PBB Provider Backbone Bridging
PBB (Provider Backbone Bridging) is a networking technology that is designed to enhance the scalability and efficiency of Ethernet networks. It is primarily used by service providers to deliver high-performance and reliable network services to their customers. PBB overcomes the limitations of traditional Ethernet bridging by introducing a hierarchical structure and implementing a set of advanced protocols and mechanisms.
In traditional Ethernet bridging, each device in a network is assigned a Media Access Control (MAC) address, and frames are forwarded based on the MAC address lookup table. However, as the number of devices and the scale of networks grow, this approach becomes inefficient and leads to broadcast storms and network congestion. PBB addresses these issues by introducing a new concept called the Provider Backbone Bridge (PBB).
At its core, PBB separates the customer-facing network from the provider-facing network by introducing a Provider Edge (PE) device. The PE device acts as a bridge between the customer network and the provider network. The customer network consists of Customer Edge (CE) devices, which are connected to the PE device. The provider network, on the other hand, consists of Provider Edge (PE) devices connected to each other forming a backbone.
The PE devices in the provider network use a protocol called Provider Backbone Bridge Protocol (PBBP) to communicate with each other. PBBP is responsible for establishing and maintaining the hierarchical structure of the provider network. It assigns a unique 48-bit Backbone Service Instance Identifier (I-SID) to each PE device, which is used for frame forwarding and identification within the provider network.
One of the key features of PBB is the introduction of a new Ethernet frame format called the Provider Backbone Bridge (PBB) frame. The PBB frame encapsulates customer Ethernet frames and adds a 32-bit Service Instance Identifier (I-SID) field, which allows for efficient and scalable forwarding within the provider network. The I-SID field is used by the PE devices to identify the appropriate forwarding path for the encapsulated frames.
PBB also introduces a technique called MAC-in-MAC encapsulation, which allows the PBB frames to be transported across the provider network. MAC-in-MAC encapsulation involves adding an additional MAC header to the PBB frame, which contains the MAC addresses of the PE devices. This allows the PBB frame to be forwarded through the provider network based on the MAC address lookup table of the PE devices.
Furthermore, PBB provides mechanisms for loop prevention and broadcast storm control. It employs a technique called split-horizon forwarding, which ensures that frames are not sent back to the same PE device they originated from. Additionally, PBB supports the use of the Spanning Tree Protocol (STP) to eliminate loops in the provider network.
The scalability of PBB is enhanced through the use of I-SID-based forwarding. Unlike traditional Ethernet bridging, which relies on MAC address lookup tables, PBB uses I-SID-based forwarding tables. These tables are maintained by the PE devices and allow for efficient and scalable forwarding based on the I-SID field of the PBB frames.
PBB also provides support for Quality of Service (QoS) mechanisms, allowing service providers to prioritize and manage different types of traffic. It enables the mapping of different Service Level Agreements (SLAs) to specific I-SIDs, ensuring that traffic is treated according to the specified QoS requirements.
In conclusion, PBB (Provider Backbone Bridging) is a powerful networking technology that enhances the scalability and efficiency of Ethernet networks, particularly in the context of service provider networks. By introducing the concept of Provider Backbone Bridges and implementing advanced protocols and mechanisms, PBB provides a hierarchical and scalable framework for delivering high-performance and reliable network services. With features such as MAC-in-MAC encapsulation, I-SID-based forwarding, loop prevention, and QoS support, PBB addresses the limitations of traditional Ethernet bridging and offers a robust solution for building large-scale and efficient networks.