Transmission Control Protocol/Internet Protocol (TCP/IP) is the suite of communications protocols used to connect hosts on the Internet.
Internet protocol suite
From Wikipedia, the free encyclopedia
The
Internet protocol suite is the
computer networking model and set of
communications protocols used on the
Internet and similar computer networks. It is commonly known as
TCP/IP, because its most commonly used protocols, the
Transmission Control Protocol (TCP) and the
Internet Protocol (IP) were the first networking protocols defined during its development. It is occasionally known as the
Department of Defense (DoD) model, because the development of the networking model was funded by
DARPA, an agency of the
United States Department of Defense.
The Internet protocol suite provides end-to-end data communication
specifying how data should be packetized, addressed, transmitted,
routed
and received. This functionality is organized into four abstraction
layers which are used to sort all related protocols according to the
scope of networking involved.
[1][2] From lowest to highest, the layers are the
link layer, containing communication methods for data that remains within a single network segment (link); the
internet layer, connecting independent networks, thus providing
internetworking; the
transport layer handling host-to-host communication; and the
application layer, which provides process-to-process data exchange for applications.
Technical standards specifying the Internet protocol suite and many of its constituent protocols are maintained by the
Internet Engineering Task Force (IETF).
History
Early research
Diagram of the first internetworked connection
The Internet protocol suite resulted from research and development conducted by the Defense Advanced Research Projects Agency (
DARPA) in the late 1960s.
[3] After initiating the pioneering
ARPANET in 1969, DARPA started work on a number of other data transmission technologies. In 1972,
Robert E. Kahn joined the DARPA
Information Processing Technology Office,
where he worked on both satellite packet networks and ground-based
radio packet networks, and recognized the value of being able to
communicate across both. In the spring of 1973,
Vinton Cerf, the developer of the existing ARPANET
Network Control Program
(NCP) protocol, joined Kahn to work on open-architecture
interconnection models with the goal of designing the next protocol
generation for the ARPANET.
By the summer of 1973, Kahn and Cerf had worked out a fundamental
reformulation, in which the differences between network protocols were
hidden by using a common
internetwork protocol,
and, instead of the network being responsible for reliability, as in
the ARPANET, this function was delegated to the hosts. Cerf credits
Hubert Zimmermann and
Louis Pouzin, designer of the
CYCLADES network, with important influences on this design. The protocol was implemented as the
Transmission Control Program (TCP), first published in 1974.
[4]
Initially, the TCP managed both
datagram transmissions and routing, but as the protocol grew, other researchers, including
Jon Postel, recommended a division of functionality into protocol layers. Postel stated, “
we are screwing up in our design of Internet protocols by violating the principle of layering”.
[5]
Encapsulation of different mechanisms was intended to create an
environment where the upper layers could access only what was needed
from the lower layers. A monolithic design would be inflexible and lead
to scalability issues. The Transmission Control Program was split into
two distinct protocols, the Transmission Control Protocol and the
Internet Protocol. The new suite replaced all protocols used
previously.,
[6] PRnet,
[7] and SATnet
[8][9]
The design of the network included the recognition that it should
provide only the functions of efficiently transmitting and routing
traffic between end nodes and that all other intelligence should be
located at the edge of the network, in the end nodes. This design is
known as the
end-to-end principle.
Using this design, it became possible to connect almost any network to
the ARPANET, irrespective of the local characteristics, thereby solving
Kahn's initial problem. One popular expression is that TCP/IP, the
eventual product of Cerf and Kahn's work, will run over "
two tin cans and a string." (Years later, as a joke, the
IP over Avian Carriers formal protocol specification was created and successfully tested.)
A computer called a
router is provided with an interface to each network. It forwards
packets back and forth between them.
[10] Originally a router was called
gateway, but the term was changed to avoid confusion with other types of
gateways.
Specification
From
1973 to 1974, Cerf's networking research group at Stanford worked out
details of the idea, resulting in the first TCP specification.
[11] A significant technical influence was the early networking work at
Xerox PARC, which produced the
PARC Universal Packet protocol suite, much of which existed around that time.
DARPA then contracted with
BBN Technologies,
Stanford University, and the
University College London
to develop operational versions of the protocol on different hardware
platforms. Four versions were developed: TCP v1, TCP v2, TCP v3 and IP
v3, and TCP/IP v4. The last protocol is still in use today.
In 1975, a two-network TCP/IP communications test was performed
between Stanford and University College London (UCL). In November, 1977,
a three-network TCP/IP test was conducted between sites in the US, the
UK, and Norway. Several other TCP/IP prototypes were developed at
multiple research centers between 1978 and 1983. The migration of the
ARPANET to TCP/IP was officially completed on
flag day January 1, 1983, when the new protocols were permanently activated.
[12]
Adoption
In March 1982, the US Department of Defense declared TCP/IP as the standard for all military computer networking.
[13] In 1985, the Internet Advisory Board (later renamed the
Internet Architecture Board)
held a three-day workshop on TCP/IP for the computer industry, attended
by 250 vendor representatives, promoting the protocol and leading to
its increasing commercial use.
In 1985, the first
Interop
conference focused on network interoperability by broader adoption of
TCP/IP. The conference was founded by Dan Lynch, an early Internet
activist. From the beginning, large corporations, such as IBM and DEC,
attended the meeting. Interoperability conferences have been held every
year since then. Every year from 1985 through 1993, the number of
attendees tripled.
[citation needed]
IBM, AT&T and DEC were the first major corporations to adopt TCP/IP, despite having competing internal protocols (
SNA,
XNS,
DECNET). In IBM, from 1984,
Barry Appelman's group did TCP/IP development. (Appelman later moved to
AOL
to be the head of all its development efforts.) They navigated the
corporate politics to get a stream of TCP/IP products for various IBM
systems, including
MVS,
VM, and
OS/2. At the same time, several smaller companies began offering TCP/IP stacks for
DOS and
MS Windows, such as the company
FTP Software, and the
Wollongong Group.
[14] The first VM/CMS TCP/IP stack came from the University of Wisconsin.
[15]
Some of these TCP/IP stacks were written single-handedly by a few programmers. Jay Elinsky and
Oleg Vishnepolsky of IBM Research wrote TCP/IP stacks for VM/CMS and OS/2, respectively.
[16]
In 1984 Donald Gillies at MIT wrote a 'ntcp' multi-connection TCP which
ran atop the IP/PacketDriver layer maintained by John Romkey at MIT in
1983-4. Romkey leveraged this TCP in 1986 when FTP Software was founded.
[17][18] Phil Karn created KA9Q TCP (a multi-connection TCP for ham radio applications) starting in 1985.
[19]
The spread of TCP/IP was fueled further in June 1989, when AT&T agreed to place the TCP/IP code developed for
UNIX
into the public domain. Various vendors, including IBM, included this
code in their own TCP/IP stacks. Many companies sold TCP/IP stacks for
Windows until Microsoft released a native TCP/IP stack in Windows 95.
This event was a little late in the evolution of the Internet, but it
cemented TCP/IP's dominance over other protocols, which began to lose
ground.
[citation needed] These protocols included
IBM Systems Network Architecture (SNA),
Open Systems Interconnection (OSI), Microsoft's native
NetBIOS, and
Xerox Network Systems (XNS).
[citation needed]
Key architectural principles
An early architectural document,
RFC 1122, emphasizes architectural principles over layering.
[20]
- End-to-end principle:
This principle has evolved over time. Its original expression put the
maintenance of state and overall intelligence at the edges, and assumed
the Internet that connected the edges retained no state and concentrated
on speed and simplicity. Real-world needs for firewalls, network
address translators, web content caches and the like have forced changes
in this principle.[21]
- Robustness Principle:
"In general, an implementation must be conservative in its sending
behavior, and liberal in its receiving behavior. That is, it must be
careful to send well-formed datagrams, but must accept any datagram that
it can interpret (e.g., not object to technical errors where the
meaning is still clear)."[22]
"The second part of the principle is almost as important: software on
other hosts may contain deficiencies that make it unwise to exploit
legal but obscure protocol features."[23]
Abstraction layers
Two Internet hosts connected via two routers and the corresponding
layers used at each hop. The application on each host executes read and
write operations as if the processes were directly connected to each
other by some kind of data pipe. Every other detail of the communication
is hidden from each process. The underlying mechanisms that transmit
data between the host computers are located in the lower protocol
layers.
|
|
|
Encapsulation of application data descending through the layers described in RFC 1122
|
Encapsulation
is used to provide abstraction of protocols and services. Encapsulation
is usually aligned with the division of the protocol suite into layers
of general functionality. In general, an application (the highest level
of the model) uses a set of protocols to send its data down the layers,
being further encapsulated at each level.
The layers of the protocol suite near the top are logically closer to
the user application, while those near the bottom are logically closer
to the physical transmission of the data. Viewing layers as providing or
consuming a service is a method of
abstraction to isolate upper layer protocols from the details of transmitting bits over, for example,
Ethernet and
collision detection, while the lower layers avoid having to know the details of each and every application and its protocol.
Even when the layers are examined, the assorted architectural
documents—there is no single architectural model such as ISO 7498, the
Open Systems Interconnection (OSI) model—have
fewer and less rigidly defined layers than the OSI model, and thus
provide an easier fit for real-world protocols. One frequently
referenced document,
RFC 1958,
does not contain a stack of layers. The lack of emphasis on layering is
a major difference between the IETF and OSI approaches. It only refers
to the existence of the internetworking layer and generally to
upper layers;
this document was intended as a 1996 snapshot of the architecture: "The
Internet and its architecture have grown in evolutionary fashion from
modest beginnings, rather than from a Grand Plan. While this process of
evolution is one of the main reasons for the technology's success, it
nevertheless seems useful to record a snapshot of the current principles
of the Internet architecture."
RFC 1122, entitled
Host Requirements,
is structured in paragraphs referring to layers, but the document
refers to many other architectural principles not emphasizing layering.
It loosely defines a four-layer model, with the layers having names, not
numbers, as follows:
- The application layer is the scope within which applications create
user data and communicate this data to other applications on another or
the same host. The applications, or processes, make use of the services
provided by the underlying, lower layers, especially the Transport Layer
which provides reliable or unreliable pipes to other processes. The communications partners are characterized by the application architecture, such as the client-server model and peer-to-peer networking. This is the layer in which all higher level protocols, such as SMTP, FTP, SSH, HTTP, operate. Processes are addressed via ports which essentially represent services.
- The transport layer performs host-to-host communications on either
the same or different hosts and on either the local network or remote
networks separated by routers. It provides a channel for the
communication needs of applications. UDP is the basic transport layer
protocol, providing an unreliable datagram service. The Transmission
Control Protocol provides flow-control, connection establishment, and
reliable transmission of data.
- The internet layer has the task of exchanging datagrams across
network boundaries. It provides a uniform networking interface that
hides the actual topology (layout) of the underlying network
connections. It is therefore also referred to as the layer that
establishes internetworking, indeed, it defines and establishes the
Internet. This layer defines the addressing and routing structures used
for the TCP/IP protocol suite. The primary protocol in this scope is the
Internet Protocol, which defines IP addresses.
Its function in routing is to transport datagrams to the next IP router
that has the connectivity to a network closer to the final data
destination.
- The link layer defines the networking methods within the scope of
the local network link on which hosts communicate without intervening
routers. This layer includes the protocols used to describe the local
network topology and the interfaces needed to effect transmission of
Internet layer datagrams to next-neighbor hosts.
The Internet protocol suite and the layered
protocol stack
design were in use before the OSI model was established. Since then,
the TCP/IP model has been compared with the OSI model in books and
classrooms, which often results in confusion because the two models use
different assumptions and goals, including the relative importance of
strict layering.
This abstraction also allows upper layers to provide services that
the lower layers do not provide. While the original OSI model was
extended to include connectionless services (OSIRM CL),
[24] IP is not designed to be reliable and is a
best effort delivery
protocol. This means that all transport layer implementations must
choose whether or how to provide reliability. UDP provides data
integrity via a
checksum
but does not guarantee delivery; TCP provides both data integrity and
delivery guarantee by retransmitting until the receiver acknowledges the
reception of the packet.
This model lacks the formalism of the OSI model and associated
documents, but the IETF does not use a formal model and does not
consider this a limitation, as illustrated in the comment by
David D. Clark,
"We reject: kings, presidents and voting. We believe in: rough
consensus and running code." Criticisms of this model, which have been
made with respect to the OSI model, often do not consider ISO's later
extensions to that model.
For multi-access links with their own addressing systems (e.g.
Ethernet) an address mapping protocol is needed. Such protocols can be
considered to be below IP but above the existing link system. While the
IETF does not use the terminology, this is a subnetwork dependent
convergence facility according to an extension to the OSI model, the
internal organization of the network layer (IONL).
[25]
ICMP & IGMP operate on top of IP but do not transport data like
UDP or TCP. Again, this functionality exists as layer management
extensions to the OSI model, in its
Management Framework (OSIRM MF)
[26]
The SSL/TLS library operates above the transport layer (uses TCP) but
below application protocols. Again, there was no intention, on the part
of the designers of these protocols, to comply with OSI architecture.
The link is treated as a black box. The IETF explicitly does not
intend to discuss transmission systems, which is a less academic
[citation needed] but practical alternative to the OSI model.
The following is a description of each layer in the TCP/IP networking model starting from the lowest level.
Link layer
The
link layer has the networking scope of the local network connection to which a host is attached. This regime is called the
link
in TCP/IP literature. It is the lowest component layer of the Internet
protocols, as TCP/IP is designed to be hardware independent. As a
result, TCP/IP may be implemented on top of virtually any hardware
networking technology.
The link layer is used to move packets between the Internet layer
interfaces of two different hosts on the same link. The processes of
transmitting and receiving packets on a given link can be controlled
both in the
software device driver for the
network card, as well as on
firmware or specialized
chipsets. These perform
data link functions such as adding a
packet header to prepare it for transmission, then actually transmit the frame over a
physical medium.
The TCP/IP model includes specifications of translating the network
addressing methods used in the Internet Protocol to data link
addressing, such as
Media Access Control
(MAC). All other aspects below that level, however, are implicitly
assumed to exist in the link layer, but are not explicitly defined.
This is also the layer where packets may be selected to be sent over a
virtual private network or other
networking tunnel.
In this scenario, the link layer data may be considered application
data which traverses another instantiation of the IP stack for
transmission or reception over another IP connection. Such a connection,
or virtual link, may be established with a transport protocol or even
an application scope protocol that serves as a
tunnel in the link layer of the protocol stack. Thus, the TCP/IP model does not dictate a strict hierarchical encapsulation sequence.
The TCP/IP model's link layer corresponds to the Open Systems
Interconnection (OSI) model physical and data link layers, layers one
and two of the OSI model.
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.
The Internet Protocol performs two basic functions:
- Host addressing and identification: This is accomplished with a hierarchical IP addressing system.
- Packet routing: This is the basic task of sending packets of data
(datagrams) from source to destination by forwarding them to the next
network router closer to the final destination.
The internet layer is not only agnostic of data structures at the
transport layer, but it also does not distinguish between operation of
the various transport layer protocols. IP carries data for a variety of
different
upper layer protocols. These protocols are each identified by a unique
protocol number: for example,
Internet Control Message Protocol (ICMP) and
Internet Group Management Protocol (IGMP) are protocols 1 and 2, respectively.
Some of the protocols carried by IP, such as ICMP which is used to
transmit diagnostic information, and IGMP which is used to manage
IP Multicast
data, are layered on top of IP but perform internetworking functions.
This illustrates the differences in the architecture of the TCP/IP stack
of the Internet and the OSI model. The TCP/IP model's internet layer
corresponds to layer three of the Open Systems Interconnection (OSI)
model, where it is referred to as the network layer.
The internet layer provides an unreliable datagram transmission
facility between hosts located on potentially different IP networks by
forwarding the transport layer datagrams to an appropriate next-hop
router for further relaying to its destination. With this functionality,
the internet layer makes possible internetworking, the interworking of
different IP networks, and it essentially establishes the Internet. The
Internet Protocol is the principal component of the internet layer, and
it defines two addressing systems to identify network hosts' computers,
and to locate them on the network. The original address system of the
ARPANET and its successor, the Internet, is
Internet Protocol version 4 (IPv4). It uses a 32-bit
IP address
and is therefore capable of identifying approximately four billion
hosts. This limitation was eliminated in 1998 by the standardization of
Internet Protocol version 6 (IPv6) which uses 128-bit addresses. IPv6 production implementations emerged in approximately 2006.
Transport layer
The
transport layer establishes basic data channels that applications use
for task-specific data exchange. The layer establishes
process-to-process connectivity, meaning it provides end-to-end services
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.
For the purpose of providing process-specific transmission channels for applications, the layer establishes the concept of the
port.
This is a numbered logical construct allocated specifically for each of
the communication channels an application needs. For many types of
services, these
port numbers
have been standardized so that client computers may address specific
services of a server computer without the involvement of service
announcements or directory services.
Because IP provides only a
best effort delivery, some transport layer protocols offer reliability. However, IP can run over a reliable data link protocol such as the
High-Level Data Link Control (HDLC).
For example, the TCP is a connection-oriented protocol that addresses numerous reliability issues in providing a
reliable byte stream:
- data arrives in-order
- data has minimal error (i.e., correctness)
- duplicate data is discarded
- lost or discarded packets are resent
- includes traffic congestion control
The newer
Stream Control Transmission Protocol
(SCTP) is also a reliable, connection-oriented transport mechanism. It
is message-stream-oriented—not byte-stream-oriented like TCP—and
provides multiple streams multiplexed over a single connection. It also
provides
multi-homing
support, in which a connection end can be represented by multiple IP
addresses (representing multiple physical interfaces), such that if one
fails, the connection is not interrupted. It was developed initially for
telephony applications (to transport
SS7 over IP), but can also be used for other applications.
The User Datagram Protocol is a connectionless
datagram protocol. Like IP, it is a best effort, "unreliable" protocol. Reliability is addressed through
error detection using a weak checksum algorithm. UDP is typically used for applications such as streaming media (audio, video,
Voice over IP etc.) where on-time arrival is more important than reliability, or for simple query/response applications like
DNS lookups, where the overhead of setting up a reliable connection is disproportionately large.
Real-time Transport Protocol (RTP) is a datagram protocol that is designed for real-time data such as
streaming audio and video.
The applications at any given network address are distinguished by their TCP or UDP port. By convention certain
well known ports are associated with specific applications.
The TCP/IP model's transport or host-to-host layer corresponds to the
fourth layer in the Open Systems Interconnection (OSI) model, also
called the transport layer.
Application layer
The
application layer
includes the protocols used by most applications for providing user
services or exchanging application data over the network connections
established by the lower level protocols, but this may include some
basic network support services, such as many routing protocols, and host
configuration protocols. Examples of application layer protocols
include the
Hypertext Transfer Protocol (HTTP), the
File Transfer Protocol (FTP), the
Simple Mail Transfer Protocol (SMTP), and the
Dynamic Host Configuration Protocol (DHCP).
[27] Data coded according to application layer protocols are
encapsulated into transport layer protocol units (such as TCP or UDP messages), which in turn use
lower layer protocols to effect actual data transfer.
The TCP/IP model does not consider the specifics of formatting and
presenting data, and does not define additional layers between the
application and transport layers as in the OSI model (presentation and
session layers). Such functions are the realm of
libraries and
application programming interfaces.
Application layer protocols generally treat the transport layer (and lower) protocols as
black boxes
which provide a stable network connection across which to communicate,
although the applications are usually aware of key qualities of the
transport layer connection such as the end point IP addresses and port
numbers. Application layer protocols are often associated with
particular
client–server applications, and common services have
well-known port numbers reserved by the
Internet Assigned Numbers Authority (IANA). For example, the
HyperText Transfer Protocol uses server port 80 and
Telnet uses server port 23.
Clients connecting to a service usually use
ephemeral ports,
i.e., port numbers assigned only for the duration of the transaction at
random or from a specific range configured in the application.
The transport layer and lower-level layers are unconcerned with the specifics of application layer protocols. Routers and
switches do not typically examine the encapsulated traffic, rather they just provide a conduit for it. However, some
firewall and
bandwidth throttling applications must interpret application data. An example is the
Resource Reservation Protocol (RSVP). It is also sometimes necessary for
network address translator (NAT) traversal to consider the application payload.
The application layer in the TCP/IP model is often compared as
equivalent to a combination of the fifth (Session), sixth
(Presentation), and the seventh (Application) layers of the Open Systems
Interconnection (OSI) model.
Furthermore, the TCP/IP reference model distinguishes between
user protocols and
support protocols.
[28]
Support protocols provide services to a system. User protocols are used
for actual user applications. For example, FTP is a user protocol and
DNS is a support protocol.
Layer names and number of layers in the literature
The following table shows various networking models. The number of layers varies between three and seven.
| RFC 1122, Internet STD 3 (1989) |
Cisco Academy[29] |
Kurose,[30] Forouzan [31] |
Comer,[32] Kozierok[33] |
Stallings[34] |
Tanenbaum[35] |
Mike Padlipsky's 1982 "Arpanet Reference Model" (RFC 871) |
OSI model |
| Four layers |
Four layers |
Five layers |
Four+one layers |
Five layers |
Five layers |
Three layers |
Seven layers |
| "Internet model" |
"Internet model" |
"Five-layer Internet model" or "TCP/IP protocol suite" |
"TCP/IP 5-layer reference model" |
"TCP/IP model" |
"TCP/IP 5-layer reference model" |
"Arpanet reference model" |
OSI model |
| Application |
Application |
Application |
Application |
Application |
Application |
Application/Process |
Application |
| Presentation |
| Session |
| Transport |
Transport |
Transport |
Transport |
Host-to-host or transport |
Transport |
Host-to-host |
Transport |
| Internet |
Internetwork |
Network |
Internet |
Internet |
Internet |
Network |
| Link |
Network interface |
Data link |
Data link (Network interface) |
Network access |
Data link |
Network interface |
Data link |
|
|
Physical |
(Hardware) |
Physical |
Physical |
|
Physical |
Some of the networking models are from textbooks, which are secondary sources that may conflict with the intent of
RFC 1122 and other
IETF primary sources.
[36]
Comparison of TCP/IP and OSI layering
The
three top layers in the OSI model, i.e. the application layer, the
presentation layer and the session layer, are not distinguished
separately in the TCP/IP model which only has an application layer above
the transport layer. While some pure OSI protocol applications, such as
X.400,
also combined them, there is no requirement that a TCP/IP protocol stack
must impose monolithic architecture above the transport layer. For
example, the NFS application protocol runs over the
eXternal Data Representation (XDR) presentation protocol, which, in turn, runs over a protocol called
Remote Procedure Call (RPC). RPC provides reliable record transmission, so it can safely use the best-effort UDP transport.
Different authors have interpreted the TCP/IP model differently, and
disagree whether the link layer, or the entire TCP/IP model, covers OSI
layer 1 (
physical layer) issues, or whether a hardware layer is assumed below the link layer.
Several authors have attempted to incorporate the OSI model's layers 1
and 2 into the TCP/IP model, since these are commonly referred to in
modern standards (for example, by
IEEE and
ITU).
This often results in a model with five layers, where the link layer or
network access layer is split into the OSI model's layers 1 and 2.
The IETF protocol development effort is not concerned with strict
layering. Some of its protocols may not fit cleanly into the OSI model,
although RFCs sometimes refer to it and often use the old OSI layer
numbers. The IETF has repeatedly stated
[citation needed] that Internet protocol and architecture development is not intended to be OSI-compliant.
RFC 3439, addressing Internet architecture, contains a section entitled: "Layering Considered Harmful".
[36]
For example, the session and presentation layers of the OSI suite are
considered to be included to the application layer of the TCP/IP suite.
The functionality of the session layer can be found in protocols like
HTTP and
SMTP and is more evident in protocols like
Telnet and the
Session Initiation Protocol
(SIP). Session layer functionality is also realized with the port
numbering of the TCP and UDP protocols, which cover the transport layer
in the TCP/IP suite. Functions of the presentation layer are realized in
the TCP/IP applications with the
MIME standard in data exchange.
Conflicts are apparent also in the original OSI model, ISO 7498, when
not considering the annexes to this model, e.g., the ISO 7498/4
Management Framework, or the ISO 8648 Internal Organization of the
Network layer (IONL). When the IONL and Management Framework documents
are considered, the ICMP and IGMP are defined as layer management
protocols for the network layer. In like manner, the IONL provides a
structure for "subnetwork dependent convergence facilities" such as
ARP and
RARP.
IETF protocols can be encapsulated recursively, as demonstrated by tunneling protocols such as
Generic Routing Encapsulation (GRE). GRE uses the same mechanism that OSI uses for tunneling at the network layer.
Implementations
The Internet protocol suite does not presume any specific hardware or
software environment. It only requires that hardware and a software
layer exists that is capable of sending and receiving packets on a
computer network. As a result, the suite has been implemented on
essentially every computing platform. A minimal implementation of TCP/IP
includes the following:
Internet Protocol (IP),
Address Resolution Protocol (ARP),
Internet Control Message Protocol (ICMP),
Transmission Control Protocol (TCP),
User Datagram Protocol (UDP), and
IGMP. In addition to IP, ICMP, TCP, UDP, Internet Protocol version 6 requires
Neighbor Discovery Protocol (NDP), ICMPv6, and IGMPv6 and is often accompanied by an integrated
IPSec security layer.
Application programmers are typically concerned only with interfaces
in the application layer and often also in the transport layer, while
the layers below are services provided by the TCP/IP stack in the
operating system. Most IP implementations are accessible to programmers
through
sockets and
APIs.
Unique implementations include
Lightweight TCP/IP, an
open source stack designed for
embedded systems, and
KA9Q NOS, a stack and associated protocols for amateur
packet radio systems and
personal computers connected via serial lines.
Microcontroller firmware in the network adapter typically handles
link issues, supported by driver software in the operating system.
Non-programmable analog and digital electronics are normally in charge
of the physical components below the link layer, typically using an
application-specific integrated circuit
(ASIC) chipset for each network interface or other physical standard.
High-performance routers are to a large extent based on fast
non-programmable digital electronics, carrying out link level switching.
See also
Bibliography
- Douglas E. Comer. Internetworking with TCP/IP - Principles, Protocols and Architecture. ISBN 86-7991-142-9
- Joseph G. Davies and Thomas F. Lee. Microsoft Windows Server 2003 TCP/IP Protocols and Services. ISBN 0-7356-1291-9
- Forouzan, Behrouz A. (2003). TCP/IP Protocol Suite (2nd ed.). McGraw-Hill. ISBN 0-07-246060-1.
- Craig Hunt TCP/IP Network Administration. O'Reilly (1998) ISBN 1-56592-322-7
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References
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