TCP/IP Model: Process/Application Layer


TCP/IP Model: Process/Application Layer

Same as OSI model, in TCP/IP Model, the Process/Application Layer comprises of the first three layers from top of OSI Model, and deals with similar tasks like, deciding the application to be used for data transfer, data encryption and decryption, and mainting dialog control betweens sessions to keep different applications data separate in network while data transfer.
Protocols used in this layer are: Telnet, FTP, TFTP, NFS, SMTP, LPD, X Window, SNMP, DNS, DHCP, BootP.


Telnet:

Telnet is the Process/Application Layer protocol. It allows a user on a remote client machine, called the Telnet Client, to access the resourceof another machine, the Telnet Server. Telnet is CLI (Command Line Interface). User begins a Telnet Session by running the Telnet Client Software and then logging into the Telnet Server. But the Session created by a Telnet, is not secure, as the data is not encrypted, and the data is transferred in clear text format, but a session created by SecureShell (SSH) is secure because it uses encryption before data is transferred. Telnet and SSH is almost same, but the only the difference is that it is more secure than Telnet.


File Transfer Protocol (FTP):

FTP is a protocol that lets transfer file, between two machines using it. FTP is not just a protocol, but also a program used by Application.
Ftp is used for File-Handling Task. FTP teams up with Telnet to transparently log into the FTP server and then provides for the transfer of files. FTP server is restricted by the Administrator by using secure username and password. One can get around this somewhat by typing the username as anonymous, but will have very limited access.

FTP functions are limited to:
        ·         Listing and manipulating directories
        ·         Typing file contents
        ·         Copying files between hosts.

Note: It cant execute remote files as programs.


Trivial File Transfer Protocol (TFTP):

TFTP is a stripped down, stocked version of FTP. But it does not have abundance of functions like FTP. TFTP does not have directory browsing facilities. It is not secured as it does not have any authentication like a username and password, all files are kept in root directory, and any one can access the access the TFTP server, and the files in the root directory can be accessed. It can simply send and receive files.


Network File System (NFS):

This protocol is used in File sharing. It allows two different type of file systems to inter-operate.
It works like this: Suppose the NFS server is running on an NT server and the NFS client software is running on an UNIX host. NFS allows a portion of RAM on the server to store UNIX file, which can then be used by the UNIX users.
Even though the NT File system and the UNIX File System are unlike, they can still access the same file with their own normal file systems, in their own way.


Simple Mail Transfer Protocol (SMTP)

SMTP, this protocol is used for sending mail, which uses a spooled or queued method of mail delivery.


Line Printer Daemon (LPD):

LPD protocol is used for printer sharing. The LPD along Line Printer (LPR) program, allows print jobs to be spooled and sent to the networks printer using TCP/IP.


X Window:

This is designed for Client/Server Operation. X Window defines a protocol for writing Client/Server applications based on a Graphical User Interface (GUI). This is a kind of Remote Desktop Sharing.


Simple Network Management Protocol (SNMP):

SNMP protocol is basically used to check the network status. SNMP helps in collecting and manipulating valuable network informationand report to the Management Station on the network.
When the network is fine, SNMP receives something called baseline – a report delimiting a healthy network.
This protocol can also stand as watchdogs over the network, to quickly notify the management station of an error. These network watchdogs are called Agents.
An alert called a “Trap” is sent to the management station in case of any abberations.


Domain Name Service (DNS):

DNS protocol is used to resolve the host name. Hosts on a network or websites are called by their IP Addresses. But it is not possible to remember the IP address. Hence DNS wasdesigned to resolve these IP addresses. DNS is used to resolve the Fully Qualified Domain Name (FQDN).
Dynamic Host Configuration Protocol (DHCP) / BootP
DHCP and BootP is a protocol which assigns IP addresses to Hosts.
Difference between the two is, in BootP, hosts hardware address has to be entered manually in a BootP table, whereas DHCP is dynamic, DHCP can be referred to as a dynamic BootP.
BootP is used to send an operating system that a host can boot from, DHCP doesn’t do that.
DHCP is more advanced than BootP, because it can provide lot more information than a BootP when a Client requests for assigning IP addresses, like;
         ·         IP Address
         ·         Subnet Mask
         ·         Default Gateways
         ·         Domain name
         ·         DSN
         ·         WINS info
In order to receive an IP address from a DHCP server, client sends out a DHCP discover message, which is a broadcast message at both Layer 2 and Layer 3.
In Layer 2, its all in F’s (Hex) : FF:FF:FF:FF:FF:FF
In Layer 3, its 255.255.255.255
DHCP is connectionless, i.e. it uses User Datagram Protocol (UDP)


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