Breakout connectivity is becoming increasingly popular and important with the development of network bandwidth and speed. Breakout mode enables high-speed ports of switches or routers to access lower-speed interfaces, which provide significance to improve port density and network upgrades. This article will introduce the breakout mode in detail, the types of QSFP28 transceivers supported breakout, and give you a breakout connectivity guide on QSFP28 100G transceivers.

Breakout Connectivity Introduction

Before introducing the 100G QSFP28 breakout connectivity guide, it is necessary to straighten out what is breakout connectivity. Breakout mode connectivity stands for the connectivity between high-speed ports and lower-speed ports on network equipment like switches, routers, and servers, which comes to meet the increasing demand for bandwidth and higher-speed transmission data. Based on the breakout mode connectivity, communication service providers enable easily upgrading their current network connectivity to fulfill the higher data rate demands.

Transceivers breakout mode connectivity refers to the transceivers that feature multiple lane structures, including QSFP+, QSFP28, and QSFP56-DD, which are placed on the high-speed ports side while single lane transceivers, such as SFP+, SFP28, and SFP56 are placed on the lower-speed ports side, as shown in table 1 and 2.

Table 1 — Higher-speed Ports in Breakout Mode

Table 2 — Lower-speed Ports in Breakout Mode

Which QSFP8 Transceivers Can be Used in QSFP28 Breakout Connectivity and How to Realize?

As the above introduction to breakout mode, we are able to learn that to work in a breakout mode, the QSFP28 transceiver must enable 4 individual parallel lanes, each of which supports a 25G data rate, so QSFP-100G-SR4 optical transceiver module and QSFP-100G-PSM4 transceiver is the answer. They are in common with an MTP/MPO-12 connector.

For QSFP-100G-SR4, the 4x25G QSFP28 breakout connectivity is achieved based on a parallel 12-fiber MTP to 4x LC multimode breakout cable, which connects a 100GBASE SR4 transceiver to four 25G SFP28 SR transceivers.

Figure 1 –  QSFPTEK Cisco Compatible QSFP-100G-SR4 Transceiver

For QSFP-100G-PSM4, the 4x25G breakout connectivity is achieved using a parallel MTP to 4x LC single-mode breakout cable, which connects a 100GBASE PSM4 transceiver to four 25G SFP28 LR transceivers. It is worth noting that when using 4x25G breakout mode, the switch or router ports may need a corresponding configuration.

Table 3 — QSFP28 Types Supported 4x25G Breakout Mode

Figure 2 — QSFP-100G-SR4 in 4x25G Breakout Connectivity

Breakout Cables Used in 100G QSFP28 Breakout Connectivity

100G QSFP28 DAC Breakout Cable

100G QSFP28 to 4x25G SFP28 breakout DAC cable (Direct Attached Cable) consists of a Twinax copper cable terminated with a QSFP28 form factor module on one end and four SFP28 form factor modules on the other end. It has the advantage of convenient installation since the structure of modules is permanently attached to each end. The 100G breakout DAC cables are suitable for very short-distance transmission. They are generally 1 meter to 5 meters long in passive configuration and 7 m to 10 m long in active configuration.

100G QSFP28 AOC Breakout Cable

100G QSFP28 to 4x25G SFP28 breakout AOC cable (Active Optical Cable) consists of a multimode fiber optic cable terminated with a QSFP28 form factor module on one end and four SFP28 form factor modules on the other end. 100G breakout AOC cables are also suitable for short-distance transmission, but they support longer lengths than DAC breakout cables. They are generally 1 meter to 25 meters long.

What are the Advantages and Disadvantages of 100G QSFP28 Breakout Connectivity?

Advantages of 100G QSFP28 Breakout

1. Increasing switched/routers port density. Compared to a switch with single-lane ports, the switch that supports breakout connectivity mode can provide higher port density.

2. Interoperate with lower-speed ports. For example, the QSFP-100G-SR4 transceiver enables a switch with only QSFP ports to connect 4x 25G SR interfaces per port.

Disadvantages of 100G QSFP28 Breakout

1. Difficult for replacement. When one of the ports on a breakout transceiver, AOC, or DAC is broken, it requires the replacement of the whole transceiver or cable.

2. Not customizable. In switches with single-channel downlinks, each port is configured separately. For example, a single port can be 10G, 25G, 50G, or 100G and can accept any type of transceiver, AOC, or DAC. However, in breakout mode, a QSFP28-only port needs group-wise, in which all interfaces of a transceiver or cable are the same type.

Conclusion

From mentioned above, we learn QSFP-100G-SR4 and QSFP-100G-PSM4 support QSFP28 to SFP28 4×25 breakout connectivity by interoperating with 25G SFP28 SR and 25G SFP28 LR over MMF/SMF MTP to 4x LC breakout cables. Breakout connectivity mode is becoming increasingly important today, which features the advantages of high interoperability, high density, and cost-effectiveness.QSFPTEK offers a variety of 40G QSFP and 100G QSFP28 breakout transceivers and MTP to 4x LC breakout cables. All transceivers and cables have been tested on target original brand switches or routers, such as Cisco, Arista, Juniper, Brocade, Intel. Welcome to visit qsfptek.com.