User's Manual

Understanding Silver Spring Networks Access Points 1 About Access Points
Understanding Silver Spring Networks Access Points Rev 3 22 January 2013 Silver Spring Networks 13
Customers have used the following alternative backhaul technologies:
• Distribution Substation Backhaul (for example, fiber)
• WiMAX
• Satellite Radios
The design rule for Access Point to RF devices is 1 to 5,000. At this ratio, the maximum data
throughput required from a WAN solution is 40kbps per Access Point.
Based on real-world data on a network of this size, the average wireless speed is measured at
2.6Mbps downstream and 700Kbps upstream, which is well in excess of requirements.
The backhaul is fairly insensitive to latency (that is, in remote locations, Silver Spring already
proven successful connection using satellite radios which have a ~1.5s RTT - or Round Trip
Time).
Silver Spring recommends that the network design for a particular deployment limit
exposure to single points of failure and proactively design for redundancy by allowing each
RF device to be reached from more than one Access Point. In all but rural densities, having
up to 5,000 RF devices per AP generally results in most RF devices being able to reach more
than one Access Point.
Throughput Performance
Typical data packet sizes observed in Smart Grid systems is between 150 bytes for DA or
other simple command and control applications. A normal HCM and AMI meter read packet
is approximately 350 bytes including full measurement intervals, event logs, and
instantaneous register reads. At 100 Kbps (10 bytes / ms), delivery of 150 byte packets occurs
at 10 full transactions per second.
The larger AMI/HCM packets are delivered at 3-5 transactions per second. These are typical
observed rates and it should be mentioned that for reliability reasons all transactions are
completely acknowledged four-way confirmed events.
Though final data is not available, raising on-air data rates from 100 Kbps to 300 Kbps will
roughly double the PPS rates at the aggregation points (Access Points). This moves the daily
capacity of an Access Point from approximately 400,000 transactions per day to nearly a
million.
The bandwidth being fed to the WAN side of the Access Point is determined by what
backhaul is being used.
With the Access Point being a router and not a collector, data is constantly being transmitted
through the WAN, eliminating the need to store data for later transmission (Store and
Forward). The Access Point, using 100Kbps on the NAN side, aggregates 3000-5000 meters,
bridges, or other RF devices, while processing approximately 5 transactions per second and
delivering upwards of 500,000 transactions per day to the back office.
The raw throughput in the RF NAN in the Silver Spring smart grid solution is 100 Kbps
node-to-node. This means that between each device, there is 100 Kbps of available
bandwidth. On average, the amount of traffic is relatively low with respect to the amount of
available bandwidth.