Virtual Active Networks
Gong Su
Mar. 9, 2000
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
VAN: Middleware for Edge-Computing

VAN is a middleware architecture that enables
applications to


Configure network topology
Allocate node and link resources
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
Virtual spec.
A
1mbps
B
1mbps
D
Logical
hierarchy
AS1 D
C AS2
1mbps
1mbps
C
A
B
D
C
Mapping
by VAN
AS5 B
A AS4
AS3
VAN Contributions

Enable applications to configure network


Acquire distributed node and link resources


Algorithm that maps VAN specification to physical resources
Deadlock-free VAN resource provisioning protocol
Recover from underlying network failure

Protocol that preserves VAN service semantics under
failures
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
C AS2
VDS
VDS
AS5 B
A AS4
VDS
administrative
domain
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
A
1mbps
AS1 D
B
1mbps
D
C AS2
1mbps
1mbps
AS3
0
1
2
0
1
0
1
1
0
C
AS5 B
0
1
A AS4
Resource Acquisition Protocol

Acquires node and link resources



Deadlock among competing VANs for shared resources can occur
because



Intra-domain: VDS – VLM
Inter-domain: VDS – VLM and VDS – VDS
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
VDS2
VDS1
VAN1
VLM1
VAN2
VDS3
VDS4
VAN1
VAN2
VLM2
Deadlock Prevention Protocol
B
A

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
1 VDS’es
happens
request resource
VDS2
VAN1:3
6 VLM notifies VDS’es with the
arbitration decision
VLM2
VAN2:6
VLM1
B
4
A
3
VDS2
1 2
2
3
4
1
VDS4
VDS3
VDS1
2 VLM detects conflict and
initiates arbitration
5 VDS’es ack arbitration request
VAN2:2
VAN1:7

3 VDS broadcasts to all other
VDS’es requesting global PI
Other VDS’es ack sync request
4 synchronization
VDS4
VDS3
VDS1
VLM2
VLM1
B
A
VDS4
VDS3
VDS1
VDS2
5 6
6
VLM1
5
VLM2
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
1
Physical link
Virtual link
3
4
5
6
2
1
Reliability
violation
3
4
5
6
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
VDS1
through 2, 1,VDS1
4, and 3 2
2
1
1
Physical link
3
4
Virtual link
5
VDS2
VDS3
6
3
4
VDS3
5
VDS2
6
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
Summer 2000
(second half)
Algorithm for computing dynamic priority (PI)
and analyze conflict resolution protocol
Fall 2000
(first half)
Efficient local repair mechanism (study MPLS
fast rerouting, ATM self-healing, etc.)
Fall 2000
(second half)
Incremental global repair mechanism