Download Communication

Middleware Protocols
RPC, Message oriented
Communication, etc.
2-5
An adapted reference model for networked communication.
Remote Procedure Call
Conventional Procedure Call i.e. read(fd,buf,bytes)
a) Parameter passing in a local procedure call: the stack before the call to
read
b) The stack while the called procedure is active
Client and Server Stubs
Principle of RPC between a client and server program.
Remote Procedure Call (1)
Steps in making a remote procedure call
– the stubs are shaded gray
Steps of a Remote Procedure Call
(RPC)
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Client procedure calls client stub in normal way
Client stub builds message, calls local OS
Client's OS sends message to remote OS
Remote OS gives message to server stub
Server stub unpacks parameters, calls server
Server does work, returns result to the stub
Server stub packs it in message, calls local OS
Server's OS sends message to client's OS
Client's OS gives message to client stub
Stub unpacks result, returns to client
Remote Procedure Call (2)
Implementation Issues
• Cannot pass pointers
– call by reference becomes copy-restore (but might fail)
• Weakly typed languages
– client stub cannot determine size
• Not always possible to determine parameter types
• Cannot use global variables
RPC protocol definition
• Define message format
• Define data representation
• Define transport service type (i.e. TCP)
Asynchronous RPC (1)
useful when there is no result to return
2-12
a) The interconnection between client and server in a traditional RPC
b) The interaction using asynchronous RPC
Asynchronous RPC (2)
2-13
A client and server interacting through two asynchronous
RPCs (deferred synchronous RPC)
Message oriented communication
RPCs, i.e., enhance access transparency but they are
not always appropriate to distributed system.
Persistence and Synchronicity
Different types of communications
Persistent communication
2-20
General organization of a communication system in which hosts are connected through a network
Example : E-mail system. If the target server is unreachable, the local one continue to store
messages ( in contrast with a transient communication method).
Persistence and Synchronicity in Communication
2-22.1
a)
b)
Persistent asynchronous communication
Persistent synchronous communication
Persistence and Synchronicity in Communication
2-22.2
c)
d)
Transient asynchronous communication (one way RPC)
Receipt-based transient synchronous communication
Persistence and Synchronicity in Communication
e)
f)
Delivery-based transient synchronous communication at
message delivery(asynchronous RPCs)
Response-based transient synchronous communication (RPCs)
The need for persistent communication services is clear
in developing middleware for large-scale distributed
applications.
Only transient or persistent communications, like only
synchronous or asynchronous communications, are not
sufficient!
Message passing communication
Message oriented transient communications
Berkeley Sockets
Primitive
Meaning
Socket
Create a new communication endpoint
Bind
Attach a local address to a socket
Listen
Announce willingness to accept connections
Accept
Block caller until a connection request arrives
Connect
Actively attempt to establish a connection
Send
Send some data over the connection
Receive
Receive some data over the connection
Close
Release the connection
Socket primitives for TCP/IP.
With new high performance multicomputer systems standard
socket primitives are insufficient.
Primitives have to be at a good level of abstraction and suitable for new
high speed interconnection protocols
The Message-Passing Interface (MPI)
Primitive
Meaning
MPI_bsend
Append outgoing message to a local send buffer
MPI_send
Send a message and wait until copied to local or remote buffer
MPI_ssend
Send a message and wait until receipt starts
MPI_sendrecv
Send a message and wait for reply
MPI_isend
Pass reference to outgoing message, and continue
MPI_issend
Pass reference to outgoing message, and wait until receipt starts
MPI_recv
Receive a message; block if there are none
MPI_irecv
Check if there is an incoming message, but do not block
Some of the most intuitive message-passing primitives of MPI.
MPI uses the underlying network and it assumes communication take place within a
known group of processes
MPI supports all the previous transient communication diagrams except for (d)
Message oriented persistent communications
Message-Queuing Model
basic idea: applications communicate by inserting messages in specific queues
2-26
Four combinations for loosely-coupled communications using queues.
Message-Queuing Model
Primitive
Meaning
Put
Append a message to a specified queue
Get
Block until the specified queue is nonempty, and remove the first message
Poll
Check a specified queue for messages, and remove the first. Never block.
Notify
Install a handler to be called when a message is put into the specified
queue.
Basic interface to a queue in a message-queuing system.
General Architecture of a Message-Queuing System (1)
The collection of queues is distributed across multiple machines
queue names db
The relationship between queue-level addressing and network-level
addressing.
General Architecture of a Message-Queuing System (2)
2-29
A message-queuing system with routers (or relays) can solve the problem
of a static large scale system queue-to-location mapping
Message Brokers
it converts incoming messages to a format compatible with the destination application
2-30
The general organization of a message broker in a message-queuing system.
It is generally not considered an integral part of the queuing system.
Data Stream (1)
Sometime timing is crucial for communication…
asynchronous, synchronous and isochronous mode for data stream
Setting up a stream between two processes across a network.
Data Stream (2)
2-35.2
Setting up a stream directly between two devices.
Data Stream (3)
An example of multicasting a stream to several receivers.
Specifying QoS (1)
Time dependent requirements are expressed as QoS
Characteristics of the Input
•maximum data unit size (bytes)
•Token bucket rate (bytes/sec)
•Toke bucket size (bytes)
•Maximum transmission rate
(bytes/sec)
Service Required
•Loss sensitivity (bytes)
•Loss interval (sec)
•Burst loss sensitivity (data units)
•Minimum delay noticed (sec)
•Maximum delay variation (sec)
•Quality of guarantee
A flow specification.
Specifying QoS (2)
The principle of a token bucket algorithm
A token is a fixed number of bytes that an application can pass to the network.
Tokens are buffered in buckets
Setting Up a Stream
Resources required for streaming: bandwidth, buffers, processing capacity
Resource reSerVation Protocol
The basic organization of RSVP for resource reservation in a distributed system.
Receiver-initiated protocol
Synchronization Mechanisms (1)
The principle of explicit synchronization on the level data units. The application is
responsible for synchro.
Synchronization Mechanisms (2)
2-41
The principle of synchronization as supported by high-level interfaces.