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Comparison of Virtual-Circuit and Datagram Networks
Virtual-circuit and datagram networks are two fundamental approaches to packet switching in computer networks. In virtual circuits, a virtual path is established between the source and destination systems through which all data packets are transferred. In datagram networks, each data packet contains adequate header information so that they can be individually routed by intermediate network switching devices to the destination.
Key Differences
| Aspect | Virtual-Circuit Networks | Datagram Networks |
|---|---|---|
| Connectivity | Connection-oriented networks requiring setup phase | Connectionless networks with no setup required |
| Path Selection | Fixed path established during setup; all packets follow the same route | Each packet routed independently using dynamic routing tables |
| Resource Allocation | Resources (buffers, bandwidth) reserved in advance for the entire session | Resources allocated on-demand using First-Come First-Serve basis |
| Communication Phases | Three phases: setup, data transfer, and teardown | No distinct phases; immediate packet transmission |
| Header Information | Contains only virtual circuit identifier (VC number) | Contains full source and destination addresses |
| Cost | Higher installation and maintenance costs | Lower cost for installation and maintenance |
| Reliability | More reliable due to guaranteed resources and fixed paths | Less reliable due to dynamic routing and resource contention |
| Complexity | Lower complexity once circuit is established | Higher complexity due to per-packet routing decisions |
| Common Examples | ATM networks, traditional telephone systems | Internet Protocol (IP), UDP-based communications |
How They Work
Virtual-Circuit Network Operation
In a virtual-circuit network, communication follows these steps:
-
Setup Phase − A virtual circuit is established by sending a setup request through the network
-
Data Transfer − All packets follow the predetermined path using the assigned VC number
-
Teardown Phase − The virtual circuit is released when communication ends
Datagram Network Operation
In datagram networks, each packet is treated independently:
-
Individual Routing − Each packet contains complete addressing information
-
Dynamic Path Selection − Routers make forwarding decisions based on current network conditions
-
No State Information − Network devices don't maintain connection state
Advantages and Disadvantages
| Network Type | Advantages | Disadvantages |
|---|---|---|
| Virtual-Circuit | Guaranteed resources, ordered delivery, predictable performance | Higher overhead, setup delay, less flexible to failures |
| Datagram | No setup overhead, flexible routing, fault-tolerant | No delivery guarantees, potential packet reordering, variable delay |
Conclusion
Virtual-circuit networks provide reliable, connection-oriented communication with guaranteed resources but require setup overhead. Datagram networks offer flexible, connectionless communication that's more fault-tolerant but with no delivery guarantees. The choice depends on application requirements for reliability versus flexibility.
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