Cells Vs Packets
ATM designers choose cells over packets because:
1. Cells are fixed sized and do not cause memory fragmentation and are simpler to manage.
2. Since packets are of variable lengths, they need additional data to indicate the start and the end. With cells, we can just count them as they arrive.
3. Since the packet sizes are variable, there have to be complex interrupt schemes because they take variable times to complete the transmission.
ATM Speed
ATMs are designed to operate with optical fibers but can also work with twisted wired pair.
The throughput speed is OC-3 (155Mbps).
ATM Critique
- ATM is far more expansive than the typical LAN hardware.
- Connection setup time may be excessive for short communications.
- Call tax consumes 10% of network capacity.
- QoS requirements might be unknown, leading to applications picking values that are too high or too low.
Network Ownership
There are 2 categories
Private Network
This is also called intranet and is usually a LAN technology, owned by single or multiple organizations.
Private Network Architecture
It usually includes one or few closely managed external connections.
They may restrict access at connections.
Managing Private Network
An organization buys hardware and hires staff to design, implement and manage the networks.
Extending Private Network
The large organizations may have separate campuses.
They can install cables on their own property.
They can also contact leased lines for common carrier.
Public Network
This is owned by common carrier such as a phone company.
These are networks which are managed by common carriers by using leased lines.
| Networks | Advantages | Disadvantages |
|---|---|---|
| Public | They are flexible | There is no decision making equipment or policies |
| Private | The owner has complete control over technical decision and policies | They are expensive to install and maintain |