Protocol:
Protocol is a set of Rules. Which is used to carry data from node to node through media (wire or wireless). Like bus driver he know the routes from source to destination through some vehicle (Ethernet,token ring) .Here bus is a Ethernet, bus driver is protocol and road is a media.
Each and every layer has its own protocols but here we took Application layer protocols. I will describe the different applications and services typically used in IP networks.
Telnet It is the chameleon of protocols its specialty is terminal emulation. It allows a user on a remote client machine, called the Telnet, to access the resources of another machine, the Telnet server. Telnet achieves this by pulling a fast one on the Telnet server and making the client machine appear as through it were a terminal directly attached to the local network. This projection is actually a software image a virtual terminal that can interact with then chosen remote host.
These emulated terminals are of the text-mode type and can execute defined procedures such as displaying menus that give users the opportunity to choose options and access the applications on the duped server. Users begin a Telnet session by running the Telnet client software and then logging into the Telnet server.
File Transfer Protocol (FTP) It is the protocol that actually lets us transfer files, and it can accomplish this between any two machines using it. But FTP isn't just a protocol; it's also a program. Operating as a protocol, FTP is used by applications. As a program, it's employed by users to perform file tasks by hand. FTP also allows for access to both directories and files and can accomplish certain types of directory operations, such as relocating into different ones.
Accessing a host through FTP is only the first step, through. Users must then be subjected to an authentication login that's probably secured with passwords and usernames implemented by system administrators to restrict access. You can get around this somewhat by adopting the username anonymous- through what you'll gain access to will be limited.
Trivial File Transfer Protocol (TFTP) It is stripped-down, stock version of FTP, but it's the protocol of choice if you know exactly what you want and where to find it, puls it's so easy to use and it's fast too. It doesn't give you the abundance of function that FTP does, though. TFTP has no directory-Browsing abilities; it can do nothing but send and receive files. This compact little protocol also skimps in the data department, sending much smaller blocks of data than FTP, and there's no authentication as with FTP, so It's even more insecure. Few sites support it because of the inherent security risks.
Network File System (NFS) It is a jewel of a protocol specializing in file sharing. It allows two different types of file system to inter-operate. It works like this: suppose the NFS server software is running on a windows server and the NFS client software is running on a Unix host. NFS allows for a portion of the RAM on the windows server to transparently store Unix file system are unlike- they have different case sensitivity, file name lengths, security, and so on both Unix users and Windows users can access that same file with their normal file systems, in their normal way.
Simple MAil Transfer Protocol (SMTP) SMTP, answering our ubiquitous call to email, uses a spooled, or queued, method of mail delivery. Once a message has been sent to a destination, the message is spooled to a device-usually a disk. The server software at the destination posts a vigil, regularly checking the queue for messages. When it detects them, it proceeds to deliver them to their destination. SMTP is used to send mail; POP3 or IMAP is used to receive mail.
Post Office Protocol (POP) It gives us a storage facility for incoming mail, and the latest version is called POP3. (sound familiar). Basically, how this protocol works is when a client device connects to a POP3 server, message addressed to that client are released for downloading. It doesn't allow message to be downloaded selectively, but once they are, the client/server interaction ends and you can delete and tweak your messages locally at will. Lately we're seeing a newer standard, IMAP, beging used more and more in place of POP3.
Internet Message Access Protocol, Version 4 (IMAP4) It makes it so you set control over how you download your mail, and with it, you also gain some much-needed security. It lets you peek at the message header or download just a part of a message-you can now just nibble at the bait instead of swallowing it whole and then choking on the hook hidden inside.
With it, you can choose to store message on the email server hierarchically and link to documents and user groups too. IMAP even gives you search commands to use to hunt for message on there subject, header, or content. As you can imagine, it has some serious authentication features it actually supports the Kerberos authentication scheme that MIT developed. And yes,IMA n in the current version.
Transport Layer Security (TLS) Both transport layer security and ists forerunner, secure sockets layer (SSL), are cryptography protocols that come in really handy for enabling secure online data transfer activities like browsing the web, instant messaging, Internet faxing, and soon.
Session Initiation Protocol(SIP) It is a hugely popular signaling protocol used to construct and deconstruct multimedia communication sessions for many things like voice and video calls, video conferencing, streaming multimedia distribution, instant messaging. presence information, and online games over the internet.