Communications IC makers are now beginning to supply chips that will relay Ethernet packets over Sonet or synchronous digital hierarchy (SDH) telecom networks. The focus of the move to Ethernet over Sonet (EoS) is to build transparent tunnels for LANs sitting at different sites that can use existing Sonet or SDH infrastructure.
Philip Gadd, marketing manager for Agilent's networking chips division, said: "Service providers need a cost-effective way to offer enterprise data services via their legacy Sonet/SDH infrastructure."
Last year, Agere Systems and PMC-Sierra launched devices or designs aimed at hooking up Gigabit Ethernet networks to 622Mbit/s, STM-4 or 2.5Gbit/s, STM-16 links. Last week, Agilent pitched in with a device, the HDMP-3001, which is aimed at 100Mbit/s Ethernet and 155Mbit/s wide-area links. The company said it expects the STM-1/OC-3 connection to be a commonly used leased-line type to join lans at different campuses.
Agere's offering is based on a mixture of intellectual property (IP) cores intended for the FPGA line that the company is selling to Lattice Semiconductor together with hardwired devices. The design is aimed at switches with four Ethernet ports and a wide-area port.
PMC-Sierra's Arrow-2xGE handles two Gigabit Ethernet channels, mapping them onto an STM-16 ring.
All of the companies have decided to adopt the generic framing procedure (GFP) to encapsulate Ethernet packets so they can be sent over a Sonet link. However, Agilent has decided to extend encapsulation support to the HDLC-like link-access procedure for SDH (LAPS).
Although GFP is not yet a fully ratified standard, it has reached the point of becoming a stable draft, G.7041. One useful aspect of GFP is that it does not incur any net bandwidth expansion in the translation from Ethernet frames to Sonet or SDH frames, as the GFP frame header is the same size as the Ethernet preamble.
Because the aggregate datarates of Ethernet and Sonet differ substantially, the companies have also embraced a technique known as virtual concatenation. This is a more flexible way of using Sonet bandwidth by tying together non-contiguous payload envelopes into virtual frames. That allows for better ring usage with the bursty traffic that is typical of Ethernet data networks.
PMC-Sierra said the approach is analogous to the multilink point-to-point protocol used to aggregate ISDN channels for higher-speed Internet dial-up connections.