agents transacting in open environments two phases: locating appropriate agents through different...
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Agent Name Service andDiscoveryKatia Sycara
The E-Commerce Institute
www.cs.cmu.edu/~softagents
Teaching assistant: Joe Giampapa
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
Agent Name Service v.2 (ANS)
The ANS is a name registration and lookup service to facilitate communication among agent applications.
Agent 1 Agent 2
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
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
ANS acts as an extension to DNS
Agent
ANS Infrastructure
DNS Infrastructure
Name lookup
Partial resolution but with extra info:Location = protocol://hostname:port-number
hostname lookup
IP Address
Agent Communications
Agent 1
I want totalk on thenetwork to
other agents
Agent 1
Now, I need to findother agents,and let them
find me
Agent 1
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
ANS Client Initializationinitialize internal list of ANS servers
Agent 1
ANSServer
“banana”File withlist of servers
•apple•lemon
•apple•lemon
ANSServer“pear”
ANSServer“apple”
1
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)
ANS Client Initializationsearch via SSDP discovery process
Agent 1
ANSServer
“banana”•apple•lemon
ANSServer“pear”
ANSServer“apple”
2
ANS Client Initializationactive servers reply that they are available
Agent 1
ANSServer
“banana”
•apple•lemon•pear
ANSServer“pear”
ANSServer“apple”
3
I’m here
I’m here
ANS Client Operationnew servers announce that they are alive
Agent 1
ANSServer
“banana”
•apple•lemon•pear
•banana
ANSServer“pear”
ANSServer“apple”
4
HeyEveryone
I just cameonline
ANS Client Operationentries are “pruned” if they are unreachable
Agent 1
ANSServer
“banana”
•apple•lemonlemon•pear
•banana
ANSServer“pear”
ANSServer“apple”
5 To:apple
?To:lemon
To:pear
To:banana
ANS Client Operationclient can interact with one or all servers
Agent 1
ANSServer
“banana”
•apple•lemonlemon•pear
•banana
ANSServer“pear”
ANSServer“apple”
5 To:apple
?To:lemon
To:pear
To:banana
ANS Client/Server OperationAgent Registration with Server “Push”
Agent 1
ANSServer
“banana”
•apple•lemonlemon•pear
•banana
ANSServer“pear”
ANSServer“apple”
To:apple
Pushto
pear
Push tobanana
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
ANS Client/Server OperationAgent Lookup with Server Forwarding
Agent 1 Lookup “Susan”
ANSServer“apple”
To:apple
1
Lookup in Local Cache
2 CheckwithGroupPartners
3
CheckHierarchyServers
Branching Nature of Extended ANS Lookup
AgentPrimary ANS
Primary’sdiscoveredpartners
Discoveredpartners ofother serversin hierarchy
•Discovery Group-Partners provide scaling and fault tolerance•Hierarchy Partners allow linking different organizational groups
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Linked ANS Organizations
YouAreHere
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Lookup“Bubba”
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
NotfoundNotfound
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Notfound
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Notfound
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
1
2 3
4
5
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.
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
MicrosoftNotfound
Notfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
MicrosoftNotfound
Linked ANS Organizations
YouAreHere
CMUAgentsGroup
Software Eng Robotics
ComputerServices
EnglishArt
Nokia
Microsoft
BubbaFound!
Linked ANS Organizations
CMUAgentsGroup
Nokia
Microsoft
Bubba “Learned”(registered)
Bubba “Learned”(registered)
Bubba “Learned”(registered)
Answer to BubbaLookup “Learned”
Bubba Found
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 service’s list
ANS summary
• Provides name resolution of agent’s 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 DA’s) and uses unicast for the back channel
• Uses TCP sockets for client lookup queries• Uses TCP sockets for agent registration
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
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
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
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)
Matching Engine for Service Providers & Requesters
matching capabilities with requests
capability parametersservice request
(LARKS) matching capabilities with requests
capability parametersservice request+ parameters
(LARKS)
unsorted list of agent contact info
decision algorithm
sorted list of agent contact info
Broadcaster
BroadcasterRequester
Provider 1 Provider n
Request for service
Broadcast service request
Delegation of serviceResults of
service request
Offer of service
Yellow Page
Yellow PageRequester
Provider 1 Provider n
Request for service
Unsorted list of contact info of (P1,P2, …, Pk)
Advertisementof capabilities
Delegation of service
Results of service request
Matchmaking
MatchmakerRequester
Provider 1 Provider n
Request for service
Unsorted full description of (P1,P2, …, Pk) Advertisement
of capabilities+para.
Delegation of service
Results of service request
Classified Ads
Classified AdsRequester 1
Provider 1
Request for service+pref.
(R1,R2, …, Rk)contact info.
Advertisementof capabilities
Offer of service
Service results
Requester nRequest fo
r service+pref.
Delegation of serviceProviderselects
requester
Recommender
RecommenderRequester
Provider 1 Provider n
Request for service+pref.
Sorted full description of (P1,P2, …, Pk) Advertisement
of capabilities+para.Delegation
of serviceResults of
service request
FacilitatorCombines Agent Location and Transaction Phases
FacilitatorRequester
Provider 1 Provider n
Request for service+pref.
Advertisementof capabilities
+ para.
Results of service
Serviceresult
Delegationof service
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
Contract Net
ManagerRequester
Provider 2 Provider n
Request for service+ preferences
Broadcast service request + pref
Delegationof service
Results of service
Offer of service
Provider 1
BroadcastBroadcast
Offer of service
Results ofService
Conclusions
• Flexible services for locating agents are crucial for agile e-commerce
• Emerging competing standards
• No thought or standards at the knowledge level yet