1. Virtual Active Networks
Gong Su
Mar. 9, 2000

2. Network Computing Models
Traditional: end-to-end,
Client-server software at end nodes
The network is but a packet-transport wire
Emerging: edge-to-edge
Application services/components deployed at edge nodes
Examples: web proxies, firewalls, QoS/bandwidth brokers…
Applications need to interact with network resources & topology
Configure resources to provide appropriate service
Adapt to availability and performance of network components

3. VAN: Middleware for Edge-Computing
VAN is a middleware architecture that enables applications to
Configure network topology
Allocate node and link resources

4. A Driving Example A web caching application needs…
Coverage for certain network area
Connectivity among caching service components
Resources to move cached contents
Solution: requests a VAN that provides
Coverage: spans a ring between AS1, AS2, AS4, and AS5
Resources: provides at least 1mbps for all connections
Reliability: prohibits more than 2 virtual links from traversing the same physical link
Physical network
AS3
Virtual spec.
AS1 D
1mbps
AS2 A B C
1mbps
1mbps D C
1mbps
AS4
Mapping
by VAN
AS5 A B A B
Logical
hierarchy D C

5. VAN Contributions Enable applications to configure network
Algorithm that maps VAN specification to physical resources
Acquire distributed node and link resources
Deadlock-free VAN resource provisioning protocol
Recover from underlying network failure
Protocol that preserves VAN service semantics under failures

6. VAN Service Arch Components
VAN Local Manager (VLM)
Manages local node resources
Supports deadlock-free VAN provisioning
Monitors & reports resource status
VAN Domain Server (VDS)
Provides VAN services to application
VAN provisioning
Resource acquisition
Performance monitoring
Manages VAN to recover from physical network failure
Active node with VLM
AS3
AS1 D
AS2 C
VDS
VDS
VDS administrative domain
AS4
AS5 A B

7. Specification Mapping
Heuristic mapping algorithm
Sort VNs and PNs by degree; map VN to PN by degree-order
Mark all PL without enough bandwidth for the VLs as infeasible
Each PL has a “mapped-onto” counter, initially 0
pick a VL and map it to a physical path with lowest maximum counter among all PLs traversed
After each VL is mapped, increment counter and subtract available bandwidth for each PL; mark a PL infeasible as appropriate
Repeat until all VLs are mapped
AS3
AS1 1 2 D
1mbps
AS2 A B 1 C
1mbps
1mbps 1 1 D C
AS4
1mbps
AS5 1 A B

8. Resource Acquisition Protocol
Acquires node and link resources
Intra-domain: VDS – VLM
Inter-domain: VDS – VLM and VDS – VDS
Deadlock among competing VANs for shared resources can occur because
One VAN is built in many domains distributedly
Many VANs are built in many domains simultaneously
Example
VDS1 and VDS2 build VAN1 and VAN2 in domain A respectively
VDS3 and VDS4 build VAN1 and VAN2 in domain B respectively
VAN1 preempts VAN2 in domain A
VAN2 preempts VAN1 in domain B B A
VDS4
VDS3
VDS2
VDS1
VAN1
VAN2
VAN1
VAN2
VLM2
VLM1

9. Deadlock Prevention Protocol
How does the solution work
Assign “weight” to VNs and VLs
Each VDS computes a “Progress Index” (PI), indicating “how much” a VAN has been built
PIs are globally synchronized and used as the priority for preemption when conflict happens 1
VDS’es request resource
VLM detects conflict and initiates arbitration 2
VDS broadcasts to all other VDS’es requesting global PI synchronization 3 4
Other VDS’es ack sync request 5
VDS’es ack arbitration request 6
VLM notifies VDS’es with the arbitration decision

10. Failure Recovery
When a physical link fails, the VLs it carries must be restored
First try Local repair
Find an alternative path with adequate resources between the two disconnected AS’es
Fast, and preserve original topology
But
May violate reliability constraint
Alternative path may not exist
Example
Physical link between 2 and 3 goes down
Alternative path goes through 2, 1, 4, and 3 2 2 1 1
Physical link
Reliability
violation 3 3
Virtual link 4 4 5 5 6 6

11. Failure Recovery: Global Repair
Local repair may violate reliability constraints or it may not be able to find an alternative path
Global repair
Computes substitute VL based on global topology and resource information
Reconstruct topology when local repair cannot; guarantee reliability constraint
But
Computationally expensive
Communication delay between root VDS and local VDS’es
Example
Substitute VL computed between 5 and 6, replacing the VL going through 2, 1, 4, and 3
VDS1
VDS1 2 2 1 1
Physical link 3 3
Virtual link 4 4
VDS3
VDS3 5 5 6 6
VDS2
VDS2

12. Schedule
End of Spring 2000
Efficiently obtain global topology and resource information
Summer 2000
(first half)
Heuristics for virtual specification to physical network mapping with constraints
(second half)
Algorithm for computing dynamic priority (PI) and analyze conflict resolution protocol
Fall 2000
Efficient local repair mechanism (study MPLS fast rerouting, ATM self-healing, etc.)
Incremental global repair mechanism