Since the website face-lift a year ago, 3GPP is actively involved in more than just producing Technical Specs and Reports. I regularly read the 3GPP News column and the latest one from Nov. 4^th has the conspicuous title “Dispelling LTE Myths” . I wonder if these so called Myths are the product of competing technology campaigns or the result of self-inflicted “accidents” such as CS Fallback (CSFB) and Single Radio Voice Call Continuity (SRVCC). Well, with UMB in ruins and mobile WiMAX shrinking in size to the footprint of a loaded UMTS cell (ouch!), there is little to fear from the competition nowadays…

The article dispels four “common myths” in LTE. (1) No Voice, (2) No SMS, (3) IMS isn’t ready and (4) No E911 calls. My aim in here is to enhance the descriptions with references to the 3GPP documents and add a few neutral and hopefully insightful comments.

Myth 1: No Voice in LTE. It is true that the carriers have been reluctant in throwing out their CS core and jumping on IMS as the universal all-IP service platform. For this and other reasons, LTE has full IMS solution arrives. CS-Fallback is one such solution. In CSFB the call is handed over to 2G/3G at the beginning of the call. This involves signaling between an upgraded 2G/3G MSC and the MME. IMS standards have become more VoIP friendly without compromising the emergency call requirements. Finally, one-way handover from IMS to legacy 2G/3G is supported via SRVCC. This can be done during an ongoing call. The following is a quick reference to 3GPP specs for further reading.

(For a guide about how to find your way around the 3GPP site, take a look at my earlier post)

a.       CS-Fallback                                       TS 23.272 Rel8

b.      Enhanced VoIP in IMS R7                  TS 23.228 and TS 24.229 Rel7

c.       IMS to 2G/3G handover for voice     TS 23.216 (SRVCC) Rel8

Myth 2: No SMS in LTE. SMS is supported in a couple of ways in LTE. In one approach, the SMS is carried on the user plane over IP (unlike 2G/3G for example). This is SMS over IMS and was standardized in 3GPP in Release 7. The other approach keeps SMS on the control plane and uses the new SGs interface between the MMEs and at least one MSC that is upgraded with the required protocol. Even supplementary services (SS) can be supported in either way.

d.      SMS over IP                                        TS 23.204, TS 24.341 and TR 23.804 Rel7

e.      SMS over SGs                                     TS 23.272, TS 29.118 and TS 24.301 Rel8

Myth 3: IMS is not here! IMHO this is not much of a myth, but a sad state of affairs. IMS specs have been around for a looong time and certain operators on both sides of the pond have very ambitious deployment programs. However IMS has still some convincing to do as a reliable voice anchor (and other CS based services) in mobile environments. The Rich Communication Suite initiative (RCS) may be the final push needed to get over the hurdle.

f.        IMS: IMS is covered over a large number of specifications. A good reference is TS 21.202 from which you can jump to all other IMS related specs

g.       RCS: Rich Communication Suite is not a 3GPP feature. RCS is more like a service package that will use the ‘always-on’ paradigm of IMS based services and provide feature rich services to end-users and will make mobile applications easier to develop and deliver for the providers – How about getting your SMS on the TV screen in the hotel room….The RCS initiative is now under GSMA (www.gsmworld.com).

Myth 4: No Emergency calls in LTE. This is a genuine problem in Rel8 LTE. In fact emergency call handling has been pushed to Release 9 in the specifications. UE positioning techniques in LTE are not fully defined yet and until Rel9 is in place, carriers will have to redirect E911 calls to 2G/3G. It is interesting to speculate on how this deficiency will impact the provision of VoIP in LTE. Today, many carriers redirect emergency calls in 3G to legacy 2G where they do support (sometimes proprietary) positioning techniques which satisfy the stringent regulatory requirements. Early LTE deployments will have to deal with the same problem. Meanwhile carriers with UMTS who are on the LTE path are facing a difficult choice (if any) about support of full emergency-class positioning infrastructure in their 3G networks.

h.      Location Services in LTE                                        TS 23.271, TS 44.031, TS36.455

i.         UE Positioning in E-UTRAN                                   TS 36.305

/Hooman