Section Four: State of the Art, First Quarter 1999
Scalability

Scalability is the ability to provide expanded service, as use increases and needs change, beyond the requirements of the initial installation, without replacement of major system components. Scalability, in this white paper, includes

• support for more simultaneous streams;
• support for more video files;
• file service to additional locations;
• more bandwidth, even if file and stream quantities do not change. An example would be the decision to move from MPEG1 to MPEG2 for the file format.

Server Architecture
What are the elements of a scalable system? The most critical is support for an efficient distributed server architecture (or, alternatively, a centrally-located server farm), where files can be stored on many different servers and selected for streaming according to availability, user authorization or location. File distribution across servers requires centralized file management for efficient use of bandwidth. Centralized file management should provide load balancing among servers, at a minimum. The best file management systems will push assets to servers closest to the heaviest end node use and will select among duplicate assets according to availability, bandwidth requirements and network path. All servers should support remote management via the Web.

A distributed server architecture should also insure high availability, providing hot failover to a duplicate asset on another server, without interrupting the stream, so that server failure is imperceptible to the user. Windows NT and UNIX both support server clustering. It is critical to verify, however, that clustering and hot failover occur at the application (e.g. video on demand and video multicast) level and not just at the native file system level, to insure transparent service to your users.

The distributed server architecture with centralized file management provides a way to grow your system without significant management overhead. There is considerable up-front expense involved in a distributed server system. The initial server purchased should be scalable to support at least two years of need without upgrade. A scalable server should support high bandwidth streaming -- for a single stream and for the aggregate bandwidth of multiple streams. The initial server should support 100-300 MPEG-1 streams (at 1.5 Mbps). High speed LAN protocols and high-density storage devices should be supported, as well as failover clustering for high availability.

All ten systems that are discussed in this paper support multiple high-density and high-speed storage options, as well as high-speed network protocols. Most vendors offer centralized file management options for video network expansion. IBM's RS/6000 server family with AIX uses data pump architecture where data pumps are added on additional servers but all servers and data pumps operate under the management of a single control server with a single system image. The RS6000 SP system allows a single node to serve as the control server while additional nodes provide stream delivery. The IBM RS6000 model F50 can deliver 200 streams at 1.5 Mbps, which scales to 1,000 through the addition of more servers. IBM's Digital Library product separates object management from storage and streaming management. IBM also offers the Network Storage Manager for managing high-capacity storage and disaster recovery.

SGI's WebFORCE MediaBase servers can be configured with IRIS FailSafe software, to automatically failover in case of server failure in a clustered environment. Failover can be "active/standby" where one server remains in standby until needed or "dual active" where each server works until required for failover. The Origin server platform is field upgradeable with a "pay as you grow" model for adding node cards. Each node card contains two processors and can handle 150-200 1.5 Mbps streams. Origin servers range from the Origin 200 (scalable to 300 streams) to the Origin 2000, which can support 64 node cards (9600-12,800 streams). CISCO's Local Director product can be purchased to manage front-end traffic and load balancing on a server cluster with distributed assets.

Starlight's StarWorks VOD server supports 100 streams at 1.5 Mbps with a Pentium II-based server with dual PCI buses. Servers may be clustered together to aggregate to 1000 streams or more, with centralized file management provided by the StarCenter product. In development is the ability to share files between clusters, each independently managed by a StarCenter server, which has potential for campuswide and consortial implementations. StarCenter can be provided as a failover service through a commercially available checkpointing and mirroring product. StarCenter supports media servers from Starlight, Microsoft and Real Networks. StarCenter distributes requests for assets according to client capability, authorization and resource availability, providing the highest-quality version of an asset for which bandwidth is available.

Panasonic's Video Network Server, running on a Sun Solaris platform, supports a maximum file size of 1 TB of data and a maximum file system size of 1 TB. Four multimedia file systems, which can each be optimized to a specific codec, can be supported within the VNS software. Content can be remotely managed. Content replicated at varying bandwidths is made available at the highest bandwidth supported by the client, based on the connection type registered by the client at log-in. Sun offers several cluster topologies for providing failover capability and for adding video streams.

CyberStorage does not currently provide clustering for video on demand with all the features of the CBV software. Remote sharing and file maintenance is supported. CyberStorage supports up to 300 users on a single server. The CBV server can be multi-homed with multiple physical network interfaces and is designed to provide load balancing across its configured network interfaces The vendor states that 100s to 1000s of users can be supported through shared computing and storage. CyberStorage offers integrated high-speed storage solutions with its Ultra Fast storage system providing a sustained transfer rate of more than 115 MB/sec.

Concurrent Computer Corporation sells a turnkey solution incorporating its MediaHawk Video Server. Concurrent provides servers that support from 10s to 1000s of MPEG1 and/or MPEG2 streams, up to 12 Mbps. MediaHawk servers are field-upgradeable with hot-swappable disks and can be configured for no single point of failure. File management is provided by the MediaHawk System Administration Software, which holds and manages video files, provides server configuration, system performance monitoring and diagnostic features.

Advanced Modular Solutions/Digital Bitcasting Corporation's Modular Video Server supports sharing of media storage devices by all servers. Multi-terabyte storage is supported. Servers are rackmounted, modular components that can be configured for scalability and redundancy.

The ixJet Streaming Server from 3CX delivers up to 100 MPEG1 video on demand streams per server. 3CX's multiple server solution (in development in November, 1998 for RFI response) can scale to more than 800 streams using eight PCs connected to an FC-AL storage network with a throughput rate of 100 Mbps. A server manager program provides for the creation, export, download and deletion of video assets. In version 2.0, remote management via the Web will be provided.

Bandwidth Supported
Standard information was not received from all vendors indicating bandwidth ranges supported for each file format. MPEG-1 bandwidth ranges should include 1.5 - 3 Mbps, while MPEG-2 should support, at a minimum, 2 Mbps through at least 10 Mbps (broadcast quality but less than HDTV quality). Depending on your application needs, you may want to require MPEG-2 per-stream bandwidths in the HDTV range (12-20 Mbps). Vendors should use 1.5 Mbps to indicate number of simultaneous MPEG-1 streams supported, for aggregate bandwidth. Advanced Modular Solutions/Digital Bitcasting Corporation states they will support on-demand or live MPEG streams at bandwidths ranging from 100 KBPS to 15 Mbps. However, for live and simulated live streams only, RealServer G2 currently imposes a ceiling of 900 Kbps. Digital Bitcasting states that this "maximum bit rate will be increased in the coming months." This ceiling does not apply to video on demand streams.

IP Multicast Streams
Bandwidth ranges for IP multicast will vary from the bandwidth ranges supported for video on demand streams, so each range should be verified. Also verify the maximum number of clients per multicast stream, whether unlimited or a specified number, such as 900.