DSLAM Backhaul White Paper

IP DSLAM Backhauling Solutions over Bonded Copper

A White Paper by Actelis Networks® Inc.

March 2008

ALL RIGHTS RESERVED . 2008Property of Actelis Networks® Copyright © 2

Executive Summary More and more service providers are moving from legacy-based ATM DSLAMs to new IP DSLAMs. In addition, customer bandwidths are constantly increasing and, furthermore, service providers are being pressured to provide global services even in areas which do not have fiber connectivity. Service providers, therefore, require a cost-effective alternative to fiber to connect mini-DSLAMs over tens of kilometers and provide service in even the most rural areas. Actelis Networks’® solution, based on our award winning EFMplus™ technology and using our first-in-the-market Ethernet in the First Mile (EFM) repeaters, provides an efficient solution that has been deployed by many tier one carriers worldwide. This white paper provides some insight into the challenges in backhauling IP-DSLAMs, and how Actelis has managed to provide a cost-effective and manageable solution. The Challenges of Backhauling IP DSLAMs Service Providers today have been using E1/T1s and ATM technology to backhaul DSLAMs in areas where no fiber exists. The growing bandwidth requirements and cost of the legacy equipment makes this solution extremely expensive. E1/T1 connections require two copper pairs and can deliver a maximum of 2Mbps. In comparison, EFM over copper technology provides up to 5.7Mbps per single copper pair—more than five times bandwidth per pair than E1/T1 technology (and even more if throughput is considered as ATM overheads are much higher than EFM overheads). So on the face of it, it would seem to be a simple decision to migrate existing installations from E1/T1 to EFM over copper, or install new IP DSLAMs via this technology. However, there are a number of challenges and concerns that service providers face when backhauling IP DSLAMs, and especially remote IP DSLAMs, which make the decision more complicated.

1. E1/T1 and ATM is a tried and tested technology. Is Ethernet-based service as stable and reliable for backhauling multiple customers?

2. Service providers often have other technologies on the same copper binder. Will the EFM and G.SHDSL technology adversely affect these services?

3. Often IP DSLAMs have GE uplinks, or the connection to the central office (CO) is via GE. Will there be any connectivity issues, or will additional hardware need to be installed in the DSLAM or CO switch?

4. Repeater locations are remote and there is no local powering. Will this be an issue?

5. Replacing existing E1/T1 repeater enclosures is a costly procedure. Won't this make the solution cost-prohibitive?


6. Managing a network with multiple repeaters makes troubleshooting complex.

Actelis has unique technology that has solved all of the above concerns and has enabled many of our customers to provide up to 45Mbps connectivity to remote IP DSLAMs over distances up to 40km (25Miles). IP DSLAM Backhauling Solutions Actelis' ML600 Ethernet Access Device (EAD) is an 8-pair EFM device that can support up to 45Mbps symmetrical bandwidth. It can be used in a point-to-point configuration as both the CPE and the CO, or connected to one of Actelis ML130/ML2300 aggregation devices. For connectivity up to approximately 2 miles1 (3.6km) repeaters are not required. The ML600 is a hardened device that supports temperatures from -40°C to +65°C and can be installed in a street cabinet or any other non-cooled location. The ML600 connects up to the CO switch or DSLAM using four 10/100Base-T connectors, or a FE/GE SFP connector. This flexible connectivity makes it ideal for different equipment requirements. The ML600 supports Quality of Service (QoS) at the CPE side, and also at the CO side. This is critical when providing backhauling services as the copper pairs are typically the bottleneck and, therefore, it is crucial to prioritize services before the bottleneck and not at the CO after the bottleneck. Services can be classified by different criteria and mapped into 4 priority queues.

ML628(Remote node)

Remote DSLAM

Remote Office / Outdoor CabinetCentral OfficeML628

(Head-end node)

10/100BaseT

Data NetworkData

Network

SwitchSwitch

Note: 8 pairs per segment

Figure 1: IP DSLAM Backhauling Configuration To support extremely long range deployments, Actelis has XR239 EFM repeaters that can be spaced almost two miles (3.6 kms) apart, stretching the total length the Ethernet spans to over 25 miles (40 kms). This is accomplished by linking up to eight Actelis XR239 repeaters in series, sufficient to reach nearly all the remote DSLAMs deployed in rural communities. By utilizing unique EFMplus technology, Actelis' IP DSLAM backhauling solution can ensure that the “Three R's of EFM: Rate, Reach and Reliability” are maximized. Specifically, the following techniques are part of the EFMplus technology, which is implemented and results in a reliable link with minimal interference with other technologies on the binder:

• Cross-Talk Management (CTM), which coordinates the training process across multiple pairs resulting in increased total link data rate, balanced SNR margins across pairs, and improved BER performance.

1 The maximum distance depends on a number of parameters, the most important being the copper cable type.


• Automatic compliance with regional spectral regulations, which uses sophisticated estimates of loop attenuation and loop length to eliminate the need for complicated inputs from the user.

• Cut-line protection to ensure that the service will continue unaffected even in the case of a copper-pair being disconnected. This combined with QoS at the CPE ensures that high priority traffic is unaffected by adverse conditions on the copper.

• Dynamic Spectral Shaping™ (DSS), which improves the “spectral friendliness” of the Actelis EFM service to residential DMT-based services without sacrificing performance

Actelis' expertise in this area has ensured that it remains the market leader of EFM over copper technology. EFM Repeater Technology Actelis Networks is the only company to have field-deployed repeater installations. Actelis uses a XR239 form factor for its repeaters, the standard in the U.S. for repeater enclosures. This provides a simple replacement strategy for older T1 or HDSL technology and allows existing enclosures to be reused by simply replacing the repeaters.

ML628(Remote node)

Remote DSLAM

Remote Office / Outdoor CabinetCentral Office

XR239(Repeaters)

ML628(Head-end node) PFU-8

10/100BaseT

Data NetworkData

Network

SwitchSwitch


5 segments - single powered from CO

Figure 2: Single-Sided Repeater Powering In Europe and other parts of the world where XR239 form factor is less common, Actelis has developed repeater adapters that allow all of our major customers to use their existing enclosures and use Actelis' repeaters with the relevant adapter. This ensures that the solution remains cost effective as replacing enclosures is a costly and time-consuming task. For Greenfield installations, Actelis has enclosures for pole-mounted, street cabinet or underground installations. Each repeater supports two copper pairs and is remotely powered to remove the additional cost of local powering. A link can be either powered from the CO for up to four repeater hops (single sided powering for up to about 20km/12miles) as in Figure 3. The remote powering is provided by Actelis' PFU-8 (Power Feeding Unit for 8 pairs) devices which provide power meeting US and/or European standards.


Remote DSLAM

Remote Office / Outdoor CabinetCentral Office

XR239(Repeaters)

ML628(Head-end node) PFU-8

10/100BaseT

Data NetworkData

Network

SwitchSwitch


ML628(Remote node) PFU-8

9 segments - dual powered from CO and remote location

Figure 3: Dual-Sided Repeater Powering When deploying configurations with multiple hops, the installation and troubleshooting becomes more complicated. Actelis recognizes this and, therefore, has developing various tools to quickly and easily detect any faults. For instance, Actelis' management system shows a per-hop view of the installation where the SNR is measured per-hop. This enables service providers to locate a particularly noisy copper pair or segment. Each segment can then be enabled or disabled (per copper pair) to allow lower level diagnostic capabilities, and TDR (Time Domain Reflectometry) can be used to locate the distance to a copper fault (open wire, short wire, etc) on that specific hop. This allows the maintenance technicians to determine whether the fault is in the near-side connector, the far-side connector, or in the cable itself. Without tools like this, repeater configurations with multiple hops would be unmanageable. Although it is relatively uncommon, point-to-multipoint configurations can also be deployed using Actelis' ML130 or ML2300 DSLAMs. Remote powering is provided for repeaters in the same manner as with Point-to-point configurations. Summary Actelis has years of experience providing solutions for Carrier Ethernet over Copper™ solutions. Utilizing Actelis' expertise in the area of EFM over copper and repeater installations, we have developed a solution for IP DSLAM backhauling which we believe is unbeatable in its functionality and simplicity, and answers all of the challenges that such a complex configuration poses. It is no accident that Actelis has been chosen as the vendor for major IP DSLAM backhauling projects worldwide. The combination of Actelis' award-winning products and ease of management for multiple repeater hops make it the ideal choice for service providers.

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DSLAM Backhaul White Paper