DESIGN AND ANALYSIS OF QOS IN AN ETHERNET ACCESS RING


Currently LAN technology is predominantly Ethernet based. Active research is underway to extend Ethernet beyond LANs into Metro Area Networks (MAN) and further into Wide Area Networks (WAN). However Ethernet protocols need extensions to succeed as MAN technology in terms of scalability, QoS, resiliency and Operations, Administration and Maintenance (OAM). The emerging trends to carry Ethernet transport across MAN can be classified into native Ethernet protocol extensions using encapsulation scheme such as VLAN stacking (QinQ) and Multi Protocol Label Switching (MPLS) or by other transportation technology such as Resilient Packet Ring (RPR) and Ethernet Over Sonet (EOS).


The RPR/MPLS/EOS solution in the access ring is expensive due to the additional hardware required and also the overhead of conversions between different packet formats for these transport protocols. Gigabit Ethernet in the access ring is a low cost and less complex solution for small-scale deployments. But the Gigabit Ethernet solution is weak in terms of providing SLA guarantees.


Currently native Ethernet supports only QoS by priority marking. Priority marking does provide differentiation between different traffic types but it fails to give bandwidth guarantee and fairness. The QoS mechanism existing in Ethernet is localized in each node and affected by the spatial properties. Hence in order to enhance the QoS level in Ethernet, a distributed QoS mechanism is required which ensures fairness and bandwidth guarantees. We propose and analyze one such approach in this research.


The proposal describes the required steps for realizing Quality of Service in access ring when Ethernet is extended beyond LAN into the access network. The steps are categorized as a) Classification based on the Customer VLAN, b) Traffic contract specification per Customer VLAN at the User to Network Interface, c) Policing as per the traffic contract, d) Scheduling/Shaping at the egress queue at all the nodes in the ring e) Admission control. The mechanism ensures global fairness in the access ring that gives every node in the ring a fair share of the ring bandwidth. The QoS solution discussed here is implemented in M2404, a Metro Ethernet Switch developed by Midas Communication Technologies and analysed in a ring network.