 which saves on signaling and switching hardware. The process of switching a waveband can be viewed as an LSP tunnel that switches each of the payload wave- All-Optical Networks length LSPs in the same way. Additionally, waveband switching may help to reduce the optical distortion that may be introduced by separating out and switching the individual lambdas. Time Division Multiplexing (TDM) A fiber's bandwidth can also be divided by time slots. In this model, the optical signal is seen as a sequence of data frames, with N frames each of size S traveling every second (mak- ing up the total fiber bandwidth NXS), and bandwidth is allocated for a particular data flow by reserving a portion of each frame. The basic frame sizes and the hierarchies by which a single frame can be divided into time slots are the subject of several standards, notably SONET and SDH. Switching Quantities, Bandwidth, and Quality of Service (QoS) Switching quantities in optical networks are inextricably linked with band- width and QoS. Bandwidth is determined exactly by the type and size of the switching unit reserved (one fiber, one wavelength, one OC-48, and so on). QoS boils down to this bandwidth together with complete reliabil- ity and very low burstiness/jitter. In Chapter 8, we discuss how optical- switching quantities are interpreted and represented as GMPLS labels and how limitations on the types of switching that an optical switch is physi- cally able to perform translate into constraints on the selection of GMPLS label values. Out-of-Band Signaling Because all the data traffic passing through an optical switch can be switched without reference to individual data pack- ets, there is no need for the data plane part of the optical switch to have any understanding of the protocol stacks (IP, Transmission Control Proto- col [TCP], User Datagram Protocol [UDP], and so on) that are needed for the handling of control messages. In particular, it may not be necessary for optical switches to electronically terminate individual links. Between a