User's Manual

Understanding Silver Spring Networks Access Points 1 About Access Points
Understanding Silver Spring Networks Access Points 4 March 2013 Silver Spring Networks 13
ThedesignruleforAccessPointtoRFdevicesis1to5,000.Atthisratio,themaximumdata
throughputrequiredfromaWANsolutionis40kbpsperAccessPoint.
Basedonrealworlddataonanetworkofthissize,theaveragewirelessspeedismeasuredat
2.6Mbpsdownstreamand
700Kbpsupstream,whichiswellinexcessofrequirements.
Thebackhaulisfairlyinsensitivetolatency(that is,inremotelocations,SilverSpringalready
provensuccessfulconnectionusingsatelliteradioswhichhavea~1.5sRTT‐orRoundTrip
Time).
SilverSpringrecommendsthatthenetworkdesignforaparticulardeploymentlimit
exposure
tosinglepointsoffailureandproactivelydesignforredundancybyallowingeach
RFdevicetobereachedfrommorethanoneAccessPoint.Inallbutruraldensities,having
upto5,000RFdevicesperAPgenerallyresultsinmostRFdevicesbeingabletoreachmore
thanone
AccessPoint.
Throughput Performance
Typicaldatapacketsizesobserved inSmartGridsys temsisbetween150bytesforDAor
othersimplecommandandcontrolapplications.AnormalHCMandAMImeterreadpacket
isapproximately350bytesincludingfullmeasurementintervals,eventlogs,and
instantaneousregisterreads.At100Kbps(10bytes/ms),
deliveryof150bytepacketsoccurs
at10fulltransactionspersecond.
ThelargerAMI/HCMpacketsaredeliveredat35transactionspersecond.Thesearetypical
observedratesanditshouldbementionedthatforreliabilityreasonsalltransactionsare
completelyacknowledgedfourwayconfirmedevents.
Thoughfinaldata
isnotavailable,raisingonairdataratesfrom100Kbpsto300Kbpswill
roughlydoublethePPSratesattheaggregationpoints(AccessPoints).Thismovesthedaily
capacityofanAccessPointfromapproximately400,000transactionsperdaytonearlya
million.
Thebandwidthbeingfedtothe
WANsideoftheAccessPointisdeterminedbywhat
backhaulisbeingused.
WiththeAccessPointbeingarouterandnotacol lector,dataisconstantlybeingtransmitted
throughtheWAN,eliminatingtheneedtostoredataforlatertransmission(Storeand
Forward).TheAccessPoint,using100Kbpson
theNANside,aggregates30005000meters,
bridges,orotherRFdevices,whileprocessingapproximately5transactionspersecondand
deliveringupwardsof500,000transactionsperdaytothebackoffice.
TherawthroughputintheRFNANintheSilverSpringsmartgridsolutionis100Kbps
nodetonode.
Thismeansthatbetweeneachdevice,thereis100Kbpsofavailable
bandwidth.Onaverage,theamountoftrafficisrelativelylowwithrespecttotheamountof
availablebandwidth.
Figure4illustratesdatacollectedfromalivecustomernetworkoveraperiodofoneweek.
Asshown,theaveragebandwidthconsumedbyAdvancedMetering trafficisapproximately