Understanding Key ePMP System Scalability Features

ePMP 1000 is designed for scalability and supports up to 120 subscribers without degrading overall system performance. ePMP 1000 features which contribute to this scalability are explained below:

GPS Synchronization and Frequency Reuse

GPS Synchronization minimizes interference generated by the system onto itself, making AP co-location and frequency reuse feasible. A stable timing source is utilized by every AP in the system to precisely synchronize the start of every transmit and receive cycle within the TDD framing structure used in the Cambium Networks ePMP solution. In other words, no parts of the ePMP system transmit during a receive cycle or receive during a transmit cycle.

With GPS synchronization the network can scale to significantly larger sizes without any AP’s transmission interfering with the reception of other APs. Under these conditions, a more efficient frequency reuse plan across sectors and towers can be employed. Less spectrum requirements means more opportunity for radio deployment.

For details about ePMP configuration in a frequency reuse deployment or ABAB frequency reuse deployment, see https://support.cambiumnetworks.com/files/epmp/ .

Media Access Layer (MAC) Design

An ePMP Access Point can support a maximum of 120 active SMs transferring bidirectional data. Part of the ePMP’s scalability and consistency of performance lies in the sophistication of the ePMP air interface protocol – the Media Access Layer (MAC) protocol. The key features that enable its performance are:

  • GROUP POLLING – The ePMP polls and schedules uplink transmissions for multiple SMs at one time greatly reducing the overhead that comes from dealing with one SM at a time.
  • UPLINK TX TIMING ADVANCE – This is a sophisticated technique that comes from cellular systems where each SM knows its distance from the Access point and hence the transmission propagation delay. When the SM transmits on the uplink, it sends its data in advance of its allocated uplink time slot so that by the time the data arrives at the AP, it arrives exactly when it is supposed to. The data transmissions can then be “packed” very tightly in time and a minimum of RF bandwidth is wasted.
  • SCHEDULING ALGORITHM – The ePMP employs a sophisticated priority-based, air fairness, starvation avoidance algorithm for allocating RF resources to SMs. The allocations are based on airtime instead of throughput and so we avoid the situation where SMs in poor RF conditions take up an excessive amount of time and therefore available capacity.

Quality of Service (QoS)

The ePMP platform supports three QoS priority levels (not available in ePTP Master mode) using an air fairness, priority-based starvation avoidance scheduling algorithm. As the network grows, QoS rules may be applied to make sure that certain types of network traffic continue to be served with quality (like VoIP, video, or other high-priority traffic).

The ePMP platform also supports radio data rate limiting (Maximum Information Rate, or MIR). By implementing rate-limiting mechanisms in your network, you can scale up your network assured that each SM is only operating at the rate configured in the SM field MIR Profile Setting. Operators may add up to 16 MIR profiles on the AP, each with unique limits for uplink and downlink data rates.


By deploying a centralized RADIUS server in the management network, subscriber authentication and MIR configuration may be handled from one location, minimizing the need to log into subscribers individually.