Two types of packets

• UDP: unreliable datagram
• TCP: reliable byte stream

Actually it takes the same amount of time to send UDP packet and TCP packet!!
Even streaming services uses TCP these days.

UDP

• no handshaking before sending data (no connection!)
• sender explictly attaches IP destination address and port number to each packet
• receiver extracts sender IP address and port number from received packet

Programming UDP

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int socket(PF_INET, SOCK_DGRM, IPPROTO_UDP);
int close(int socket);

int sendto(int socket, char *msg, int msg_len, int flags, const struct sockaddr* dest_addr, socklen_t addrlen);
int recvfrom(int socket, char *buff, int buff_len, int flags const struct sockaddr* src_addr, socklen_t* addrlen);

For historical reasons, intel uses little endian, and internet uses big endian... You need to tkae care endianness!

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int port;
struct sockaddr_in saddr;

saddr.sin_port = htons(port);

Programming TCP

UDP just sends sockets.
TCP must make connection before sending sockets!
Usually server opens well-known port. (e.g. HTTP: 80)

1. Client contact server
2. Server creates new socket dedicated for that client
3. Client and server sends messages

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int connect(int socket, struct sockaddr *address,int addr_len);
int send(int socket, char *msg, int msg_len,int flags);
int recv(int socket, char *buff, int buff_len, int flags);

int listen(int socket, int backlog);

listen's arguments accepts queue size!
Probably your server need 1024 queue size, if you're not accepting fast enough.

Unfortunately, listen use signle queue, and it's not designed with a multi-core environment in mind.