There are two additional mechanisms that will further enhance convergence over Ethernet, but are not absolutely required, these are:
- Link level congestion management - this effort is focused on creating a standard mechanism that can control unicast traffic in networks with long-lived data flows with respect to their bandwidth-delay product. Link level congestion management provides a mechanism for detecting congestion and backing off the traffic flowing on the congested traffic class.
- Link level shortest path first based routing protocol - this effort is focused on creating a standard mechanism that can provide shortest-path frame routing in multi-hop IEEE 802.1-compliant Ethernet fabrics with arbitrary topologies, using existing link-state routing protocol technology. Note, this standard is being pursued in the IETF's TRILL working group.
Figure 6 also shows that Fibre Channel traffic can take advantage of CEE. IBM is working with Brocade, Cisco, Emulex, Intel and several other companies to create a set of IEEE 802 standard functions that improve Ethernet's ability to converge fabrics in the data center. The next section will describe how CEE can be used in fabric convergence scenarios.
CEE Convergence Options
CEE enhances the NAS and iSCSI option covered earlier, by providing traffic differentiation at the link layer. Today, data center switches can use network layer traffic differentiation, but that level requires switches with layer 2+ capabilities, which have higher latencies (and cost) than layer 2 switches. Similar to layer 2+ switches that support traffic differentiation, CEE switches must support per traffic class resources, which means more buffer resources than switches that don't support traffic differentiation. However, unlike today's layer 2+ switches that support traffic differentiation, CEE switches do not have to retain IP routing tables or associated contexts.
As shown in Figure 7, CEE also enables an emerging convergence option, FC directly over CEE. On the server side, this option uses either FC or FCoCEE based adapters to connect servers to storage. If FCoCEE is used, then the same adapter can also be used to connect the server to other servers or networking equipment. That is, the same adapter can be used to carry other traffic classes, such as HPC, LAN or IPC messages. On the storage side, this option uses either FC or FCoCEE based adapters to connect servers.
7. FCoCEE based Convergence
For data centers that have a large FC install base, FCoCEE enables new servers or storage deployed in that data center to use a single link for both Ethernet and FC communications. Many enterprise data center customers will likely want the infrastructure required to enable this option to be vetted out before production deployment begins. That infrastructure includes: interoperable support from FCoCEE adapter vendors, interoperable support from FCoCEE switch and gateway vendors and most importantly the management software required to interlink the virtual and physical FC fabric to the physical CEE fabric. Given that a portion of the HPC and Analytics markets is interested in network convergence today, we expect FCoCEE to fare well in these two market segments (esp. when IB's high bandwidth and low latency are not needed).
8. Interlinks between management layers