Provider Backbone Bridging ( IEEE 802.1ah).Several Ethernet encapsulation technologies have emerged in the last few years, which aim to overcome these limitations and provide new facilities required by network operators:
A flat addressing scheme which fails to isolate MAC addresses from different customers.Insufficient numbers of service identifiers (VLANs).Provider Bridging is widely used in the telecommunications industry, but suffers from some limitations. By introducing the extra level of tagging provided by the S-tag, up to 4,094 customer LANs can be aggregated together into a higher-speed Ethernet stream. Each tag is a 4-byte header which is inserted into the Ethernet frame between the existing customer MAC addresses and the Ethertype field. 802.1ad, which was standardised in 2005, specifies C-tags and S-tags, which can be applied independently or together to allow local area networks to be extended across metro and regional transport networks. How do Ethernet networks identify and segregate streams of customer data as they are transported through a metro or regional network? How do service providers deploy Virtual LAN services, allowing the cost-effective provision of Ethernet services over transport networks? In this post, I look at current solutions and their limitations, and describe some new technologies designed to enhance this market segment.Įthernet access and optical platforms use VLAN tagging based on the frame formats defined in IEEE standard 802.1ad (known as Provider Bridging, or Q-in-Q) to tag frames received on customer ports.