Improving the automatic congestion control functionality in SS7-signaling networks Gerta K oster * Siemens AG, ICN WN CS SEK 3, Hofmannstrasse 51, 81359 M unchen, Germany Received 19 September 2000; received in revised form 15 January 2001; accepted 29 January 2001 Responsible Editor: L.G. Bouma Abstract We investigate the performance of automatic congestion control ACC) ± a congestion control algorithm widely used in TDM networks. With network convergence its use spreads to congestion control at the interface to IP-networks. ACC aims to protect a node from overload by reducing the trac at its neighbors. However, the current ITU- standard speci®es very coarse information and regulation mechanisms that lead to low network throughput while there is a risk of buer over¯ow. We oer an enhancement to standard ACC that vastly improves the network and node performance. The standard itself and in particular all the interfaces between exchanges remain unaected. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Automatic congestion control; Signaling networks; Overload; Network performance; Media gateway controller 1. The standard ACC algorithm Congestion control is a key factor when trying to guarantee seamless and high-quality transmis- sion for real-time applications. At present, voice remains the most important real-time application especially as far as carrier revenues are concerned. Voice trac volume is still continuously increas- ing, while services become more and more diverse. New interfaces between classical telephony net- works and IP-networks further complicate the picture. This often leads to higher trac ¯uctua- tions making network utilization less predictable. Thus, the need for overload protection algorithms in telecommunication networks is reinforced. We now give a technical overview of the ACC to make the ®ndings described later easier to fol- low. We also give an example of the ACC usage at the interface of an SS7-network and an IP-network see Fig. 2). Automatic congestion control ACC) is a net- work wide algorithm speci®ed by the ITU for the signaling system number 7 SS7, #7) protocol in [3±6]. Its aim is to protect a switch when the call processing application causes overload due to ISDN user part ISUP, B±ISUP) or telephony user part TUP) processing. Although ACC was originally conceived for congestion control in #7-signaling networks it is also appropriate to protect border products at the interface between IP- and #7-networks such as the Computer Networks 36 2001) 617±624 www.elsevier.com/locate/comnet * Tel.: +49-722-25-625. E-mail address: gerta.koester@icn.siemens.de G. K oster). 1389-1286/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S1389-128601)00177-3