پاورپوینت شبکه های Overlay و کاربردهای آنها (pptx) 27 اسلاید
دسته بندی : پاورپوینت
نوع فایل : PowerPoint (.pptx) ( قابل ویرایش و آماده پرینت )
تعداد اسلاید: 27 اسلاید
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بنام خدا
شبکه های Overlay و کاربردهای آنها
شبكه هاي Overlay
شبكه هاي Overlay چيست؟
به هر شبكه اي بر روي يك شبكه ديگر ايجاد مي شود Overlay گفته مي شود. ولي امروزه شبكه هاي Overlay به شبكه هايي اطلاق مي شود كه در لايه كاربرد و برروي شبكه IP تشكيل مي شوند. شبكه هاي اشتراك فايل از قبيل Gnutella, KaZaA و غيره نمونه هايي از شبكه هاي Overlay هستند.
كاربردهاي شبكه هاي Overlay :
سيستم هاي اشتراك فايل (Peer-to-Peer File Sharing)
چند پخشی در اينترنت (Multicasting in the Internet)
کنفرانس ويدئوِيی
بازی ها ی گروهی در شبکه
....
سيستم هاي اشتراك فايل Peer-to-Peer
Example
Alice runs P2P client application on her notebook computer
Intermittently connects to Internet; gets new IP address for each connection
Asks for “Hey Jude”
Application displays other peers that have copy of Hey Jude.
Alice chooses one of the peers, Bob.
File is copied from Bob’s PC to Alice’s notebook: HTTP
While Alice downloads, other users uploading from Alice.
Alice’s peer is both a Web client and a transient Web server.
All peers are servers = highly scalable!
P2P: centralized directory
original “Napster” design
1) when peer connects, it informs central server:
IP address
content
2) Alice queries for “Hey Jude”
3) Alice requests file from Bob
P2P: problems with centralized directory
Single point of failure
Performance bottleneck
Copyright infringement
file transfer is decentralized, but locating content is highly decentralized
Query flooding: Gnutella
fully distributed
no central server
public domain protocol
many Gnutella clients implementing protocol
overlay network: graph
edge between peer X and Y if there’s a TCP connection
all active peers and edges is overlay net
Edge is not a physical link
Given peer will typically be connected with < 10 overlay neighbors
Gnutella: protocol
File transfer:
HTTP
Query message sent over existing TCP connections
peers forward Query message
QueryHit sent over reverse path
Scalability:
limited scope flooding
Gnutella: Peer joining
Joining peer X must find some other peer in Gnutella network: use list of candidate peers
X sequentially attempts to make TCP with peers on list until connection setup with Y
X sends Ping message to Y; Y forwards Ping message.
All peers receiving Ping message respond with Pong message
X receives many Pong messages. It can then setup additional TCP connections
Peer leaving: see homework problem!