Osi Layers

Front 1

This layer 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. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Back 1

Application Layer
(Layer 7)

Front 2

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa.

Back 2

Presentation Layer
(Layer 6)

Hint 2

This 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 network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Front 3

This layer establishes, manages and terminates connections between applications.

Back 3

Session Layer
(Layer 5)

Hint 3

This layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination

Front 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.

Back 4

Transport Layer
(Layer 4)

Front 5

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.

Back 5

Network Layer
(Layer 3)

Front 6

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.

Back 6

Data Link Layer
(Layer 2)

Front 7

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.

Back 7

Physical Layer
(Layer 1)

Hint 7

Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Front 8

The OSI, or Open System Interconnection

Back 8

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

Front 9

143

Back 9

IMAP4

Front 10

22

Back 10

SSH

Front 11

110

Back 11

POP3

Front 12

25

Back 12

SMTP

Front 13

123

Back 13

NTP

Front 14

53

Back 14

DNS

Front 15

69

Back 15

TFTP

Front 16

80

Back 16

HTTP

Front 17

23

Back 17

TELNET

Front 18

443

Back 18

HTTPS

Front 19

20

Back 19

FTP

Front 20

21

Back 20

FTP

Front 21

119

Back 21

NNTP

Front 22

The data link layer is divided into two sublayers:

Back 22

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.