Cisco ONS 15600 Series

Cisco ONS 15600: Defining the Multiservice Switching

White Paper

Defining the

Multiservice Switching Platform (MSSP)

Defining the Multiservice Switching Platform in the Metropolitan Network

When the Multiservice Provisioning Platform (MSPP) was introduced in the North American metropolitan market a clear demarcation was created between what is considered 'legacy' optical transport equipment and what is now considered 'next-generation' optical transport equipment. In a significant leap in technology and product migration, the MSPP offered traditional TDM and SONET services ranging from DS1 to OC-192 as well as Ethernet service interfaces in a platform the fraction of the size of legacy SONET equipment. In addition to providing greater scalability and functionality from a platform that requires less space, the MSPP was extremely cost effective and clearly defined the requirements for a new market segment.

Before the introduction of the MSPP, the primary bandwidth handled on metro networks was slowing evolving from DS0s for voice and modem traffic, fractional T1s, T1s, and some DS3s with the introduction of frame relay and ATM services. Legacy SONET and SDH networks at the edge were optimized for transporting these low-bandwidth circuits, and cross connect functionality for bandwidth management was handled in a more centralized model. The introduction of the MSPP caused an inflection point that enabled service providers to build large high bandwidth networks at price points that were previously unrealizable. Access and metro networks quickly began to scale from OC-3/STM1 and OC-12/STM-4 rings to OC-48/STM-16 rings, multiplying the available bandwidth. With this influx of bandwidth, the service mix also began to change as it became less expensive to offer higher bandwidth services, and enterprise demand grew for Ethernet services. As the service provider's revenues shifted from primarily DS1s, and DS3s up to OC-n/STM-n and Ethernet services, the bandwidth management requirements shifted as well. In addition to an influx of bandwidth, the MSPP combined the functions of legacy SONET ADMs and cross-connects into a single cost effective platform. The resultant network design is highly simplified with lower price points and additional functionality. What once required multiple network elements was now addressed with one. However, while this migration toward distributed bandwidth management by moving cross-connect functionality to the edge of the metro network aided in the handling of new high-bandwidth metro traffic patterns, it also shifted the bandwidth bottleneck to the metro core.

Figure 1
MSPP and MSSP effects on service and bandwidth migration.

The global success of the MSPP has created another inflection point in bandwidth and traffic patterns, creating the need for a new, metro-optimized switching platform to aggregate and switch that higher bandwidth traffic. With higher bandwidth services now starting to dominate the metro, bandwidth management focus has shifted to STS or VC-4 levels, as opposed to DS0s and T1s. The introduction of the Multiservice Switching Platform (MSSP), has taken this design approach one step further. Providing more efficient scaling in large metropolitan areas, the MSSP enables more bandwidth in the metro core for an even greater density and diversity in higher bandwidth services. The MSSP also unlocks the additional service potential hidden within the MSPP Multiservice traffic originating at the edge of the Metro network can now be aggregated through a single, scalable multiservice network element at Metro hubbing sites—the MSSP.

In the diagram below a typical model of a metro optical network is presented. At the edge of the network, rings (represented by the green dotted loops) collect traffic from end users and enterprises networks. The metro edge rings are then aggregated onto the metro core rings (represented by the blue loops) by MSPPs (represented with blue barrels). MSPPs have enabled metro rings to grow from OC-3/STM-1 and OC-12/STM-4 up to OC-48/STM-16 and OC-192/STM-64 speeds. As the metro ring speed grows, the need to aggregate these higher bandwidth rings onto the inter-office network (represented by a red loop) grows as well. Traditional broadband digital cross-connects (BBDXC) could not optimally handle the aggregation role through the higher bit rates, creating a missing link between the metro ring aggregation point and the interoffice ring. It is at this point that an MSSP is placed.

Figure 2
Model of the Optical Network and the optimal placement of the MSSP.

Multiservice Switching Platform Requirements

In this white paper the characteristics that are necessary for a platform to fit the title of a true a carrier class Multiservice Switching Platform will be described.

Multiservice Capability

The MSSP is a true multiservice platform. In addition to having interfaces such as OC-48/STM-16 and OC-192/STM-64 for the high bandwidth metro aggregation, the MSSP also needs to eventually have interfaces for Ethernet and integrated DWDM as well. This multiservice functionality allows service providers to support current TDM services and carry the benefits of next generation services (such as Ethernet) into the central office while still utilizing their existing SONET or SDH infrastructure. The multiservice functionality also gives the MSSP and the MSPP tighter integration, allowing the service provider to carry the strengths and benefits of an MSPP from one edge of the optical network through the metro core and out to the other edge point.

In addition to data switching functionality, the MSSP must be able to leverage integrated DWDM functionality. Integrated DWDM allows the service provider to accomplish more in a single switching platform by mitigating the need to purchase another adjunct transponder to place traffic onto the DWDM infrastructure. By offering integrated DWDM, Ethernet, and STS/STM switching capabilities in a single switching platform, a service provider will be able to place the MSSP in the central office and use it not only for today's STS/STM switching and inter-office transport demands but also to generate additional high margin services as they are requested.

Figure 3
MSSP provides DWDM, Ethernet and STS/STM Switching in a single platform.

The basic multiservice functionality of the MSSP extends beyond the data and DWDM services mentioned above. Traditional services such as voice, carried on TDM circuits, and transport of ATM services are also handled by the MSSP in the Service Provider Point-of-Presence. The ability to aggregate diverse traffic types, efficiently pack the associated optical transport circuits and switch this traffic to TDM, ATM, and/or Packet routers and switches is a key feature of MSSPs. Traffic that is destined for another metropolitan area will be directed through the long haul network by the MSSP.

Figure 4
MSSP handling all services in the Service Provider PoP.

High Port Densities, Small Footprint

In order to aggregate the numerous high-speed metropolitan rings the MSSP needs to have a high port density, especially for OC-48/STM-16 and OC-192 / STM-64, the predominate metro core interfaces today. In addition to having higher port densities, the MSSP also removes inter-shelf matrix connections to achieve a footprint that is reduced significantly from legacy broadband cross-connect systems. The small footprint of the MSSP not only provides savings for the service provider, but also signifies that the MSSP is a leap in technological innovation.

Flexible Topologies for Network Planners

An MSSP needs to support a wide variety of network topologies. In SONET networks the ability to support path protection as stated by Telcordia's GR-1400, 2 Fiber BLSR and 4 Fiber BLSR as stated by Telcordia's GR-1230, and 1+1 APS is essential. In SDH networks the need for SNCP, MS-SPRing, and MSP topologies defined by ITU recommendations are also necessary.

Figure 5
SONET topologies supported by MSSPs.

Figure 6
SDH topologies supported by MSSPs.

Figure 7
Path Protected Mesh Network Topology.

The flexibility of PPMN not only offers ease of management and provisioning, but can also provide significant cost savings. These cost savings are realized when network span needs to be scaled to a higher bandwidth. Without PPMN functionality a complete path protection ring would have to be upgraded with new higher rate optics, even if only a fraction of the ring needs the additional bandwidth. With PPMN only those spans which require the additional bandwidth are upgraded, reducing the overall cost for supporting additional higher bandwidth services.

Carrier Class Scalability

The MSSP must scale beyond what is required in today's optical network. It must not only scale in terms of optical bit rates and number of channels, but also in terms of number of ports. Today's metro core networks are made up primarily of OC-48/STM-16 and OC-192/STM-64. However, as network traffic increases and higher speed rings are added to the metropolitan networks the MSSP must be able to scale to this demand. The MSSP platform needs to also be able to handle the future requirements of 40 GB and 160 GB interfaces as well as multiple optical channels using integrated DWDM technology. As the sheer number of supported interfaces grows, the MSSP needs the ability to expand beyond a single chassis to a multi-shelf system level, allowing the service provider to manage several thousand ports as if they were one cohesive network element. This increases the switching capacity from hundreds to thousands of ports, allowing it to meet the growing demands of metro ring aggregation as more and more higher bandwidth services are delivered.

Carrier Class Availability

The MSSP needs to support availability that meets the high standards of carrier class platforms. In addition to complying with all Telcordia and ITU recommendations on availability, the MSSP contributes to availability within the platform with the following functionality:

  • Complete Redundancy: There should NOT be a single point of failure on the MSSP. All common cards should be redundant, as well as any control or data connections on the backplane.

  • Faster Switch Times: Since applications are becoming more and more delay sensitive, the MSSP needs to improve on industry-standard switching times, targeting performance that exceeds the Telcordia or ITU recommendation by at least 50%. This allows the MSSP to support today and tomorrow's delay sensitive applications by providing new performance levels in the industry. Protection switching one ring or 64 rings at once should always produce the same dependable result.

Management and Provisioning Similar to MSPP

As the MSSP is introduced into the network, it should not have a detrimental effect on current provisioning times for services on today's MSPP network. Integration with existing MSPP provisioning software is key to reducing provisioning times and providing a common management look and feel for the network operators. Some of the key functions are listed below:

  • GUI and CLI interface options: The MSSP should have a graphical user interface (GUI) similar to that of an MSPP. This type of interface has gained acceptance among service providers, allowing technicians to perform operations, administrating, maintenance and provisioning (OAM&P) functions intuitively and with less training. In addition to the GUI the MSSP should have traditional command line interfaces (CLI) such as the widely accepted Telcordia TL1 interface.

  • Cross-Network Circuit Provisioning: The MSSP provisioning software should have the ability to provisioning circuits across network elements without the need to provision the circuit on a node-by-node basis. By providing cross-network circuit provisioning the MSSP can reduce the required time to provision a circuit to less than one minute.

  • Procedure Wizards: The MSSP management and provisioning software should employ the use of wizards. Wizards provide a step-by-step procedure for complicated functions. By employing wizards such features as span upgrade, software installations, and circuit provisioning the MSSP dramatically reduces the complexity of many OAM&P tasks.

Figure 8
Cross-Network Circuit Provisioning.

Designed with the Future in Mind

The MSSP needs to be designed to handle the demands for today's need of metro ring aggregation. In time, packet oriented traffic will begin to displace circuit oriented traffic and the demand will materialize for a platform that can not only handle the packet traffic, but can also aid in the transition form circuit traffic to packet traffic. The MSSP should be designed with this in mind. The MSSP platform needs to perform predominately TDM switching today for TDM, as well as Ethernet and IP encapsulated in TDM for transport. However, as the network increasingly migrates toward more of a pure packet infrastructure, the MSSP needs to have an architecture that can perform concurrent Layer 2 switching or even Layer 3 routing functions.

MSPP + MSSP: Circuit to Packet Transition Accelerated

Data services that are collected by MSPPs are characterized by bursty packet flow. Nailing up circuits that get used only a fraction of the time becomes an expensive proposition for the service provider. With the tight integration of MSSPs and MSPPs there is an opportunity to inspect the packets before transport and groom them into circuits at the packet level, not at the circuit level. The MSSP platform needs to recognize this important aspect of data service delivery and be designed to offer a variety of packet services at the metro core. The MSSP/MSPP integrated architecture offers the ability for data interfaces, as well as circuits carrying data, to have their packets inspected and forwarded on a variety of different headers. These include layer-2 Ethernet packets with VLAN IDs, IP packets with their TOS bits defined, or MPLS fields within the packet. Moreover, the packet inspection and forwarding work seamlessly with the data interface cards that are widely deployed within the MSPP platform to create an end-to-end, profitable data service. These cost saving are easily recognizable since Gigabit Ethernet integration into the MSSP can eliminate the need for an additional MSPP in the Service Provider PoP. The service provider immediately realizes savings from capital expenditure perspective (approximately $70K average selling price for an MSPP), and also realizes savings from an operations perspective since there is one less network element that requires management and valuable rack space. Utilizing the data capabilities of the MSSP in conjunction with the MSPP will result in a metro transmission network that will understand data, and deliver data services like Ethernet transport, TLS, Internet access or any Transport over MPLS in a profitable manner to the service provider.


Now that the need for the MSSP and its requirements have been defined, lets summarize the value it brings to a service provider. An MSSP can bring greater revenue potential, coupled with a lower first cost and lower life cycle cost. compared to today's BBDCXs. Over 40% in first cost savings is realized with the deployment model shown below.

Figure 9
MSSP capital expenditures savings model.

Following the economic downturn in recent years, Service Providers have been focused on reducing capital expenditures and looking to achieve the most value from every dollar spent on new optical equipment. The MSSP can address both of these needs. As illustrated in the figure above, current optical networks are constructed using separate elements for the broadband digital cross-connect functions and ADM functions. This deployment scenario has the traffic grooming done by the BBDXC and the optical service provisioning done by the ADM. With the MSSP, both functions in the Service PoP are combined into a single network element. This provides significant cost savings (>40%) not only in the initial capital investment but also provides cost savings over the life cycle of the product through reduced operational costs such as space savings (85%) and power consumption (75%).

With the MSSP solution, network management requires fewer resources due to features such as A-Z provisioning and flexible topologies such as PPMN. In addition, since the MSSP solution requires fewer ADMs, the total solution requires fewer network elements to manage and therefore can provide lower operational costs.

With the introduction of the MSPP the metropolitan optical network experienced new efficiencies and provided a foundation for new, profitable services. These efficiencies deliver an optical network that is a step ahead in cost and intelligence while providing greater revenue opportunities for service providers. While the MSPP has opened up new revenue streams, it has also driven the need for a new product in the metro. Optimized for today's high density TDM deployments but enabling a migration path to higher margin data services in the future, the Multiservice switching platform provides service providers a platform with scalability and carrier class features necessary to handle the demands of transport networks today and in the future.