Paper Review: IP Multicast Channels: EXPRESS Support for Large-Scale Single-Source Applications
Reviewer: Kenneth Chin
This paper attempts to introduce a mechanism designed to support for large-scale single-source multicast applications. Explicitly Requested Single-Source (EXPRESS) is the name of the mechanism.
Advantages of EXPRESS:
3 Main ideas:
- access control; through authentication of a key provided by a receiver, a source can accept or reject the receiver.
- number of subscribers; each router periodically sends a query message to obtain the number of active subscribers using a channel.
- generous channel space; each source can have up to 2^24 channels.
- simple and unified protocol - ECMP
- no unwanted materials; unlike grouping model, subscribers do not receive non-requested data from unsubscribe sources.
- billing; EXPRESS provides a metric for an ISP to charge a source.
- new services; new application level features can be provided based on "count". For example, voting.
Unaddressed issues and unrealistic assumptions:
- multicast channel model versus group model.
- single protocol that maintains the distributing tree and supports source-directed counting.
- extends EXPRESS to support for multi-source applications by session relay approach.
This paper is a very good paper in the sense that it provides a more complete solution for multicast applications. The nice thing I learnt from this paper is that a small change (including a count parameter) gives recognizable achievement.
- it is assumed that all routers on the distribution tree are trusted.
- caching of keys in intermediate routers besides the source for fast authentication leads to key inconsistency. What makes things worst is when a channel key is compromised and has to be changed, how a copy of an old key is treated.
- efficient key management and key distribution were not mentioned in the paper.
- incremental employment of EXPRESS to the Internet.