Virtual Active NetworksVirtual Active Networks

Gong SuMar. 9, 2000

Network Computing ModelsNetwork 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-ComputingVAN: Middleware for Edge-Computing

VAN is a middleware architecture that enables applications to

Configure network topology Allocate node and link resources

A Driving ExampleA 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

A

D C

BAS1

AS2

AS5 AS4A

AS3

B

C

D1mbps

1mbps 1mbps

Virtual spec.Physical network

Mappingby VAN

A

D C

B

1mbps

Logicalhierarchy

VAN ContributionsVAN 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

VAN Service Arch ComponentsVAN 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

AS1

AS2

AS5 AS4A

AS3

B

C

D

VDSVDS

VDS administrative domain

Active node with VLM

Specification Mapping Specification Mapping Heuristic mapping algorithm

A

D C

BAS1

AS2

AS5 AS4A

AS3

B

C

D1mbps

1mbps 1mbps

1mbps

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

0

0

0

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

1

Repeat until all VLs are mapped

1

1

1

01

2

Resource Acquisition ProtocolResource 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

VDS1 VDS2

VLM1

VDS3 VDS4

VLM2VAN1

VAN1VAN2

VAN2

AB

Deadlock Prevention ProtocolDeadlock Prevention Protocol

VDS1VDS2

VDS3VDS4

VLM1

VLM2

AB

VAN1:3VAN1:7

VAN2:6

VAN2:2

VDS1VDS2

VDS3VDS4

VLM1

VLM2

AB

1 12 2

3

3

4

4

VDS1VDS2

VDS3VDS4

VLM1

VLM2

AB

5 56 6

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

1VDS’es request resource

2

3

4

5

6

VLM detects conflict and initiates arbitration

VDS broadcasts to all other VDS’es requesting global PI synchronizationOther VDS’es ack sync request

VDS’es ack arbitration request

VLM notifies VDS’es with the arbitration decision

Failure RecoveryFailure 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

4

12

5

3

6

4

12

5

3

6

Reliabilityviolation

Physical link

Virtual link

Failure Recovery: Global RepairFailure 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

4

12

5

3

6

4

12

5

3

6

VDS1

VDS2

VDS3

VDS1

VDS2

VDS3

Physical link

Virtual link

ScheduleSchedule

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