Feature

DECTweb aims to bring you occasional timely feature articles from well known names in the cordless telecommunications industry.   If you feel you would be a suitable contributor and would like to offer an article for consideration please e-mail us with your biographical details and an outline for the proposed feature. 

Back to Features Index

Direct Mode DECT:
Handset-to-Handset Communication

For additional information on Direct Mode (Walkie Talkie Mode) please click here

Direct Mode seems to be one of the best-kept secrets of DECT telephony.   With minor changes to the software, DECT phones can be enabled to talk to each other in direct 'walkie-talkie' mode, enabling you to take your DECT phones with you and keep in touch with your partner or kids as you split up and wander around the shopping centre.   Obviously this will only work as long as you stay within range, (typically 100m) - however, DECT phones can be enabled, as indeed some already are, to alert the user when he goes out-of-range.

DECTweb is very grateful to Guenter Kleindl, who leads ETSI's DECT standardisation team, for providing the information included in this feature.  Who knows, maybe it will prompt some manufacturers to add such features to their phones, as they seek a competitive edge in today's price-driven domestic market, to the benefit of the end users.

If there is a demand for more information or discussion of Direct Mode, DECTweb may endeavour to see if we can persuade Gunther Kleindl to join us for an on-line chat session - if you would welcome this please e-mail DECTweb, so we can ascertain the potential interest.

Baseline Information Sources
The key reference document for Direct Mode is section 5.5 of the basic DECT standard, EN 300175-6, available from ETSI and downloadable from the ETSI website from our ETSI resources page.   This section of the standard deals with the issue of 'ARI (Access Rights Identity) Class E'.  The other key source is Annex G of the latest version of the relevant Technical Basis for Regulation, TBR6, dated June 1999, from which the information given below, relating to the conformance testing of handsets incorporating direct mode capabilities, is extracted.

To aid the understanding of the text below, here a quick guide to DECT ETSI-speak:

• PP - portable part - the cordless portable handset
• RFP - Radio Fixed Part - a DECT basestation, to you and me
• GAP - Generic Access Profile - the specificatuion which allows all DECT phones to work with all basestations, regardless of manufacturer
• ARI - Access Rights Identity - a software identifier which determines what other DECT equipment a handset can talk to
• PARK - Public Access Rights Key - the software 'key' that allows a handset access rights to a public DECT system
• EUT - Equipment Under Test - the handset, when tested for specification conformance

Requirements for PPs with Direct PP to PP Communication Mode
PPs are not attached to a public network when operating in a direct PP to PP communication mode. Therefore only TBR 6 testing is mandatory for this mode of operation. In addition it may be tested according to a specific interoperability profile (e.g. GAP). 

1.    Description of Operation in Direct PP to PP Communication Mode
Most PPs will be able to operate also in the normal non-direct communication mode. In this case the direct mode will be temporary, and all PPs in a group of PPs intended to communicate in direct communication mode have to be manually switched into this mode, since a PP in non-direct mode can only receive paging information from the system to which it is locked.

The access rights class E and related PARK E are reserved for direct communication only, see EN 300 175-6 [6] second edition, subclauses 5.5, 6.1.5 and 6.3.2. The Access Rights Identity (ARI) class E requires a key pad entry of only 5 digits to provide all identity and subscription data required to form a group of PPs for direct communication. The use of class E identities is normally of temporary nature and does not contain an ETSI distributed code.

When there is no communication all PPs are active unlocked, no (dummy) bearer transmission exists, and all PPs are regularly, e.g. every 10 seconds, scanning all access channels with carrier numbers c < 10, for a (dummy) bearer transmission with proper Radio Fixed Part Identity (RFPI). When a PP wants to initiate a connection, it acts like an RFP, selects a channel within carriers c < 10 and starts transmitting a simplex (dummy) bearer with the relevant page message and Q T information. Only the paged PP is allowed to enter idle locked mode, and shall respond with a normal bearer setup. If ARI class E is used, the initiating PP is not required to perform receiver scanning, and the paged PP shall make the bearer setup attempt on the channel pair where it received the paging and intracell handover is not possible. The initiating PP shall seize transmitting and revert to PP active unlocked state, if a duplex bearer has not been established within 20 seconds. The initiating PP, when acting as an RFP, is allowed to apply PP timer stability requirements and PP channel selection rules for simplex bearers. A PP entering RFP mode is also allowed to derive over the air slot synchronization from a "non ARI E" DECT system, e.g. a large office system.

2.    Testing Requirements
PPs in direct communication mode shall meet the PP requirements for normal non-direct communication with the amendments defined below.

2.1    Setting the PP In Direct Communications Mode
The EUT shall be set in direct communications mode provided with proper identities. Entering and leaving the direct communications mode shall be made by manual key pad entries.

The applicant shall inform the test laboratory about the applied identities and the value of T, see below.

When not processing a call, the EUT shall be in active unlocked PP state. When initiating a call the number of the wanted subscriber shall be entered via the key pad, and the EUT shall at off-hook enter the RFP active idle state continuously sending the page message for the wanted subscriber. See EN 300 175-3 [3], subclause 4.3.

2.2     When the EUT has Initiated a Handset-to-Handset Call
The EUT shall meet the RFP requirements with the following amendments:

General:

a) operation is only allowed on carriers with numbers 0 to 9. See EN 300 175-1 [1], subclause 7.1;
b) the applicant shall declare if identities class E are used, in which case the N T message will not contain an ETSI distributed code. See subclause 16.2. last paragraph;
c) the EUT shall use FP or PP simplex bearer channel selection rules for the RFP active idle state. See subclause 17.1;
d) the 25 ppm PP timer stability requirements apply. See subclause 8.4;
e) the EUT is not required to do receiver scanning for ARI class E. See EN 300 175-6 [6], subclause 5.5;

When in RFP Active Idle State:

a) the page message shall be transmitted in every frame for at least T seconds;
b) the short page format shall be used for ARI class E;
c) the EUT shall revert to PP active unlocked state, if a duplex bearer has not been established within 20 seconds.

2.3     When the EUT has Not Initiated a Call

a) The EUT shall scan all channels on carriers c < 10 at least every T seconds.
b) The EUT is only allowed to stay in idle locked state if it is being paged.
c) If ARI class E is used, the paged EUT shall make the bearer setup attempt on the channel pair where the initiating PP transmits.

Back to Features Index

Back to Top