Conectronica Revista Maganize industrial de electronica

At present a great activity in relation to the development and standardization of future products and 100 exists devices Ethernet Gigabit. In this article we will comment some of these initiatives

The spectacular increase in the requirements of bandwidth of the networks, motivated to a great extent by Internet (Web 2,0) and the applications of video under demand (IPTV), is bringing about the continuous update of routers of the suppliers on watch with new interfaces 10G. In fact, are either unfolding 40 interfaces to Gb/s and some routers DWDM of long distance or transport channels 40G. Nevertheless, the necessity of 100 Ethernet Gigabit (100GbE) is more and more evident (figure 1). The rate of 100 Gb/s supposes the natural extension of the Ethernet hierarchy (10M/100M/1G/ /10G) that has been great successful during the last decades. Although there are some who think that 100GbE arrives behind schedule. One is which are been working with salesmen who own 100 propietary solutions to Gb/s and consider that the standards 100GbE had to finalize long before. Both main organisms of standardization that have participated in these tasks are the IEEE (802,3 Higher Speed Study Group, HSSG) and the Union the International of Telecomunicaciones (ITU-T). Nevertheless, a series of alliances and associations also exist that been have involved in the process of specification of the standard 100GbE, eg: for Alliance Telecommunication Industry Solutions (ATIS), Optical Internetworking Forum (OIF), Ethernet Alliance, Road to 100G Alliance, Optoelectronics Industry Development Association (OIDA). One of the most delicate points of the standardization process is regarding the definition of the specification 40GbE, because as we know, nowadays routers of greater capacity Gb/s is developed with 40 ports to and compatibility between Ethernet Gigabit is needed and the hierarchy SONET/SDH whose standardized rates of bit are defined using multiple of four. This he is possibly one of the majors discussion points at present, to which it is united the fact that Ethernet Gigabit yes that is preparation to handle asynchronous traffic, but SONET/SDH does not turn out the most efficient means to handle the present volume of traffic IP. In this article we will comment the standardization initiatives that are being carried out nowadays in relation to 100GbE, while we will present/display some of the technologies that are going away to use in the implementation of the first commercial devices. Activities of standardization The IEEE group 802,3 HSSG has actively participated in the definition of the parameters of layer MAC and the specifications of physical interface LAN of the standard 100GbE. This process of standardization turns out key to assure the correct interconnection the Ethernet equipment from the companies and datacenters with the systems transport WAN. The optical network of transport (Optical Transport Network, OTN) is the future platform for the interchange of all type of digital information. The ITU-T has standardized the OTN through series G of recommendations: structures of plot (G.709), architectures (G.872) and functions of management (G.798). Concretely, it consists of a multiplexada hierarchy of optical units of data (optical data units, ODUs) that are organized inside units of optical transport (optical transport units, OTUs), which form the base of the services of data GFP-Framed or GFP-Transparent. Containers OTU name from the 1 to the 4 and they correspond with the following rates of bit:

1 - OTU1/ODU1: 2.5 Gb/s

2 - OTU2/ODU2: 10 Gb/s

3 - OTU3/ODU3: 40 Gb/s

4 - OTU4/ODU4: 120 Gb/s

The development of the specification of container OTU4 is at the moment in march in the work group ITU-T SG 15, and constitutes the model of 100 reference of Gb/s in the group IEEE HSSG. Containers OTU4 will be able to transport of form is transparent 9 signals 10GbE, or a unique signal 100GbE. The complementary activities of the IEEE and the ITU-T regarding the standard 100GbE summary in table I. In figure 2 is to a model of architecture 100GbE MAC, denominated schematically 100GE, with 10 sub-layers I/O of physical codification 10G for 10 km of optical fiber monoway (SMF). The challenge at the time of standardizing this type of applications is to be able to develop to transceivers of first generation using the present technology, and later to be improving in cost, power and size as they appear new technological possibilities. In any case, the election of the wavelengths of operation must be in agreement with the present technologies as as much future. Technologies 100GbE At the time of analyzing the optoelectronic technology of the 100 systems GbE we can differentiate between two types of applications. First of them Gb/s talks about to networks LAN to 100 on SMF, whereas second multiway corresponds with the case of fiber (MMF). In both cases it is possible to be spoken of two technological generations: the present technology and the one that will be necessary in 8 or 10 years. The 100 systems Gb/s LAN SMF can be implemented using diverse alternatives: existing technology 10G LAN NRZ on channels WDM, modulations outposts on a unique optical carrier and technical of compensation of dispersion, or new 25 technologies NRZ to Gb/s on channels WDM. In all the cases, as much to 1310 nm as to 1550 nm. The specification 10GBASE-ER supports 40 km to 1550 nm, which is equivalent to 8 losses of dB in the balance of powers, against the 16 dB to 1310 nm. However, 10GBASE-LR supports 10 km to 1310 nm, which is equivalent to 4 losses of dB. The majors losses to 1310 nm are resisted with the fact of not needing compensation dispersion, reason why they can be used laser with direct modulation. The rate of bit of 100 Gb/s forms from 10 10 channels WDM of Gb/s, reason why it names habitually like 10x10G. Anyone of the previous technologies 10GBASE can be used to implement this type of systems. For example, CyOptics and Cray has developed a transceiver to 1550 nm using 20 window CWDM of nm.

As one commented previously, another one of the alternatives is the use of schemes of optical modulation advanced such as QPDSK or DQPSK (CONECtrónica, number 114, pp. 8-12, February 2008). In this case, the rate of symbol is reduced to half, being two 50 channels of Gb/s that can be placed inside a unique channel DWDM. Additionally, by means of the use of orthogonal polarizations, it is possible to be secured a new reduction of the rate of symbol and to be obtained four 25 orthogonal channels of Gb/s.

Finally, the third alternative consists of multiplexación WDM of four 25 signals NRZ of Gb/s (4x25G). This option is especially attractive since characteristic such as cost, consumption of power, size and reliability improve with the reduction of the number of channels, reason why advantages in front of the option are obtained 10x10G. The scheme is quite similar to the one of the standard 10GBASE-LX4, although in this case for fibers SMF. The block diagram of the transceiver architecture 4x25G imagines in figure 3. The connection with the electrical interface is realised using 10 signals of Gb/s, typical rates of input/output of main technologies CMOS used for layer MAC.

The 10 conversions of Gb/s to 25 Gb/s and vice versa secure by means of the use of serializadores circuits 10:4. In transmission, the signals are modulated using 4 lasers with electroabsorción modulators (EML), which generate 4 wavelengths different that they are multiplexan on the same fiber. For reaches inferiors to 4 km, it can be used as much second as third window. The possibility also exists of using 4 lasers with direct modulation, but in this case to 1550 nm techniques of compensation of dispersion are required. In reception the inverse process is realised, 4 optical channels WDM are demultiplexed and they fotodetectan with individual receivers composed of fotodiodo PIN and a transimpedancia amplifier (AUNT). The spaced ones of channels WDM admit different possibilities that are enumerated next: grid 25 IEEE LX-4 of nm, grid CWDM ITU G.694.2 of 20 nm, or grids DWDM ITU 800 G.694.1 from 400 to GHz (2 to 4 nm). The two first allow the use of lasers without temperature control. Finally, simply to comment that since the power losses are majors to 1310 nm, the use of optical amplifiers of semiconductor is required (SOA) in the case of metropolitan networks (I reach inferiors to 40 km). Although these can also replace by lasers of high power in transmission and avalanche photodetectors (APD) in reception. In the case of 1550 nm, the techniques of control of the dispersion that usually are used are: pre-chirping in the transmitters, compensating fibers or circuits of electronic compensation of the dispersion (EDC). The 100 applications Gb/s LAN MMF essentially concentrate in internal connections between racks on distances inferiors to the 100 M.s These connections on fiber multiway usually are constructed using laser 850 VCSEL to nm (CONECtrónica number 91, pp. 8-10, October 2005). Technology VCSEL works relatively well up to 10 Gb/s, but to majors speeds high currents of polarization are needed that finish considerably degrading the time of life of the device. Therefore, the unique option in this case consists of using a scheme 10x10G to generate the signal of 100 Gb/s. Of form similar to the 10GBASE-MR. standard, one sets out to use fiber multiway of the type OM3 that owns a nominal bandwidth of 2000 MHz/km to 850 nm of such form that stops 100 ms the dispersion that undergoes a 10 signal NRZ of Gb/s is minimum. However, older fiber models as for example type OM1 defined in the specification 10GBASE-LRM is not adapted.