MCR Minimum Cell Rate

MCR (Minimum Cell Rate) is a parameter used in ATM (Asynchronous Transfer Mode) networks to define the minimum guaranteed bandwidth that a connection or a virtual channel (VC) should receive. It is an important parameter used in traffic management to ensure that each connection or VC gets the bandwidth required to transmit its data with minimal delay and jitter.

In this article, we will discuss in detail the concept of MCR, its importance in ATM networks, and its implementation.

What is MCR?

MCR is the minimum rate of data transfer that is guaranteed for a connection or a virtual channel (VC) in an ATM network. It represents the guaranteed minimum bandwidth that a connection or VC can receive under any network condition. It is expressed in cells per second (cps).

MCR is an important parameter in traffic management in ATM networks. It is used to allocate network resources to different connections or VCs based on their bandwidth requirements. MCR ensures that each connection or VC gets the minimum required bandwidth to transmit its data without any delay or jitter. It also prevents over-subscription of network resources, which can lead to congestion and performance degradation.

Importance of MCR

MCR is a critical parameter in ATM networks. It is essential to ensure that the network resources are utilized efficiently and fairly among the connections or VCs. The following are the key benefits of MCR:

2.1 Quality of Service (QoS)

MCR is an important parameter for providing Quality of Service (QoS) in ATM networks. It ensures that each connection or VC gets the guaranteed minimum bandwidth required for its transmission, regardless of the network conditions. This guarantees a certain level of service quality for each connection or VC, which is important for applications that require a consistent and reliable data transfer rate, such as voice and video.

2.2 Fairness

MCR ensures fairness in resource allocation among different connections or VCs in ATM networks. It guarantees that each connection or VC gets the minimum required bandwidth, regardless of the network conditions. This prevents some connections or VCs from consuming more resources than others, which can lead to unfairness and poor network performance.

2.3 Congestion Management

MCR is an important parameter for managing network congestion in ATM networks. It ensures that each connection or VC gets the minimum required bandwidth, even under heavy network traffic. This prevents over-subscription of network resources, which can lead to congestion and performance degradation.

2.4 Resource Utilization

MCR ensures efficient utilization of network resources in ATM networks. It guarantees that each connection or VC gets the minimum required bandwidth, regardless of the network conditions. This prevents wastage of network resources and ensures that they are used efficiently.

Implementation of MCR

MCR is implemented using traffic shaping and policing mechanisms in ATM networks. Traffic shaping is a mechanism that regulates the traffic flow by delaying or buffering excess traffic to meet the MCR requirement. Policing, on the other hand, drops the excess traffic that exceeds the MCR requirement.

3.1 Traffic Shaping

Traffic shaping is a mechanism used to regulate the traffic flow and enforce the MCR requirement. It buffers or delays excess traffic to ensure that the transmission rate of each connection or VC does not fall below the MCR value. Traffic shaping is implemented using a token bucket algorithm.

The token bucket algorithm works as follows. A token bucket is used to store tokens at a constant rate. Each token represents a fixed amount of data, typically one cell. The tokens are used to allow or disallow data transmission from a connection or VC. When a connection or VC wants to transmit data, it must first request a token from the token bucket. If the token bucket has tokens, it grants the request, and the data can be transmitted. If the token bucket is empty, the request is denied, and the data is buffered or delayed until a token becomes available.

The token bucket algorithm ensures that the transmission rate of each connection or VC does not exceed the MCR value. It limits the transmission rate by regulating the rate at which tokens are generated in the token bucket. If the token bucket becomes full, the excess tokens are discarded. This ensures that the transmission rate does not exceed the MCR value.

3.2 Policing

Policing is a mechanism used to drop excess traffic that exceeds the MCR requirement. It ensures that each connection or VC does not consume more bandwidth than the MCR value. Policing is implemented using a leaky bucket algorithm.

The leaky bucket algorithm works as follows. A leaky bucket is used to store cells at a constant rate. Each cell represents a fixed amount of data, typically 53 bytes. The cells are used to determine whether a connection or VC is transmitting data at a rate higher than the MCR value. The leaky bucket is set to the MCR value, and any excess cells are dropped.

If a connection or VC is transmitting data at a rate higher than the MCR value, the leaky bucket fills up, and the excess cells are dropped. This ensures that the transmission rate does not exceed the MCR value. Policing can be implemented at various points in the network, such as at the edge of the network or at the core.

Conclusion

MCR is an important parameter used in ATM networks to ensure that each connection or VC gets the minimum guaranteed bandwidth required for its transmission. It is essential for providing Quality of Service (QoS), fairness, congestion management, and efficient resource utilization in ATM networks. MCR is implemented using traffic shaping and policing mechanisms, which regulate the traffic flow and drop excess traffic that exceeds the MCR requirement. MCR is a critical parameter in ATM networks and is essential for ensuring optimal network performance and user experience.