• Connection Admission Control (CAC)

• Network Admission Control (NAC)

Connection admission control (CAC) is a set of actions and permissions in network communication that identifies where the connection is permitted on the basis of network ability. This designed set of network actions is initiated during the call setup or when calls are reconnected. It is based on a simple algorithm used to discriminate the incoming or outgoing network traffic. CAC is also used to decide which traffic should be allowed or rejected by a specific network. CAC is most often used in ATM networks.

It is also known as call admission control.

In terms of communication, the existence of CAC is common, especially in network-oriented connections (CAC does not provide any service to connectionless networks). In addition, in connection-oriented networks, CAC plays an important role, particularly for congestion control.

The basic role of connection admission control in connection-oriented networks is to decide whether there are enough free system resources available before establishing a new connection. An end-to-end connection is only established when the availability of free resources is assured.

CAC performs the following two operations while establishing a connection:

1. It establishes a connection when resources are free and available.

2. If the connection is rejected in the absence of free/available resources, a notification is sent back to the originator or requester of the call or connection.

The following factors are to be considered when establishing or requesting a connection:

• The type of service required

• Traffic parameters (source traffic parameters are analyzed)

• Both directions request their required Quality of Service (QoS), which is also considered when establishing a connection.

To ensure that the quality is the most important step control access of incoming data flows. This control is provided by AC method. The main purpose of these methods is to estimate the expected bandwidth for the incoming data stream and determine whether it is possible to assign needed bandwidth and effectively use of resources, to avoid congestion. AC methods are most used for delay-sensitive and jitter-sensitive services, respectively, for real-time applications. There are a lot of admission control methods, and their difference consists mainly in the different types of operation and method of implementation. Some AC methods are based on mathematical calculations and statistical indicators, others on measuring traffic.

In general, the control methods are represented by two categories: parameter based admission control (PBAC) and measurement based admission control (MBAC). PBAC method is based only on the current active traffic and on the characteristics of the total active traffic. This method may not be optimal, because it does not rely on a new incoming traffic. MBAC method does not specify for obtaining the parameters of the source, but to make measurements on the network running in real time. This method achieves higher network utilization because serving a new data flows in network is common. Common criteria of admission control methods are the ability to allocate bandwidth for all actual data flows in case of not exceeding the total capacity of the line. It is very important that the nodes on which the method is applied to are in direct contact with QoS parameters (e.g., delay, loss rates). The result is QoS produced by algorithm, which should be independent of traffic type and should be as close to the desired value as it is possible. In this case it is not necessary that an administrator has to change the AC algorithm value in case of changing the traffic type.

1. Parameter-Based Admission Control

PBAC may be preferred because of their ease of implementation in network management. They work with parameters such as peak or the effective bandwidth of incoming data flow instead of the values measured in the network. Using PBAC methods is possible to avoid the limitations incurred by measuring and monitoring the network. In these methods, there may be unequal use of network resources when some data flows are often idle or sending at the top transmission rates. In this case, the new data stream may be rejected even though it would not affect the QoS of ongoing data flows .

2. Measurement-Based Admission Control

MBAC methods use measurement of the current state of network traffic, if present, to support the incoming data flow. MBAC methods perform decision-making process, which depends on the measurement of the traffic and QoS parameters. In case of measuring and monitoring the network, we can more effectively use resources (compared to PBAC). MBAC methods offer the possibility of providing QoS to priori data flows. When compared to the PBAC methods, MBAC methods are adaptive, since measurement is performed at specific intervals, and so there is no waste of resources