1. Outline Communications in Distributed Systems Socket Programming
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2. Distributed Systems
A distributed system is a collection of independent computers that appears to its users as a single coherent system
Independent computers mean that they do not share memory or clock
The computers communicate with each other by exchanging messages over a communication network
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3. Distributed Systems – cont.
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4. Necessity of Protocols
Due to the absence of shared memory, all communication in distributed systems is based on exchanging messages at low level
When process A wants to communicate with process B, it builds a message in its own space and then executes a system call to send it to B
To prevent chaos, A and B must agree on the meaning of the bits being sent
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5. Layered Protocols Layers, interfaces, and protocols in the OSI model.
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6. Layered Protocols – cont.
A typical message as it appears on the network.
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7. Physical Layer It is concerned how to transmit 0’s and 1’s
There are technical issues involved such as unidirectional or bidirectional
These issues are not interesting to us
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8. Data Link Layer
Discussion between a receiver and a sender in the data link layer.
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9. Network Layer The primary task of a network layer is routing
The most widely used network protocol is the connection-less IP (Internet Protocol)
Each IP packet is routed to its destination independent of all others
A connection-oriented protocol is gaining popularity
Virtual channel in ATM networks
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10. Transport Layer
This layer is the last part of a basic network protocol stack
In other words, this layer can be used by application developers
An important aspect of this layer is to provide end-to-end communication
The Internet transport protocol is called TCP (Transmission Control Protocol)
The Internet protocol also supports a connectionless transport protocol called UDP (Universal Datagram Protocol)
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11. Client-Server TCP Normal operation of TCP. Transactional TCP. 2-4
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12. Higher Level Protocols
In the OSI model, there are three additional layers above the transport layer
In practice, only the application layer is ever used
In the Internet protocol suite, everything above the transport layer is grouped together
In the face middleware systems, it has two layers above the transport layer
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13. Application Protocols
File Transfer Protocol (FTP)
It defines a protocol for transferring files between a client and a server
HyperText Transfer Protocol (HTTP)
Designed to remotely manage and handle the transfer of web pages
Mainly used by web servers and browsers
It is also used in other applications such as Java’s RMI (Remote Method Invocations)
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14. HTTP Methods Operations supported by HTTP. Operation Description Head
Request to return the header of a document
Get
Request to return a document to the client
Put
Request to store a document
Post
Provide data that is to be added to a document (collection)
Delete
Request to delete a document
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15. Application Protocols – cont.
HTTPS
HTTP protocol running on Transport Layer Security (TLS), originally known as Secure Socket Layer
TLS is an application-independent security protocol that is logically on top of the transport layer
TLS implementations are usually based on TCP
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16. Middleware Protocols
An adapted reference model for networked communication.
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17. Sockets Socket primitives for TCP/IP. Primitive Meaning Socket
Create a new communication endpoint
Bind
Attach a local address to a socket
Listen
Announce willingness to accept connections
Accept
Block caller until a connection request arrives
Connect
Actively attempt to establish a connection
Send
Send some data over the connection
Receive
Receive some data over the connection
Close
Release the connection
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18. Sockets – cont.
Connection-oriented communication pattern using sockets.
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19. Socket Programming Socket Programming
Based on TCP/UDP.
TCP Transmission control protocol.
connection-oriented, reliable, full duplex, byte stream service
Interface: socket, bind, listen, accept, connect, read, write, close.
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20. An analogy Socket: telephone
Bind: assign telephone number to a telephone
Listen: turn on the ringer so that you can hear the phone call
Connect: dial a phone number
Accept: answer the phone
Read/write: talking
Close: Hang-up
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21. The Basics To send: To receive: TCP endpoint: Socket, connect write
Socket, bind, listen, accept read
TCP endpoint:
IP address + port number
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22. Basic TCP Sockets #include <sys/socket.h>
int socket(int family, int type, int protocol);
Family: AF_INET (PF_INET).
Type: SOCK_STREAM (TCP) SOCK_DGRAM (UDP)
Protocol: = 0
Return descriptor, -1 on error.
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23. Connect #include <sys/socket.h>
int connect(int sockfd, const struct sockaddr* servaddr, socklen_t addrlen);
Servaddr: socket address structure (ip address and port)
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24. Socket Address structure:
struct in_addr {
in_addr_t s_addr; }
struct sockaddr_in {
uint8_t sin_len;
sa_family_t sin_family;
in_port_t sin_port;
struct in_addr sin_addr;
char sin_zero[8];
Always use sockaddr_in type for manipulation and convert it to sockaddr. See example1.c.
struct sockaddr {
uint8_t sa_len;
sa_family_t sa_family;
char sa_data[14]; }
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25. Bind
Client does not have to bind, system assigns a dynamic port number.
#include <sys/socket.h>
int bind(int sockfd, const struct sockaddr &myaddr, socklen_t addlen);
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26. Myaddr Myaddr (address, port) = (INADDR_ANY, 0) = (INADDR_ANY, !0)
system assigns addr and port.
= (INADDR_ANY, !0)
system selects addr, user selects port
=(Local IP address, 0)
user selects addr, system selects port
=(Local IP address,!0)
user selects both addr and port
See example2.c
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27. Listen Convert a socket into a passive socket
#include <sys/socket.h>
int listen(int sockfd, int backlog)
Backlog: number of connections that the kernel should queue for the socket.
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28. Accept Accept Blocking by default #include <sys/socket.h>
int accept (int sockfd, struct sockaddr *cliaddr, socklen_t *addrlen);
Return client’s address in cliaddr
See example2.c
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29. sin_port and sin_addr must be in network byte order.
What happen when we run example2.c as server on diablo and example1.c as client on linprog?
Sockaddr_in revisit
sin_port and sin_addr must be in network byte order.
Check example3.c, what is the difference between diablo and quake?
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30. Functions to Convert Byte Orders
#include <netinet/in.h>
uint16_t htons(uint16_t host16bitvalue);
uint32_t htonl(uint32_t host32bitvalue);
uint16_t ntohs(uint16_t net16bitvalue);
Uint32_t ntohl(uint32_t net32bitvalue);
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31. Some Useful Functions Some byte manipulation functions:
#include <strings.h>
Void *memset(void *dst, int c, size_t len);
Void *memcpy(void *dst, void *src, size_t nbytes);
Void *memcmp(const void *ptr1, const void *ptr2,
size_t nbytes);
Address conversion functions
inet_aton/inet_addr/inet_ntoa
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