Editing Line code (section)

== Transmission and storage ==
After line coding, the signal is put through a physical communication channel, either a [[transmission medium]] or [[data storage medium]].<ref name="paulsen">Karl Paulsen. [http://www.tvtechnology.com/media-servers/0150/coding-for-magnetic-storage-mediums/186738 "Coding for Magnetic Storage Mediums"] {{Webarchive|url=https://web.archive.org/web/20140521215946/http://www.tvtechnology.com/media-servers/0150/coding-for-magnetic-storage-mediums/186738 |date=2014-05-21 }}.2007.</ref><ref>{{citation|author1=Abdullatif Glass |author2=Nidhal Abdulaziz |author3=and Eesa Bastaki |url=http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1285&context=dubaipapers|title=Slope line coding for telecommunication networks|year=2007|page=1537|journal=IEEE International Conference on Signal Processing and Communication|publisher=IEEE|location=Dubai|quote=Line codes ... facilitates the transmission of data over telecommunication and computer networks and its storage in multimedia systems.}}</ref> The most common physical channels are:
* the line-coded signal can directly be put on a [[transmission line]], in the form of variations of the voltage or current (often using [[differential signaling]]).
* the line-coded signal (the ''[[baseband]] signal'') undergoes further [[pulse shaping]] (to reduce its frequency bandwidth) and then is [[modulation|modulated]] (to shift its frequency) to create an ''[[RF signal]]'' that can be sent through free space.
* the line-coded signal can be used to turn on and off a light source in [[free-space optical communication]], most commonly used in an infrared [[remote control]].
* the line-coded signal can be printed on paper to create a [[bar code]].
* the line-coded signal can be converted to magnetized spots on a [[hard drive]] or [[tape drive]].
* the line-coded signal can be converted to pits on an [[optical disc]].

Some of the more common binary line codes include:
{| class="wikitable"
|-
! Signal !! Comments !! 1 state !! 0 state
|-
| NRZ–L || [[Non-return-to-zero]] level. This is the standard positive logic signal format used in digital circuits.
| forces a high level
| forces a low level
|-
| NRZ–M || Non-return-to-zero mark
| forces a transition
| does nothing (keeps sending the previous level)
|-
| NRZ–S  || Non-return-to-zero space
| does nothing (keeps sending the previous level)
| forces a transition
|-
| RZ  || Return to zero
| goes high for half the bit period and returns to low
| stays low for the entire period
|-
| Biphase–L  || Manchester. Two consecutive bits of the same type force a transition at the beginning of a bit period.
| forces a negative transition in the middle of the bit
| forces a positive transition in the middle of the bit
|-
| Biphase–M || Variant of Differential Manchester. There is always a transition halfway between the conditioned transitions.
| forces a transition
| keeps level constant
|-
| Biphase–S  || Differential Manchester used in Token Ring. There is always a transition halfway between the conditioned transitions.
| keeps level constant
| forces a transition
|-
| Differential Manchester (Alternative)|| Need a Clock, always a transition in the middle of the clock period
| is represented by no transition.
| is represented by a transition at the beginning of the clock period.
|-
| Bipolar || The positive and negative pulses alternate.
| forces a positive or negative pulse for half the bit period
| keeps a zero level during bit period
|}

[[File:Digital signal encoding formats-en.svg|class=skin-invert-image|framed|center|An arbitrary bit pattern in various binary line code formats]]

Each line code has advantages and disadvantages. Line codes are chosen to meet one or more of the following criteria:
* Minimize transmission hardware
* Facilitate synchronization
* Ease error detection and correction
* Achieve a target [[spectral density]]
* Eliminate a [[DC component]]