Interworking Units Research Articles

Standardized TTCN-3 specifications for SIP-ISUP/ISDN interworking testing

ETSI technical committee TISPAN currently funds the development of TTCN-3 network integration test suites using TTCN-3. Specialist task forces (STF) have already been initiated to implement and validate abstract test suites focusing on, e.g., SIP/ISUP and SIP/ISDN interworking units. In this paper, we report on our implementation approach and experiences made in the STF on testing interworking between SIP and ISDN/ISUP. Special attention has been given to the reuse of know-how and of existing TTCN-3 code available due to the existing SIP conformance test suite and the TTCN-3 test framework developed by ETSI for IPv6. Validation has been done using the test laboratory of a telecom network provider.

Cost-Efficient Design of Future Broadband Fixed Wireless Access Systems

In future broadband fixed wireless access systems the overall design procedure is critical for their successful commercial deployment as well as their efficient operation and management. The problem addressed in this paper is twofold. Specifically, at a first phase the radio access network planning problem is addressed, which aims at finding the minimum-cost configuration of Access Point Transceivers (APTs) given the geographical layout of the area to be covered. At the second phase, the interconnecting planning problem is addressed and aims at finding the minimum-cost configuration of the Access Point Controllers (APCs) and Inter-Working Units (IWUs) given the Access Point Transceivers layout. Both problems are formally defined, optimally formulated, and solved by computationally efficient heuristics. Finally, results are provided and subsequent conclusions are drawn.

Performance of integrated interlan telephony service over an ATM network

The demand for a seamless interconnection between the end subnetworks using ATM technology is steadily arising in the customer premises. A great demand also exists in enterprise networks for obtaining interLAN telephony service integrated with asynchronous data services. We determine the end-to-end performance of internetworked integrated services ATM LANs by using a simulation based approach. We further demonstrate the feasibility of providing interLAN telephony service integrated with asynchronous data services in internetworked ATM LANs. This entails the implementation of a crucial technique, which we have developed in the interworking units so as to segregate the voice data from the asynchronous data. The end subnetworks considered in case of the integrated services homogenous ATM LANs are IEEE 802.5 LANs, whereas the end subnetworks considered in case of integrated services heterogenous ATM LANs are IEEE 802.5 and the standardised 802.9 (isoEthernet) LANs. A significant issue addressed in this case is the internetworking of the packet based IEEE 802.5 LAN to the 802.9 LAN.

Buffer and bandwidth allocation for TCP data traffic: experimental results

This paper discusses the dimensioning of buffers and the bandwidth allocation for data traffic in the ATM network. Data traffic is notoriously complex and bursty, making such dimensioning a difficult task. However, the COMBINE project, when dimensioning their InterWorking Units (IWUs), adopted a Poissonian packet arrival model, based upon the argument that burstiness at timescales higher than that of a packet arrival are a problem to be tackled by flow control at higher layers. This paper presents experimental results from the COMBINE testbed that show that this hypothesis was justified and that good TCP goodput was obtained based upon this dimensioning approach, due to TCP's ability to adapt to network congestion. However, it is also shown that it was the TCP algorithm that was ultimately responsible for controlling the packet loss ratio in the network and not the bandwidth allocation or buffer size. The results highlight the importance of taking into account the mutual influence between the ATM layer and the transport layer congestion control algorithms.

Adaptive traffic enforcement control mechanism for LANs interconnected by a high-speed network

In this paper, a novel traffic enforcement control scheme is presented. The main aim of this scheme is to regulate the flow of traffic through a high-speed backbone network interconnecting multiple LANs. The scheme is implemented at the interworking units where the traffic from each source-destination LAN pair is monitored and enforced. This scheme aims to provide a fair sharing of the network resources. The interconnection of LANs through high-speed backbone networks is of particular interest as the deployment of this kind of system is seen as one of the most promising architecture to the development of the future Broadband-ISDN.

An adaptive multipath routing scheme for connectionless traffic in an ATM network

This paper addresses the problem of routing connectionless traffic through an ATM network. A solution is proposed based on a per-packet adaptive multipath routing scheme which is added to the routing algorithm implemented at the Inter-Working Units. A scheme is presented that distributes packets among multiple Virtual Paths (VPs) according to the utilization of the links on these VPs. The utilization of the VPs is determined by a periodic feedback mechanism. Simulation studies show the effectiveness of the proposed adaptive multipath routing scheme.

A dual bus approach for LAN interworking with ATM networks

The interworking between conventional legacy LANs and the ATM network plays an important role in the initial step of the ATM roadmap. This paper presents a dual bus approach for connecting LAN interworking units (IWU) to ATM networks. Several IWUs connecting heterogeneous LANs are configured into a dual bus structure and the end of the buses are directly connected to the ATM ports. Each IWU transforms the connectionless frame from the legacy LAN to fixed-length time-slots on the dual bus. To provide reliable connectionless services, a cell-based flow control scheme is proposed for dynamically adjusting the cell input rate so as to match with the current resources in the ATM switch. The scheme is further verified to be able to provide an optimal, best-effort and reliable interconnection scenario through simulations. The results show that the total throughput obtained by each local subnetwork dynamically matches with the cell processing throughput of the ATM switch. Besides, each IWU on the dual bus shares a fair bandwidth.

Interconnection of high-speed data networks: contribution of dynamic control and quality of service

This paper describes the implementation of a functional simulator for the interconnection of heterogeneous high-speed data networks. After trying several approaches, we use the object-oriented conception and language to permit the use of dynamic control of each protocol (FDDI, DQDB, ATM). We studied the most interesting QOS parameters for our context. For the administration aspect of a heterogeneous network, the simulator permits the evaluation of the evolution of the QOS for the interworking units.

Throughput measurements in a 2 Mbps X.25 network

National and international X.25 based networks in Europe (JANET, WiN, IXI) carry rapidly increasing traffic. 2 Mbps access points to the network and increased bandwidth within the networks would contribute to higher speeds. Strong criticism concerning the suitability of X.25 for higher speeds led the DFN Association to investigate the behavior of X.25 for transmission speeds of 2 Mbps and beyond. The test setup consisted of a test environment with workstations connected to an ethernet, the ethernet connected to a test-WAN, a system under test (a public network with two access points, a private network with various commercial switches). With this test setup investigations have been made with different protocol stacks (TCP/IP over X.25 via RFC 877, CONS) and the appropriate LAN attachments (IP-routers, CONS interworking units), different types of switches. Measurements have been performed using analytical test programs at the transport level to determine the throughput as a function of the packet size, applications (e.g. FTP) to determine the benefits for the user. The analytical tests show that a bandwidth of 1.92 Mbps, as offered in public networks, can be filled with 256 byte packets by a number of commercial switches. The maximum throughput achievable for small packets (of length 64) was about 1500 packets/ s or 40% bandwidth utilization. The maximum throughput for FTP using IP/X.25 encapsulation was 230 kByte/s. Investigations showed that the achievable throughput was limited by the workstations used to generate load. Increasing load on a switch (by a factor of about 2) and the use of an additional switch did not noticeably affect the throughput. With a clockrate of 5 Mbps full bandwidth utilization could be reached with a packet size of 1024.