Minimum Number of TCP Sessions for H.323 Call using Slow Start

C.

H.323 has two modes of operation: slow start and fast start.

The initiation of a call may proceed in a slow start or fast start in H.323

In a slow start, H.323 signaling consists of Setup, Call Proceeding, Alerting, and Connect steps.

After these steps, the H.245 media negotiation is performed.

When a call is initiated in H.323 fast start, the H.245 media negotiation is performed within the initial Setup message.

With slow start, multiple TCP connections are needed for an H.323 call, such as one H.225 signaling channel and one H.245 signaling channel if required (minimum of these two).

To understand the minimum number of TCP sessions needed to complete an H.323 call between two H.323 gateways using slow start, we need to understand the H.323 protocol and the concept of TCP slow start.

H.323 is a protocol used for real-time multimedia communication over IP networks. It is commonly used for video conferencing, voice over IP (VoIP), and other multimedia applications. H.323 uses TCP as its transport protocol for call signaling and media control.

TCP slow start is a mechanism used by TCP to avoid congestion in the network. When a TCP connection is established, the sender starts sending data at a low rate and gradually increases the rate until it reaches the maximum allowed by the network. This gradual increase is known as slow start.

Now, coming back to the question, the minimum number of TCP sessions needed to complete an H.323 call between two H.323 gateways using slow start is 3.

Here's why:

1. The first TCP session is established between the H.323 endpoints for call signaling. This TCP session is used to exchange messages such as setup, call proceeding, alerting, and connect messages. This TCP session is set up using the slow start mechanism.

2. Once the call signaling is complete, a second TCP session is established for media control. This TCP session is used to exchange messages such as flow control, congestion control, and feedback messages. This TCP session is also set up using the slow start mechanism.

3. Finally, a third TCP session is established for the actual media stream. This TCP session is used to transport the audio or video data between the H.323 endpoints. This TCP session is also set up using the slow start mechanism.

Therefore, the minimum number of TCP sessions needed to complete an H.323 call between two H.323 gateways using slow start is 3. Option D (3) is the correct answer.