Author : David Wetherall
(djw@cs.washington.edu)
Presented By : Gokul Nadathur
(gokul@cs.wisc.edu)
Tour Guide ...
 Introduction
 Design of ANTS
 Implementation of ANTS
 Protection and resource management issues
 What’s beyond active networks …
Active Networks : Visions and
Reality
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What is an Active Network
?
• Network architecture that allows :
– Application Customized Code to be dynamically
deployed in the network
– Code to be Executed in a controlled framework
within the network
• Similar to extensible operating systems (SPIN,
Synthesize etc)
• Packet = Code + data
Active Networks : Visions and
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Motivation
Client
Result
Client
Bid
Server
Schema for Auction Service
 Dynamic deployment of
new Internet services
 Online Auctions
Client submits bids
Central Server processes bids
Responds to requests for
current price
During high load on server,
current price may become
invalid by the time it reaches
the client
Active Networks : Visions and
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Auction Service in an Active
Network
Client
Bid
Active
Router
Fail
Bid
Filter
 Customized forwarding
routine in active router
if (bid is valid) success else
fail
Filters low bids in the
network before they reach
server
 Server periodically updates
current prices to active
routers
 Lowers load on server
Server
Active Networks : Visions and
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Apprehensions
 Security
Untrusted user code executing in core routers - Is it safe ?
 Efficiency
Dynamic code distribution consumes bandwidth
Every packet now requires additional processing
Auction Service example :Every router has to check if ( user bid > current bid )
Kills packet forwarding performance
Active Networks : Visions and
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ANTS
 Architecture designed to provide extensible network
layer service
 Routers are active
 Extendable at packet level in the form of Capsules
 A code distribution scheme
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Entities in ANTS
 Active Nodes :
 Programmable routers connected to IP routers through network
channels
Maintain a cache of forwarding code (protocols) and data used
by different services
Responsible for secure execution of forwarding code
Active Networks : Visions and
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Capsules
ANTS Header
IP header
Version
Type
Previous Address
Dep fields Payload
 Type
 Identifier for the forwarding routine to be executed (carries code
by reference)
 Previous address
 Where to get the forwarding routine from if it is not available in
the present node (Code Distribution)
 Dependent Fields
 Parameters for the forwarding code
 Payload
 Header + data of higher layers
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Example
Client
Bid
Code
Code Request
Active Router
(Caches
Forwarding
Code)
Previous Address field
Server
 Online Auction :
 FILTER Capsule : Sent
periodically by server to
update current bids
 BID Capsule : Used by client
to submit bid
 Forwarding Code not found ?
 Code provided by end user
software
 Light weight Code
Distribution within the
network
Active Networks : Visions and
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Code Distribution
Capsule
Capsule
Extract
Type
Continue
Execution
Wake up
Capsule
No
Check in
Cache
Yes
Bootstrap
code to cache
Active Networks : Visions and
Reality
Suspend
Execution
Discard on
Timeout
Fetch code from
Previous Addr
Receive
Response
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Code Distribution (Contd)...
 Need for Bootstrap Capsules to transfer code
 Well known type (System Capsules)
 Directory service for selecting protocols
 Advantages
Adapts to packet loss, node failures, changing routes
 Disadvantages
High Latency of loading can trigger end-system timeouts
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Implementation
Active
Node
Runtime
• User level process in Java
• Node Runtime :
Application
CH 1
Soft Store
Cached
code + data
– Schedules and executes
capsule instances
– Controlled access of soft
store using restricted API
Node API
CH 2
• Channel Class : Creates
Capsule instance from IP
packet
• Capsule : Execute custom
forwarding routines from cache
Active Networks : Visions and
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Protection Schema
 Type : MD5 fingerprint of forwarding routine
Prevents code spoofing
Provides authentication free foundation
 Java SandBox
Prevents untrusted code from corrupting node runtime
type field is defined as constant
Impossible to create a Firewall
Very Slow ( PLANet - 3 times faster)
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Protection Schema ...
 Code is read-only
 Data is protected by hashing the store on the type of
service to which it belongs
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Shared State Protection
 R/W sharing of Cached state between related capsule
types
 Auction Example :
FILTER Capsule sent by server updates current bids
BID Capsule sent by client uses this data to validate its bid
 Hierarchical Fingerprint for shared state :
Complex Type identifiers for shared state
Forwarding routines A and B share state
Type identifier for shared state: (A,(A, B)H )H and (B,(A, B)H )H
Identifies a single service (A, B)H to which both A and B belong
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Resource Management
 Unbounded utilization of
Computing resources (Long forwarding routines)
Network Bandwidth ( Flooding child capsules )
 Solutions :
Watchdog timers for breaking long forwarding routines
TTL to limit number of hops
Static limit on fanouts
 Application floods Network
network based resource allocation
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Open Issues
Administrative Issues
 Who can introduce new services ?
Hackers Paradise
Open Research Area : A Killer Application ?
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And Beyond …
 Radio Active Networks
Adaptable Wireless Network Architecture
Extend programmability to physical layer
Uses Software Radios and Active Networks
Higher layers interact with physical layer to observe changing
conditions
Based on the change appropriate physical layer is selected
 Example : Basestation to mobile system
Dynamically create channels according to mobile host
population
Create channels of different priority and QoS
Active Networks : Visions and
Reality
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