NATO Narrowband Waveform (NBWF) - multilevel-level precedence and preemption for IP traffic

Abstract

NATO has an ongoing activity with the objective to develop a narrowband waveform (NBWF) standard. This is a single-channel mobile ad-hoc network (MANET) which shall serve voice traffic and data traffic over a 25 kHz radio channel. A Multi-Level Precedence and Preemption (MLPP) service is regarded as a mandatory service in military MANETs that operate in the tactical domain. MLPP is a network service supporting priority labelling of the IP packets according to their importance as determined by the IP clients. During network congestion, the NBWF core protocols shall first serve the packets with the highest priority. IP Quality of Service (QoS) classes and MLPP are two different subjects. The former specifies a method to differentiate between application types which demand different communication channel characteristics (e.g., low jitter, short delay). This in contrast to the MLPP priority level that shall reflect the importance of the information content. A narrow band network has low throughput capacity, and to experience network congestion during usage must be regarded as an ordinary event. Therefore it is important to have a robust MLPP service which increases the passability of the highest priority traffic during periods of network congestion. Many tactical communications scenarios may take benefit of the MLPP service: 1) Unforeseen external events imply need for more network capacity than predicted; or 2) The radio environment became more difficult than expected (e.g., higher pathloss, network jamming or network interference from friendly forces); or 3) Higher user mobility than planned introduces more routing traffic and more radio hops. The MLPP service is based on a cross layer design where each layer implements priority handling. Each node has a priority aware buffer system for storing the input traffic from the IP clients. A node internal flow control function between the adjacent layers provides for service of the highest priority traffic. This document addresses also adaptive MAC scheduling. The purpose of adaptive MAC scheduling is to maintain an optimum throughput/delay-performance under changing traffic load in a fully meshed network. NBWF uses a radio with a large coverage area and a typical network has good connectivity. The benefit of adaptive MAC scheduling increases as the network size (number of nodes) increases. The adaptive MAC scheduling works in consort with the MLPP but is not a prerequisite for the MLPP service. The MLPP service shall be a mandatory service for NBWF, while the adaptive MAC scheduling may be specified as optional since this function has less importance for the network users than the MLPP service. However, some of the simulation experiments indicate increased network performance when the adaptive MAC scheduling is implemented in addition to MLPP.

Nato har en pågående aktivitet for standardisering av en smalbånds bølgeform (NBWF) for bruk i VHF området. FFI har en modellerings- og simuleringsaktivitet som skal bidra til Nato aktiviteten ved å vurdere alternative protokollfunksjoner for betjening av tale og datatrafikk i distribuerte mobile nett. Dette dokumentet omhandler flernivåprioritet (MLPP) i NBWF. En MLPP tjeneste skal sikre god fremkommelighet for IP-trafikk med høy prioritet i de perioder der nettet ikke har kapasitet til å betjene all trafikk. Et smalbåndnett har lav trafikkapasitet og metningssituasjoner kan lett oppstå. I et IP-nett uten MLPP har ikke IP-klientene et verktøy som lar dem bestemme hvilken trafikk som skal avvikles i nettet. En robust MLPP tjeneste er derfor påkrevd når nettet skal betjene militær trafikk i taktisk sone. Her kan uforutsette eksterne hendelser medføre at trafikkbehovet blir større en planlagt. Samtidig medfører bruk av radio med rundtstrålende antenner at transmisjonskapasiteten er vanskelig og predikere. Jamming og interferens fra andre radio systemer er ofte også en utfordring i taktisk sone. Denne rapporten beskriver også en adaptive MAC (Medium Access Control) protokoll der en rekke MAC-parametre reguleres dynamisk etter påtrykt IP trafikk. Hensikten med dette er å gi optimal IP-ytelse (minimum forsinkelse og minimum pakketap) under alle lastnivåer. Rapporten inneholder en rekke simuleringseksperimenter som kvantifiserer gevinsten av MLPP og adaptiv MAC. Rapporten konkluderer med at MLPP er et nødvendig verktøy for IP-klientene, mens det å utelate adaptive MAC ikke er så kritisk.