Performance Measures

The performance measures are the Channel Throughput (TPC) and the Average Transmission Delay (DAVG). The Average Queue Length (LAVG) of the mobile's buffer illustrates the effects on CBR traffic. The performance parameters are defined as follows:

1. Channel Throughput (TPC): TPC is defined as the ratio of the total number of transmitted packets and the total number of time slots. That is, TP C = Pt/Ttl , where PT is denoted as the total number of transmitted packets, and Ttl is denoted as the total number of time slots. The TPC is measured as the number of packets transmitted per time slot.

2. Average Transmission Delay (DAVG): DAVG is defined as the ratio of the total packet transmission delay and the number of active mobiles. Hence, DAVG = DTL/M, where DTL is the total packet transmission delay and M is the number of active mobiles. DTL is the sum of each packet transmission delay in every active mobile. Each delay is defined as the time (number of time slots) taken, when a packet first arrives at the mobile's buffer to the time the packet reaches the BS. DAVG is measured by the number of time slots.

3. Average Queue Length (LAVG): LAVG is defined as the ratio of the total number of packets in all the mobiles' buffer and the number of active mobiles. Thus, LAVG = LTl/M, where LTl is the total number of packets in all the mobiles' buffer, and M is the number of active mobiles. LAVG is measured by the number of packets.

Protocol design goal is to reduce DAVG while maintaining a reasonable TP C. ARCMA protocol offers better performance in terms of channel throughput and average delay under most traffic conditions. It provides better overall channel utilization by reducing contention in the RA channels. Depending on the delay tolerance of the traffic, ARCMA can achieve very high TPC. Future high-speed cellular networks (e.g., picocell) may provide a higher delay (in time slots) tolerance enabling throughput of over 90% under suitable traffic conditions.

ARCMA protocol is designed to efficiently share the limited spectral resources of a wireless network. With the proliferation of multimedia portables, support for integrated multimedia traffic is increasingly important. In addition to the limited wireless bandwidth, new protocols are required to support real-time delay-sensitive traffic. ARCMA protocol is designed to handle some of these requirements in the MAC sublayer. There are few wireless protocols that can satisfy the high bandwidth and low Bit Error Rate (BER) of ATM networks in the wireless environment. Most of them do not provide support for the requirements of different ATM service types. The ARCMA scheme provides better support for delay-sensitive CBR traffic by prioritizing the transmission scheduling policy. In addition, ARCMA improves channel utilization by reducing collision in the request subchannel. ARCMA protocol provides request-free transmission for CBR and bursty traffic (within the same burst). An adaptive request channel can increase the request (without collision) probability by exploiting idle TA channels.

ARCMA performs better than DQRUMA regardless of the traffic load. Under heavy traffic, ARCMA protocol is capable of producing significantly higher channel throughput than DQRUMA. The worst traffic scenario for ARCMA protocol is nonbursty (single packet burst) traffic. Every packet arrival requires transmission request, causing heavy collisions in the RA channel. Conversely, ARCMA performs extremely well with bursty traffic (e.g., VBR) capable of achieving over 85% channel throughput with limited transmission delay. The CBR extension enables ARCMA to satisfy the delay-sensitive CBR traffic while reducing collisions in the RA channel. This result justifies the added complexity and overhead for CBR support.

Although the ARCMA protocol does not provide direct support to the other timesensitive traffic (e.g., VBR), the strategies implemented in ARCMA protocol significantly reduce contention in the RA channel, allowing such traffic to transmit with less delay. ARCMA provides an efficient DAMA that is practical for implementation in a Wireless ATM (WATM) network. It brings us a step closer to designing a complete protocol suite that could be used in the wireless integration of ATM networks.

ARCMA protocol can be extended to provide direct support for other ATM services such as VBR and ABR traffic. Access delay can be further reduced if there exists a mechanism to specifically handle VBR or ABR mobiles. Such a mechanism alleviates the need for retransmitting requests packets through the RA channel. ARCMA protocol does not include services for network management. To provide a complete MAC sublayer support, we need to include services such as call admission and cell handoff.

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