Summary
In this project, we focused on the control mechanisms in the nodes
of the Universal Mobile Telecommunication System (UMTR) terrestrial
access network (UTRAN). In particular, we studied the following
problems:
- The transport layer of the wireline part in the UTRAN is based
on AAL2/ATM, i.e., streams of UMTS packets are equipped with an AAL2
header and multiplexed back-to-back
into consecutive ATM cells. This works well on a single line, but it
requires the switching of AAL2 packets in the UMTS Mobile Switching
Centers (UMSC). Thus, we developed fast and scalable hardware
algorithms to perform AAL2 multiplexing, ATM cell spacing, and ATM
cell multiplexing in a single unit.
- The Radio Network Controller (RNC) schedules the UMTS packets for
the transmission over the air interface and sends them over the Iub
interface to the NodeB
that just transmits the data. Thus, all traffic from the RNC to the
NodeB has real-time requirements. However, speech and circuit switched
data have even stricter requirements because they should not suffer from
packet loss due to delayed data. Thus, the scheduler at the RNC must
handle several classes of real-time traffic with different delay
requirements. This is basically possible with weighted fair queuing
(WFQ) approaches, but the knowledge of the traffic mix is required for
its configuration which is usually not available in practice.
We developed the Modified Earliest Deadline First (MEDF)
algorithm whose single control parameter can be set in an optimal way
independently of the traffic mix.
- The transport layer in the wireline part of the UTRAN is based on
ATM technology. An AAL2/ATM path is limited to 255 different AAL2 connections.
These require a bandwidth in the order 2 Mbit/s. The corresponding
ATM connection must be spaced according to this bandwidth for transportation
over several network domains although it is
carried over a large STM1 trunk. This can lead to significant
delay in the order of several milliseconds which is not tolerable as
only a small delay budget of 5 ms is allowed for this purpose in the standards.
Therefore, admission control (AC) is required for UTMS connections on AAL2/ATM
paths. We developed suitable AC admission control algorithms
for the multiplexing of speech data compressed by the Adaptive
Multirate (AMR) vocoder and circuit switched data.
- The UMSC offers many features, e.g., to mix different call or for
lawful interception. This makes the internal bandwidth management of
the UMSC more complex and we developed an algorithmic framework to
manage that complexity.
Research results of this project were integrated into Siemens products such as
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