Link layer fragmentation in packet based Radio Access Networks

3G Radio Access Networks (RANs) generally have to transport traffic with a variety of heterogeneous Quality of Service (QoS) requirements. In today’s 3G RANs, Asynchronous Transfer Mode (ATM) technology is used to provide the desired QoS. However, packet based RANs have been subject to recent standardization. In this case, Differentiated Services can be deployed to offer the required QoS using priority queuing or weighted techniques to implement services for packets of various priorities. In such networks, the transmission of relatively large packets (as opposed to ATM cells) on Plesiochronous Digital Hierarchy (PDH) links like E1 entails the problem of large low-priority non-urgent packets blocking high-priority urgent packets. This problem can be tackled by link layer fragmentation. This paper studies the quantitative benefit of fragmentation. Since the analytical model for M |G|1 priority queuing with fragmentation only allows for the derivation of mean response times being of limited use for network dimensioning, an ns-2 simulation has been deployed with which the complete response time distributions can be obtained. The results provide essential information for a trade-off between delay on the one hand and fragment size and link utilization on the other hand.