IPTV - The Software behind SDV

Introduction

In a cable network, groups of homes are connected on a common branch of coax cable. That is, groups of subscribers share access to the same downstream frequencies, and race for access to shared upstream frequencies. Where as, the traditional wireline networks are considered point to point, from a central office directly to a subscriber. Therefore, with sufficient switching capacity placed at the central office, infinite amount of content can be delivered to a single household. Switched Digital Video (SDV) is a cable technology that attempts to answer this challenge. It was designed as a cost-effective method to expand program availability.

With SDV, as with IPTV, and unlike traditional digital broadcasting, programming terminates at the hub and does not go through the network unless requested. Instead, a receiver, such as set-top-box, signals upstream to request programming, and a hub-based controller receives the request and enables the stream into the network by means of a pool of allocated frequencies. In another word SDV allows operators to switch, rather than broadcast, some channels to individual service groups. A service group is typically made up of 250 or more set-top-boxes off a given node. Channels selected for a "switched tier" are delivered via a multicast stream only when a customer in a service group selects them for viewing.

The advantage of using SDV is that cable companies have more bandwidth available to convert into Internet channels during periods of high customer demand. The cable companies can also determine which channels are in more demand and develop localized advertising mechanism for those customers.

How SDV works

Every time you change the channel in an SDV system, your set-top box engages in a complex digital conversation with the SDV network.

The following diagram depicts how SDV systems works:

1. When the customer changes the channel the Set-Top-Box sends a signal to SDV server requesting a program to view
2. SDV server sends a signal to ERM
3 & 4. ERM communicates with Edge QAM device to identify the requested channel’s frequency and pull it from SDV system’s transport section
5. ERM send tuning parameters for the requested channel’s frequency to SDV server
6. SDV server sends the tuning parameters to customer’s set-top-box, which tunes to available frequency.

SDV Software

Much of the brains of any SDV deployment are contained in the software that manages the session management (processing individual session and channel change requests from set-top boxes) and edge resources (the dynamic setting up and tearing down of a session to individual QAMs). The Quadrature Amplitude Modulation (QAM) device, encrypts the content and forwards it to the Set-Top-Box to unscramble and playback. QAM technique allows cable companies to send multiple digital signals across the same line.

In an SDV system, metadata that describes all broadcast programming is amended to indicate which programs are SDV programs. When an SDV program is selected, tuning software in the receiver sends an upstream signal. An SDV session manager receives the request and maps the program to a frequency within the allocated pool. This dynamic tuning information is returned to the receiver. If the program is already being viewed within the same subscriber group, then the task is as simple as reusing the session frequency information.

Through some centralized software systems the health of entire SDV system can be managed and reported. It can also monitor and determine the bandwidth of a sevice group or if an edge QAM is failed, it can send an alarm. BigBand recently introduced Video Management System (VMS) in this category.

SDV software products vendors

Here are some vendors that produces SDV software:

The BigBand Networks Inc., Switched Broadcast Session Server (SBSS) serves as the control plane of the SDV system. It performs two major functions: session management and edge resource management. BigBand packages both of those functions together.

The Cisco Systems Inc. Universal Session Resource Manager (USRM) is the second generation of the vendor's SDV server. It's capable of handling the edge and resource management functions together or separately.

The Motorola Inc. Switched Video Manager 1000 (SVM 1000) receive the channel change request, but work in conjunction with the company's ERM 1000, an edge resource manager.