Issue III

cover III 01

Voice over IP

Volume: 2001, No.III

Date: April 2001

Guest Editors: David Fernández Cambronero and Eberhard Zangger

Contents: Download full issue (PDF 1.78MB)

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Voice over IP

Traditionally, telephony and data services have been served by separate networks with distinct technologies. Voice was carried over conventional switching networks specially suited to the needs of voice traffic: a traffic of - initially analogic, and later digital - signals characterized by a constant flow of information over resources assigned to each call.

VoIP technologies use the networks’ bandwidth much more efficiently, reducing in some cases the 64 kbits/s of telephone calls over conventional networks by as much as an order of magnitude. Also housing a single network for both services reduces the costs of network management and operation.

VoIP replaces a technology that was established more than a hundred years ago and has since reached a high level of maturity and reliability. Its introduction is hindered by a number of factors:

  • Quality of service (QoS). IP networks presently cannot guarantee an acceptable level of quality of service for each call. Compared to switched networks that assign resources to each call, the “best effort” service offered by IP is inadequate. In spite of all of the efforts invested, a widely accepted model that provides QoS on Internet telephony has not yet been found. In the meantime, VoIP is restricted to LAN IP.
  • Reliability. The reliability of the present wire networks is very high: 99.999%. The technologies used with the Internet for VoIP are still far from reaching such a high percentage of reliability.
  • Security. The security in IP networks and the Internet is deficient in many aspects. Denial of service and conversation confidentiality violations are, among others, problems that must be solved before VoIP will be put to use on a large scale.
  • Tariff. The operators of conventional telephony base their income on the accounting of calls made by each user. The “flat cost” schemes of the Internet are radically different. It is necessary to harmonize both tariff schemes.
  • Human Resources. The universality and quality of the present telephone service rest on a host of people trained in circuit switching technologies. The transition to VoIP will demand more attention to the retraining of these personnel.


The following papers are included in this issue:

  • Parameters Affecting QoS in Voice over Packet Networks by Antonio Estepa, Rafael Estepa and Juan M. Vozmediano
  • Signalling in Voice over IP Networks by José Ignacio Moreno, Ignacio Soto and David Larrabeiti
  • Naming and Addressing in Voice over IP Networks by David Fernández, John Michael Walker, José A. G. Cabrera and Juan Carlos Dueñas
  • Multimedia Services over the IP Multicast Network by Antonio F. Gómez-Skarmeta, Angel L. Mateo and Pedro M. Ruizs
  • Implementing Voice over IP by André J. Hes and Ronald van Teeffelen
  • Voice over IP Virtual Private Networking by Olivier Hersent
  • VoIP in Public Networks: Issues, Challenges and Approaches by Francisco González Vidal
  • Voice Communication over the Data Network Convergence of Services by LAN Telephony by Robert Bertels