Packet Switching: Datagrams and Virtual Circuits
Packet Switching
Switching is a technique that helps us make efficient use of physical links in a network of computers. There are two basic techniques:
Datagram
- Technical Datagram: Each packet fragment is sent with sufficient information, such that the network can simply route the fragment to the data terminal equipment.
- Considered the most sensitive method.
- No call setup phase.
- The passing of data is more secure.
- Not all packets follow the same route.
- Packets can reach the destination in disarray because their treatment is independent.
- A packet can be destroyed in transit, whose recovery is the responsibility of the destination station.
Virtual Circuits
- Technical Virtual Tours: It is a communication system whereby a user data source can be transmitted to another user station, through more than one real communications circuit during a certain period of time, but in which the switching is transparent to the user.
- They are the most used.
- Its operation is similar to circuit-switched networks.
- Prior to the transmission, a path is established through a packet call request and call accepted. There is the exchange of data, and once completed, a liberation request packet is presented.
- Each packet has a virtual circuit identifier instead of a destination address.
- The packets are received in the same order they were posted.
Packet
A group of information that consists of two parts: the actual data and control information, which specifies the path to follow along the network to the destination of the packet.
- Propagation Delay: Time in passing information between nodes.
- Transmission Time: Time it takes the transmitter to send the block.
- Node Delay: Time a node takes for switching.
Other Features
Circuit Switching
- Transparent service and constant speed.
- Suffers delay due to call setup.
- Analog or digital data ranging from origin to destination.
Packet Switching
- The data must be converted from analog to digital through a virtual circuit before transmission.
- Has extra bits on.
- There is a delay before the transmission.
Datagrams
- Their arrival is in a different order.
- There is no call setup.
External and Internal Operations
- Depends on the specific objectives in designing the network and the cost of priority.
- The most important feature of a packet-switched network is the use of datagrams or virtual circuits.
External Virtual Circuit
- It provides a logical connection between two stations. The packets are marked with a virtual circuit number and a sequence, the packets are received in order.
Internal Virtual Circuit
- A route is defined and marked for packets between two stations. All packets of the virtual circuit follow the same route and the destination is received in order.
External Datagram
- Each packet is transmitted independently, labeled with a destination address, and received in a disorderly way.
Internal Datagram
- The network treats each packet independently. The packets are marked with a destination address and can be received in a disorderly way at the destination node.
Routing
Routing is how to establish an optical path to select an instance of communication from one source to a destination.
Requirements:
- Accuracy
- Impartiality
- Optimization
- Robustness
- Efficiency
- Simplicity
- Stability