Computer Networking: Difference between revisions
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Computer networking theory | |||
==Reference Models== | |||
===OSI Model=== | |||
{{main | Wikipedia: OSI model}} | |||
The OSI model presents the network stack using multiple layers. | |||
As a set of abstractions, each layer has their own standards which let it interoperate with layers above and below. | |||
The layers are: | |||
<ol reversed> | |||
<li>Application layer</li> | |||
<li>Presentation layer</li> | |||
<li>Session layer</li> | |||
<li>Transport layer</li> | |||
<li>Physical layer</li> | |||
<li>Network layer</li> | |||
<li>Data link layer</li> | |||
<li>Physical layer</li> | |||
</ol> | |||
The physical layer is comprised of the literal copper, fiber, and wireless frequencies used to transport bits, 0s and 1s.<br> | |||
The data link layer focuses on transmitting data frames between directly connected nodes. Medium access control (MAC) and logical link control (LLC) work at this layer.<br> | |||
The network layer allows packets to flow between nodes which are not directly connected. Routing with IPs between networks happens at this layer.<br> | |||
The transport layer focuses on levels of reliability. TCP and UDP are used at this layer.<br> | |||
The session layer focuses on connections.<br> | |||
The presentation layer focuses on standardizing protocols and data representations (e.g. XML).<bR> | |||
Finally, the application layer is what highest-level, whatever service is being provided to the user. | |||
===TCP/IP=== | |||
{{main | Wikipedia: Internet protocol suite}} | |||
TCP/IP has four layers: | |||
<ol reversed> | |||
<li>Application layer</li> | |||
<li>Transport layer</li> | |||
<li>Internet layer</li> | |||
<li>Link layer</li> | |||
</ol> | |||
==Link Layer== | |||
===Hardware=== | |||
* Hub - A hub connects multiple devices and will pass around data frames to every single connection. It has no logic and is equivalent to wiring all the cables together. | |||
* Repeater - A repeater is used to boost signals. It will read the pattern (e.g. voltage representing bits) and repeat it on another wire. | |||
* Bridge or Switch - A switch connects multiple devices and does routing at this layer using mac addresses. | |||
* Router - Routers work at the network layer to route packets across different networks (e.g. across VLANS or LAN to WAN). | |||
==Network Layer== | |||
===Routing=== | |||
====Distance Vector==== | |||
In Distance Vector routing, or Bell-ford Algorithm, each node incrementally builds up it's own routing table to identify the next hop to reach each destination. | |||
===Internet=== | |||
====BGP==== | |||
==Physical Layer== | |||
There are several protocols at the physical layer such as ethernet, LTE, and DOCSIS. | |||
===Multiplexing=== | |||
Multiplexing is used to send or receive multiple signals along the same wire. Note that, sending and receiving count as two separate signals. | |||
Duplex means that the upstream and downstream are the the same speed. Full duplex (FDX) means the up and down can operate at the same time. | |||
* Time-division Multiplexing/Duplex (TDD) - if you don't have enough frequencies, you spend some time sending and some time receiving the signal. This is inherently not full duplex. | |||
* Frequency-division Multiplexing/Duplex (FDD) - with multiple frequencies, you can send and receive at the same time on separate frequencies. If the frequencies are evenly divided, you will have full duplex. | |||
* Echo Cancellation - by sending and receiving on the same frequencies at the same time, you can get full duplex. This is more complicated than the other options. | |||
===Terminology=== | |||
* US/DS - Upstream and downstream | |||
* OOB - out of band, additional signals on a separate frequency or wire | |||