Figure 7-8: Virtual circuit Operation Virtual Circuit Sw itch a Sw itch b Frame w ith VC Number 47 Sw itch c Sw itch d The internal cloud network is a mesh of switches Sw itch a Sw itching table Virtual circuit port This creates multiple alternative paths 47 270 982 2331 This gives reliability 5 7-16
7-16 Figure 7-8: Virtual Circuit Operation Virtual Circuit Virtual Circuit Sw itch A Sw itching Table Virtual Circuit Port 47 2 270 3 982 3 5 1 Sw itch A Sw itch B Sw itch E Sw itch C Sw itch D Server Frame w ith VC Number 47 The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability
Figure 7-8: Virtual circuit Operation Virtual Circuit Sw itch a Sw itch b Frame w ith VC Number 47 Sw itch c Sw itch d Mesh switching is slow because each switch must evaluate Sw itch a Sw itching table Virtual circuit port available alternative paths and select the best one 47 270 982 2331 This creates expensive switching 5 7-17
7-17 Figure 7-8: Virtual Circuit Operation Virtual Circuit Virtual Circuit Sw itch A Sw itching Table Virtual Circuit Port 47 2 270 3 982 3 5 1 Sw itch A Sw itch B Sw itch E Sw itch C Sw itch D Server Frame w ith VC Number 47 Mesh switching is slow because each switch must evaluate available alternative paths and select the best one. This creates expensive switching
Figure 7-8: Virtual Circuit Operation Before communication begins between sites, the Psdn computes Virtual Circuit a best path called a virtual circuit Frame w ith Sw itch a All frames travel along this virtual circuit VC Number 47 Sw itch c Sw itch d Circuit Sw itch a Sw itching table Sw itch e Virtual circuit port Server 47 270 982 2331 5 7-18
7-18 Figure 7-8: Virtual Circuit Operation Virtual Circuit Virtual Circuit Sw itch A Sw itching Table Virtual Circuit Port 47 2 270 3 982 3 5 1 Sw itch A Sw itch B Sw itch E Sw itch C Sw itch D Server Frame w ith VC Number 47 Before communication begins between sites, the PSDN computes a best path called a virtual circuit. All frames travel along this virtual circuit
Figure 7-8: Virtual Circuit Operation Virtual Each frame has a virtual circuit number Circuit instead of a destination address Switch a Frame w ith VC Number 47 Each switch looks up the vc number in its switching table sends the frame out the indicated port MCs greatly reduce switching costs Sw itch d e Circuit Sw itch a Sw itching table Sw itch e Virtual circuit port Server 47 270 982 2331 5 7-19
7-19 Figure 7-8: Virtual Circuit Operation Virtual Circuit Virtual Circuit Sw itch A Sw itching Table Virtual Circuit Port 47 2 270 3 982 3 5 1 Sw itch A Sw itch B Sw itch E Sw itch C Sw itch D Server Frame w ith VC Number 47 Each frame has a virtual circuit number instead of a destination address. Each switch looks up the VC number in its switching table, sends the frame out the indicated port. VCs greatly reduce switching costs
Public switched data Networks(PSDNs) Frame Relay ATM Metropolitan area ethernet Carrier P Networks
Public Switched Data Networks (PSDNs) Frame Relay ATM Metropolitan Area Ethernet Carrier IP Networks