OTN processors from the core to the network edge

The latest silicon design announcements from PMC and AppliedMicro reflect the ongoing network evolution of the Optical Transport Network (OTN) protocol.

"There is a clear march from carriers, led in particular by China, to adopt OTN in the metro"

Scott Wakelin, PMC

The OTN standard, defined by the telecom standards body of the International Telecommunication Union (ITU-T), has existed for a decade but only recently has it emerged as a key networking technology. 

OTN's growing importance is due to the enhanced features being added to the protocol coupled with developments in the network. In particular, OTN enhances capabilities that operators have long been used to with SONET/SDH, while also supporting packet-based traffic. Moreover chip vendors are unveiling OTN designs that now span the core to the network edge.

"OTN switching is a foundational technology in the network"

Michael Adams, Ciena 

OTN supports 1 Gigabit Ethernet (GbE) with ODU0 framing alongside ODU1 (2.5G), ODU2 (10G), ODU3 (40G) and ODU4 (100G). The standard packs efficiently client signals such as SONET/SDH, Ethernet, video and Fibre Channel, at the various speed increments up to 100Gbps prior to transmission over lightpaths. Meanwhile, the Optical Internetworking Forum (OIF) has recently developed the OTN-over-Packet-Fabric standard that allows OTN to be switched using packet fabrics.

"OTN switching is a foundational technology in the network," says Michael Adams, Ciena’s vice president of product & technology marketing.

Operator benefits

Whereas 10Gbps services matched 10Gbps lightpaths only a few years ago, transport speeds have now surged ahead. Common services are at 1 and 10 GbE while transport is now at 40Gbps and 100Gbps speeds. OTN switching allows client signals to be combined efficiently to fill the higher capacity lightpaths and avoid stranded bandwidth in the network. 

OTN also benefits network connectivity changes. With AT&T's Optical Mesh Service, for example, customers buy a total capacity and, using a web portal, can adapt connectivity between their sites as requirements change. "It [OTN] can manage GbE streams and switch them through the network in an efficient manner," says Adams. 

The ability to adapt connectivity is also an important requirement for cloud computing, with OTN switching and a mesh control plane seen as a promising way to enable dynamic networking that provides guaranteed bandwidth when needed, says Ciena.

OTN also offers an alternative to IP-over-DWDM, argues Ciena. By adding a 100Gbps wavelength, service routers can exploit OTN to add 10G services as needed rather than keep adding a 10Gbps wavelength for each service using IP-over-DWDM. "To enable service creation quickly, why not put your router network on top of that network versus running it directly?" says Adams.

OTN hardware announcements

The latest OTN chip announcements from PMC and Applied Micro offer enhanced capacity when aggregating and switching client signals, while also supporting the interfacing to various switch fabrics. 

PMC has announced two metro OTN processors, dubbed the HyPHY 20Gflex and 10Gflex. The devices are targeted at compact "pizza boxes" that aggregate residential, enterprise and mobile backhaul traffic, as well as packet-optical and optical transport platforms.

AppliedMicro's TPACK unit has unveiled two additions to its OTN designs: a 100Gbps chipset and the TPO134. The company also announced the general availability of its 100Gbps muxponder and transponder OTN design, now being deployed in the network.

Source: AppliedMicro

"OTN has long had a home in the core of the network," says Scott Wakelin, product manager for HyPHY flex at PMC. "But there is a clear march from carriers, led in particular by China, to adopt OTN in the metro, whether layer-zero or layer-one switched." 

Using various market research forecasts, PMC expects the global OTN chip market to reach US $600 million in 2015, the bulk being metro.

PMC and AppliedMicro offer application-specific standard product (ASSP) OTN ICs while AppliedMicro also offers FPGA-based OTN designs.

The benefits of using an FPGA, says AppliedMicro, include time-to-market, the ability to reprogramme the design to accommodate standards’ tweaks, and enabling system vendors to add custom logic elements to differentiate their designs. PMC develops ASSPs only, arguing that such chips offer superior integration, power efficiency and price points. 

Both companies, when developing an ASSP, know that the resulting design will be adopted by end customers. When PMC announced its original HyPhy family of devices, seven of the top nine OEMs were developing board designs based on the chip family. 

PMC's metro OTN processors

The HyPHY 20Gflex has 16 SFP (up to 5Gbps) and two 10Gbps XFP/SFP+ interfaces, whose streams it can groom using the device's 100Gbps cross-connect. The cross-connect can manipulate streams down to SONET/SDH STS-1/ STM-0 rates and ODU0 (1GbE) OTN channels.

Both ODU0 and ODUflex channels are supported. Before adding ODU0, a Gigabit Ethernet channel could only sit in a 2.5Gbps (ODU1) container, which wastes half the capacity. Similarly by supporting ODUflex, signals such as video can be mapped into frames made up of increments of 1.25Gbps. "For efficient use of resources from the metro into the core, you need to start at the access," said Wakelin.

Source: PMC

The chip also supports the OTN-over-Packet-Fabric protocol. The devices can interface to OTN, SONET/SDH and packet switch fabrics.

The 20Gflex offers 40Gbps of OTN framing and a further 20Gbps of OTN mapping. The OTN mapping is used for those client signals to be fitted into ODU frames. With the additional 40Gbps interfaces that connect to the switch fabric, the total interface throughput is 100Gbps, matching the device's cross-connect capacity.

Other chip features include Fast Ethernet, Gigabit Ethernet and 10GbE MACs for carrier Ethernet transport, and support for timing over packet standards, including IEEE 1588v2 over OTN, used to carry mobile backhaul timing information.

The 10Gflex variant has similar functionality to the 20Gflex but with lower throughput.

PMC is now sampling the HyPHY Gflex devices to lead customers.  

AppliedMicro's OTN designs

AppliedMicro's TPACK unit has unveiled two OTN designs: a TPO415/C415 OTN multiplexer chipset for use in 100Gbps packet optical transport line cards, and the TPO134 device used at the network edge.

The two devices combined - the TPO415 and TPOC415 - are implemented using FPGAs, what AppliedMicro dubs softsilicon.  The two devices interface between the 100Gbps line side and the switch fabric.  The TPO415 takes the OTU4 line side OTN signal and demultiplexes it to the various channel constituents. These can be ODU0, ODU1, ODU2, ODU3, ODU4 and ODUflex - capacity from 1Gbps to 100Gbps.

 "The [100Gbps muxponder] design comes with an API that makes it look like one component"

Lars Pedersen, AppliedMicro 

The TPOC415 has a 100Gbps, 80-channel segmentation and reassembly function (SAR) compliant with the OIF OTN-over-Packet-Fabric standard. The TPOC415 also has a 100Gbps, 80 channel packet mapper function for the transport of Ethernet and MPLS-TP over ODUk or ODUflex. The device's 100Gbps Interlaken interface is used to connect to the switch fabric for packet switching and ODU cross-connection. The devices can also be used in a standalone fashion for designs where the switch fabric does not use Interlaken, or when working with integrated switches and network processors.

Source: AppliedMicro

"This is the first solution in the market for doing these hybrid functions at 100Gbps," says Lars Pedersen, CTO of AppliedMicro's TPACK.

The second design is the softsilicon TPO134, a 10Gbps add/drop multiplexer that can take in up to 16 clients signals and has two OTU2 interfaces. In between is the cross-connect that supports ODU0, ODU1 and ODUflex channels.  Two devices can be combined to support 32 client channels and four OTU2 interfaces. Such a dual-design in a pizza-box system would be used to combine multiple client streams.

Being softsilicon, the TPO134 can also be used for packet optical transport systems. Here by downloading a different FPGA image, the design can also implement the segmentation and reassembly function required for the OIF's OTN-over-Packet-Fabric standard. "The interface to the switch fabric is Interlaken again," says Pedersen. 

The TPO134 design doubles the capacity of AppliedMicro's previous add/drop multiplexer designs and is the first to support the OIF standard.

AppliedMicro has also announced the general availability of its 100G muxponder design. The muxponder design is a three-device chipset based on two PQ60 ASSPs and a TPO404 softsilicon design.

The PQ60T devices map 10 and 40Gbps clients into OTN and the TPO404 performs the multiplexing to OTU4 with forward error correction. The client signals supported include SONET/SDH, Ethernet and Fibre Channel. On the line side the design also supports various FEC schemes including an enhanced FEC.  The TPO404 differ from the TPOT414/424 devices that link 100GbE and 100Gbps line side.

"The [100Gbps muxponder] design comes with an API [application programming interface] that makes it look [from a software perspective] like one component with some client and line ports, similar to the TPO134 device," says Pedersen.

Further reading:

Transport processors now at 100 Gigabit