The & Layers of the OSI Model
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.
and end-user processes. Communication partners are identified,
quality of service is identified, user authentication and
privacy are considered, and any constraints on data
are identified. Everything at this layer is
application-specific. This layer provides application services
applications that exist entirely in the application level.
Tiered application architectures are part of this layer.
layer provides independence from differences in data
by translating from application to network format, and vice
versa. The presentation layer works to transform data into the
form that the application layer can accept. This layer formats
and encrypts data to be sent across a
providing freedom from compatibility problems. It is sometimes
called the syntax layer.
layer establishes, manages and terminates connections between
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.
layer provides transparent transfer of data between end systems,
and is responsible for end-to-end error recovery and
It ensures complete data transfer.
technologies, creating logical paths, known as
for transmitting data from
node. Routing and forwarding are functions of this layer, as
control and packet sequencing.
layer, data packets are
and decoded into bits. It furnishes
knowledge and management and handles errors in the physical
layer, flow control and frame synchronization. The data link
layer is divided into two sub layers: The Media Access
layer and the
Logical Link Control
(LLC) layer. The MAC sub layer controls how a computer on the
network gains access to the data and permission to transmit it.
The LLC layer controls frame
flow control and error checking.
layer conveys the bit stream - electrical impulse, light or
radio signal -- through the
at the electrical and mechanical level. It provides the
means of sending and receiving data on a carrier, including
defining cables, cards and physical aspects.
with physical layer components.
OSI MODEL, LAYERS & PROTOCOLS
Browser, Email, Print Serivces, SIP, SSH and SCP, NFS, RTSP, Feed, XMPP,
Whois, SMB; DNS; FTP; TFTP; BOOTP; SNMP;RLOGIN; SMTP; MIME; NFS; FINGER;
TELNET; NCP; APPC; AFP; SMB
ASN.1, SMB, AFP, NCP, MIDI, HTML, GIF, TIFF, JPEG, ASCII,
SSH, X.225, RPC, NetBIOS, ASP, Winsock, BSD
UDP, RTP, SCTP, SPX, ATP
Gateway, Advanced Cable Tester, Brouter
ICMP, IGMP, BGP, OSPF, RIP, IGRP, EIGRP, ARP, RARP, X.25, NETBEUI
Brouter, Router, Frame Relay Device, ATM Switch, Advanced Cable Tester,
Ethernet, Token ring, StarLAN, HDLC, Frame relay, ISDN, ATM, 802.11 WiFi,
FDDI, PPP, Bridge, Switch, ISDN Router, Intelligent Hub, NIC, Advanced
Cable Tester, ARCNET, LocalTalk, FDDI, ATM. NIC Drivers: Open Datalink
Interface (ODI), Network Independent Interface Specification (NDIS)
Twisted Pair, Coax, Fiber Optic, Wireless Media, Repeater, Multiplexer,
Hubs, (Passive/Active), TDR, Oscilloscope, Amplifier, Carrier pigeon
Application (OSI - Layers5 through 7)
HTTP, FTP, DNS
(Routing protocols like BGP and RIP, which for a variety of reasons run
over TCP and UDP respectively, may also be considered part of the
Transport (OSI - Layers4 and 5)
UDP, RTP, SCTP
(Routing protocols like OSPF, which run over IP, may also be considered
part of the Internetwork layer)
Internetwork (OSI - Layer 3)
TCP/IP this is the Internet Protocol (IP)
(Required protocols like ICMP and IGMP run over IP, but may still be
considered part of the Internetwork layer; ARP does not run over IP)
Link (OSI - Layers 1 and 2)
Ethernet, Wi-Fi, MPLS, etc.