en sends the message back to the originator for compar- ison with the original transmission. Loopback testing may be performed within a locally attached device or conducted remotely over a communications circuit. loss A decrease in signal power in transmission along the circuit as a result of the resistance of impedance of the circuit or equipment. lossless compression In data compression, the process by which information is recovered without any alteration after the decompression stage. This technique is used for computer-based data or programs. It may also be required in certain multimedia applications where the accuracy of the information is essential, such as in medical imaging. Lossless compression is also called bit-preserving or reversible compression. Examples of lossless compression include run-length encoding and Huffman encoding. lossy compression In data compression, a situation in which the decompressed information is different from the original uncompressed information. This mode is suitable for most continu- ous media, such as sound and motion video, as well as for many images. That the decompressed information is different from the original in lossy compression does not imply that the perceptual response of an observer is different. Also called irreversible compression. low frequency Generally, frequencies between 30KHz and 300KHz. Glossary low-level language low-level language A programming language in which instructions have a one-to-one rela- tionship with machine code. LPC (linear predictive coding) A vector-quantization-based compression scheme for speech. LPC can compress speech down to 2.4Kbps. LSP (label-switched path) A path through an MPLS network that is set up by a signaling protocol based on criteria in the forwarding equivalence class (FEC). LSR (label-switching router) An MPLS-enabled router and/or MPLS-enabled ATM switch. As each packet enters the network, an ingress LSR assigns it a label, based on its destination, VPN membership, ToS bits, and other considerations. At each hop, a