Unicast, Multicast, Multiple Unicast, and Broadcast
Unicast, Multicast, Multiple Unicast, and Broadcast
1. Unicasting
Unicasting is one-to-one communication.
- There is one source and one destination.
- A packet is sent to a single destination host.
- At each router, the packet is normally forwarded through one interface toward the destination.
Example:
A student sends a message to one particular student.
Communication:
One Source → One Destination
2. Multicasting
Multicasting is one-to-many communication.
- There is one source and a group of destinations.
- The source sends only one packet with a multicast group address.
- Routers duplicate the packet only when necessary to deliver it to different networks containing group members.
- Only one copy of the packet normally travels over a link between two routers.
Example:
A professor delivers the same online lesson simultaneously to a group of registered students.
Communication:
One Source → A Group of Destinations
3. Multicasting vs Multiple Unicasting
| Feature | Multicasting | Multiple Unicasting |
|---|---|---|
| Communication | One-to-many | One-to-many using separate unicast packets |
| Packets created by source | One packet | Multiple packets |
| Destination address | Same multicast group address | Different unicast address for each destination |
| Packet duplication | Done by routers when required | Done by the source/application |
| Bandwidth usage | More efficient | Less efficient |
| Traffic on common links | Only one copy normally travels | Multiple copies may travel |
| Delay | Less delay between receivers | Delay may occur when sending many packets |
Simple Example
Suppose one source wants to send the same information to three destinations: D1, D2, and D3.
Multiple Unicasting
The source creates:
- Packet → D1
- Packet → D2
- Packet → D3
So, three separate packets are transmitted.
Multicasting
The source creates:
- One multicast packet → Group G1
The routers copy the packet only at places where the network branches toward group members.
Main Advantage of Multicasting
Multicasting is more efficient because:
- It uses less bandwidth.
- The source creates only one packet.
- Routers create copies only when necessary.
- There is less delay when delivering information to a large number of receivers.
4. Applications of Multicasting
According to the textbook content, important applications include:
1. Access to Distributed Databases
A database request can be multicast to several database locations.
- The user may not know where the required information is stored.
- The request is sent to all relevant locations.
- The location containing the information responds.
2. Information Dissemination
A business can send the same information to many customers.
Examples:
- Software updates
- News distribution
- Common announcements
Instead of sending separate copies to every customer, one multicast transmission can be used.
3. Teleconferencing
In a teleconference, all participants need to receive the same information at approximately the same time.
Multicasting is therefore suitable for:
- Online conferences
- Group meetings
- Video communication
4. Distance Learning
A lesson taught by one professor can be delivered to a specific group of students simultaneously.
Example:
One professor → Many students in different locations
5. Broadcasting
Broadcasting is one-to-all communication.
- One host sends a packet to all hosts in a network or domain.
- Broadcasting to the entire Internet is generally not provided because it could create a huge amount of traffic and consume excessive bandwidth.
- However, partial or controlled broadcasting may be used in limited situations.
Communication:
One Source → All Hosts
Summary
| Communication Type | Relationship |
|---|---|
| Unicast | One-to-One |
| Multicast | One-to-Many (group) |
| Multiple Unicast | One-to-Many using separate packets |
| Broadcast | One-to-All |
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