Transcript MIDDLEWARE - Zhejiang University

DISTRIBUTED SYSTEMS
AND THE INTERNET
Lan Jin
Tsinghua University
California State University-Fresno
 Distributed System Fundamentals
 Basic Structure of Distributed System
 Computing Models in Distributed System
 Networking and Internetworking
 The Internet
 Technical Issues in Distributed System
DISTRIBUTED SYSTEM
FUNDAMENTALS
General Characteristics of DS
 Multiple computers + communication network
+ message passing + single system image
 Lack of central memory and a global clock
 Distributed hardware - multicomputer & network
 Distributed software and information
 Distributed control not relying on global state, but
on consensus and agreement protocol
Major goal: Transparency with no knowledge of
what, where, and how.
DISTRIBUTED SYSTEM
FUNDAMENTALS
Challenges of Distributed Systems
 Transparency: access, location, mobility, replication,
concurrency, parallelism, scaling, failure, network
 Heterogeneity: network, computer h/w, OS, prog.
languages, vendors
 Openness or Flexibility: microkernel & open services
 Scalability & Reconfigurability
 Reliability & Availability: redundancy, fault tolerance
 Security: firewall, encryption
 Concurrency & Performance
DISTRIBUTED SYSTEM
FUNDAMENTALS
Why Distributed Systems ?
 Economics: A decisive price/performance advantage
over traditional time-sharing systems
 Improved reliability & availability thru replication
 Modular scalability
 Many applications are inherently distributed, with a
great demand for communication, information
sharing, and resource sharing among computers.
 The Internet is the greatest worldwide distr. system.
BASIC STRUCTURE OF
DISTRIBUTED SYSTEM
Middleware in Distributed System
 Network connecting multiple computer platforms
 Middleware as the infrastructure between:
 OS + comm. protocol
 distributed applications
interacting via the network
Distributed applications
Middlewaree
Operating system
Computer & network h/w
platform
BASIC STRUCTURE OF
DISTRIBUTED SYSTEM
Basic Functions of Middleware
 masks the heterogeneity of computer architectures
 hides the underlying networked environment’s
complexity
 facilitates the interaction among distributed
software modules
 QoS management, information security, RPC,
RMI, remote DB access, …
BASIC STRUCTURE OF
DISTRIBUTED SYSTEM
Middleware Environments
 RPC, RMI, ROI middleware
 OMG Corba, DCOM middleware
 Integrating QoS management into middleware
 Middleware supporting mobile computing
 Middleware supporting ubiquitous computing
 Mobile code and mobile agent
 Jini, JavaSpaces, JavaBeans,…middleware
COMPUTING MODELS
 Client-server (Pull) model
— Connectionless Request-Reply protocol
— Synchronous, RPC-style communication model
 Push model
— Publish/subscribe system, workflow system
— Asynchronous communication model
 Peer-to-peer (P2P) interaction model
— Serverless file sharing
— Event-based middleware architecture
COMPUTING MODELS
Variations on the Computing Models
 Servers may in turn be clients of other servers
request
Client
reply
request
Client
request
Server
reply
Server
(Client)
reply
 Partitioned or replicated servers
Server
request
Client
Client
reply
Server
request
reply
Server
COMPUTING MODELS
Variations on the Computing Models (continued)
 Proxy servers and caches
Client
proxy
server
 Mobile code
Client
Web
Server
Client
Web
Server
Applet code
Client
 Mobile agent
 Network computer
 Thin client
Web
Server
Applet
code
(Local site)
Web
Server
NETWORKING &
INTERNETWORKING
Types of Networks

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
Personal Area Network (PAN), WPAN (wireless)
Local Area Network (LAN), WLAN (wireless)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
Internetworks, the Internet
Type
Range Data rate(Mbps) Latency(ms) Examples
LAN 1-2 Km
10-1000
1-10
Ethernet,Token ring
WPAN >10m
1-2
Bluetooth
WLAN 0.15-1.5 Km 2-11
5-20
WaveLAN
MAN
2-50 Km
1-600
1-10
DSL, ATM
WAN worldwide 0.010-600 100-500
ISDN,BISDN,ATM
WWAN worldwide 0.010-2
100-500 the Internet (wireless)
NETWORKING &
INTERNETWORKING
Optical Networks
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WDM/DWDM handle 160-320 wavelengths/fiber.
Optical Ethernet and MAN: 10 - 40 Gbps over 70 Km.
TDM reduces the cost: 2000 Gb/s on a single fiber.
Advanced optical fiber eliminates cross-talk problem.
The last-mile problem: LEC on DSL or wireless links.
Wireless Networks
 2G: ≤ 14.4 Kbps; 3G: 2 Mbps; 4G: > 50 Mbps.
 band system bit-rate users radius spatial capacity
SRW 802.11b 11 Mbps 3 100m
1 Kpbs/m2
SRW Bluetooth 1 Mbps 10 10m
30 Kbps/m2
SRW 802.11a 54 Mbps 12
50m
83 Kbps/m2
UWB
50 Mbps 6
10m 1000 Kbps/m2
THE INTERNET
Internet Protocols — TCP/IP Protocol Suite
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TCP directly supports applications (e.g., HTTP).
TCP — reliable connection-oriented communication
UDP — unreliable connectionless communication
IP datagrams — basic Internet transmission mechanism
IP supports WAN applications, e.g., file transfer, email.
Internet application protocols: HTTP, SMTP, FTP,
telnet, NNTP by TCP; DNS by UDP
Layers
Message
Interne tworking
Application
The Internet
Messages (UDP) or streams (TCP)
Transport
Internetwork
Internetwork packets
Network interface
Network-specific packets
Underlying network
UDP or TCP packets
IP datagrams
Network-specific frames
THE INTERNET
UDP vs. TCP in Client-Server Computing
UDP: unnecessary to establish and release a connection.
TCP: needs to establish a connection - a connect request
is followed by an accept from the server.
UDP transmits datagrams w/o acknowledgement or retries.
TCP retransmits if not acknowledged within a timeout.
UDP: inadequate for using the limited length of datagrams.
TCP: avoids implementing multi-packet protocols.
UDP: difficult to decide on the server buffer size.
TCP: Message size is decided before transmitting it.
UDP: no flow control
TCP: Flow control matches the speeds of writing to and
reading from a stream by a producer/consumer paradigm.
THE INTERNET
History of the Internet
1957 Forming of ARPA
1967 1st paper on the ARPAnet - the 1st WAN
1969 1st 4 hosts on the ARPAnet (UCLA,UCSB,UofUtah,Stanford)
1972 1st email program and Telnet standard
1973 1st international connection to ARPAnet
1973 FTP developed
1981 BITnet, CSnet using ARPAnet tech.
1982 TCP/IP est’d as an Internet standard
1982 The name Internet is assigned
1984 DNS introduced
(To be continued)
THE INTERNET
History of the Internet (continued)
1989 130,000 computers connected to the Internet
1990 First commercially available dial-up Internet access
1991 Gopher created as a nongraphics-based browser
1991 1st code for the World Wide Web
1993 Mosaic, the 1st graphics-based browser
1993 1,776,000 computers, 130 Web servers
1995 Java released by Sun microSystems
1995 6,642,000 comp, 23,500 Web servers
1997 19,540,000 comp, 1,203,096 Web sv.
1999 56,218,000 comp, 6,598,697 Web sv.
THE INTERNET
Wireless Internet
 WAP (Wireless Application Protocol)
Wireless network
WAP
microbrowser
running on
WAP-enabled
devices
WAP
TCP/IP
HDML protocol WAP
/WML
gateway stack
stack
HTML
/XML
Web
server
WAP offers a small, extensible protocol stack to handle
mobile communications more efficiently.
XML — a powerful extensible alternative to HTML
WML — a small set of XML for wireless network
HDML — compact HTML for handheld devices
THE INTERNET
Bringing the Internet to Next Generation
 Limitations of current WAN:
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do not deal with congestion effectively
poor support for QoS
low reliability
no clear definition of the semantics of shared state
 Internet2 Project
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High-speed gigapops at > 155 Mbps
vBNS at 622 Mbps - 2.4 Gbps
IP Multicast protocol and IPv6
Digital audio and video frameworks
QoS
Distributed storage management
 NGI - a US government program along with vBNS
THE INTERNET
Extending Internet Markup Languages
 Limitations of HTML:
◊ Presentations rather than content orientation
◊ No extensibility
◊ No data validation capabilities
 Enter XML
◊ Let information publishers invent their own tags.
◊ addresses only content.
◊ supports validation by using OTS XML parsers.
 XML Benefits
◊
◊
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◊
◊
extensibility
presentation/content
support for multiple views of the same content
support for document and validation of structured data
selective (field-sensitive) queries over the Internet
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Interprocess Communication
 Primitive operations of communication and synchronization
 Message-Passing mechanism: synchronous or blocking
vs. asynchronous or non-blocking
 Network communication mechanism
 Multicast communication between groups of processes
 Client-server communication
◊ Blocking vs. non-blocking primitives
◊ Buffered vs. unbuffered primitives
◊ Reliable vs. unreliable primitives
 Client-server exchange protocols
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Remote Procedure Call (RPC) /
Remote Method Invocation (RMI)
 Programmable models for distributed applications
◊ Remote procedure call (RPC)/Remote method invocation (RMI)
◊ Event notification — event-based prog. model
 Middleware layer — RPC, RMI, and events built on
request-reply protocol and external data representation
 RMI by Java
◊
◊
◊
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Request invocation - Response
Interface compiler generates client stub & server skeleton by IDL.
Stub & skeleton perform marshaling and unmarshaling.
RMI passes full objects as operation parameters & return values.
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Unavailability of Up-to-Date Global State
 Unavailability of global memory and global clock
 Unpredictable message delays
 To implement distributed system-wide control:
◊ Algorithms based on arriving at a consensus
◊ Clock synchronization for temporal ordering of events
 Logical clock: Lamport’s virtual time or vector time
 Message ordering in group communication
 Defining a coherent (consistent) global state
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Distributed Control Algorithms
 Distributed mutual exclusion
 Distributed deadlock detection
 Distributed election algorithms
 Processor (workload) allocation
 Distributed (process, thread) scheduling
 Fault tolerance in DS
 Distributed agreement
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Distributed File System
 Distributed file model
 Naming and name transparency
 File and directory service interface
 Semantics of file sharing
 Caching and cache consistency
 File replication and update
 Network file systems
TECHNICAL ISSUES
IN DISTRIBUTED SYSTEM
Atomic Transactions
 Transaction Model
 ACID Properties of transactions
 Implementation of transactions:
◊ Private workspace
◊ Writeahead log
 Two-phase commit protocol
 Concurrency control
◊ Compatible locks and deadlock prevention
◊ Optimistic concurrency control
◊ Timestamp ordering