Overview of LTE Handovers

From the NTT Docomo Technical journal:


The LTE handover is broadly divided into a backward handover (PS handover) and forward handover. In the former, the network performs cell switching and notifies the mobile terminal of the destination cell, and in the latter, the mobile terminal performs autonomous switching to pick up the destination cell.


To control packet loss due to a momentary cutoff at the time of radio switching, PS handover supports a data forwarding process that transfers undelivered data from the switching-source eNodeB to the switching-destination eNodeB and a reordering process that corrects sequencing mistakes between forwarded data and new data.


The forward handover can be classified into Release with Redirection triggered by a cutoff signal from the network and Non Access Stratum (NAS) Recovery in which the mobile terminal autonomously performs a NAS recovery, either of which is accompanied by data loss due to a momentary cutoff. From a different perspective, handover can be classified in the following two ways according to whether it is accompanied by Radio Access Technology (RAT) or frequency switching or by eNodeB or EPC switching (Figure 7).


1) Intra-RAT handover: This is a handover that occurs within the LTE system in which node transition occurs between sectors within an eNodeB, between eNodeBs within an EPC switch, or between EPC switches. 


A handover between eNodeBs within an EPC switch may be an X2 or S1 handover. In an X2 handover, signal processing is performed by the X2 logical interface between eNodeBs, while in an S1 handover, signal processing is performed by the S1 logical interface between an eNodeB and the EPC switch. There is a tradeoff between the cost of maintaining an X2 link and the cost incurred by an S1 handover, and operations are configured accordingly.


Handover can also be classified by whether the center frequency is the same before and after handover, that is, whether the handover occurs within the same frequency or between frequencies.


2) Inter-RAT handover: This is a handover that occurs between RATs either as a transition from LTE to 3G or from 3G to LTE.

A detailed post on LTE to 3G Inter-RAT handover is available here.

Testing and Optimising LTE

JDSU: Testing and Optimising LTE

View more presentations from Zahid Ghadialy

An interesting presentation from JDSU

IEEE standards impacting the future home

Interesting graphic from IEEE-SA depicting various IEEE standards impacting the home - via Steven Crowley on Twitter

Release 12 study item on Continuity of Data Sessions to Local Networks (CSN)

LIPA was defined as part of Release-10 that I have already blogged about. Imagine the situation where a user started accessing local network while camped on the Home eNode B (aka Femtocell) but then moved to the macro network but still wants to continue using the local network. Release 12 defines this feature and is called Continuity of Data Sessions to Local Networks (CSN). This study item was originally part of Release 11 but has now been moved to Rel-12.

From SP-100885:

Justification

Basic functionality for Local IP Access (LIPA) has been specified in Rel-10.

LIPA signifies the capability of a UE to obtain access to a local residential/enterprise IP network (subsequently called a local network) that is connected to one or more H(e)NBs.

The current study item investigates extending LIPA functionality to allow access to the local network when a UE is under coverage of the macro network and provide related mobility support.

LIPA allows a UE to work with devices in the local network – e.g. printers, video cameras, or a local web-server. If the local network offers services that enable exchange of digital content (e.g. UPnP) LIPA allows the UE to discover supporting devices and to be discovered.

Examples for services that become available by LIPA are:

·         The pictures stored in a UE’s digital camera may be uploaded to a local networked storage device or printed out at a local printer.

·         A portable audio player in the UE may fetch new content from a media centre available on the local network.

·         A UE may receive video streams from local surveillance cameras in the home.

·         A local web-server in a company’s intranet may be accessed by the UE.

·         Support of VPN.

LIPA does not require the local network to be connected to the Internet but achieves IP connectivity with the UE through one or more H(e)NBs of the mobile operator.

In Release 10  3GPP has only specified the support of LIPA when the UE accesses the local network via H(e)NB.

On the other hand an operator may, e.g. as a chargeable user service, wish to provide access to the local network also to a UE that is under coverage of the macro network. Access to the local network when a UE is under coverage of the macro network should be enabled in Rel-11.

In Rel-10 it had been required for a UE to be able to maintain IP connectivity to the local network when moving between H(e)NBs within the same local network.

However, access to the local network may be lost as a UE moves out of H(e)NB coverage into the macro network, even if other services (e.g. telephony, data services, SIPTO) survive a handover to the macro network and are continued. This may result in an unsatisfactory user experience.

The current study item will allow continuation of data sessions to the local network when the UE moves between H(e)NB and the macro network.

Therefore, in Rel-11, the 3GPP system requires additional functionality to allow

·         A UE to access the local network from the macro network

·         A UE to maintain continuity of data sessions to the local network when moving between a H(e)NB and the macro network

Objective:              to propose requirements and study feasibility for the following scenarios:

Provide a capability to the mobile operator to allow or restrict

­        Access to an enterprise/residential IP network when a UE is under coverage of the macro network, assuming that the IP address of the local IP network (e.g. residential/enterprise gateway) is available to the UE.

­        Continuity of data session(s) to an enterprise/residential IP network when a UE moves between a H(e)NB in an enterprise/residential environment and the macro network.

The support of Continuity of Data Sessions to Local Networks should be an operator option that may or may not be provided by individual PLMNs.

Service Aspects

The user should be able to decline access to the local network from the macro network. The user should also be able to decline continuity of data sessions to local networks when moving between H(e)NB and the macro network (e.g. in the case when data sessions to local networks is charged differently if accessed from macro coverage or via the H(e)NB).

A difference in QoS may be noticeable by the user when the local network is accessed from the macro network or via the H(e)NB.

ETSI INT IMS/EPC Interoperability Standardisation: Motivation, Roadmap & First Results

INT = IMS Network Testing. ETSI INT website here. More details below the presentation:

ETSI INT IMS/EPC INTEROPERABILITY STANDARDISATION

View more presentations from Zahid Ghadialy

This was presented by Giulio Maggiore, Telecom Italia, ETSI TC INT Chairman in the 2nd FOKUS FUSECO Forum 2011, Berlin 17-18 Nov. 2011

From the ETSI leaflet (note that this is quite old information but still on the ETSI website here):

IMS interoperability is a key issue for boosting IMS (IP Multimedia Subsystem) roll-out and more specifically network interconnection between operators. Only through thorough testing in practical scenarios can operators ensure operational excellence in a multi-vendor and multi-provider environment.


IMS comprises a set of specifications designed to enable network operators to implement IP-based networks that can carry services for both fixed and mobile customers simultaneously.


IMS was developed originally in the mobile world (specifically in the specifications created by the 3rd Generation Partnership Project, 3GPP), and was adopted for fixed networks by ETSI’s TISPAN Technical Committee (Telecoms & Internet Converged Services & Protocols for Advanced Networks).


However this promise of advanced communications over the next generation network will only be delivered if those same networks can interconnect.


ETSI’s Technical Committee INT: IMS Network Testing


ETSI is bridging the existing gap between 3GPP IMS Core Network standards and the initial industry IMS implementations through the organization of IMS interoperability events in connection with ETSI’s Centre for Testing & Interoperability (CTI) and Plugtests™ interoperability testing service.


Our Technical Committee for IMS Network Testing (TC INT) is actively establishing close contact with a number of industry fora and organizations dealing with IMS interoperability, including 3GPP, GSMA, MSF (Multi Service Forum), IMS Forum and the ITU-T. TC INT develops IMS test specification according to conformance, network integration and interoperability testing methodologies. Other ongoing work includes development of tests for Supplementary Services based on regulatory requirements and IMS tests with legacy networks (e.g. SIP-I).


ETSI has already held two IMS interoperability events. The first examined interconnection aspects of 3GPP IMS Release 6, including such issues as basic call on the Mw interface. The second event had a wider scope that included the testing of 3GPP IMS Release 7 interworking, roaming, border control, and integration of application servers executing selected Multimedia Telephony supplementary services.


Future ETSI activities and events will go even deeper towards bridging 3GPP IMS standards and industry implementations. These will include the organization of further IMS interoperability events designed to boost the roll-out and take-off of IMS services and operators’ network interconnections.

AT&T on Distributed Antenna System (DAS)

From the 4th LTE North America Conference, 8 - 9 November 2011, Dallas, Texas, USA

More about DAS on Wikipedia here.

AT&T comparing In-Building Solutions

Gemalto presentation on Soft SIM

Will a Soft SIM Change Everything?

View more presentations from Zahid Ghadialy

How Mobile Broadband users use their data allowance

Interesting picture of what MBB users use their data allowance on. Interesting to see that Social Networking is far popular in the North America whereas Real-time entertainment is much more popular in APAC. It is understandable that the downstream Real-time entertainment would contain of VOD services like Youtube and Hulu but not sure what Upstream would consist of. 

US Trends and Updates on Mobile Broadband, VoIP and Mobile Service Status

Presentations From the 2nd FOKUS FUSECO Forum 2011, Berlin 17-18 Nov. 2011

Mobile Service Status and Trends in the US

View more presentations from Zahid Ghadialy

Mobile Broadband and VoIP in the US: Trends and Updates

View more presentations from Zahid Ghadialy