XML 期末報告 Overview of JXTA. Adviser: 葉慶隆 教授 Reporter:GI2 16 黃凱聖. JXTA 簡介. 創辦人為昇陽電腦的 Bill Joy 昇陽電腦認為，只有互通才能真正發揮出 P2P 的優勢，就好像即時通訊 IM(Instant Messaging) ，能互連的人越多，越有價值。所以 Sun 決定出面發佈一個平台，使所有 P2P 系統都能連接起來，為了達到互通性 發表了一款概念最簡單的系統 如果成功，這就會是今後大家構架信息系統的基本模塊. JXTA 簡介.
Adviser: 葉慶隆 教授
昇陽電腦認為，只有互通才能真正發揮出P2P的優勢，就好像即時通訊IM(Instant Messaging)，能互連的人越多，越有價值。所以Sun決定出面發佈一個平台，使所有P2P系統都能連接起來，為了達到互通性 發表了一款概念最簡單的系統 如果成功，這就會是今後大家構架信息系統的基本模塊
名稱起源於Juxtapose(並列之意) 漂亮而優美地描繪未來完整的 P2P世界
The JXTA protocols are a set of protocols that have been specifically designed for ad hoc, pervasive, and multi-hop peer-to-peer (P2P) network computing.
What this all means is that JXTA is a framework with a set of standards that support peer-to-peer applications.
JXTA is made up of three distinct layers. The first is the platform.
The platform contains core functionality used by services, which are the second layer.
Services provide access to the JXTA protocols.
Finally, there are applications that use services to access the JXTA network and utilities.
Operating system independence.
Providing services and infrastructure for P2P applications.
XML is the basis for most of the protocol in JXTA.
The key reasons are its ability to be read by many languages and its ability to be validated.
There is a downside to using XML.
XML is simply not a compact way to express data.
Messages written in XML will be much larger than a binary equivalent.
There are techniques that can be used, such as replacing tags with binary tokens or compacting data, but none of these are currently employed in JXTA because there are no widely accepted standards at this time.
Consequently, the core JXTA developers have created a simple binary message transport and have used terse language and acronyms for tag names.
A rendezvous is a peer that processes queries from other peers. The rendezvous can also delegate queries to other peers, which must also be a rendezvous.
A key purpose of rendezvous is to facilitate searching of advertisements beyond a peer's local network.
A router in JXTA is any peer that supports the peer endpoint protocol. Not all peers need to implement the protocol because, like traditional network routers, you only need a few to support a large network. JXTA routers are very similar to a traditional router. The primary difference is that a P2P network is less stable and includes many addresses that are not static.
A gateway is a peer that acts as a communications relay. Don't confuse gateways with rendezvous. A gateway is used to relay messages between peers, not requests.
Gateways are like radio repeaters or a middleman between peers used to relay messages.
Peers may also seem to disappear and reappear. We also have to consider wireless devices that are usually only on-line for very short periods. In these cases, the peer may even seem to pop up in a different city in a completely different network topology!
Because of the possibility of such changes, it is very important to be able to invalidate a route and reroute connections.
JXTA protocols are used to help peers discover each other, interact, and manage P2P applications.
The protocols hide a lot of detail, which makes writing JXTA applications much easier than developing a P2P applications from scratch.