With the rapid development of public cloud, Internet of Things (IoT) and artificial intelligence (AI), we are entering into the era of 100G optical transceivers. It is well known that in March 2013 Cisco launched its proprietary 100G optical transceiver module called CPAK, which offers a high-density 100Gbps connectivity selection for enterprises, service provider data centers and edge networks. With the rapid development of technologies in the past several years, does CPAK 100G optical transceiver still win a place as before? Let’s take a close look at it again.
CPAK, a proprietary 100G form factor for Cisco switches and routers incorporating IEEE standard interfaces available in several different types: 100GBASE-SR10, 100GBASE-ER4L, 100GBASE-LR4, 10x10G-ERL, 10x10GBASE-LR, can support 100G connections with a variety of distance and fiber type requirements. It supports 10X 10Gbps and 4X 25Gbps mode for an aggregate of 100Gbps data rate. CPAK 100G can also operate high-density 10G breakout with MPO-24 cables. With the application of CMOS photonics, Cisco CPAK 100G modules combine the greatest density and bandwidth with the lowest power consumption available in the market before the emergence of QSFP28.
Figure: CPAK 100G Transceivers
The following table shows detailed information on different types of CPAK 100G.
|CPAK Module||Wavelength||Cable||Connector||Max Cable Transmission|
|CPAK-100G-LR4 / CPAK-100GE-LR4||1310nm||SMF Duplex||SC/LC||10km|
|CPAK-10x10G-LR||1310nm||SMF (24 fibers)||MPO/MTP||10km|
|CPAK-100G-SR10||850nm||OM3 / OM4||MPO/MTP||100m / 150m|
|CPAK-10x10G-ERL||1550nm||SMF (24 fibers)||MPO/MTP||25km|
|CPAK-100G-SR4||850nm||OM3 / OM4||MPO||70m / 100m|
|CPAK-100G-CWDM4||1271nm, 1291nm, 1311nm, 1331nm||SMF Duplex||LC||2km|
|CPAK-100G-PSM4||1295nm - 1325nm||SMF (12 fibers)||MPO||500m|
The most unique feature of CPAK 100G is that it is the first 100G optical module using CMOS photonics. CMOS photonics, also called silicon photonics, is a technology that can control the flow of photons in place of electrons by integrating multiple circuit components in a highly efficient design, and then printing entire circuits directly on silicon wafers to produce optical devices. Hence, the CPAK 100G transceiver utilizing CMOS technology has a smaller footprint but higher port density, which enables extremely efficient, low-power optical circuits.
CPAK 100G accommodates a variety of distance and fiber type requirements. The distance varies from 70m to 25km. For connectors and cabling, CPAK can be compliant with SC/LC connector and MPO/MTP connector. CPAK also has strong interoperability. Generally, different 100G module types can communicate with each other under the same standard and the same speed rate. For example, 100GBASE-LR4 whether from CFP/CFP2/CFP4 or CPAK 100G will interoperate.
In a comparison with CFP2 modules, CPAK optical transceivers are 20% smaller and consume 40% less power. In other words, if you use CPAK 100G other than CFP2 modules in your data center switches, it can offer 20% greater port density and front-panel bandwidth. But it is a little higher than CFP4 and QSFP28.
QSFP28 optical transceiver, due to its smallest form factor and lowest power consumption, is regarded as the most promising 100G optical module. In terms of the form factor, QSFP28 is more compact than CPAK modules. And Cisco CPAK 100GBASE-LR4 module supports links up to 10km over SMF with a nominal power consumption of less than 5.5W, while QSFP28 100GBASE-LR4 supporting up to 10km consumes nearly 3.5W. CPAK 100G optics obviously don’t have a shot when competing with QSFP28 optical transceivers. The following table shows their differences.
|Applications||Ethernet, Sonet/SDH, OTN||Infiniband, Ethernet|
|Dimensions (W x L x H, mm)||34.8x101.2x11.6||18x52x8.5|
|Electrical Interface||CAUI-4, CAUI||CPPI-4|
CPAK transceiver definitely stands for an important advancement in optical networking with its proprietary CMOS photonics technology for high port density and front panel bandwidth. However, in such a fiercely competitive market environment, it is hard to say which product will maintain popularity for a long period. After all, technology decides everything. Today, it comes out that CPAK is not irreplaceable any more. So far, the biggest challenge to win the market comes from QSFP28 transceivers that have delivered fabulous results in developing 100G networks. The utilization rate of CPAK 100G has greatly decreased, but it is still irreplaceable for some old equipment.
Nowadays, 100G transceiver technology is gradually becoming mature. CPAK 100G transceiver module is popular for its smaller size and lower power consumption. However, when competing with open-source 100G products (CFP/CFP2/CFP4/QSFP28), CPAK cannot be the ideal one for 100G high-density connectivity. CXP, CFP, CFP2, CFP4, QSFP28 also offer good selections for customers and are the mainstream in the market.