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Provider Backbone Bridges (PBB)
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MAC address explosion in carrier networks hinders the scalability of traditional Ethernet in the Metro since each customer could potentially contribute thousands of MAC addresses. To overcome this problem, greater 'Customer LAN' - 'Service Provider Network' separation can be ensured in the metro network through the use of MAC-in-MAC (also known as 'Provider Backbone Bridges', PBB). This concept, introduced by the IEEE 802.1ah standard, involves the encapsulation of all Ethernet frames with the Source "Edge-node" MAC address and Destination "Edge-node" MAC address. PBB drastically reduces the number of MAC addresses that intermediate nodes have to learn, thus making an Ethernet network more scalable.
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What PBB enables
- Secure Demarcation:
The use of PBB provides Service Providers with a secure and clear demarcation point, where the user/customer networks can be cleanly separated from provider network. This demarcation point is called UNI (User Network Interface). Providing such clear demarcation can serve several purposes. The demarcation point is the point from where services are provisioned and from where fault management and performance management is performed for the service provided. Customer networks may have overlapping addresses, which could cause forwarding conflicts in the Service Provider network. This issue is avoided by PBB by providing a completely independent encapsulation mechanism. The key requirements for a fully secure demarcation point (UNI) are to have full/complete encapsulation of the incoming Ethernet frames at the UNI. PBB provides complete encapsulation of customer frames thus ensuring a very secure demarcation point.
- Customer Separation & Service Scalability:
One aspect of administrating Quality of Service to different services is the ability to segregate customer flows into distinct uniquely identifiable Service Flows through the network. Hence, Service Flow Identifiers must be highly scalable and should have the ability to mark millions of flows. PBB provides 16 million unique service identifiers for this purpose, apart from providing 2^60 bit Transport Tunnels.
- Single-ended Provisioning:
A PBB network relies on time-tested Ethernet operation's principles based IEEE 802.1 bridge relay technology. As a result, only the end-nodes have to be provisioned, while the intermediate nodes need not be provisioned. The backbone forwarding table are automatically built.
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