CS 603 Naming in Distributed Systems January 28, 2002

This week: Naming in Distributed Systems Today: Overview –What is a name –Issues –Examples Wednesday and Friday: Name Resolution –Historical (Telephone, mail, …)? –DNS? –DCE? –Others?

What is a name? An identifier that: Identifies a resource –Uniquely? –Describes the resource? Enables us to locate that resource –Directly? –With help? Is it really an identifier? –Bijective, persistent

Key issues in Naming How is name used? –Disambiguate only –Access resource given the name –Build a name to find a resource Do humans need to use name? –Construct? –Recall?

Key issues in Naming (cont.) Is resource static? –Never moves –Change in location should change name –Resource may move –Resource is mobile Performance requirements

Approaches to naming Globally unique identifier –Ethernet –Solves identification, but not description or location Hierarchically assigned globally unique identifier –Telephone number, IP address –Solves identification, not description –Helps with location

Approaches to naming Hierarchically assigned name –Domain Name Service, URL –Solves identification –Helps with description –Still problems with location Globally unique name –TCP/IP Protocol Ports –Extensibility problems

Approaches to naming Registries and name spaces –Uniform Resource Name (URN) –Solves identification and location If we can get to the registry –Helps with description Registry can describe in detail –Complicated!

URI, URL, URN URI: Uniform Resource IdentifierURI –IETF meta-standard –Defines naming schemes / protocols –Each naming scheme has it’s own mechanism URL: Uniform Resource LocatorURL –Uses DNS to map to host –Host knows how to map remainder to resource URN: Uniform Resource NameURN –Idea: Permanent URL

URN Each URN maps to a namespacenamespace –Currently 10 formally defined: IETF, ISBN, XMLORG, …formally defined –Also informal: (3 current) and experimental (unregistered) Syntax: “urn:” “:” –urn:ISBN: urn:ISBN: –urn:ietf:rfc:2141urn:ietf:rfc:2141 (Bad) Example: –URN: : : –urn:x-1234:

Naming: Why an Issue for Application Developers? DNS is widely accepted standard –Only names machines –Doesn’t handle mobility URI / URN will become standard –Can be descriptive –Globally unique –Persistent –But expensive to create

Applications that might need custom solutions Distributed Database –Needs persistence –May be multiple resources for single name (replication) –May need to support mobility –PERFORMANCE! Small-scale applications –Do you really want to register with IANA? –Is persistence necessary?

Distributed Database Example: R* R* developed at IBM Almaden Research – first distributed relational database Wanted mobility of resources –Supports fault tolerance –But movement rare Performance is critical Solution: Two components to name –Unique ID assigned by “birthplace” –Local catalog maps ID to: Birthplace (maintains current location) Presumed current location

Security Considerations Does name give away information? –Social Security Numbers –URL –Batched IDs (e.g., Ethernet) –Sequentially assigned IDs Solution: Define what name SHOULD do –Ensure it meets goals –Look for reasons it doesn’t

Name Resolution: What would you like? Historical? –Mail –Telephone DNS? X.500 / LDAP? DCE? ActiveDirectory?