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Network terminology

networks collision domain linjekodning cidr

Some of the terms used in networking.

Ludde127 2023-01-03
L

Collision domain

A network segment connected by a shared medium where simultaneous data transmissions collide with each other. Collisions often occur in wireless networks. Collisions occur when more than one node sends data over the same medium at the same time. Members of a collision domain may have collisions with each other.


Collision domain are also fond in environments with Ethernet hubs or repeaters where each host segment connects to a hub.

Classless Inter-Domain Routing (CIDR)

CIDR is used to handle IP-addresses, CIDR improves efficiency when splitting IP-address blocks into smaller chunks. In CIDR the length of subnet masks are variable. This way of splitting addresses is also called classless routing as the old network classes are ignored.

Subnet mask

A subnet mask shows where an IP addresses network address stops and the host addresses start.

Linjekodning

Linjekodning används för att överföra bitar över ett medium och betyder att potentiallen förändras för att indikera vilken som nästa bit är, exempel är NRZ(Non return to zero) och Manchester kodning.

PCM - Pulse code modulation

PCM is used to convert analog signals to digital, this is done trough three steps:

  1. Sampling where the analog and continuous stream is cut into chunks which will be treated as individual bits in the digital format.
  2. Quantization where it is decided if the bit should be a one or zero.
  3. Coding, this is where the data is lastly packed with some other inf

Spread spectrum [OSI 1]

Spread spectrum is used by different technologies such as Bluetooth and IEEE 802.11 (WLAN, Wireless Ethernet). With spread spectrum the spectrum used by the technologies is large and a smaller (still rather large) chunk is then chosen depending on current noice-levels and potential interference.

Ethernet access method

Ethernet uses CSMA/CD (Carrier Sense Multiple Access Collision Detection) which works by the sender listening to the link before sending, if no data is being transmitted the unit starts sending their data while still listening. Collisions are detected by checking the amplitude of the waves. If a collision is found a jamming signal is sent. If a collision happens the sender waits until the line has been quiet for some unit of time and then again retries the procedure.

RTS/CTS (Request to send/Clear to send)

RTS/CTS is a control flow mechanism used in IEEE 802.11 to reduce frame collisions created by the hidden node problem.

The hidden node (terminal) problem is when a node can communicate with an wireless access point (AP) while being unable to directly communicate with any other nodes also connected tho said AP. This leads to issues in the medium access control sublayer as different nodes could send data simultaneously creating interference and packet loss.

RTS/CTS partially solves this by having nodes send a short request package (and getting a clear to send message) before sending their data. As all nodes can see responses by the AP they can synchronize to not interfere.

An issue with RTS/CTS is that it introduces latency for each package. For small packages this can be very noticeable.

CSMA/CA

--Carrier-sense multiple access with collision avoidance--

CSMA/CA [OSI 2 - Link layer] is used in computer networks to give nodes access to send. It works by having nodes listen to their channel, when the channel seams to be idle they wait a certain time, then listens again, if still idle; they entirely transmit their packet data.

WIFI - IEEE 802.11

Wifi uses a combination of RTS/CTS and CSMA/CA to give access to devices. RTS/CTS is used to solve the hidden node problem and CSMA/CA to make the network easier to configure and to improve the network if nodes are not sending the same amount of data. If another node was heard when listening the node waits a random amount of time before again listening.

NAT - Network Address Translation

NAT is used to translate IP address to other IP addresses, a number of private IP addresses can be setup to point to another (often smaller) number of public addresses.

A common use of NAT is in most home networks which have all devices operating behind a common public IP. This is used to limit the amount of IP addresses in use.

NAT also works as a firewall as only lets trough packages which answers requests made from within the network.