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Simple SIP Implementation (Ver 2.0)
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- tcsip.cpp
The main entrypoint for the code. This configures the device, creates
instances of the ADPCM and CMysocket classes. The main function goes
into a loop and checks the different file descriptors using select()
function call. Depending on the state the program is in (i.e., RTP
transmission started or not), the number of descriptors waited on
by select() vary.
This file also implements the state diagrams for user-input and
packet reception from the network.
- tcsip.h
This defines the various dta structures used in the program. The comments
provided in the header file is detailed.
- adpcm.cpp adpcm.h
This implements the ADPCM class. The class object can be initialized
as either encoder or decoder, and be used for the corresponding action.
- CUdpSock.cpp CUdpSock.h
These implement the Socket interface for data communication. This is a
UDP based interface, with provisions to add reliability on top of it.
- helper.cpp
This file implements a number of miscellaneous function that are
used at various places in the code. See the comments provided for
each function.
- README
What you are reading now :)
## Compile and run info. :
- compile command
g++ adpcm.cpp CUdpSock.cpp helper.cpp tcsip.cpp -lpthread -o simplesip
- run command
./simplesip
## Description of scheme :
Continuing with the previous assignments, we followed our modular approach
in this assignment also. We re-used the adpcm and CUdpSock classes from the
previous assignments. This is a multi threaded program. The SIP session happens
in a single thread.. and whenever the audio session is to be started,
an audio thread is spawned to do the audio reception.
Inside this large loop we wait on 2 file descriptors depending on the
program state. If the media transmission has started, the program does a
select() wait on the audio-file-descriptor and RTP-socket in a second thread.
If the media transfer has not started, then the program waits only on the
stdin and SIP sockets in the main thread.
I used two global variables to control the state of the program.
g_sip_mode: this carries the information whether the program is server or
client or neither
g_sip_state: this carries the state of the client or server. the four states
I use are idle, connection_pending, connected, disconnect_pending
The program starts in 'none' mode and idle state. Depending on whether the
user types in a valid invite or a remote host sends a valid INVITE message
the program will turn into a server or client. From this point the communication
proceeds as the state-transition diagram dictates.
We provided a reasonably interactive shell kind of an interface for using this
program. Although this is not super-cool, this does take care of all the
requirements of the assignment.
## Running scenarios and result captures :
Since the RTP, RTCP, and SIP port numbers are fixed in the program (as per the
homework question), all that one needs to do is to run the program without
any command-line arguments.
When the interactive shell comes up, the user can enter "help" or one of the
available options.
## Problems :
After moving the audio session to the second thread, the voice clarity has been
nice with no static. This is a huge improvement over the first version of the
program.
## Comments :
- Please make sure that the sound recoder is configured in the Linux PC where you are
running the program in record mode.
- Also, if you want to use different port numbers please modify the port
number (#define in the tcsip.cpp)
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