IEG 4180 Tutorial 2

1
IEG 4180 Tutorial 2

• Prepared by Zero
• (Note Certain content adopt from Li Kins
  tutorial notes)

2
Outline

• Winsock Programming
• Check for Packet Loss
• Rate Control
• Statistics Display

3
Winsock Programming (UDP)
UDP Program Flow
Captured from Lecture Note
4
Winsock Programming (TCP)
TCP Program Flow
Captured from Lecture Note
5
Winsock Programming

• Winsock is a library from Microsoft
• Initialization and de-initialization are needed.

WSADATA wsaData int iResult / Request Winsock
2.0 Details of actually obtained winsock version
is in wsaData / //Initialization iResult
WSAStartup( MAKEWORD(2,0), wsaData ) / Your
Network Program Codes are here / / Release
resources / //De-initilization iResult
WSACleanup()
Alternative samplehttp//en.wikipedia.org/wiki/U
ser_Datagram_Protocol
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Winsock Programming

• SOCKET skt
• // Create a TCP socket.
• // AP_INET is the internet address family formats
  for IPv4
• // SOCK_STREAM tells function to create a stream
  socket.
• skt socket(AP_INET, SOCK_STREAM, 0)
• // Create a UDP socket.
• // SOCK_DGRAM tells function to create a datagram
  socket.
• skt socket(AP_INET, SOCK_DGRAM, 0)
• / other network programming codes /
• // To close a socket
• closesocket(skt)

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Winsock Programning

• Address structure
• Winsock provides an address structure specific to
  IPv4 addresses.

struct sockaddr_in uint8_t sin_len
//length of structure sa_family_t sin_family
//AF_XXXX value in_port_t sin_port
//TCP/UDP port no. struct in_addr sin_addr
//IPv4 address char sin_zero8
//unused struct in_addr in_addr_t s_addr
//IPv4 addr, Big-endian
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Winsock Programming

• // Declare a socket address structure
• sockaddr_in addr
• // Prepare to bind socket to address
  127.0.0.112345
• addr.sin_family AF_INET
• addr.sin_addr.s_addr inet_addr( "127.0.0.1" )
• addr.sin_port htons( 12345 )
• // bind the socket to the address
• bind( skt, (SOCKADDR) addr, sizeof(addr) )

• unsigned long inet_addr ( const char cp )
• Convert from dot notation
• returns an unsigned long value containing a
  suitable binary representation of the Internet
  address given.

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Winsock Programming

• Different machines use different ways for
  representing multi-byte integers.
• The number 137.189.96.168 (89.BD.60.A8 in hex)
  can be represented in two ways

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Winsock Programming

• Byte Ordering Functions
• Winsock provides functions for converting numbers
  from one byte order to another

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Winsock Programming

• Accept returns a new socket
• Use new socket for sending or receiving packet

Captured from Lecture Note
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Winsock Programming

• send() / sento()
• returns the total number of bytes sent, which can
  be less than the number indicated by len.

int send ( SOCKET s, const char buf, int len,
int flags ) int sendto ( SOCKET s, const char
buf, int len, int flags, const struct sockaddr
to, int tolen )
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Winsock Programming

• recv() / recvfrom()
• returns the number of bytes received. If the
  connection has been gracefully closed, the return
  value is zero.

int recv ( int s, char buf, int len, int flags
) int recvfrom ( int s, char buf, int
len, int flags, struct sockaddr from, int
fromlen )
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Winsock Programming

• The return codes of the socket APIs only specify
  whether the operation is successful or not.
• To obtain a more detailed error code, invoke
  WSAGetLastError() immediately after the error
  occurred. Error codeshttp//msdn2.microsoft.com/
  en-us/library/ms740668(VS.85).aspx

if( connect( skt, (SOCKADDR) ServerAddr,
sizeof(ServerAddr) ) SOCKET_ERROR
) switch(WSAGetLastError()) case
WSAENETUNREACH printf(Unreachable network
address\n) break
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Other Useful Functions

• int atoi( const char string )
• Convert strings to interger.
• Reference
• http//msdn2.microsoft.com/en-us/library/yd5xkb5c
  (VS.80).aspx
• VOID WINAPI Sleep(DWORD dwMilliseconds)
• The minimum time interval for which execution is
  to be suspended, in milliseconds.
• Only Windows 2000 and beyond are supported
• Reference
• http//msdn2.microsoft.com/en-us/library/ms686298
  (VS.85).aspx

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Check for Packet Loss

• Both TCP and UDP contain checksum to ensure
  correctness of received packet
• TCP is reliable, packet loss can be assumed as
  zero
• UDP is un-reliable (allowing packets to be
  dropped)
• Adding sequence no. to the data part can help
• Then simply check for gaps in-between

char pkt128 ((int ) pkt) 1
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Rate ControlPacketized vs Fluid-like Transmission

• Fluid-like transmission
• Continuous flow of data
• Achieve target transmission rate Tx at any
  instance
• Packetized transmission
• Data is sent in a packet-by-packet manner
• Packets, with size P, are sent into the network
  at speed of Tx
• Control average transmission rate by adjusting
  the interval between packet transmissions

Data
Time
P/Tx
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Rate ControlPacketized Transmission

• Target
• Sending Rate 1024 bytes / second

While ( condition ) . . Send(1024byes) Sleep(1
second) . .
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Rate ControlPacketized Transmission

• To maintain average transmission rate
• Send out one packet in every fixed interval?
• Probably results in lower average transmission
  rate
• There is (non-deterministic) overhead in
  preparing, processing and sending out packets
• Dynamically adjust the transmission intervals by
  keep tracking time spent in previous
  transmissions

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Statistics Display

• All values can be shown in the same line
• Achieve refreshing through Carriage-Return
  character

for (int i 0 I lt 10 i) printf(\r2d, i)
0
...
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