Top 1 question for 10 Gigabit switch with MultiMode Fiber(and how to fixed )

Fancy Wang 10/22 2019

Although the original standard was published in 2002, it’s only more recently that 10 Gigabit Ethernet has started to gain traction. As the name suggests, the networking standard is 10 times faster than the current ubiquitous Gigabit Ethernet standard. But, do you really need these speeds, and what hardware do you need to get it working reliably?

Not for clients

The truth is that, a few specialist cases aside, such as high-end graphics development, your average desktop computer doesn’t need a 10Gbit/s connection. In fact, many computers would struggle to use the full bandwidth, which comes in at a quick 1,250-megabytes per second (MB/s). Currently, Gigabit Ethernet (1Gbit/s or 125MB/s) is more than fast enough for any application.

That doesn’t mean that 10 Gigabit Ethernet is pointless. In fact, it’s going to become an increasing requirement for modern businesses. Thanks to higher internet speeds, more cloud services, and more intensive applications running on servers, computers are starting to use a lot more data.

With everything running at 1Gbit/s, bottlenecks can soon develop. For example, in a business network where there are 10 computers all trying to talk to a server cluster, they have to share the bandwidth, effectively giving each computer a throughput of 100Mbit/s. Up that to 100 computers, and each is only getting 10Mbit/s. Suddenly, Gigabit Ethernet doesn’t seem so fast, and 10Gbit Ethernet starts to look like a winner.



Faster backbones

One of the main uses for 10 Gigabit Ethernet is as a backbone to your business. Several clients may be connected via Gigabit Ethernet to a switch, but the data connection to your server room could be upgraded to 10 Gigabit Ethernet. This relieves pressure and speeds up access to critical services around your company.

Installing 10 Gigabit Ethernet in the right locations, then, can work to alleviate bottlenecks and give a perceived speed boost to your computers. It’s sensible to monitor your network and work out where crunch points are, so that you can plan where to install 10 Gigabit Ethernet. 

As 10 Gigabit Ethernet (10GbE) is introduced into networks the physical limitations and properties of optical fiber introduce new challenges for a network designer. Due to the increased data rate, fiber effects, such as dispersion (intermodal, chromatic or polarization), become a factor in the achievable distances of 10GbE links. This leaves the network designer with new decisions and trade-offs that he/she must understand and overcome.This paper provides an introduction to the world of optical fiber and covers the unique network design issues that 10GbE introduces into an optical fiber network.

MultiMode Fiber

Multimode fiber is used extensively in the campus LAN environment where distances between buildings are 2 km or less. The broad market penetration and acceptance of 62.5/125 micron multimode fiber was initiated by its inclusion in the Fiber Distributed Data Interface (FDDI) standard. FDDI, developed under ANSI in the late 1980s, drove the use of 62.5 micron multimode fiber into the campus LAN environment. The “FDDI grade” multimode fiber specification is currently referenced in many networking standards (such as Ethernet, Token Ring, and ATM) and in the TIA/EIA 568-A cabling standard.

During the development of the FDDI standard, a number of commercially available multimode and single-mode fiber types were considered to meet the FDDI objective of achieving a 100 Mbps data rate (125 Mbaud) over distances of up to 2 km on fiber cable. Multimode was favored over single-mode because it met the 2 km distance objective and had the advantage of lower cost transceivers. At that time, the commercially available multimode fiber types were 50/125, 62.5/125, 85/125, and 100/140 micron. 50/125 micron fiber continues to be popular in Japan and Europe and is supported in the ISO/IEC 11801 standard (Generic cabling for customer premises). The 85/125 micron fibers were based on international initiatives and its use as a LAN fiber alternative. The 100/140 micron product is specified in a number of networking applications and used in military applications.

Fiber information carrying capacity is typically rated in terms of a bandwidth length product (MHz-km), which can be used to determine how far a system can operate at what bit rate (e.g., 1 Gbps or 10 Gbps). Naturally, as transmission speed goes up, for a given modal bandwidth, the distance that the signal can travel is reduced.

At transmission speeds up to 622 Mbps (OC-12/STM-4) multimode fiber can be driven with a light emitting diode (LED). However, beyond those speeds an LED can’t turn on and off fast enough and therefore a laser source is required. During the development of the 1 Gigabit Ethernet standard, it was discovered that multimode fiber bandwidth using a laser launch could be lower than the bandwidth when measured with a light emitting diode (LED) launch. To mitigate this affect and achieve acceptable multimode fiber optic operating distances for 1 GbE and 10GbE, specifications had to be created to address the fiber optic transmitter launch conditions, the fiber optic receiver bandwidth, and the fiber cable characteristics.

Multimode Fiber and 10 Gigabit Ethernet

The IEEE 802.3ae 10 Gigabit Ethernet specification includes a serial interface referred to as 10GBASE-S (the “S” stands for short wavelength) that is designed for 850 nm transmission on multimode fiber. Table 2 provides the wavelength, modal bandwidth, and operating distance for different types of multimode fiber operating at 10 Gbps. Technical issues relating to the use of laser sources with multimode fibers (discussed in the previous section) has significantly limited the operating range of 10GbE over “FDDI grade” fiber. The “FDDI grade” multimode fiber has a modal bandwidth of 160 MHz*km at 850 nm and a modal bandwidth of 500 MHz*km at 1300 nm.

To address the operating range concern, a new multimode fiber specification had to be created for 10GbE to achieve multimode fiber operating distances of 300 m (as specified in the TIA/EIA-568 and ISO/IEC 11801 cabling standards). This new fiber is referred to by some as “10 Gigabit Ethernet multimode fiber” and is an 850 nm, laser-optimized, 50/125 micron fiber with an effective modal bandwidth of 2000 MHz•km and is detailed in TIA-492AAAC. Its key difference, relative to legacy multimode fibers, are the additional requirements for DMD specified in TIA-492AAAC enabled by a new measurement standard for DMD (TIA FOTP-220). As shown in Table 2, this fiber can achieve 300 m of distance with a 10GBASE-S interface. Many leading optical fiber vendors are actively marketing this new multimode fiber for 10GbE applications.

There are two major factors which will likely drive use of this new “10GbE multimode fiber”: 1) the popularity of short reach (300 m or less) 10GbE applications and 2) the cost of 10GBASE-S interfaces relative to the others. Evidence of the popularity of low cost, short distance 850 nm multimode Ethernet applications can be found in the number of 1000BASE-SX ports shipped for 1 Gigabit Ethernet. 1000BASE-SX operates up to 550 meters on multimode fiber and has garnered a large percentage of the total number of 1 GbE switch ports shipped. Ultimately the marketplace will determine the popularity of “10GbE multimode fiber”. The alternative is to use single-mode fiber over a 10GBASE-L or 10GBASE-E interface or the 10GBASE-LX4 interface, which supports both single-mode and multimode fiber over distances of 10 km and 300 m, respectively.