OSI 7 Layers

์˜์–ด๋กœ ๋œ ๋ถ€๋ถ„์€ ์ฒ˜์Œ์— ๊ณต๋ถ€ํ•œ ๋‚ด์šฉ & ํ•œ๊ธ€๋กœ ๋œ ๋ถ€๋ถ„์€ ์ฑ…๋ณด๋ฉฐ ๋‹ค์‹œ ๊ณต๋ถ€ํ•œ ๋‚ด์šฉ

Reference: [์ฑ…] IT ์—”์ง€๋‹ˆ์–ด๋ฅผ ์œ„ํ•œ ๋„คํŠธ์›Œํฌ ์ž…๋ฌธ

Before getting started

  • ๊ณผ๊ฑฐ์—๋Š” ํ†ต์‹ ์šฉ ๊ทœ์•ฝ์ด ํ‘œ์ค€ํ™”๋˜์ง€ ์•Š์•„์„œ ํ˜ธํ™˜๋˜์ง€ ์•Š๋Š” system์ด๋‚˜ application์ด ๋งŽ์•˜๊ณ  ํ†ต์‹ ์ด ๋ถˆ๊ฐ€๋Šฅ ํ–ˆ์Œ

    • ์ด๊ฒƒ์„ ํ•˜๋‚˜์˜ ๊ทœ์•ฝ์œผ๋กœ ํ†ตํ•ฉ ํ•˜๋ ค๋Š” ๋…ธ๋ ฅ์ด ํ˜„์žฌ์˜ OSI 7 Layers ๋กœ ๋‚จ์•„์žˆ๋‹ค!

  • OSI 7 Layers๊ฐ€ network ๋™์ž‘์„ ๋‚˜๋ˆ„์–ด ์ดํ•ดํ•˜๊ณ  ๊ฐœ๋ฐœํ•˜๋Š”๋ฐ ๋„์›€์ด ๋˜๋ฏ€๋กœ main network reference model๋กœ ํ™œ์šฉ๋˜๊ณ  ์žˆ์ง€๋งŒ,

    • ํ˜„์žฌ ๋Œ€๋ถ€๋ถ„์˜ protocol์€ TCP/IP protocol stack ๊ธฐ๋ฐ˜์œผ๋กœ ๋˜์–ด ์žˆ๋‹ค

What is OSI 7 Layers?

OSI 7 Layers

  • OSI (= Open Systems Interconnection) is a 7 layer architecture with each layer having specific functionality to perform.

  • All these 7 layers work collaboratively to transmit the data from one person to another across the globe.

OSI 7 Layers

OSI 7 Layers๋Š” ๊ณ„์ธต์˜ ์—ญํ• ๊ณผ ๋ชฉํ‘œ์— ๋”ฐ๋ผ ๋‘ ๊ฐ€์ง€ ๊ณ„์ธต์œผ๋กœ ๋‚˜๋ˆŒ ์ˆ˜ ์žˆ๋‹ค.

1~4 ๊ณ„์ธต

  • Lower Layer

  • Data Flow Layer

    • data๋ฅผ ์ƒ๋Œ€๋ฐฉ์—๊ฒŒ ์ž˜ ์ „๋‹ฌํ•˜๋Š” ์—ญํ• ์„ ๊ฐ–๊ณ  ์žˆ๋‹ค

5~7 ๊ณ„์ธต

  • Upper Layer

  • Application Layer

    • data๋ฅผ ๋งŒ๋“œ๋Š” ์—ญํ• ์„ ํ•˜๋Š” ๋ถ€๋ถ„์ด๋‹ค

  • application ๊ฐœ๋ฐœ์ž

    • data flow layer๋ฅผ ๊ณ ๋ คํ•˜์ง€ ์•Š๊ณ  data๋ฅผ ํ‘œํ˜„ํ•˜๋Š” ๋ฐ ์ดˆ์ ์„ ๋งž์ถ˜๋‹ค

    • Top-down ํ˜•์‹์œผ๋กœ network๋ฅผ ๋ฐ”๋ผ๋ณธ๋‹ค

  • network engineer

    • application layer๋Š” application ๊ฐœ๋ฐœ์ž๋“ค์ด ๊ณ ๋ คํ•ด์•ผ ํ•  ์˜์—ญ์ด๋ฏ€๋กœ network engineer๋Š” ์ด ๋ถ€๋ถ„์— ๋Œ€ํ•ด ์ผ๋ฐ˜์ ์œผ๋กœ ์‹ฌ๊ฐํ•˜๊ฒŒ ๊ณ ๋ฏผํ•˜์ง€ ์•Š๋Š”๋‹ค

    • Bottom-up ํ˜•์‹์œผ๋กœ network๋ฅผ ๋ฐ”๋ผ๋ณธ๋‹ค

Details

1. Physical Layer (Layer 1)

  • The lowest layer of the OSI reference model is the physical layer.

  • It is responsible for the actual physical connection between the devices.

  • The physical layer contains information in the form of bits.

    • It is responsible for transmitting individual bits from one node to the next.

    • When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together.

img

  • ๋ฌผ๋ฆฌ์  ์—ฐ๊ฒฐ๊ณผ ๊ด€๋ จ๋œ ์ •๋ณด๋ฅผ ์ •์˜

  • ์ฃผ๋กœ ์ „๊ธฐ ์‹ ํ˜ธ ๋ฅผ ์ „๋‹ฌํ•˜๋Š”๋ฐ ์ดˆ์ ์ด ๋งž์ถ”์–ด์ ธ ์žˆ์Œ

    • ๋“ค์–ด์˜จ ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ๊ทธ๋Œ€๋กœ ์ž˜ ์ „๋‹ฌํ•˜๋Š” ๊ฒƒ์ด ๋ชฉ์ ์ด๋ฏ€๋กœ ์ „๊ธฐ ์‹ ํ˜ธ๊ฐ€ 1๊ณ„์ธต ์žฅ๋น„ ์— ๋“ค์–ด์˜ค๋ฉด ์ด ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ์žฌ์ƒ์„ฑํ•˜์—ฌ ๋‚ด๋ณด๋‚ธ๋‹ค

  • 1๊ณ„์ธต ์žฅ๋น„๋Š” ์ฃผ์†Œ์˜ ๊ฐœ๋…์ด ์—†๋‹ค!

    • ์‹ ํ˜ธ๊ฐ€ ๋“ค์–ด์˜จ port๋ฅผ ์ œ์™ธํ•˜๊ณ  ๋ชจ๋“  port์— ๊ฐ™์€ ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ์ „์†กํ•œ๋‹ค

      • ์ฆ‰, ์ถœ๋ฐœ์ง€์™€ ๋ชฉ์ ์ง€๋ฅผ ๊ตฌ๋ถ„ ํ•  ์ˆ˜ ์—†๋‹ค

  • The data link layer is responsible for the node to node delivery of the message.

  • The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer.

  • When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address.

  • Data Link Layer is divided into two sub layers :

    1. Logical Link Control (LLC)

    2. Media Access Control (MAC)

  • The packet received from Network layer is further divided into frames depending on the frame size of NIC(Network Interface Card).

  • DLL encapsulates Sender and Receiverโ€™s MAC address in the header.

  • The Receiverโ€™s MAC address is obtained by placing an ARP(Address Resolution Protocol) request onto the wire asking โ€œWho has that IP address?โ€ and the destination host will reply with its MAC address. img

  • ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ๋ชจ์•„ ์šฐ๋ฆฌ๊ฐ€ ์•Œ์•„๋ณผ ์ˆ˜ ์žˆ๋Š” data ํ˜•ํƒœ๋กœ ์ฒ˜๋ฆฌํ•œ๋‹ค

  • 1๊ณ„์ธต๊ณผ๋Š” ๋‹ค๋ฅด๊ฒŒ ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ์ •ํ™•ํžˆ ์ „๋‹ฌํ•˜๊ธฐ ๋ณด๋‹ค๋Š” ์ฃผ์†Œ ์ •๋ณด๋ฅผ ์ •์˜ํ•˜๊ณ  ์ •ํ™•ํ•œ ์ฃผ์†Œ๋กœ ํ†ต์‹ ํ•˜๋Š”๋ฐ ์ดˆ์ ์ด ๋งž์ถ”์–ด์ ธ ์žˆ๋‹ค

  • ์ถœ๋ฐœ์ง€ ์™€ ๋„์ฐฉ์ง€ ์ฃผ์†Œ๋ฅผ ํ™•์ธํ•˜๊ณ  ๋‚ด๊ฒŒ ๋ณด๋‚ธ ๊ฒƒ์ด ๋งž๋Š”์ง€ or ๋‚ด๊ฐ€ ์ฒ˜๋ฆฌํ•ด์•ผ ํ•˜๋Š”์ง€์— ๋Œ€ํ•ด ๊ฒ€์‚ฌํ•œ ํ›„์— data ์ฒ˜๋ฆฌ๋ฅผ ์ˆ˜ํ–‰ํ•œ๋‹ค

  • 2๊ณ„์ธต์—์„œ๋Š” ์ฃผ์†Œ ์ฒด๊ณ„ ๊ฐ€ ์ƒ๊ธฐ๋ฉด์„œ ์—ฌ๋Ÿฌ ํ†ต์‹ ์ด ํ•œ๊บผ๋ฒˆ์— ์ด๋ฃจ์–ด์ง€๋Š” ๊ฒƒ์„ ๊ตฌ๋ถ„ํ•˜๊ธฐ ์œ„ํ•œ ๊ธฐ๋Šฅ์ด ์ฃผ๋กœ ์ •์˜๋œ๋‹ค

  • ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ ๋ชจ์•„ data ํ˜•ํƒœ๋กœ ์ฒ˜๋ฆฌํ•˜๋ฏ€๋กœ data์— ๋Œ€ํ•œ error๋ฅผ ํƒ์ง€ํ•˜๊ฑฐ๋‚˜ ๊ณ ์น˜๋Š” ์—ญํ• ์„ ์ˆ˜ํ–‰ํ•  ์ˆ˜ ์žˆ๋‹ค

    • Ethernet ๊ธฐ๋ฐ˜ network์˜ 2๊ณ„์ธต์—์„œ๋Š” error๋ฅผ ํƒ์ง€ํ•˜๋Š” ์—ญํ• ๋งŒ ์ˆ˜ํ–‰ํ•œ๋‹ค

  • ์ฃผ์†Œ ์ฒด๊ณ„๊ฐ€ ์ƒ๊ธด๋‹ค๋Š” ๊ฒƒ์€ ํ•œ ๋ช…๊ณผ ํ†ต์‹ ํ•˜๋Š” ๊ฒƒ์ด ์•„๋‹ˆ๋ผ ๋™์‹œ์— ์—ฌ๋Ÿฌ ๋ช…๊ณผ ํ†ต์‹ ํ•  ์ˆ˜ ์žˆ๋‹ค๋Š” ๊ฒƒ์ด๋ฏ€๋กœ ๋ฌด์ž‘์ • data๋ฅผ ๋˜์ง€๋Š” ๊ฒƒ์ด ์•„๋‹ˆ๋ผ ๋ฐ›๋Š” ์‚ฌ๋žŒ์ด ํ˜„์žฌ data๋ฅผ ๋ฐ›์„ ์ˆ˜ ์žˆ๋Š”์ง€ ํ™•์ธ ํ•˜๋Š” ์ž‘์—…๋ถ€ํ„ฐ ํ•ด์•ผ ํ•œ๋‹ค

    • ์ด ์—ญํ• ์„ Flow Control ์ด๋ผ๊ณ  ๋ถ€๋ฅธ๋‹ค

      • Flow Control

        1. ์„œ๋ฒ„์—์„œ ์Šค์œ„์น˜๋กœ data ์ „์†ก

        2. ์Šค์œ„์น˜ ํ˜ผ์žก ์ƒํ™ฉ ๋ฐœ์ƒ. ์Šค์œ„์น˜๋Š” ์„œ๋ฒ„๋กœ Pause frame ์ „์†ก

        3. ์„œ๋ฒ„๋Š” Pause frame ์ˆ˜์‹  ์ˆ˜ ๋Œ€๊ธฐ

  • 2๊ณ„์ธต์˜ network ๊ตฌ์„ฑ ์š”์†Œ๋Š” Network Interface Card์™€ Switch์ด๋‹ค

  • 2๊ณ„์ธต์˜ ๊ฐ€์žฅ ์ค‘์š”ํ•œ ํŠน์ง•์€ MAC ์ฃผ์†Œ๋ผ๋Š” ์ฃผ์†Œ ์ฒด๊ณ„๊ฐ€ ์žˆ๋‹ค๋Š” ๊ฒƒ์ด๋‹ค

    • 2๊ณ„์ธต์—์„œ ๋™์ž‘ํ•˜๋Š” Network Interface Card์™€ Switch ๋ชจ๋‘ MAC ์ฃผ์†Œ๋ฅผ ์ดํ•ดํ•  ์ˆ˜ ์žˆ๊ณ , Switch๋Š” MAC ์ฃผ์†Œ๋ฅผ ๋ณด๊ณ  ํ†ต์‹ ํ•ด์•ผ ํ•  port๋ฅผ ์ง€์ •ํ•ด ๋‚ด๋ณด๋‚ด๋Š” ๋Šฅ๋ ฅ์ด ์žˆ๋‹ค

      • Network Interface Card ๋™์ž‘ ๋ฐฉ์‹

        1. ์ „๊ธฐ ์‹ ํ˜ธ๋ฅผ data ํ˜•ํƒœ๋กœ ๋งŒ๋“ ๋‹ค

        2. ๋ชฉ์ ์ง€ MAC ์ฃผ์†Œ์™€ ์ถœ๋ฐœ์ง€ MAC ์ฃผ์†Œ๋ฅผ ํ™•์ธํ•œ๋‹ค

        3. Network Interface Card์˜ MAC ์ฃผ์†Œ๋ฅผ ํ™•์ธํ•œ๋‹ค

        4. ๋ชฉ์ ์ง€ MAC ์ฃผ์†Œ์™€ Network Interface Card๊ฐ€ ๊ฐ–๊ณ  ์žˆ๋Š” MAC ์ฃผ์†Œ๊ฐ€ ๋งž์œผ๋ฉด data๋ฅผ ์ฒ˜๋ฆฌํ•˜๊ณ , ๋‹ค๋ฅด๋ฉด data๋ฅผ ํ๊ธฐํ•œ๋‹ค

      • Switch ๋™์ž‘ ๋ฐฉ์‹

        • Swtich๋Š” ๋‹จ๋ง์ด ์–ด๋–ค MAC ์ฃผ์†Œ์ธ์ง€, ์—ฐ๊ฒฐ๋œ port๋Š” ์–ด๋А ๊ฒƒ์ธ์ง€ ์ฃผ์†Œ ์Šต๋“ (Address learning) ๊ณผ์ •์—์„œ ์•Œ ์ˆ˜ ์žˆ๋‹ค

          • ์ด data๋ฅผ ๊ธฐ๋ฐ˜์œผ๋กœ ๋‹จ๋ง๋“ค์ด ํ†ต์‹ ํ•  ๋•Œ port๋ฅผ ์ ์ ˆํžˆ filtering ํ•˜๊ณ , ์ •ํ™•ํ•œ port๋กœ forwarding ํ•ด์ค€๋‹ค

        • Switch์˜ ์ ์ ˆํ•œ filtering๊ณผ forwarding ๊ธฐ๋Šฅ์œผ๋กœ ํ†ต์‹ ์ด ํ•„์š”ํ•œ port๋งŒ ์‚ฌ์šฉํ•˜๊ณ , network ์ „์ฒด์— ๋ถˆํ•„์š”ํ•œ ์ฒ˜๋ฆฌ๊ฐ€ ๊ฐ์†Œํ•˜๋ฉด์„œ

          • Ethernet network ํšจ์œจ์„ฑ์ด ํฌ๊ฒŒ ํ–ฅ์ƒ๋˜์—ˆ๊ณ ,

          • Ethernet ๊ธฐ๋ฐ˜ network๊ฐ€ ๊ธ‰์ฆํ•˜๋Š” ๊ณ„๊ธฐ๊ฐ€ ๋˜์—ˆ๋‹ค!

3. Network Layer (Layer 3)

  • Network layer works for the transmission of data from one host to the other located in different networks.

  • It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available.

  • The sender & receiverโ€™s IP address are placed in the header by the network layer.

  • The functions of the Network layer are :

    1. Routing

      • The network layer protocols determine which route is suitable from source to destination.

      • This function of network layer is known as routing.

    2. Logical Addressing

      • In order to identify each device on internetwork uniquely, network layer defines an addressing scheme.

      • The sender & receiverโ€™s IP address are placed in the header by network layer.

      • Such an address distinguishes each device uniquely and universally.

  • Segment in Network layer is referred as Packet. img

  • Network layer is implemented by networking devices such as routers

  • 3๊ณ„์ธต์—์„œ๋Š” IP ์ฃผ์†Œ์™€ ๊ฐ™์€ ๋…ผ๋ฆฌ์ ์ธ ์ฃผ์†Œ๊ฐ€ ์ •์˜๋œ๋‹ค

    • data ํ†ต์‹ ์„ ํ•  ๋•Œ์—๋Š” ๋‘ ๊ฐ€์ง€ ์ฃผ์†Œ๊ฐ€ ์‚ฌ์šฉ๋œ๋‹ค

      1. 2๊ณ„์ธต์˜ ๋ฌผ๋ฆฌ์ ์ธ MAC ์ฃผ์†Œ

      2. 3๊ณ„์ธต์˜ ๋…ผ๋ฆฌ์ ์ธ IP ์ฃผ์†Œ

    • MAC ์ฃผ์†Œ์™€ ๋‹ฌ๋ฆฌ IP ์ฃผ์†Œ๋Š” ์‚ฌ์šฉ์ž๊ฐ€ ํ™˜๊ฒฝ์— ๋งž๊ฒŒ ๋ณ€๊ฒฝํ•ด ์‚ฌ์šฉํ•  ์ˆ˜ ์žˆ๋‹ค

    • IP์ฃผ์†Œ๋Š” ๋„คํŠธ์›Œํฌ ์ฃผ์†Œ ๋ถ€๋ถ„๊ณผ ํ˜ธ์ŠคํŠธ ์ฃผ์†Œ ๋ถ€๋ถ„์œผ๋กœ ๋‚˜๋‰œ๋‹ค

      • 3๊ณ„์ธต์„ ์ดํ•ดํ•  ์ˆ˜ ์žˆ๋Š” ์žฅ๋น„๋‚˜ ๋‹จ๋ง์€ ๋„คํŠธ์›Œํฌ ์ฃผ์†Œ ์ •๋ณด๋ฅผ ์ด์šฉํ•ด์„œ

        1. ์ž์‹ ์ด ์†ํ•œ ๋„คํŠธ์›Œํฌ์™€ ์›๊ฒฉ์ง€ ๋„คํŠธ์›Œํฌ๋ฅผ ๊ตฌ๋ถ„ํ•  ์ˆ˜ ์žˆ๊ณ 

        2. ์›๊ฒฉ์ง€ ๋„คํŠธ์›Œํฌ๋ฅผ ๊ฐ€๋ ค๋ฉด ์–ด๋””๋กœ ๊ฐ€์•ผํ•˜๋Š”์ง€ ๊ฒฝ๋กœ๋ฅผ ์ง€์ •ํ•  ์ˆ˜ ์žˆ๋‹ค

  • 3๊ณ„์ธต์—์„œ ๋™์ž‘ํ•˜๋Š” ์žฅ๋น„๋Š” Router๋‹ค

    • Router๋Š” 3๊ณ„์ธต์—์„œ ์ •์˜ํ•œ IP ์ฃผ์†Œ๋ฅผ ์ดํ•ดํ•  ์ˆ˜ ์žˆ๋‹ค

    • Router๋Š” IP ์ฃผ์†Œ๋ฅผ ์‚ฌ์šฉํ•ด ์ตœ์ ์˜ ๊ฒฝ๋กœ๋ฅผ ์ฐพ์•„์ฃผ๊ณ , ํ•ด๋‹น ๊ฒฝ๋กœ๋กœ packet์„ ์ „์†กํ•˜๋Š” ์—ญํ• ์„ ํ•œ๋‹ค

4. Transport Layer (Layer 4)

  • Transport layer provides services to application layer and takes services from network layer.

  • The data in the transport layer is referred to as Segments.

    • It is responsible for the End to End Delivery of the complete message.

  • The transport layer also provides the acknowledgement of the successful data transmission and re-transmits the data if an error is found.

  • Transport layer is operated by the Operating System.

    • It is a part of the OS and communicates with the Application Layer (Layer 7) by making system calls.

  • Transport Layer is called as Heart of OSI model.

  • 4๊ณ„์ธต์€ 1~3๊ณ„์ธต๊ณผ๋Š” ๋‹ค๋ฅธ ์—ญํ• ์„ ํ•œ๋‹ค

    • ํ•˜์œ„ ๊ณ„์ธต (Layer 1~4)์€ data๋ฅผ ์ชผ๊ฐœ ์ •๋ณด๋ฅผ ๋ถ™์—ฌ ๋ชฉ์ ์ง€๊นŒ์ง€ ์ž˜ ์ „๋‹ฌํ•˜๋Š” ์—ญํ• ์„ ํ•˜๋Š”๋ฐ,

      • 1~3๊ณ„์ธต์€ ์‹ ํ˜ธ์™€ data๋ฅผ ์˜ฌ๋ฐ”๋ฅธ ์œ„์น˜๋กœ ๋ณด๋‚ด๊ณ , ์‹ค์ œ ์‹ ํ˜ธ๋ฅผ ์ž˜ ๋งŒ๋“ค์–ด ๋ณด๋‚ด๋Š”๋ฐ ์ง‘์ค‘ํ•œ๋‹ค

      • ๋ฐ˜๋ฉด 4๊ณ„์ธต์€ ์‹ค์ œ๋กœ ํ•ด๋‹น data๋“ค์ด ์ •์ƒ์ ์œผ๋กœ ์ž˜ ๋ณด๋‚ด์ง€๋„๋ก ํ™•์ธํ•˜๋Š” ์—ญํ• ์„ ํ•œ๋‹ค

  • Packet network ๋Š” data๋ฅผ ๋ถ„ํ• ํ•ด packet์— ์‹ค์–ด๋ณด๋‚ด๋‹ค ๋ณด๋‹ˆ ์ค‘๊ฐ„์— packet์ด ์œ ์‹ค๋˜๊ฑฐ๋‚˜ ์ˆœ์„œ๊ฐ€ ๋’ค๋ฐ”๋€Œ๋Š” ๊ฒฝ์šฐ๊ฐ€ ์ƒ๊ธธ ์ˆ˜ ์žˆ๋‹ค

  • ์ด๋Ÿด ๋•Œ ๋ฐ”๋กœ ์žก์•„์ฃผ๋Š” ์—ญํ• ์„ 4๊ณ„์ธต์—์„œ ๋‹ด๋‹นํ•œ๋‹ค

    • 4๊ณ„์ธต์—์„œ packet์„ ๋ถ„ํ• ํ•  ๋•Œ packet header์— ๋ณด๋‚ด๋Š” ์ˆœ์„œ์™€ ๋ฐ›๋Š” ์ˆœ์„œ๋ฅผ ์ ์–ด ํ†ต์‹ ํ•˜๋ฏ€๋กœ

      • packet์ด ์œ ์‹ค๋˜๋ฉด ์žฌ์ „์†ก์„ ์š”์ฒญํ•  ์ˆ˜ ์žˆ๊ณ ,

      • ์ˆœ์„œ๊ฐ€ ๋’ค๋ฐ”๋€Œ๋”๋ผ๋„ ๋ฐ”๋กœ ์žก์„ ์ˆ˜ ์žˆ๋‹ค

    • Packet์— ๋ณด๋‚ด๋Š” ์ˆœ์„œ๋ฅผ ๋ช…์‹œํ•œ ๊ฒƒ์ด ์‹œํ€€์Šค ๋ฒˆํ˜ธ(Sequence Number)์ด๊ณ ,

    • Packet์— ๋ฐ›๋Š” ์ˆœ์„œ๋ฅผ ๋ช…์‹œํ•œ ๊ฒƒ์ด ACK ๋ฒˆํ˜ธ(Acknowledgement Number)์ด๋‹ค

    • ์žฅ์น˜ ๋‚ด์˜ ๋งŽ์€ application์„ ๊ตฌ๋ถ„ํ•  ์ˆ˜ ์žˆ๋„๋ก ํฌํŠธ ๋ฒˆํ˜ธ(Port Number)๋ฅผ ์‚ฌ์šฉํ•ด ์ƒ์œ„ application์„ ๊ตฌ๋ถ„ํ•œ๋‹ค

  • 4๊ณ„์ธต์—์„œ ๋™์žฅํ•˜๋Š” ์žฅ๋น„๋Š” Load Balancer์™€ ๋ฐฉํ™”๋ฒฝ์ด๋‹ค

    • ์ด ์žฅ๋น„๋“ค์€ 4๊ณ„์ธต์—์„œ ๋ณผ ์ˆ˜ ์žˆ๋Š” application ๊ตฌ๋ถ„์ž (Port Number)์™€ Sequence, ASK number ์ •๋ณด๋ฅผ ์ด์šฉํ•ด์„œ

      • ๋ถ€ํ•˜๋ฅผ ๋ถ„์‚ฐํ•˜๊ฑฐ๋‚˜ ๋ณด์•ˆ ์ •์ฑ…์„ ์ˆ˜๋ฆฝํ•ด packet์„ ํ†ต๊ณผ, ์ฐจ๋‹จํ•˜๋Š” ๊ธฐ๋Šฅ์„ ์ˆ˜ํ–‰ํ•œ๋‹ค

5. Session Layer (Layer 5)

  • The Session layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security.

  • The functions of the session layer are :

    1. Session establishment, maintenance and termination

      • The layer allows the two processes to establish, use and terminate a connection.

    2. Synchronization

      • This layer allows a process to add checkpoints which are considered as synchronization points into the data.

      • These synchronization point help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided.

    3. Dialog Controller

      • The session layer allows two systems to start communication with each other in half-duplex or full-duplex.

  • 5๊ณ„์ธต์ธ **์„ธ์…˜ ๊ณ„์ธต(Session Layer)**์€ ์–‘ ๋๋‹จ์˜ ์‘์šฉ ํ”„๋กœ์„ธ์Šค๊ฐ€

    • ์—ฐ๊ฒฐ์„ ์„ฑ๋ฆฝํ•˜๋„๋ก ๋„์™€์ฃผ๊ณ ,

    • ์—ฐ๊ฒฐ์ด ์•ˆ์ •์ ์œผ๋กœ ์œ ์ง€๋˜๋„๋ก ๊ด€๋ฆฌํ•˜๊ณ ,

    • ์ž‘์—… ์™„๋ฃŒ ํ›„์—๋Š” ์—ฐ๊ฒฐ์„ ๋Š๋Š” ์—ญํ• ์„ ํ•œ๋‹ค

  • Session์„ ๊ด€๋ฆฌํ•˜๋Š” ๊ฒƒ์ด ์ฃผ ์—ญํ• ์ธ session layer๋Š” TCP/IP session์„ ๋งŒ๋“ค๊ณ  ์—†์• ๋Š” ์—ญํ• ์„ ํ•œ๋‹ค

  • Error๋กœ ์ค‘๋‹จ๋œ ํ†ต์‹ ์— ๋Œ€ํ•œ ๋ณต๊ตฌ์™€ ์žฌ์ „์†ก๋„ ์ˆ˜ํ–‰ํ•œ๋‹ค

6. Presentation Layer (Layer 6)

  • Presentation layer is also called the Translation layer.

  • The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.

  • The functions of the presentation layer are :

    1. Translation

      • For example, ASCII to EBCDIC.

    2. Encryption/ Decryption

      • Data encryption translates the data into another form or code.

    3. Compression

      • Reduces the number of bits that need to be transmitted on the network.

  • 6๊ณ„์ธต์ธ presentation layer๋Š” ํ‘œํ˜„ ๋ฐฉ์‹์ด ๋‹ค๋ฅธ application์ด๋‚˜ system ๊ฐ„์˜ ํ†ต์‹ ์„ ๋•๊ธฐ ์œ„ํ•ด ํ•˜๋‚˜์˜ ํ†ต์ผ๋œ ๊ตฌ๋ฌธ ํ˜•์‹์œผ๋กœ ๋ณ€ํ™˜์‹œํ‚ค๋Š” ๊ธฐ๋Šฅ์„ ์ˆ˜ํ–‰ํ•œ๋‹ค

    • ์ผ์ข…์˜ ๋ฒˆ์—ญ๊ธฐ๋‚˜ ๋ณ€ํ™˜๊ธฐ ์—ญํ• ์„ ์ˆ˜ํ–‰ํ•˜๋Š” ๊ณ„์ธต์ด๊ณ ,

    • ์ด๋Ÿฌํ•œ ๊ธฐ๋Šฅ์€ ์‚ฌ์šฉ์ž system์˜ ์‘์šฉ ๊ณ„์ธต์—์„œ data์˜ ํ˜•์‹์ƒ์˜ ์ฐจ์ด๋ฅผ ๋‹ค๋ฃจ๋Š” ๋ถ€๋‹ด์„ ๋œ์–ด์ค€๋‹ค

    • MIME encoding์ด๋‚˜ ์•”ํ˜ธํ™”, ์••์ถ•, ์ฝ”๋“œ ๋ณ€ํ™˜๊ณผ ๊ฐ™์€ ๋™์ž‘์ด ์ด ๊ณ„์ธต์—์„œ ์ด๋ฃจ์–ด์ง„๋‹ค

7. Application Layer (Layer 7)

  • At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications.

  • These applications produce the data, which has to be transferred over the network.

  • This layer also serves as a window for the application services to access the network and for displaying the received information to the user.

    • Ex: Application โ€“ Browsers, Skype Messenger etc.

  • Application Layer is also called as Desktop Layer.

  • OSI 7 Layers์˜ ์ตœ์ƒ์œ„ 7๊ณ„์ธต์ธ application layer๋Š” application process๋ฅผ ์ •์˜ํ•˜๊ณ  application service๋ฅผ ์ˆ˜ํ–‰ํ•œ๋‹ค

    • Network software์˜ UI ๋ถ€๋ถ„์ด๋‚˜ ์‚ฌ์šฉ์ž I/O ๋ถ€๋ถ„์„ ์ •์˜ํ•˜๋Š” ๊ฒƒ์ด application layer์˜ ์—ญํ• ์ด๋‹ค

    • application layer์˜ protocol์€ ์—„์ฒญ๋‚˜๊ฒŒ ๋งŽ์€ ์ข…๋ฅ˜๊ฐ€ ์žˆ์ง€๋งŒ ๋Œ€ํ‘œ์ ์ธ Protocol๋กœ๋Š” FTP, SMTP, HTTP TELNET์ด ์žˆ๋‹ค

Summary

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๊ณ„์ธต๋ณ„ ์ฃผ์š” ํ”„๋กœํ† ์ฝœ ๋ฐ ์žฅ๋น„

Layer
Protocol
์žฅ๋น„

Application Layer

HTTP, SMP, SMTP, STUN, TFTP, TELNET

ADC, NGFW, WAF

Presentation Layer

TLS, AFP, SSH

Session Layer

L2TP, PPTP, NFS, RPC, RTCP, SIP, SSH

Transport Layer

TCP, UDP, SCTP, DCCP, AH, AEP

LB, Firewall

Network Layer

ARP, IPv4, IPv6, NAT, IPSec, VRRP, Routing protocol

Router, L3 Switch

Datalink Layer

IEEE 802.2, FDDI

Switch, Bridge, NIC

Physical Layer

RS-232, RS-449, V.35, S ๋“ฑ์˜ cable

Cable, Hub, TAP

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