Quantifying IP/optical integration synergies

Next Generation Communications Blog

Quantifying IP/optical integration synergies

By:  Alcatel-Lucent’s:

  • Ben Tang, Distinguished Member of Technical Staff in the Bell Labs Consulting Services department
  • Mohcene Mezhoudi, Senior Consultant Member of Technical Staff in the Bell Labs Consulting Services department
  • Arnold Jansen, Senior Product Marketing Manager

From original Alcatel-Lucent TechZine posting

IP/optical integration typically results in cost savings, but maintaining service availability is also essential when measuring total return on investment (ROI). An analysis of 3 modes of operation found multi-layer protection and restoration to be the most cost efficient while meeting availability requirements.

Run a hotter network without traffic melt downs

Service providers are always looking for ways to run their networks hotter in order to maximize returns on network investments. But when trying to economize it is important to keep an eye on service availability, as the cost of service outages can easily undo any savings.

Traditional 1+1 optical network protection keeps 50% of network capacity in reserve. The alternative approach of only leveraging MPLS-based protection and restoration mechanisms at the routing layer is equally inefficient, even though these inefficiencies are less immediately apparent. Nevertheless, in many networks this is the present mode of operation (PMO).

State-of-the-art optical transport networks and reconfigurable optical add/drop multiplexer technologies do provide a better alternative. Agile optical transport and an intelligent control plane enable transport layer resiliency with a cost-effective utilization of networks resources.

These protection capabilities leverage the generalized multiprotocol label switching (GMPLS – RFC 3945) architecture. GMPLS adopts key concepts from the MPLS control plane used in IP routing with functional enhancements to support multi-layer optical transport networks.


Figure 1. GMPLS protection and restoration options

Service providers can leverage GMPLS to drastically expand their existing toolkit of network traffic protection and restoration capabilities (Figure 1, left). With the right architecture, GMPLS-based transport layer recovery can be combined with protection mechanisms in the IP/MPLS routing layer to offer and implement differentiated availability service level agreements (SLAs) for different classes of service (Figure 1, right).

SLA requirements can subsequently be mapped on an appropriate multi-layer traffic protection and restoration strategy in order to balance availability, redundancy and resource utilization for the best returns on network investments.

Bell Labs TCO study on multi-layer cost synergies

Alcatel-Lucent commissioned Bell Labs to compare the relative cost of MPLS and GMPLS-based resiliency mechanisms. The TCO analysis is based on a backbone reference network consisting of 6 core routing nodes and 5 optical transport nodes. The physical transport network topology is partially meshed, while the core routing topology is a logical mesh.

The network resource requirements for a mixed traffic matrix were compared, with traffic growing evenly at 40% annually over a 5 year study period:

  • 10% is expedited forwarding (EF) traffic. This is typically “lifeline traffic” such as VoIP that is sensitive to delay, jitter, packet loss, and outages. Protecting and restoring EF traffic has the highest priority. It must be resilient to multiple failures with restoration within 50 msec.
  • 30% is assured forwarding (AF) traffic. This is mission critical, high revenue data traffic that requires reliable transport but can compensate for limited packet loss, for instance through retransmission by the transmission control protocol (TCP). It must be resilient against a single failure with restoration within 500 msec.
  • 60% is load-balanced best effort (BE) traffic. This is predominantly high volume Internet traffic with low revenue per bit and the most relaxed availability requirements. Nevertheless, service providers want to prevent long and frequent outages, and 1+N redundancy will provide resiliency against a single failure without nominal capacity loss.

The study compared 3 different network protection and restoration strategies (Figure 2):

  1. Leverage MPLS to protect and restore all service traffic at the routing layer (PMO)
  2. Leveraging GMPLS to protect all IP traffic at the photonic switching layer (FMO1)
  3. Leveraging both MPLS and GMPLS/UNI in a multi-layer resiliency scheme (FMO2)

Present mode of operation (PMO)
The PMO applied 1+1 redundant LSPs with MPLS fast reroute over unprotected but physically disjoint transport links to protect EF traffic end-to-end against multiple failures, with very fast restoration times below 50 msec.

AF traffic is carried by non-redundant LSPs with MPLS fast reroute over unprotected but physically disjoint transport links. For BE it uses N+1 unprotected, physically disjoint LSPs in an ECMP load sharing model. This scheme protects against capacity degradation when a single LSP or optical link segment fails.

Future mode of operation 1 (FMO1)
FMO1 applies optical segments with GMPLS 1+1 protection and restoration combined to protect IP overlay traffic, which protects EF traffic against multiple failures with a restoration time below 50 msec. The difference with the PMO is that service restoration is transparent to the IP layer and acts on aggregated traffic in the optical transport layer.

Future mode of operation 2 (FMO2)
FMO2 applies a combination of MPLS fast reroute over optical transport links with GMPLS guaranteed restoration to protect both EF and AF traffic against multiple failures, with rapid protection switching within 50 msec.

As wavelength restoration times at the photonic switching layer are in the order of seconds, MPLS FRR provides rapid restoration over alternate optical segments while the failed primary segment is being restored by GMPLS. Optical segments will be able to share spare resources for restoration purposes. During FRR restoration, full bandwidth recovery is guaranteed for EF traffic only, which means that potentially packet loss can occur for AF traffic in case of failure.

ALU.IP.3.2.15.b.JPGFigure 2. Network service protection and restoration strategies for IP over DWDM

Study results on multi-layer cost synergies

Optical transport network costs are mostly determined by the amount of optical transponders required and wavelength consumption. Optical transponder count tracks closely to router port requirements, and are by far the most expensive component in the optical transport path, while wavelength consumption can impact the scaling requirements of intermediate ROADM systems that are switching the wavelengths.

The study results in Figure 3 indicate that FMO2 requires 46% fewer optical transponders over the 5 year period than the PMO, and even 10% fewer than FMO1. FMO2 shows significant cost savings over PMO in the initial years, with 47% savings over PMO and 51% savings over FM01 in Year 1.


Figure 3. Summary of network TCO savings

In the initial years, the transport network build-out is driven by 100GE connectivity requirements for the IP link topology — and many wavelengths will be lightly loaded.

FMO1 starts out with the largest cost because its connectivity requirements are higher than PMO and FMO2 due to the need for 1+1 link redundancy to protect EF and AF traffic, which results in a full mesh.

The PMO and FMO2 link topologies, on the other hand, are only partially meshed because MPLS FRR and GMPLS guaranteed restoration can dynamically create detours around link failures.

As traffic grows and wavelengths fill up, the incremental network build out is primarily driven by capacity growth and FMO1 catches up in cost over the PMO due to its greater efficiency.

FMO1 and FMO2 are virtually tied in the amount of router ports required, both consuming 37% less 100GE ports than the PMO over the 5 year period. The PMO consumes more router ports and optical transponders because it relies on intermediate routers to restore traffic on failed segments through MPLS 1+1 protection and FRR. FMO1 and FMO2, on the other hand, can restore optical link segments in the transport layer itself through GMPLS.

FMO1 and FMO2 can deploy transport layer shortcuts and build direct adjacencies between routers, which reduces the amount of router hops in the data path and consequently the amount of router ports and optical transponders.

The FMO2 using multi-layer protection and restoration is more cost efficient than FMO1 in the initial build-out years of the network, and effectively accelerates the cost savings of FMO1 by 4 to 5 years. The reason is that both the FMO2 and PMO link topology only need to be partially meshed due to the ability to use dynamic restoration (MPLS FRR over GMPLS GR), while the FMO1 link topology is fully meshed due to the use of 1+1 link protection.

Although FMO1 has a higher connectivity requirement than FMO2 and PMO in the initial years, it rapidly catches up in later years when the further network build-out is driven by incremental capacity needs. FMO1 surpasses the PMO in Year 1.5 because GMPLS-based protection of aggregate traffic at the optical transport layer is more resource efficient than using MPLS-based protection at the routing layer.

FMO2 is able to maintain its initial cost advantage also in later years because it benefits from the same incremental GMPLS cost savings as FMO1, while enjoying additional savings from deploying GMPLS UNI as well. Cost savings are predominantly obtained from the way that EF and AF traffic is being carried in the various mode of operation, because best effort traffic is unprotected in each mode of operation with 1+N passive redundancy.

Service availability

The average service availability calculations for each traffic category in each mode of operation verify that the various network protection and restoration schemes do not trade off a lower cost against reduced service availability.


Figure 4. Service availability comparison

The results in Figure 4 show that for the given link availability, failure rate, and mean time to repair of fiber cuts, it is possible to meet the service availability expectation with any of the 3 design options.

Yet FMO1 and FMO2 meet these levels of service availability in a far more cost effective manner. In addition, the multi-layer protection and restoration FMO2 offers the highest and quickest returns on investments.

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To contact the author or request additional information, please send an email to techzine.editor@alcatel-lucent.com.

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