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What is a socket ?

It is an interface between application layer and transport layer within a host.

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Application Layer

SocketTransport Layer

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Why socket ?

For IdentificationKannadasan Yamuna

?

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Why socket ?

Hostel Name + Room No

IP address + Port number

Socket

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listen() accept()

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listen()Called only by TCP serverPerforms two actions

Convert the socket in to passive socket Specify the maximum number of connections the

kernel should queue

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For a listening socket the kernel maintains two queuesAn incomplete connection queue

Waiting for 3-way handshakeA complete connection queue

Completed 3-way handshake

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client server

Connect called

Connect returns

Create entry on incomplete queue

Entry moved from incomplete queue to complete queue

SYN 100

SYN 240, ACK 101

ACK 241

3-way handshaking

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int listen(int sockfd, int backlog)

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Questions ?What is the default size of backlog ?Which queue is longest one

(complete/incomplete) ?What will happen when queue is full ?

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accept()

Completed connection queue

Incomplete connection queue

Arriving SYN

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accept()

If success return a brand new descriptor ie descriptor of connected socket.

int accept(int sockfd, socket addr, socket addrlen)

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References Unix Network Programming

W.Richard Stevens

Computer Networking a top down approach James F Kurose

Wikipedia pubs.opengroup.org

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Questions