Changes between Initial Version and Version 1 of pjsip-doc/consider


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Timestamp:
Dec 4, 2013 3:26:13 AM (8 years ago)
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bennylp
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  • pjsip-doc/consider

    v1 v1  
     1{{{ 
     2#!rst 
     3 
     4 
     5Development Considerations 
     6************************** 
     7 
     8Let's review various aspects that you need to consider when developing your application. 
     9 
     10 
     11Target Platforms 
     12================ 
     13Platform selection will affect all aspects of development, and here we will cover  considerations for each platforms that we support. 
     14 
     15Windows Desktop 
     16--------------- 
     17Windows is supported from Windows 2000 up to the recent Windows 8 and beyond. All features are expected to work. 64bit support was added recently. Development is based on Visual Studio. Considerations for this platform include: 
     18 
     19#. because Visual Studio file format keeps changing on every release, we decided to support the lowest denominator, namely Visual Studio 2005. Unfortunately the project upgrade procedure fails on Visual Studio 2010, and we don't have any solution for that. But VS 2008 and VS 20012 work. 
     20 
     21MacOS X 
     22------- 
     23All features are expected to work. Considerations include: 
     24 
     25#. development with XCode is currently not supported. This is **not** to say that you cannot use XCode, but PJSIP only provides basic Makefiles and if you want to use XCode you'd need to arrange the project yourself. 
     26#. Mac systems typically provides very good sound device, so we don't expect any problems with audio on Mac.  
     27 
     28Linux Desktop 
     29------------- 
     30All features are expected to work. Linux considerations: 
     31 
     32#. use our native ALSA backend instead of PortAudio because ALSA has less jitter than OSS and our backend is more lightweight than PortAudio 
     33 
     34 
     35iOS for iPhone, iPad, and iPod Touch 
     36------------------------------------ 
     37All features except video are expected to work (video is coming soon!). Considerations for iOS: 
     38 
     39#. you need to use TCP transport for SIP for the background feature to work 
     40#. IP change (for example when user is changing access point) is a feature frequently asked by developers and you can find the documentation here: http://trac.pjsip.org/repos/wiki/IPAddressChange 
     41#. there are some specific issues for iOS 7 and beyond, please see http://trac.pjsip.org/repos/ticket/1697 
     42#. if SSL is needed, you need to compile OpenSSL for iOS 
     43 
     44 
     45Android 
     46------- 
     47All features except video are expected to work (video is coming soon!). Considerations for Android: 
     48 
     49#. you can only use pjsua2 Java binding for this target 
     50#. it has been reported that Android audio device is not so good in general, so some audio tuning may be needed. Echo cancellation also needs to be checked 
     51#. this is also a new platform for us  
     52 
     53 
     54Symbian 
     55------- 
     56Symbian has been supported for a long time but it doesn't get too many attention recently. In general all features (excluding video) are expected to work, but we're not going to do Symbian specific development anymore. Other considerations for Symbian: 
     57 
     58#. the MDA audio is not very good (it has high latency), so normally you'd want to use Audio Proxy Server (APS) or VoIP Audio Service (VAS) for the audio device, which we support. Using these audio backends will also provide us with high quality echo cancellation as well as low bitrate codecs such as AMR-NB, G.729, and iLBC. But VAS and APS requires purchase of Nokia development certificate to sign the app, and also since APS and VAS only run on specific device type, you need to package the app carefully and manage the deployment to cover various device types. 
     59 
     60 
     61Blackberry 10 
     62------------- 
     63Blackberry 10 is supported since PJSIP version 2.2. As this is a relatively new platform for us, we are currently listening to developer's feedback regarding the port. But so far it seems to be working well. Some considerations for BB10 platform include: 
     64 
     65#. IP change (for example when user is changing access point) is a feature frequently asked by developers and you can find the documentation here: http://trac.pjsip.org/repos/wiki/IPAddressChange 
     66 
     67 
     68Windows Mobile 
     69-------------- 
     70This is the old Windows Mobile platform that is based on WinCE. This platform has been supported for a long time, but doesn't seem to attract any attentions recently. We expect all features except video to work, but there may be some errors every now and then because this target is not actively maintained. No new development will be done for this platform. 
     71 
     72Other considerations for Windows Mobile platform are: 
     73 
     74#. the quality of audio device on WM varies a lot, and this affects audio latency. Audio latency could go as high as hundreds of millisecond on bad hardware. 
     75#. echo cancellation could be a problem. We can only use basic echo suppressor due to hardware limitation, and combined with bad quality of audio device, it may cause ineffective echo cancellation. This could be mitigated by setting the audio level to low. 
     76 
     77 
     78Windows Phone 8 
     79--------------- 
     80Windows Phone 8 (WP8) support is being added to PJSIP version 2.2 and is still under development. Specific considerations for this platform are: 
     81 
     82#. WP8 governs specific interaction with WP8 GUI and framework that needs to be followed by application in order to make VoIP call work seamlessly on the device. Some lightweight process will be created by WP8 framework in order for background call to work and PJSIP needs to put it's background processing in this process's context. Currently this feature is under development. 
     83 
     84 
     85 
     86Embedded Linux 
     87-------------- 
     88In general embedded Linux support is similar to Linux and we find no problems with it. We found some specific considerations for embedded Linux as follows: 
     89 
     90#. the performance of the audio device is probably the one with most issues, as some development boards have not so descent sound device that has high audio jitter (or burst) and latency. This will affect end to end audio latency and also the performance of the echo canceller. Also we found that ALSA generally works better than OSS, so if you can have ALSA up and running that will be better. Use our native ALSA backend audio device instead of PortAudio since it is simpler and lighter. 
     91 
     92 
     93QNX or Other Posix Embedded OS 
     94------------------------------ 
     95This is not part of our officially supported OSes, but users have run PJSIP on QNX and Blackberry 10 is based on QNX too. Since QNX provides Posix API, and maybe by using the settings found in the configure-bb10 script, PJSIP should be able to run on it, but you need to develop PJMEDIA sound device wrapper for your audio device. Other than this, we don't have enough experience to comment on the platform.  
     96 
     97 
     98Other Unix Desktop OSes 
     99----------------------- 
     100Community members, including myself, have occasionally run PJSIP on other Unix OSes such as Solaris, FreeBSD, and OpenBSD. We expect PJSIP to run on these platforms (maybe with a little kick). 
     101 
     102 
     103Porting to Other Embedded OSes 
     104------------------------------ 
     105It is possible to port PJSIP to other embedded OSes or even directly to device without OS and people have done so. In general, the closer resemblance the new OS to existing supported OS, the easier the porting job will be. The good thing is, PJSIP has been made to be very very portable, and system dependent features are localized in PJLIB and PJMEDIA audio device, so the effort is more quantifiable. Once you are able to successfully run *pjlib-test*, you are more or less there with your porting effort. Other than that, if you really want to port PJSIP to new platform, you probably already know what you're doing.  
     106 
     107 
     108 
     109Which API to Use 
     110================ 
     111 
     112PJSIP, PJMEDIA, and PJNATH Level 
     113-------------------------------- 
     114At the lowest level we have the individual PJSIP **C** libraries, which consist of PJSIP, PJMEDIA, and PJNATH, with PJLIB-UTIL and PJLIB as support libraries. This level provides the most flexibility, but it's also the hardest to use. The only reason you'd want to use this level is if: 
     115 
     116#. you only need the individual library (say, PJNATH) 
     117#. you need to be very very tight in footprint (say when things need to be measured in Kilobytes instead of Megabytes) 
     118#. you are **not** developing a SIP client 
     119 
     120Use the corresponding PJSIP, PJMEDIA, PJNATH manuals from http://trac.pjsip.org/repos/ for information on how to use the libraries. If you use PJSIP, the PJSIP Developer's Guide (PDF) from that page provides in-depth information about PJSIP library.   
     121 
     122PJSUA-LIB API 
     123------------- 
     124Next up is PJSUA-LIB API that combines all those libraries into a high level, integrated client user agent library written in C. This is the library that most PJSIP users use, and the highest level abstraction before pjsua2 was created.  
     125 
     126Motivations for using PJSUA-LIB library includes: 
     127 
     128#. developing client application (PJSUA-LIB is optimized for developing client app) 
     129#. better efficiency than higher level API 
     130 
     131 
     132pjsua2 C++ API 
     133-------------- 
     134pjsua2 is a new, objected oriented, C++ API created on top of PJSUA-LIB. The API is different than PJSUA-LIB, but it should be even easier to use and it should have better documentation too (such as this book). The pjsua2 API removes most cruxes typically associated with PJSIP, such as the pool and pj_str_t, and add new features such as object persistence so you can save your configs to a file, for example. All data structures are rewritten for more clarity.  
     135 
     136A C++ application can use pjsua2 natively, while at the same time still has access to the lower level objects if it needs to. This means that the C++ application should not loose any information from using the C++ abstraction, compared to if it is using PJSUA-LIB directly. The C++ application also should not loose the ability to extend the library. It would still be able to register a custom PJSIP module, pjmedia_port, pjmedia_transport, and so on. 
     137 
     138Benefits of using pjsua2 C++ API include: 
     139 
     140#. cleaner object oriented API 
     141#. uniform API for higher level language such as Java and Python 
     142#. persistence API 
     143#. the ability to access PJSUA-LIB and lower level libraries when needed (including the ability to extend the libraries, for example creating custom PJSIP module, pjmedia_port, pjmedia_transport, etc.) 
     144 
     145 
     146Some considerations on pjsua2 C++ API are: 
     147#. instead of returning error, the API uses exception for error reporting 
     148#. pjsua2 uses standard C++ library 
     149#. the performance penalty due to the API abstraction should be negligible on typical modern device 
     150 
     151 
     152 
     153pjsua2 API for Java, Python, and Others 
     154--------------------------------------- 
     155The pjsua2 API is also available for non-native code via SWIG binding. Configurations for Java and Python are provided with the distribution. Thanks to SWIG, other language bindings may be generated relatively easily. 
     156  
     157The pjsua2 API for non-native code is effectively the same as pjsua2 C++ API. However, unlike C++, you cannot access PJSUA-LIB and the underlying C libraries from the scripting language, hence you are limited to what pjsua2 provides. 
     158 
     159You can use this API if native application development is not available in target platform (such as Android), or if you prefer to develop with non-native code instead of C/C++. 
     160 
     161 
     162 
     163 
     164Network and Infrastructure Considerations 
     165========================================= 
     166 
     167NAT Issues 
     168---------- 
     169 
     170 
     171TCP Requirement 
     172--------------- 
     173If you support iOS devices in your service, you need to use TCP, because only TCP will work on iOS device when it is in background mode. This means your infrastructure needs to support TCP.  
     174 
     175 
     176Sound Device 
     177============ 
     178 
     179Latency 
     180------- 
     181 
     182 
     183Echo Cancellation 
     184----------------- 
     185 
     186 
     187 
     188 
     189}}}