OSI Model

Layer 1

physical Layer

• Transmission of bits across the network.

• Physical and electrical characteristics

Examples: Ethernet cables

Layer 2

Data Link Layer

• Packages data into frames and transmitting those frames on the network, performing error detection/correction and uniquely identifying network devices with an address (MAC) and flow

Exmaples:

• Network Interface Cards (NIC)

• Bridges

• Switches

Layer 3

Network Layer

• Forward traffic(routing)with logical address

Examples:

• Routers

• Multilayer switches

• IPv4 protocol

• IPv6 protocol

• Internet Control Message Protocol ( ICMP)

Layer 4

Transport Layer

• Dividing line between upper and lower layers of the OSI model

• Data is sent as segments

TCP/UDP

Windowing

Buffering

Examples:

• TCP

• UDP

• WAN Accelerators

• Load Balancers

• Firewall

TCP

Transmission Control Protocol - provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.

UDP

User Datagram Protocol. Used instead of TCP when guaranteed delivery of each packet is not necessary. UDP uses a best-effort delivery mechanism.

Layer 5

Session Layer

• Think of a session as a conversation that must be kept separate from others to prevent intermingling of the data

• Setting up sessions

• Maintaining sessions

• Tearing down sessions.

Examples:

• H.323

Used to set up , maintain , and tear down a video/video connection

• NetBIOS

Used by computers to share files over a network

Layer 6

Presentation Layer

Responsible for formatting the data exchanged and securing that data with proper encryption.

• Functions

• Data Formatting

• Encryption

Examples:

• HTML , XML, PHP, Java script ....

• ASC II , EBCDIC , UNICODE, ....

• GIF , JPG , TIF, SVG, PNG, .

• MPG, MOV .....

• TLS, SSL ......

Layer 7

Application Layer

provides application - level services. Not Microsoft Word or Notepad.

Layer where the users communicate with computer.

Function:

• Application Services

• Service advertisement

Examples:

• E-mail ( POP 3, IMAP, SMTP)

• Web Browsing (HTTP, HTTPS)

• Domain Name Service (DNS)

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