With the price of 100G optics cutting down, 2017 witnesses the great expansion of `100G hardware market. QSFP28 and CFP 100G optical transceivers are becoming popular among customers. Not only Cisco, HPE, Brocade, and Huawei, but the third party vendors like FS.COM offer 100G devices including the 100G switches, MTP/MPO cables, QSFP28, CFP/CFP2/CFP4 and so on. In this blog, I will compare 100G QSFP28 SR4 with CFP SR10 modules, and analyze the electrical and optical diagram.

CFP 100GBASE-SR10 Module Outlook

CFP 100GBASE-SR10 is a MSA specified 100G C-form factor supporting link lengths of 100 m/150 m over laser-optimized OM3/OM4 cable, respectively. It is mainly used in 10 x 10 Gigabit Ethernet mode along with MTP Harness cables for connectivity to 10 10GBASE-SR optical interfaces. It usually enables high-bandwidth 100Gbps links over 24-fiber MPO/MTP ribbon cables.

100G QSFP28 100GBASE-SR4 Outlook

QSFP28 100GBASE-SR4 module is a parallel 100G optics designed with optical/electrical connection and digital diagnostic interface. It offers 4 independent transmit and receive channels, each capable of 25Gbps operation for an aggregated data rate of 100Gbps for 100m on 12-fiber MPO/MTP OM4 fiber cable. Figure 1 shows the CFP SR10 (left) and QSFP28 modules (right).

The QSFP28 SR4 transceiver (such as Cisco 100G-QSFP28-SR4) is compatible with 100G QSFP 100GBASE-SR4 standards that meets IEEE 802.3 and MSA requirements with power dissipation well under 3.5W. It supports both 100GBASE-SR4 as well as 4x25G breakout, 100G QSFP28 to QSFP28 DAC and 100G QSFP28 SR4 to 4SFP28 break-out cables.

Comparison Between CFP 100GBASE-SR10 and 100G QSFP28 100GBASE-SR4

• Size Comparison

CFP module is the old generation 100G transceivers. It is designed after SFP modules, but quite larger to support 100Gbps in 10 x 10Gbps lanes. QSFP28 is the newly released 100G form factor, which further increase port density and reduce footprint & power consumption. QSFP28 100GBASE-SR4 has the same form factor as the 40G QSFP optics, supporting 4x25Gbps mode.

The above image shows the size comparison between CFP 100GBASE-SR10 and 100GBASE SR4 QSFP transceiver. Obviously, QSFP28 is much smaller than CFP 100G modules, which just in time explains the reason that QSFP28 optics is more popular than CFP transceivers.

• Working Principle

As noted before, QSFP28 SR4 modules work on 4x25G lanes and CFP SR10 operates over 10x10G lanes.

100GBASE-SR4 supports higher speed per channel (25Gbps) than 100GBASE-SR10 (10Gbps), so that QSFP28 can reduce port density with compact footprint.

• Terminating Cables—12F Vs. 24F MTP/MPO MMF

Both CFP 100GBASE-SR10 and 100G QSFP28 100GBASE-SR4 terminates with MTP/MPO OM3/OM4 cables for 100G transmission. However, QSFP28 100GBASE-SR4 modules uses a 12 fibers MPO/MTP multimode cable for connectivity (4 Tx and 4 Rx, each lane providing 25 Gbps of throughput) while CFP 100GBASE-SR10 optics use a 2×12-fiber or 24-fiber strand MPO/MTP multimode cable for connectivity (10 Tx and 10 Rx, each lane providing 10 Gbps of throughput).

CFP 100GBASE-SR10, compared with QSFP28 SR4 optics uses two 12-fiber or one 24-fiber MPO/MTP cable. It is not a cost-effective solution in terms of the cable management.

Conclusion

100GBASE-SR10 CFP and 100GBASE-SR4 QSFP28 are the 100G multimode optics. QSFP28 SR4 transceivers, like 40GBASE-SR4, use a 12 fiber MPO cable with 4 strands for transmit and 4 for receive. While CFP 100GBase-SR10 optics uses a 24 strand MPO cable: 10 strands for transmit and 10 strands for receive. From the above article, we know that 100GBase-SR4 QSFP28 is more cost-effective than 100GBase-SR10 CFP in port density and cable management.