48 lines
2.6 KiB
Markdown
48 lines
2.6 KiB
Markdown
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---
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tags: [networks, internet]
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created: Friday, September 06, 2024
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---
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# Example scenario of data transfer accross the internet
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- A client device is connected to a wireless WiFi network.
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- This network is connected to the internet via a router.
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- Elsewhere on the internet is a server also connected to the internet via
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router.
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- A user of the client device opens a web browser and requests a web page hosted
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on the server (we will assume it already knows the IP address)
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- The web browser knows HTTP - a protocol of the
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[Application Layer](Application_Layer_of_Internet_Protocol.md) - and forms an
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HTTP request intended for the destination server.
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- The browser hands off the HTTP request to the TCP/IP software stack of the
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device's [operating system](Basic_model_of_the_operating_system.md), asking
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that the data be delivered to the server on its IP address and at port 80.
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- The TCP/IP software stack on the client OS encapsulates the HTTP payload in a
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TCP segment (at the
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[Transport Layer](Transport_Layer_of_Internet_Protocol.md)), setting the
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destination port to 80 in the segment header.
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- The [Internet Layer](Internet_Layer_of_Internet_Protocol.md) software on the
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client then wraps the TCP segment in an IP packet, which includes the
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destination IP address of the server in the packet header.
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- At the [Link Layer](Link_Layer_of_Internet_Protocol.md) of the client device,
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the IP packet is encapsulated in a frame with the
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[MAC_address](MAC_addresses.md) of the local router in its header. The frame
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is wirelessly transmitted by the client device's WiFi hardware.
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- The wireless access point receives the frame and passes to the router. The
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router examines the internet layer packet to determine the destination IP
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address.
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- To reach the server, the request needs to travel through multiple routers on
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the internet and the process is replicated (looking up MAC address of the
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device and determining IP target). Eventually, the request reaches the router
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on the network where the server is connected.
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- The last router puts the packet in a frame suitable for the server's local
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network and in the frame's header is the MAC address of the server.
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- The server receives the frame and the packet is passed to the TCP/IP software
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stack. This passes the HTTP data to the process listening on TCP port 80.
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- Web server software, listening on port 80 handles the request and replies to
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the client, start ing the process again in reverse order.
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