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Bridging The Last Mile With DSLARs
Despite all the hype about amazing, super fast, "always-on,"
Internet access technology that speeds way past good ol' tortoise-slow
56K, it remains an unfortunate reality that distance constraints are still
a very real problem for small office/home offices (SOHOs) and small-to-medium
enterprises (SMEs) who want DSL access. Most DSL technologies have a set
distance limitation of about 17,500 feet between the customer premise
and the telephone company's CO. These last mile limitations are due to
poor quality, limited-bandwidth copper wire in the loop. The farther you
are from the CO, the weaker the transmission. Today, it is an accepted
fact that if your business is too far from the DSLAM at the "nearby"
CO (Central Office), you're out of luck. Or are you?
The Traditional Solution
DSLAMs -- Digital Subscriber Line Access Multiplexers -- are network
devices that receive signals from several customers' DSL connections,
and puts those signals on a high-speed backbone using multiplexing techniques.
The traditional "out-of building" DSLAM solution for MTUs
(Multi-Tenant Units) is based on the remote DSLAM model which has the
device located away from the MTU at the CO. There, data traffic is consolidated
from individual DSL connections on the customer side into large, high-capacity
backbone networks that connect to an ISP or corporate networks. The
DSLAM serves as a platform for DSL service aggregation as well as a
gateway for IP routing, switching, and virtual private networking. In
the case of ADSL, currently the most popular DSL flavor for MTUs, the
DSLAM splits DSL's digital signal away from the analog voice service
and routes the voice traffic to the PSTN (Public Switched Telephone
Network).
New MTU-Based Solutions: Introducing DSLARs
The solution to the last mile distance conundrum is the introduction
of a new line of in-building, MTU-specific DSLAM platforms called DSLARs
(DSL Access Routers). These mini-DSLAMs are located at the base of the
MTU premises and are equipped with powerful routing features such as
IP routing, RIP (Routing Information Protocol), DHCP (Dynamic Host Configuration
Protocol) + NAT (Network Address Translation), and a wide range of WAN
interface options.
These new DSLARs bring the DSLAM to the MTU building site and connect
the MTU to the CO via a variety of WAN access technologies, such as
T1 or OC-3 (fiber optics). Now -- via this high-speed WAN connection
such as a T1, OC-3, Gigabit Ethernet or 100 Base-T -- these new DSLARs
aggregate all the various lines from the customer premise at the base
of the MTU premises, and allocate the bandwidth out to the individual
tenant units at rates up to 8 Mbps over the existing POTS copper wire
infrastructure. Thus, from a single WAN access point in the building,
an entire MTU property can be readily provisioned with high-speed Internet
services, voice over DSL, and video-on-demand without requiring recabling.
A DSLAR in-building MTU solution addresses the DSL distance limitation
issue for the MTU customer. The only limitation left is the distance
between the customer premise and the DSLAR at the base of the MTU premises.
With DSL technologies designed to cover up to 17,500 feet, and the highest
skyscrapers in existence being no taller than 2,000 feet, the last mile
is no longer a concern.
Choosing DSLARs
Some of the leading DSLAR players in the MTU space are Tut Systems,
Copper Mountain Networks, ARESCOM, AccessLan, Interspeed, and Elastic
Networks. Recently, major networking players like Cisco and 3Com have
jumped on the DSLAR bandwagon with their own MTU broadband solutions
as well. Though each DSLAR may vary in shape, size, and specific feature
sets, these are the basics components you should look for when choosing
a DSLAR: An end-to-end DSL access service platform utilizing in-building
POTS. Multiple WAN interface options (T1/T3, OC-3, Ethernet, etc.).
Stackable/scalable or line card-based shelf platform architecture. Rack-mounted
for installation at the base of the MTU. Advanced routing functions
such as IP routing, RIP, and DHCP + NAT. Independent bandwidth management
capabilities, for QoS. Web-based network management software.
With the new DSLAR in-building MTU solutions, businesses no longer need
to concern themselves with last mile limitations. DSL availability and
high-speed broadband access will finally be a reality for SOHOs and
SMEs in all MTU environments. The on-premise DSLAM solution provided
by DSLARs will at last ensure full dedicated DSL broadband speeds for
every MTU office environment in any location.
You can find this article also at 
http://www.tmcnet.com/tmcnet/articles/0401ar.htm
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