BROADBAND COMMUNITIES is the leading source of information on digital and broadband technologies for buildings and communities. Our editorial aims to accelerate the deployment of Fiber-To-The-Home and Fiber-To-The-Premises.
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JANUARY/FEBRUARY 2014 | www.broadbandcommunities.com | BROADBAND COMMUNITIES | 65 Carriers are looking to take advantage of PON's cost-saving ability to address their customers' bandwidth addictions by employing PON strategies close to, as well as to, subscriber homes. One key characteristic of DSL is that its realized speeds are sensitive to distance. For this reason, fber to the node (FTTN), fber to the cabinet (FTTC) and fber to the distribution point (FTTdp) are emerging as mechanisms for deploying fber with DSL to enable faster data rates by bringing cabinets and delivery points closer to end consumers. In fact, a large percentage of today's FTTx subscribers use VDSL2 connections in which fber runs to an intermediate node – installed in a street cabinet, neighborhood or basement of a multiple-dwelling-unit building – through which VDSL2 copper broadband service is ofered to the end consumer. Tis deployment method is better known as FTTN or FTTC. COMBINING PON WITH VDSL2 Te way this combination of technologies works in the real world is relatively straightforward. Typically, a fber from a PON optical line terminal (OLT) is pulled close to end subscribers and terminated by a corresponding PON optical network terminal (ONT) designed on the uplink of an IP-based DSL access multiplexer (DSLAM), which is housed in a cabinet unit. Te DSLAM supports multiple line cards, each of which has as many as 24 to 72 central ofce–side VDSL2 modems installed. Tese, in turn, communicate with their VDSL2 customer premises– side counterparts in subscribers' homes. A DSLAM usually serves between 96 and 384 customers. At the same time, carriers continue to install pure FTTH PON networks along cable routes, fed from the same fber that is fed to the FTTC cabinets, to serve FTTH subscribers who need guaranteed higher speeds. Tough VDSL2 uplink architectures are certainly not limited to PON systems (many carriers deploy point-to-point fber to their DSLAMs), service providers stand to realize fairly substantial benefts by leveraging VDSL2 over a "universal" fber-based PON deployment. Tis approach allows telcos to beneft from the incremental increased bandwidth possible with VDSL2 along with the host of advantages available to a native FTTH PON deployment. For example, PON architecture can provide up to 10 Gbps bandwidth to support emerging services – a highly desirable feature for network operators whose long-term plan is to upgrade to all-fber networks and take advantage of PON's economics for applications that include residential, business, 3G/ LTE wireless and small-cell backhaul. In addition, PON's low operating expense, coupled with lower total power use (due to its passive feld components) compared with point-to- point architectures, puts more money in their pockets. THE ROLE OF VECTORING Of course, that's not the end of the story. Tough using a PON access network with VDSL2 ofers signifcant increases in bandwidth, there is always room for improvement. Vectoring technology is one improvement that promises to signifcantly improve VDSL2 bit rates by canceling the interference and crosstalk among the copper lines in a binder (bundle of twisted pairs in a conduit). Canceling interference allows VDSL2 to deliver consistent, reliable broadband at speeds in excess of 100 Mbps. (Speeds of 120 Mbps downstream/40 Mbps upstream have been measured and tested by various carriers in locations where 50 Mbps services were provisioned earlier.) One variety of vectoring technology, G.Vector (ITU-T G.993.5), is now enabling global operators to quickly, easily and cost-efectively deliver speeds in excess of 100 Mbps. By extending the performance of existing copper connections, operators ofer high- bandwidth broadband services, such as high-speed Internet, IPTV and VoIP, from street cabinets approximately 500–1,000 meters away from end consumers. In efect, G.Vector allows today's deployed FTTN/FTTC VDSL2 street cabinets to ofer about twice the aggregate bandwidth of previous VDSL2 bandwidth oferings while using existing telco infrastructure. A vectoring solution inside a DSLAM generally consists of three components: a DSL digital signal processor (which implements the G.Vector protocol, collects vectoring measurements and combines the cancellation vector with transmit data), a vector processor (which performs matrix multiplications of cancellation coefcients with real-time transmit data), and vector control entity software (which manages the vectoring system and calculates cancellation coefcients). In simple terms, G.Vector removes most of DSL's crosstalk noise, providing a very-high-throughput connection. Tis enables DSL speeds to achieve their theoretical maximum rates, seen only in very low-noise environments. Similar principles have been used in the past in technologies such as multiple- input, multiple-output (MIMO) wireless deployments. Tus, G.Vector provides an afordable, seamless upgrade path Vectoring cancels interference among the copper lines in a binder (a bundle of twisted pairs in a conduit) and allows DSL speeds to achieve their theoretical maximum rates seen in very low-noise environments. BBC_Jan14.indd 65 1/27/14 1:48 PM