Saturday, April 21, 2007

The professional content on-the-Internet video bug

In this post I try to unravel the forces that are working to implement professional video content dissemination with the Internet as the distribution platform. So I am speaking about the iTunes stores that try to peddle TV shows to paying customers, for example.

Why Internet Service Providers love it?

  • Its the best killer application for "broad" broadband services. And marketing-wise it is "scalable" - customers get the video quality that is directly proportional to how good their Internet connection is, providing the perfect temptation to upgrade and pay for the newer broadband being rolled out. Oh and its perfectly legal with no liabilities like P2P class of applications - after all the content providers have already got the IPRs of the content worked out with the MPAA!
  • The same video content can be transcoded into different qualities (bit-rates) according to the end users' Internet connection and devices. Gosh they sell $2 TV shows on iTunes for a tiny iPod screen and get away with it!
Why web companies love it?

Video content++ = users++ = ad-revenue++

Why Content providers love it?

Content is like Prada bags. Expensive to create and cheap to reproduce. Every conceivable way of getting more copies of it out to a paying customer is quick easy money. More so when the distribution channel is easy to deal with and cheap. Yep: costs about $1 to stream (unicast) a movie over the Internet using a CDN infrastructure. Compare that with the hefty tab of producing and distributing a DVD to a video store. Renting on the Internet is way more profitable.

Do end customers love it?

Well, so everyone is trying to convince customers to love it but there are some significant shortfalls before it is universally "the" way to rent movies.
  • Media bridge Most customers don't have the media bridge to connect their Internet content to their AV equipment (TV, home theater). And when they do connect it, the quality doesn't always work out as compared to the old fashioned DVD (and definitely not the HDTV quality blue-ray DVDs).
  • Time-to-download Latency is still an issue for some situations. And most people dont have broad-broadband in their homes yet. The ballpark number of hours to download a DVD is
10/ (Broadband download speed in Mbits)
  • Offcourse media codecs provide "play as you download" formats, but customers will get annoyed if the download rate doesnt keep pace with the bitrate of the video: i.e. their decoder freezes in the middle of the movie and the screen says "buffering".
  • Video-store fun factor Theres always the fun factor of reading the back of a DVD cover. If I know which movie I exactly want to see, then I may just rent it online. But what if I really want to "see a movie". I haven't seen a replacement of the video store browser yet. And they still can't sell popcorn and skittles over the Internet as I wait for my turn at the register!
  • Its not TV so theres no quick channel zapping Internet TV is poor at for one key factor: channel zapping. Even good IPTV solutions are noticeably slow when it comes to channel zapping. Perhaps unfortunately, most Internet TV solutions were marketed as "TV" solutions. So maybe there is a lack of expectation management in this area.

Tuesday, April 17, 2007

Challenges in realizing mobile P2P networks

This is a short paper I wrote sometime ago about the challenges in realizing scalable mobile p2p networks.

Mobile p2p: A list of challenges and todos

Mobile peer-to-peer networks that share content among mobile devices using multiple network interfaces have been proposed recently. We highlight the important research issues in this area in order to foster further discussion in the important multidisciplinary problems surrounding mobile peer-to-peer networks.

1 Introduction and Motivation

Newer mobile devices such as cell phones and PDAs are capable of connecting to heterogeneous networks over multiple interfaces such as WLAN, WiMAX, cellular 3G networks (UMTS, GPRS, etc.), USB (to PCs), and Blue tooth. Simultaneously, generous amounts of persistent storage such as flash memory and mini-hard drives make these devices candidates for in-network storage and dissemination of multimedia content in a mobile p2p network. Such p2p collaboration can result in significant cost savings: for example, by limiting the amount of data downloaded over expensive cellular data links and instead downloading data over WLAN or Blue tooth from a nearby mobile device, there can be significant cost savings for mobile device users.

There are a number of technical challenges in mobile p2p system design. These can be broadly categorized into content discovery, resource allocation (shared wireless channel contention, bandwidth, battery power), security (content integrity, user anonymity), high churn (due to mobility and unreliable wireless channels), and building incentives for users to participate in mobile p2p networks. The objective of this paper is to enumerate these challenges in order to spur further research in these areas. This list of challenges will also serve as a checklist for mobile p2p system design.

Before we digress into the specific research problems in mobile p2p networks, it is insightful to visualize the concept of a mobile p2p network. Figure 1 shows various mobile devices in a region covered by a cellular data network. These devices are also equipped with WLAN and/or Blue tooth (near-network) interfaces over which ad-hoc networks are formed in proximity situations, such as when many users carrying mobile devices are riding a public bus. These devices hold content that may be interesting to other riders on the bus, for example, a user may have downloaded a newscast into his device earlier that day.

Near-networks are highly dynamic and change rapidly as users carrying the mobile devices move and toggle their device interfaces on or off. The persistence of the various interface connections on mobile devices also varies, with near-network interfaces being more prone to channel interruptions than cellular data connections. Similarly, the costs and throughputs of the various network interfaces vary significantly.

2 Challenges in mobile p2p

There are several important open issues in mobile p2p systems that we enlist below.

1. Content discovery Near-networks change quickly and unpredictably due to mobility and network interfaces on devices being turned on and off. A distributed hash table content discovery algorithm may not function in this environment, especially since the content available in a mobile p2p network will itself change quickly with device mobility. A reactive (on-demand) flooding content discovery approach may be feasible for a small p2p network. Another approach may be to use a centralized directory server accessed through the Internet where mobile devices register their content at the time of joining and leaving the p2p network (assuming Internet connectivity).

2. Session Mobility Session mobility is one of the primary issues of mobile device networks. Mobile devices should seamlessly and transparently handover p2p sessions between interfaces. For example, when a user moves out of a WLAN access point range, the p2p application should switch over to the cellular data network interface, locate the content on this new network, and recommence the p2p session. The handover should be content based, not device based, in the sense that the system should strive to reconnect to the relevant content, and not necessarily the same peer as before.

3. Power efficient protocol design Conserving power is of prime importance, given that mobile devices usually run on batteries. Power efficient design has to be a part of the mobile p2p protocol itself. For example, a centralized content discovery lookup will avoid flooding the p2p network with content discovery query packets, thus conserving power on the mobile devices comprising the network.

4. Delay tolerant protocol Content dissemination in mobile p2p networks will be highly asynchronous due to the transient nature of the underlying physical network. Moreover, a p2p session may span long periods of disconnected operation. The p2p protocol should adapt to long periods of network disconnects.

5. Human mobility Modelling the spread of information in mobile p2p networks is closely related to human mobility. For example, a content file is ‘transferred’ from the near-network of a bus to a cafe’s when a user moves from the bus to the cafe. Designing around human mobility models is crucial for the proper functioning of mobile p2p protocols.

6. Broadcast property of wireless networks Transports such as WLAN offer the possibility of a one-to-many broadcast in the p2p network. This is useful when one device shares popular content with it’s (nearby) peers. The challenge here is exploiting the broadcast property without incurring excessive power drain on only one broadcasting peer. Moreover, long periods of broadcast create channel contention with other competing sessions on the same transport channel.

7. Costs and incentives In addition to bandwidth, battery consumption, and storage space is also a cost to users. Modeling these in incentive mechanisms will significantly influence user participation in mobile p2p networks.

8. Content integrity Mobile p2p networks are arguably more prone to content integrity problems than their wired counterparts because a malicious peer may join a mobile p2p network, pollute p2p content, and leave undetected, owing to the inherent mobility in these systems. Moreover, in a purely near-network p2p setting, downloading checksums of data from a centralized location (as is done, for example, in Bittorrent) is not possible.

9. User privacy Traditional wireline p2p networks provide a degree of privacy by only revealing the IP address of the other peers in the p2p network (only traceable up to the ISP). A near-network mobile p2p network may reveal the identity of a user, especially in a small area. For example, people in a bus downloading content off another mobile device know that the content is coming from a mobile device belonging to someone amongst them.

10. IP rights management Suitable DRM mechanisms for (Internet) disconnected near-networks will need to be developed for any mobile p2p network that serves legal content. Mobile p2p networks may exist independent of Internet connectivity, and this makes download-time centralized licensing impossible. One possible solution to this problem is prepaid licence ‘credit’ that users purchase in anticipation of future licensing requirements when disconnected from the Internet.

3 Concluding remarks

Mobile p2p networks have a different set of design constraints than their wired counterparts. More importantly, users will probably use mobile p2p networks for applications other than just traditional p2p file sharing. Therefore the design of these systems needs to be carefully thought of, rather than just trying to port legacy p2p applications to mobile devices. The challenges listed in this paper need to be addressed suitably while designing these new p2p networks of the future.

All rights reserved. Any reproduction or copying only with consent of author.

This is a test post

And we are up!