Application layer protocol

Application Layer Protocol

Amitava Nag

Assistant Professor

[email protected]

April 6, 2012

Amitava Nag (Academy of Technology) Application Layer Protocol April 6, 2012 1 / 37

Architecture of WWW


Architecture of WWW

The WWW is a distributed client-server service, in which a clientusing a browser can access a service using a server.


Architecture of WWW

The WWW is a distributed client-server service, in which a clientusing a browser can access a service using a server.

The service provided is distributed over many locations called sites.


Architecture of WWW


Browser


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


Web Page Identifier


Web Page Identifier

Known as Uniform Resource Locator (URL)


Web Page Identifier


Encodes


Web Page Identifier


Encodes

- Access protocol to use


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server- Protocol port number (optional)


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server- Protocol port number (optional)- Path through servers file system (optional)


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server- Protocol port number (optional)- Path through servers file system (optional)- Parameters (optional)


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server- Protocol port number (optional)- Path through servers file system (optional)- Parameters (optional)- Query (optional)


Web Page Identifier


Encodes

- Access protocol to use- Domain name of server- Protocol port number (optional)- Path through servers file system (optional)- Parameters (optional)- Query (optional)

Formathttp: // hostname [: port] / path [; parameters] [? query]


Web and HTTP


Web and HTTP

Web page consists of objects


Web and HTTP


Object can be HTML file, JPEG image, Java applet, audio file,


Web and HTTP



Web page consists of base HTML-file which includes severalreferenced objects


Web and HTTP




Each object is addressable by a URL


Web and HTTP




Each object is addressable by a URL

Example URL:www.someschool.edu/someDept/pic.gif


HTTP Characteristics



Application level



Application level

Request / response paradigm



Application level


Stateless



Application level


Stateless

Permits bi-directional transfer



Application level


Stateless


Offers capability negotiation



Application level


Stateless



Support for caching



Application level


Stateless



Support for caching

Support for intermediaries


HTTP overview


HTTP overview ( continued )

Uses TCP :



Uses TCP :

HTTP client initiates TCP connection (creates socket) to (www.someschool.edu/ ) server on port 80 (default port number forHTTP).



Uses TCP :


HTTP server accepts TCP connection from client



Uses TCP :



HTTP messages (application-layer protocol messages) exchangedbetween browser ( HTTP client ) and Web server ( HTTP server )



Uses TCP :



HTTP messages (application-layer protocol messages) exchangedbetween browser ( HTTP client ) and Web server ( HTTP server )

TCP connection closed


HTTP connections

Nonpersistent HTTP Persistent HTTP

At most one object is sent over Multiple objects can be sent overa TCP connection. single TCP connection between

client and server.

HTTP/1.0 uses nonpersistent HTTP HTTP/1.1 uses persistentconnections in default mode


FTP: the file transfer protocol



transfer file to/from remote host




client/server model




client/server model

client: side that initiates transfer (either to/from remote)




client/server model


server: remote host




client/server model


server: remote host

ftp: RFC 959




client/server model


server: remote host

ftp: RFC 959

ftp server: port 21


FTP overview


FTP:connections


Opening the control connection


Creating the data connection


FTP: separate control, data connections



FTP client contacts FTP server at port 21, specifying TCP astransport protocol




Client obtains authorization over control connection





Client browses remote directory by sending commands over controlconnection.






When server receives a command for a file transfer, the server opens aTCP 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









Control connection: out of band

FTP server maintains state: current directory, earlier authentication


Remote Login: Telnet



TELNET is a general-purpose client-server application program



TELNET is a general-purpose client-server application program

TELNET enables the establishment of a connection to a remotesystem in such a way that the local terminal appears to be a terminalat the remote system.


Figure:Local login


Figure:Remote login


Electronic Mail


Electronic Mail

Three major components:


Electronic Mail

Three major components:1 user agents


Electronic Mail

Three major components:1 user agents2 mail servers


Electronic Mail

Three major components:1 user agents2 mail servers3 simple mail transfer protocol: SMTP


Electronic Mail


Electronic Mail: mail servers

Mail Servers



Mail Servers

mailbox contains incoming messages for user



Mail Servers


message queue of outgoing (to be sent) mail messages



Mail Servers



SMTP protocol between mail servers to send email messages



Mail Servers




client: sending mail server



Mail Servers




client: sending mail serverserver: receiving mail server


Electronic Mail: SMTP [RFC 2821]



uses TCP to reliably transfer email message from client to server, port25




direct transfer: sending server to receiving server





three phases of transfer






handshaking (greeting)






handshaking (greeting)transfer of messages






handshaking (greeting)transfer of messagesclosure







command/response interaction








commands: ASCII text








commands: ASCII textresponse: status code and phrase








commands: ASCII textresponse: status code and phrase

messages must be in 7-bit ASCII


Scenario: Alice sends message to Bob



1 Alice uses UA to compose message and to [email protected]




2 Alices UA sends message to her mail server; message placed inmessage 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







5 Bobs mail server places the message in Bobs mailbox

6 Bob invokes his user agent to read message


Figure: Alice sends message to Bob


Mail access protocols



SMTP: delivery/storage to receivers server




Mail access protocol: retrieval from server




Mail access protocol: retrieval from serverPOP: Post Office Protocol [RFC 1939]





authorization (agent < −− >server) and download






IMAP: Internet Mail Access Protocol [RFC 1730]







more features (more complex)







more features (more complex)manipulation of stored msgs on server







more features (more complex)manipulation of stored msgs on server

HTTP: Hotmail , Yahoo! Mail, etc.


Figure:Mail access protocols


Network Management


Network Management

Management =


Network Management

Management = Initialization,


Network Management

Management = Initialization, Monitoring,


Network Management

Management = Initialization, Monitoring, Control


Network Management


Today: automated, reliable diagnosis, and automatic control are stillin a primitive stage


Network Management



Architecture: Manager, Agents and Management Information Base(MIB)


Network Management



Architecture: Manager, Agents and Management Information Base(MIB)

Observe that management-plane has a new interface to the networkdistinct from data and control-plane


Simple Network Management Protocol (SNMP)



SNMP is a framework for managing devices in an internet using theTCP/IP protocol suit




A manager, usually a lost that, controls and monitor a set ofagents,usually routers





The manager is a host that runs the SNMP client program.





The manager is a host that runs the SNMP client program.

The agent is a router or host that runs the SNMP server program


Figure:Mail access protocols


MANAGEMENT COMPONENTS



SNMP requires the use of two other protocols:



SNMP requires the use of two other protocols:1 Structure of Management Information (SMI) and



SNMP requires the use of two other protocols:1 Structure of Management Information (SMI) and2 Management Information Base (MIB)



SNMP requires the use of two other protocols:1 Structure of Management Information (SMI) and2 Management Information Base (MIB)

Network management on the Internet is done through thecooperation of SNMP, SMI, and MIB.


Management Information Base(MIB)



MIB is a second component used in network management



MIB is a second component used in network management

Each agent has its own MIB, a collection of all the objects that themanager can manage.


Figure:Management Information Base, version 2 (MIB2)


SNMP


SNMP

SNMP is an application program that allows


SNMP

SNMP is an application program that allows1 a manager to retrieve the value of an object defined in an agent;


SNMP

SNMP is an application program that allows1 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


SNMP

SNMP is an application program that allows1 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; and3 an agent to send an alarm message about an abnormal situation to the

manager


Figure:SNMP


The End


Engineering

Application layer protocol