Differentiated back-off for Ethernet

The network devices in the IEEE 802.3 based Ethernet networks use a carrier-sense-multiple-access with collision-detection (CSMA/CD) protocol to access the shared bus. There is no priority based access control to the shared bus in this protocol. All stations (nodes) run the same algorithm to access the bus and perform an exponential back-off when contention arises. This makes it difficult to achieve quality-of-service (QoS) guarantees (relative or quantitative) among different applications. Even if priority queuing is implemented, all the stations on the network use the same back-off algorithm at the medium access control (MAC) layer and thus does not provide any priority-based access to the bus. As there is a wide deployment of Ethernet networks, any modification to the protocol should inter-operate with existing devices, as it would be very difficult to upgrade all devices. This paper proposes a modification to the back-off scheme which does not require any modifications to the existing devices, but newer devices, such as voice-over-IP (VoIP) phones and multimedia devices can make use of the modification to get a relative priority over others. Both analysis and simulation results confirm that, using differentiated back-off, high-priority traffic get quicker access to the bus (higher throughput and lower delay) than low priority traffic