This document describes the system architecture and communication protocol for a peer-to-peer voice messaging application. It discusses using (1) threads to handle server, receiver, and keypad functions, (2) sockets for communication between users with a central server, and (3) codecs for recording and playing voice messages. The socket implementation was modified to use dynamic ports for senders and receivers to allow multi-user communication through a central server.

1. Pine Line
0360250 邱聖倫
0360241 吳嘉彬
National Chiao Tung University
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A simple tool to connect with your friends

2. System architecture
• PXA
– 7-segment: commnication time
– lcd screen: communication text
– Microphone: voice record
– Keypad: patterns and voice recording
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3. System architecture
• Kernal functions
– Pthread: server, recever, keypad
– Timer: 7-segment counting
– Socket: communication
– Mutex: lock socket, users’ data
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4. System architecture
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4
User 1 User 2
send
send receive
Internet
LCD
LCDkeyboard
keyboard
audio output
audio output
receive
microphone
microphone
keypad
keypad
7 segment 7 segment

5. User BUser A
Socket problem
• Socket
– Peer-to-peer communication
– Client and server have the same port number
– Can not be used for multi-user communication
without central server
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server
client
server
client

6. User BUser A
Socket problem
• Solution
– Sever -> receive and server, client -> send
– Sever uses static port number N but receiver and
sender use dynamic port number
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server
sender
receiver
server
sender
receiver
User A turn off his server and his sender uses port number N to
send a request with his receiver port number to user B. User B
askes his group that user A can join or not.
If yes, user B sends ‘OK’ as ACK to user A; if not, user B sends ‘No’
as ACK to user A.

7. User BUser CUser DUser A
Socket problem
• Solution
– Sever -> receive and server, client -> send
– Sever uses static port number N but receiver and
sender use dynamic port number
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server
sender
receiver
server
sender
receiver
User B sends group information to user A through user A’s
receiver port number.
User A sends his information to every member of the group; then,
user A joins the group.

8. User BUser A
Socket problem
• Solution
server
sender
receiver
server
sender
receiver
User D
server senderreceiver
User C
server senderreceiver

9. Codec problem
• Codec
– Codec_record
• Recod 4 seconds voice to an inner buffer
• Need to give 4*sample rate
– Codec_play
• Display the inner buffer
– Can read the inner buffer
– Can not write the inner buffer
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10. Codec problem
• Codec
– Codec_record
• Recod 4 seconds voice to an inner buffer
• Need to give 4*sample rate
– Codec_play
• Display the inner buffer
– Can read the inner buffer
– Can not write the inner buffer
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