Adaptive Web Cache

AI³ developed a network of web cache servers, called AI³ Cache Bone, from the early phase of AI³ to 2000. AI³ Cache Bone is a hierarchical network of web cache servers designed based on the star-shaped topology of AI³ satellite network. AI³ Cache Bone consisted of a hub cache, which is located at NAIST, and rim caches placed at the AI³ partner sites.

Rim caches in AI³ Cache Bone used an intelligent prefetch mechanism, where the rim caches analyzed users' access patterns to generate a list of the frequently accessed URLs that should be prefetech. The prefetching strategy of a rim cache is based on the statistical pattern analysis of users' access patterns. Traffic monitoring was used to control both prefetching and pushing object operations. In order to reduce satellite bandwidth consumptions, AI³ Cache Bone introduced multicast transmission to distribute the prefetch WWW objects from the hub cache to rim caches. This mechanism proved to give more than 50% web cache hit rate at the rim cache at AIT.

IPv6

Internet Protocol version 6 (IPv6) is the new standard protocol for the Internet, which improves the functionalities of the previous persion, IPv4. IPv6 was started to be develop in the mid 1990s. AI³ started to deploy IPv6 in its network in 1999 under the name of AI³ 6Bone using the prefix assigned by WIDE 6Bone. Since then, IPv6 network has been expanding to include all AI³ partners. AI³ received a /32 IPv6 address space from APNIC in April 2003 and immediately assigned address spaces to partners' networks. At this point, IPv6 became fully operational in AI³ and it is no longer called AI³ 6Bone. AI³ Project also assigned IPv6 address space to SOI Asia partners, that are connected using an unidirectional link, and now IPv6 is the main protocol for SOI Asia operations. AI³ network is now peering with APAN Tokyo NOC, WIDE Fujisawa NOC, and NSP-IXP6, besides the peerings with AI³ partners.

IP Multicast

IP Multicast is a many-to-many communication model on the Internet. Satellite links are considered to be good for IP multicast due to its broadcast nature. AI³ multicast test-bed network, called AI³ Mbone, was started in 1997. AI³ Mbone was first operated using Distance Vector Multicast Routing Protocol (DVMRP) and tunnels between partner sites to NAIST. AI³ conducted several multimedia transmission experiments on AI³, such as the Hong Kong Handover Ceremony on July 1, 1997, and UNFCC Conferences in 1997 and 1998. This multicast network became fully operational when the unidirectional link started to operate in 2001 with the SOI Asia classes and file distributions as the main application. IP Multicast on AI³ unidirectional link enables SOI Asia to conduct real-time classes with receivers located across Asia.

AI³ stopped using DVMRP and started to use Protocol Independent Multicast - Sparse Mode (PIM-SM) as the multicast routing protocol in October 2003. AI³ switched to IPv6 Multicast in October 2005, and SOI Asia successfully conducted its first class using IPv6 in the same month. AI³ IPv6 multicast network is peering with RENATER and WIDE networks, and we plan to extend the connectivity to other research and education networks.

Unidirectional Link Routing

AI³ designed a unidirectional link on its network to become a test-bed for the Unidirectional Link Routing (UDLR) technology in 1999. One of the goals was to do a research in integrating point-to-point and point-to-multipoint satellite links as a satellite based network infrastructure. This integration technique is useful to control satellite link bandwidth in response to temporal increases of one-way traffic. Another goal was to develop applications for receive-only site using on-demand data feed mechanism on unidirectional links.

The operation of the AI³ unidirectional link was started in 2001 and since then it has become the network infrastructure of SOI Asia Project and various experiments, such as multicast, and policy routing. AI³ is running a 13Mbps unidirectional link, doubling the capacity compared to the bandwidth of the original test-bed, which was 6Mbps.

QoS Control

AI³ are running a Quality of Service (QoS) control in AI³ network to prioritize SOI Asia related traffic. Two main technologies used for the QoS control are Policy Routing and ALTQ. Policy Routing load-balances unicast traffic between bidirectional links and the unidirectional link and control the maximum amount of traffic to be routed via the unidirectional link. Meanwhile ALTQ is used to control bandwidth sharing between SOI Asia traffic, transit traffic and others. Policy Routing and ALTQ are implemented with their configuration parameters tuned for lecture and non-lecture periods.

Policy Routing

Policy Routing is an application developed by AI³ to load-balance traffic among its alternative links to maximize links’ bandwidth utilization. Policy routing is implemented at a network’s core router and monitors the bandwidth usage of links. If traffic exceeds a predefined threshold, e.g., 70% of link bandwidth, Policy Routing forwards some traffic flows to an alternative link, hence load-balances traffics. Policy Routing can define maximum bandwidth to be forwarded to an alternative link to prevent link overload. Policy Routing uses a stateful forwarding, i.e. packets belonging to a flow are forwarded to same link.

Using Policy Routing technology in AI³ network, transit traffic can be forwarded to the satellite UDL to utilize the available bandwidth. Policy Routing reduces the maximum allowable bandwidth for transit traffic when SOI Asia is conducting real-time classes or distributing archived lectures.

ALTQ

Alternate Queuing (ALTQ) is a technology to manage network traffic for resource sharing. It defines traffic classes, assigns traffic priorities, controls traffics with queuing mechanisms. We use ALTQ with Hierarchical Fair Service Curve (HFSC) as the resource sharing algorithm. AI³ implements ALTQ at the feed router of the unidirectional link and classifies traffic into: 1. transit traffic load-balanced by the Policy Routing; 2. traffic for Receive Only sites, which are the SOI Asia partner sites; 3. SOI Asia class traffic; and 4. control traffic, such as routing protocol traffic. AI³ uses different configurations between SOI Asia classes and non-classes periods, where we allocate more bandwidth during SOI Asia classes to ensure the classes run smoothly.

SOI Asia Application Technologies

The learning activities in SOI Asia can be divided into real-time learning and on-demand learning, the technologies used in both learning activities are described in next sections.

Real-time Lecture Application

In SOI Asia real-time class, it is composed of one lecture site and a number of student sites. To create a virtual classroom environment, lecturer and students must be able to communicate through the means of video/audio, bulletin board system, text chat, or even telephone/fax depending on the available communication means at each site. The communication from lecturer to students in SOI Asia environment could be achieved by video/audio conferencing/streaming system because the satellite UDL has enough bandwidth to accommodate lecture traffic. On the other hand, the communications from student sites to lecture site, e.g., questions, are varies depending on their local Internet connectivity as shown in in the table below. Applications used for each model are selected based on bandwidth requirement.

VIC/RAT
VIC (VIdeo Conferencing tool) is an application for video conferencing and RAT (Robust Audio Tool) is an application for audio conferencing. The VIC/RAT combination enables many-to-many communication model with IPv6 Multicast support. In SOI Asia, VIC/RAT is used as a main application to deliver lecture and to get feedbacks or Q/A from student sites using video/audio system. Student sites can also see and interact with each other with VIC/RAT. The bandwidth used to send lecture video is 1 Mbps and lecture audio is 256kbps. The bandwidth used to send student sites’ video and audio are adjusted based on the available bandwidth at each site.

WMT
Windows Media Technology (WMT) is a video/audio streaming application. In SOI Asia, WMT is used to stream lecture to students over the satellite UDL with 512kbps IPv6 Multicast. Since WMT does not support many-to-many communication, students cannot use it to send video/audio back to lecturer. WMT has clear video/audio but with longer delay comparing to VIC/RAT due to encoding. Therefore, WMT cannot be used in Full interactive model but it can be used in Semi interactive and unidirectional models.

VIC/RAT and WMT are the two main video/audio applications widely used in SOI Asia student sites, they are used in IPv6 Multicast communication mode to save bandwidth usage on the satellite UDL link and more extensible IPv6 addresses for more scalable student sites. However, the lecturer site which could be anywhere on the Internet may not always support them because lecturer site does not have IPv6 Multicast connectivity to the Satellite UDL or the applications are not commonly used in lecturer's institution. Therefore the gateway site provides alternative applications to accept video/audio from the lecturer site and then relay to VIC/RAT, WMT so that student sites can receive it. Currently DVTS and H.323 are supported for lecture-gateway sites connection.

DVTS
DVTS (Digital Video Transport System) is an application to deliver very high quality uncompressed video/audio, giving very clear picture and sound. DVTS consumes 30 Mbps per one-way transmission, therefore the underlying network must have a broad bandwidth. At gateway site of SOI Asia, it can send/receive DVTS stream with a lecture site and relay to VIC/RAT, WMT through analog conversion.

H.323
SOI Asia's gateway site is also equipped to support H.323 Video conferencing which are commonly supported in many video conferencing applications and products.

BBS
BBS (Bulletin Board System) is a web-based system for communication sharing point. SOI Asia uses BBS for text-based Q/A and discussion between lecturer and students during and after lecture.

IRC
IRC (Internet Relay Chat) is an online application where all participating parties can join to a single communication channel to interactively exchange messages. SOI Asia uses IRC for quick communication between students and lecturer for Q/A and discussion.

In addition to applications to support communication between lecturer and students, presentation slides are another instruction mean that lecturers use to explain the lecture content. In a distance learning environment with many student sites, it is not inefficient that each student site manually change the presentation slide to keep up with lecture, therefore, an application called RPT was developed to automatically synchronize the slide movement between lecture and student sites.

RPT
RPT (Remote Point) is an application developed by SOI to automatically synchronize the PowerPoint's slide movement at student sites according to the changes at lecturer site. RPT uses the IRC channel to exchange messages of slide movement.

During each realtime lecture, video/audio from lecturer will be recorded and slide will be kept to produce an on-demand lecture as will be explained in next section.

On-demand Lecture Application

In addition to participating in the real-time lecture, it is more beneficial if students can also review the lecture content later for more understanding or in case of absent. In SOI Asia, lectures are also provided in on-demand format. An on-demand lecture is shown in the figure below, it is comprises of HTML page collecting lecture slides and also a video, which contains lecturer video synchronized with slides.

On-demand Lecture Production

To produce an on-demand lecture video, SMIL technology is used to synchronize lecturer's video with lecture slides according to the timing provided.

SMIL
SMIL (Synchronized Multimedia Integration Language) is an HTML-like script language for authoring interactive audiovisual presentations which integrate streaming video/audio with other media, e.g., images, text. In SOI Asia, during the lecture period, lecture video and slide changing timing are recorded, then SMIL script is generated for video/slide synchronization using the applications shown in the table below.

Real Producer
Real producer is a video encoding application producing video in RealVideo format. Real supports the SMIL integration for synchronizing video/audio streaming with other media.

RPT
RPT (Remote Point) is an application used to synchronize slides between lecture and student sites. It also has a function to record the timing that lecturer changed slides for later use in SMIL script production.

TRecorder
TRecorder (Timing Recorder) is an application developed by SOI for slide time recording besides the RPTapplication. TRecorder can generate the SMIL script that is used to synchronize video/audio with slide images according to the given timing.

On-demand Lecture Mirror System

Once an on-demand lecture is generated, easy access is considered an important factor to encourage students to use the on-demand content. The on-demand content should be placed near to students to avoid loss or delay problems caused by underlying network condition. For this purpose, SOI Asia established a mirror system that each partner has a mirror server, as shown in the figure above, containing copies of on-demand content that fall in their interests. Therefore, students can easily access the content from local server.

Since on-demand content is big file-size video/audio and there are many student sites to receive the content, the file distribution from master server to mirror servers must support IPv6 Multicast to save bandwidth used on the satellite UDL. SOI Asia uses an application called MTM which supports the IPv6 Multicast file distribution.

MTM
MTM (Multicast Tree Mirroring) is an application developed by SOI Asia to support the bandwidth-optimized file distribution using IPv6 Multicast. Since IPv6 multicast does not support reliable data transmission, MTM implemented a reliable multicast protocol to ensure completeness of file transmission.