PDF of this tutorialWave Division Multiplexing (WDM)
WDM is an emerging technology that supports the multiplexing of multiple ATM/SONET streams onto a single fiber-optic cable. WDM hardware will be colocated with ATM switches and will be used to create long-haul point-to-point fiber-optic connections between these switches. In some cases, it will be used to create a mesh structure with the redundancy of a SONET ring but with much greater capacity (for example, 32 x OC–48 instead of the more typical x OC–48 SONET ring). The immediate benefit to service providers will be to significantly increase the bandwidth available for a point-to-point ATM connection and thus offset the 15 percent cell tax that is often associated with ATM transport. The long term benefit will be to ensure that the future capacity of IP networks will be sufficient to accommodate the current 100+ percent year-over-year growth.
Figure 5. Using WDM to Consolidate Bandwidth Demand
Multiprotocol Label Switching (MPLS)
When completed, MPLS will provide additional functionality in IP over SONET/SDH implementations by appending labels onto each IP packet. These labels are associated with paths through the network and may be used (in an as yet undefined manner) to specify traffic-handling characteristics in order to guarantee a QoS or CoS. The goal of MPLS is to take advantage of the higher bandwidth offered by IP over SONET/SDH, without the additional overhead of ATM.
Version 1 of MPLS, due out some time in 1999, provides public Internet functions and enables routing equipment to set up a path through the network for a particular packet stream. The primary advantage of this implementation will be to allow operators to increase the efficiency of their router networks, because a label is easier to switch than an IP packet is to route. Version 2, which has an undefined ratification date, may offer some VPN and QoS guarantees, but there is no clear definition of this part of the standard at this point in time.
Figure 6. IP over ATM and IP over SONET/SDH: A Comparative View
