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Service Discovery

Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III. 2. Service Discovery: What?. Protocol suites for building highly dynamic client/server architecturesAutomatic discovery and configuration of new devices plugged into a networkSelf-healing networks: automatic ?demise" o

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Service Discovery

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    1. Service Discovery Golden G. Richard III Associate Professor Dept. of Computer Science University of New Orleans New Orleans, LA 70148 golden@cs.uno.edu http://www.cs.uno.edu/~golden

    2. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 2 Service Discovery: What? Protocol suites for building highly dynamic client/server architectures Automatic discovery and configuration of new devices plugged into a network Self-healing networks: automatic “demise” of devices removed from a network Highly dynamic system configurations Cooperation between resource poor devices Solves form-factor vs. peripheral richness problem for mobile devices Printing, FAX, storage, long-range networking services can be obtained from nearby servers Helps reduce duplication of functionality… …eliminates "toolbelt" syndrome Affects both mobile and wired systems See Service and Device Discovery: Protocols and Programming (G. G. Richard III, McGraw-Hill, 2002)

    3. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 3 Service Discovery: Who? Jini Sun Microsystems (Java) www.jini.org Universal Plug and Play Microsoft www.upnp.org Service Location Protocol Internet Engineering Task Force (IETF) www.srvloc.org Salutation Salutation Consortium www.salutation.org Bluetoooth (SDP) Bluetooth Special Interest Group www.bluetooth.com Ninja system at Berkeley ninja.cs.berkeley.edu

    4. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 4 Dynamic Device Discovery

    5. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 5 Dynamic System Configuration

    6. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 6 Dynamic Client/Server Architectures

    7. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 7 Service Discovery: Capabilities Protocol suites provide most or all of the following: Ability to advertise available services Automatic discovery of nearby services Potential to discover services that aren’t nearby Ability to "discuss" service capabilities Abstraction “I just need a printer” Service catalogs (some) Garbage collection facility (catalogs, service advertisements)

    8. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 8 Jini Java-based protocol suite A federation of clients and services Entities in federation provide and/or obtain services to/from other entities All development in Java Code mobility Relies heavily on: Object serialization RMI: Remote Method Invocation Interesting services because of mobile code

    9. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 9 Jini Entities

    10. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 10 Jini, The Big Picture

    11. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 11 What is a Jini Service? A client in need of service ultimately downloads a Java object The object can either: Provide the service locally (e.g., entirely algorithmically) Provide the service by invoking operations on a remote server using a private protocol Proxy object is an RMI stub (object is remote) (Provide the service by interacting with a remote human being, through a remote server…) To the client, there is no essential difference between these choices Client generally doesn’t know the location of service or wire protocol used to communicate with service

    12. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 12 Finding a Lookup Service: Protocols Unicast discovery protocol TCP: Protocol for communication with a specific lookup service Scope: Global Internet Multicast request protocol UDP: Used to discover nearby lookup services via multicast Local or administrative scope Multicast announcement protocol UDP: Used to announce availability of a lookup service via multicast Local or administrative scope These protocols are not coded by a Jini applications programmer—they form a foundation for Jini’s LookupDiscovery class (discussed on the previous slide).These protocols are not coded by a Jini applications programmer—they form a foundation for Jini’s LookupDiscovery class (discussed on the previous slide).

    13. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 13 Jini: Unicast Discovery Protocol

    14. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 14 Jini: Multicast Request Protocol

    15. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 15 Jini: Multicast Request Protocol

    16. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 16 Jini: Multicast Request Protocol

    17. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 17 Jini: Multicast Request Protocol

    18. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 18 Jini: Multicast Announcement Protocol

    19. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 19 Service Registration: ServiceItem public ServiceItem(ServiceID id, Object service, Entry [] attributes) Registration describes an available service: universally unique id, object to provide to client, and set of attributes (which are Entry objects) On registration, lookup service returns an object that allows leasing to handled, possibly assigned universally unique ID

    20. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 20 Search for Services is by Interface Lookup is based on object interfaces, not simply name/value pairs So client might hold the following interface, which defines a remote file storage service: public interface StorageService { public boolean open(String username, String password,…) public boolean close(); public boolean store(byte[] contents, String pathname); public byte[] retrieve(String pathname); public boolean delete(String pathname); public String[] listFiles(); } Client generally does not know the implementation of the service Just asks lookup for services matching this interface and having certain attribute values Once it has an instance, invokes methods in interface

    21. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 21 Other Jini Stuff LeaseRenewalManager JoinManager ServiceDiscoveryManager JavaSpaces Linda-like object spaces Transactions Provides a 2PC-based transaction framework Distributed Events (Used for notification of lookup and/or appropriate services becoming available)

    22. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 22 Jini Security Based on Java 2 security system Digital signatures Verify authenticity of downloaded code Encryption Security Manager uses access control lists A variety of actions can be controlled Security Manager can be subclassed and customized extensively By default, very tight security Novice Jini users often “cheat” and turn off security by using a very liberal (or wide open) policy file

    23. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 23 Jini Security (2)

    24. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 24 Java Security Manager Terminate application Read from a specified file Write to a specified file Delete files Accept socket connections Open a socket connection Use IP multicast Use native methods Load a class from a specified package Can have different policies depending on where the class files originated…

    25. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 25 Jini: Thoughts Ubiquitous use will require standardization of Java interfaces e.g., What interface defines a printer? Nice, fuzzy feeling about high-level, object-oriented approach Requires adoption of Java In general, device must be capable of supporting a Java VM, and all the core Java 2 classes Raises the computational bar slightly higher than other approaches Security is very important for mobile-code approaches like Jini

    26. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 26 UPnP (Universal Plug and Play) Microsoft’s offering UPnP "core" AutoIP SSDP (Simple Service Discovery Protocol) SOAP (Simple Object Access Protocol) GENA (Generic Event Notification Architecture) Discussion based on 1.0 specs No mobile code—instead, standardized protocols and service descriptions XML-based service descriptions and device ?? client protocols Some discussion about a new spec which replaces SOAP with WSDL? (If so, not right away) A very interesting standardization process (…)

    27. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 27 UPnP: Device Model

    28. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 28 UPnP Device Model Example

    29. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 29 UPnP: Six Steps Addressing For the IP address impaired… Discovery Discovery and advertisement Description What are the characteristics of a service? Control Making a service do its thing(s) Eventing Updates on interesting service state changes Presentation Device GUI SSDP = “Simple Service Discovery Protocol” SOAP = “Simple Object Access Protocol” GENA = “SSDP = “Simple Service Discovery Protocol” SOAP = “Simple Object Access Protocol” GENA = “

    30. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 30 Intel SDK for Linux Schematic

    31. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 31 Addressing: AutoIP IP address assignment w/o DHCP Try to find DHCP server …on failure… Pick a random address from a range of local addresses (169.*.*.* range) ARP: Verify address is not in use If in use, retry until some max attempts exceeded Configure and use address Periodically try to find DHCP server by sending discover query If DHCP offer is received, use it These addresses are not routable!!

    32. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 32 AutoIP

    33. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 33 Discovery: SSDP Simple Service Discovery Protocol Supports both discovery and advertisement Based on UDP multicast / HTTP local administrative scope multicast address 239.255.255.250 (see RFC 2365) Weak search capabilities service type (multiple responses) or unique device name (at most one response) Responses to discovery are URLs that identify device description documents Description document must be retrieved using standard HTTP to learn more about the device

    34. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 34 SSDP in Action

    35. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 35 SSDP Service Announcement

    36. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 36 UPnP Description Documents XML description document contains: Essential characteristics of device Presentation URL Provides link to HTML GUI for device Service types offered by device Control URLs for services Entry point for device commands Event subscription URLs for services Allows subscription to device's event service Significant device changes will result in notification Provide our own event sink URL to subscribe Pointers to Service Control Protocol (SCP) documents for services (these are also XML)

    37. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 37

    38. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 38

    39. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 39

    40. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 40

    41. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 41 Sample of SCPD Data Types ui1, ui2, ui4: One, two, and four byte unsigned integers. i1, i2, i4: One, two, and four byte signed integers. r4, r8: Four and eight byte signed floats. char: A single character Unicode string. string: A Unicode string of arbitrary length. date: A standard ISO 8601 format date (e.g., YYYY-MM-DD). time: ISO 8601 format without date and without time zone. boolean: Boolean value (0, 1, false, true, yes, no). bin.base64: Unlimited length MIME-style Base64 data. bin.hex: Stream of hexadecimal digits of unlimited length. uri: Universal Resource Identifier. --and others– Unlike Jini, no complex types “out of the box”

    42. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 42 UPnP: Control via SOAP

    43. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 43 UPnP: Events (GENA) General Event Notification Architecture Expired IETF Draft (Microsoft authors) Subscription-based event notification service Subscribe (service of interest, callback URL) Resubscribe Unsubscribe Reports changes in state variable values for UPnP devices Event messages contain XML-encoded state variables/values Unreliable, administratively-scoped UDP multicast and extensions to HTTP

    44. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 44 GENA Message Formats (1) Subscription request (NT is notification type) SUBSCRIBE publisher path HTTP/1.1 HOST: publisher host:publisher port CALLBACK: <delivery URL> NT: upnp:event TIMEOUT: Second-requested subscription duration Response: HTTP/1.1 200 OK DATE: when response was generated SERVER: OS/version UPnP/1.0 product/version SID: uuid:subscription-UUID TIMEOUT: Second-actual subscription duration

    45. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 45 GENA Message Formats (2) Device sends a notification when important service changes occur: NOTIFY delivery path HTTP/1.1 HOST: delivery host:delivery port CONTENT-TYPE: text/xml CONTENT-LENGTH: Bytes in body NT: upnp:event NTS: upnp:propchange SID: uuid:subscription-UUID SEQ: event key <e:propertyset xmlns:e="urn:schemas-upnp-org:event-1-0">   <e:property>     <variableName>new value</variableName>   </e:property>   Other variable names and values (if any) go here. </e:propertyset>

    46. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 46 Concrete GENA Subscription

    47. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 47 Concrete GENA Subscription Response

    48. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 48 Concrete GENA Event

    49. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 49 UPnP: Presentation

    50. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 50 UPnP: Thoughts Lighter weight than Jini Some serious limitations… No directory agents No security architecture Limited search capabilities (…) How much community involvement? Some scary language (to me) in the standardization process Widespread adoption almost certain

    51. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 51 SLP: Service Location Protocol SLP: IETF draft protocol Defines three types of agents: User Agents: acquire service handles for apps Service Agents: advertise service handles Directory Agents: catalogs of available services, cache service handles Interesting stuff: Allow UAs to obtain service handles with or without DAs Tries to avoid being “chatty”… More powerful search capabilities than UPnP Eliminate some device responses during discovery Scoping to tame administrative hassles Security considered very important

    52. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 52 SLP Schematic (from whitepaper)

    53. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 53 Thoughts (or, SLP vs. UPnP) SLP <> UPnP Major differences More limited queries in UPnP SLP: Supports attribute searches (see next slide) SSDP: Search by type or unique device name only Protocol used for SSDP SSDP “based” on HTTP Some concerns about how complexity of HTTP headers No DAs in UPnP (at all) Client ?? service application protocol outside SLP scope Security framework, including digital signatures for SLP messages to verify authenticity New SLP service types will not even be considered for standardization w/o addressing security issues! !! No scary Microsoft stuff in the standardization process !!

    54. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 54 Attribute Searches (Echo) Can use an LDAP-style filter in a service request: “(manufacturer=ibm)” will restrict the set of discovered services to those that have an attribute “manufacturer” with a case-insensitive value of “ibm”. “(&(manufacturer=ibm)(model=printstar*))” restricts the set of discovered services to those with an attribute “manufacturer” with a case-insensitive value of “ibm” and which further have an attribute “model” with a value beginning with “printstar”. “(|(contactname=golden)(contactname=gerrod))” matches only services with an attribute “contactname” whose value is either “golden” or “gerrod” (case-insensitive, as above). Can significantly reduce the number of responses to a discovery request…

    55. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 55 Ninja Project (UC Berkeley) Java-based service discovery protocol XML service descriptions and queries Focus on higher security All communication encrypted (Authenticated RMI) All entities have digital certificates Authentication of endpoints (e.g., clients, services) Rather than only restrict access to services, restrict knowledge of existence of services See “An Architecture for a Secure Service Discovery Service” (Czerwinski, Zhao, Hodes, Joseph, Katz), Mobicom ’99, pp. 24-35.

    56. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 56 Interoperability Some protocol enhancements are done outside the various special interest groups e.g., mSLP (Mesh-enhanced SLP) Interoperability an important research area for the rest of us Why? Jini, UPnP, SLP (at the least) are all healthy Want enabled devices supporting one protocol to be usable by all clients Cheap devices aren’t going to support more than one protocol In current “dog eat dog” phase, not too much work on interoperability coming out of the SIGs themselves If you’re a systems type, fun!

    57. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 57 Jini ?? UPnP Interoperability Interoperability both ways UPnP clients can use Jini services Jini clients can use UPnP services Light (?) coding required for each service type Must write “virtual” UPnP and Jini service implementations Virtual clients provided by framework, perform discovery of services Virtual Jini service is instantiated when UPnP service of corresponding type is discovered, vice versa

    58. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 58 Jini ?? UPnP Interoperability (2) See “Jini Meets UPnP: An Architecture for Jini/UPnP Interoperability” (J. Allard, V. Chinta, S. Gundala, G. G. Richard III), to appear at SAINT 2003 (Orlando).

    59. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 59 Other Interoperability Salutation uses SLP directories beyond the local network segment There is a Jini ? SLP bridge “Smart” agent finds Jini-enabled SLP services and registers them with Jini lookup services “Enabled” means the service has a bundle of static Java code Static code is a factory—can instantiate a live object to speak the appropriate protocol for communicating with the service Simply: The static code is a Java device driver Service does not run a JVM One direction only—does not provide access to SLP services for Jini clients See “Automatic Discovery of Thin Servers: SLP, Jini and the SLP-Jini Bridge” (E. Guttman, J. Kempf), IECON, San Jose, 1999.

    60. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 60 Interoperability (2) Everything over Bluetooth Can run IP over Bluetooth, thus Jini et al Either use Bluetooth as data link protocol and forget Bluetooth SDP, or map protocol operations to Bluetooth SDP operations Salutation over Bluetooth As above (Salutation over IP over Bluetooth) Some work on mapping Salutation API directly to Bluetooth SDP See paper “Mapping Salutation Architecture APIs to Bluetooth Service Discovery Layer” http://www.salutation.org/whitepaper/BtoothMapping.PDF

    61. Service Discovery @ Wayne State, October 2002 -- Prof. Golden G. Richard III 61 Summary Service discovery great for building highly dynamic systems Enabler for small information appliances Lots of contenders for the title Best technical approach won’t necessarily be the winner So far, very little standardization of service types (for any of the protocol suites) Good device standards critical Interoperability important Security very important Lots of industrial need ? consulting, contracts

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