25GbE Cabling vs 40GbE Cabling

In recent years, 40 Gigabit Ethernet (GbE) has gained more popularity and the market of 40GbE is encouraging. But with the rapid growth of the new standard 100GbE, a new voice is announcing, namely 25GbE. As the increasing bandwidth requirements of private and public cloud data centers and communication service providers, 25GbE will to have a significant impact on server interconnect interfaces. Now you have two upgrade paths to 100G, 10G-25G-100G and 10G-40G-100G. Which one to choose? This post will make a comparison of 25GbE and 40GbE cabling, hoping it can help you make an appropriate decision.

25GbE Cabling Overview

25GbE is a standard developed by developed by IEEE 802.3 task forces P802.3by, used for Ethernet servers and switches connectivity in a datacenter environment. The single-lane design of 25 GbE gives it a low cost per bit, which enables cloud providers and large-scale data center operators to deploy fewer switches to meet the needs while still scaling their network infrastructure.

25GbE physical interface specification supports two main form factors, SFP28 (1x25 Gbps) and QSFP28 (4x25 Gbps). 25GBASE-SR SFP28 is an 850nm VCSEL 25GbE transceiver available in the market. It is designed to transmit and receive optical data over 50/125µm multi-mode optical fiber (MMF) and support up to 70m on OM3 MMF and 100m on OM4 MMF (LC duplex). In fact, using an SFP28 direct attach copper (DAC) cable for switches direct connection is a preferred option now. In addition, a more cost-effective solution is to use a QSFP28 to 4xSFP28 breakout cable to connect a 100GbE QSFP28 switch port with four SFP28 ports. DAC cable lengths are limited to three meters for 25GbE. Thus, active optic cable (AOC) solutions are also used for longer lengths of applications.

40GbE Cabling Overview

40GbE is a standard developed by the IEEE 802.3ba task force. The official development of 40GbE standards first began in January 2008, and were officially approved in June 2010. At the heart of the 40GbE network layer is a pair of transceivers connected by a fiber optic cable, OM4 or OM3 fiber cable. Fiber optic transceivers are plugged into either network servers or a variety of components, including interface cards and switches.

There are several standard form factors of 40GbE transceivers in the whole evolution. The CFP (C form-factor pluggable) transceiver uses 12 Tx and 12 Rx 10Gbps lanes to support one 100GbE port, or up to three 40GbE ports. With its large size, it can meet the needs of single-mode optics and can easily serve multi-mode optics or copper. But it is gradually falling behind since the increasing demand for high density. Another form factor is the CXP. It also provides twelve 10Gbps lanes in each direction, but is much smaller than the CFP and serves the needs of multi-mode optics and copper. At present, the most commonly used 40GbE form factor is the QSFP+ (quad small form-factor pluggable plus). It has the similar size with CXP but can provide four Tx and four Rx lanes to support 40GbE applications for single-mode, multi-mode fiber and copper.

Fiber optic cabling and copper cabling are both available for 40 GbE. The supportable channel length depends on the cable and the transceiver type. For data center 40GbE fiber optic cabling, OM3 and OM4 multi-mode cables are generally recommended because they can support a wider range of deployment configurations compared to copper solutions, and lower costs compared to single-mode solutions. MPO/MTP connectors are used at the multimode transceivers to support the multifiber parallel optics channels. For copper solutions, you can use QSFP+ direct attach copper cables, such as Cisco QSFP+ breakout cable. There are a lot of options, both active and passive, like Cisco QSFP-4SFP10G-CU5M compatible 40G QSFP+ to 4x10G SFP+ passive direct attach copper breakout cable (as shown below).

25GbE Cabling vs 40GbE Cabling

Compared to 40 GbE, 25GbE seems to be more suitable and cost-effective for cloud and web-scale data center applications. Using 25GbE with QSFP28 transceivers, users can deliver a single-lane connection, similar to the existing 10GbE technology but with 2.5X faster performance. In addition, 25GbE can provide superior switch port density by requiring just one lane (vs. 4 lanes with 40 GbE). Thus, it costs less and requires lower power consumption. Benefits of 25GbE compared to 40GbE are shown as below:

• Greater port density vs 40 GbE (one lane vs. four lanes)
• Maximum switch I/O performance and fabric capability
• Lower cost versus 40 GbE
• Reduced capital expenditures (CAPEX) and operational expenditures (OPEX)
• Fewer ToR switches and fewer cables
• Requires less power, cooling, and footprint
• Leverage of the existing IEEE 100GbE standard

Summary

25GbE seems to be a preferred option in the next step. It can provide up to 2.5 times faster performance than the existing 10GbE connections while maximizing the Ethernet controller bandwidth/pin and switch fabric capability. It can also provide greater port density with lower cost compared to 40GbE solutions. The trend will always be wider band and higher speed and port density. 25GbE or 40 GbE, let's wait and see how things play out.

Transceiver Choices for 40 Gigabit Ethernet

40GbE (Gigabit Ethernet) is Ethernet standard developed by the IEEE 802.3ba, enabling the transfer of Ethernet frames at speeds of up to 40 gigabits per second (Gbps). Now 40 Gigabit Ethernet is becoming more and more popular, suitable for high-speed, high-demand, and computing applications. For a 40GbE network, transceiver modules are one of the most basic components for transmission, used to plugged into either network servers or various of components such as interface cards and switches. 40GbE transceivers are being developed along several standard form factors. Some basic knowledge of 40GbE transceivers will be provided in the following text.

CFP Transceiver

The CFP (C form-factor pluggable) transceiver features twelve transmit and twelve receive 10Gbps lanes to support one 100GbE port, or up to three 40GbE ports. Its larger size is suitable for the needs of single-mode optics and can easily serve multimode optics or copper as well. The following picture shows a CFP transceiver. 40GBASE CFP transceiver modules are hot-swappable input/output devices that plug into a 40 Gigabit Ethernet CFP port of a switch or router. CFP modules offer customers versatile 40 Gigabit Ethernet connectivity options in core and distribution layers of data center, enterprise, and service provider networks. Main features of 40GBASE CFP modules include:

• Support for 40GBASE Ethernet and OTU3 standards
• Support for "pay-as-you-populate" model
• Support for digital optical monitoring (DOM)
• Variety of interface choices for 40 Gigabit Ethernet connectivity
• Interoperability with respective industry IEEE- and/or OTU3-compliant interfaces
• Support for the Cisco quality identification (ID) feature, which enables a Cisco switch or router to identify whether the module is certified and tested by Cisco

 

CXP Transceiver

The CXP transceiver form factor also provides twelve lanes in each direction but is much smaller than the CFP and serves the needs of multimode optics and copper. The Roman number X means that each channel has a transmission rate of 10 Gbps. CXP is a kind of hot-pluggable transceiver with data rate up to 12×10 Gbps. It provides twelve 10 Gbit/s links suitable for single 100 Gigabit Ethernet, three 40 Gigabit Ethernet channels, or twelve 10 Gigabit Ethernet channels or a single Infiniband 12× QDR link. The C is the Roman numeral for 100 as a memory aid.

QSFP/QSFP+ Transceiver

The QSFP/QSFP+ (quad small-form-factor pluggable) is similar in size to the CXP and provides four transmit and four receive lanes to support 40GbE applications for multimode and single-mode fiber and copper today. It is the most popular interface of 40G transceivers now. Two main types of QSFP+ transceivers used in the data center are QSFP-40G-SR4 and QSFP-40GE-LR4. The following picture shows an Arista QSFP-40G-SR4 QSFP+ transceiver and a Cisco QSFP-40GE-LR4 QSFP+ transceiver. QSFP-40G-SR4 is used in 4x10G mode along with ribbon to duplex fiber breakout cables for connectivity to four 10GBASE-SR optical interfaces. 40GBASE-LR4 QSFP+ module supports link lengths of up to 10km over a standard pair of G.652 single-mode fibres with duplex LC connectors. In addition, there are other types of QSFP+ modules, such as QSFP-40G-ER4, 40GBASE-PLRL4, etc. Main features of 40GBase QSFP+ modules include:

• Support for 40GBASE Ethernet
• Flexibility of interface choice
• Hot-swappable input/output device that plugs into a 40-Gigabit Ethernet QSFP+ switch port
• Interoperable with other IEEE-compliant 40GBASE interfaces available in various form factors
• Support for "pay-as-you-populate" model

 

Conclusion

Fiberstore offers customers a wide variety of high-density 40 Gigabit Ethernet connectivity options for data center, high-performance computing networks, enterprise core and distribution layers, and service provider transport applications. If you have any demand for the 40GbE components or product solutions, please contact Fiberstore team over sales@fs.com or have a livechat on www.fs.com.

A Guide to 40 Gigabit Ethernet

The 802.3ba Ethernet standard introduced by the IEEE in June 2010 was in response to the increasing bandwidth demands facing data centers, paving the way for the introduction of 40Gb/s and 100Gb/s Ethernet operations. As you begin to think about the future of your network, understanding all the 40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) optical components can be confusing. In this post, a brief overview of the current 40 Gigabit Ethernet to aid in planning for future high-performance Ethernet needs will be given.

What Is 40 Gigabit Ethernet?

40GbE is a standard that enables the transfer of Ethernet frames at speeds of up to 40 gigabits per second (Gbit/s). The 40GbE standard is intended for local server connectivity. One of the most attractive characteristics of 40 Gigabit Ethernet is broad applications and design flexibility. 40 Gigabit Ethernet runs on quad small form factor pluggable (QSFFP) cabling, a high-density fiber connector with 12 strands of fiber. According to the task force, 40GbE fulfills the following requirements and objectives:

• Preserve existing 802.3 frame format, minimum size, and maximum size.
• Support high-bandwidth applications such as video on demand (VoD) and high-performance computing (HPC).
• Support high-speed switching, routing, and application functions in data centers.
• Exhibit a bit error rate (BER) of 10-12 or better.
• Provide support for optical transport network (OTN).
• Provide specifications for operation over single-mode optical fiber, laser optimized multi-mode optical fiber, copper cables, and backplanes.

How Does 40 Gigabit Ethernet Work?

40 Gigabit Ethernet can be deployed using the same cabling systems in use today. Multi-mode will employ parallel optics using MPO interconnects and require additional cable infrastructure depending on the system deployed while single mode fiber will employ serial transmission and use LC or SC connectors. The approach used for the higher speed data rates is based on advanced transceiver technologies engineered to take advantage of the full bandwidth of laser optimized fibers. The 40 Gigabit Ethernet specification calls for a 12-fiber cabling solution, implemented using eight of the twelve fibers in an MPO connector, with each channel featuring four dedicated transmit fibers and four dedicated receive fibers. The middle four fibers remain unused, or dark. Each Tx/Rx pair is operating at 10G.

40 Gigabit Ethernet Cables

Cabling for 40 Gigabit Ethernet can be optical fiber or copper. The supportable channel length depends on the cable and the transceiver type. With regard to connectors, the only significant change outlined in the 802.3ba standard is the use of MPO (Multi-Fiber Push On) type connectors at the multi-mode transceivers to support the multi-fiber parallel optics channels. For data center environments operating at 40Gbps, OM3 and OM4 multi-mode cabling is generally recommended because its reach supports a wider range of deployment configurations compared to copper solutions, and the cost is lower compared to single-mode solutions.

40 Gigabit Ethernet Transceivers

40 Gigabit Ethernet transceivers are being developed along several standard form factors. The C form-factor pluggable (CFP) transceiver features 12 transmit and 12 receive 10Gbps lanes to support up to three 40 Gigabit Ethernet ports. Its larger size is suitable for the needs of single-mode optics and can easily serve multi-mode optics or copper as well. The CXP transceiver form factor also provides 12 lanes in each direction, but is much smaller than the CFP and serves the needs of multi-mode optics and copper. The quad small form-factor pluggable (QSFP) is similar in size to the CXP and provides four transmit and four receive lanes to support 40 Gigabit Ethernet applications for multi-mode fiber and copper. And quad small form-factor pluggable plus (QSFP+) gradually replaces QSFP and is widely used by people as it can provide higher bandwidth. The picture below shows a Cisco WSP-Q40GLR4L compatible QSFP+ transceiver.

Migrating to 40 Gigabit Ethernet will prove very cost-effective for those who do it right. One critical step is to choose appropriate cables and transceivers. Fiberstore is a professional manufacturer and supplier, which offers a large amount of cables and transceivers for your 40GbE applications. For example, HP 805755-B21 compatible QSFP+ transceiver, and Juniper JNP-QSFP-4X10GE-IR compatible QSFP+ transceiver offered by Fiberstore are cost-effective and high-performance transceiver modules fully compatible with major brands.