مرجع دانلود پاورپوینت های درسی

حجم فایل : 311.3 KB
نوع فایل : پاور پوینت
تعداد اسلاید ها : 27
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<...