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Jul 02 2014

LTE network: How it all comes together

Mobile network operators that want to deploy LTE now want to do so on their own terms. They want to roll out ultrafast mobile broadband safe in the knowledge that one vendor’s solution will work efficiently with another, while delivering the high level of service that subscribers expect. A standards-based network will ensure the goal is met and help drive down cost for operators, but understanding how to pull it all together can be a challenge. So how does it all come together? This blog and the LTE Architecture Technical Poster we have produced were born out of a couple of conversations between the two of us. We were trying to find the best way to illustrate LTE networking, show the various network nodes, explain the many interfaces, acronyms and standards that surround LTE and what people really need to know about modern mobile networks. We quickly came to the conclusion that our previous poster, and many of the other published documents explaining LTE architectures, do not do a good job of showing how the latest standards from 3GPP work together nor how LTE interworks with other radio access technologies. So we felt it was time for a refresh. With that in mind we set about designing and producing the Alcatel-Lucent LTE Architecture Technical Poster. We felt it would be useful to highlight the most important things that people need to know and understand about LTE - how LTE fits into existing mobile networks, how it interworks with Wi-Fi, how it extends to enable new services like VoLTE, eMBMS, and so on.

What we need to know about LTE Architecture

In mapping out our comprehensive LTE network, we came to the conclusion that overall LTE architecture can be broken down into a few “blocks” of related functionality, so we’ve tried to communicate those in our poster. As we began whiteboard this idea, we quickly realized a few things. One was that we needed to map out the base LTE network as a central image and include the other blocks around it. Then another was that to help make it as engaging and comprehensible as possible we would need to color-code it, so that radio, broadcast, packet core and other functions were clear and easy to identify. Next we felt that it would be useful to split the interfaces using dashed lines for those that only carry control plane information and plain lines for user plane connections. Then other parts of the LTE map came into view – so we decided that we would include a table of the radio and network bearers, a table of standardized frequency bands and then a section which shows how the key LTE protocols and security work together. Finally we decided that each block should have a short text explaining the alphabet soup of acronyms, the role of the key network elements and what this brings to the end-user.

All LTE, all in one place

With this plan in place we then attacked the poster itself. First off we placed the main LTE and Evolved Packet Core (EPC) networking functions into a large “global view” diagram. We add the new broadcasting mode for LTE called eMBMS to this diagram as well along with the charging nodes plus the way IP networking connects to the EPC. Underneath we placed a more detailed view on mobility and roaming support plus the new VoLTE solution for voice over LTE which is now being deployed in commercial networks. The top right-hand section of the poster illustrates how LTE can interwork with legacy 2G or 3G infrastructure that is already in place and here we covered both non-3GPP (CDMA and WLAN) and 3GPP (GSM, WCDMA and TD-SCDMA) legacy networks. Finally in the top left corner we placed a large table listing the main radio bands, each with its band number and frequency ranges. It is interesting to note that before LTE was launched people tended to talk about radio bands by their frequencies – 850, 900, 1800, etc. With LTE however, we’ve noticed that people refer more to band numbers – band 2, band 17 and so on. Being able to look up the FDD and TDD bands, their commonly-used names and their frequencies seemed to us a smart idea. We also decided to highlight in bold the radio bands most commonly used in the networks. So that was the target –provide the best possible supporting tool showing the network and how its components all fit together. . We hope you like it and will use it each time you need to review the exact role of any of those network entities and how it interworks with the others. If you would like to request a printed or electronic copy of the LTE network poster, please complete our Wilson-Street registration form and sign up for Wilson-Street updates.

About Alistair Urie
Alistair URIE is currently Architecture Strategy Director and lead for 5G Strategy in the Alcatel-Lucent Wireless Product Division and Bell Labs Fellow. His main interests include 5G mobile systems, LTE/EPC networking, legacy and IMS interworking, small cell systems, cellular/WLAN interworking and spectrum management. He has previously worked in Alcatel-Lucent on end-to-end network solutions, network strategy, hybrid terrestrial-satellite broadcast networks, standardisation management, mobile systems product strategy and international research programmes (European RACE Programme) for GSM and UMTS systems. Prior to joining Alcatel in 1991 he had been involved in both line and radio transmission system research at the Telecom Australia Research Laboratories and had also worked at the Dept. of Science Antarctic Division in Australia. Mr. URIE was Vice-Chair of the ETSI Board and Chair of ETSI OCG. He has published numerous papers in conferences, IEEE magazines, Alcatel Telecommunications Review (ATR) and Bell Labs Technical Journal (BLTJ) and was guest editor for special editions of both ATR and BLTJ.