Socket

• Interface between the application layer and transport layer
• OS controlled interface into which application process can both send and recieve messages

Addressing:

• Host address and process identifier
• Ip address + Port number

Socket is an endpoint for communication. A combination of host IP address and port number

Socket types

UDP sever: Connectionless (Iterative)

• All wil go to the same port
• ALl will go to the same queue

We can pqaralised

TCP server: Connection oriented (COncurrent)

• Create a seperate child process
• Child process may use same or new port
• The port is that dedicated to that client
• The next client will then go to the next child server
• Given that each socket is identified by local ip and port and remote ip and port, no need for emphemeral port at server sides (Uniquely identifieable)
• Can be iterative but now majority are concurrent

Socket Data structure

UNIX LINUX SOCKET API (C/C++)

Creating a socket

• sockDes = new Socket(pf, type, protocol)
  • pf : protocol family
  • type : SOCK_STREAM for TCP, SOCK_DGRAM for UDP, SOC_SEQPACKET for sctp, SOCK_RAW only for priviledge programs
  • Protocol : Is always 0 by default.. There was suppose to be more protocol but until it still the same

Binding

• `bind(sockDes, localaddr, addrlen)
  • socket will have a wild card foreign destination
  • localaddr is pointer to a structure defined in socket.h which specifies the local socket address

UDP Server

1. sockDes = new Socket(pf, type, protocol)
2. bind(sockDes, localaddr, addrlen)
   • socket will have wild-card foreign destination; foreign addr is yet to be assigned
3. rescfrom(sockDes, buffer, length,flags, fromaddr, addrlen)
   • OS will record the fromaddr and addlen based on datagram recievedf
4. sendto(sockDes, message, length, flags, destaddr, addrlen)
5. close(sockDes)

UDP Client

1. sockDes = new socket(pf, type, protocol)
2. sendto(sockDes, message, length, flag, destaddr, addrlen)
3. recvfrom(sockDes, buffer, length, flags, fromaddr, addrlen)
4. close(sockDes)

Bind is optional.. our client could take a random port address

TCP Server

1. sockDes = new socket(pf, type, protocol)
2. bind(sockDes, localaddr, addrlen)
   • socket will have wild-card foreign destination; foreign addr is yet to be assigned
3. listen(sockDes, qlength)
4. newSockDes = accept(sockDes, addr, addrlen)
   • new socket will have requesting client as dest and returns newSockDes to server, connection is establised to specific client
5. read/write(newSockDes, buffer, length)
6. close(sockDes); close(newSockDes)

TCP Client

1. sockDes = new socket(pf, type, protocol)
2. connect(sockDes, destaddr, addrlen)
3. read/write(sockDes, buffer, length)
4. close(sockDes)

Raw socket

See the slides for commands

Slides