Making Sonet Ethernet-Friendly

A survey of Sonet/SDH chip developments that promise to help carriers offer data services over existing infrastructure * Market Overview * Technology Update * Product Matrix

March 25, 2003

19 Min Read
Making Sonet Ethernet-Friendly

The development of next-generation Sonet/SDH technologies – such as Generic Framing Procedure (GFP), Virtual Concatenation (VCAT), and Link Capacity Adjustment Scheme (LCAS) – is giving carriers a new opportunity to market Ethernet and storage services, in addition to voice services, without replacing their metro Sonet/SDH networks.

By replacing Sonet/SDH add/drop multiplexers (ADMs) with multiservice platforms that support Ethernet and other packet-based protocols, as well as TDM, carriers can achieve significant returns on their scarce investment dollars.

The supply of next-gen Sonet/SDH silicon, supporting line rates as high as 10 Gbit/s, continues to grow as semiconductor vendors – including Agere Systems (NYSE: AGR/A), Multilink Technology Corp. (Nasdaq: MLTC), and West Bay Semiconductor Inc. – look to cash in on a market that is predicted to grow threefold by 2006.

In this report Light Reading looks at the market drivers for next-gen Sonet/SDH framer/mapper devices, the core technologies involved, and issues of integration with Ethernet. For each framer/mapper device, the report will review its features, availability, and cost.

Here is a hyperlinked summary:


This report was previewed in a Webinar moderated by the author and sponsored by Multilink Technology. It may be viewed free of charge in our Webinar archives by clicking here.

Background Reading

  • Column: GFP: Good For Positioning

  • Report: Next-Gen Sonet Silicon

  • Report: Next-Gen Sonet

  • Report: 10-Gigabit Ethernet

  • Report: Metro Ethernet

  • Report: Resilient Packet Ring Technology

  • Beginner's Guide: Protocol Basics

  • Beginner’s Guide: Sonet and SDH

  • Beginner’s Guide: Ethernet

— Simon Stanley is founder and principal consultant of Earlswood Marketing Ltd. He is also the author of several other Light Reading reports, including 10-Gigabit Ethernet, 10-Gig Ethernet Transponders, and Next-Gen Sonet Silicon.

Customers with Ethernet-based enterprise networks, are demanding new, Ethernet-based services from carriers. These services include Ethernet private lines and private LANs as well as storage transport.

Carriers, however, have significant investments in their existing Sonet/SDH core infrastructures. This investment has run to hundreds of billions of dollars over a significant period of time.

New capital expenditure (capex) is being limited largely to incremental development of these standing infrastructures. Where possible, this new investment must also reduce operating expenditure (opex), so the business case for most new capex is driven by the combination of delivering new services and reducing opex.

To deliver these new services, carriers are expanding Ethernet in their metro and access networks using their existing Sonet/SDH cores. Carriers in the Asia/Pacific region already support Ethernet in their access networks. Alternative greenfield technologies – primarily replacing the Sonet/SDH cores with Ethernet-based networks – are now seen to be too expensive.

“This is a very conservative industry. It does not move at the speed that people think it will,” says Richard Deboer, CEO at Galazar Networks Inc. “We think the network will stay Sonet/SDH for the next decade.”

To deliver Ethernet services in the access market, carriers need multiservice ADMs that can support 10-Mbit/s Ethernet and 100-Mbit/s (Fast) Ethernet to their customers (see Figure 1).

30194_1.gifTo provide incremental service provisioning, carriers are looking to deliver services over Gigabit Ethernet in multiples of 50 Mbit/s. This avoids the potential jumps in cost that have been a problem when going from T1 (1.5 Mbit/s) to T3 (45 Mbit/s) in North America or E1 (2 Mbit/s) to E3 (34 Mbit/s) elsewhere.

Gigabit Ethernet has been successfully promoted as a suitable technology to expand bandwidth in the metro edge and access network. By mapping Ethernet over the existing core, carriers can provide the Ethernet services demanded by their customers and still take advantage of the significant reliability and quality of service (QOS) benefits delivered by Sonet/SDH.

A further application for GFP in the metro is through Resilient Packet Ring (RPR). So far however, RPR has seen very little deployment in carriers’ infrastructures. Its main use has been in private, campus-type networks (see Siemens Is Shaping Up and Who Knew? Big Carriers Like RPR).

IDC has defined multiservice ADMs, switches, edge routers, and access concentrators as “multiservice provisioning platforms” (MSPPs). A recent report from IDC forecasts revenue for this market growing from just over $1 billion to more than $3 billion by 2006 (see Figure 2).

30194_2.gif “Introducing GFP and virtual concatenation is relatively easy,” says Robert Schwaber, product line manager at TranSwitch Corp. (Nasdaq: TXCC). “This is a link-layer technology and protocol that can be introduced using new devices into new or existing ADMs.”

These are the key applications for the latest GFP framer/mapper devices.

“From our side, what we see is a lot of systems customers building a virtual concatenation, GFP card for their existing ADM, as well as for their next-generation platform,” notes Jon Ames, strategic marketing leader with PMC-Sierra Inc. (Nasdaq: PMCS). “It seems that everybody is looking to adopt this technology.”

There is significant activity in this market, with products from 10 companies covering bandwidths from 155 Mbit/s to 10 Gbit/s and a large concentration on 2.5 Gbit/s.

Figure 3 shows a typical Sonet/SDH subsystem. This could be a line card or a complete system.

30194_3.gifOn the left-hand side is the Sonet/SDH optical interface. On the right are the packet and TDM mappers and interfaces. The packet mapper may be connected to an Ethernet MAC or a network processor.

The Sonet/SDH frames come in on the left from the optics as a serial stream to the serial/deserializer (SerDes) block, which includes the clock and data recovery (CDR) unit. The frames are now passed to the framer over a parallel interface. Most devices now support the SerDes Framer Interfaces, SFI-3 and SFI-4, defined by the Optical Internetworking Forum (OIF). The framer handles the overhead processing and statistics for the Sonet/SDH connection.

In the center there may be a Sonet/SDH multiplexer or pointer processor, or a crossbar switch. This function may be integrated into the framer device or may be on a separate card, depending on the complexity of the system. Where separate framers and mappers are used, the interfaces between them and any switch are usually based on the Telecom Bus or TFI-5.

The cell and packet mappers on the right are usually connected to the rest of the system using the OIF System Physical Interfaces, SPI-3,4 and SPI-5.

With increasing demand for GFP/Virtual Concatenation devices in the access market, companies like Agere are introducing multiple versions of their 2.5-Gbit/s framer/mappers to support 622-Mbit/s and 1.2-Gbit/s rates.

“From the Sonet side we are developing complete multi-rate functionality,” says Chris Hamilton, segment manager with Agere, “the ability to operate the chip on a single interface OC3, OC12, OC48, on a plug-and-play basis.”

A Table of vendors and next-gen Sonet/SDH mapper/framers is given below:

Dynamic Table: Sonet/SDH Mapper/Framers

Select fields:
Show All Fields
CompanyDevice NumberDevice NameBandwidthTransparent GFPLAPSATM TerminationVirtual ConcatenationVCAT GroupsDifferential DelayLCASSingle LineMultiple LinesAPSTDM XCSystem InterfaceEthernet MACsPowerPriceSample Availability


Agere Systems (NYSE: AGR/A)

  • Agere Unveils 'Universal' Framer

  • Agere Gets Mapper-Happy

  • Agere Intros Mapper, Framer

  • Agere Intros Transport Chips

  • Agere Ships Chips to Huawei

Agilent Technologies Inc. (NYSE: A)

  • Agilent Intros EoS Mapper

  • Telica Launches Wireless Apps

Cypress Semiconductor Corp. (NYSE: CY)

  • Cypress Samples GFP Framer Chip

  • Corvis Unveils Optical Protector

  • Cypress Sampling Sonet Framer

  • Cypress Preps Ethernet-Over-Sonet Chip

  • Cypress Improves Its Line Card Lineup

Galazar Networks Inc.

  • Galazar Unveils Multiservice Framer

  • TranSwitch Sues Galazar

  • Galazar Networks Opens With $11.2M

Intel Corp. (Nasdaq: INTC)

  • Intel Extends 10-Gig Optical Line

Multilink Technology Corp. (Nasdaq: MLTC)

  • Multilink Unveils VCat-10

  • Multilink Makes Sonet Flexible

  • Multilink Debuts, Quietly

PMC-Sierra Inc. (Nasdaq: PMCS)

  • PMC-Sierra Intros Framer

  • PMC Launches Sonet Chips

TranSwitch Corp. (Nasdaq: TXCC)

  • TranSwitch Releases Ether/Sonet Mapper

  • TranSwitch Sues Galazar

  • Onex Chip Sees Light of Day

  • TranSwitch Expands EOS Line

Vitesse Semiconductor Corp. (Nasdaq: VTSS)

  • Chip Trio Faces Post-Bubble Blues

  • Vitesse Joins Next-Gen Sonet Party

West Bay Semiconductor Inc.

  • West Bay Ships Sonet Chip

  • West Bay Ships Its Chip

  • Has West Bay Got the Best Way?

It should be noted that many of the devices can also be used at lower rates than the ones given in than Table.

The rest of this report explains the technology behind GFP, VCAT, and LCAS. We end with a look at Ethernet aggregation and a summary of power, price, and availability.

The features listed in the table are explained in the text with the headings highlighted in bold. In order to follow the detailed product comparisons, it’s best to print out the Table.

GFP provides a standard mapping of Layers 1 and 2 protocols onto Sonet/SDH or OTN (Optical Transport Network – see ITU Approves Optical Standards). The initial application for GFP has been in Packet-over-Sonet (POS) applications, currently using LAPS (link access procedure for SDH) and HDLC (high-level data link control). The use of GFP extends to Ethernet and RPR as well as storage protocols and beyond.

There are two methods for mapping protocols onto GFP:

  • Frame-mapped is a direct replacement for HDLC. It has defined parameters for mapping all flavors of Ethernet, including 10/100, Gigabit, and 10-Gigabit Ethernet, as well as Point-to-Point Protocol (PPP) and RPR.

  • Transparent GFP has been defined to provide generic protocol mapping onto Sonet/SDH and OTN. Transparent GFP is used to map storage protocols such as Fibre Channel, ESCON, and FiCON, as well as other protocols such as Digital Video Broadcast (DVB).

30194_4.gifFigure 4 shows the mapping of GFP to Sonet/SDH using VCAT. IP data services that have previously been mapped to Sonet/SDH through ATM and HDLC, both tightly coupled with Sonet/SDH, can now be mapped through Ethernet and GFP.

All the devices listed in the Table on the previous page support frame-mapped GFP and can therefore be used to map Ethernet over Sonet/SDH. Only the latest 2.5-Gbit/s devices from Cypress Semiconductor Corp. (NYSE: CY) and TranSwitch and the new 2.5-Gbit/s and 10-Gbit/s devices from Vitesse Semiconductor Corp. (Nasdaq: VTSS) support Transparent GFP. These devices can be used to map storage networks based on Fibre Channel, ESCON, and FiCON. Competing devices require an external FPGA (field-programmable gate array) to handle transparent GFP.

For legacy systems, the most important mappings are POS using LAPS and ATM. LAPS is particularly important in China. The West Bay WB4500 is the only device to support LAPS and ATM in addition to GFP.

Virtual Concatenation is used to split Sonet/SDH bandwidth up into right-sized groups. These virtually concatenated groups can be used to support different customers and services and bill accordingly. VCAT works across the existing infrastructure and can significantly increase network utilization by effectively spreading the load across the whole network.

Sonet/SDH is a hierarchical network. At each level, payloads are a concatenation of lower-order payloads. So, for example, an STS192 (10 Gbit/s) payload consists of four OC48 (2.5 Gbit/s) payloads concatenated together.

With VCAT, an STS192 payload could consist of a number of virtually concatenated groups, each with up to 192 non-contiguous STS1 (51 Mbit/s) payloads. Each STS1 within a group may be provisioned over different parts of the network. VCAT supports both high-order paths and low-order tributary paths.

High-Order VCAT

  • Each path within a group is approximately 51 Mbit/s (STS1/VC3) or 155 Mbit/s (STS3c/VC4). Bandwidth is allocated using the H4 byte within the path overhead.

    Bandwidth is allocated in multiples of 51 Mbit/s and therefore high-order VCAT can be used to provision sub-rate traffic across Gigabit Ethernet. This makes high-order VCAT ideal for the metro application.

Low-Order VCAT

  • Each path within a group is approximately 1.5 Mbit/s (VT1.5/VC11) or 2 Mbit/s (VT2/VC12). Bandwidth is allocated using the Z7/K4 byte within the path overhead.

    Bandwidth is allocated in 2-Mbit/s chunks and therefore low-order VCAT can be used to provision sub-rate traffic across 10/100-Mbit/s Ethernet used in the access network.

As shown in the Table, most of the GFP devices with Virtual Concatenation support only high-order, as the metro was expected to be the main application. Over the past year it has become clear that the access network is a significant application for VCAT, and therefore many companies are planning to join TranSwitch and Galazar by introducing low-order VCAT devices. The Galazar MSF250 is the only device now available that supports both high- and low-order VCAT.

“I think there is a perception on a lot of people's part that initial acceptance would be with Gigabit Ethernet, and that was more towards the metro part of a network,” notes Dave Huff, VP of marketing at Multilink. “I think what has happened instead is that the most interesting part has turned out be with Ethernet and Fast Ethernet as an access technology.”

Currently available devices support between 2 and 64 VCAT Groups. At one extreme, the PMC-Sierra Arrow 2xGE with 2 VCAT groups is designed to support the mapping of two full-rate Gigabit Ethernet links onto a single OC48/STM16. At the other extreme, the Multilink VCat-10 with 64 VCAT groups is designed to map multiple full- or sub-rate Gigabit Ethernet links or many Fast Ethernet links.

When paths within a group are provisioned over different parts of the network, the order and phase alignment of the original payload must be reconstructed. VCAT devices support internal and external data buffering to handle the variation in delay between different paths. The standards allow for up to +/- 128ms of differential delay (enough to go ‘round the world).

A differential delay of up to 128µs is supported with embedded memory in most devices. This is adequate to compensate for the variation between adjacent fibers. As shown in the Table, most of the framer/mapper devices support at least +/- 25ms of Differential Delay using external memory. This is adequate for divergent routes across the U.S. Galazar and Multilink are the only companies supporting the full +/- 128ms, while the Cypress POSIC2GVC only supports +/-16ms.

The Link Capacity Adjustment Scheme (LCAS) is designed to allow the dynamic provisioning of bandwidth, using VCAT, to meet customer requirements. Integrating support for LCAS has a significant impact on the management software in carrier networks.

The initial application of LCAS has been limited to relatively small networks where the management software can be easily upgraded. Once in place, LCAS enables hitless service upgrade and improved response to network outage by eliminating the need for manual provisioning.

This combination of improved customer service and lower operation costs, due to fewer truck rolls, is very attractive to carriers. In the future, LCAS will also be used to enable the truly dynamic bandwidth provisioning required for time-of-day services.

“We see LCAS as being very important, as people move to selling services over Ethernet,” notes Andrew Schmitt, product marketing manager at Vitesse. “The more services you have – for example, remote backup services – the more you need bandwidth at certain hours of the day.”

LCAS can be used with both high-order and low-order VCAT. To support hitless rollover from one service level to another, low-level protocol support in the framer/mapper devices is required. The devices with LCAS support are shown in the Table. This support can either be in hardware, as in the TranSwitch EtherMap-3, or using an embedded RISC to offload the host processor, as in the TranSwitch Ethermap-48.

The importance of LCAS has grown significantly since our last report on this subject last June. Most new systems are likely to require LCAS support in the hardware even if the software is not upgraded for several years to take advantage of it. This is going to be a major issue for those semiconductor vendors that do not yet have LCAS support included in their devices.

“What we hear is a change over the last year,” notes Nilam Ruparelia, strategic marketing manager with Cypress. “Boxes need to be LCAS-compliant as soon as possible, but the carriers will not actually start using LCAS before 2005 or 2006.”

The devices listed in the Table support a Single Line interface, and in many cases Multiple Line interfaces as well, on the Sonet side. All the devices support the equivalent SDH rates. The Cypress and Galazar devices can be configured to support a single STS48/STM16, STS12/STM4 or STS3/STM1 port.

About half the devices provide support for Automatic Protection Switching (APS). The MARS2G5 P-MaxLT from Agere and MSF250 from Galazar include dual Sonet/SDH interfaces. One interface is active, with the other connected to the backup link.

Figure 5 shows a typical Framer/Mapper device with dual framer support for APS and an integrated TDM crossconnect.

30194_5.gifBy integrating a full STS1-level crossconnect on the framer/mapper device, the TDM switching in a system can be distributed across the line cards rather than being centralized in a TDM switch fabric. Devices from Agere, Transwitch, and West Bay support this TDM XC function.

“On the metro access side, I see a trend towards a more cost-effective, flexible architecture,” says Tino Varelas, president and CEO of West Bay Semiconductor, “including a form of TDM switching which I would call distributed TDM switching.”

Also shown in Figure 5 are the typical system interfaces. Most of the devices in the Table support an OIF SPI-3/4 System Interface or, if an Ethernet MAC (media access controller) is integrated, the Ethernet Media-Independent Interfaces (MII, GMII, and XGMII). The West Bay WB4500 supports both SPI-3 and Utopia Level 3, while the Agere devices have an enhanced Utopia Level 3 interface.

As discussed earlier, a major application of GFP and VCAT is to support the mapping of sub-rate Ethernet services. In many cases, metro customers do not require a full gigabit of bandwidth but may require 50-, 100-, or 200-Mbit/s.

By using GFP, VCAT, and LCAS combined with some policing, multiple Gigabit Ethernet links can be aggregated onto a single OC48 pipe, as shown in Figure 6.

A service supporting bandwidths between 50 Mbit/s and 1 Gbit/s is provisioned over each Gigabit Ethernet link. If a customer requires an increase in bandwidth of 100 Mbit/s or 200 Mbit/s, this can be provisioned without changing the underlying equipment.

A similar approach can be taken in the access network to provision bandwidth across Ethernet and Fast Ethernet, using low-order VCAT.

Several devices in the Table include either 10/100-Mbit/s, Gigabit, or 10-Gigabit Ethernet MACs. The Transwitch EtherMap-48 is unique, as it includes four Gigabit Ethernet MACs and the buffering to multiplex traffic from the four gigabit links onto a single 2.5-Gbit/s Sonet/SDH line.

A further development in the access market will be the aggregation of 10/100-Mbit/s Ethernet over Gigabit Ethernet and then onto the Sonet/SDH network.

“Ideally, you would like to be able to map streams of data with different characteristics on the same Ethernet into different VCAT pipes,” says Multilink’s Dave Huff.

Also included in the Table is the Multilink MTC6310 Varakai. This device is unique, with support for GFP, a 10-Gigabit Ethernet MAC, and 16 Gigabit Ethernet MACs – but no Sonet framer. This device also supports Ethernet buffering on-chip and has 16 1.25-Gbit/s serial links for Gigabit Ethernet and four 3.125-Gbit/s XAUI links for 10-Gigabit Ethernet.

In this final section we review the devices available for each of the bandwidths and discuss the last three columns in the Table, covering Power, Price and Availability. Unless otherwise stated, the power number is typical and the price is for volume production.

155-Mbit/s Devices

There are only two 155-Mbit/s GFP devices available; however, some higher bandwidth devices do support OC3 rates.

The HDMP-3001 from Agilent Technologies Inc. (NYSE: A) does not support VCAT and LCAS – but it is in production and is the cheapest GFP device at $50.

The Ethermap-3 from TranSwitch has hardware support for LCAS and handles low-order VCAT with eight groups, ideal for mapping from the eight integrated Ethernet or single Gigabit Ethernet ports. The device is sampling with a low power consumption of just 2W.

622-Mbit/s – 1.2-Gbit/s Devices

Agere is now sampling lower-bandwidth versions of the MARS2G P-VC and MARS2G P devices. These have the same features and system interface as their higher-bandwidth brothers but are available at significantly lower costs. Other vendors are likely to follow suit.

2.5-Gbit/s Devices

Most of the GFP devices available support 2.5-Gbit/s bandwidth.

“OC48 remains the sweet spot in this market,” says Cypress’s Ruparelia. “A lot of our customers want to go for second-generation OC48 for cost cutting and future enhancement. We have changed gears and put a higher priority on OC48 feature enhancement rather than OC192.”

The majority of devices have typical Power consumption between 4W and 5W. The exceptions are the Vitesse VSC9115, which is really the 10-Gbit/s VSC9118 slowed down, at 8W; and the low power WB4500 from West Bay at 3W.

Prices for OC48 devices range from $180 for the Cypress POSIC2G without VCAT and LCAS, to the fully spec’d TranSwitch Ethermap-48 at $550.

The TranSwitch EtherMap-48 will be the most integrated OC48 device, with support for transparent GFP, VCAT with 48 groups, and LCAS, as well as integrated Gigabit Ethernet MACs. This device is expected to sample towards the middle of 2003.

Close behind the EtherMap-48, and expected to sample ahead of it, is the Galazar MSF250. This $500 device will support high- and low-order VCAT with 24 groups. The device has integrated TDM interfaces and Fast Gigabit Ethernet MACs. The MSF250 will be the first product from Galazar, a company that started out designing systems.

Cypress has the only two OC48 GFP framer/mapper devices in production; the POSIC2GVC with VCAT supporting 16 groups, and the POSIC2G just supporting GFP. Both devices support transparent GFP. Future development is expected to include support for low-order VCAT.

Agere has a range of 2.5-Gbit/s devices, all based on the MARS2G5 P-VC. Prices range from $343 to $522, and samples are available. All the devices have an enhanced Utopia system interface rather than SPI-3.

Agilent and PMC-Sierra offer 2.5-Gbit/s devices as well. The PMC-Sierra Arrow 2xGE has two integrated Gigabit Ethernet MACs. Neither product includes LCAS support.

10-Gbit/s Devices

Intel Corp. (Nasdaq: INTC) is the only company shipping 10-Gbit/s GFP framer/mapper devices. The IXF18101/102 devices support a number of modes, including GFP over Sonet/SDH. No support is provided for VCAT or LCAS.

The Vitesse VSC9118 is now sampling. With volume pricing at $536 and 10W power dissipation, this could be a very attractive device for OC192 applications. The 2.5-Gbit/s VSC9115 is a very similar device, with the same 10-Gbit/s SPI-4.2 system interface and the number of VCAT groups reduced from 64 to 48.

The Multilink Vcat-10 was announced in 2002, and samples are expected to be available during the second quarter of 2003. Like the TranSwitch EtherMap-48, the Multilink Vcat-10 has an integrated RISC to offload the host processor for LCAS.

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