1. Dr. Kalpakis CMSC621 Advanced Operating Systems Naming

2. CMSC 621 2 Naming Access point & address Location independent naming Identifier It refers to at most one entity Each entity has at most one id An id always refers to the same entity Name-to-address binding Name resolution vs message routing Flat naming Broadcasting and multicasting

3. CMSC 621 3 Naming versus Locating Entities a) Direct, single level mapping between names and addresses. b) T-level mapping using identities.

4. CMSC 621 4 Forwarding Pointers The principle of forwarding pointers using (proxy, skeleton) pairs.

5. CMSC 621 5 Forwarding Pointers Redirecting a forwarding pointer, by storing a shortcut in a proxy.

6. CMSC 621 6 Home-Based Approaches The principle of Mobile IP.

7. CMSC 621 7 Distributed Hash Tables CHORD FT_p[i] = first node in range [p+2^(i-1), p+2^i). Enhance by storing r nodes in the range and during lookup use closest to query

8. CMSC 621 8 Chord Searching for 26 from 1 Searching for 12 from 28

9. CMSC 621 9 Hierarchical Approaches Hierarchical organization of a location service into domains, each having an associated directory node.

10. CMSC 621 10 Hierarchical Approaches An example of storing information of an entity having two addresses in different leaf domains.

11. CMSC 621 11 Hierarchical Approaches Looking up a location in a hierarchically organized location service.

12. CMSC 621 12 Hierarchical Approaches a) An insert request is forwarded to the first node that knows about entity E. b) A chain of forwarding pointers to the leaf node is created.

13. CMSC 621 13 Pointer Caches Caching a reference to a directory node of the lowest-level domain in which an entity will reside most of the time.

14. CMSC 621 14 Pointer Caches A cache entry that needs to be invalidated because it returns a nonlocal address, while such an address is available.

15. CMSC 621 15 Scalability Issues The scalability issues related to uniformly placing subnodes of a partitioned root node across the network covered by a location service.

16. CMSC 621 16 Structured Name Spaces A general naming graph with a single root node. Absolute vs relative path names

17. CMSC 621 17 Name Spaces The general organization of the UNIX file system implementation on a logical disk of contiguous disk blocks.

18. CMSC 621 18 Linking and Mounting The concept of a symbolic link vs a hard link explained in a naming graph.

19. CMSC 621 19 Linking and Mounting Mounting remote name spaces through a specific process protocol. Mount point vs mounting point

20. CMSC 621 20 Linking and Mounting Organization of the DEC Global Name Service

21. CMSC 621 21 Name Space Distribution An example partitioning of the DNS name space, including Internet-accessible files, into three layers.

22. CMSC 621 22 Name Space Distribution A comparison between name servers for implementing nodes from a large-scale name space partitioned into a global layer, as an administrational layer, and a managerial layer. ItemGlobalAdministrationalManagerial Geographical scale of networkWorldwideOrganizationDepartment Total number of nodesFewManyVast numbers Responsiveness to lookupsSecondsMillisecondsImmediate Update propagationLazyImmediate Number of replicasManyNone or fewNone Is client-side caching applied?Yes Sometimes

23. CMSC 621 23 Implementation of Name Resolution The principle of iterative name resolution.

24. CMSC 621 24 Implementation of Name Resolution The principle of recursive name resolution.

25. CMSC 621 25 Implementation of Name Resolution Recursive name resolution of. Name servers cache intermediate results for subsequent lookups. Server for node Should resolveLooks up Passes to child Receives and caches Returns to requester cs # -- # vu # # # # ni # # # # # # root # # # # # # # #

26. CMSC 621 26 Implementation of Name Resolution The comparison between recursive and iterative name resolution with respect to communication costs.

27. CMSC 621 27 The DNS Name Space The most important types of resource records forming the contents of nodes in the DNS name space. Type of record Associated entity Description SOAZoneHolds information on the represented zone AHostContains an IP address of the host this node represents MXDomainRefers to a mail server to handle mail addressed to this node SRVDomainRefers to a server handling a specific service NSZoneRefers to a name server that implements the represented zone CNAMENodeSymbolic link with the primary name of the represented node PTRHostContains the canonical name of a host HINFOHostHolds information on the host this node represents TXTAny kindContains any entity-specific information considered useful

28. CMSC 621 28 DNS Implementation An excerpt from the DNS database for the zone cs.vu.nl.

29. CMSC 621 29 DNS Implementation Part of the description for the vu.nl domain which contains the cs.vu.nl domain. NameRecord typeRecord value cs.vu.nlNISsolo.cs.vu.nl A130.37.21.1

30. CMSC 621 30 Attribute-based naming Describe an entity via (attribute,value) pairs Partial match queries in DB lingo LDAP and X.500 Scalability issues Decrentralized implementations Attribute-value tree: hash-index for all paths to nodes in XML-like tree

31. CMSC 621 31 The X.500 Name Space A simple example of a X.500 directory entry using X.500 naming conventions. AttributeAbbr.Value CountryCNL LocalityLAmsterdam OrganizationLVrije Universiteit OrganizationalUnitOUMath. & Comp. Sc. CommonNameCNMain server Mail_Servers--130.37.24.6, 192.31.231,192.31.231.66 FTP_Server--130.37.21.11 WWW_Server--130.37.21.11

32. CMSC 621 32 The X.500 Name Space (2) Part of the directory information tree.

33. CMSC 621 33 The X.500 Name Space (3) Two directory entries having Host_Name as RDN. AttributeValueAttributeValue CountryNLCountryNL LocalityAmsterdamLocalityAmsterdam OrganizationVrije UniversiteitOrganizationVrije Universiteit OrganizationalUnitMath. & Comp. Sc.OrganizationalUnitMath. & Comp. Sc. CommonNameMain serverCommonNameMain server Host_NameStarHost_Namezephyr Host_Address192.31.231.42Host_Address192.31.231.66

34. CMSC 621 34 The Problem of Unreferenced Objects An example of a graph representing objects containing references to each other.

35. CMSC 621 35 Reference Counting (1) The problem of maintaining a proper reference count in the presence of unreliable communication.

36. CMSC 621 36 Reference Counting (2) a) Copying a reference to another process and incrementing the counter too late b) A solution.

37. CMSC 621 37 Advanced Referencing Counting (1) a) The initial assignment of weights in weighted reference counting b) Weight assignment when creating a new reference.

38. CMSC 621 38 Advanced Referencing Counting (2) c) Weight assignment when copying a reference.

39. CMSC 621 39 Advanced Referencing Counting (3) Creating an indirection when the partial weight of a reference has reached 1.

40. CMSC 621 40 Advanced Referencing Counting (4) Creating and copying a remote reference in generation reference counting.

41. CMSC 621 41 Tracing in Groups (1) Initial marking of skeletons.

42. CMSC 621 42 Tracing in Groups (2) After local propagation in each process.

43. CMSC 621 43 Tracing in Groups (3) Final marking.