opus audio codec.
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The application will operate without requesting root permission unless "Mesh" network support is explicitly requested by the user. No attempt will be made to modify the phone's network settings, test for Adhoc support or request permission to run as root on the initial install of the application.
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New network connection screen replaces the old On/Off switch. This screen has been designed to guide the user in how to establish a network connection with other nearby phones.
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Significant changes have been made to the method the application uses to deliver packets reliably across the network. A new routing algorythm has been implemented. The previous distance vector approach to routing could be confused by highly dense networks and reacted very slowly to changing conditions. Serval's new link state router will react to changing network conditions more accurately and rapidly. When network packets are lost, they will be retransmitted on a per-hop basis, greatly increasing the reliability of the network even over multiple very lossy network links.
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Add support for the Opus audio codec. This codec can greatly reduce the bandwidth required for a voice call without noticibly reducing audio quality or adding to delay.
This release of Serval Mesh has been extensively used and tested on the following devices with no problems:
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Huawei IDEOS X1 u8180, running Android 2.2.2 (rooted) and CyanogenMod 2.3.7
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HTC Sensation, running Android 2.3.4 (rooted) and HTC Sense 3.0
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HTC One S
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Motorola Milestone
Prior releases of Serval Mesh are known to work on the following devices, which is a strong indication that this release may also work:
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Huawei IDEOS u8150
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Samsung Galaxy Tab 7 inch
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Samsung Galaxy Gio S5660, running Android 2.3.6 (rooted)
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Samsung Vitality SCH-R720
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ZTE Score X500
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HTC/Google G1 (“Dream”)
This release of Serval Mesh is known to work on the following devices with minor problems:
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Samsung Galaxy S2 GT-I9100, running Android 2.3 (rooted): Ad-Hoc Wi-Fi is not completely compatible with the Ad-Hoc Wi-Fi on other devices, specifically the Huawei IDEOS phones listed above. If the Galaxy S2 is the first device to join the mesh, then IDEOS phones cannot join. However, if an IDEOS phone is the first device, then the Galaxy S2 does join okay.
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Google Nexus 1: does not interoperate well with HTC/Google G1.
The following devices have major known problems in this or prior releases:
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HTC Wildfire A3335
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Samsung Galaxy Nexus: Wi-Fi Ad-Hoc mode does not start; Wi-Fi mode reverts to Off.
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Motorola Razr i XT890: Wi-Fi control does not work.
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Samsung Galaxy Note 2: does not detect peers. Possibly the same problem as the Galaxy S2 described above, but not tested.
See the Mobile Device Compatability Table for more details and devices.
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While Serval Mesh services are enabled and you are connected to a Wi-Fi network, Android will be prevented from sleeping. This will drain the battery quickly -- see batphone issue #91.
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Voice call quality degrades whenever Rhizome or MeshMS operations or transfers are in progress. Rhizome can worsen network congestion, transfers are not throttled and can lead to additional network latency and packet loss due to a problem known as Bufferbloat. -- see serval-dna issue #1.
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Voice call quality is variable. There is no echo cancellation, so echo may have to be controlled by lowering speaker volume or using earphones. Audio latency (delay) can exceed one second in some situations -- see batphone issue #93.
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Voice call audio has been observed to be missing on a Nexus 4 running 4.2.1, and upgrading to a 4.2.2 custom ROM restored audio -- see batphone issue #77 and batphone issue #96.
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VoMP does not play a "ringing" sound while placing a call, nor a "hangup" sound when the other party hangs up -- see batphone issue #76.
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Every new MeshMS message increases the size of the Rhizome payload that contains all the messages in that conversation ply. So every MeshMS conversation will consume more network bandwidth and SD Card space as it grows -- see serval-dna issue #28. This cannot be worked around.
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If a user starts a Serval Hotspot on the "Connect" screen, then the application overwrites the user's own personal hotspot name (and settings) with "ap.servalproject.org". When the Serval Hotspot is turned off, Serval Mesh restores the user's own personal hotspot settings, which involves turning the user's Wi-Fi hotspot on and off briefly. This could cause some concern or confusion, but is the only way that Android provides to restore hotspot settings.
There are more known bugs and issues listed under the GitHub Issues page for batphone issues and serval-dna issues.
Serval Mesh is free software produced by the Serval Project and many contributors. The copyright in all source code is owned by Serval Project Inc., an organisation incorporated in the state of South Australia in the Commonwealth of Australia.
The Java/XML source code of Serval Mesh is licensed to the public under the GNU General Public License version 3. The serval-dna component of Serval Mesh is licensed to the public under the GNU General Public License version 2.
All technical documentation is licensed to the public under the Creative Commons Attribution 4.0 International license.
All source code and technical documentation is freely available from the Serval Project's batphone and serval-dna Git repositories on GitHub.
This release was made possible by the generous donors to the Speak Freely crowdfunding campaign, in particular our "True Believers":
- Douglas P. Chamberlin
- Walter Ebert
- Andrew G. Morgan, California, USA
- Fred Fisher
This release was funded by a grant from OpenITP.
Earlier development of Serval Mesh has been funded by the New America Foundation's Open Technology Institute, the Shuttleworth Foundation, and Nlnet Foundation.
The Serval Project was founded by Dr Paul Gardner-Stephen and Romana Challans, both academic staff at the School of Computer Science, Engineering and Mathematics at Flinders University in South Australia. Their work on the Serval Project is made possible by the ongoing support of the university.
SERVAL MESH refers to the software, protocols, systems and other goods, tangible and intangible produced by The Serval Project, Serval Project, Inc., and Serval Project Pty Limited.
SERVAL MESH COMES WITH NO WARRANTY, EXPRESSED OR IMPLIED, AND IS NOT FIT FOR MERCHANTABILITY FOR ANY PURPOSE. USE AT YOUR SOLE RISK.
SERVAL MESH WILL REDUCE THE BATTERY LIFE OF DEVICES ON WHICH IT RUNS.
SERVAL MESH MAY CONSUME ALL STORAGE, both LOCAL and EXTERNAL (eg, MICRO SD CARD) ON THE DEVICES ON WHICH IT RUNS.
SERVAL MESH SHOULD NOT BE INSTALLED ON DEVICES WHICH ARE DEPENDED UPON FOR EMERGENCY COMMUNICATION.
SERVAL MESH MAY TRANSMIT SOME DATA, INCLUDING TELEPHONE CALLS, MESSAGES AND OTHER POTENTIALLY PRIVATE DATA IN THE CLEAR.
SERVAL MESH PROTECTIONS against IMPERSONATION or OTHER MISAPPROPRIATION of IDENTITY ESTABLISHING FACTORS MAY BE DEFECTIVE and MAY NOT PERFORM AS EXPECTED.
SERVAL MESH SHOULD NOT BE RELIED UPON IN AN EMERGENCY is it is an INCOMPLETE PROTOTYPE and BEST EFFORT in nature, and may FAIL TO OPERATE.
SERVAL MESH may COST YOU MONEY if you have a MOBILE DATA PLAN by TURNING OFF WI-FI NETWORK ACCESS or by allowing NEARBY DEVICES TO USE YOUR DATA PLAN WITHOUT YOUR KNOWLEDGE OR CONSENT.
SERVAL MESH may REVEAL AND/OR BROADCAST YOUR LOCATION, IDENTITY OR OTHER INFORMATION through its normal operation.
SERVAL MESH is an INCOMPLETE, PRE-PRODUCTION software, experimental in nature and is not to be considered fit for merchantability for any purpose. It has many defects, omissions and errors that will hamper its fulfilling of its intended purposes.
Copyright 2014 Serval Project Inc.
This document is available under the Creative Commons Attribution 4.0
International licence.