PBT/PBB-TE Guide: Vendor Talk

We get 17 telecom equipment and components vendors to position themselves with respect to PBT/PBB-TE

April 3, 2008

53 Min Read
PBT/PBB-TE Guide: Vendor Talk

For Light Reading's ongoing coverage of PBT and PBB-TE, click here.

In the process of researching the report, A Guide to PBT/PBB-TE, Light Reading contacted several vendors with known or potential interest in PBT/PBB-TE or related technologies. While getting their views on the various aspects of the technology and its potential market, we found it helpful to summarize these discussions and publish the vendor remarks here in a separate report – a sort of standalone appendix.

With that in mind, what follows is an edited summary of each vendor's take on PBT/PBB-TE. For each company, we cited our primary source and noted what the company's network interests are in the service provider sector. Rather than bore you by reprinting every single question and every single response, we've summarized the discussions into the following headings:

Key characteristics and relation to other approaches

Key applications

Technology aspects (such as standards issues)

Market development and company approach

One more note: Yes, we know Ciena and World Wide Packets are the same company now. (See Ciena Completes WWP Buy.) But these interviews were done prior to the completion of the acquisition, and we found it interesting to spotlight both vendors' reactions separately. We're confident that you'll agree.

Here's the vendor commentary you'll find on the following pages:

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— Tim Hills is a freelance telecom writer and journalist. He's a regular author of Light Reading reports.

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Provides carrier-grade technology for Ethernet services delivery and OAM&P (operations, administration, maintenance, and provisioning). Comments from Scott Sumner, VP Marketing.

Key characteristics and relation to other approaches: No comments.

Key applications: Expects PBT to remain a transport function for the next couple of years, after which time it will begin to affect the edge of the network for establishing end-to-end Ethernet virtual circuits.

Technology aspects: No comments.

Company approach and market development: Has not seen a strong demand for PBT in its domain of Ethernet demarcation and end-to-end SLA (sevice-level agreement) creation and monitoring. Currently, sees Q-in-Q and S/C-VLAN tagging as sufficient for encapsulating customer traffic to provide transparent E-line and E-LAN services.

Related company news:

  • Accedian Touts Ethernet

  • FiberTower Deploys Accedian

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  • Accedian Targets Backhaul




Provides carrier-class Ethernet equipment solutions for delivering cost-effective metro Ethernet services over fiber, copper, and wireless access networks. Comments from Greg Gum, VP Marketing and Business Development.

Key characteristics and relation to other approaches: Sees PBT offering Layer 2 simplicity, lower cost, and deterministic behavior. From a carrier perspective, determinism is good, compared to to MPLS, which can dynamically take different routes through the network. Lower cost follows from providing a strong Layer 2 Ethernet transport, and only doing routing and switching further into the core, thus eliminating more costly Layer 3 (and above) devices. PBT solves some of the scaleability problems with MPLS, and also issues with traditional Ethernet switches, such as broadcast storms, MAC learning scale, and so on.

Believes that PBT compares quite well to MPLS particularly for scaleable, cheap Ethernet transport services. However, MPLS-VPLS for E-LAN-type services is more mature, while newer PLSB (Provider Link State Bridging – a multipoint option being developed by Nortel Networks Ltd. and being considered within the 802.1aq Working Group) options with PBT/PBB-TE are still in their infancy.

Key applications: E-Tree and a modified E-LAN via PLSB or hybrid PBT access/metro to MPLS core. Also could allow for scale when trying to combine residential IPTV and business services on a common platform for smaller carriers.

Technology aspects: Latest standards proposals are complete enough for point-to-point and point-to-multipoint deployments, which currently form the vast majority of Ethernet connections. However, several areas around PBT technologies remain to be solidified for it to be successful. Evolving areas of work, for example, are how it handles multipoint E-LAN, the standards ratification of 802.1Qay, and provisioning and management plane systems and OSS solutions for ease of dynamically provisioning, managing, and activating real-time Q-in-Q or PBT-based Ethernet service types.

There are several proposals for multipoint, and it is possible today to use a hybrid PBT approach with MPLS in the metro core, and also newer pure PBT approaches such as PLSB. However, as with all large multipoint implementations, regardless of approach, convergence time and recovery continue to be challenging.

Company approach and market development: ANDA is an Ethernet access, aggregation, and transport company focusing on providing access solutions over any media type supporting both PBT and Q-in-Q technology to large carriers. As PBT is deployed alongside Q-in-Q-based networks, the company’s access and aggregation boxes support conversions and crossconnect/switching between carriers (wholesale Ethernet-ENNI), as well as intermediary conversion and management of VLANs or PBT tunnels for carriers' business Ethernet services.

Sees PBT has become, and is becoming, more popular, and this is supported in the company’s access and aggregation systems. Believes that the development of resiliency, ring, and multipoint capabilities will be necessary for PBT to be a true contender to MPLS.

MPLS-core/PBT-metro solutions are likely for larger carriers with already deployed MPLS infrastructure investments in Cisco, Alcatel-Lucent, Juniper, Nortel, etc. equipment. Points out that only rarely do carriers retire/uninstall key network elements. However, some of the carriers have greenfield opportunities and could move more quickly to PBT/PBB.

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Provides carrier access Ethernet equipment. Comments from Mark McDonald, VP Product Management.

Key characteristics and relation to other approaches: In the access market there is little need for full-blown routing functionality. There is a need for efficient connection management and robust traffic management. End-points talk to one or possibly two other nodes, so the complexity found in Layer 3 protocols is overkill. Thus, Ceterus is studying both of the Layer 2+ protocols: MPLS and PBT. Believes that PBT is the simpler and more scaleable approach and is therefore more compatible with the lower price points and lower sophistication of CPE devices.

Does not see PBT replacing MPLS completely, but believes that PBT will evolve on its own and will be separate from MPLS. Each will have its place in the network, with PBT being the more suitable choice for access networks.

Key applications: Company argues that the complexity inherent with MPLS protocols is too great for the access "problem," and that the simplest technique, PBT, is therefore more desirable.

Technology aspects: No comments.

Company approach and market development: PBT will in general be the company’s preferred implementation, but will take the lead from its customers. Thus it has joined Nortel's EcoSystem initiative and will be providing PBT capability in its products when and where it makes sense to do so.

For Ceterus's aggregator product line, which is a combination Ethernet Switch and 3/1 DCS, the company is considering having both an MPLS option and a PBT option. This device is positioned most often close to the core of the network and may need to interface with an MPLS core device or a PBT device for control-plane capabilities. So the aggregator will likely need to be able to interface with both types of device in this application. If it is positioned closer to the edge of the network, PBT will likely be the favored option.

Related company news:

  • Alpheus Picks Ceterus

  • Nortel Pushes More PBT



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Provides optical, Ethernet, and data networking, and focuses on helping customers transition their networks for maximum value using innovative technology. Comments from Mitch Auster, Senior Director of Solutions Marketing.

Key characteristics and relation to other approaches: Although MPLS/VPLS is the most mature technology available today, it is also commonly viewed as cost-prohibitive for access and even metro deployments. That T-MPLS is being defined as a simplified version of MPLS to reduce complexity and cost and add transport capabilities supports this view.

Providers are left with only two options: T-MPLS or PBB-TE. Despite being at different stages of the standardization process, a comparison of the two expected standardized specifications shows many similarities:

  • Creation of connection-oriented transparent tunnels

  • Support for pseudowire and Ethernet services

  • Scaleability needed for large provider network deployments

  • Requirement to configure explicit paths

  • Definition of hard QOS and sub-50ms fault-recovery mechanisms

  • Standard definition of OAM capabilities

These two specifications are very similar from a functional perspective, but PBB-TE offers something that T-MPLS does not: a direct tie-in with Ethernet.

PBB-TE is a Layer 2 transport standard that builds on a Layer 2 standard that has its own Layer 2 addressing scheme, Layer 2 OAM standards, and universal Layer 2 client. T-MPLS is a Layer 2 transport standard without an inherent Layer 2 (MAC) addressing scheme, with its own OAM standards, and with support for alien clients.

From a standardization perspective, T-MPLS contains definitions for the transport of IP/MPLS and pseudowire services for legacy applications (ATM, frame relay, Ethernet, etc.), with relatively well defined functional architecture and transport hierarchy specifications. T-MPLS forwarding has been demonstrated by a number of vendors. On the other hand, although T-MPLS includes the adoption of ITU-T's Y.1711 recommendation for its OAM methodology, it lacks some of the management tools provided by transport networks, and control-plane signaling is still a key area for future development, with the expectation of perhaps using generalized multiprotocol label switching (GMPLS) protocols. The interoperability of MPLS and T-MPLS is a work in progress.

Key applications: Wireless backhaul, E-line services.

Technology aspects: PBB-TE (also known as 802.1Qay) is the standard version of provider backbone transport (PBT) as defined by the IEEE. PBB-TE tailors PBB to become suitable for point-to-point deterministic transport. It disables the flooding/broadcasting behavior of PBB and eliminates spanning tree, replacing it with explicit (and optional) redundant-path configurations and built-in continuity checks, yielding sub-50ms fault recovery. The B-VID field is used together with the destination MAC address to indicate a unique primary and secondary path and optionally segregated QOS levels across the network.

As in traditional bridged networks, PBB-TE provides element and topology auto-discovery while giving the provider full control over the establishment of network paths on a per-service basis. Its connection-oriented nature enables connection admission control to allow for hard QOS. Being Ethernet based, PBB-TE benefits from the 802.1ag standard, also known as Connectivity Fault Management (CFM), as well as other standards that define the OAM tools necessary to deploy and manage carrier Ethernet networks. Because of the flexible nature of Ethernet and the deterministic nature of PBB-TE, hard QOS and sub-50ms fault recovery are supported in all network topologies (ring, mesh, hub-and-spoke, etc.)

From a standards track perspective, the PBB standard is at Revision 3.8, approved in October 2007. Version 4.0, proposed in November 2007, provides minor changes to the functional specification. As with T-MPLS, the PBB-TE standard is still being defined. It has reached the stage where multi-vendor interoperability has been demonstrated.

Company approach and market development: Argues that telcos currently investing in PBB-TE are laying the foundation for a next-generation all-Ethernet network, where the provider infrastructure will be tightly wrapped around Ethernet standards, and benefiting from the costs of Ethernet technologies. PBB-TE delivers the scaleability and feature set required to transport the full suite of business services, along with the routed residential traffic. As such, PBB-TE could be poised to become the converged infrastructure many have been seeking.

Strategy is centered on the notion of using connection-oriented Ethernet to backhaul traffic from the customer premises, as well as end offices themselves, to a more metro-centralized service edge. Two versions of this are supported in the CN 4200 G10 module that was announced recently.

The first implementation is a VLAN crossconnect, which is very similar to PBB-TE: It is provisioned, deterministic, and eliminates everything that makes traditional LAN Ethernet unpredictable – Spanning Tree, flooding, and so on. Secondly, PBB-TE is supported in the CN3100 Ethernet Access Series, as selected by BT, and will be added to the CN4200.

Strategically, the company will add PBB-TE into any product from the customer premises and through the access and aggregation portions of the network – at least through the metro. It is likely to be supported by the core products, but the company will wait to see whether this will mean a gateway from PBB-TE to IP/MPLS in the backbone, or whether there is a movement to use PBB-TE to replace, or at least cap or minimize, the investment in IP/MPLS in the core.

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  • PBT Key to Ciena Acquisition

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  • Ciena Enhances 4200 With Ethernet

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Provider of network routing and switching solutions. Comments from Ian Hood, Market Manager, Service Provider Routing and Switching.

Key characteristics and relation to other approaches: PBB-TE has obvious and potentially desirable characteristics – an extension and simplification of carrier Ethernet networking and provisioning that may increase its cost-effectiveness. However, it is currently very limited to simple point-to-point manually provisioned connections and lacks the high scaleability and functionality, such as multipoint, QOS, and resilience, of MPLS, which is a well established and widely implemented multiservice technology.

Company does not plan to support T-MPLS, primarily because MPLS can already do whatever T-MPLS will when it is completed. In this LRTV custom video, Cisco makes a case for Ethernet and MPLS in carrier networks:
Key applications: Possibly for a purely point-to-point scenario with manual provisioning, such as tying Ethernet at the very edge of the network into a provider’s MPLS network.

Technology aspects: PBB-TE is as yet incomplete, and is moving in the direction of becoming a full multipoint and traffic-engineering standard. This is a large task and effectively risks re-inventing technologies already used within MPLS. No work has yet been done on some crucial areas, such as signaling.

{column}Company approach and market development: Supports native IEEE Ethernet 802.1ah (PBB) and is monitoring the development of PBB-TE, where it supports the work on the developing IEEE 802.1aq control plane. However, maintains its long-held view that MPLS is the preferred solution, and as yet sees no substantial demand for PBB-TE.

Argues that there is likely to be a balance between MPLS and native Ethernet technologies, with MPLS moving progressively outwards from the core into the aggregation networks and beyond because of its combination of high functionality and multiservice capabilities. In some cases, MPLS will go end-to-end to the CPE; but in others, carriers will use native Ethernet-based infrastructures to connect to the MPLS aggregation and core networks.

Related company news:

  • Carrier Ethernet: Who's in Control?

  • PBT Cost Claims Questioned

  • Cisco Takes Hold of the Edge




Provides networking infrastructure equipment for carrier and service provider networks. Comments from Jeremy Brayley, Director of Technology Strategy.

Key characteristics and relation to other approaches: Says PBB is a way to scale multipoint Ethernet services by using MAC-in-MAC tunneling. PBB’s chief advantage over Provider Bridging (Q-in-Q) is to hide customer MAC addresses from a service provider core through the use of MAC-in-MAC tunnels. Once encapsulated in service-provider MAC frames, the frame forwarding is based on the familiar flooding, learning, and Spanning Tree model of bridged Ethernet. PBB is used for multipoint services and can be used for point-to-point services. However, PBB offers no significant advantages for point-to-point services. For example, there is no way to do traffic engineering for point-to-point services. There are no fast protection or recovery techniques outside Spanning Tree.

PBT essentially makes PBB useful for point-to-point Ethernet services. It uses the same kind of MAC-in-MAC tunnels, but rather than using the flooding, learning, and Spanning Tree, the service provider can explicitly configure the MAC-in-MAC tunnels. This is a lot like building static bridge table entries in the PBT core devices. Once there are static tunnels like this, there will have to be a protection mechanism. For PBT, the approach is usually to offer end-to-end 1:1 or 1+1 protection by building two paths between a pair of service endpoints.

MPLS is fairly well entrenched as a core technology and useful for delivering a large variety of services across a core network. Those services are not limited to Ethernet, and include other pseudowire types (Frame Relay and ATM) as well as IP VPNs. PBT will compete with MPLS for point-to-point Ethernet applications. PBT might be useful for point-to-point Ethernet access scenarios where mesh connectivity and restoration are not available or perhaps not needed.

Some key characteristics of PBT are:

  • It is for point-to-point services only. It cannot be used for multipoint services because broadcast, multicast, and unknown packets are discarded at the edges, so they are not forwarded through the core.

  • To offer multipoint services, there are two choices: (a) Place a PBB node as the edge device facing the PBT core (PBB node and PBT node in a serial arrangement); or (b) run PBB and PBT in parallel on a single node. This means that multipoint services will use non-traffic-engineered PBB, and point-to-point services could use PBT.

  • PBT is described as "pure" Ethernet when compared to Ethernet-over-MPLS techniques, because it uses a hierarchy of VLANs and MAC-in-MAC encapsulation to carry customer frames, whereas MPLS requires separate labels.

  • Signaling is out of the scope for PBB-TE, meaning that PBT paths must be provisioned by network management.

In comparison to MPLS, PBT is only for point-to-point Ethernet services such as MEF-defined EPL and EVPL services. An apples-to-apples comparison would be between PBT and PWE3 (Ethernet Pseudowires over MPLS).

PBT advantages compared to MPLS include:

  • PBT networks can use the same Ethernet service OAM protocols in both the customer and provider networks. PBT proponents will point out that MPLS requires MPLS OAM protocols in addition to Ethernet services OAM.

  • There is a "sniffer in the middle" argument that says that a customer can look at a PBT frame anywhere in the network and can tell its destination, because MAC addresses are global. MPLS uses link-local labels, and the label can change along the path, so a sniffer can’t tell the ultimate destination of the MPLS tunnel. This is a popular argument, but meaningless, because customers do not troubleshoot networks with sniffers, and normal MPLS tracing protocols can determine the path of a tunnel if MPLS signaling does not already give the interceptor enough information.

  • PBT proponents will also claim that PBT hardware is less expensive. However, often they are comparing PBT switches with core routers and not with the latest generation of Ethernet-optimized carrier-Ethernet/MPLS platforms.

MPLS advantages compared to PBT include:

  • MPLS provides several protection and restoration options, not just end-to-end protection. RSVP-TE Fast Reroute allows scaleable local repair for MPLS-based services.

  • MPLS already supports signaling or static provisioning of tunnels and Ethernet services.

  • MPLS has a long history of deployment and interoperability.

Key applications: It is possible that PBT could be appealing for cellular backhaul applications in the short term. However, the next generation of cellular data networks (WiMax and LTE) will require multipoint backhaul not supported by PBT.

Technology aspects: The IEEE PBB-TE work is fairly immature, and it normally takes several years to produce a ratified standard. Multipoint and multicast are not currently supported, nor do they seem to be on the radar for PBB-TE at the moment.

More work is needed on how 1:1 protection will be accomplished by using PBB-TE. PBT proponents claim that 802.1ag service OAM would be used as a failure-detection mechanism for protection switching. However, since it is an IEEE protocol, 802.1ag was not intended for protection switching. The ITU-T Y.1731 flavor of Ethernet OAM is intended to be applicable for protection switching.

Company approach and market development: The company has ensured that its carrier Ethernet products can support the MAC-in-MAC forwarding required for PBT. However, it believes it is more likely to use such capabilities to support multipoint services using PBB, rather than to support PBT.

Is interested in PBB for multipoint application, and thinks that the MAC-in-MAC technique of hiding customer MAC frames is potentially useful for large-scale bridged services. Plus, PBB can be combined with MPLS to reduce MAC learning in certain H-VPLS deployment scenarios. Can see future deployments where PBB is used in access or aggregation domains, with MPLS used in metro core and backbone domains.

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Provides connection-oriented metro Ethernet, and focuses on a service-centric approach based on dynamic adaptation to traffic conditions to optimize transport efficiency. Comments from Adam Dunsky, co-founder. Dunsky, it's worth noting, is also featured in the following LRTV custom report:

Key characteristics and relation to other approaches: Says that, in essence, the PBT concept comprises two groups of technology.

(1) IEEE PBB-TE (802.1Qay): An Ethernet standard in progress that turns Ethernet’s learning behavior into deterministic and managed behavior. PBB-TE introduces several unique features that differentiate it from "regular" Ethernet, and these are commonly identified with PBT:

  • Spanning Tree is disabled

  • Learning is disabled

  • Forwarding tables are managed externally and centrally

  • Traffic engineered (with path provisioning).

The result is a connection-oriented Ethernet technology that creates predefined paths across an Ethernet provider network.

(2) Additional tools and protocols that include:

  • IEEE 802.1ag provides OAM, adding CCM to Ethernet, which enables protection similar to Sonet/SDH UPSR and is instrumental in turning plain Ethernet into carrier and managed transport behavior. PBT derives connection monitoring from IEEE 802.1ag (Connectivity Fault Management) to enable the use of protection paths.

  • IEEE 802.1ah (also known as MAC-in-MAC or Provider Backbone Bridges) enables the separation between a provider network and a customer network, and enhances scaleability.

  • ITU-T Y.1731 generates alarm indication signals to spawn switch protection.

  • External Path Management application/NMS is used to calculate paths in a PBT network.

{column}Argues, as a result of the preceding, that the key characteristics of PBT are:

  • A (simple) Ethernet technology

  • The ability to provision deterministic paths similarly to Sonet/SDH

  • Centralized manageability similar to Sonet/SDH

  • Using tunnels to multiplex EVCs at edges, while the use of tunneling creates a scaleable solution

  • An edge/core approach by using existing Ethernet core switches, which contributes to lower operational and capital expenditures, while an external control-plane enables simple SDH-like manageability, with correspondingly lower opex

MPLS was deployed initially as an IP-helper to provide connection-oriented tunnels through carrier IP networks. These MPLS tunnels provided scaleability, traffic engineering, QOS, and resilience over a single IP/MPLS network. On top of this tunnel infrastructure, service providers began offering new converged Layer 3 (IP-VPN) and Layer 2 (VPWS, VPLS) MPLS services. MPLS uses Ethernet only as a data-link frame format, and all network/traffic engineering is done by other/additional protocols.

MPLS and PBT have some contrasting characteristics:

  • While PBT is a centric approach (where the control plane is external and all paths in the network are managed centrally), MPLS is based on IP and IP routing protocols such as OSPF (a node-by-node approach).

  • MPLS is a much more extensive solution that handles much more than connectivity – for example, bandwidth management, QOS, and so on – by using extensions such as MPLS-TE and RSVP-TE.

  • As a result, MPLS is more complex, using bigger routers and requiring more knowledge to control – but it also has a better fit to IP applications that are more natural to IP technology.

  • Relying on IP routing schemes, MPLS has an inbuilt support for a vast addressing scheme, and is therefore considered to be a more scaleable technology.

Key applications: No comments.

Technology aspects: Important challenges remain to be met, including:

  • Development of external control mechanism with strong optimization and provisioning tools

  • Achieving feature-rich yet simple QOS mechanisms

  • Adding efficient robust multipoint support

  • Matching MPLS feature-rich capabilities, while keeping the technology simple.

Company approach and market development: Supports PBT, and argues that PBT’s simplicity is its core appeal, but to win in the market it must offer more advanced features, such as traffic engineering, end-to-end QOS support, and dynamic bandwidth management similar to what is available with MPLS technology. In evolving to these advanced capabilities, however, PBT must not lose its simplicity and low cost. Overall, PBT’s deterministic nature can enable a solution that can be both simple and feature-rich.

Believes that PBT is likely to prevail where the dominance of MPLS slows down – essentially, at the metro and access networks. In these areas, MPLS equipment does not make economic sense while there is a strong demand for Ethernet and Ethernet services. The core networks will likely be predominantly MPLS-based. Sees a broad agreement that PBB-TE equipment will, at minimum, replace the switch portion of the CESR market by 2012 as the PBB-TE standard matures and becomes the new de facto carrier Ethernet standard for the metro.

Currently, company offers a Service Provisioning Platform and Metro Aggregation Edge Switches running Dynamic Traffic Engineering (DynTE), a traffic-management technology that controls traffic at the network edge in real-time, based on prevailing traffic conditions, to provide connection-oriented services with QOS and high-capacity utilization across an Ethernet core (whether supported by MPLS, Sonet/SDH, or native Ethernet).

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Provides Ethernet solutions for network connectivity and IP-based communications. Comments from Peter Lunk, Director of Service Provider Marketing.

Key characteristics and relation to other approaches: Offers low costs and familiar Sonet/SDH-style point-and-click circuit provisioning for carrier Ethernet networks.

Company sees MPLS as encountering some scale and cost problems as it extends further towards the network edge, although its capabilities are highly desirable. PBT/PBB-TE offers way of extending services to and from the MPLS core, which overcomes these issues.

Key applications: Initially MEF E-line and leased-line-replacement services, mobile backhaul, and Frame Relay replacement/upgrade.

Technology aspects: No comments.

Company approach and market development: Sees PBT/PBT-TE complementing MPLS, as carriers are keen to maintain their existing MPLS core investments. Some smaller providers, without existing MPLS cores may consider a PBT/PBB-TE core as well. MPLS interworking will therefore be crucial, and company has had MPLS capabilities on its products for some time.

Argues that vendor differentiation will flow from underlying switch resources that will help to solve service-layer issues, for example, VLAN tag translation and tag manipulation in passing between two different carrier networks, or QOS or rate limiting for residential applications.

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  • Extreme Launches PBT

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Provides Layer 2.5 aggregation, interworking, and migration solutions for new Ethernet (E-line, E-LAN, and E-tree) and existing circuit-based data services. Comments from Rob Keil, VP Marketing and Business Development.

Key characteristics and relation to other approaches: Compared to IP/MPLS in metro networks, PBT promises to offer lower costs and less operational complexity. PBT is expected to require far less capital to deploy than Layer 3 IP/MPLS routers for metro deployments. Possibly more important than the capital costs, some service providers contend that the operating complexity and cost of IP/MPLS networks increases dramatically with scale. This is because IP/MPLS provides a dynamic network that becomes difficult to manage with mass deployments. Another appeal of PBT for transport applications is that it uses operator-initiated point-to-point circuits to deliver services. From a transport perspective, this makes PBT a potentially disruptive alternative to Sonet/SDH because of its familiar Sonet/SDH-like provisioning and management attributes, with significantly lower costs/bit for data transport.

PBT is expected to gain momentum in metro access networks, while MPLS will continue to be successful in regional and wide-area core networks. Given this relationship, carriers will need a cost-effective, scaleable interworking solution between PBT metros and MPLS cores.

Key applications: PBT addresses service provider needs for point-to-point (E-line) services such as EVPL (Ethernet Virtual Private Line) applications in the metro network. From a transport perspective, this makes PBT a disruptive alternative to Sonet/SDH. PBT is also appealing for wireless backhaul, which is inherently a point-to-point application that requires stringent QOS support – main attributes of PBT.

PBT does not directly address multipoint-to-multipoint (E-LAN) and point-to-multipoint (E-tree) applications. Therefore, PBT alone is not a complete carrier Ethernet solution for service providers. However, Hammerhead Systems has presented recent innovations to address PBT-based E-LAN and E-tree capabilities.

Technology aspects: PBT is being addressed by the IEEE 802.1Qay project under the name PBB-TE. To keep PBT’s appeal to carriers, it must remain a simple and cost-effective technology. This means that PBT must retain its intrinsic point-to-point nature. However, it does not mean that metro networks cannot support E-LAN and E-tree services over PBT. As demonstrated by Hammerhead, E-LAN and E-tree services can be provided over metro networks using point-to-point PBT trunks. Thus, multipoint and multicast services can be supported over PBT networks without requiring changes or extensions to PBT.

Company approach and market development: Hammerhead says it is agnostic on the philosophical debates between MPLS and PBT. Feedback from customers has led the company to create solutions for a hybrid network model, which assumes MPLS cores and the introduction of PBT-based metro networks. Hammerhead’s HSX 6000 multiservice MPLS switch was enhanced in April 2007 by the launch of the PBT Service Gateway software feature. This allows direct interworking between PBT networks and MPLS/VPLS networks, without requiring any special hardware.

In November 2007, Hammerhead introduced its Carrier Ethernet Multicast Framework (CEMF), which enables new innovations to address PBT-based E-LAN and E-tree capabilities, as well as E-tree for MPLS. It enables service providers to realize multipoint and multicast capabilities in carrier Ethernet PBT networks as well as MPLS networks, and includes seamless interworking of PBT-based E-LAN and PBT E-tree services with their counterparts in MPLS networks via the PBT Service Gateway software feature. Service providers can thus support both MPLS cores and PBB-TE metro networks for services such as IPTV, business videoconferencing, managed enterprise video service offerings, L2 VPN business services, and financial multicast applications.

The HSX 6000 PBT solutions are created with an open model that enables partnering with a broad set of OSS and control-plane vendors. In November, 2007, Hammerhead announced the first of these partnerships with its collaboration with Soapstone, a provider of centralized control plane software solutions for provisioning PBT-based networks. This will involve developing Soapstone’s software adapters to support Hammerhead’s products.

Related company news:

  • Hammerhead Unveils PBT Smarts

  • Hammerhead Demos PBT




Provides test and measurement equipment. Comments from Mike Haugh, Senior Product Line Manager.

Key characteristics and relation to other approaches: Sees PBB-TE as a significant component of the area of carrier Ethernet, as it relies on two next-generation technologies – MAC-in-MAC and CFM.

Key applications: Next-generation medium-haul or metro networks.

Technology aspects: Assessment of realistic scaleability is currently of interest. The theoretical scaleability is very high because of the large PBB address space for path building. However, the network must run an OAM CFM continuity check, and there is also a control plane protocol running over the tunnels for status of the tunnel -- so the true scaleability has to be measured.

Company approach and market development: Sees the typical trend of testing occur, with a move from functional, single-vendor testing, to the testing of interoperability, signaling, and performance, together with high availability and QOS testing. Company has developed what it refers to as stateful PBB-TE, where the test equipment becomes a tunnel endpoint and can initiate continuity check messages, for example. This allows more statistics to be exposed from the tunnel state, and a traffic wizard allows the generation of unique Layer 2 flows over the tunnel.

Company is looking at expanding its test suites with conformance testing once PBB-TE becomes a finished standard. Is also interested in potentially new areas of testing that PBB-TE may introduce, such as the active automatic testing of paths as they become established by the provisioning system.

Related company news:

  • Ixia Tests MACSec

  • THUS Deploys Ixia




Provider of IP networking and security products. Comments from David Boland, Senior Product Marketing Manager, MX-series of Ethernet Services Switches.

Key characteristics and relation to other approaches: PBT is a new transport technology, which requires new standards, and new provisioning, protection, interworking, and troubleshooting mechanisms. IP/MPLS provides a proven and reliable service transport, and also the substantial benefit integrating the metro with the core by using common forwarding and control planes, since IP/MPLS is already used in the core.

PBT proponents claim that it can offer significant operational-expenditure savings compared to MPLS, which is unproven and questionable considering the increased cost associated with an OSS-driven control plane, as well as the additional cost to add services via a different service layer like MPLS.

PBT has received some interest from service providers and has been deployed in small network pockets or in lab or preproduction environments.

Key applications: PBT is a pre-standard transport technology with limited applicability in small, vendor-specific portions of primarily metro networks.

Technology aspects: No comments.

Company approach and market development: Juniper has been monitoring PBT developments and will continue to do so as the technology matures and standards emerge. Company remains focused on strategy of delivering a suite of best-in-class, next-generation infrastructure solutions that meet the requirements of its customers.

Related company news:

  • Juniper Splits Out Its Control Plane

  • Scott Kriens, CEO, Juniper Networks




Provides ASIC carrier Ethernet silicon solutions. Comments from Steve Christo, Director of Product Marketing, and Maurice Gleeson, Chief Technology Officer.

Key characteristics and relation to other approaches: PBT is primarily a point-to-point technology. It is provisioned, and it is easier to manage and traffic-engineer point-to-point technologies. Carriers understand this model very well from their Sonet/SDH legacy.MPLS will stay at the core as a Layer 3-routed protocol and will not go away overnight, if at all – but it is less proven as edge/access technology. So the relationship between PBT and MPLS is probably one of coexistence.

Key applications: Connection-oriented circuits in an Ethernet world. Sonet/SDH has fixed-sized pipes, which can be arbitrarily aggregated with VCAT/LCAS. There are no fixed bandwidth increments for Ethernet – instead, the pipe is sized with traffic management, which may be per VLAN or per COS per VLAN, etc. This produces variable and exactly right-sized bandwidth. Argues that PBT has a self-fulfilling destiny: Ethernet is well understood; Layer 2 has lower opex than Layer 3; and momentum is behind PBT.

Technology aspects: PBB and PBB-TE are well defined, and no change is expected in the data plane, as was proven through the EANTC 2007 interoperability event. The IEEE 802.1ag specification is also fairly far along. However, there are some areas that will need to be cleaned up to avoid any misinterpretation or confusion among vendors.

The PBB-TE standard does support point-to-multipoint now. Multipoint-to-multipoint is neither explicitly covered nor precluded, and there is some debate as to whether this can or should be supported.

Company approach and market development: Fully supports PBT, but argues that the issue is not just about PBT, and that the whole system needs to be carrier grade – not just providing PBT protocol support on enterprise silicon. Some of the carrier features that are required include network scaleability, traffic management (QOS), OAM, and protection.

Company says it has a second-generation approach compared to first-generation solutions that use either enterprise Ethernet silicon with FPGAs or NPUs, which do not scale and add complexity to design. Says NPUs typically do not have the CPU processor cycles to handle more than a few protocols at any one time.

Sees PBT marking a potential paradigm shift, as it starts to enable a centralized management plane – as opposed to a distributed and costly protocol stack – and also lower-cost, carrier-class Layer 2 switches that can be managed through such centralized management applications.

Has recently launched the Brooklyn-10 ASIC, which supports both IEEE and IETF services for diverse deployments: provider bridging (PB, PEB, PBB, PBB-TE) and MPLS-based L2 VPN services (VPLS, VPWS, H-VPLS). It gives a network scaleability of up to 8k EVCs, 4k VLANs per port, up to 128k MAC addresses, and up to 16k pseudowires. It supports service- and link-layer OAM standards and QOS, with classification, policing, congestion avoidance, queuing, and scheduling.

Related company news:

  • Startup Spotlight: Lightstorm Networks Inc.

  • Lightstorm Charges Into Ethernet



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Provides packet optical networking equipment for service providers and large enterprises. Comments from Ken Davison, VP Marketing and Business Development.

Key characteristics and relation to other approaches: Company's CET solution integrates PBT/PBB-TE (as a connection-oriented technology) with wavelength (Layer 0, 2.5, and 10 Gbit/s) and subwavelength (Layer 1, OTN/GFP-based GigE) switching, to deliver a highly scaleable, multilayer, packet optical transport platform. Sees PBT/PBB-TE as providing an underlying transport and grooming infrastructure, and gives a more flexible, "Ethernet friendly" alternative to using Sonet/SDH alone in this role. PBT/PBB-TE's traffic engineering, determinism, and path-restoration capabilities retain essential elements of a solid, carrier-grade transport layer. Additionally, PBT/PBB-TE enables access into the Layer 2 traffic to enable grooming and aggregation of services, and so on, which are presented on a single interface. Argues that, as more and more equipment incorporates Ethernet as its primary networking interface, connection-oriented Ethernet will over time displace Sonet/SDH as a transport networking technology.

Key applications: Company is focused on integrating PBT/PBB-TE capability to support its CET solution in the following key applications:

  • Ethernet access and backhaul – aggregation and backhaul of Ethernet services across the growing number of service provider access points to the metro edge

  • Private-line replacement

  • Mobile backhaul, with the addition of Synchronous Ethernet Support (G.8261).

Technology aspects: No comments.

Company approach and market development: Company has implemented PBT/PBT-TE on its 7200 OSP platform – an Intelligent Ethernet Gateway (IEG). The IEG is a purpose-built packet transport engine that can originate, terminate, transit, and aggregate PBT/PBB-TE traffic directly onto Layer 1 / Layer 0 optical transport.

The key premise of the company’s CET approach to the packet optical transport network (POTN) is to ensure that service-provider architectures can separate the service layer (Layer 3) from the underlying transport topology. By introducing a fully integrated, multilayer (Layers 0, 1, and 2) transport switching capability that enables switching, aggregation, and grooming of traffic at different granularity, on an end-to-end, fully managed basis, the POTN can deliver traffic to the required service delivery platform (SDP) in the service layer only for traffic that needs to be terminated/processed by that specific SDP. Says that this removes the need for the service layer to be involved in basic transport switching at tandem nodes – a function that not only uses up expensive service-layer processing for basic transport, but increases the utilization of ports between the transport and service layer (as traditional WDM nodes and/or IP-over-WDM architectures need to deaggregate traffic back to the client interface to the switch).

Argues that this new model of transport networking – with the emphasis on multi-layer switching, rather than closed ring transmission – decouples the service and transport layers, so that:

  • A single POTN can support multiple service-provider IP service layers and have a dedicated point of interconnect/handover of traffic to the relevant SDP for added security and regulatory compliance.

  • Capex savings are obtained as non-revenue-generating client ports on both the WDM and service layer (PE routers and Ethernet switches) are not required for tandem switching.

  • Operational-expenditure savings are obtained by consolidating transport and Ethernet aggregation and switching onto a single network element.

  • Time-to-revenue and service velocity are improved as provisioning of services is done end-to-end across the transport layer without the need for manual patch cords of client interfaces between the transport and service layers, and the reprogramming of complicated IP switches.

  • Delay, jitter, packet loss, and security are reduced for real-time traffic as a CET solution uses deterministic, traffic-engineered connections across a multilayer transport architecture. CET uses the function of Tunnel Resource Management (TRM) to determine the optimum path across the POTN. Where possible, all transit traffic is switched at Layer 0 or Layer 1 to minimize the cost and QOS effect of transit-packet processing.

Related company news:

  • Vendors Clash Over PBT

  • Meriton Joins Ecosystem

  • Nortel Touts Ecosystem




Prime mover of PBT. Comments from John Hawkins, Senior Marketing Manager, Carrier Ethernet.

Key characteristics and relation to other approaches: PBT is but one of several technologies (along with PBB, 802.1ag/Y.1731 and, more recently, Provider Link State Bridging (PLSB), a multipoint option being developed by Nortel (described below) that comprise the overall solution Nortel calls carrier Ethernet. Each of these technologies provides several benefits.

(1) PBB: Defines separate backbone and end-user MAC addresses, along with unique service IDs. This provides:

  • Scale: Hierarchical MAC addressing allows added scale by eliminating the so-called address explosion problem. End-user addressing need not be learned in the core of the network. The service ID allows for millions of service instances to be identifiable on the network. Core systems can now treat differentiated services appropriately.

  • Security: Separation of end-user and provider domains eliminates a variety of security issues (such as man in the middle and denial of service) by maintaining strict customer separation.

  • OA&M: The globally unique service ID and the backbone address allow immediate identification of packets throughout the network, which leads to robust tools that can readily diagnose and react to problems when they occur, and also facilitates performance measurement.

(2) PBT: Turns off Spanning Tree Protocol (STP) and the flooding of unknown MACs. Instead, the forwarding database is populated by an offline management tool. This provides:

  • Scale: With STP out of the way, no links/ports are blocked simply for loop avoidance. The routes taken through the network are now predetermined and totally predictable, which in turn leads to the ability to traffic-engineer the network, avoiding congestion and guaranteeing SLAs. Also, single-endpoint provisioning means new services can be provisioned across the network without "touching" each and every network element.

  • Security: Since packets with unknown destination addresses aren’t forwarded, they don’t end up in places where they aren’t supposed to be, avoiding an additional security concern.

  • OA&M: Paths through the network are easily defined, provisioned, and monitored for end-to-end performance. Anomalies are readily apparent without a knowledge of the state of the network, avoiding considerable complexity and cost.

(3) 802.1ag/Y.1731: Provides the tools needed for end-to-end performance monitoring. Benefits include:

  • OA&M: Continuity checks, loopbacks, path traces, and performance metrics (latency, jitter, and loss) are defined in these two standards.

  • Resilience: End-to-end 50ms protection in a multivendor environment is made possible by the CCM capabilities.

  • Scale: A network cannot be grown if the services that flow over it cannot be monitored.

(4) PLSB: Provides a replacement for Spanning Tree Protocol as the control plane for an Ethernet network and allows rapid provisioning of any-to-any services, minimizing operational costs.

  • Scale: Using a link-state protocol (IS-IS) it is possible to provision the shortest paths to each end-point in a multicast network, allowing better performance and efficient use of links (replication only where appropriate, no blocked links to avoid loops).

PBT is Ethernet, so it uses normal Ethernet forwarding behavior to create Ethernet tunnels. The network can be based on standard Ethernet switches and therefore retains the simplicity and cost-effectiveness that made carrier Ethernet attractive in the first place. MPLS, in contrast, uses a battery of protocols to accomplish what carrier Ethernet does in two or three (one of them being Ethernet itself). Each of these adds significant complexity and significant cost to the network infrastructure. To hear Nortel's CTO, John Roese opine on PBT's merits, check out this LRTV interview from NXTcomm 2007:

Key applications: Three major applications are currently driving interest in PBT-enabled carrier Ethernet: residential service backhaul, business services, and mobile backhaul. All three are in turn driven by the high growth of video-based, end-user, IP-based applications. The deterministic, secure, and reliable tunnels made possible by PBT make it a technology of interest, given it also enjoys significant cost advantages over the sole alternative available today.

Technology aspects: Work on PBT/PBB-TE is well underway, but will require 12 to 18 months before being considered stable. There are few contentious items, and progress has been brisk to date. The major discussion topics have been on protection mechanisms required to define backup tunnels in the event of failures, and on the appropriate formats for the continuity fault checking messages that flow through the system. The recent interoperability tests at the Carrier Ethernet World Congress and MPLS & Ethernet World Congress were based on the current draft PBB-TE standard. The successful interoperability demonstrated shows that there is good progress being made.

Work on PLSB is ongoing in the 802.1aq Working Group under the general topic of Shortest Path Bridging. Work is in its early days, but progress has been seen, notably in areas of service identification and symmetric shortest-path-tree computation. These should address the biggest issues remaining with multicast service support in an Ethernet context – how to avoid a Spanning Tree Protocol-based network.

Company approach and market development: PBT represents a cornerstone technology that Nortel will incorporate into many carrier Ethernet-enabled product families as the market demands. The company stresses that PBT is but one technology in a suite that comprises carrier Ethernet, but is nonetheless a key one. This reimagining of Ethernet allows for the notion that Ethernet switches can be deterministically programmed as connection-oriented elements, and thus opens a new way of thinking about architectures that dramatically reduce network costs while maintaining the Sonet/SDH network-management paradigm. The company contends that, with this approach, opex is expected to exceed the capex reductions already documented to be in the 40 to 60 percent range (although operational savings are harder to quantify, given the number of variables involved).

Company approach calls for virtually identical traffic engineering approaches across the Layers 0, 1, and 2 infrastructure, and the same OA&M tools support the entire range of solutions with provisioning, fault-detection, and performance monitoring functions.

Related company news:

  • Nortel Aims for Ethernet Profits

  • Nortel Demos Ethernet Backhaul

  • NTT Joins PBT Roll Call

  • Nortel Lands PBT Wins

  • Nortel Preps New PBT Switch

  • BT Goes Live With PBT




Provides multi-vendor, multi-technology resource and service control software. Comments from Esmeralda Swartz, Senior VP Marketing and Business Development.

Key characteristics and relation to other approaches: Sees PBB-TE bringing new capabilities to address the limitations of MPLS service scaling and its lack of predictability for services. It also enables more cost-effective Ethernet transport with substantially simplified network management. The need for service predictability makes PBB-TE’s circuit-like behavior very appealing as a foundation for services. Argues that, fundamentally, there was a universal recognition on the part of PBB-TE suppliers that, for Ethernet to be viable in a carrier environment, the focus needed to be in the management (OAM&P) area. This is in direct contrast with MPLS, where management was added well after the initial technology was rolled out to customers. Says that the use of an external service control plane like the company’s PNC enables multivendor interoperable solutions to be deployed quickly, and also to provide service automation to accelerate service deployment. For example, the PNC is providing service restoration, which distinguishes the dynamic control plane from a simple provisioning system. After a 50 ms failover event on the switch, the external control plane, which keeps a complete topology of the multivendor network, is responsible for restoring the service. The PNC is thus responsible for managing the service lifecycle and ensuring that the service stays up and the SLA is met.

In this LRTV interview, Soapstone founder Larry Dennison explains the rationale for getting out of the router business and into the service control software space:

Key applications: The first application for PBB-TE has been to replace Sonet/SDH for leased-line services now standardized by the MEF as E-line services, and carriers want to extend PBB-TE to support a full Ethernet services portfolio, including E-LAN and E-tree services. Says that, from an implementation perspective, there are solutions already that leverage the data plane and external control plane to multipoint-to-multipoint services. The implementation would look as follows: The data plane implements a virtual switch instance (VSI), which functions like a MAC learning bridge, and PBB-TE is deployed at the core instead of LSP tunnels, with split horizon being used to avoid loops, and with service instances (I-SIDs) being used instead of pseudowires. On the control plane, the company’s external control plane replaces discovery and signaling mechanisms (BGP and LDP). This solution looks like VPLS without MPLS. Argues that, by working with switch vendors that have implemented E-LAN and E-tree, and by using the Soapstone external control plane to program these services, the interoperability issue created by combined data plane/control solutions is avoided, thus giving carriers the flexibility to work with many different vendors.

Technology aspects: Says that there were two missing components to PBB-TE being ready for prime time – the lack of a control plane, and the need to support point-to-point and multipoint-to-multipoint services. Argues that there is wide recognition that existing distributed IP/MPLS control planes are not scaling effectively, and do not easily support a services paradigm. For example, RSVP-TE was designed for distributed path set-up, and is not powerful enough to deal with policy needed for services. Equally, vendors need to avoid adding complexity into carrier Ethernet and avoid adding to equipment what rightly belongs at the services/OSS layer.

{column}Company approach and market development: Company believes market development is about the separation of services from transport and, ultimately, which technology is best suited as a foundation for services. Argues that there are only two possibilities for transport: carrier Ethernet or the emulation of Ethernet by using MPLS. The critical distinction between MPLS and PBB-TE is in OAM&P. Argues that the ITU-T and IEEE are very good in picking an implementation and making it mandatory – as occurred with carrier Ethernet OAM&P (for example, the CFM messaging).

Soapstone is developing solutions that are designed to manage the complexities between carrier service offerings and applications and the underlying transport equipment and technologies. The solutions are based on key industry standards, including Service-Oriented Architecture (SOA), the TeleManagement Forum (TM Forum), International Telecommunication Union (ITU), and next-generation networks (NGNs) among others, and utilize open APIs between the network and OSS, such as Multi-Technology Operations System Interface (MTOSI). The Soapstone PNC is a multi-vendor, software-based service control plane designed to take advantage of the opportunity created by the emergence of carrier Ethernet, the need for service automation, and the adoption of next-generation network architectures.

The initial technology module of the Soapstone PNC framework is targeted at carrier Ethernet because by design it requires an external control plane. However, it is expanding the capabilities of the Soapstone resource and service control software to cover MPLS, optical, and integrated optical Ethernet networks, as the company says all will benefit from the advantages of an external control plane solution.

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Provides infrastructure solutions for wireline and mobile networks, including Ethernet and MPLS. Comments from John Sauer, Senior Principal Engineer.

Key characteristics and relation to other approaches: For point-to-point services, PBB-TE is a switch-based alternative to MPLS that will enable Layer 2 networks to support assured Ethernet service implementation with Ethernet-based systems. Work underway in the IETF will marry PBB-based approaches with MPLS via H-VPLS extensions for multipoint VPLS-based networks. Tellabs supports these efforts, which will improve scaleability.

The choice of technology depends on the customers’ needs and evolution requirements, so Tellabs provides both MPLS and Ethernet-based routing and transport solutions to best meet customers’ needs. For example, T-MPLS is supported because customers were asking for a simpler method than full MPLS for point-to-point applications. As PBB-TE is standardized, these same customers' needs can be addressed with this new technology. In the following marketing video, Tellabs engineer Tom Rarick firmly straddles the fence with respect to taking a position on PBT vs. MPLS:

Key applications: PBB-TE will offer traffic-engineered paths between switches and routers, ensuring the QOS required within the network.

Technology aspects: Tellabs sees the marriage of optical transport and Ethernet packet switching as very promising. For example, the use of ROADM technology and switching in combination will enable both optical and Ethernet optimization.

802.1Qay provides traffic engineering by providing a subset of functionality in 802.1ah (PBB), as well as extensions for traffic engineering. Given the success of IEEE 802 standards, the company expects that these standards will have wide adoption. Additional work is needed to provide dynamic signaling mechanisms and performance monitoring, and this may or may not take place in IEEE.

Company approach and market development: Tellabs sees assured Ethernet-based services as a key to future developments companywide. PBB and PBB-TE are on the roadmaps for products in optical transport and routing, and will be deployed as customer demand dictates. It sees 2009 as a key year for deployment of these technologies.

Tellabs supports industry efforts to standardize packet transport technology. These efforts include IETF, IEEE, and ITU-based work. For Ethernet-based approaches, Tellabs supports the standard Ethernet-based approach based on IEEE 802.1 efforts embodied in Provider Backbone Bridge Traffic Engineering (802.1Qay). These industry efforts will help provide an interoperable packet transport option.

Related company news:

  • Fujitsu Sues Tellabs

  • Tellabs Tackles Network Pains

  • Ethernet Backhaul Battle Brews



{column}
Provides Softsilicon chip solutions for carrier Ethernet and packet transport networks. Comments from Daniel Joseph Barry, Director of Marketing.

Key characteristics and relation to other approaches: Sees PBT and T-MPLS as natural heirs to Sonet/SDH by allowing a fully packet-based, scaleable, and deterministic transport network to be developed independently of IP/MPLS-based service networks.

PBT and T-MPLS both resemble Sonet/SDH, with:

  • Centrally controlled configuration and provisioning

  • OAM packets for end-to-end monitoring

  • Fast protection switching on predefined path

But they have different starting points – Ethernet/PBB and MPLS.

The goal for PBT was to make Ethernet a carrier-class transport mechanism by solving Ethernet’s scaleability and flooding issues, while also addressing the shortcomings of Spanning Tree Protocol. The PBB frame format, which was already available, provided a solution to scaling through the use of MAC-in-MAC encapsulation and a 24-bit service identifier (I-SID). By allowing a management system to populate the Forwarding Information Databases (FIDs), it was possible to turn off Spanning Tree and the flooding of unknown addresses. Thus the issues with Ethernet were solved, with the added bonus of hierarchical layering allowing full separation of customer, provider, and operator (carriers’ carrier) domains.

By adding the Continuity Check Messaging (CCM) and Automatic Protection Switching (APS) mechanisms defined in IEEE 802.1ag and ITU-T Y.1731, PBT also provided an end-to-end, fully protected, bi-directional connection with the resilience that could be expected from Sonet/SDH.

With T-MPLS, the starting point was MPLS. But, as MPLS was designed to assist performance issues in IP, many of the features in MPLS are IP-related and are neither useful nor desirable in a transport application. The key issue was to ensure OAM integrity to allow end-to-end protection of Label Switched Paths (LSPs).

By removing optional functionality such as Penultimate Hop Popping (PHP), Equal Cost Multiple Path (ECMP), and LSP Merging, OAM packets could now remain in an MPLS format end-to-end, traversing a deterministic path. These OAM packets can now be used to perform end-to-end protection with fast switch-over to a predefined backup LSP.The removal of LSP merge meant that Fast Re-Route (FRR) cannot be used, so the protection mechanism was based on existing ITU-T MPLS protection mechanisms.

T-MPLS is an approved standard in the ITU-T defined in the following approved standards:

  • G.8110 – MPLS Layer Network Architecture

  • G.8101 – T-MPLS Definitions and Terminology

  • G.8110.1/Y.1370.1 – Application of MPLS in the Transport Network

  • G.8112 – Interfaces (UNI/NNI) for the Transport MPLS (T-MPLS) Hierarchy

  • G.8121 – Characteristics of Transport MPLS Equipment Functional Blocks

  • G.8131/Y.1382 – Linear Protection Switching for T-MPLS Networks

  • Y.1711 – Operation and Maintenance Mechanism for MPLS Networks

  • G.8113/Y.1372 (ex-Y.17tor) – Requirements for OAM Function in T-MPLS based networks

  • G.8114/Y.1373 (ex-Y.17tom) – Operation and Maintenance Mechanism for T-MPLS-Based Networks.

Work is continuing on these standards:

  • G.8132/Y.1382 – Ring Protection Switching for T-MPLS Networks

  • G.tm-mg – Management Aspects of the T-MPLS Network Element

  • G.tm-im – Protocol-Neutral Management Information Model for the T-MPLS Network Element

In comparing PBT and T-MPLS to MPLS, it is important to realize that they were designed for a specific application, namely transport, and not primarily as a replacement for MPLS and IP services. PBT, T-MPLS, and MPLS are actually compatible, if one subscribes to the view that service and transport networks should be separate, independently scaleable, intelligent networks. This is not a view supported by all. Router vendors in particular see IP/MPLS providing both service and transport capabilities in a single network. However, many carriers agree that separation is necessary for scaleable deployment of multiple, dynamic, packet-based services – a dynamic IP/MPLS services network with autonomous routing capabilities, but supported by a reliable, deterministic transport layer.

Key applications: Both PBT and T-MPLS were designed for packet transport applications, so Tpack believes that is where they will see their first applications – and this is already happening. Examples are the access and mobile backhaul applications of PBT thus far and the adoption of the technology by many smaller carriers, which can better justify the replacement of Sonet/SDH in their networks. For larger carriers, it is a greater undertaking to introduce these technologies on a large scale, but Tpack argues that all carriers know that they must eventually move to a fully packet-based solution and also replace Sonet/SDH. Choices include a pure connection-oriented Ethernet infrastructure or one of the new developments in packet optical transport platforms. Tpack believes that the solution will probably be a combination of both.

Company views as an open question the extent to which PBT and T-MPLS will be used as service platforms. IP/MPLS does an excellent job of this today, but the increasing interest in carrier Ethernet services could lead to new developments in this area. PBT, in particular, would seem to be a good candidate for E-line services, but multipoint E-LAN services would still seem to be an open question. Believes the right approach currently is to concentrate on deploying PBT and T-MPLS for what they were designed for, namely packet transport, and not to be distracted by other considerations.

Technology aspects: Says T-MPLS is already well defined, and argues that the key issue is whether the ITU-T and the IETF can reach an agreement on how to implement a seamless interface between the T-MPLS and MPLS domains. If they can, T-MPLS could become the natural extension of MPLS beyond the core, and an ideal transport layer for IP/MPLS services.

PBT and PBB-TE in particular are just embarking on the standardization process, which could provide a number of surprises over the coming year or two. Given the controversy that PBT/PBB-TE has already stirred, it would be surprising if this standardization work does not become contentious. However, the lack of standardization has not deterred carriers from considering and even deploying PBT. It will be interesting to see to what extent carriers become involved in driving the process, as this should be beneficial for all parties and ensure that work remains properly focused.

The multipoint and multicasting issues will continue to rage. Company believes that both PBT and T-MPLS can have a significant impact as point-to-point technologies, especially when supporting IP/MPLS or PBB, which can provide the multipoint services required. The reduction in the need for routers at all switching points in the network is in itself a considerable reduction in cost and complexity, which should make these technologies attractive.

Company approach and market development: Has helped telecom systems vendors to support carrier Ethernet functionality on platforms – both multiservice provisioning platforms and dedicated carrier Ethernet switches – since 2001. Says it was the first vendor to provide a commercial chip solution that could support PBT: the TPX3100 released in June 2007, which also supports Ethernet, MPLS, VPLS, PWE3, and T-MPLS, and is currently the only off-the-shelf solution to provide this simultaneous support.

Approach is to provide a standard chip solution, which can be quickly adapted to support new market developments. Says that this "Softsilicon" approach is based on the latest field-programmable gate-array (FPGA) technology, which no longer suffers from the cost and power consumption challenges of earlier generations. The result is a comprehensive PBT and T-MPLS switching chip solution, which can be updated quickly as new developments in these technologies or other protocols need to be supported.

Related company news:

  • PBT Parties On

  • TPack Talks Ethernet

  • Tpack Intros Packet Mapper Engine



(acquired by Ciena Corp. in March 2008)
Provides carrier Ethernet solutions. Comments from Kevin Daines, former Chief Technology Officer.

Key characteristics and relation to other approaches: PBB-TE offers an enhanced Ethernet transport technique for building connection-oriented paths across a diverse network. By adding an Ethernet MAC header, operators and carriers can securely separate the customer MAC address domain and the provider’s domain. In addition, primary and backup tunnels (called Ethernet Switch Paths in the draft standard) are constructed by using straightforward static forwarding entries. This allows PBB-TE to ride on top of existing and legacy equipment, thus lowering overall costs of deployment. In other words, it does not require wholesale forklifts.

MPLS-based alternatives have comprehensive and complex control planes. Generally speaking, these require more sophistication to configure and manage. The protocols discover the network, optimize the connectivity, and respond to an array of congestion or failure conditions. PBB-TE offers a circuit-like connectivity that has been compared to Sonet/SDH or TDM circuits. In some instances, operators want proscribed primary and backup paths across a given infrastructure – wireless backhaul for packet-based 3G/4G mobile is one such example. The overhead of a fully signaled and dynamic control plane is overkill for these environments.

Believes that MPLS will continue to own the core. It represents an existing sizable investment and is suited to the multiprotocol (Ethernet, FR, ATM, etc.) nature of many core networks. Large provider and provider edge routers are suited for this application.

PBB-TE will find application in access and aggregation applications where the complexity and extra expense of MPLS-based solutions are unwarranted. The resiliency schemes and network redundancy requirements may be adequately addressed by PBB-TE solutions.

Key applications: Company has successfully developed and deployed PBB-TE in several 3G/4G wireless backhaul applications, where the company’s equipment is placed at the aggregation POP and the base station and provides resilient connectivity for mobile services. This is seen as an important application for PBB-TE.

Technology aspects: IEEE 802.1Qay will provide an interoperable specification for PBB-TE. It will contain extensions to CFM to support PBB-TE connectivity and management. The draft standard contains both P2P and P2MP Ethernet Switched Paths covering important use cases.

WWP’s interoperable and conforming implementation supports multipoint/LAN connectivity today.

A non-goal of the IEEE 802.1Qay committee is the topic of provisioning and path cost discovery. This will likely be left to other groups to handle.

PBB-TE supports either manual configuration (which can be instrumented through element management systems) or future dynamic configuration using control plane protocols. Vendors and carriers are still discussing the best approach.

Company approach and market development: Suggests that one of the primary attractions of its products to carriers is that they provide both MPLS and PBB-TE support. This is in contrast to many vendors, which provide only one or the other.

Its PBB-TE solution approach has been to provide scaleable data-plane performance, reliable control plane, and efficient management plane functionality – a comprehensive solution-wide approach addressing service delivery, resilience, and the operator’s ability to deploy the technology, add locations, and manage the network.

However, the company has an agnostic approach in terms of carrier Ethernet service transport. It has several customers using MPLS/H-VPLS in metro and access networks, and many use 802.1ad Provider Bridging or Q-in-Q based connectivity. Argues that there is no one-size-fits-all technology, and that it engineers its solutions to provide best-in-class capabilities.

Has long promoted its sub-50 ms failover using RSTP on rings, and demonstrated 50 ms failover using PBB-TE at the Carrier Ethernet World Congress in fall 2007.

Sees the market for PBB-TE expanding rapidly. The company’s initial successes in wireless backhaul will provide excellent proof points for further market and customer expansion. The technology has achieved standards traction and multivendor adoption, and has proven to cost less than comparable MPLS-based technologies. Sees, in general, that the technology has moved from proprietary/nascent to a full-fledged alternative to traditional Q-in-Q Ethernet in the access and MPLS in the metro.

— Tim Hills is a freelance telecom writer and journalist. He's a regular author of Light Reading reports.



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