 require cooperation among the users, and requires a minimum of cooperation between the users and the provider of the MAC service. The address limitation of 802.1Q is further aggravated if the customers (enterprises) have their own VLAN tags (from their internal networks), then the provider cannot use the same tag ID which would otherwise lead to potential conflicts. To solve this problem, the Q-in-Q technique was proposed, whereby a customer's VLAN tag was preserved by adding a service provider's VLAN tag (S-tag), appended to the customer's VLAN tag (C-tag). This double stacking of VLANs ensures that the C-tag is untouched and the provider can differentiate customers and services. This method of stacking VLANs has gained wide acceptance. IEEE 802. lad also standardizes the architecture and protocols to allow Ethernet frames carrying multiple tags. However, the standard still suffers scalability issues due to availability of only 4094 addresses. IEEE 802. .1ah The IEEE 802.1ah or Provider Backbone Bridges (PBB) [33] is a set of architecture and protocols for routing of a customer network over a provider's network allowing interconnection of multiple Provider Bridge Networks (802.1a without losing each customer's individually defined VLANs. Apart from address limitation of 802. lad and 802.1Q, another drawback is that the customer's MAC address is visible to nodes within the network, implying that customer's privacy is in jeopardy. To address this limitation, PBB standard was proposed and it was approved in June 2008. In PBB, a customer's frame is completely encapsulated in a provider's frame, providing a clear demarcation between customer contents and provider transport. This process is called MAC-in-MAC. PBB header is composed of a source and destination backbone MAC, (B-MAC) address, a backbone VLAN ID (B-VID) to divide the backbone into broadcast domains and a 24-bit service identifier (I-SID). The 24-bit I-SID defines a maximum of 16 million service instances thereby solving the scalability issue to a large e