While the age-old debate of copper versus fibre is one that has crept up time and time again over the past two decades, it is an argument that no longer has basis since neither can be considered the better of the two cabling options when we look at networks as a whole—from the desktop to the LAN to the data centre, explains Narender Vasandani, RCDD, Technical Manager, Siemon Middle East.
Decades ago, many fibre proponents declared that category 6 balanced twisted-pair cabling would be the limit for copper. However, the advancements that have since brought us category 6A and category 7A, and will soon bring us category 8, have done more than simply prove that mind-set wrong. Instead, they have paved the way for copper to remain the de-facto media in the LAN for several more years than anyone thought possible. And advancements happening now with copper cabling technology and within IEEE standards will uphold a long-term position for copper in data centre switch-to-server connections.
Nonetheless, optical fibre cabling remains, and will remain, the standard for backbone cabling in the LAN, the data centre and in the outside plant arena. New fibre technologies and standards are making it easier, cost-effective and less complex than ever to deploy high speed links in these areas where there is a need to quickly and efficiently move large amounts of data over longer distances.
To the device
In the LAN, optical fibre cabling is used for the backbone where distances longer than copper cabling can support are typically required. As speeds increase in the horizontal, a fibre backbone in the LAN also offers the bandwidth capability required for future expansion. In the horizontal LAN from the telecom closet to the device, copper remains the primary cabling media due to its low cost, easy installation and flexibility, as well the ubiquitous RJ45 network interface.
Fibre to the desk is typically limited to specialised applications or highly secure networks. Required speeds in the horizontal LAN have also remained within copper’s capabilities with very few requirements for 10 gigabit Ethernet to the desktop. However, there is another reason why copper cabling is the better option in this environment—power.
In less than a decade, remote powering technology has revolutionised the look and feel of the IT world. Unlike fibre, copper balanced twisted-pair cabling has the capability to deliver dc power to IP-enabled devices such as surveillance cameras, wireless access points, RFID readers, digital displays, IP phones and other equipment. The popularity of this technology is staggering—more than 100 million power over Ethernet (PoE) enabled ports are shipping annually.
Remote powering applications are also continuing to advance. IEEE 802.3bt is currently developing standards for using all four pairs in a copper cable to deliver even higher levels of remote power than has previously been available in existing Type 1 and Type 2 PoE technologies that use just two balanced twisted pairs.
Referred to as 4PPoE, this four-pair PoE project will augment the capabilities of existing Power Sourcing Equipment (PSE) and Powered Device (PD) specifications with Type 3 (≤ 60W at the PSE) and Type 4 (≤ 100W at the PSE) requirements.
While copper obviously wins out over fibre in the LAN due to its remote powering capabilities, there are some considerations. Many IT managers are not aware that remote power delivery produces temperature rise in cable bundles and electrical arcing damage to connector contacts. In extreme environments, temperature rise and contact arcing can cause irreversible damage to cable and connectors.
Choosing higher-quality and specially qualified shielded category 6A and category 7A cabling systems like Siemon’s Z-MAX 6A shielded and TERA category 7A can eliminate these risks. It is highly recommended that only connecting hardware independently certified for compliance to IEC 60512 99 001 be used to support remote powering applications. This standard was specifically developed to ensure reliable connections for remote powering applications.
Exceeding the operating temperature range for copper cabling, which is specified as -20°C to 60°C by ISO/IEC, can also have an irreversible effect on transmission performance. Since deployment of certain remote powering applications can result in a temperature rise of up to 10°C within bundled cables, the typical rule of thumb is to not install cables in environments above 50°C.
This restriction can be problematic in regions such as the Middle East where temperatures in enclosed ceiling, plenum and riser shaft spaces can easily exceed 50°C. Again, using higher-quality shielded category 6A and 7A cables that are qualified for mechanical reliability up to 75°C can overcome this obstacle. Because insertion loss is directly proportionate to temperature, these higher performing cables can also reduce or eliminate insertion loss length de-rating that most minimally compliant copper cables require.
At the edge
In the data centre environment, copper and fibre cabling tend to co-exist in a similar fashion—copper in horizontal switch-to-server links and fibre in backbone switch-to-switch links.
Category 6A balanced twisted-pair copper cabling able to support 10GBASE-T make it the preferred choice for today’s data centre switch-to-server connections. With cabling channel lengths supported up to 100 metres and transceiver costs still well below that of fibre, category 6A copper cabling is well suited to support a variety of architectures for these switch-to-server connections, including top of rack, middle of row and end of row scenarios. But what about switch-to-server connection speeds beyond 10 gigabit?
TIA and ISO/IEC cabling-standard development groups have already initiated work on category 8 cabling to support 40 gigabit Ethernet (i.e., 40GBASE-T) over balanced twisted-pair copper cabling, and in November 2014 an IEEE Study Group was formed to investigate 25 gigabit Ethernet. The opportunity for 25GBASE-T lies in the 30-metre reach zone as a cost-optimised step on the speed migration path to 40GBASE-T to support switch-to-server connections.
Intended for operation over the same two-connector ISO/IEC Class I/Class II and TIA Category 8 channels planned for 40GBASE-T, 25GBASE-T is technically feasible, building on the existing and well-established 10GBASE-T technology that is evolving to support 40GBASE-T.
Because it shares open and common specifications, ensures interoperability and backwards compatibility, and offers the reach to support a broad range of switch-to-server architectures, 25GBASE-T will positively fit within the successful balanced twisted-pair copper Ethernet ecosystem—preserving copper’s place in data centre for several years to come.
In the core
While copper cabling’s position is now stable in the horizontal LAN and at the data centre edge, outside plant and backbone switch-to-switch deployments for networking and SANs require fibre. Not only are the distances in these environments typically beyond the range supported by copper, but transmission speeds here have evolved to 40 and 100 gigabit for Ethernet-based networks and 16 and 32 gigabit for Fibre Channel-based SANs. While fibre is really the only choice in these environments, again there are considerations.
Staying within optical insertion loss budgets is essential for ensuring proper transmission of data signals between switches. The lengths and number of connections within a channel all contribute to link loss, and higher speeds have more stringent loss requirements.
Today’s flattened architectures with fewer switch tiers also result in longer lengths between switches and the need for distribution points or cross connects to maintain flexibility, facilitate upgrades and limit access to critical switches. This adds more connections and link loss within the channel.
The use of low loss MTP connectors deployed for switch-to-switch connections in the data centre is therefore essential. They better support multiple mated connections for flexibility over a wide range of distances and configurations while remaining within the loss budget.
For example, MTP connectors with a typical insertion loss value between 0.3 dB and 0.5 dB can only support two mated connections in a 40/100 gigabit OM4 multimode fibre Ethernet channel. Alternatively, low loss MTP connectors that offer a loss of 0.2 dB can support five mated connections.
While being able to support multiple mated connections within link loss budgets is vital for flexible and manageable backbone fibre deployments, the huge demand for information has also drastically increased the density of fibre connections in the data centre.
Data centre managers are therefore demanding solutions that support higher numbers of fibre ports in less rack units of space while offering features that enable accessibility and ensure fibre management and protection.
Another concern is the ability to easily migrate from 10 to 40 to 100 gigabit speeds. Modular components that can be swapped to upgrade from LC interfaces used for 10 gig applications to MTP interfaces used for 40 and 100 gigabit applications make it easier to migrate. Another concerns is maximising fibre utilisation. 40 gigabit transmission is based on 8 fibres—4 transmitting and 4 receiving at 10 gigabits each.
The upcoming 100GBASE-SR5 standard for 100 gigabit will also be based on 8 fibres—4 transmitting and 4 receiving at 25 gigabits each. With MTPs being a 12-fibre connector but only requiring 8 for transmission, 33% of the fibre goes unused. An ideal way for data centre managers to ensure 100% utilisation of fibre in both 40 and 100 gigabit applications is to use conversion cords that transition two 12-fibre MTPs from backbone cabling to three 8-fibre MTPs for connecting to equipment.
The war is over
Unlike fibre, category 6A copper systems support the remote power requirements of the horizontal LAN. And with the upcoming category 8 twisted-pair cabling positioned to support cost-effective 25GBASE-T and 40GBASE-T applications in data centre switch-to-server connections, copper is here to stay.
At the same time, fibre is the only cable media able to handle longer distance 40 and 100 gigabit channels in the data centre and the outside plant. While there are several considerations—from the ability to adequately handle emerging remote power applications like 4PPoE, to ensuring low loss, flexible and scalable fibre connectivity—it’s obvious that copper and fibre both have their place in the network and will co-exist for many years to come. The age-old debate between copper and fibre has finally come to an end.
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