5.4 KiB
5.4 KiB
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| 03. How the TCPIP Model Actually Works |
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How the TCPIP Model Actually Works
Protocols and Standards
A Protocol is a set of rules defining how data should be communicated between devices over a network.
- The "Languages" that computers use to communicate. Since the early days of computer networking, there have been several attempts to define the functions needed for computers to communicate with each other
- Often developed by a specific vendor (e.g, IBM) to be used with their own products.
- With a proprietary approach, enabling communications between different vendor's products was difficult. A standard is an agreed-upon specification that describes how a protocol or technology should work
- With vendor neutral standards, devices of all types can communicate with each others.
- An Apple Macbook can access a website hosted on a web server running Linux.
- A PC running WIndows can send an email that can be read on a smartphone running Android
A bit of history
Early work on the computer netowrks that would evolve into today's Internet began in the 1960s
- The US Department of Defense's ARPA funded ARPANET, which came online in 1969 to connect mainframes at universities and labs
- Originally used a protocol called NCP Vint Cerf and Bob Kahn (working on DARPA) began developing TCP in 1974
- Later divided into two protocols still used today:
- TCP
- IP THese two protocols form the fundation of the protocol suite known as TCP/IP today
- ARPANET fully switched to TCP/IP in January 1, 1983. TCP/IP became dominant over vendor-proprietary solutions at the time because it was published as a set of open standards that any vendor could implement, and it could run over many different types of networks.
Who defines the standards?
Most netwoking standards are developed by independent standards organizations, not by a single vendor, with participation from engineers at many companies
Layered models
Networks do a lot of different jobs to move data from one computer to another.
- Physical transmission of signals, local delivery on a LAN, routing traffic between networks, end-to-end conversations, applications, etc. A model lets us group related jobs into layers.
- Each layer has a specific role.
- Each layer uses the services of the layer below and provides services to the layer above Protocol live (mostly at one layer)
- Examples later: IP, TCP, HTTP, etc.
- Together they form a stack of protocols that work as a team (the network stack)
- Application Layer : telnet, FTP, TFTP
- Transport Layer: TCP, UDP
- Internet Layer: IP, ICPM
- Link Layer: cables, WIFI
The model is description, not a law.
- Different textbooks/courses use slightly different models (4-layer, 5 layer...)
TCP/IP Layers
Layer 1 : the physical layer
- The physical Layer (Layer 1) sends and receives bits as electrical, optical, or radio signals over the medium
- Defines things like cables, connectors, signal levels, and link speeds.
- Examples: copper UTP cables, fiber-optic cables, WI-FI radios and antennas, network interface cards NIC's
- The physical aspects of transmitting data are very complex
Layer 2 : Local Network Layer
- The Local Network Layer provides hop to hop delivery of messages on a local network.
- A hop is one step along the path between two devices:
- From one router or host, to the next router or host in the path
- Switches don't countL a switch just extends the local network, allowing multiple devices to connect.
- A hop is one step along the path between two devices:
- Uses MAC addresses to identify interfaces.
- Protocols at this layer includes
- Eternet
- Wifi
Layer 3 : The Internet Layer
- The Internet Layer provides end-to-end delivery between hosts across multiple networks
- Uses IP addresses to identify hosts in the network.
- Routers operate mainly at this layer, using the message's destination IP address to forward the message toward its final destination host
- Protocols at this layer includes
Layer 4 : The Transport Layer
- The Transport Layer provides end-to-end communication between application processes.
- Also called "process to process" or "service-to-service"
- Uses port numbers to identify the processes on each host.
- Runs mainly on the communicating hosts; routers normally operate based on IP, not on Transport layer informations
- Protocols at this layer includes
- UDP
- TCP
Layer 5 : Application Layer
- The application Layer is where network communications meet applications.
- Usually called Layer 7
- Defines how application processes format, send, and interpret data
- Protocols at this layer define message formats and rules for specific tasks, such as:
- Network infrastructure devices (routers, switches) don't care about Application-layer details.
- They just move messages across the network.
- Only the communicating hosts interpret the data