Naming in Distributed Systems

Lecture # 5

Overview

Pure vs impure names IDs, Addresses,Name Space, Name

Resolution Implementation of a Naming Service Case Studies: Telephone System. DNS,

SLP(X.500), INS Reading:

– Jerome, Kaashoek: Chapter 3 – Coulouris: Distributed Systems, Addison Wesley,

Chapter 9

Pure vs impure: What’s in a namePure Names: Uninterpreted string of

bits– Independent of object location or

semanticsImpure Names:

– Encode object semantics and/or locationTelephone Numbers?Descriptions

– Always Search

Naming Scheme

Name Space– Syntax: Different naming conventions– 128.67.34.255– 92-42-5722670– StringBuffer

Naming Resolution AlgorithmValue: DestinationFrequently: Context

Examples of Naming

Telephone System

Numeric name space (length dependant on the size of the city)

Hierarchical Structuring of Names– 92-42-5722670

Hierarchical Name Resolution– Lookup: Directories

Value? Context?

Naming Examples

Naming Variables– Naming convention

Variable Names: start with an alphabetClass Names: start with capitalization

– Value: Address of Memory LocationPointers: Indirection

– Resolution:Symbol Tables

– ContextScoping?

– Dynamic – Lexical: Static

– Hierarchical NamesJava: Derived from directory structure

Naming Examples

DNS Names as Path Names

Root

n1

k1

n2

Root.n1.k1.lums

Root.yahoo

Closure in Naming

Names closed under composition– Using a root

Absolute Vs. Relative Paths– Context

DNS– Mailto: zahoor (from within lums)

Directory– Working directory

Name Resolution

DNS Terminology– Iterative vs. Recursive

Essentially– State management in resolution– Caching– Communication Cost

Iterative

Client-sideName

Resolver

root

edu

pk

lums

www.lums.edu.pk IP number

cs.lums.edu.pk

cs.lums.edu.pk

cs.lums.edu

cs.lums.edu

cs

cs.lums

cs.lums

cs

IP # CS

Recursive

Client-sideName

Resolver

root

edu

pk

lums

www.lums.edu.pk IP number

cs.lums.edu.pk

IP # cscs.lums.edu

cs.lums.edu

cs

cs.lumscs.lums

csIP # CS

Recursive vs iterative

StateCachingCommunication latency