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MP2: P2P File Server

Hoang Nguyen

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Outline

• Basic network concepts revisited – Client/Server, Peer-to-peer– IP address, TCP/UDP

• Basic network programming revisited– Server socket, Client Socket– Send/Receive data– Data Serialization: converting objects to bits

• Network Design: Control/Data plane– MP explanation– Implementation suggestions/hints

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Basic network concepts revisited

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Basic network concepts (1)

• Client/server– Servers = machines providing network services– Clients = machines connecting to servers and

use network services– Example: FTP server/FTP client

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Basic network concepts (2)

• A server provides a network service through a “port”– Has to “bind” to a particular port

• Clients requests for a specific service at a server via a pre-defined port

• E.g.: Port 21: FTP control, Port 20: FTP data• Port: (0..65535)

– 0..1023: well-known ports, requiring admin right to bind– 1024..49151: registered ports (for propriety apps)– The rest: dynamic/private ports

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Basic network concepts (3)

• What is a Protocol?– A convention standard that controls or enables the

connection, communication and data transfer between two parties.

• Example: – “Protocol” to apply to UIUC– “Admission protocol”

• In our MP, we will have to define our own “protocols” and use some existing network protocols

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Basic network concepts (3)

• IP address: a tuple of four 8-bit integers– E.g.: 128.174.252.84

• Host name: name representative of IP– E.g.: www.cs.uiuc.edu

• TCP: Transmission Control Protocol– Reliable, ordered, heavy-weight, streaming

(connection-oriented/stateful)– Suitable for any applications requiring reliability such as FTP

• UDP: User Datagram Protocol – Unreliable, not-ordered, light-weight, datagrams

(connectionless/stateless)– Suitable for any protocols that can tolerate reasonable losses such as

video/audio/real-time streaming

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Basic network programming revisited

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Basic network programming revisited

• Highly recommended tutorial– Beej's Guide to Network Programming

Using Internet Sockets

• http://beej.us/guide/bgnet/• Make sure you go through until

Section 7 (esp. Section 6 and Section 7.4)

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Network Socket

• A socket is a one end of a two-way communications link between two programs running on the network– In UNIX, socket is just a file descriptor on which

send() and recv() can be used.

• As mentioned above, a socket can be – SOCK_STREAM: streaming, reliable, connection-

oriented, ordered– SOCK_DGRAM: datagram, unreliable, connection-

less, not-ordered

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How to create a server socket?

• Pseudo-code & examplefill out address informationsock_fd = create/set socket optionbind to the portlisten for incoming connectionswhile (forever || not crash)

client_fd = accept a client socketcreate a process/thread to

communicate with the client

… // ready to send/recv

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Comments

• sock_fd: Server socket keeps listening for incoming connections– If the accept() function is not invoked, no client

connection can be accepted

– If the number of pending connections exceeds the backlog, any incoming requests are refused.

• client_fd: socket to communicate with the client – Think of it like a file descriptor.

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How to create a client socket?

• Pseudo-code & examplefill out address information (hostname, port)sock_fd = connect to the server

… // ready to send/recv

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Sending/Receiving data

• no_send = send(sock_fd, data, len, flag)

• no_recv = recv(sock_fd, buf, max_len, flag)

• Example

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Data serialization

• Converting data objects into bits• Three ways:

1) Use readable string description: e.g. “text ‘this is a text’, int 1, float 1.1234”

2) Sending raw data, passing it send() (dangerous, un-portable)double d = 3490.15926535;send(s, &d, sizeof d, 0);

3) Encode the data into a portable binary form. The receiver encodes it. (see pack(), unpack() in the tutorial)

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Control/Data Plane

• Control plane: a set of protocols/software to bootstrap/setup and control the communication

• Data plane: a set of protocols/software to transmit data

• E.g.: FTP has two ports for control channel (21) and data channel (20)

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In our MP…

Stream (Play, FF, Rewind) A/V Files

Insert (Upload) A/V Files

Setup UDP Connection between Client and a Specific

Peer-Server

Setup TCP Connection between Client and a Specific

Peer-Server

UDP/IP Protocol Stack

TCP/IP Protocol Stack

Insert/Delete/Search Stream Request Control Protocols and Services

Dispatcher setup Peer-Server addition/Connection setup between

Dispatcher and Peer-Servers for Control Purposes

TCP/IP Protocol Stack

Data Plane Functions Control Plane Functions

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An example implementation of control plane

for our MP1) Dispatcher setup peer-to-peer

connections

2) Handling a client request

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Entities (1)

• A server has– a server socket listening on port 7000 for

dispatcher setup connection request– a client socket to communicate with dispatcher

obtained once accepting dispatcher setup connection request

– an on-demand server socket listening on a on-demand port for the client to send/recv data

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Entities (2)

• A dispatcher has– several client sockets for connections to each

server– a server socket listening on port 8000 for

clients to send/recv control messages

• A client has – A client socket to send/recv control messages

to the dispatcher– A client socket to send/recv data to the server

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Dispatcher setup connection

Socket on port 7000

Setup connection request

socket

Socket on port 8000

socketSetup connection request

Bi-directional

Bi-directional

cairo

cairosanjose

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Handling a client request

socket

socket

Bi-directional

Bi-directional

Socket on port 8000

cairo

cairosanjose

1. request2. request

3. response

4. response