Switched Digital Video (SDV) - The Benefits

Telco and cable operators are recognizing numerous benefits of SDV and getting more attractive to deploying it. Prior to SDV, the digital video broadcasting started with satellite DTH (Direct To Home) which gave to the cable industry the ability to provide a mixed of analog and MPEG-2 digital services as follows:

• 70 to 90 analog 6 MHz channels


• 8 to 10 MPEG-2 simulcast standard definition (SD) 6 MHz QAM channels


• 8 to 10 high definition (HD) 6 MHz QAM channels


• 4 to 6 video-on-demand (VOD) 6 MHz QAM channels


• 1 to 2 high-speed data (HSD) and voice-over-IP (VoIP) channels

With DTH the badwidth is wasted and, with the exception of the premium channels, the MPEG-2 standard definition (SD) programs are predominantly simulcast analog channels. The MPEG-2 High Defination (HD) content consists of between 15 to 30 HD programs and is also, in large part, duplicating the SD content. Worse, MPEG-2 HD content is a bandwidth hog, where only two to three programs can be put in one 6 MHz QAM channel, so there is limited space to add more HD content.

SDV optimizes the bandwithd and uses 50 to 75 percent less bandwidth as compared to traditional broadcast model. For broadcast services, all services go to all homes all the time, regardless of whether anyone is watching those services. The SDV provides dynamic switching of digital services hence the cable operators are able to broadcast only the programs that are requested by the subscribers. Niche programs switched at service group level instead of broadcast to all subscribers. Unwatched digital tier programs will no longer waste valuable bandwidth.

They can monitor the channel programming and determine if a requested program is already being watched. If so, the requested program is placed into the group of the realted viewers. If there is no one watching a show, then the operator removes that show from the list of broadcast which creates more bandwidth for other programs.

The SDV can be desinged to be intgelligent to determine which video format the subscriber's reciever is capable of and based on this data broadcasts the best format to subscriber. For example, the oprerator can determine whether to send MPEG2 or MPEG4 based on the subscriber's set-top-box capability.

MPEG4 format is twice as faster as MPEG2 and provides High Defination (HD). Of course the subscribers want to see all program in HD. This will force the cable operators to provide MPEG4 capable set-top-boxes to the subscribers. Mirgrating from MPEG2 to MPEG4 can cost billions of dollars and has to be done in phases. The SDV can provide efficient mechanism to cable operators to migrate from MPEG2 to MPEG4 in phases. Also see SDV Architecture for more info.

The following lists benefits SDV can offer cable operators.

SDV Benefits:

• Bandwidth optimizmation. More HD Services. More Digital Simulcast.


• Provides ability to monitor channel programming effectively.


• Provides ability to transmit the best format to the subscribes.


• Delivers the requested content to subscribers in real-time.


• Provides efficeint mechanism for migrating from MPEG2 to MPEG4.


• Facilitates the creation of new services.


• More International & Special Interest Content


• Boosts total number of channels available.


• Enables market-specfic niche, including high definition programming.


• Increases the level of concurrent video on demand (VOD) sessions being served to various nodes.


• Provides methods for advanced targeted ad-insertion solutions.


• Frees up bandwidth for data delivery. Increased high speed data [internet / VoIP] via DOCSIS 3.0 channel bonding

About me:

bruce atlasi is a professional computer engineer, skilled in telecomm and datacomm technologies and architecture. He has diverse working experience with many telecomm start-ups and fortune 100 companies, including Cisco Systems, IBM, and Siemens. He regularly blogs on About Telecomm site.

Switched Digital Video (SDV) Architecture

Switched Digital Video (SDV)


With sufficient switching capacity placed at the central office, the amount of content that can be delivered to a single household is infinite. The ability to offer such an amount of video programming in a telco network could be exploited as a competitive advantage. 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, in a way different from the previously used methods of plant upgrades or video compression enhancements.

SDV is the first implementation of a broadcast video service in which only requested programs are sent to the group of subscribers (the subscriber group). SDV is the first broadcast video service that requires two-way communication with the subscriber for content selection. SDV is sent to a subscriber’s Set-Top-Box (STB) where it is decoded/uncompressed for playback on a TV.

With traditional digital broadcast a video program is carried to customer, whether it is being watched or not. With SDV, as with IPTV, programming terminates at the headend and hub does not explicitly send the video program unless requested. Instead, a receiver signals upstream to request programming, and a hub-based controller receives the request and enables the stream into the HFC network by means of a pool of allocated frequencies. See SDV Benefits for more.

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.

The following diagram depicts the SDV overall architecture.

Headend (HE)
The HE of SDV architecture is where the video and Internet feed sources enter the system. The HE is also where most of the backoffice systems, including billing systems, asset management systems, authorization systems, and so on, reside. HE includes the following equipment that are directly connected to the cable company:

• MPEG encoders, which convert the raw digital or analog signal into an MPEG format
• A bulk encryptor, which scrambles the signal in such a way that only the appropriate set-top box (STB) can unscramble it.
• Internet servers, which allow customers to access the Internet using cable modems.
• Applications servers, including a Session and Resource Manager (SRM), which determine how much system bandwidth each application can access, and another server that monitors and manages other system component (SDV systems can be very complex and require powerful machines dedicated to keep them properly configured.)
• A Groomer which translates content into a maximum bandwidth, limiting the rate of video bursts.
  

The IP network
Once the headend converts the video feed into MPEG format and encrypts it, it sends the signal on to the transport system of the SDV architecture. This section consists of nodes and routers where cable connections intersect and branch off. Nodes and routers redistribute the signal to other nodes and routers so that the original feed covers the cable company's entire customer base. The transport system's path connects the headend to the hub (access system).

Hub
Hub is where the control of bandwidth-intensive applications, such as on Demand streaming, and HFC-connected components reside. The hub (access system) is where the actual digital switching takes place. The core of the access system is the SDV server. It's the SDV server's job to keep track of customers' channel change requests. The server sends commands to an Edge Resource Manager (ERM) and several Edge QAM devices to meet demands. An edge QAM modulates the multiple program transport stream (MPTS) and places the active channels on the HFC plant.

HFC network
HFC network is the fiber-coax access network for distribution to the subscriber. The HFC network is a shared medium, where groups of homes are connected on a common branch of coax cable. Groups of subscribers share access to the same downstream frequencies, and arbitrate for access to shared upstream frequencies.

Subscriber Site
Subscriber Site is a business or residential location where coax receivers, such as the Set-Top-Box (STB) and cable modems are placed. A set-top box receives and decrypts signals from the access system and a cable modem if the customer subscribes to cable Internet service. Each company uses a different interface between the customer network and the access system. A STB also contains a SDV client that communicates with SDV server.

SDV sequence of operations:

1. A software client in the set-top box sends channel change requests to the SDV server.
2. The SDV server and Session/Resource Manager support the channel switching, by allocating the requested channel to an edge QAM, and telling the set-top client where it can be found, by providing the program's frequency and MPEG program number.
3. The client then tunes the set-top to the channel. In addition, the client periodically sends a "heartbeat" message to indicate that it is still tuned to that service.
4. While the channel is active, the SDV server in conjunction with Session/Resource Manager periodically generates a "fast channel map" of active channels and carousels it out to the clients.
5. When the SDV server determines that no subscribers are tuned to a channel, it communicates with edge QAM and tears the channel down, freeing the bandwidth for use by other channels.

For more detail of SDV sequence of operation, see my article "SDV Sequence of operations".

About me:

bruce atlasi is a professional computer engineer, skilled in telecomm and datacomm technologies and architecture. He has diverse working experience with many telecomm start-ups and fortune 100 companies, including Cisco Systems, IBM, and Siemens. He regularly blogs on About Hi-Tech site.

Switched Digital Video (SDV) - issues and challenges

The SDV is becoming more and more attractive among telco and cable operators for number of benefits it brings to telcos. In this article some of the common and major issues of SDV with possible solutions is described.

Prior to SDV system

When satellite DTH started to offer digital video, the cable industry response was a mixed analog and MPEG-2 digital plant with provisions for:

• 70 to 90 analog 6 MHz channels
• 8 to 10 MPEG-2 simulcast standard definition (SD) 6 MHz QAM channels
• 8 to 10 high definition (HD) 6 MHz QAM channels
• 4 to 6 video-on-demand (VOD) 6 MHz QAM channels
• 1 to 2 high-speed data (HSD) and voice-over-IP (VoIP) channels

SDV Benefits:

• Optimizes bandwidth; SDV uses 50 to 75 percent less bandwidth as compared to traditional broadcast model. Without SDV, with the exception of the premium channels, the MPEG-2 standard definition (SD) programs are predominantly simulcast analog channels. The MPEG-2 High Defination (HD) content consists of between 15 to 30 HD programs and is also, in large part, duplicating the SD content. Worse, MPEG-2 HD content is a bandwidth hog, where only two to three programs can be put in one 6 MHz QAM channel, so there is limited space to add more HD content.
• Provides ability to monitor channel programming effectively
• Provides ability to transmit the best format to the subscribes
• Delivers the requested content to subscribers in real-time
• Provides efficeint mechanism for migrating from MPEG2 to MPEG4
• Facilitates the creation of new services
• Boosts total number of channels available
• Enables market-specfic niche, including high definition programming
• Increases the level of concurrent video on demand (VOD) sessions being served to various nodes
• Provides methods for advanced targeted ad-insertion solutions
• Frees up bandwidth for data delivery

SDV Issues and challenges:

Some of the common issues cable and telco operators face when deploying SDV are as outlined below:

• RF access network
• Long-haul transport issues
• Signaling between many hetrogence components that must operate in unison
• Scalability of SDV implementation is one of the major challenges of telco operators which will require industrial-strength software control systems with a provision for hardware redundancy and hitless upgrades to support millions of subscribers
• Adopting MPEG4 technology is another major challenge for the cable operators, which has twice badwidth effieciency as MPEG2. Replacing millions of existing MPEG2 set-top-boxes with MPEG4 is a multi-billions dollars proposition.

SDV common implementation requirements

Among the most common SDV implementation requirements are the following:

• Converting video streams from multi-program transport streams (MPTSs) to single program transport streams (SPTSs)
• Converting from variable bit rate (VBR) to constant bit rate (CBR)
• Increasing exponentially the number of multicast flows
• Increasing the required network computing resources of routers, switches, edge quadrature amplitude modulation (QAM) modulators and other components
• Reducing the relative throughput of those devices while increasing the chances of queuing overflows or underflows
• Increasing network communication overhead for both the video delivery (data plane) and control plane networks (control and signaling)
• Associating and switching video flows to the home to enable seamless channel changes

Current SDV technology

Current SDV systems consist of the following functional elements:

• A staging processor, which breaks a multiple program transport stream (MPTS) into single program transport streams (SPTS), and "clamps" the video bit rate of the streams (that is, converts any variable bit rate streams into constant bit rate streams). It also assigns Multicast IP/UDP port addresses to each SPTS.
• The SDV server and Session/Resource manager, which processes set-top box channel change requests, sets up and tears down active channels on the QAMs, and generates a list of the current service group (collection of users) active channels for inclusion in the mini-carousel that is continuously sent to the STB.
• A bulk encryptor, which provides payload scrambling to support conditional access.
• A content routing network that transports the multicast streams to the QAMs.
• An edge QAM that modulates the MPTS and places the active channels on the HFC plant.
• An SDV software client in the set-top box.

Also see "SDV Architecture" for more information on current SDV architecture.

Issue with current SDV technology

Because the SDV system is not aware that there are multiple types of set-top boxes, and only HD set-tops can decode HD channels, the cable operator must rely on an often-times confused subscriber to make the right channel choice. That's because the SDV system transmits to the subscriber the same program in two different format, one in HD and another one in SD, available in two different channels. There is no correlation in the numbering scheme to relate the two as the same programming, just different video resolutions. This creates confusion for the viewer. The owner of HD set-top-box must know which channel is showing HD version of the program, otherwise, he might be watching SD digital version of the program which of course has lower quality of HD but paying for more expensive HD set-top-box.

A possible solution for this confusion problem is to add a set-top awareness capability to SDV system. By adding this capability, the SDV selects the format that's desirable for the subscribers set-top-box and displays on one channel. Implementing set-top awareness capability requires a number of new functions as described below:

• A device manager that maintains information on the capabilities of set-tops, edge QAMs, service groups, transcoders, and stream processors, as well as the source of different formats of the content for delivery to each service group.
• A subscriber manager that connects a subscriber to the devices that are used to deliver services to that subscriber. It also maintains a heuristic analysis of subscriber viewing patterns.
• An SDV manager provides centralized management and control of the SDV system. It registers all of the SDV servers/RM, edge QAMs, and service groups, maintains a central database for the events associated with the channel change requests for each subscriber, and tracks set-up and tear-down of active channels in each service group. Additionally, it provides the interface with the global session resource manager (GSRM) for request and allocation of shared QAM resources. Finally, it provides control, configuration management, and reporting functions of the entire SDV system.
• A bank of shared transcoders for dynamically creating different formats for replicated versions of the same program.
• A monitoring/reporting function is critically important for optimizing and troubleshooting the network, and ensures that the operator knows when a service is switched to a service group and that the content was actually transmitted over the HFC.

A hybrid model to managed transition to MPEG-4 set-tops

A hybrid model provides ability to cable operators to gradually swap out the STBs to customers based on their programming preferences and location in the system. With hybrid model, the SDV system automatically makes the most bandwidth efficient format decision for each program being transmitted within each service group based on which subscribers are watching the program and their STB capabilities.

An intelligent management layer

An intelligent management layer can help cable operators to configure the SDV system easier as cable system become more complex through regional clustering. The following outlines the elements of an intelligent management layer:

• A workflow engine manages and tracks the processes needed to implement new services, devices and even software applications. Additionally, it manages and tracks the creation of the different video resolutions and compression formats for all content to support installed STBs.
• An element manager monitors and assists in the configuration management of hardware and software within the network, and provides reports to the operator on impairments, loading and outages.
• A device (and subscriber) manager maintains a database of each device in the network and in use by subscribers, including hardware and software versions, compatibilities and incompatibilities of the same, and the video resolutions and compression formats supported by each device.
• A global session resource manager (GSRM) arbitrates bandwidth usage between services based on loading balancing, value of the services, and subscriber experience.
• A service manager maintains a database for how each subscriber device receives and supports service information.
• A code download manager manages the distribution of code objects, easing the operator involvement in upgrading code to the set-tops and other network devices.
  

About me:

bruce atlasi is a professional computer engineer, skilled in telecomm and datacomm technologies and architecture. He has diverse working experience with many telecomm start-ups and fortune 100 companies, including Cisco Systems, IBM, and Siemens. He regularly blogs on About Telecomm site.

References:
"Raising the bar on SDV", by Chip Paryzek and Michael Adams.
"Gaining Visibility into the Complexities of SDV", by Gino Dion

Switched Digital Video (SDV) - Monitoring and Reporting Mechanism

The Switched Digital Video (SDV) requires a reporting and monitoring systems (let's call it SVRM for simplicity) for the telco operators to make decision about program expansion, network design and to determine where to roll out new programming and advertising to increase advertising.

The SVRM architecture consists of a receiving agent, a database system, a reporting agent, and a User Interface, preferably a Web based UI.

The receiving agent gets it's data from a Switched Video Session Manager server (SVSM) and tracks the subscriber’s set-top-box activity, channel ownership, and performance diagnostics data in real-time. The scalability should be factored in when designing the SVRM to support large number of SDV servers, support large number of subscribers to monitor and support unlimited number of channels. For example, some vendors provide monitoring capacity of a 1,000,000 subscribers per single SVRM server, 100 SDV servers and unlimited number of channels.

The data base system stores all data collected by receiving agent in an organized and secure way with fault tolerant ability. As an example, database can be built on a Oracle database that resides on a secure and fault tolerant RAID array storage systems.

The reporting agent builds customized report from database system providing traffic patterns and viewership statistics data. The report allows cable operators to optimize program lineups and enhance utilization of network infrastructures. Through viewership statistics, the operators can identify the available and niche programming, also called “long tail content”.

The operator can use SVRM to monitor both switched and broadcast programming in real-time to measure channel popularity and identify additional long tail content best suited for SDV. The SVRM monitoring can be extended to a broad range of performance and reliability metrics to optimize network utilization, and for service assurance purposes. It can also be used to identify trends, such as unanticipated viewership changes, that can impact system performance and content delivery before they impact subscribers.

The following diagram depicts a typical SVD Reporting and Monitoring architecture.

The Switched Video Session Manger (SVSM) is the network element that captures the subscriber data activity. It provides session and response management support. The set-top-boxes send channel change requests signals to SVSM over cable network. The SVSM then interacts with local edge QAM device to set up and tear down mappings. See my article: IPTV - software behind SDV for SDV architecture.