Application Layer Protocols - E-Commerce - Lecture Slides, Slides of Fundamentals of E-Commerce

Download Application Layer Protocols - E-Commerce - Lecture Slides and more Slides Fundamentals of E-Commerce in PDF only on Docsity!

Application Layer Protocols

Application Layer Protocols

Those protocols run on top of/over TCP/IP:

Telnet - File Transfer Protocol (FTP) - Hyper Text Transfer Protocol (HTTP)

Simple Mail Transfer Protocol (SMTP), POP3, IMAP

Network News Transfer Protocol (NNTP)

Domain Name System (DNS)

Dynamic Host Configuration Protocol (DHCP)

• Covered in previous lectures

Telnet Communications Options

7- or 8-bit compatibility

Use of different terminal nodes

Character echoing at sending and receivingends

Synchronized communications

Transmission of character streams or singlecharacters

Flow control

FTP

FTP – File transfer protocol. Commonly used over theInternet.

Numerous FTP servers over the world allow peopleanywhere on the Internet to log in and downloadwhatever files they have placed on the FTP server, orupload other files. - Uses two TCP ports (20 data channel and 21 controlchannel) – this is in active mode. In passive FTPmode, it uses 21 for the control channel, and anephemeral port for the data channel. - Commonly used on the Internet - Not a secure protocol

SMTP

Designed for exchange of email between networked systems - Within the Internet, email is delivered by having the sourcemachine establish a TCP connection to port 25 of thedestination machine / server. Listening on this port would bean SMTP (Simple Mail Transfer Protocol) daemon / servicethat speaks SMTP. - This daemon accepts incoming connections and copiesmessages from them into the appropriate mailboxes. If amessage cannot be delivered, an error report of theundeliverable message is returned to the sender, whichcontains the first part of the message.

SMTP

SMTP is a simple ASCII protocol. - After establishing the TCP connection to port 25, thesending machine, operating as the client, waits forthe receiving machine, operating as the server, totalk first. - The server starts by sending a line of text giving itsidentity and telling whether or not it is prepared toreceive mail. - If it is not, the client releases the connection andtries again later.

SMTP

POP
Until now, we assumed that all users workon machines that are capable of sendingand receiving email. Sometimes this is notthe case.
For example, at many companies, userswork at desktop PCs that ar enot on theInternet and are not capable of sending orreceiving email from outside the company.Instead, the company has one or moreemail servers that can send and receiveemail.
To send or receive messages, a PC musttalk to an email server using some kind ofdelivery protocol.

IMAP

A more sophisticated delivery protocol is IMAP(Interactive Mail Access Protocol). - It was designed to help the user who uses multiplecomputers, perhaps a workstation in the office, a PCat home, and a laptop on the road. - The basic idea behind IMAP is for the email server tomaintain a central repository that can be accessedfrom any machine. - Thus unlike POP3, IMAP does not copy email to theuser’s personal machine because the user may haveseveral.\

EMail

Independent of whether email is delivered directly to theuser’s workstation or to a remote server, many systemsprovide hooks for additional processing of incoming email. - An especially valuable tool for many email users is the abilityto set up filters . These are rules that are checked when email comes in or when the user agent is started. - Each rule specifies a condition and an action. For example, arule could say that any message from Angelina Tzachevashould be displayed in a 24-point flashing red boldface font(or alternatively, be discarded automatically withoutcomment).

NNTP

To acquire recent articles, a client must first establisha TCP connection with port 119 on the newsfeedserver.

Behind this port is the NNTP daemon/service, whichis either there all the time waiting for clients or iscreated on the fly as needed. - After the connection has been established, the clientand server communicate using a sequence ofcommands and responses.

DHCP

With the growth of the Internet, TCP/ IP has now become amust-have protocol for most computer networks. It provides asingle network protocol that is supported by almost everytype of computer system, a plethora of applications that useit, and it is well suited to both large and small networks. It’salso essential if one wishes to set up an intranet. - However, TCP/ IP needs addresses and configuration settingsto be defined on each computer or peripheral on thenetwork. This can entail an immense amount of systemadministration work.

DHCP

DHCP works across most TCP/ IP routers and allocates IPs according tothe subnet the request came from. This means one won’t need toreconfigure a PC that is moved from one subnet to another. - Addresses can be leased for periods of time - so an IP address that isnot used for the duration of the lease is put back into the unallocatedpool. This helps recover TCP/ IP addresses that are no longer used. - Internet Service Providers are often using DHCP to provideclients with IP address as well.