Kennedy: Transport, routing and switching converge

by Michael Kennedy, Managing Partner of Network Strategy Partners, LLC (NSP)

Technological progress in underlying component technologies, new architectural standards initiatives, and a changing network traffic mix have all spawned an architectural competition for the next generation of converged networking.

Network traffic measured by bandwidth is primarily IP. However, the majority of access ports and most metro transport continue to be TDM/PDH and SONET/SDH based. This legacy infrastructure is still in place because it is reliable and resilient; and the operations, administration and maintenance (OAM) procedures are mature and effective. Comparable, capabilities and business processes for IP/Ethernet technology are just emerging.

SONET/SDH is well regarded for its resilience-less than 50ms circuit restoration time, path provisioning mechanisms, and effective OAM capabilities. ATM, another legacy technology, offers effective traffic engineering methods and guaranteed QoS.  ATM's approach to traffic engineering which features centrally managed and deterministically controlled traffic flows across the network are highly valued by the architects of large networks.

IP and Ethernet, however, make more efficient use of bandwidth and are more flexible than SONET/SDH and ATM. The efficiency is achieved through statistical multiplexing of packets while packet flow control techniques offer fine levels of packet control by customer, traffic type and application.

The emerging architectural competition, therefore, seeks to bring the connection-oriented approach, traffic management capabilities, resilience, and OAM capabilities of SONET/SDH and ATM to a new packet oriented network design.

At a high-level the competing architectures are aligned with vendors of routers, Ethernet switches and optical transmission equipment. The corresponding architectures are MPLS Router over DWDM, Connection-Oriented Ethernet, and Packet Optical transport.

MPLS Router over DWDM is the best established of these architectures though it has gained market traction only recently. This design features the IP/MPLS router as the central network element. The router provides multi-service support using protocols such as Pseudowire, provides traffic and path control using vehicles such as Label Switched Paths (LSP), and a distributed approach to traffic control through advanced routing algorithms. The router ports are equipped with optical transponders that deliver specific DWDM wavelengths (colored wavelengths) to DWDM transmission equipment. The role of the DWDM equipment in this design is strictly limited to Layer 1 activities such as transmitting and amplifying optical signals, switching optical signals among different paths, and adding or dropping optical signals at router nodes. This design minimizes optical-electrical-optical (O-E-O) interfaces which reduces both CapEx and OpEx and greatly simplifies the management of the DWDM network.

Connection-Oriented Ethernet resembles MPLS Router over DWDM to some extent in that it also limits the DWDM transport equipment to Layer 1 (Optical) activities only. It differs from the router-based design in that it features Ethernet Switch/Routers rather than MPLS routers. Network control and traffic management functions are handled by a centralized network manager using PBB-TE (IEEE 802.1Qay-2009)--its connection-oriented features and OAM approach are inspired by SONET/SDH.

Packet Optical Transport extends the SONET/SDH concept to permit sub-wavelength multiplexing and packet switching over DWDM transport. It could be viewed as the mirror image of the MPLS Router over DWDM architecture. IP routers, Ethernet Switch/Routers, and SONET/SDH Add/Drop multiplexers and cross connect switches set at the edge of the network while the Packet Optical Transport system handles multi-service, multiplexing and packet switching functions internally. This also minimizes O-E-O interfaces just like the other alternatives.  OTN (Optical Transport Network ITU G.709) and MPLS-TP (MPLS Transport Profile) are standards efforts important to the creation of Packet Optical Transport. This design is especially attractive when large quantities of SONET and other traffic must be carried alongside the IP traffic.

Architectural competitions are often debated on technical grounds while the actual winners are usually determined by the market power of the systems vendors and the traffic mix in service provider networks. Within core networks a handful of routing and transmission vendors dominate the market. I do not expect much competitive movement in this marketplace. The existing router vendors will maintain their positions while the transmission vendors will gradually upgrade their optical switching (cross connect) systems to include Packet Optical Transport capabilities. Metro aggregation networks, however, offer opportunities for all three architectures because the largest wireline service providers have not made much progress in moving to converged architectures. I believe there is an opportunity for transport vendors to succeed because legacy traffic will remain for many years.  Connection-Oriented Ethernet solutions provide an attractive boost to Ethernet switch vendors that previously could not offer a truly carrier-class transport solution. Finally, the fundamental business driver is IP video which plays to the strengths of the router vendors.

Michael Kennedy is co-founder and Managing Partner of Network Strategy Partners, LLC (NSP) ([email protected])--management consultants to the networking industry. Hear Michael talk about next-gen IP and optical technologies in FierceTelecom's December 2nd webinar Growth Opportunities in the Telco Industry: What You Need to Know to Compete.