Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg

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Lerne jetzt mit Karteikarten und Zusammenfassungen für den Kurs Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg.

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What are features of web services?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What are web services?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What is the main part of CORBA?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What is CORBA?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What are the two stubs in an RPC?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What are remote procedure calls?

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What is HTTP?

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What is multicasting?

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What is a socket?

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What is the TCP protocol?

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What is the UDP protocol?

Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

What is the bizantine agreement problem?

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Beispielhafte Karteikarten für Distr.syst.dhbw an der Duale Hochschule Baden-Württemberg auf StudySmarter:

Distr.syst.dhbw

What are features of web services?
  • Web service features
  • loosely coupled – each service exists independently of other services that make up application
  • easier integration – providing easier communication between organizations
  • service reuse – combining services to make a new functionality
  • Web services can be „roughtly“ devided into two categries:
  • SOAP based
  • REST style

Distr.syst.dhbw

What are web services?
  • web service is a distributed application whose components are executed on distinct devices
  • web services provide a common communication platform for applications built in various programming languages
  • language transparency is the key to web serviceinteroperability

Distr.syst.dhbw

What is the main part of CORBA?
  • main part of CORBA is Object Request Broker (ORB)
  • object residing in a client make remote requests using an interface to the ORB running on the local machine
  • local ORB sends the request to the remote ORB (which resides on the server) and sends back an object reference to the requester
  • object residing on the client can now make a remote method invocation of the remote object
  • ORB marshals arguments and sends invocation over the network to the remote object’s ORB
  • remote object’s ORB calls the method locally and sends results back to the client.

Distr.syst.dhbw

What is CORBA?
  • Common Object Request Architecture (CORBA) is offered as a solution by Object Management Group (OMG)
  • CORBA is an architecture that specifies interoperability between distributed objects on the network
  • it is an object-oriented middleware paradigm
  • primary feature is interoperability between various programming languages
  • CORBA is based on RPC and extends RPC framework by object-oriented mechanisms

Distr.syst.dhbw

What are the two stubs in an RPC?
  • RPC achieves transparency by offering client stub to the calling client
    • client stub has the same calling sequence as normal procedure on the server side
    • client stub doesn’t execute operation but just sends messages to the server
  • server has a server stub (often referred to as a skeleton) which is a server-side equivalent to the client stub
    • server stub transforms requests comming from the network into local procedure call
    • when local procedure is executed it packs results in a message and calls send to return it to the client

RPC – PARAMETER PASSING

  • client stub has a function to take parmeters, pack it in a message and send it to the server stub
    • packing parameters into a message is called parameter marshaling
  • sever stub has to unpack the message and take sent parameters
    • unpacking parameters from the message is called unmarshaling
  • marshaling and unmarshaling should transform data into neutral formats
    • transforation to neutral formats is necessary because different machines can have differnt byte-ordering rules and other differences
    • Intel processors for instance use little endian (numbering bytes form right to left) and older ARM processors use big-endian

RPC – PARAMETER PASSING ISSUES

  • languages has mostly two types of parameter passing
    • copy-by-value
    • copy-by-reference
  • copy-by-reference (using pointers) is specialy problematic for RPC
    • when we copy-by-reference we basically copy the address in our local address space and when we transfer it to the server it’s there useless
    • one part of a solution is to copy these parameters by value if they would be only read on the server side

Distr.syst.dhbw

What are remote procedure calls?
  • RPC provides a way to call a function on a remote server using the same syntax as if you call it in the local library
  • RPC is, for example, useful in the following situations:
  • due to the size of the program there is a need to spread it accross several machines
  • there is a need to process information which is only available on a remote network
  • when a process on machine A calls procedure(function) on B it stops and wait while it’s executed
  • no message passing should be visible to the programmer
  • remote procedure call should look as a local procedure call

Distr.syst.dhbw

What is HTTP?
  • Probably the most widely used application layer protocol in the world today
  • used to deliver resources across WWW
  • delivered resources are mostly HTML HyperTextMarkupLanguage files, but also audio, video, etc…
  • users enter a URL address in a browser to obtain a resource

Distr.syst.dhbw

What is multicasting?
  • Multicasting is the ability to have one device send a message to more recepients
  • Idea is to use single ip address to send messages to many users
  • Multicasting is used in our example to send messages to a group on a periodic basis
  • example of a time server
  • server will send a date and time every second
  • identical message is sent to all members of the group
  • server only broadcast messages, it receives no messages from clients
  • command Thread.sleep(1000) is used to make a break of 1 second

Distr.syst.dhbw

What is a socket?
  • many distributed systems built on top of the simple message-oriented model offered by the transport layer
  • socket is conceptually a communication end point
  • to which an application can write data to be sent over an underlying network
  • from which incoming data can be read
  • socket is a specialized software used for communication between a client and a server
  • one socket is located on the server side and one on the client side
  • socket makes an abstraction over the actual port that is used by the local operating system for a specific transport protocol

Distr.syst.dhbw

What is the TCP protocol?
  • TCP is a connection-oriented protocol which belongs to the transport layer
  • connection is maintained from the beginning till the end of exchange
  • handshaking – exchange of control messages – sender, receiver state before data exchange
    • to agree to establish connection
    • to agree on connection parameters
  • full duplex data- bi directional data flow in same connection

Distr.syst.dhbw

What is the UDP protocol?
  • UDP is a simple transport protocol which extends host-to-host delivery of packets
    • connectionless protocol which belongs to the transport layer
  • abstract port numbers used to identify which processes communicate
  • port numbers hold for a single host
  • that’s why pair port, host-ip is used for demultiplexing in UDP
  • unreliable, unordered delivery

Distr.syst.dhbw

What is the bizantine agreement problem?
  • Problem first defined and solved (under processor failures) by Lamport et al.
  • arbitrarily chosen processor (source processor) brodcast to other processors its initial value
  • Byzantine agreement should garantee that all nonfaulty processor agree on the same value
  • processors must exchange values through messages to reach a consensus
  • processors receive values and relay values to other processors
  • faulty processors may confuse other processors by sending conflicting values
  • Byzantine agreement problem should meet the following objectives:
  • Agreement – all nonfaulty processors agree on the same value
  • Validity – if the source processor is not faulty, then the common agreed upon value should be initial value of the source

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