To keep up with the global demand for higher bandwidth, Arista has designated 7500E series switch to address 100G long-hual dense wavelength division multiplexing (DWDM) connectivity. Arista 100G interconnect solution combines Layer 2/Layer 3 switching, wire-speed encryption and coherent DWDM into a high-density line card for the Arista 7500E data centers. Along with the introduction of Arista 7500E series switches, this article will illustrate several 100G DWDM solutions for distance up to 80 km, 150 km and 3000 km as well.
Arista 7500E Series Switch & Line Card
Arista 7500E series is the second generation of 7500 series switch that delivers scalable and deterministic network performance for mission critical data centers, enterprise and HPC environments. Available in a compact 7RU (4-slot) or 11RU (8-slot), Arista 7500E offers over 30Tbps of total capacity for 1,152 ports of 10GbE, 288 ports of 40GbE and support for 96-port 100GbE with a broad choice of interface types that support flexible combinations of 10G, 40G and 100G modes on a single port.
The 7504 and 7508 are the two types of Arista 7500E series switches. The 7508 systems support 8 linecards, dual supervisor modules and 6 fabric modules to provide a full 30Tbps of capacity. The smaller 7504 systems share a common architecture with the 7508 with the primary difference being support for 4 linecards and 15Tbps of forwarding capacity. The most unique feature of this switch is that it can connect with 10G SFP+, 40G QSFP+, 100G QSFP28 and CFP2 modules.
Arista 7500E series line card for addressing 1/10G, 40G and 100G with full support for industry standard connections and comprehensive layer 2 and 3 features for flexible deployment choice. The line card delivers error-free performance up to 3000 km of fiber and consumes less than 140W per 100Gbps. Similar to any other Arista platform, the DWDM line card utilizes the single binary image of Arista’s extensible operating system (EOS). Line cards with CFP2 and QSFP support standard 100G for both single and multimode fiber for distance up to 40 km.
Why Need 100G DWDM Solution?
100G optical transceivers provide the most straightforward method to connect 100G traffic over long-hual applications. 100G optics like CFP and QSFP28 offer cost-optimized solutions for connecting 100G switches together in a rack or data center. Nevertheless, the small and cost-effective QSFP28 100G optics now can only handle connections over distances of less than 10 km. For example, QSFP28 LR4 is compliant with 100GBASE-LR4 standard that operates over duplex LC cables for a link length of 10 km.
As to the CFP form factors, coherent CFP modules is designed to support metro and long-hual DWDM applications. CFP 100GbASE-ER4 can support up to 40 km. However, owing to its large size and high power consumption, CFP transceivers are less popular on the market. If you want to use CFP optics for 100G deployment, keep in mind, CFP modules are too large to fit in the Ethernet switches and will significantly reduce port counts and increase power usage, making 100G switches poor performance in cost-effectiveness. Therefore, customers who want to upgrade 100G network can only cover a distance of 10 km, which is obviously insufficient for geographically separated data centers or metro infrastructures. Figure 2 shows the basics of DWDM system.
To realize 100G long-distance transmission, Arista 100G DWDM solution combines DWDM optics with a fully passive Mux/Demux system that can handle up to 3,000 km. Arista 100G DWDM solution is a 6 x 100G Coherent DWDM line card for the 7500E series with integrated wire-speed encryption and analog coherent CFP2 optical interfaces. Several use cases for the Arista 7500E Series DWDM card in multi-site data center networks exist. The following sections identify three use cases for Arista 7500E DWDM solutions.
Use Cases for Arista 7500E DWDM Solution
- Use Case 1—Less Than 80KM Dark Fiber Connection
For a typical metro link that is less than 80 km, Arista 7500E Series DWDM line cards can directly terminate a dark fiber connection providing a point-to-point connection between two locations.
Just as figure 3 shows, Arista DWDM solution is ideal for metro applications transmitting up to 9.6Tbps traffic without the need for any additional amplification.
- Use Case 2—Greater Than 80 km But Less Than 150 km
When extending the distance beyond 80 km, there is a need to amplify the signal to offset heavy signal loss that occurred in the light signal when passing through fiber cables, patch panels and other optical devices. Under this circumstance, EDFA’s or Erbium Doped Fiber Attenuators are employed to give the aggregated wave a boost.
By using EDFAs (seen in Figure 4) to the transmit side of each end of the dark fiber link, the signal can be boosted to achieve distances of up to 150 km. Exact distances will be dependent on the number of patches, fiber splices and quality of the fiber.
- Use Case 3—Greater Than 150 km But Less Than 3,000 km
Arista 7500E DWDM solutions can also cover the distance of greater than 150 km but less than 3000 km. Employing further EDFAs at a spacing of approximately 80 km along the fiber route allows the length of a connection to be extended to over 3,000 km. As shown below, EDFAs are used on both paths to boost the signal.
Supported Optics for Arista 7500E Series
All Arista 10G SFP+ transceivers, with the exception of LRM, are supported on the Arista 7500E SFP+ ports.
| Interface Type | SFP+ ports |
| 10GBASE-CR | 0.5m-5m |
| 10GBASE-AOC | 3m-30m |
| 10GBASE-SRL | 100m (OM3) / 150m (OM4) |
| SFP-10G-SR | 300m (OM3) /400m (OM4) |
| SFP-10G-LRL | 1km |
| SFP-10G-LR | 10km |
| SFP-10G-ER | 40km |
| 10GBASE-DWDM | 80km |
| SFP-10G-ZR100 | 100km |
| 100Mb TX, 1GbE SX/LX/TX | Yes |
The 40G QSFP+ transceivers and cables allow for 4x10G mode support with the use of fiber breakout cables, MTP to LC cassettes, or QSFP to SFP+ cables. See the below table for details on the latest supported 40G transceivers.
| Interface Type | QSFP+ ports |
| 40GBASE-CR4 | 0.5m-5m |
| 40GBASE-AOC | 3m-100m |
| QSFP-40G-UNIV | 150m (OM3) / 150m (OM4), 500m (SM) |
| QSFP-40G-SRBD | 100m (OM3) /150m (OM4) |
| QSFP-40G-SR4 | 100m (OM3) / 150m (OM4) |
| QSFP-40G-XSR4 | 300m (OM3) / 400m (OM4) |
| QSFP-40G-PLRL4 | 1km (1km 4x10G LR/LRL) |
| QSFP-40G-PLR4 | 10km (10km 4x10G LR/LRL) |
| QSFP-40G-LRL4 | 1km |
| QSFP-40G-LR4 | 10km |
| QSFP-40G-ER4 | 40km |
100G QSFP28 and CFP2 Optics
| Interface Type | 100G CFP2 Ports | 100G QSFP Ports |
| 100GBASE-XSR10 | 300m OM3 / 400m OM4 Parallel MMF | |
| 100GBASE-SR4 | 100m OM3 / 150m OM4 Parallel MMF | |
| 100GBASE-LR4 | 10km SM Duplex | 10km SM Duplex |
| 100GBASE-LRL4 | 2km SM Duplex | |
| 100GBASE-ER4 | 40km SM Duplex | |
| 100GBASE-CWDM4 | 2km SM duplex | |
| 100GBASE-PSM4 | 500m SM Parallel | |
| 100GBASE-AOC | 3m to 30m | |
| 100GBASE-CR4 | 1m to 3m |
Conclusion
Arista 7500E DWDM solution works in conjunction with passive Optical Mux/Demux devices and in-line amplifiers to support additional bandwidth and extended reaches. Arista 7500E DWDM solution can directly reach up to 80 km without requiring in-line amplification, which is ideal for metro applications. With an Optical Signal to Noise ratio (OSNR) of 11.6dB, it can be used effectively for point to point long-haul applications up to 3,000kms with in-line amplifiers and multiplexers.
Related article : How to Deploy QSFP28 Modules for 100G Deployment
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