design

一个C编写网络广播的程序

0) Concepts - Server side

Stage 0: Startup
   * Await connections (tcp) 
   + Send initialization data (mcast params)
   * Wait for specified number of clients

Stage 1: Init block
   * Read data from input 
   * Send block header to clients 
   * All clients reply with CLIENT_READY

Stage 2: Data transmission
   * Server sends ROUND packets of data (eg. 1024*1500 bytes)
   * Send END_OF_DATA ('!') through TCP
   * Clients send (tcp) : confirmations (CLIENT_START) 
                        : requests for retransmission (CLIENT_REQ) 

Stage 3: Finishing block
   + TCP Servers handle requests 
   * Wait for all confirmations
   * Goto 1 if more data. 

1) Network schematics:

            ______TCP___________________,
           /                     /-> client
       [SERWER]====>Multicast===<--> client<-,
        \ \                      \-> client  | 
         \ ~~~~~~~~~~TCP~~~~~~~~~~~~~~~^    /
          ~~~~~~~~~~~TCP~~~~~~~~~~~~~~~~~~~~

TCP -> synchronisation
Multicast -> data

2) Modules - server
   

      (input)         (tcp)             mdist: splits input into parts
         |              |               awaits for clients
       [data]       [control]           serves data
         !              |               
       mdist<========>mdtcp-srv         mcast-srv: transfers data
         |              |               through multicast sockets
         !              !               
     mcast-srv        (tcp)             mdtcp-srv: handles confirmations and
         |                              retransmissions - i.e. keeps 
      [blocks]                          transmission synced.
         !
      (mcast)
      
mcast-srv and mdtcp-srv are running as separate threads. This enables 
doing 'live' transmissions, with clients connecting at run-time and so on.
(Well, this requires a bit of work, at least for now).
There may be limitless tcp servers. They act concurrently, synchronizing
only between blocks. 

3) client modules

      (mcast)         (tcp)             client communicates through
         |              |               tcp & multicast udp , 
         !              !               mdist takes care of buffering
         >===>client<===<               and joining the block together.
         |              |               Single thread.
       mdist            |
         !              ! 
      (output)        (tcp)