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Remote Procedure Call
Outline
Protocol Stack Presentation Formatting
based on section 5.3 of Peterson & Davies book
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RPC Timeline
Client
Reque st
Server Blocked
Blocked
Reply
Computing
Blocked
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Where RPC fits in OSI model
Application Applications NFS SMTP FTP TELNET DNS SNMP RPC Session TFTP Presentation
Transport
TCP
UDP
ICMP Network
IGMP
IP
ARP RARP
Data link Protocols defined by the underlying networks Physical
3 From: TCP/IP Protocol Suite, McGraw-Hill, 2000
RPC Components
Protocol Stack
fragments and reassembles large messages (BLAST) synchronizes request and reply messages (CHAN) dispatches request to the correct process (SELECT)
Stubs
Caller (client) Arguments Client stub Request Reply Return value Callee (server) Arguments Return value
Server stub Request Reply
RPC protocol
RPC protocol
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Programming Benefits
The programming is easier since little or no network programming involved. If an unreliable protocol such as UDP is used, details like timeout and retransmission are handled by RPC package. The RPC library handles any required data translation for the arguments and return values.
TCP/IP Illustrated, Vol. I, Chap. 29
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Simple RPC Stack
Client Caller xCall Callee Server
SELECT
xCallDemux SELECT
SELECT xCall
CHAN
xCallDemux
CHAN
CHAN
BLAST
xPush xDemux xPush xDemux
IP
ETH
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SunRPC
IP implements BLAST-equivalent
except no selective retransmit
SunRPC UDP
SunRPC implements CHAN-equivalent
except not at-most-once
IP ETH
UDP + SunRPC implement SELECT-equivalent
UDP dispatches to program (ports bound to programs) SunRPC dispatches to procedure within program
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SunRPC Header Format
XID (transaction id) is similar to CHANs MID Server does not remember last XID it serviced Problem if client retransmits request while reply is in transit
0 XID MsgType = CALL RPCVersion = 2 Program Version Procedure Credentials (variable) Verifier (variable) Data 31 0 XID MsgType = REPLY Status = ACCEPTED Data 31
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Port Mapper
Just another RPC program Listen to UDP port 111 and TCP port 111 Provide server procedures:
PMAPPROC_SET: Called by an RPC server on startup to register a program no,
version no, protocol with port no.
PMAPPROC_UNSET: Called by server to remove a previously registered mapping. PMAPPROC_GETPORT: Called by an RPC client on start up to obtain the port no
for a given program no, version no, and protocol.
PMAPPROC_DUMP: Returns all entries (program no, version no, protocol, and port
no) in the port mapper database.
Port mapper starts first (listen to 111) RPC Server prog. starts (register with PMAPPROC_SET) RPC Client prog. starts (PMAPPROC_GETPORT) RPC Client sends an RPC call message
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DCE-RPC
Distributed Computing Environment (DCE) was defined by Open Software Foundation (OSF). DCE-RPC is the PRC protocol at the core of the DCE and (Common CORBA Object Request Broker Architecture) . Run on top of UDP. Besides RPC, DCE also includes security services, LAN namespace services, and network time services. (Sun has a Secure RPC for authentication.)
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Presentation Formatting
Marshalling (encoding) application data into messages Unmarshalling (decoding) messages into application data
Application data Application data
Presentation encoding Message Message
Presentation decoding Message
Data types we consider
integers floats strings arrays structs
Types of data we do not consider
images video multimedia documents
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Difficulties
Representation of base types
floating point: IEEE 754 versus non-standard integer: big-endian versus little-endian (e.g., 34,677,374)
Big-endian (2) (17) 00000010 00010001 (34) 00100010 (34) (126) 00100010 01111110 (17) 00010001 (2) 00000010
(126) Little-endian 01111110
High address
Low address
Compiler layout of structures
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Taxonomy
Data types
base types (e.g., ints, floats); must convert flat types (e.g., structures, arrays); must pack complex types (e.g., pointers); must linearize
Application data structure
Marshaller
Conversion Strategy
canonical intermediate form receiver-makes-right (an N x N solution)
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Taxonomy (cont)
Tagged versus untagged data
type = INT len = 4 value = 417892
Stubs
compiled interpreted
Call P
Interface descriptor for Procedure P Specification Code Stub compiler
P Arguments Server stub Marshalled arguments RPC
Arguments Client stub Code
Marshalled arguments RPC Message Peterson & Davie
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eXternal Data Representation (XDR)
Defined by Sun for use with SunRPC C type system (without function pointers) Canonical in...