Question

Datagram networks route each packet as a separate unit, independent of all others. Virtual-circuit networks do not have to do this, since each data packet follows a predetermined route. Does this observation mean that virtual- circuit networks do not need the capability to route isolated packets from an arbitrary source to an arbitrary destination? Explain your answer.

Short answer

Virtual-circuit networks do not need the capability to route isolated packets traditionally, as they use predetermined routes. However, they require some mechanism to reroute if issues arise during transmission.

Step-by-step solution

Understanding Datagram Networks

In datagram networks, each packet is routed independently of the others. This means that packets from the same message may take different paths to reach the destination and can arrive out of order. Their routing decisions are made dynamically at each router based on the current network state.

Understanding Virtual-Circuit Networks

Virtual-circuit networks establish a predefined path before data transmission begins. Once a virtual circuit is established, all data packets follow the same path in sequence, maintaining order and potentially making routing decisions more efficient.

Examine Packet Routing Needs

Since virtual-circuit networks have a designated path for data packets, unlike datagram networks, there may be less need for mechanisms to route individual packets to arbitrary destinations. They rely on pre-established routes for a series of packets.

Evaluating the Need for Isolated Packet Routing

While virtual-circuit networks do not rely on routing each packet individually under normal circumstances, they should still maintain a capability to reroute in cases of network failure or changes. However, the primary operation does not require routing isolated packets from arbitrary sources to arbitrary destinations under normal conditions.

Key concepts

Understanding Datagram Networks

In a datagram network, each packet is an independent traveler. It can choose its path like a solo explorer deciding which road to take. This means each packet within the same message can arrive through different routes, sometimes even appearing out of order when finally reaching its destination.
This system mimics how traditional mail is sent: every letter or parcel might take a different truck or plane, depending on the traffic and road conditions at the moment.

• Each packet has complete freedom and routes are determined dynamically.
• Network traffic and conditions at each intermediate router inform routing decisions.
• There is a need for more robust error checking and packet reordering at the receiver's end due to potential for packets arriving in any sequence.

In practice, this means datagram networks require dynamic decision-making at every step of the way, which can be both a strength and a complexity when managing large networks.

Exploring Virtual-Circuit Networks

Virtual-circuit networks take a different approach by setting a single, predetermined path right from the start. This is akin to booking a flight itinerary where all segments are predetermined before the journey begins.
Before any packets are sent, the path is reserved, and all packets follow in the exact same footsteps, ensuring they arrive in order.

• Once a virtual circuit is established, the network doesn’t need to make new decisions for each packet.
• This setup can enable more efficient use of resources as the path's expectations are managed.
• It resembles a train moving on fixed tracks, ensuring predictable arrival times and sequence.

However, while virtual-circuit networks excel in maintaining order and predictability, they still need some flexibility for rerouting if a snag or failure occurs on the predefined path.

The Mechanics of Packet Transmission

Packet transmission is the process by which data is sent from one node to another across a network. Regardless of the network type, understanding how packets are transmitted is essential. In both datagram and virtual-circuit networks, packets consist of control information and raw data, known as payload.

• In datagram networks, packets "talk" to the router every step of the way, allowing them flexibility but requiring routers to be communicative and adaptable.
• Conversely, in virtual-circuit networks, once a path is set, packets "relax" and proceed, assured that their route is pre-set and disruptions rare but possible.

Efficient packet transmission is vital for ensuring data integrity and performance. As data is segmented into packets, properly managing these packets becomes key to maintaining the seamless operation of a network—like ensuring each box in a conveyor belt reaches its destination smoothly and in sequential order.