Agent Name Service v.2 (ANS)

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(No Transcript)
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Agents Transacting in Open Environments

• Two phases
• Locating appropriate agents through different
  kinds of discovery infrastructure
• Agent Name Services (System level)
• Middle Agents (Knowledge level)
• Performing the transaction
• with or without middleware infrastructure

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Agent Name Service v.2 (ANS)
The ANS is a name registration and lookup service
to facilitate communication among agent
applications.
Agent 2
Agent 1
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DNS

• Most hosts that have an IP address know of (are
  preconfigured or learned via DHCP) of at least
  one DNS server
• Entries hardcoded and infrequently changed
• New specs (DNS update/DDNS) allow for dynamic
  updates of entries
• Hierarchical and distributed
• Primary and secondary masters for redundancy
• Local caching for learned entries to speed up
  future resolution requests
• New SRV Resource Records to indicate service
  type, address, port, and load balencing
  information

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ANS Features Benefits

• Acts as a white-pages service similar to the
  Domain Name Service (DNS)
• Provides extended features that do not exist in
  DNS
• Integrates new features that have not yet been
  standardized, or made widely available with DNS
  (service type and port numbers, service
  discovery)
• Provides platform for testing agent interactions
  without requiring immediate implementation and
  integration of new technologies into centrally
  administered network infrastructure

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ANS acts as an extension to DNS
Agent
Name lookup
ANS Infrastructure
Partial resolution but with extra info Location
protocol//hostnameport-number
hostname lookup
DNS Infrastructure
IP Address
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Agent Communications
Now, I need to find other agents, and let them
find me
I want to talk on the network to other agents
Agent 1
Agent 1

Agent 1

Communicator
Communicator
ANS Client
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Recent Enhancements

• Automatic fail-over from one ANS server to
  another
• Ability to dynamically discover ANS servers (in
  both clients and servers)
• Ability for Client to perform operations on all
  known ANS servers
• Ability for Server to automatically push
  register and unregister requests
• Ability for Server to propagate lookup requests
  to other ANS Server systems
• Multiple avenues for Server to gain knowledge of
  Agent registration entry

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ANS Client Initializationinitialize internal
list of ANS servers
ANS Server apple
Agent 1

• apple
• lemon

ANS Server pear
Communicator
ANS Client
ANS Server banana
1
File with list of servers

• apple
• lemon

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Dynamic discovery of ANS servers

• Available in both clients and servers
• Search for existing servers on system startup
• Discover new servers as they come online
• Remove servers that cleanly shut down and leave
  the network
• Remove servers that are unreachable (avoid future
  delays)
• Search for previously undiscovered servers when
  server-list falls below safe threshold
• Limit repeated discovery requests to avoid
  multicast storms
• Allow discovery to be disabled for single server
  sites, or in installations where Multicast
  traffic is prohibited
• Core discovery module based on Universal
  Plug-N-Play (UPnP) Simple Service Discovery
  Protocol (SSDP)

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ANS Client Initializationsearch via SSDP
discovery process
ANS Server apple
2
Agent 1

Who's Out There?
ANS Server pear
Communicator
ANS Client
ANS Server banana

• apple
• lemon

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ANS Client Initializationactive servers reply
that they are available
ANS Server apple
Im here
Agent 1

ANS Server pear
3
Communicator
ANS Client
Im here
ANS Server banana

• apple
• lemon
• pear

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ANS Client Operationnew servers announce that
they are alive
ANS Server apple
Agent 1

ANS Server pear
4
Communicator
ANS Client
ANS Server banana

• apple
• lemon
• pear
• banana

Hey Everyone I just came online
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ANS Client Operationentries are pruned if they
are unreachable
ANS Server apple
5
To apple
Agent 1

To lemon
ANS Server pear
?
Communicator
ANS Client
To pear
ANS Server banana

• apple
• lemon
• pear
• banana

To banana
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ANS Client Operationclient can interact with one
or all servers
ANS Server apple
5
To apple
Agent 1

To lemon
ANS Server pear
?
Communicator
ANS Client
To pear
ANS Server banana

• apple
• lemon
• pear
• banana

To banana
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ANS Client/Server OperationAgent Registration
with Server Push
ANS Server apple
Push to pear
To apple
Agent 1

ANS Server pear
Communicator
Push to banana
ANS Client
ANS Server banana

• apple
• lemon
• pear
• banana

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Server propagation of lookup requests

• Lookup in local cache, then possibly in SQL
  database
• Lookup with partner ANS servers in same discovery
  group
• Lookup sent to a user defined set of
  non-discoverable servers that can be used to
  implement an cross-organizational hierarchy of
  ANS systems
• Discovery group partners look in local cache only
• Hierarchy ANS servers look locally, then to their
  partners, then to their hierarchy systems
• Search path is propagated with lookup request to
  assist in loop avoidance and handling request
  Time-To-Live limits
• Successful non-local searches result in interim
  ANS servers learning and registering agent
  entry in their local cache

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ANS Client/Server OperationAgent Lookup with
Server Forwarding
To apple
Agent 1

Lookup Susan
Check Hierarchy Servers
ANS Server apple
3
2
Check with Group Partners
1
Lookup in Local Cache
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Branching Nature of Extended ANS Lookup
Agent

• Discovery Group-Partners provide scaling and
  fault tolerance
• Hierarchy Partners allow linking different
  organizational groups

Primary ANS
Primarys discovered partners
Discovered partners of other servers in hierarchy
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
Not found
Lookup Bubba
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Not found
Computer Services
Nokia
Not found
Not found
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
Not found
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
Not found
CMU Agents Group
Not found
Not found
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Not found
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Not found
Not found
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
Not found
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
28
Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Not found
Computer Services
Nokia
Not found
Not found
Microsoft
You Are Here
29
Linked ANS Organizations
Not found
Art
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
5
Art
Robotics
Software Eng
English
2
3
4
CMU Agents Group
1
Computer Services
Nokia
A Time-To-Live (TTL) of 5 (default) has been
reached! Lookup will occur to local cache of
English ANS server, but will not be forwarded
to any of the English discovery group partners,
or its hierarchy systems (Art). Going back
through the progression, 5 to 4 to 3 the next
hierarchy server branch found will be checked.
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Not found
Computer Services
Nokia
Microsoft
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
Not found
Not found
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
Not found
You Are Here
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Linked ANS Organizations
Art
Robotics
Software Eng
English
CMU Agents Group
Computer Services
Nokia
Microsoft
You Are Here
Bubba Found!
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Linked ANS Organizations
Bubba Learned (registered)
CMU Agents Group
Bubba Learned (registered)
Nokia
Bubba Learned (registered)
Microsoft
Bubba Found
Answer to Bubba Lookup Learned
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JINI

• Clients Agents (CA) and Service Agents/providers
  (SA) use Directory Agents (DA) to locate needed
  resources
• Discovery mechanism used for CAs and SAs to find
  DAs
• preferred DA(s) may be pre-populated instead of
  using discovery
• UA, SA, DA in JINI must have a DA (SLP and mDNS
  allow UA to discover SA without DA)
• Lookup of service type and attributes has lookup
  service performing matchmaker-type functions
• Lookup services periodically re-announce
  themselves on the network to allow services to
  register them selves with the new or recovered
  lookup service
• Non-responding lookup services are not
  automatically pruned from registering services
  list

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ANS summary

• Provides name resolution of agents friendly
  advertised name to a location (host port)
• Augments DNS service
• May be replaced by newer DNS services
• Like JINI, SLP, and SSDP, ANS implements
  discovery search for ANS servers (as DAs) and
  uses unicast for the back channel
• Uses TCP sockets for client lookup queries
• Uses TCP sockets for agent registration

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Providers and Requesters

• Agents can be categorized as either providers of
  services or requesters
• These roles are not exclusive
• Providers and requesters want to find each other
  based on functionality/capability
• This is done through advertisement and request
  via middle agents

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Issues with Locating Agents (1)

• Evaluation criteria
• performance
• robustness
• scalability
• load balancing
• privacy
• Where the matching is done
• At the requester (preserving the privacy of
  requesters)
• middle agents
• service providers

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Transaction Phase

• Providers and requesters interact with each other
  directly
• a negotiation phase to find out service
  parameters and preferences (if not taken into
  account in the locating phase)
• delegation of service
• Providers and requesters interact through middle
  agents
• middle agent finds provider and delegates
• hybrid protocols
• Reasons for interacting through middle agents
• privacy issues (anonymization of requesters and
  providers)
• trust issues (enforcement of honesty not
  necessarily keep anonymity of principals) e.g.
  NetBill

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Protocols

• Who to talk to principals involved
• Message content
• ex a LARKS specification
• Local processing
• ex implied by KQML performatives
  (service-request, request-for-service-providers)

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Matching Engine for Service Providers Requesters
sorted list of agent contact info
unsorted list of agent contact info
decision algorithm
matching capabilities with requests
(LARKS)
matching capabilities with requests
(LARKS)
service request parameters
capability parameters
service request
capability parameters
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Broadcaster
Request for service
Broadcaster
Requester
Broadcast service request
Offer of service
Delegation of service
Results of service request
Provider 1
Provider n
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Yellow Page
Request for service
Yellow Page
Requester
Unsorted list of contact info of (P1,P2, , Pk)
Advertisement of capabilities
Delegation of service
Results of service request
Provider 1
Provider n
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Matchmaking
Request for service
Matchmaker
Requester
Unsorted full description of (P1,P2, , Pk)
Advertisement of capabilities para.
Delegation of service
Results of service request
Provider 1
Provider n
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Classified Ads
Requester 1
Request for servicepref.
Classified Ads
Request for servicepref.
Advertisement of capabilities
(R1,R2, , Rk) contact info.
Requester n
Offer of service
Provider selects requester
Provider 1
Delegation of service
Service results
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Recommender
Request for servicepref.
Recommender
Requester
Sorted full description of (P1,P2, , Pk)
Advertisement of capabilities para.
Delegation of service
Results of service request
Provider 1
Provider n
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FacilitatorCombines Agent Location and
Transaction Phases
Request for servicepref.
Facilitator
Requester
Results of service
Advertisement of capabilities para.
Service result
Delegation of service
Provider 1
Provider n
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The Contract Net Protocol

• An agent coordination and distributed task
  allocation mechanism, where
• multiple heterogeneous agents can perform tasks
• agents can play two roles managers, contractees
• managers receive tasks, select prospective
  contractees and ask for bids
• best bid wins task, performs it, manager monitors
• Pros and cons
• simple to implement, base for many other
  protocols
• fully distributed
• performance quality not checked
• easy to manipulate (free riders), may cause loops

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Contract Net
Request for service preferences
Manager
Requester
Results of service
Delegation of service
Broadcast service request pref
Broadcast
Offer of service
Results of Service
Broadcast
Offer of service
Provider 2
Provider n
Provider 1
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Conclusions

• Flexible services for locating agents are crucial
  for agile e-commerce
• Emerging competing standards
• No thought or standards at the knowledge level yet