We've heard a lot about what companies are doing to converge networks in the data center. Today I'd like to take a quick look at some work that's being done on the standards side to enable the convergence.
The IEEE's Data Center Bridging Task Group is moving along some enhancements to existing 802.1 bridge specifications. The purpose of the enhancements is to get Ethernet to a place where it can accommodate network traffic that is very sensitive to latency or loss.
The enhancements center around 802.1Q, the standard for virtual LAN tagging. By specifying certain parameters around those VLANs, Ethernet can start to accommodate the sensitive traffic while continuing to support traffic that is fine with Ethernet the way it is.
The first enhancement in the works, 802.1Qau, specifies protocols and procedures for managing congestion of long-lived data flows within a domain where bandwidth delay needs to be limited. According to the project authorization request, the specification allows bridges or switches to communicate information about network congestion to end stations that are capable of rate limiting, to avoid frame loss. The frames that are subject to congestion control would have priority values specified in the VLAN tag. This spec is expected to be standardized next year.
The second enhancement, 802.1Qaz, specifies “enhanced transmission selection to support allocation of bandwidth amongst traffic classes.” If a traffic class isn't using all the bandwidth allocated to it, this would allow other traffic classes to use the bandwidth. The project authorization request notes that 802.1Qau would specify congestion-managed traffic classes, and 802.1Qaz is needed to allow congestion-managed traffic to share the same network as traditional traffic.
The third enhancement is 802.1Qbb, which specifies protocols and procedures for enabling flow control per traffic class. Such priority-based flow control is intended to eliminate frame loss due to congestion. The project authorization request describes the mechanism as similar to that of IEEE 802.3x PAUSE, but operating on individual priorities.
The upshot of all of these upcoming enhancements is that the IEEE is trying to make Ethernet safe for all kinds of traffic in the data center. We should start to see these specifications reach standard status either this year or next.
