SFP+ Transceiver vs. SFP+ DAC vs. fixed 10G Copper Ports - which one to choose?

The growth of the Internet caused a dramatic development of new network technologies capable to withstand the needs of the customers. This mainly caused the expansion of high speed solutions like 10 GB/s and 40 GB/s. This is particularly noticeable with 10 GB/s Ethernet solutions as today the leading IT managers are faced with a challenge to choose the appropriate equipment with the goal to gain maximum performance. Because 10 GB Ethernet is offered in both optical and copper options, they must know the various advantages and disadvantages of these technologies.

When designing a new network architecture that would be based on at least 10GB Ethernet, the one thing we must be aware of is the fact that over time it will grow a lot in order to support the future needs of complex network applications. The present trends show that the leading IT managers are refusing to deploy a new cable infrastructure for separate network traffic applications, mainly because they want to reduce the overall costs. This leads to new challenges that the cable infrastructure has to support.

As many IT managers are aware, the simple 10GBASE-T technology, which is based on copper, is a lot cheaper than the optical SFP+ solution. Even though there is noticeable step forward with the new 10GBASE-T technology, it still has some limitations. For example, because it’s based on copper, it is highly sensitive to cross-talk. The reach capability is at least 1/3 smaller than the optical 10GB SFP+ solution. With 10GBASE-T the maximum reach would be 100 meters, while with SFP+ solutions it would be 300 meters on Multi-mode fibers.

AS Datacenters grow and implement new technologies in their infrastructures, the expectations from the customers are also growing. That’s why Datacenters must concentrate on offering the best service possible. This means that they must offer a service with low packet loss and low latency.

These three technologies have different latency properties depending on the number of links installed:

As the table shows, the SFP+ solutions, both fiber and DAC, provide a significantly lower latency compared to 10GBASE-T copper based solution. This is mainly because of the process of transmission found with 10GBASE-T. Here the PHY, which is a chip required for physical layer functions, uses block encoding for an error-free data transmission. This function requires for a block of data to be read on the PHY transmitter and on the other side the reverse process is repeated. The PHY standard specifies 2.6 microseconds for the transmit-receive pair which is a quite high latency.

On the other hand SFP+ introduces simplified electronics which avoid the data encoding resulting in typical latency of 300 nanoseconds per link. Even though the 2 microseconds of the 10GBASE-T doesn’t sound too bad, in a network infrastructure of a thousand links and at least 4 hops to reach the destination this will result in 10.4usec latency and this is a significant difference compared to the SFP+ solutions which, in the same situation, would provide around 1.2usec latency. Even though these numbers are not big, this kind of latency difference, in a Datacenter environment, can result in delays in CPU and applications operations.

Another big difference is the power consumption of the 10GBASE-T compared with the SFP+ solutions. Today the IT managers are constantly trying to reduce the power consumption of their network. This is mainly because the networking devices generate a lot of heat, and as the power consumption grows, the heat also grows so additional cooling is needed. These cooling systems also consume a lot of power. The general rule is that for every watt of power consumed, additional two watts are needed for cooling.

The 10GBASE-T solution consumes a lot more power than the SFP+ solutions, approximately three to four times more. The power consumption of 10GBASE-T depends on the distance of the cable and it can vary from 2 to 5 watts per port at each end of the cable. On the other hand the SFP+ solutions consume around 0.7 watts per port regardless of the distance of the cable. This is a key difference knowing that in a typical Datacenter there are thousands of cables installed which, if SFP+ is used, would save a lot of money and headaches on a long run.

The new trends in Datacenters and Service Providers show that the deployment of new sensitive applications are demanding low latency solutions, thus the SFP+ solutions are the optimal choice for this kind of installations. They provide low latency regardless on the distance and they consume far less power than the copper solutions which on the long run saves more money for future network upgrades.