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40 gigabit ethernet is available in market since 2010, IEEE’s Higher Speed Study Group initiated research and development of the 40G and 100G ethernet standards in 2007 and came up with standard guidelines for its implementation as a standard. Since 2010, 40 Gbps ethernet is gaining popularity as the demand for higher bandwidth and faster speed data transfer is increasing day by day. The IEEE standard defines 40 Gbps ethernet as a standard that enables the transfer of ethernet frames at 40 gigabits per second. The minimum requirement to meet the standards are precisely defined as:
- Preserve the current 802.3 frame format, along with the minimum size, and the maximum size
- Support high-bandwidth applications such as video on demand (VoD) and high-performance computing (HPC)
- Support high-speed switching, routing, and application functions in data centers
- Exhibit a bit error rate (BER) of 10-12 or better (a maximum of one error bit per 1,000,000,000,000 bits transmitted)
- Provide support for optical transport network (OTN)
- Provide specifications for operation over single-mode optical fiber, laser optimized multimode optical fiber, copper cables, and backplanes
The above mentioned guidelines are the minimum requirements to meet the 40 Gbps standard. It can be observed that the 40 Gbps standard doesn’t specify the form-factor of the transceiver. Many vendors have come up with various transceiver form-factors that can support 40 Gbps ethernet. The below mentioned form-factors have been standardized to be used with 40 Gbps ethernet:
- QSFP+
- 4xSFP+ (Direct Attach Breakout Cable)
- CFP
We will be discussing the above mentioned transceiver standards in detail in the upcoming sections.
QSFP+ (Quad Small Form-factor Pluggable) transceivers are the most widely used 40 Gbps ethernet transceivers. Initially the QSFP standard was developed to support 4 x 1 Gbps channels over a single transceiver and later on the technology was introduced to allow 4 x 10 Gbps channels allowing for 40 Gbps link capacity. QSFP+ transceivers are compact and provide excellent support for extended distance links. Figure 1 illustrates a 40 Gbps QSFP+ transceiver. The QSFP+ transceivers can also support the fibre channel and Infiniband traffic. QSFP+ transceivers are being extensively deployed in datacenters to carry 40 Gbps ethernet traffic, 10G fibre channel or QDR Infiniband.
The leading original equipment manufacturers such as Cisco, HP and Juniper have a wide range of network equipment that supports 40 Gbps ethernet and QSFP+ transceivers.
4xSFP+ (Direct Attach Breakout Cable)
As mentioned in the previous section of QSFP+, the QSFP+ transceiver carry four channels of 10 Gbps ethernet simultaneously to provide 40 Gbps bandwidth. This feature allows the manufacturers to split the channels into four separate 10 Gbps links. This configuration is ideal for a high density network where number of access switches in a datacenter are very high. The access switches are connected to core over 10 Gbps independent links and the core switch aggregates the links of four switches on its single 40 Gbps port. Figure 2 shows a direct attach breakout cable which is used for this purpose. The 10 Gbps interfaces are used to connect access switches and the 40 Gbps end is connected with the core switch. The other benefit of using the direct attach breakout cable is the ability to install 10 Gbps switches in a 40 Gbps network. Furthermore, ether-channel technology can be utilized to provide 20 Gbps uplinks to the core.
CFP
The 40GBASE CFP transceivers are plugged into the CFP port of a communication equipment. The main benefits of a 40GBASE CFP transceiver are:
- Ability to upgrade to 100 Gbps ethernet in future as the CFP supports 100 Gbps ethernet
- Pay-As-You-Grow model
- Support for ribbon fiber cables
- Multi-mode and single-mode optical fiber cable support
Figure 3 shows a CFP 40 Gbps transceiver. CFP transceivers are primarily designed for 100 Gbps applications but can also support 40 Gbps networks. This makes these transceivers ideal for the networks where some portion of the network operates on 100 Gbps connectivity and some portion operates on 40 Gbps. Using the CFP transceivers in such networks eliminates the need of mix and match transceivers and provides an option to upgrade the network to 100 Gbps in future easily.
