Ted H. Kim's Weblog

Monday October 11, 2004

What is iWARP?

There is way too much to write about and not enough time. Nevertheless, a message on this topic is way overdue. So let's start off with the most basic stuff.

What is iWARP anyway? It's a rather stretched acronym for "Internet Wide Area RDMA Protocol" or more simply Remote DMA on Internet Protocol. (My apologies if you are wondering what "Remote DMA" is, but that will be a topic for another time.) If you are still with me, the heart of this work is actually a set of protocols being standardized in the IETF RDDP working group. The original submissions for this stuff came from the RDMAC.

Back to the protocols. Now just to confuse things, one of the protocols is actually called the "RDMA" protocol and the other "DDP" (Direct Data Placement). These protocols layer on top of framed reliable transports. In particular, this stuff is designed to run over SCTP or TCP with the "MPA" (Marker PDU Aligned Framing) protocol. (TCP needs MPA, because TCP is really a stream protocol, not a message oriented one.) All of this rides on IP itself.

Since IP is the foundation of everything here, this whole stack could run over anything that can do IP. But frankly what drives the whole commercial interest in iWARP is 1 or 10Gb Ethernet TCP/IP with hardware offload to do the protocol processing. Ethernet TCP/IP has the volume. The Gigabit speeds make hardware offload more compelling (otherwise a lot of CPU is wholy consumed by network protocol processing). The potential market is enough to get some big system/OS vendors, NIC vendors and a host of startups excited.

To complete the picture, the UNH-IOL has setup an iWARP Consortium to work on Interoperability. Also, the ICSC has the RNIC-PI working group to work on standardized standard programming interfaces. Also, there is an OpenRDMA group is in the process of getting organized.

iWARP also has something called the verbs. The verbs are an abstract programming interface to iWARP. The verbs are needed because the programming model for using RDMA efficiently is not the same as what most socket based network programming currently uses. Verbs are not a true API, hence the need for groups like RNIC-PI.

iWARP bears many similarities to InfiniBand, especially in its use of RDMA and the verbs. But the main difference is in the transport implementation choices. iWARP was designed to ride on IP allowing it try to ride on the coattails of the whole IP world and on the volume of Ethernet. Some folks have issues with whether this whole stack is rather awkward and ungainly, especially on TCP. But frankly the commercial side ignores all of that because the Ethernet TCP/IP base is key to the perceived market opportunity.

More to come ...

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(2004-10-11 11:00:00.0) Permalink