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Introduction to IMS


IP Multimedia Subsystem (IMS) – is now considered as some base technology for mobile 3.5G and 4G networks, for fixed IP telephony networks, convergence of mobile and fixed networks (FMC) and for integration of all IP devices with universal services.

General idea and the difference from the present state is that user terminals working with IP signaling, IP voice codecs, IP video codecs and other IP services and therefore radio interface for mobile or “last mile” for fixed networks is used with more efficiency and no need network resources for conversion of the information. That’s in fact was original idea, well revolutionary itself, but then there had appeared next logical step – for common services (such as voice, video, SMS, MMS and so on) must be used same codecs and protocols which provide an opportunity to use same services on a different type of IP network terminals – mobile phones, PDAs, fixed phones, personal computers.

At now days you can send SMS from PC to mobile using special program. But the thing is, that your Windows CodePage is not the same as CodePage in mobile terminal and must be converted. Then network of operator is working on old SS7 analogue protocol and SMS Center must convert a message gotten from IP to SS7 standard. More over – connection from Base Station to Mobile Terminal is still can be considered as analogue and even if operator has a modern network with SIP (SS7 over IP) your SMS must be converted! More over – now there is not such service as “Reply by SMS to PC user”. If it is – this is special separate server which work on it’s own rules. The same situation if you want to send a SMS to fixed phone (IP or ISDN). In other words – present status is a lack of simple services among different type of networks and whatever services are exists are using different software, protocols and principles.

IMS – is easy way to interconnect any IP device with some set of basic services by usage of common protocols.

Benefits for operators

  • For operators it mean reducing of Operational Expenses (OPEX) as “last mile” and the entire network are operating with wide usage of codecs and compression protocols. Less OPEX – cheaper price for the End-Users can be offered.
  • Reducing of Capital Expenses (CAPEX) as no need more spend money on integration with other type networks. Just to make it clear, at now days you have to develop special server for each of the following service: SMS from/to fixed network, SMS from/to PC, MMS from/to fixed network, MMS from/to PC, Voice from/to PC. Less CAPEX – cheaper price for the End-Users can be offered.
  • When there is one unique base technology instead of many servers of different vendors then Operator has more simple network and this leads to reducing OPEX once again.
  • Universal cross-network standards allow more simple services usage and lead to increasing of subscribers activity – as a result there is growth of ARPU (Average Rate Per User).
  • One specific benefit for global operators which provide mobile and fixed telephony, access to internet and other communication services same time is that with IMS they have very easy way to run common O&M (Operation & Maintenance) and Billing systems. At present days there is huge specific projects with millions dollars cost to integrate and maintain synchronous different O&M and Billing systems for such global operators! Once again there is a great opportunity to reduce OPEX and CAPEX!
  • And final important notice about Mobile Cellular Networks – is that radio interface from Base Station to Mobile Terminal is very expensive resource and further more it’s limited by regulator (government or some regional association). IMS is developed to use IP packets in radio interface which allow to use it 5-10 times more efficiently! It’s the same as PCM file and MP3 file – 72 minutes against 7-8 hours on one CD. If reduce data to the spectrum of human voice, then we can have even better compression.



There is only two pure technical points:

  • Signalization over IP instead of present channel signaling like SS7. This point was solved by introducing SIGTRAN. At now days there is a point for the equipment vendors to implement it in all network nodes (switch, radio access, service platforms and so on).
  • Coding/decoding of IP packets in user terminals. This is more less available now. Modern phones is a small computers in fact which deal with IP packets and have codecs for voice, video and messages formats.

Another important point is to setup standard set of codecs and protocols for all the devices. This is an administrative question, but it seems that level of hurdles is even more than in solving technical questions. Different vendors perform different protocols realization and by thus there is no unique compatibility. As a result – not easy to use for the subscribers and therefore no big income for operators.

My suggestion is that unique standard must be developed by big operator. This standardization is really leads to profit increase. In case of equipment vendors – it is just increase of costs. Good example is DoCoMo network in Japan.


If for operators there is dramatically new equipment, then for the users there are lot of new services. Formally – there remaining the same style mobile phone, fixed phone and PC, but now you can use it differently. For example – you can make a voice call to regular phone using PC, send SMS from fixed phone or watch TV on your mobile. If there is convergent network of one operator, then you can start a chat on mobile phone (while going home), then transfer it on fixed phone (when in home) and then transfer the same chat, without any interruption, to your PC when it power on.


As were stated in TECHNICAL part – main problem is to develop really universal standard. The aim is that IMS services are same easy use as make a regular call or send SMS.

As was mentioned before – there is only profit for the operators and therefore it must be will of operator to develop or organize development at least for it’s own network. More obvious is to establish development center (test lab) together with vendors of equipment.


Having All-IP network gives a lot of pure marketing opportunities:

  • OPEX for All-IP network is 2-4 times less than for legacy (let say) networks. You can offer very attractive tariffs which 20-50% cheaper than competitors have but your benefit will be more than they have.
  • If you run convergent network (two or more from the list - mobile telephony, fixed telephony, wireless internet access, wireline internet access) then you can offer with transfer mobile call to fixed phone or PC with cheaper price for the rest of the call. Very attractive for users, but due to All-IP you (as operator) still have very good income!
  • You can offer unique services which can’t be run on legacy network or price will be in times higher. Including corporate segment services like VPN, extended office switch.
  • More over – you can offer much more services and in shorter time as IMS can be simply considered as PC SERVER with small differences in protocols. Content providers do not need more to develop “engine” of services.

As you see – you have all the aces in hands: cheaper price, client’s cost save offerings, leading services, unique market positioning. What is important when most of competitors have All-IP networks too is that in intelligent services is very important convenient and ergonomics. You start early – you have experience in creating such services!

Just one example of business case for convergent network for corporate segment. User have got a call on his mobile. After his part of questions he has very easy transferred call (using short office number) to fixed phone in contracts department and run 3-party conference call. In time he is not deeply involved in a chat, he marked on his PC some tasks in MS Outlook which automatically were transferred in mobile phones of him, his chief and employees in contract department. Then the same situation but when manager is out of office and his Outlook appointment were done using his PDA.

What you as operator have in result?

Than easy service is than wider usage of it. If conference and appointment hard to set and must be a lot of service (machine style language) commands – then these used only for very important chats. If easy, by interactive menu on phone, for example, then used whenever it can be useful. That is the additional traffic which corporation pays! And they ready to pay, because 2-3 deal (which were won due to speed of decision making) is covering all the expenses on this traffic!

There are also some psychology points:

  • In three-party call are more questions rising as there are some things for contract department which manager do not understand clearly and clarify and contrary – some things for manager which person in contract department clarify. More questions – longer call!
  • Whatever task in Outlook is added within chat – later this will be corrected! After you got more details or just understand all the chat itself – you make corrections. More intra-system corrections – more traffic!
  • More over – you offered tariff on 20-50% cheaper than if it separate service on legacy network. Customer relaxing, not thinking about costs – in result he probably spend even more, than before.


Resume is short – All-IP communications is a firm future for operators. Part of it infrastructure can be implemented at present days. Some other things – in nearest future. May be implementing of IMS is the easiest way to stay a leader or become a leader.

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