The Internet
protocol suite is the set of communications protocols used for the Internet
and similar networks, and generally the most popular protocol
stack for wide area networks.
It is commonly known as TCP/IP, because of its most important protocols: Transmission Control Protocol (TCP) and Internet
Protocol (IP), which were the first networking protocols defined in
this standard.
It was
developed by a community of researchers centered around the ARPAnet. Certainly
the ARPAnet is the best-known TCP/IP network. However as of June, 87, at least
130 different vendors had products that support TCP/IP, and thousands of
networks of all kinds use it.
TCP/IP provides end-to-end connectivity
specifying how data should be formatted, addressed, transmitted, routed
and received at the destination. It has four abstraction layers, each with its
own protocols. From lowest to highest, the layers are:
- The link layer (commonly Ethernet) contains communication technologies for a local network.
- The internet layer (IP) connects local networks, thus establishing internet working.
- The transport layer (TCP) handles host-to-host communication.
- The application layer (for example HTTP) contains all protocols for specific data communications services on a process-to-process level (for example how a web browser communicates with a web server).
Link layer
The
link layer
is the networking scope of the local network connection to which a host is
attached. This regime is called the link
in Internet literature. This is the lowest component layer of the Internet
protocols, as TCP/IP is designed to be hardware independent. As a result TCP/IP
is able to be implemented on top of virtually any hardware networking
technology.
Internet layer
The internet
layer has the responsibility of sending packets across potentially
multiple networks. Internetworking requires sending data from the
source network to the destination network. This process is called routing.
In the Internet protocol suite, the
Internet Protocol performs two basic functions:
- Host addressing and identification: This is accomplished with a hierarchical addressing system (see IP address).
- Packet routing: This is the basic task of sending packets of data (datagrams) from source to destination by sending them to the next network node (router) closer to the final destination.
Transport layer
The
transport
layer establishes host-to-host connectivity, meaning it handles the
details of data transmission that are independent of the structure of user data
and the logistics of exchanging information for any particular specific
purpose.
Its responsibility includes end-to-end message transfer independent of
the underlying network, along with error control, segmentation, flow control,
congestion control, and application addressing (port numbers).End to end message
transmission or connecting applications at the transport layer can be
categorized as either connection-oriented, implemented in TCP, or connectionless,
implemented in UDP.
Application layer
The
application layer contains the higher-level
protocols used by most applications for network communication. Examples of
application layer protocols include the File Transfer Protocol (FTP) and the Simple Mail Transfer Protocol (SMTP). Data
coded according to application layer protocols are then encapsulated into one or (occasionally)
more transport layer protocols (such as TCP or UDP), which in turn use lower layer protocols to effect actual
data transfer.
Implementations
No
specific hardware or software implementation is required by the protocols or
the layered model, so there are many. Most computer operating systems in use
today, including all consumer-targeted systems, include a TCP/IP
implementation.
A
minimally acceptable implementation includes the following protocols, listed
from most essential to least essential: IP,
ARP, ICMP, UDP, TCP and sometimes IGMP.
In
principle, it is possible to support only one transport protocol, such as UDP,
but this is rarely done, because it limits usage of the whole implementation.
IPv6, beyond its own version of ARP (NDP), ICMP (ICMPv6) and IGMP (IGMPv6), has
some additional required functions, and often is accompanied by an integrated IPSec security layer.
Other
protocols could be easily added later (possibly being implemented entirely in userspace),
such as DNS for resolving domain names to IP addresses,
or DHCP for automatically
configuring network interfaces.
