Technology Options

n SDH: Optical fiber has vast capacity and it needs to be accessed by a protocol that can support high data rates of up to 10 Gbps per wavelength or 40 Gbps in future. The protocol also provides reliability and an extensive range of network monitoring and management functions. The protocol used in modern networks to satisfy the above features is called Synchronous Digital Hierarchy (SDH). SDH is placed at the bottom of the protocol stack in the physical layer, along with the very fiber upon which it transmits its signal. The fundamental principle of the SDH protocol is time-division multiplexing (TDM). TDM ensures that there is a constant stream of data travelling through the network and taking advantage of the fiber bandwidth available. Lower bit-rate streams of information are combined, or multiplexed, up into higher bit-rate streams at the native bit rate of the SDH system. The fundamental SDH frame is known as STM1 (synchronous transport module). Each provides a bit rate of 155 Mbps with a total frame size of around 20 kbps.

n DWDM: Called dense wavelength division multiplexing, technology increases bandwidth over existing fiber optic cable by multiplexing (communicating two or more signals over a common channel) several optical signals on to one fibre, turning it into a virtual multiple fibre and thereby increasing its load-carrying capacity by many times over. SDH and DWDM are complimentary in nature with DWDM at the backbone and SDH at the
access.

n CWDM: Coarse Wavelength Division Multiplexing is an older WDM technology and is now emerging as a low-cost alternative to DWDM especially in metro network access and enterprise applications. It is a simple device enabling quick rollout of network services without compromising on the performance of the network. It provides all kinds of services like TDM services, data services, data center services, and cable video services. CWDM is 50 percent cheaper than DWDM.

n ASON (ION): Called Automatically Switched Optical Network or Intelligent Optical Network, the technology provides the best features of all the technologies presently available. It provides the best network architecture and one also has the provision to deploy the services quickly.