Upstream Polling Protocols for Flow Control in PON/xDSL Hybrid Access Networks

TL;DR

This paper introduces gated flow control protocols for hybrid PON/xDSL networks to reduce buffer occupancy at the drop-point, ensuring efficient upstream data transmission and preventing buffer overflow.

Contribution

It proposes novel gated flow control mechanisms extending polling-based PON MAC to DSL segments, with timing analysis and simulation validation.

Findings

Gated flow control reduces buffer occupancy effectively.

Proper grant sizing policies improve upstream transmission efficiency.

Protocols enable full PON upstream bit rate transmission.

Abstract

In a hybrid PON/xDSL access network, multiple Customer Premise Equipment (CPE) nodes connect over individual Digital Subscriber Lines (DSLs) to a drop-point device. The drop-point device, which is typically reverse powered from the customer, is co-located with an Optical Network Unit (ONU) of the Passive Optical Network (PON). We demonstrate that the drop-point experiences very high buffer occupancies when no flow control or standard Ethernet PAUSE frame flow control is employed. In order to reduce the buffer occupancies in the drop-point, we introduce two gated flow control protocols that extend the polling-based PON medium access control to the DSL segments between the CPEs and the ONUs. We analyze the timing of the gated flow control mechanisms to specify the latest possible time instant when CPEs can start the DSL upstream transmissions so that the ONU can forward the upstream transmissions at the full PON upstream transmission bit rate. Through extensive simulations for a wide range of bursty traffic models, we find that the gated flow control mechanisms, specifically, the ONU and CPE grant sizing policies, enable effective control of the maximum drop-point buffer occupancies.