MPLS local protection

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MPLS Fast Reroute (also called MPLS local restoration or MPLS local protection) is a local restoration network resiliency mechanism. It is actually a feature of resource reservation protocol (RSVP) traffic engineering (RSVP-TE). In MPLS local protection each label-switched path (LSP) passing through a facility [1] is protected by a backup path which originates at the node immediately upstream to that facility. [2] [3] [4] [5] [6]

Contents

This node which redirects the traffic onto the preset backup path is called the Point of Local Repair (PLR), and the node where a backup LSP merges with the primary LSP is called Merge Point (MP). [2] [3] This mechanism (local protection) provides faster recovery because the decision of recovery is strictly local. For comparison, when recovery mechanisms are employed at the IP layer, restoration may take several seconds which is unacceptable for real-time applications (such as VoIP). In contrast, MPLS local protection meets the requirements of real-time applications with recovery times comparable to those of shortest path bridging networks or SONET rings (< 50 ms). [2] [3] [4]

Local protection approaches

There are two distinct approaches to local protection: (1) one-to-one local protection (detour) (2) many-to-one local protection (facility backup). [2] [3]

One-to-one local protection

In one-to-one backup approach, the PLRs maintain separate backup paths for each LSP passing through a facility. The backup path terminates by merging back with the primary path at a node called the Merge Point (MP). In one-to-one backup approach, the MP can be any node downstream from the protected facility. Maintaining state information for backup paths protecting individual LSPs, as in the one-to-one approach, is a significant resource burden for the PLR. Moreover, periodic refresh messages [7] sent by the PLR, in order to maintain each backup path, may become a network bottleneck.

Many-to-one local protection

In many-to-one approach, a PLR maintains a single backup path to protect a set of primary LSPs traversing the triplet (PLR, facility, MP). Thus, fewer states need to be maintained and refreshed which results in a scalable solution. The many-to-one backup approach is also called facility backup. Note that in this approach, the MP should be the node immediately downstream to the facility.

Example

Fig.1 Fast Reroute operation FRR1.1.jpg
Fig.1 Fast Reroute operation

In Fig.1 (right), there is a primary path (label-switched path, or LSP) from A to E via B and D. The traffic of customers connected to A and E will take this path in normal operation. There is also a secondary path (LSP) from A to E via C. This path can be either pre-signaled or not. For the primary LSP, FRR (Fast ReRoute) is enabled. Once enabled, the other network elements on the LSP will know that FRR is enabled. Let's assume there is a break between D and E. D will immediately know this and will inform B and A. For A to know that there is a failure between D and E takes a while, but since D knows about the failure immediately and FRR is enabled on the LSP, it uses the detour path D-C-E to get rid of the failure immediately and traffic will continue to flow along that new path. This takes less than 50ms. Once the secondary LSP is up, traffic is switched to the secondary LSP and the temporary detour path is disabled.

Local protection fault-models

An illustration of MPLS local protection Faults Modes. Note that complete network is not shown only primary and backup paths are shown. Furthermore, nodes traversed by a backup path are not shown. Localprotection.JPG
An illustration of MPLS local protection Faults Modes. Note that complete network is not shown only primary and backup paths are shown. Furthermore, nodes traversed by a backup path are not shown.

In a link protection model each link (or subset links) used by an LSP is provided protection by pre-established [8] backup paths.

Node protection

In a node protection model each node (or subset of nodes) used by an LSP is provided protection by pre-established backup paths.

Element protection

In an element protection model, protection is provided against the failure of links as well as nodes along the LSP.

Related Research Articles

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<span class="mw-page-title-main">Metro Ethernet</span> Metropolitan area network based on Ethernet standards

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Resource Reservation Protocol - Traffic Engineering (RSVP-TE) is an extension of the Resource Reservation Protocol (RSVP) for traffic engineering. It supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature of the packet streams they want to receive. RSVP runs on both IPv4 and IPv6.

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<span class="mw-page-title-main">Fast Reroute</span>

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<span class="mw-page-title-main">Optical mesh network</span> Optical network using a mesh topology

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Segment protection is a type of backup technique that can be used in most networks. It can be implemented as a dedicated backup or as a shared backup protection. Overlapping segments and non-overlapping segments are allowed; each providing different advantages.

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Fast automatic restoration (FASTAR) is an automated fast response system developed and deployed by American Telephone & Telegraph (AT&T) in 1992 for the centralized restoration of its digital transport network. FASTAR automatically reroutes circuits over a spare protection capacity when a fiber-optic cable failure is detected, hence increasing service availability and reducing the impact of the outages in the network. Similar in operation is real-time restoration (RTR), developed and deployed by MCI and used in the MCI network to minimize the effects of a fiber cut.

HSMP LSP is hub & spoke multipoint Label Switched Path (LSP), which allows traffic both from root to leaf through point-to-multipoint (P2MP) LSP and also leaf to root along the reverse path. That means traffic entering the HSMP LSP from application/customer at the root node travels downstream to each leaf node, exactly as if it is travelling downstream along a P2MP LSP to each leaf node. Upstream traffic entering the HSMP LSP at any leaf node travels upstream along the tree to the root, as if it is unicast to the root. Direct communication among the leaf nodes is not allowed.

Deterministic Networking (DetNet) is an effort by the IETF DetNet Working Group to study implementation of deterministic data paths for real-time applications with extremely low data loss rates, packet delay variation (jitter), and bounded latency, such as audio and video streaming, industrial automation, and vehicle control.

References

  1. ↑ The term facility is usually referred to a link or node.
  2. 1 2 3 4 Aslam; et al. (2005-02-02). "NPP: A Facility Based Computation Framework for Restoration Routing Using Aggregate Link Usage Information". QoS-IP 2005 : quality of service in multiservice IP network. Retrieved 2006-10-27.
  3. 1 2 3 4 Raza; et al. (2005). "Online routing of bandwidth guaranteed paths with local restoration using optimized aggregate usage information". IEEE International Conference on Communications, 2005. ICC 2005. 2005. IEEE-ICC 2005. Vol. 1. pp. 201–207. doi:10.1109/ICC.2005.1494347. ISBN   0-7803-8938-7. S2CID   5659648.
  4. 1 2 Li Li; et al. (2005). "Routing bandwidth guaranteed paths with local restoration in label switched networks". IEEE Journal on Selected Areas in Communications. IEEE Journal on Selected Areas in Communications. 23 (2): 437–449. doi:10.1109/JSAC.2004.839424.
  5. ↑ Pan; et al. "Fast Reroute Extensions to RSVP-TE for LSP Tunnels networks". RFC-4090. Retrieved 2006-10-27.
  6. ↑ Kodialam; et al. (2001). "Dynamic Routing of Locally Restorable Bandwidth Guaranteed Tunnels using Aggregated Link Usage Information". Proceedings IEEE INFOCOM 2001. Conference on Computer Communications. Twentieth Annual Joint Conference of the IEEE Computer and Communications Society (Cat. No.01CH37213). IEEE Infocom. pp. 376–385. 2001. Vol. 1. pp. 376–385. doi:10.1109/INFCOM.2001.916720. ISBN   0-7803-7016-3. S2CID   13870642.
  7. ↑ Local protection primarily uses RSVP-TE extensions, which is a soft-state protocol and requires periodic refresh messages to maintain its states.
  8. ↑ backup paths are establish before the failure
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