100GBASE-KR4 Explained
This article serves as a technical overview of the 100GBASE-KR4 standard, providing insights into its function, key features, and applications within high-speed networking environments.
What is 100GBASE-KR4?
100GBASE-KR4 is a type of backplane Ethernet standard defined by the IEEE 802.3bj amendment to the IEEE 802.3 Ethernet standard. It is specifically designed for 100 Gigabit Ethernet (100GbE) transmission over copper backplanes.
Here’s a breakdown of the meaning:
- 100G: Refers to the data rate of 100 Gigabits per second (Gbps).
- BASE: Indicates that this is a baseband transmission method, meaning the entire bandwidth of the medium is used to transmit a single data stream.
- KR: Specifies that the communication happens over backplane connections using electrical signaling, typically on copper traces on a PCB. The “K” indicates a backplane (as opposed to fiber or twisted-pair cable), and “R” refers to the use of 64b/66b encoding.
- 4: Refers to four lanes, where the data stream is split across four parallel channels, each operating at 25 Gbps.
KR4 is is a physical layer standard for Ethernet over a backplane, specifying how data is physically transmitted.
How 100GBASE-KR4 Work?
100GBASE-KR4 uses a backplane to transmit signals. A backplane is essentially the physical, circuit board-based interconnection system used within systems like servers or networking devices to connect different modules or components.
- Lanes and Data Rate:
- 100GBASE-KR4 splits the data transmission into four lanes, each capable of handling 25 Gbps.
- This parallel transmission across four lanes is what enables the total data rate to reach 100 Gbps.
- Forward Error Correction (FEC):
- Reed-Solomon FEC is used to ensure reliable data transmission by correcting errors that occur during the transmission process. This is crucial in high-speed data transmission over copper traces where signal integrity can be an issue due to interference and signal loss.
- Channel Reach:
- The channel is designed for short distances, typically around 1 meter or less, within the same system (i.e., within the chassis or system enclosure). The medium is primarily printed circuit board (PCB) traces on a backplane.
Figure1: 100G Ethernet applications on a data plane
Applications of 100GBASE-KR4
100GBASE-KR4 is primarily used in high-speed networking equipment, such as:
- Network Switches: Used for internal data transmission between different components within the same switch or chassis.
- Servers: Data centers use it for interconnecting blade servers or server components within the same enclosure.
- Telecommunications Equipment: Deployed in backplanes for telecom switches and routers that handle large volumes of data.
It is commonly found in large-scale data centres where high throughput, low latency, and reliable backplane communication are critical.
Comparison with Other 100GbE Standards
100GBASE-KR4 is just one of many 100 Gigabit Ethernet standards. Here’s how it compares to some other 100GbE standards:
| Standard | Medium | Distance | Lanes | FEC |
|---|---|---|---|---|
| 100GBASE-KR4 | Copper backplane | 1 meter (intra-rack) | 4 lanes (25G) | Reed-Solomon FEC |
| 100GBASE-CR4 | Copper cables | Up to 5 meters | 4 lanes (25G) | Reed-Solomon FEC |
| 100GBASE-SR4 | Multimode fiber | Up to 100 meters | 4 lanes (25G) | No FEC (typically) |
| 100GBASE-LR4 | Single-mode fiber | Up to 10 kilometers | 4 lanes (25G) | Reed-Solomon FEC |
Conclusion
The 100GBASE-KR4 has nothing to do with optical transmission. The KR4 is referred to the backplane of Ethernet applications. Usually for these abbreviations in optical communication we understand the distance, for example, SR is short reach, LR is long reach etc., but not for KR4. The SR, LR etc. describe the optical characteristics of a transceiver, while KR is the physical layer standard for Ethernet.
