OSI model
The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...
of
computer networking
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
, the network layer is layer 3. The network layer is responsible for
packet forwarding
Packet forwarding is the relaying of packets from one network segment to another by nodes in a computer network. The network layer in the OSI model is responsible for packet forwarding.
Models
The simplest forwarding model unicastinginvolve ...
The network layer provides the means of transferring variable-length
network packet
In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control inform ...
s from a source to a destination host via one or more networks. Within the service layering semantics of the OSI network architecture, the network layer responds to service requests from the
transport layer
In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end ...
and issues service requests to the
data link layer
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer ...
.
Functions of the network layer include:
;
Connectionless communication
Connectionless communication, often referred to as CL-mode communication,Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for ...
: For example, IP is connectionless, in that a data packet can travel from a sender to a recipient without the recipient having to send an acknowledgement. Connection-oriented protocols exist at other, higher layers of the OSI model.
; Host addressing
:Every host in the network must have a unique address that determines where it is. This address is normally assigned from a hierarchical system. For example, you can be :
:
:"Fred Murphy" to people in your house,
:"Fred Murphy, 1 Main Street" to Dubliners,
:"Fred Murphy, 1 Main Street, Dublin" to people in Ireland,
:"Fred Murphy, 1 Main Street, Dublin, Ireland" to people anywhere in the world.
:
:On the Internet, addresses are known as IP addresses (Internet Protocol).
:
; Message forwarding
:Since many networks are partitioned into subnetworks and connect to other networks for wide-area communications, networks use specialized hosts, called gateways or routers, to forward packets between networks.
Relation to TCP/IP model
The
TCP/IP model
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
describes the protocols used by the Internet.RFC 1122 The TCP/IP model has a layer called the
Internet layer
The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport network packets from the originating host across network boundaries; if necessary, to the destinat ...
, located above the link layer. In many textbooks and other secondary references, the TCP/IP Internet layer is equated with the OSI network layer. However, this comparison is misleading, as the allowed characteristics of protocols (e.g., whether they are connection-oriented or connection-less) placed into these layers are different in the two models. The TCP/IP Internet layer is in fact only a subset of functionality of the network layer. It describes only one type of network architecture, the Internet.
Datagram Delivery Protocol Datagram Delivery Protocol (DDP) is a member of the AppleTalk networking protocol suite. Its main responsibility is for socket-to-socket delivery of datagrams
A datagram is a basic transfer unit associated with a packet-switched network. Datagram ...
* EGP,
Exterior Gateway Protocol
An exterior gateway protocol is an IP routing protocol used to exchange routing information between autonomous systems. This exchange is crucial for communications across the Internet. Notable exterior gateway protocols include Exterior Gate ...
* EIGRP,
Enhanced Interior Gateway Routing Protocol
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietar ...
Internet Group Management Protocol
The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast and allows the network to direct ...
* IPsec,
Internet Protocol Security
In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in v ...
* IPv4/IPv6,
Internet Protocol
The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
...
* IPX,
Internetwork Packet Exchange
Internetwork Packet Exchange (IPX) is the network layer protocol in the IPX/SPX protocol suite. IPX is derived from Xerox Network Systems' IDP. It also has the ability to act as a transport layer protocol.
The IPX/SPX protocol suite was very ...
* LLARP,
Low Latency Anonymous Routing Protocol
Low or LOW or lows, may refer to:
People
* Low (surname), listing people surnamed Low
Places
* Low, Quebec, Canada
* Low, Utah, United States
* Lo Wu station (MTR code LOW), Hong Kong; a rail station
* Salzburg Airport (ICAO airport code: L ...
* OSPF,
Open Shortest Path First
Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous syst ...
* PIM,
Protocol Independent Multicast
400px, Example of a multicast network architecture
Protocol-Independent Multicast (PIM) is a family of multicast routing protocols for Internet Protocol (IP) networks that provide one-to-many and many-to-many distribution of data over a LAN, ...
* RIP,
Routing Information Protocol
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from sour ...
References
* {{cite book , first=Andrew S. , last=Tanenbaum , title=Computer networks , publisher= Prentice Hall , location=