Denver - The upcoming Intel Developers Forum is likely to witness a good deal of debate over competing approaches to switching PCI Express packets.
The forum, to be held in San Francisco March 1 to 3, will hear arguments favoring both the PCI Express Advanced Switching Interface (ASI) as well as the existing PCI Express standard for switching in server and storage clusters.
Semiconductor players at the forum are coming down on both sides of the debate.
StarGen Inc. (Marlborough, Mass.) will introduce its Merlin ASI switch and Kestrel ASI-to-PCI bridge, while Integrated Device Technology Inc. will launch a line of PCI Express fan-out switches and bridges.
The areas of overlap may not be as big as the complementary applications in which PCI Express and Express ASI will augment each other.
PCI Express on its own is likely to be used in data center server and storage clusters as upgrades to PCI-X, which is why IDT put a heavy emphasis on having its bridge chip support PCI-X 2.0 in both Mode 1 and Mode 2. The ASI standard is used as high-end server clusters upgrade to true communications networking duties.
"PCI Express on its own will be important in the server community for a long time," said Wade Appelman, the vice president of marketing at StarGen. "But quality-of-service features, security and multicasting are going to be the elements that drive ASI."
StarGen touts a place for its switch and bridge architecture, called AxSys, in shelf-to-shelf and system-to-system interconnect. While PCI Express and Serial Rapid I/O can have a place in chip-to-chip interconnect, competing against standards like HyperTransport, ASI will not have a role in this level of interconnect, Appelman said.
The Merlin ASI switch scales from 80 to 400 Gbits/second and can be used in PCI Express as well as ASI designs. Quality-of-service prioritization is implemented along with multiple flow-control algorithms, and the port widths are programmable. Merlin uses PCI-8 leaf bridging to support existing PCI Express devices on an ASI network.
The Kestrel PCI Express-to-ASI bridge chip also offers integrated QoS and protection mechanisms, and supports full native tunneling between Express and ASI environments. For legacy PCI Express systems, Kestrel integrates a native PI-8 switch internally. The Kestrel bridge chip can be used with any host CPU and includes a direct memory access controller for CPU offload.
Appelman said that a new subset of the Advanced Telecommunications Computing Architecture standards-called MicroTCA, or uTCA-could be an important realm for bridging the ASI and PCI Express environments.
The PCI-SIG has identified a mezzanine personality module for MicroTCA that's bigger than a PMC card. Called the Advanced Messaging Card, the standard will allow tiered combinations of PCI Express and ASI to exist in single, low-profile systems.
IDT, meanwhile, is keeping an eye on ASI for future development but is rolling a range of PCI Express switches and bridges for what the company anticipates will be the sweet spot of the PCI market, said Mario Montana, IDT's serial-switching marketing director.
IDT's serial switching division was created in April 2004 from the company's $35 million acquisition of ZettaCom Inc. Since then, server topologies have evolved to favor a tree of buses with one root and multiple endpoints.
Consequently, IDT (Santa Clara, Calif.) designed a PCI Express family with multiple switch fan-out options, as well as a bridge family with multiple modes.
The PES24N3 is a switch with 24 lanes of PCI Express and three ports, while the PES12N3 has an identical number of ports, but with 12 lanes of PCI Express. Nontransparency is a key feature of the switches, since such bridging can link two PCI Express trees. The nontransparent cut-through switches have a line-rate switching capacity of 6 Gbits/s. Each port can support x1, x2, x4 or x8 operation, with auto-link width negotiation offered on each port.
For bridge functionality, IDT is offering the PEB20N1 bridge from PCI Express to PCI X 2.0 Mode 1 (133 MHz and 64 bits), as well as the PEB20N2 to bridge PCI Express to PCI X 2.0 Mode 2 (533 MHz and 64 bits). Both versions support forward and reverse bridging in transparent and nontransparent modes. Both offer autonegotiation of line width-x1, x2 and x4 in both versions and x8 in the Mode 2 chip.
IDT is opting for aggressive pricing for server applications, with volume price on devices ranging from $22 for the Mode 1 bridge to $45 for the Mode 2 bridge, $26 for the 12-lane switch and $38 for the 24-lane switch.
StarGen will announce its pricing at the time of sampling this summer.
Meanwhile, both companies say they continue to face competition from vendors touting Ethernet as a serial switching standard.
Appelman of StarGen said that despite the ubiquity of Ethernet, the framing standard has little to offer in moving from OC-48 (2.5 Gbit/s) to 10 Gbits/s, and TCP offload engines or RDMA devices don't solve that problem of overhead. The migration from PCI Express to ASI is still the most sensible strategy for serial switching, Appelman said.