Connection-Oriented Networking and ATM

ATM is the only technology which meets the common goal of LAN and WAN.
It uses connection oriented networking.
It provides universal service of audio, video to its customers.

ATM Design and Cells

Jitter

It means variance in transmission delays.

Packet Sizes

Large packets cause fewer overheads because a very small portion is used for header information.

Optimum networks use 4 KB packet size.
Larger ones cannot be used for audio.
Example: If the speed is about

\[s = \frac{125 \micro seconds}{sample}\]

Then to fill one 4 KB packet (assuming each sample is of 8-bit).

\[\frac{125 \micro seconds}{sample} \times 8 \times 4 \times 1000 bits\]

\[\frac{125 \micro seconds}{sample} \times 4 \times 1000 \left(8 bits\right)\]

\[\frac{125 \micro seconds}{sample} \times 4 \times 1000 samples\]

\[0.5 seconds\]

ATM Cells

Each cell has 53 octets.
VPI/VCI fields identify the cells destination.
ATM header is about 10% of the cell.
Engineers sometimes call the ATM overhead as cell tax.

Connection-Oriented Service

This paradigm is similar to how telephones are used.
In data communication, a binary connection identifier is given to both parties (caller and receiver) to identify the connection.

Virtual Channel (or Circuits)

The connections in ATM are called virtual circuits since these are not physical connections but rather depend on the starting values in memory (tables).

The VC (virtual channel) is 24-bit and consists of 2 parts: 1. Virtual Path Identifier (VPI, 8-bit) which identifies a particular path through the network 2. Virtual Channel Identifier (VCI, 16-bit) which identifies the channel in the virtual path being used by the connection.