Problem Chapter 5.3: Suppose you want to make a procedure call - - PDF document

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Problem Chapter 5.3: Suppose you want to make a procedure call Remote Procedure Calls Caller and called code are on different Internet hosts Situation is remote procedure call CS/ECPE 5516: Comm. Network Prof. Abrams Spring 2000

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CS/ECPE5516 1

Chapter 5.3: Remote Procedure Calls

CS/ECPE 5516: Comm. Network

Prof. Abrams

Spring 2000

CS/ECPE5516 2

Problem

Suppose you want to make a procedure call Caller and called code are on different Internet hosts Situation is “remote procedure call”

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Sample Scenario…

You run Internet banking app on your PC. App makes RPCs to bank’s computer You want to move $100 from your checking to savings account: moveC2S(100 ) via RPC

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Try this in groups…

Is TCP a good protocol? Is UDP a good protocol? How does regular old procedure call get converted to network communication? Design your own protocol. Be sure it…

Is efficient Completes call with high probability

Include in your design…

List of tasks protocol must do Header format

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Did you consider these issues:

How do you find Internet host running the remote procedure? Any way that remote procedure could be called twice (e.g., if network duplicates a packet containing the call)? What if remote procedure host executes procedure but crashes before sending reply? How to make caller wait until receiver is done executing procedure

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Let’s answer the questions…

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?: Is TCP a good RPC protocol?

Not really…

RPC needs request/reply TCP is for streaming RPC needs messages TCP is for streaming RPC needs speed: maybe 2 messages TCP uses 3+2+4 messages

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?: Is UDP a good RPC protocol?

Not really…

UDP doesn’t care if message is lost

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?: How does proc call get converted to network comm?

A stub or proxy does conversion. It uses proc call on one side, network communication on the other. See Fig. 5.11 in Peterson/Davie Use “rcp compiler” to invisibly add proxies Proxy marshalls & unmarshalls procedure arguments.

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?: How do you find host running remote procedure?

Method 1: Caller names host to be called Method 2: Directory service:

“I want a square-root function. What host on the net has one?”

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Example: Sun’s JINI

Allows simplifies network device interconnection with a Lookup/Discovery service Each device provides services to others Devices register when they join community; publishes service

I’m a 600dpi B&W printer; my service is printing

An app can lookup a service to discover a device

More info: http://courses.cs.vt.edu/~wwwtut/Notes/Java/jini.html

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?: Any way that remote procedure could be called twice

Yes: request is duplicated Want semantics to clarify requests:

At-most-once semantics:

At most one copy of request is delivered “At most” because zero might be delivered

Alternate: idempotent procedures:

can be executed multiple times, but give same result example: square-root

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?: What if RPC executes but host crashes before sending reply?

Need transaction semantics at host. Commit protocol on server guarantees no intermediate state visible

Example:

Subtract $100 from checking Crash Oops! You lost $100 – if intermediate state visible

Implemented by list on disk of actions to execute

n reboot

Java Enterprise Beans offers transactions

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Outline of Peterson/Davie Solution (pp. 400-426)

Three sub-protocols:

BLAST: sends message from host A to B CHAN: implements request/reply over BLAST SELECT: dispatches request to correct process

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BLAST – Send Message

Sender: Fragment large message into packets Transmits packets Set timer If no response by timeout, give up If ack arrives, resend listed packets

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BLAST (2)

Receiver Set timer Receive fragments:

place in order in buffer reset timer

When last fragment arrives, send ack If timer pops, send ack Ack lists missing packets After 3 timeouts, give up

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CHAN – Implement request/reply

guarantees message delivery (retransmits) eliminats dups (via sequence number) implements at-most-once semantics allows synchronization between sender/receiver uses reply as implicit ack of request sends I’m alive messages in case procedure takes long time to execute

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SELECT

CHAN runs between one app and one proc SELECT handles set of calls between apps to common remote procedure via serialization SELECT also provides hierarchical names for destinations, vs. ports:

1

Chapter 5.3: Remote Procedure Calls

CS/ECPE 5516: Comm. Network

Spring 2000

Problem

Suppose you want to make a procedure call Caller and called code are on different Internet hosts Situation is “remote procedure call”

Sample Scenario…

You run Internet banking app on your PC. App makes RPCs to bank’s computer You want to move $100 from your checking to savings account: moveC2S(100 ) via RPC

Try this in groups…

Is TCP a good protocol? Is UDP a good protocol? How does regular old procedure call get converted to network communication? Design your own protocol. Be sure it…

Include in your design…

Did you consider these issues:

Let’s answer the questions…

2

?: Is TCP a good RPC protocol?

Not really…

?: Is UDP a good RPC protocol?

Not really…

?: How does proc call get converted to network comm?

A stub or proxy does conversion. It uses proc call on one side, network communication on the other. See Fig. 5.11 in Peterson/Davie Use “rcp compiler” to invisibly add proxies Proxy marshalls & unmarshalls procedure arguments.

?: How do you find host running remote procedure?

Method 1: Caller names host to be called Method 2: Directory service:

“I want a square-root function. What host on the net has one?”

Example: Sun’s JINI

Allows simplifies network device interconnection with a Lookup/Discovery service Each device provides services to others Devices register when they join community; publishes service

I’m a 600dpi B&W printer; my service is printing

An app can lookup a service to discover a device

More info: http://courses.cs.vt.edu/~wwwtut/Notes/Java/jini.html

?: Any way that remote procedure could be called twice

Yes: request is duplicated Want semantics to clarify requests:

3

?: What if RPC executes but host crashes before sending reply?

Need transaction semantics at host. Commit protocol on server guarantees no intermediate state visible

Example:

Implemented by list on disk of actions to execute

Java Enterprise Beans offers transactions

Outline of Peterson/Davie Solution (pp. 400-426)

Three sub-protocols:

BLAST – Send Message

Sender: Fragment large message into packets Transmits packets Set timer If no response by timeout, give up If ack arrives, resend listed packets

BLAST (2)

Receiver Set timer Receive fragments:

When last fragment arrives, send ack If timer pops, send ack Ack lists missing packets After 3 timeouts, give up

CHAN – Implement request/reply

guarantees message delivery (retransmits) eliminats dups (via sequence number) implements at-most-once semantics allows synchronization between sender/receiver uses reply as implicit ack of request sends I’m alive messages in case procedure takes long time to execute

SELECT

CHAN runs between one app and one proc SELECT handles set of calls between apps to common remote procedure via serialization SELECT also provides hierarchical names for destinations, vs. ports:

(program #, proc #) (file-server-program, read) (file-server-program, write)