This document discusses application layer protocols. It provides an overview of the architecture of the World Wide Web including how web pages are composed of multiple objects accessed via URLs. It also summarizes HTTP, describing its request/response paradigm and stateless nature. Additionally, it covers FTP for file transfer between clients and servers, including its use of separate control and data connections, and Telnet for remote login sessions.

1. Application Layer Protocol
Amitava Nag
Assistant Professor
amitavanag.09@gmail.com
April 6, 2012
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2. Architecture of WWW
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3. Architecture of WWW
The WWW is a distributed client-server service, in which a client
using a browser can access a service using a server.
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4. Architecture of WWW
The WWW is a distributed client-server service, in which a client
using a browser can access a service using a server.
The service provided is distributed over many locations called sites.
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5. Architecture of WWW
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6. Browser
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7. Internet apps: application, transport protocols
Application Application layer Underlying
protocol transport protocol
email SMTP[RFC2821] TCP
remote terminal Telnet[RFC854] TCP
access
web HTTP[RFC2616] TCP
file transfer FTP[RFC959] TCP
Remote File Server NFS UDP/TCP
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8. Web Page Identifier
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9. Web Page Identifier
Known as Uniform Resource Locator (URL)
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10. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
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11. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
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12. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
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13. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
- Protocol port number (optional)
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14. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
- Protocol port number (optional)
- Path through servers file system (optional)
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15. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
- Protocol port number (optional)
- Path through servers file system (optional)
- Parameters (optional)
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16. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
- Protocol port number (optional)
- Path through servers file system (optional)
- Parameters (optional)
- Query (optional)
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17. Web Page Identifier
Known as Uniform Resource Locator (URL)
Encodes
- Access protocol to use
- Domain name of server
- Protocol port number (optional)
- Path through servers file system (optional)
- Parameters (optional)
- Query (optional)
Format
http: // hostname [: port] / path [; parameters] [? query]
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18. Web and HTTP
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19. Web and HTTP
Web page consists of objects
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20. Web and HTTP
Web page consists of objects
Object can be HTML file, JPEG image, Java applet, audio file,
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21. Web and HTTP
Web page consists of objects
Object can be HTML file, JPEG image, Java applet, audio file,
Web page consists of base HTML-file which includes several
referenced objects
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22. Web and HTTP
Web page consists of objects
Object can be HTML file, JPEG image, Java applet, audio file,
Web page consists of base HTML-file which includes several
referenced objects
Each object is addressable by a URL
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23. Web and HTTP
Web page consists of objects
Object can be HTML file, JPEG image, Java applet, audio file,
Web page consists of base HTML-file which includes several
referenced objects
Each object is addressable by a URL
Example URL:www.someschool.edu/someDept/pic.gif
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24. HTTP Characteristics
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25. HTTP Characteristics
Application level
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26. HTTP Characteristics
Application level
Request / response paradigm
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27. HTTP Characteristics
Application level
Request / response paradigm
Stateless
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28. HTTP Characteristics
Application level
Request / response paradigm
Stateless
Permits bi-directional transfer
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29. HTTP Characteristics
Application level
Request / response paradigm
Stateless
Permits bi-directional transfer
Offers capability negotiation
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30. HTTP Characteristics
Application level
Request / response paradigm
Stateless
Permits bi-directional transfer
Offers capability negotiation
Support for caching
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31. HTTP Characteristics
Application level
Request / response paradigm
Stateless
Permits bi-directional transfer
Offers capability negotiation
Support for caching
Support for intermediaries
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32. HTTP overview
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33. HTTP overview ( continued )
Uses TCP :
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34. HTTP overview ( continued )
Uses TCP :
HTTP client initiates TCP connection (creates socket) to (
www.someschool.edu/ ) server on port 80 (default port number for
HTTP).
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35. HTTP overview ( continued )
Uses TCP :
HTTP client initiates TCP connection (creates socket) to (
www.someschool.edu/ ) server on port 80 (default port number for
HTTP).
HTTP server accepts TCP connection from client
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36. HTTP overview ( continued )
Uses TCP :
HTTP client initiates TCP connection (creates socket) to (
www.someschool.edu/ ) server on port 80 (default port number for
HTTP).
HTTP server accepts TCP connection from client
HTTP messages (application-layer protocol messages) exchanged
between browser ( HTTP client ) and Web server ( HTTP server )
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37. HTTP overview ( continued )
Uses TCP :
HTTP client initiates TCP connection (creates socket) to (
www.someschool.edu/ ) server on port 80 (default port number for
HTTP).
HTTP server accepts TCP connection from client
HTTP messages (application-layer protocol messages) exchanged
between browser ( HTTP client ) and Web server ( HTTP server )
TCP connection closed
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38. HTTP connections
Nonpersistent HTTP Persistent HTTP
At most one object is sent over Multiple objects can be sent over
a TCP connection. single TCP connection between
client and server.
HTTP/1.0 uses nonpersistent HTTP HTTP/1.1 uses persistent
connections in default mode
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39. FTP: the file transfer protocol
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40. FTP: the file transfer protocol
transfer file to/from remote host
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41. FTP: the file transfer protocol
transfer file to/from remote host
client/server model
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42. FTP: the file transfer protocol
transfer file to/from remote host
client/server model
client: side that initiates transfer (either to/from remote)
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43. FTP: the file transfer protocol
transfer file to/from remote host
client/server model
client: side that initiates transfer (either to/from remote)
server: remote host
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44. FTP: the file transfer protocol
transfer file to/from remote host
client/server model
client: side that initiates transfer (either to/from remote)
server: remote host
ftp: RFC 959
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45. FTP: the file transfer protocol
transfer file to/from remote host
client/server model
client: side that initiates transfer (either to/from remote)
server: remote host
ftp: RFC 959
ftp server: port 21
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46. FTP overview
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47. FTP:connections
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48. Opening the control connection
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49. Creating the data connection
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50. FTP: separate control, data connections
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51. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
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52. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
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53. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
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54. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
When server receives a command for a file transfer, the server opens a
TCP data connection to client
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55. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
When server receives a command for a file transfer, the server opens a
TCP data connection to client
After transferring one file, server closes connection.
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56. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
When server receives a command for a file transfer, the server opens a
TCP data connection to client
After transferring one file, server closes connection.
Server opens a second TCP data connection to transfer another file.
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57. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
When server receives a command for a file transfer, the server opens a
TCP data connection to client
After transferring one file, server closes connection.
Server opens a second TCP data connection to transfer another file.
Control connection: out of band
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58. FTP: separate control, data connections
FTP client contacts FTP server at port 21, specifying TCP as
transport protocol
Client obtains authorization over control connection
Client browses remote directory by sending commands over control
connection.
When server receives a command for a file transfer, the server opens a
TCP data connection to client
After transferring one file, server closes connection.
Server opens a second TCP data connection to transfer another file.
Control connection: out of band
FTP server maintains state: current directory, earlier authentication
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59. Remote Login: Telnet
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60. Remote Login: Telnet
TELNET is a general-purpose client-server application program
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61. Remote Login: Telnet
TELNET is a general-purpose client-server application program
TELNET enables the establishment of a connection to a remote
system in such a way that the local terminal appears to be a terminal
at the remote system.
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62. Figure:Local login
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63. Figure:Remote login
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64. Electronic Mail
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65. Electronic Mail
Three major components:
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66. Electronic Mail
Three major components:
1 user agents
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67. Electronic Mail
Three major components:
1 user agents
2 mail servers
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68. Electronic Mail
Three major components:
1 user agents
2 mail servers
3 simple mail transfer protocol: SMTP
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69. Electronic Mail
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70. Electronic Mail: mail servers
Mail Servers
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71. Electronic Mail: mail servers
Mail Servers
mailbox contains incoming messages for user
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72. Electronic Mail: mail servers
Mail Servers
mailbox contains incoming messages for user
message queue of outgoing (to be sent) mail messages
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73. Electronic Mail: mail servers
Mail Servers
mailbox contains incoming messages for user
message queue of outgoing (to be sent) mail messages
SMTP protocol between mail servers to send email messages
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74. Electronic Mail: mail servers
Mail Servers
mailbox contains incoming messages for user
message queue of outgoing (to be sent) mail messages
SMTP protocol between mail servers to send email messages
client: sending mail server
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75. Electronic Mail: mail servers
Mail Servers
mailbox contains incoming messages for user
message queue of outgoing (to be sent) mail messages
SMTP protocol between mail servers to send email messages
client: sending mail server
server: receiving mail server
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76. Electronic Mail: SMTP [RFC 2821]
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77. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
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78. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
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79. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
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80. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
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81. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
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82. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
closure
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83. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
closure
command/response interaction
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84. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
closure
command/response interaction
commands: ASCII text
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85. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
closure
command/response interaction
commands: ASCII text
response: status code and phrase
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86. Electronic Mail: SMTP [RFC 2821]
uses TCP to reliably transfer email message from client to server, port
25
direct transfer: sending server to receiving server
three phases of transfer
handshaking (greeting)
transfer of messages
closure
command/response interaction
commands: ASCII text
response: status code and phrase
messages must be in 7-bit ASCII
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87. Scenario: Alice sends message to Bob
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88. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
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89. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
2 Alices UA sends message to her mail server; message placed in
message queue
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90. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
2 Alices UA sends message to her mail server; message placed in
message queue
3 Client side of SMTP opens TCP connection with Bobs mail server
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91. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
2 Alices UA sends message to her mail server; message placed in
message queue
3 Client side of SMTP opens TCP connection with Bobs mail server
4 SMTP client sends Alices message over the TCP connection
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92. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
2 Alices UA sends message to her mail server; message placed in
message queue
3 Client side of SMTP opens TCP connection with Bobs mail server
4 SMTP client sends Alices message over the TCP connection
5 Bobs mail server places the message in Bobs mailbox
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93. Scenario: Alice sends message to Bob
1 Alice uses UA to compose message and to bob@someschool.edu
2 Alices UA sends message to her mail server; message placed in
message queue
3 Client side of SMTP opens TCP connection with Bobs mail server
4 SMTP client sends Alices message over the TCP connection
5 Bobs mail server places the message in Bobs mailbox
6 Bob invokes his user agent to read message
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94. Figure: Alice sends message to Bob
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95. Mail access protocols
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96. Mail access protocols
SMTP: delivery/storage to receivers server
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97. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
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98. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
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99. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
authorization (agent < −− >server) and download
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100. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
authorization (agent < −− >server) and download
IMAP: Internet Mail Access Protocol [RFC 1730]
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101. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
authorization (agent < −− >server) and download
IMAP: Internet Mail Access Protocol [RFC 1730]
more features (more complex)
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102. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
authorization (agent < −− >server) and download
IMAP: Internet Mail Access Protocol [RFC 1730]
more features (more complex)
manipulation of stored msgs on server
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103. Mail access protocols
SMTP: delivery/storage to receivers server
Mail access protocol: retrieval from server
POP: Post Office Protocol [RFC 1939]
authorization (agent < −− >server) and download
IMAP: Internet Mail Access Protocol [RFC 1730]
more features (more complex)
manipulation of stored msgs on server
HTTP: Hotmail , Yahoo! Mail, etc.
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104. Figure:Mail access protocols
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105. Network Management
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106. Network Management
Management =
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107. Network Management
Management = Initialization,
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108. Network Management
Management = Initialization, Monitoring,
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109. Network Management
Management = Initialization, Monitoring, Control
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110. Network Management
Management = Initialization, Monitoring, Control
Today: automated, reliable diagnosis, and automatic control are still
in a primitive stage
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111. Network Management
Management = Initialization, Monitoring, Control
Today: automated, reliable diagnosis, and automatic control are still
in a primitive stage
Architecture: Manager, Agents and Management Information Base
(MIB)
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112. Network Management
Management = Initialization, Monitoring, Control
Today: automated, reliable diagnosis, and automatic control are still
in a primitive stage
Architecture: Manager, Agents and Management Information Base
(MIB)
Observe that management-plane has a new interface to the network
distinct from data and control-plane
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113. Simple Network Management Protocol (SNMP)
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114. Simple Network Management Protocol (SNMP)
SNMP is a framework for managing devices in an internet using the
TCP/IP protocol suit
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115. Simple Network Management Protocol (SNMP)
SNMP is a framework for managing devices in an internet using the
TCP/IP protocol suit
A manager, usually a lost that, controls and monitor a set of
agents,usually routers
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116. Simple Network Management Protocol (SNMP)
SNMP is a framework for managing devices in an internet using the
TCP/IP protocol suit
A manager, usually a lost that, controls and monitor a set of
agents,usually routers
The manager is a host that runs the SNMP client program.
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117. Simple Network Management Protocol (SNMP)
SNMP is a framework for managing devices in an internet using the
TCP/IP protocol suit
A manager, usually a lost that, controls and monitor a set of
agents,usually routers
The manager is a host that runs the SNMP client program.
The agent is a router or host that runs the SNMP server program
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118. Figure:Mail access protocols
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119. MANAGEMENT COMPONENTS
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120. MANAGEMENT COMPONENTS
SNMP requires the use of two other protocols:
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121. MANAGEMENT COMPONENTS
SNMP requires the use of two other protocols:
1 Structure of Management Information (SMI) and
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122. MANAGEMENT COMPONENTS
SNMP requires the use of two other protocols:
1 Structure of Management Information (SMI) and
2 Management Information Base (MIB)
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123. MANAGEMENT COMPONENTS
SNMP requires the use of two other protocols:
1 Structure of Management Information (SMI) and
2 Management Information Base (MIB)
Network management on the Internet is done through the
cooperation of SNMP, SMI, and MIB.
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124. Management Information Base(MIB)
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125. Management Information Base(MIB)
MIB is a second component used in network management
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126. Management Information Base(MIB)
MIB is a second component used in network management
Each agent has its own MIB, a collection of all the objects that the
manager can manage.
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127. Figure:Management Information Base, version 2 (MIB2)
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128. SNMP
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129. SNMP
SNMP is an application program that allows
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130. SNMP
SNMP is an application program that allows
1 a manager to retrieve the value of an object defined in an agent;
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131. SNMP
SNMP is an application program that allows
1 a manager to retrieve the value of an object defined in an agent;
2 a manager to store a value in an object defined in an agent; and
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132. SNMP
SNMP is an application program that allows
1 a manager to retrieve the value of an object defined in an agent;
2 a manager to store a value in an object defined in an agent; and
3 an agent to send an alarm message about an abnormal situation to the
manager
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133. Figure:SNMP
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134. The End
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