Dual Waveform VSAT February 2012 SkyEdge II Accent The Operator s Dilemma Traditionally, when operators designed satellite broadband networks, they needed to make a decision on whether to implement a network system that uses time and frequency sharing schemes (TDMA), or one that uses dedicated point-to-point channels (SCPC). TDMA networks allow bandwidth resource sharing which can offer service providers distinct OPEX advantages in certain cases. In general, the more dynamic and bursty the network traffic is, the greater the advantage of bandwidth sharing. TDMA VSAT systems also have the advantage of being centrally managed by a single NMS (Network Management System) simplifying operations compared to networks that are built from point-to-point SCPC links. 1 Gilat Satellite Networks Feb-12
However, for locations where the network traffic is continuous with a high throughput, allocating dedicated bandwidth resources with SCPC has its own advantages. The links can be implemented in these cases with smaller antennas and BUCs. The network solutions that are offered today are based on SCPC or TDMA waveform or a mixture of two separate network platforms. This type of mixed solution results in increased OPEX and CAPEX. It involves either two separate management systems (or limited management for the SCPC devices), double inventory and no field upgradeability if the nature of the network changes over time. Consider for example the design of a cellular backhaul network. With the introduction of the cellular coverage in remote locations, operators need to backhaul the traffic from base stations to their controllers using satellite communications. TDMA satellite networks allow operators to efficiently make use of shared satellite capacity minimizing the overall amount space segment required and thereby reducing OPEX. Networks that operate in TDMA mode take advantage of the dynamic nature of the traffic and statistically multiplex between cell-sites that have low activity factor. However, not all cell-sites behave the same way and in cases where the cell activity factor is high, it is better to use a dedicated SCPC link. What about a mixed network where some of the cellular base stations are connected using SCPC equipment and others with TDMA equipment? This solves one problem but it creates several more. It introduces inventory and maintenance issues because of the two sets of hardware. In addition,it is impossible to manage all the VSATs from one centralized NMS as the SCPC links are either managed by a separate system or not managed at all. Because of this complexity, operators typically choose a single technology, either TDMA or SCPC, for the cellular backhaul network. But there is an alternative that allows operators to unleash the benefits of both TDMA and SCPC within a single network without the additional operational complexity mentioned above. The development that makes this possible is the Dual-Waveform VSAT. Dual Waveform VSAT The Best of Both Worlds Gilat has introduced a Dual-Waveform VSAT called the Accent. The Accent is a VSAT with an inbound (return) channel that can dynamically switch between DVB-S2 continuous (SCPC) mode or DVB-RCS burst (TDMA) mode at any time on-the-fly. The diagram below shows a cellular backhaul network where remote cell sites are equipped with an Accent VSAT. In some of the locations the Accent operates in SCPC mode and in others it operates in TDMA mode. 2 Gilat Satellite Networks Feb-12
Figure 1 -Cellular Backhaul with Dual Wavform VSATs High availability with DVB-S2 ACM Return Channel The outbound (forward) channel of the Accent Dual-Waveform VSAT is a shared DVB-S2 channel for all of the VSATs. The Accent uses DVB-S2 ACM in the return channel making use of adaptive coding and modulation in both outbound and inbound directions. The use of bi-directional ACM results in superior link and service availability withstanding signal fade caused by bad weather. Full Control & Monitoring with Single NMS In addition to having the bandwidth sharing advantages of a single outbound channel, a network with Accent Dual-Waveform VSATs also has the benefit of a single Network Management System (NMS) to manage all VSATs, whether they are in TDMA or SCPC mode. This is especially important for the VSATs that switch in and out of SCPC mode as it means that they remain connected to the NMS even when they are not being allocated a dedicated SCPC ink. The introduction of the Accent VSAT combines two waveforms in a single box, but it also does more than that 3 Gilat Satellite Networks Feb-12
Switching Modes based on Application, Schedule or Trigger Each Accent VSAT can switch from TDMA to SCPC mode and back in a number of different ways: Manually via the network management system Automatically based on a pre-defined schedule In response to an application or bandwidth threshold Triggered by a fault signal (terrestrial backup) Schedule-based triggers are managed by a schedule wizard in the SkyEdge II NMS. This enables operators to offer new, scheduled, high-throughput services such as video for a sports event. This scheduler also gives the operator the ability to monitor all active SCPC links and to schedule a link on a specific frequency and specific time of day. Network operators can get a clear view of all their current and future SCPC links on an intuitive GUI. What happens when a Dual-Waveform VSAT switches from TDMA to SCPC? An Accent VSAT in TDMA mode is just like any other SkyEdge II MF-TDMA VSAT in that it transmits data in timeslots that are dynamically assigned by the hub upon demand and according to QoS and SLA configurations. The timeslots used are allocated from a bandwidth pool shared by a group of VSATs. When the VSAT switches to SCPC mode, it is given a dedicated slice of bandwidth for its exclusive use. This dedicated SCPC link allows the VSAT optimal performance for continuous high-speed transmission (e.g. during a video upload). When a VSAT in SCPC mode switches back to TDMA mode, the slice of bandwidth is freed and returned to the common bandwidth pool. The Accent VSAT with its waveform switchover functionality creates the opportunity for new and improved services that satellite service providers can offer. The following sections illustrate a couple of examples. Satellite Backup for Terrestrial Links Figure 2 - Schedule Wizard in NMS Satellite links are frequently used as a means for backing-up terrestrial links for enterprise customers. The Operator s Dilemma that was presented in the beginning of this paper is particularly relevant here. On the one hand this is an application that would require the high-speed continuous throughput that SCPC offers, on the other hand, the bandwidth is only required to be available in the event of a fault so allocating a permanent SCPC link to each site is wasteful. 4 Gilat Satellite Networks Feb-12
The Accent Dual-Waveform VSAT is perfect for this application. An Accent VSAT can be deployed at all of the enterprise sites that require terrestrial backup. The VSATs operate in TDMA mode which allows them to keep in touch with the NMS while using minimal bandwidth. When a terrestrial link drops, the Accent VSAT at the site switches to SCPC mode for the duration of the outage. The advantage of using the Dual-Waveform VSAT is that the operator can provide a high performance backup service from a common pool of satellite bandwidth SCPC performance with TDMA bandwidth savings. In addition, even when the Accent VSATs are not allocated SCPC links, they are still visible to the NMS and they transmit keep-alive signals via a very low bandwidth TDMA connection that lets the operator know that the VSAT is fully functional. This network visibility is due the Accent s ability to switch between SCPC and TDMA and cannot be achieved on a network that only supports SCPC mode. Figure 3 - Satellite Backup for Terrestrial Links 5 Gilat Satellite Networks Feb-12
Video Transmission and DSNG Another example for an application enhanced by the Dual-Waveform VSAT is communications on the pause (COTP) combined with video. Vehicles equipped with a VSAT terminal, self-pointing antenna and a video camera are used for emergency response, homeland security and news gathering. In all of these cases, a high-speed link needs to be set up rapidly for uploading the video stream. SCPC is most suitable for this kind of transmission but the setup time for an SCPC link can take too long. With the Accent VSAT on board, a vehicle can stay connected over TDMA during the preparation for an important video transmission. As soon as the event begins, the accent can immediately switch to SCPC mode and transmit the video stream. Figure 4 - Video Transmission Summary SCPC and TDMA, the best of both worlds SCPC links offer customers high throughput continuous connectivity that is most efficient for constant and high throughput transmissions such as video, trunking and cellular backhaul TDMA networks offer service providers a platform for delivering services to multiple sites using a common bandwidth pool which is most efficient for transmissions that are dynamic or intermittent in nature. Service providers were previously forced to choose which one of these technologies to implement in their networks. With the SkyEdge II Accent Dual Waveform VSAT, service providers can create networks using a single VSAT that can dynamically switch between SCPC and TDMA upon demand. The benefits of this approach are: - Reduced CAPEX as a result of unified inventory - Reduced OPEX most efficient use of the return channel space segment - Better network visibility always-on connectivity with the NMS for monitoring - Increased performance on demand, high-throughput SCPC services The Accent is the latest addition to the SkyEdge II platform introducing Dual Waveform functionality. It includes the rich feature set already available in the platform including CacheMode! acceleration with multi-gb caching, BGP routing, VRRP redundancy, end-to-end VLANs and virtual routing, AES-256 encryption, DiffServ QoS and many other features. For more information, please visit www.gilat.com/accent 6 Gilat Satellite Networks Feb-12