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TechTalk: A Discussion With Greg Quiggle
VP of Product Management, iDirect

With iDirect’s new TDMA and SCPC Return switching capability, service providers gain the flexibility to adjust service levels to meet dynamic application needs and changing traffic patterns, while maintaining an economical way to use total network capacity and optimize operational efficiencies.

SatMagazine (SM)
What is iDirect’s new SCPC Return feature and why is it needed?

Greg Quiggle
The vast majority of satellite communications networks are either SCPC or TDMA, and service providers need to support both if they want to meet a broad range of customer applications. However, this incurs unnecessary capital expense and operational inefficiencies. For example, network operators need to invest in and manage two separate technology platforms. Changing a customer from one technology to the other involves costly site visits and service interruptions. Further, network operators are unable to share satellite capacity across their entire customer base or re-allocate excess bandwidth from typically over-dimensioned SCPC links. This is hard to justify in an industry where space segment is both scarce and expensive.

Service providers have come to accept this as a cost of doing business in the satellite industry. But all that changes with the introduction of iDirect’s new Evolution operating software — iDX 3.0. With a simple software upgrade, any Evolution router can now run in TDMA or SCPC mode on the return channel. An iDirect router can be switched back and forth between TDMA and SCPC based on time of day or the volume of traffic being carried by the remote.

TechTalkFig1 SM
What are the key differences between SCPC and TDMA technology?

Greg Quiggle
SCPC (Single Channel Per Carrier) refers to satellite channels in which only a single device is configured to transmit on the channel. SCPC equipment is a relatively simple technology, with a guarantee that bandwidth is always available at the site where it is installed. Typically, sites with high, constant bandwidth requirements are good candidates for SCPC equipment. However, if traffic is not constant, the SCPC link will need to be over-dimensioned based on peak bandwidth demand, resulting in wasted capacity when the link is under-used.

TDMA (Time Division Multiple Access) is an alternate means of using the bandwidth in which multiple devices share the same channel by transmitting short bursts of data. The benefit of this system over an SCPC link is that many devices can be supported on the link, each of them using it as the need arises. In a standard TDMA network, multiple devices share a common outbound channel. Of course, the ability to flexibly share the bandwidth between multiple devices on the inbound incurs some additional overhead, leading to some loss in throughput efficiency. Traditionally, operators would evaluate network needs and usage at a specific site, and determine whether SCPC or TDMA equipment was best suited for that site. The most important factor in that decision is the perceived need for continuous bandwidth: Sites with high bandwidth or continuous data requirements would likely get SCPC equipment, and sites with more dynamic bandwidth requirements would get TDMA equipment on an appropriately over-subscribed network.

To overcome at least part of the problem of unused capacity, particularly in links with asymmetric traffic, some networks now feature a shared outbound channel, similar to TDMA networks, but with SCPC on the return channel. Of course, any SCPC channel requires some minimum bandwidth to each site, which can still be expensive.

What is the rationale behind supporting TDMA and SCPC Return on one platform?

Greg Quiggle
There are numerous situations in which a network operator might want greater flexibility, but is limited by the availability of equipment which can operate in either TDMA or SCPC mode.

First, the bandwidth needs of the customer may not be constant enough to require a dedicated link all of the time. Since the link must be sized to accommodate the peak traffic, if there is any variance in the traffic, the customer has paid more for excess bandwidth.

Second, there might be network growth or a change in usage patterns at a remote site. Initially an operator may project very low traffic volume for a given site, but expect traffic to eventually increase enough to require a dedicated link. The operator must install SCPC equipment, and augment the channels later as traffic demands warrant. Until the projected growth occurs, that operator must maintain a large pool of underutilized SCPC links, where a properly subscribed TDMA network would be preferable.

Finally, network operators often rely on different manufacturers for their TDMA or SCPC equipment. An integrated platform reduces operating and infrastructure costs, making it far more economical to switch hardware between TDMA and SCPC, roll out new applications faster, and upsell customers as sites grow larger. With iDirect’s SCPC-Return feature, network operators can configure select remotes within an existing TDMA network, and reconfigure them to transmit in SCPC mode on the inroute. No changes to the infrastructure are required to effect this change, and the remote can be returned afterwards to TDMA operation.

What is a scenario in which an operator might want the ability to switch between TDMA and SCPC Return modes based on time requirements?

TechTalkFig2 Greg Quiggle
One example is a VSAT operator that manages a number of maritime customers, as well as networks from exploration platforms. To support this customer base, the network operator maintains a large pool of TDMA and SCPC inroutes active at all times. These inroutes could be supported on individual (single-channel) line cards, or groups of inroutes operating on the XLC-M line card in multi-channel mode. Customers on the exploration platforms periodically require an increase in inroute bandwidth for the transfer of large sets of data such as high-resolution images, seismic data or other information. These customers require the delivery of this data in a timely fashion, so a temporary increase in throughput is warranted. To support these requirements, the operator can reconfigure a remote from a pool of remotes sharing a TDMA inroute, to have its own dedicated SCPC-Return inroute. When the requirement for the increased bandwidth is over, that site could be returned to TDMA-mode operation.

Using iBuilder, the iDirect NMS configuration tool, the remote is simply removed from a shared TDMA inroute group, and assigned to one of the pre-defined SCPC-channels. The operator does not reconfigure any channels, but simply reconfigures select remotes to use one inroute channel or the other. By taking advantage of equipment that can switch between TDMA and SCPC, the network operator has avoided deploying equipment scaled to their intense requirements, which would have remained largely idle during other periods.

What is a scenario in which an operator might want the ability to switch to SCPC Return mode based on traffic volume requirements?

Greg Quiggle
Another VSAT operator is supporting cellular backhaul in a remote region, where significant traffic growth is expected in the near future. For now, TDMA is the most bandwidth efficient solution to support smaller, yet dynamic traffic volume from scattered villages. But as the traffic increases at those sites, SCPC becomes more efficient. The ideal solution is for this operator to operate the sites in TDMA mode until traffic at those sites warrants a switch to SCPC.

A smaller operator is not likely to have the resources to maintain a large pool of TDMA- and SCPC- inroutes, so instead might choose to repurpose leased space segment from a TDMA inroute for an SCPC-Return inroute. In this case, the operator would select an inroute channel from its pool of TDMA inroutes, and dynamically remove it from the system configuration. The operator would then activate a previously configured SCPC-Return channel in the same space segment and the base station site needing an SCPC-Return inroute would be configured to use this inroute. The network operator has simplified its deployment with equipment that is able to modify its mode of operation to best meet the growing needs at each site.

What hardware or software does an operator need to purchase in order to gain SCPC Return capabilities?

Greg Quiggle
For existing iDirect Evolution network operators, the SCPC-Return feature is enabled by a software upgrade to iDX 3.0, and requires no new hardware. By upgrading to iDX 3.0, an operator with existing TDMA remotes can now offer customers the efficiency of an SCPC channel on the inroute, on a temporary, semi-permanent, or permanent basis. Returning the remote to TDMA-mode is also simple, and can be achieved quickly through iBuilder.

Though not required to support SCPC-Return, operators managing a large pool of inroutes will almost certainly want to take advantage of the flexibility offered by iDirect’s new multi-channel demodulator. With software key licensing available through iDX 3.0, an Evolution line card — such as the XLC-M or the eM0DM — can now support up to 8 TDMA or 8 SCPC channels. While the multichannel demod is not required for the SCPC-Return feature, its ability to operate up to 8 return channels in SCPC mode greatly enhances the flexibility of the network on the hub side. It gives the network operator the ability to reconfigure the hub side of his network with ease. Further, it allows service providers to gain efficiencies in their hub infrastructure of up to 40 percent due to fewer line cards and chassis space required. SCPC-Return channels up to 15 MSps are supported. QuiggleHead

Greg Quiggle current serves as the VP of Product Management at iDirect. Prior to joining the team, Greg served as the Executive Vice President of Marketing for Tollgrade Communications and the Vice President of Marketing for Acterna Corporation (now JDS Uniphase). In these roles, Mr. Quiggle has spent over 18 years conceptualizing and executing successful corporate-level product strategies within the communications industry.