7 LAYER MODEL
OSI, or Open System Interconnection, model defines a networking framework
for implementing protocols in seven layers. Control is passed from
one layer to the next, starting at the application layer in one station,
proceeding to the bottom layer, over the channel to the next station
and back up the hierarchy.
Way to Remember the OSI 7 Layer Model
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supports application and end-user processes. Communication partners
are identified, quality of service is identified, user authentication
and privacy are considered, and any constraints on data syntax are
identified. Everything at this layer is application-specific. This
layer provides application services for file transfers, e-mail, and
other network software services.
6) This layer provides independence from differences
in data representation (e.g., encryption) by translating from application
to network format, and vice versa. This layer formats and encrypts
data to be sent across a network, providing freedom from compatibility
problems. It is sometimes called the syntax layer.
Session(Layer 5) This layer establishes,
manages and terminates connections between applications. The session
layer sets up, coordinates, and terminates conversations, exchanges,
and dialogues between the applications at each end. It deals with
session and connection coordination.
Transport(Layer 4) This layer
provides transparent transfer of data between end systems, or hosts,
and is responsible for end-to-end error recovery and flow control.
It ensures complete data transfer.
Network(Layer 3) This layer provides
switching and routing technologies, creating logical paths, known
as virtual circuits, for transmitting data from node to node. Routing
and forwarding are functions of this layer, as well as addressing,
internetworking, error handling, congestion control and packet sequencing.
Data Link(Layer 2) At this layer,
data packets are encoded and decoded into bits. It furnishes transmission
protocol knowledge and management and handles errors in the physical
layer, flow control and frame synchronization. The data link layer
is divided into two sublayers: The Media Access Control (MAC) layer
and the Logical Link Control (LLC) layer. The MAC sublayer controls
how a computer on the network gains access to the data and permission
to transmit it. The LLC layer controls frame synchronization, flow
control and error checking.
Physical(Layer 1) This layer conveys
the bit stream - electrical impulse, light or radio signal -- through
the network at the electrical and mechanical level. It provides the
hardware means of sending and receiving data on a carrier, including
defining cables, cards and physical aspects.
Model for concentrators
are found in the Physical Layer
Switches /Bridges/Wireless Access Point are found
in the Data Link Layer
Multilayer Switch are found in both the Data Link Layer and Network Layer
Routers are found in the Network Layer
Gateway are found in All 7 of the OSI Layers
are found in both the Data Link and Network Layer
OSI OSI 7 Layer Model
7. Application Layer - DHCP, DNS, FTP, HTTP, IMAP4, NNTP, POP3, SMTP, SNMP, SSH, TELNET and NTPmore)
6. Presentation layer – SSL, WEP, WPA, Kerberos,
5. Session layer – Logical Ports 21, 22, 23, 80 etc…
4. Transport - TCP, SPX and UDPmore)
3. Network - IPv4, IPV6, IPX, OSPF, ICMP, IGMP and ARPMP
2. Data Link- 802.11 (WLAN), Wi-Fi, WiMAX, ATM, Ethernet, Token Ring, Frame Relay, PPTP, L2TP and ISDN-ore)
1. Physical-Hubs, Repeaters, Cables, Optical Fiber, SONET/SDN,Coaxial Cable, Twisted Pair Cable and Connectors (more)