In the previous post on optical networking in service provider environments, we discussed the fascinating history of the optical transport. In this post, as promised, we are going to look at the three common methods of permitting multiple users to access this high-speed, reliable communication technology. These three methods are:
- Wavelength Division Multiple Access
- Time Division Multiple Access
- Code Division Multiple Access
Wavelength Division Multiple Access (WDMA)
The idea behind Wavelength Division Multiple Access is a simple and straightforward one. To create multiple channels for various data flows, just vary the modulation and speed slightly in order to create a channel that is separate from the others. This is exactly how it works. Simple. Each channel gets to occupy a narrow optical bandwidth slice of the central wavelength or frequency used.
As you would guess, a lot of technology needed to be created to pull this off. The lasers need to be arrayed or at least tunable in order to transmit multiple different modulations and speeds for channels.
As the engineers looked to increase the overall bandwidth with WDMA approaches, the idea for Dense Wavelength Division Multiple Access (DWDM) came to be. The idea here is also simple. Reduce the space required between channels so that we can squeeze even more bandwidth out of the media! The ITU-T recommended G.692 which defined 43 wavelength channels from 1530 to 1565 nm with a spacing of 100 GHz between each of the channels.
Time Division Multiple Access (TDMA)
As you might guess, the approach with TDMA is to create the channels needed for multiple access using pre-assigned time-slots. These time slots are interleaved against each other for “fairness”.
In case you were wondering, TDMA is the approach used for the hugely popular SDH/SONET optical networking technology.
Code Division Multiple Access (CDMA)
CDMA is one of the approaches that falls into the spread spectrum group of technologies. This is quite different from the other two approaches. With CDMA, users of the media are assigned a code. Thanks to each user having their unique code, the users send data over the same channel.
We hope you enjoyed this post on multiple access to optical networking as covered in our customer-loved Cisco SPCOR training at Lammle.com!