Long live ALL IP – Part 2

ALL-IPAs already announced in our previous blog entry, we will have a closer look into the two ALL IP approaches: migrating the ISDN PBX or replacing it via a new IP-based voice and data solution.

Migrating the ISDN PBX

Migration means continuing with the already existing PBX whilst a media gateway takes care of the ISDN connection from the PBX’s point of view. The biggest advantage related to migration is that the PBX remains unaffected. In this process the media gateway will be positioned between PBX and the ALL IP broadband connection.

It is very important to use a professional media gateway unifying all necessary interfaces and features. Sophisticated QoS (quality of services) mechanisms are in this case especially important as it guarantees the required voice quality and the solution’s reliability. One of the basic requirements is of course the available bandwidth. As a rule of thumb, a good voice quality comparable with ISDN can be obtained by allocating 100 kbit/s for each voice channel, bidirectional for up and downstream. Also qualitative parameters such as delay, jitter and an acceptable level of package loss have to be evaluated. For instance, losing 10 coherent data packages at a stretch, can lead to losing 100 to 300 ms of voice information. In order to have a smooth operation for incoming and outbound calls, the media gateway converts ISDN voice data into IP data and vice versa.

The same applies to the communication of the ISDN PBX behind. It is important to note that all data coming from or transmitted to the ALL IP platform has to be conformed and compatible with SIP which is the network protocol being used. SIP (session initiation protocol) is in charge of the control as well as the set up and dismantling of the connection. The voice data as such is transmitted via the real time protocol (RTP). Experience shows that SIP is not the same as VoIP and VoIP is not the same as ALL IP.

A simple example: The ALL IP service provider sends phone numbers in a canonical format which means that the customer number being called is for instance +49-91-196730. Without the media gateway converting the format into 091-196730 before sending it to the ISDN PBX, it is very likely that none of the phones connected to the PBX would ring. Vice versa, the same applies when calls are made from the ISDN network to the IP network.

New ALL IP solution

If the ISDN PBX which is already installed should not migrate due to technical or economic issues, then the PBX has to be replaced and an ALL IP voice data solution has to be found. However, one has to take into account that with an ALL IP solution, not only the PBX may lose functionality, but also the terminals may only be used partially or not at all. In this case new IP terminals have to be integrated. This is a cost factor not to be underestimated, especially in companies with a larger number of digital and often proprietary system terminals. However, a complete and thorough IP-based infrastructure offers plenty of opportunities to optimize working processes and thus achieves an economical benefit.

Numerous features such as DECT over IP, voice mail, IP-based door intercom including camera image of visitors on IP terminals or smart phones can be seamlessly integrated and used via professional ALL IP communication solutions. Now, wireless LAN or HotSpots for guests and customers as well as integration of home offices or mobile employees can be effectively combined.

Teldat as a qualified ALL-IP partner for SMEs, large corporations and integrators has attracted the service provider Deutsche Telekom as a customer by its various ALL-IP solutions for both approaches, migration as well as new ALL-IP solutions.

Michael Bindner:

Dismantling the ISDN and POTS networks

100039145How can we help carriers dismantle their ISDN networks easily, economically and above all, transparently?

Traditional ISDN and POTS communication networks are now obsolete.  Deployments using old technology, the devices making up these networks, etc., have reached, in many cases, the end of their lives.  Another influencing factor is that experts and technicians in this field are approaching, or have even reached, retirement.

However, there are still millions of lines in service and millions of clients who use them on a daily basis, both at home and in companies, not only for voice communications but also for data. Communication carriers, the owners of said networks, are faced with the unavoidable fact that they must replace them with new technology.  The dismantling of the old network goes hand in hand with deploying the new ultra-broadband.

Migration from traditional telephony to IP

The migration of traditional telephony to convergent services based on IP, plays a key role in dismantling the net.  While data has been transmitted over IP for quite some time now, the vast majority of telephony services still continue to use the old ISDN and POTS networks.

One of the most important goals for carriers is to keep their customers during said migration.  The latter, when faced with radical or abrupt changes, may well decide to change providers.  Given this, the change for the end-user must be as transparent and staggered as possible while still meeting customer demands.

This boils down to three main factors:

  • Customers should continue to use their existing voice infrastructure (PBX and phone handsets) for as long as they wish.
  • The new networks retain all the advanced features currently used by said customers
  • Quality of service remains optimum.

Carrier needs

The carrier must be able to efficiently mass deploy the new convergent services.  Integrated with the modern management and installation systems, all featured in ultra-bandwidth networks, the converging infrastructure, usually based on TR-69, must have zero-touch configuration ability.

Moreover, carriers require on-site product lines for customers, which integrate the advanced features of ultra-broadband networks, accessed through corporate devices, together with advanced telephony features: IP switchboards and media gateways for example.  A perfectly integrated ecosystem of features and accessories (IP and DECT telephones, or wireless access points), for both voice and data, together with access routers, provide both customer and carrier with a simple, flexible, professional approach to new fully convergent IP.

The Teldat Grouphas been selected by a major ISDN network carrier, as the principal supplier to enable customer migration from ISDN to IP.  Teldat’s expertise in telephony systems together with their successful range of access routers for carrier managed services, made them the ideal choice.

Eduardo Tejedor: Telecommunications Engineer, Teldat V.P. Strategic Marketing


toipWe live in a digital world. Entertainment, work, information, social relations… today everything is digital. The benefits are obvious. Digital information is much easier to store, transfer and handle than analog and is more powerful.  If we think about it we can find many fields where digitalization has had a remarkable impact. In this article, however, we will only consider the impact on telephone networks.

Regardless of whether the telephone was invented by Alexander Graham Bell or Antonio Meucci (or…), it is clear that it started out as analog, and it remained so for many years. Logically, improvements were made over the years but being inherently analog in operation until the mid-60s, deficiencies in the quality of transmitted voice were inevitable. This was especially the case over long distances that required signal regeneration at intermediate stages, leading to information loss and the introduction of noise. The digitalization of the telephone network was a breakthrough in this regard, since the digital signal is transmitted unchanged regardless of the distance and of the intermediate stages required between sender and receiver.

Integrated Services Digital Network (ISDN)

While the move to a digital network paved the way for its use with a range of other services in addition to voice, the final leg, the last mile, also needed to be digital. This step took place many years later with Integrated Services Digital Network, ISDN. As the name suggests, ISDN allows different services to be used over the telephone network on a single line, digital of course.

The advantages of ISDN are clear: firstly, the sound quality (which is why even today they are still widely used by the radio industry), secondly, the extra features (rapid call setup, support for multiple terminals on the same line or direct inward dialing and caller ID), and thirdly, the additional services such as data or video transmission.

ISDN was introduced by CCITT (ITU-T) in 1988 and had its golden moment during the 90s, being deployed with varying success in countries around the world such as Japan, Australia, India and the United States. The biggest impact was in Europe, however, in countries like Norway, Denmark, Switzerland and above all Germany, which had 25 million channels (29% penetration) and one in five lines installed worldwide.

In the late 90s and early twenty-first century two events mark the decline of ISDN; on the one hand, ISDN cannot keep up with market demands for greater speed, and on the other, the cost of Digital Signal Processors (DSP), which allow more advanced line modulations, lowers significantly. It is the beginning of ADSL and the decline of ISDN.

ISDN, the new paradigm in communications

During the first decade of the twenty-first century, ISDN gradually loses ground to ADSL and from 2010 all ISDN service carriers gradually announce its withdrawal. In 2010, for example, NTT announces its intention to migrate all ISDN phone lines in Japan to IP technologies, in 2013 Verizon decides not to install anymore ISDN lines in the USA and in 2015 BT announces its intention to discontinue the network in the UK. Curiously, however, Deutsche Telekom (DT) in Germany adopts the most aggressive stance. By far the world’s largest ISDN provider, it has already begun migration to ADSL/IP technologies having set an aggressive horizon of 2018 for cutting off ISDN completely.

All carriers with active ISDN networks will no doubt be following the transition of the German DT network very closely and it will likely mark the way forward. DT’s commitment is to network modernization and improving customer service while minimizing the impact on the customer. The proposal, therefore, is to offer data services and voice over IP on the same telephone line (ADSL/VDSL) but at the same time giving the customer the opportunity to keep their existing ISDN infrastructure, emulating the ISDN lines from the EDC to their current ISDN PBX.

The use of xDSL and IP services allowing the customer to maintain their internal ISDN infrastructure practically eliminates any impact on the customer, who controls the evolution of the network to an integrated and up-to-date service.

This is an ambitious project and key for Deutsche Telekom. For this reason, following a rigorous selection process, the company has forged close relationships with partners who have proven ability in providing the solvency, experience and agility needed. Within this framework, Teldat has been entrusted by Deutsche Telekom with the task of supplying the access devices.

Marcel Gil: graduated in Telecommunication Engineering and Master in Telematics (Polytechnic University of Catalunya), is a SD-WAN Business Line Manager at Teldat.

VoIP Security

voip solutionsSome countries switch off their telephone network in the near future. ALL IP is as previously mentioned one of the main buzz words. The shift to VoIP has already started and now is the right time to ask ourselves: “Do we need VoIP security?”


Randolf Mayr:

The ABC of SBC: definition, characteristics and advantages

wireless lan controllerThe Firewall is the quintessential element providing network security when you need to interconnect with other networks, allowing outgoing traffic and blocking unsolicited incoming traffic. The Firewall is a necessary element, although it is insufficient for security purposes since some threats are hidden from network firewalls within legitimate-appearing traffic, thus resulting in the need for other specialized protective elements such as antivirus or antispam.

The case of Voice over IP is even more special. Firewalls are generally based on NAT but, unfortunately, VoIP connections are incompatible with NAT. A possible solution would be to open exceptions in the NAT Firewall for Voice over IP. This this is not a good idea, though, because it compromises security and does not protect against Denial of Service and intrusion attacks. Intrusion control deserves special mention, not only at the network layer (which a Firewall could perform) but, primarily, at the application layer, aimed at ensuring legitimate call traffic, avoiding attacks, intrusions and fraud. On top of this and to make matters worse, the VoIP sessions are created randomly as calls are established, further complicating control.

A new element is required to address these risks. This element should monitor and be actively involved in the VoIP sessions established between the internal and external network, ensuring that these connections are properly established and that they are legitimate, secure and reliable. This element is the Session Border Controller (SBC).

What is SBC?

An SBC is basically a Firewall for voice traffic and its job is to ensure that the sessions are legitimate, detecting and blocking potential attacks and intrusions. Another important safety feature (similar to what a Firewall does for data services) is concealing voice services on the internal network from the outside. To perform all of these functions, the SBC sits, like the Firewall, on the border between the internal and external network (hence the name “Border Session Controller”), but at a more internal layer than the Firewall (usually in an intermediate network between the Firewall and the internal network, or DMZ -“Demilitarized Zone” -).

The SBC doesn’t just monitor and control sessions between the internal and external network, it reconstructs them in order to have complete control. That is, when a session is established between the internal and external network, two sessions are actually established, one from the internal element to the SBC, and the other from the SBC to the external element; with the SBC negotiating the call parameters to both ends separately. Not only does this allow for full control of the sessions (who can connect, to where, when, how, detection of attacks and intrusions…) but it also conceals the internal network from the outside. This is a basic SBC behavior that is known as Back to Back User Agent (B2BUA).

Characteristics and advantages

While the SBC’s main feature is usually security, it is by no means the only one. The SBC is usually responsible for the following functions, among others:

  • Interoperability: Establishing sessions even with internal and external network elements that have different signaling (due to the use of different SIP versions or signaling protocols or because of additional security requirements on one side)
  • Numbering plan management: Allowing legitimate connections and blocking attacks and intrusions
  • Transcoding: Converting incompatible codecs
  • Admission Control: Limiting the number of sessions established to avoid exceeding the WAN line capacity
  • Remote user connectivity: For example, using VPNs
  • Quality of Service Management
  • Others…

SBCs arose out of need, catching standards bodies off balance, which created some ambiguity about their roles and limits. Initially SBCs were dedicated devices located at the border between provider networks and their customers or the Internet, evolving towards virtualized networks at times integrated with Firewall and routers. Today it is common to deploy SBC functions even in remote areas to protect the central office’s internal network, especially where there is a direct connection to the internet.

SBCs in Teldat

Teldat routers implement an advanced, comprehensive SBC using various functions included in the software, such as the B2BUA functionality that allows complete control of Voice over IP sessions established between the internal and external network, ensuring interoperability and security, together with other security features like IPSec and securitization of RTSP, TLS and SRTP voice sessions, plus complete control of the IP Quality of Service, Admission Control for VoIP calls based on various parameters, routing table/call screening or codec selection.

Marcel Gil: graduated in Telecommunication Engineering and Master in Telematics (Polytechnic University of Catalunya), is a SD-WAN Business Line Manager at Teldat.