SP: Alcatel Lucent showcased multi-carrier bandwidth virtualization technology at Satellite 2013. Please explain the rationale behind this development and the general characteristics of this new technology
Purohit: Effective use of transponder bandwidth and being able to satisfy customer requests even when contiguous blocks of the desired bandwidth are not available were the key initial drivers. As the technology called VSA has evolved, significant advantages have also been realized in the areas of interference mitigation, hitless bandwidth adjustment, and virtualization of physical layers to include fiber and satellite aggregation.
SP: The concept of channel bonding (also known as inverse multipliplexing) is not new; what are the key differentiating characteristics and how service providers and satellite operators can benefit from these?
Purohit: There are traditional ways of doing inverse multiplexing, such as Ethernet Link Aggregation that relies on Layer2/3 header fields for classification of traffic into flows with different flows mapped to randomly chosen physical pipes. The significant drawback of this approach is its inability to deal with traffic comprised of just a single flow – such as a video streaming session or a large file transfer – which all maps to a single physical link and keeps other links unused. That same scheme is also incapable of dealing with traffic such as TS over DVB-ASI that does not natively carry any layer 2/3 information. In other words, broadcast video requires adaptation over a Layer 2/3 transport mechanism before it can be inverse multiplexed using traditional inverse multiplexing, and this approach wastes bandwidth.
The VSA technology solves all of the above limitations thus allowing satellite operators to utilize their transponder capacity for both video and data traffic even in the presence of fragmented spectrum. Support for up to 64QAM constellations allows setup of high-throughput links with a high degree of resiliency due to the multiple levels of interference mitigation options. For e.g., an IP trunk can be setup using multiple disjoint carriers such that a complete loss of one of the carriers – either due to interference or equipment failure – is hitless from a packet perspective. Another option is the rapid and automatic reconfiguration of the IP trunk in the event of a complete loss of one of the carriers. Being able to increase the spectral bandwidth (for increased throughput) without interrupting the service is another advantage of this technology.
SP: Please elaborate on the technical characteristics: Number of carriers, Aggregate Thorughput (Mbps), Diversity and Interference Mitigation, etc.
Purohit: The technology is flexible, but we currently support aggregation of up to four links with aggregate throughput of up to 1Gbps. Higher aggregate bandwidth and number of links is certainly possible and will be driven by market requirements. Interference mitigation options such as Multi-Carrier FEC (MFEC) or Protection Groups allows service to be configured for hitless tolerance of failure of one of the constituent carriers.
SP: Given performance´s proximity to the theoretical limits of satellite transport gear, do you believe that focus will now turn to improving satcom operational processes, rather than squeezing more bits per hertz?
Purohit: Yes, while spectral efficiency (bits per Hertz) will always be relevant from an OpEx standpoint, new levels of operational flexibility in how transponder bandwidth is managed using the VSA is proving very attractive. Each organization or operator has a different lens and formula for how that additional flexibility is quantified in dollar terms, but there’s no doubt about the value it provides. We think that flexibility will be increasingly important (as customers realize it’s actually feasible) and considered equally – or in some cases more – important than spectral efficiency.
SP: Given ALU´s wide range of products and markets, do you envision that developments such as this could also trickle down to terrestrial and wireless transport markets?
Purohit: Absolutely, and, yes, it’s already happened – independently – with LTE carrier aggregation. The approach there is quite different than what’s done with the VSA where we provide a lot more flexibility in channel bandwidth parameters (symbol rate granularity is 1Ksps) and support a much wider frequency range per modem. VSA was initially targeted for the satellite segment although its value proposition has evolved to other areas such as point-to-point microwave links and fiber.
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