Naming Chapter 4. Name Spaces (1) A general naming graph with a single root node. - презентация

1 Naming Chapter 4

2 Name Spaces (1) A general naming graph with a single root node.

3 Name Spaces (2) The general organization of the UNIX file system implementation on a logical disk of contiguous disk blocks.

4 Linking and Mounting (1) The concept of a symbolic link explained in a naming graph.

5 Linking and Mounting (2) Mounting remote name spaces through a specific process protocol.

6 Linking and Mounting (3) Organization of the DEC Global Name Service

7 Name Space Distribution (1) An example partitioning of the DNS name space, including Internet-accessible files, into three layers.

8 Name Space Distribution (2) 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

9 Implementation of Name Resolution (1) The principle of iterative name resolution.

10 Implementation of Name Resolution (2) The principle of recursive name resolution.

11 Implementation of Name Resolution (3) Recursive name resolution of. Name servers cache intermediate results for subsequent lookups. Server for node Should resolve Looks up Passes to child Receives and caches Returns to requester cs # -- # vu # # # # ni # # # # # # root # # # # # # # #

12 Implementation of Name Resolution (4) The comparison between recursive and iterative name resolution with respect to communication costs.

13 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

14 DNS Implementation (1) An excerpt from the DNS database for the zone cs.vu.nl.

15 DNS Implementation (2) 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 A

16 The X.500 Name Space (1) 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 , , FTP_Server WWW_Server

17 The X.500 Name Space (2) Part of the directory information tree.

18 The X.500 Name Space (3) Two directory entries having Host_Name as RDN. AttributeValueAttributeValue CountryNLCountryNL LocalityAmsterdamLocalityAmsterdam OrganizationVrije UniversiteitOrganizationVrije Universiteit OrganizationalUnitMath. & Comp. Sc.OrganizationalUnit Math. & Comp. Sc. CommonNameMain serverCommonNameMain server Host_NamestarHost_Namezephyr Host_Address Host_Address

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

20 Forwarding Pointers (1) The principle of forwarding pointers using (proxy, skeleton) pairs.

21 Forwarding Pointers (2) Redirecting a forwarding pointer, by storing a shortcut in a proxy.

22 Home-Based Approaches The principle of Mobile IP.

23 Hierarchical Approaches (1) Hierarchical organization of a location service into domains, each having an associated directory node.

24 Hierarchical Approaches (2) An example of storing information of an entity having two addresses in different leaf domains.

25 Hierarchical Approaches (3) Looking up a location in a hierarchically organized location service.

26 Hierarchical Approaches (4) 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.

27 Pointer Caches (1) Caching a reference to a directory node of the lowest-level domain in which an entity will reside most of the time.

28 Pointer Caches (2) A cache entry that needs to be invalidated because it returns a nonlocal address, while such an address is available.

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

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

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

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

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

34 Advanced Referencing Counting (2) c)Weight assignment when copying a reference.

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

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

37 Tracing in Groups (1) Initial marking of skeletons.

38 Tracing in Groups (2) After local propagation in each process.

39 Tracing in Groups (3) Final marking.