RDMA over TCP
Ethernet is the most prevalent network interconnect in use today. IT organizations have invested
heavily in Ethernet technology and most are unwilling to tear out their networks and replace them.
Reliance on Ethernet is justified by its low cost, backward compatibility, and consistent bandwidth
upgrades over time. Today's Ethernet networks, which use TCP/IP operations, commonly operate at
100 megabits per second (Mb/s) and 1 gigabit per second (Gb/s). Next-generation speeds will
increase to 10 Gb/s. Customer migration to 10-Gb Ethernet will be tempered by the input/output
(I/O) processing burden that TCP/IP operations place on servers.
The addition of RDMA capability to Ethernet will reduce host processor utilization and increase the
benefits realized by migrating to 10-Gb Ethernet. Adding RDMA capability to Ethernet will allow data
centers to expand the infrastructure with less effect on overall performance. This improves
infrastructure flexibility for adapting to future needs.
RDMA over TCP is a communication protocol that moves data directly between the memory of
applications on two systems (or nodes), with minimal work by the operating system kernel and without
interim data copying into system buffers (Figure 2). This capability enables RDMA over TCP to work
over standard TCP/IP-based networks (such as Ethernet) that are commonly used in data centers
today. Note that RDMA over TCP does not specify the physical layer and will work over any network
that uses TCP/IP.
Figure 2. Data flow with RDMA over TCP (Ethernet)
RDMA over TCP allows many classes of traffic (networking, I/O, file system and block storage, and
interprocess messaging) to share the same physical interconnect, enabling that physical interconnect
to become the single unifying data center fabric. RDMA over TCP provides more efficient network
communications, which can increase the scalability of processor-bound applications. RDMA over TCP
also leverages existing Ethernet infrastructures and the expertise of IT networking personnel.