SFP+ to RJ45 connection in Data Center

When you expand or upgrade your Data Center, there can be a situation when you need to connect 10G SFP+ to RJ45 ports. Most Server NIC (Network Interface Card) and Storage Appliance units have fixed 10GBASE-T ports with RJ-45 connectors and on the other side of the link ToR (top-of-rack) switches have SFP+ slots.  Question arises – what would be the most efficient way to make SFP+ to RJ45 connection? Answer – in short, 10G Copper SFP+ transceiver modules (10G-SFP-T) can be used in ToR switches as adapters from SFP+ to RJ-45 to enable RJ45 to RJ45 connection.

If you would like to know more details about this topic, like:

• SFP+ to RJ-45 Use Case in Datacenter
• 10G SFP+ to RJ-45 Transceiver Types, Data Rate, Max Distance
• Ubiquity, Mikrotik, Cisco, HP, Aruba, Extreme Networks Compatible SFP+ to RJ-45
• Data Rates? 10GBASE-T, 5GBASE-T, 2.5GBASE-T, 1000BASE-T
• Twisted Pair Cable Categories? CAT5e ,CAT6a, CAT7
• Latency
• Power consumption and heat
• What is another industry wide application for 10G SFP+ to RJ-45?
• Conclusion

Please – Read On !

SFP+ to RJ-45 Use Case in Datacenter

Figure 1. 10G RJ45 Connectivity in Data Center

Already for some few years 10GBASE-T (IEEE 802.3ae) Ethernet standard is the most widely used communication standard in datacenter. Datacenter networks mostly rely on 10G links at the server, switch and NAS storage levels (with future upgrade to 25/40Gbps fiber optic links). These links consist of copper infrastructure which terminates in RJ45 ports, and a mix of optical infrastructure which is established through SFP+ transceivers and fiber optic cables.

Twisted pair cabling and RJ45 connector has been around for some time as it has quicker termination, less expensive equipment and backward compatibility with 1000BASE-T and other legacy data rates. As a result migration from 1G to 10G Ethernet can happen over a longer period of time. As a matter of fact, some manufacturers’ storage and server-side equipment has built-in, fixed RJ45 ports that support from 1000BASE-T to 10GBASE-T data transmission. This makes for an easy side-to-side connection.

If cable infrastructure consists of twisted pair cables and equipment has 10GBASE-T RJ45 ports then in this kind of situation there are no problems with connection implementation. However, many ToR (top-of-rack) switches (as they are aggregating many servers) usually have only 10G SFP+ [Optical] ports. This can cause a headache! How to connect a RJ45 to a SFP+ port? Connecting SFP+ to RJ45 directly is not possible only with CAT cable. A special 10G Copper RJ-45 Transceiver (10G-SFP-T) is required to connect SFP+ port to RJ45. This transceiver is inserted in SFP+ port (cage) – used as an adapter. It allows connecting server/storage side Cat6/7 cable to SFP+ port transceiver with RJ45 connector. At this stage the added benefit is that it uses the familiar RJ45 connector and provides backward compatibility with legacy networks and enables data center expansion and expenditure to occur incrementally. Furthermore, 10G copper transceivers allow 10G bandwidth over existing Copper cable infrastructure and makes life easier because using 10G Copper SFP+ is a much more economical then a new RJ-45 to SFP+ switch and is a much more stable solution then RJ-45 to SFP+ media converter.

10G SFP+ to RJ-45 Transceiver Types and Max Distance

10G Copper RJ45 transceivers can have different capabilities, based on the data rate requirements and can be used with Cat 5e and newer Cat6a/7 category copper cables.
We have available several hardware options for RJ-45 to SFP+ Transceivers as below:

Table 1. 10G RJ45 Hardware Options

Below would be more details on each of provided hardware version:

1) 10G-SFP-T version (002):

This transceiver supports following data rates: 10 Gbps, 5 Gbps, 2.5 Gbps and 1 Gbps. Maximum Cat 6a/7 cable distance till 30 meters. It has the following specifics:
-It can be inserted only in 10G SFP+ port
-Device which it connects has to be with 10 Gbps, 5 Gbps, 2.5 Gbps or 1 Gbps interface respectively

2) 10G-SFP-T2 version (001):

This transceiver supports following data rates: 10 Gbps, 5 Gbps, 2.5 Gbps and 1 Gbps. Maximum Cat 6a/7 cable distance till 30 meters. It has the following specifics:
-It can be inserted only in any of 10 Gbps, 5 Gbps, 2.5 Gbps and 1 Gbps ports
-Device to which it connects to can be 10 Gbps, 5 Gbps, 2.5 Gbps or 1 Gbps fixed speed interface respectively. In other words: the data rate between 10G-SFP-T2 and the other end must match.

3) 2.5G-SFP-T version:

This is a completely different hardware version transceiver than 10G-SFP-T. It can only be used for 2.5 Gbps Ethernet. With Cat 5e/6a/7 cable it can reach 30 meters.

4) 10G-SFP-T-80 version:

This transceiver supports following data rates: 10 Gbps.
Maximum distance Cat 6a 30 meters and Cat 7 till 80 meters. It has the following specifics:
-It can be inserted only in 10G SFP+ port;
-Device which it connects to has to be with 10G interface;
-It can reach 80 meters via Cat 7 cable.

Ubiquity, Mikrotik, Cisco, HP, Aruba, Extreme Networks Compatible SFP+ to RJ-45

Additionally EDGE Optical Solutions 10G SFP+ to RJ45 transceivers can be made compatible with other manufacturer devices. For more information please refer to the table below. 

Table2. 10G RJ45 Compatibility with popular brands

Data Rates? 10GBASE-T, 5GBASE-T, 2.5GBASE-T, 1000BASE-T

There is a lot of confusion regarding intermediate data rates between 1000BASE-T, also named Gigabit Ethernet, and 10GBASE-T, also named 10 Gigabit Ethernet. Some equipment may use 2.5GBASE-T and 5GBASE-T data rates (in most of the cases these data rates are used in WIFI Scenarios). How can this be achieved?
Simple answer is that the 10G-SFP-T adapter/transceiver is capable of supporting 1000BASE-T, 2.5GBASE-T, 5GBASE-T and 10GBASE-T Ethernet (EDGE Optical Solution engineers can help with adjusting the data rate). Additionally, we have a 2.5G-SFP-T transceiver in our portfolio that is a more cost-efficient alternative than to use 10G-SFP-T for 2.5GBASE-T applications.
On a side note, 2.5 Gigabit and 5 Gigabit Ethernet is defined under IEEE 802.3bz  communication standard. It defines 2.5GBASE-T and 5GBASE-T use over Cat6 infrastructure with added support to legacy Cat5e infrastructure – this in fact led to 2.5Gbps standard introduction in the first place.

Twisted Pair Cable Categories? CAT5e ,CAT6a, CAT7

Twisted pair cables consist of two conductors of a single circuit twisted together for the purpose of improving electromagnetic compatibility. Nowadays cables include aluminum foil shielding for increased protections from neighboring pair crosstalk. Twisted pair cable naming is in the form of Categories. For example, Category 5e cable (Cat 5e for short). Cat 5e nowadays is the most commonly deployed and used day to day cable. Newer projects which require more than 5GBASE-T Ethernet use newer generation twisted pair cables, like Cat 6a and Cat 7.

More detailed: 

• Cat 5e cable is designed for 10/100/1000/2500/5000 Mbps systems;
• Cat 6a cable is designed for 10 Gbps systems, but is as well backward compatible with Cat 5e and support 10/100/1000/2500/5000 Mbps speeds;
• Cat 7 cable is designed for 10 Gbps systems with improved crosstalk and at the same time is backward compatible with Cat 5e and Cat 6a and supports 10/100/1000/2500/5000 Mbps speeds.

Latency

Nowadays, in Data Centers there are three most common ways to connect devices:

• Optical Links (using optical transceivers or AOC – Active Optical Cables)
• DAC (Direct Attach Cables)
• Twisted pair cable with Copper infrastructure

Most common are optical links, but due to recent technology advancement Copper based DAC cables are a close second option. One of the main aspects when choosing what connection type or types to use for data center needs is latency. Below is the comparison for approximate latency of each connection type in Data Center:

• Optical link using 10G-SFP-SR MMF(Multi-Mode Fiber) transceivers and OM4 fiber optic patch cables – link latency is about 0.1ms;
• Direct Attach Cables (Twinax) – link latency is about 0.3ms;
• Twisted pair cable with Copper infrastructure using a 10G Copper SFP+ transceiver module (10G-SFP-T) – link latency is about 2.6ms. Increase in latency is due to extra line encoding overhead in the conventional IEEE 802.3an, mathematical tasks are being performed that ensure error correction for all data packets sent. 

2.6ms per hop is acceptable, while hop count is kept to a minimum. Otherwise, resulting latency causes negative side effects.

Power consumption and heat

Power consumption is the second key focus factor in Data Centers. It is a significant part of data center OPEX. Data center networking professionals are very interested in how much electrical power does an active equipment consume. This is because each watt consumed by equipment means consumption of two additional watts for datacenter cooling.

Typical power consumption by connection type:

• 10G SFP+ 850nm 10G-SFP-SR optical transceiver equipped port is about 1W, regardless of distance.
• Direct Attach Cables (Twinax) equipped port consumes about 1.5W in case of 10m or shorter distance
• Twisted pair cable with Copper infrastructure using a 10G Copper SFP+ transceiver module (10G-SFP-T) consumes from 2W to 4W, depending on cable length.

If there are only two ports in use, it will not have a big impact on power consumption figures, however, in the datacenter scenario there can be much more ports in use which can cause significant power consumption increase when compared to optical connections.

What is another industry wide application for 10G SFP+ to RJ-45? 

Another industry wide application for SFP+ to RJ-45 Copper transceivers which we would like to mention are Wi-Fi solutions. Wi-Fi Access points directly benefit from SFP+ to RJ-45 Copper Transceiver module (10G-SFP-T), when Wi-Fi Access Point to Wi-Fi Controller has optical infrastructure between both. To elaborate, modern Wi-Fi access points usually do not directly support optical fiber connection and come with twisted pair RJ45 ports. Therefore, when a Wi-Fi access point has to be connected to a Wi-Fi controller over optical fiber infrastructure – a switch with SFP+ optical ports is used.
On one end, the switch connects directly to a Wi-Fi Access point over twisted pair cable with the help of a 10GBASE-T copper adapter. On the other end, the switch connects to a Wi-Fi controller over fiber with the help of optical SFP+ module. Important: Older copper cabling infrastructure like Cat 5e for instance does not support 10 Gbps data rate. However – 10GBASE-T copper transceiver data rate can be adjusted from 10GBASE-T to 5GBASE-T or 2.5GBASE-T, or even 1000BASE-T.

Conclusion

With help of 10G-SFP-T Copper transceiver SFP+ to RJ45 connection in Data Center  can be easily realized and transforms modern 10G SFP+ switch port to RJ45 compatible interface, which allows to connect any end point equipment with built-in 1G or 10G RJ45 ports. This can help in network upgrade scenarios migrating from 1G to 10G utilizing existing twisted pair cable infrastructure.
Below would be some Strong and Weak points to consider when using 10G-SFP-T Copper transceivers for SFP+ to RJ45 connection in Data Center:

Strong:

• More economical solution than replacing 10G SFP+ switch to 10GBASE-T RJ45 port switch
• More stable solution than 10G SFP+ to RJ-45 Media Converter
• Quick setup
• Multiple data data rate support
• 80 meters reach with 10G-SFP-T-80 version

Weak:

• Higher power consumption comparing to optical links, especially if several units used in switch
• Increased Heat generated compared to optical links, if more than few units used in switch
• Increased Latency, especially if used to connect several hops
  
  

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