QoS-Aware MPLS Forwarding via EXP Bit Segmentation
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Solution Overview
Problem
Conventional routing techniques fail to efficiently separate and direct different types of network traffic, such as voice and data, along specific paths within a network, often resulting in high latency links being used for all traffic types due to the overshadowing of LDP LSPs by RSVP LSPs in the forwarding plane.
Innovation Solution
The extension of the Label Distribution Protocol (LDP) allows core routers to dynamically build forwarding information that maps MPLS labels to different paths based on packet classes of service, using Experimental (EXP) bits to identify service types and redirect packets accordingly, enabling service-specific Quality of Service (QoS)-aware traffic engineering without requiring a full dual-topology approach or a full mesh of RSVP LSPs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RSVP LSPs are deployed in the network core, then QoS-aware traffic engineering is improved, but LDP LSP visibility is lost and all traffic types are forwarded over the same path
Solution Approach 1:
The patent segments the forwarding decision process by creating separate forwarding tables for RSVP LSPs and LDP LSPs. The forwarding information base (FIB) is divided into multiple segments, each maintaining visibility of different LSP types. This allows the system to preserve both RSVP and LDP LSP information simultaneously, enabling selective traffic steering based on service type while maintaining protocol coexistence.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a unified forwarding information base that mediates between RSVP and LDP protocols. This intermediary structure allows both protocol types to coexist and be visible simultaneously, enabling the system to make informed forwarding decisions that consider both RSVP-established paths and LDP-established paths without one overshadowing the other.
2Adaptability or versatility
If a full mesh of RSVP LSPs is deployed, then service-specific path control is improved, but device complexity and deployment overhead increase
Solution Approach 1:
The patent applies partial action by deploying RSVP LSPs only where specifically needed for certain service types, rather than requiring a full mesh deployment. The system allows selective activation of RSVP traffic engineering for specific services or paths, while other traffic can continue to use LDP-based forwarding. This reduces the overall complexity and deployment overhead while still providing service-specific path control where required.
3Productivity
If ECMP is used for load balancing, then network utilization is improved, but control over traffic paths is lost
Solution Approach 1:
The patent applies local quality by enabling different forwarding behaviors for different traffic types at specific network nodes. Instead of uniform ECMP behavior across all traffic, the system allows LDP LSPs to use ECMP for load balancing on a local basis, while RSVP LSPs maintain their explicit path definitions. This localized approach allows ECMP to improve network utilization where appropriate without sacrificing path control for services that require it.
Data Source
AI summary
A router comprises an interface for receiving packets, wherein the packets include Multiprotocol Label Switching (MPLS) labels having the same label value that corresponds to an MPLS label switched path (LSP), and wherein each of the MPLS packets includes MPLS experimental (EXP) bits defined to identify a class of service to which the respective packet belongs. The router is a transit router along the MPLS LSP, and further includes a control unit that, for each of the packets, accesses forwarding information to determine whether to forward the packet along the LSP or to redirect the packet along a second LSP based on the classes of service specified in the EXP bits. The router receives policies via a user interface, and applies the policies to index into the forwarding information to select a forwarding entry, wherein the index is responsive to the label value in combination with the EXP bits.