Network layer - The 3rd level of the OSI network model , designed to determine the data transmission path. He is responsible for translating logical addresses and names into physical ones , determining the shortest routes, switching and routing , tracking problems and network congestion. A network device such as a router works at this level.
| OSI Network Model | |
|---|---|
| 7 | Application level |
| 6 | Executive Level |
| five | Session level |
| four | Transport level |
| 3 | Network layer |
| 2 | Channel level
|
| one | Physical level |
Within the semantics of the hierarchical representation of the OSI model, the Network layer responds to service requests from the Transport layer and forwards service requests to the Link layer .
The maximum network layer packet length can be limited by the ip mtu command .
Content
Classification
Network layer protocols route data from source to destination and can be divided into two classes: protocols with and without connection setup.
- Establishing connection protocols begin by transferring data from a call or by establishing a packet route from source to destination. Then they start serial transmission of data and then, at the end of the transfer, disconnect.
- Protocols without establishing a connection send data containing complete address information in each packet. Each packet contains the address of the sender and receiver. Next, each intermediate network device reads the address information and makes a decision about data routing. A letter or data packet is transferred from one intermediate device to another until it is delivered to the recipient. Protocols without establishing a connection do not guarantee the receipt of information by the recipient in the order in which it was sent, since different packets can go through different routes. Transport protocols are responsible for restoring data order when using network protocols without establishing a connection.
Network Layer Features:
- For models with connection establishment - connection establishment:
- The network layer of the OSI model can be either with or without a connection. For comparison, the Internet layer of the protocol stack of the DoD Model (TCP / IP Model) supports only the IP protocol, which is a protocol without establishing a connection; connection protocols are at the next levels of this model.
- Assigning an Address to a Network Host
- Each host on the network must have a unique address that determines where it is located. This address is usually assigned from a hierarchical system. On the Internet, addresses are known as IP addresses.
- Data promotion
- Since many networks are subnetted and connected to other networks by broadcast channels , networks use special hosts called gateways or routers ( routers ) to deliver packets between networks. It is also used in the interests of mobile applications when a user moves from one base station to another, in which case packets (messages) must follow him. In IPv4, this idea is described, but practically not applied. IPv6 provides a more streamlined solution.
Relation to the TCP / IP Model
The TCP / IP model describes the Internet protocol suite ( RFC 1122 ). This model includes a layer called the Gateway , located above the Link layer. In many textbooks and other secondary sources, the Internet layer is often associated with the Network layer of the OSI model. However, this is misleading in characterizing the protocols (that is, whether it is a protocol with or without a connection), the location of these levels is different in the two models. The TCP / IP gateway layer is actually just a subset of the network layer functionality. It only describes one type of network architecture, the Internet.
In general, direct or strict comparisons between these models should be avoided, since hierarchical representation in TCP / IP is not the main criterion for comparison and is generally considered to be βharmfulβ ( RFC 3439 ).
Protocols
- IPv4 / IPv6, Internet Protocol
- DVMRP, Distance Vector Multicast Routing Protocol
- ICMP, Internet Control Message Protocol
- IGMP, Internet Group Management Protocol
- PIM-SM, Protocol Independent Multicast Sparse Mode
- PIM-DM, Protocol Independent Multicast Dense Mode
- IPsec, Internet Protocol Security
- IPX, Internetwork Packet Exchange
- RIP Routing Information Protocol
- DDP, Datagram Delivery Protocol
- BGP, Border Gateway Protocol
- OSPF, OSPF
See also
- Router
- Decnet
Sources
Links
- OSI Reference Model β The ISO Model of Architecture for Open Systems Interconnection PDF (776 KB) , Hubert Zimmermann, IEEE Transactions on Communications, vol. 28, no. 4, April 1980, pp. 425-432.