1.9GHz DECT Headset Security Guidelines
Products covered are the CS55, CS70, CS351/CS361, Savi, and derivatives that operate in the 1.9GHz DECT radio band.
What is DECT?
These products operate in the 1920 – 1930 MHz (1.9GHz) UPCS/LE-PCS radio band. UPCS refers to the Unlicensed Personal Communications Services band designation used in the USA. The equivalent designation in Canada is LE-PCS, for License-Exempt Personal Communications Service.
The voice transmission method is digitization, 32kbit/s ADPCM vocoding, encryption of the vocoded data, then formatting into TDMA format and PSK modulation. The transmitter operates at a low duty cycle in non-constant-envelope mode. The radio communications protocol is based on the European DECT standard, slightly modified to comply with the regulatory requirements for the UPCS/LE-PCS spectral etiquette, and for operating in the 1920 – 1930 MHz band instead of the 1880 – 1900 MHz band specified for Europe and countries sharing frequency bands with the European allocations.
Certification and type-acceptance
Each of these products is certified according to the requirements of 47 CFR Ch. 1 ss 15D for UPCS systems, the regulations established by the Federal Communications Commission of the United States. These products (when so marked with an IC registration number) are also certified for sale in Canada according to the requirements of Canada’s RSS-213 Issue 2.
Transmit levelsTransmitter signal level (transmitter output power) is 10mW peak and 0.4mW average. Measured maximum SAR level amongst all products is 0.013 W/kg. The transmitter used in these products is a low-power transmitter. For comparison, the average transmitter signal level is about 1/1000th of the maximum transmit signal level used b cellular phones.
These products use a TDMA/TDD transmission system. This transmission system turns the transmitter on periodically and at a low duty cycle to send voice data packets. This is similar to some modern cellular telephone systems, though at much lower transmit power. The low transmit power level generally permits operation of the products in all environments, the exception being within a few feet of EKG, EEG, pulse oximetry, or similarly sensitive equipment. The general rule about electromagnetic compatibility for the products is that units can be used wherever cellular phones can be used, and will be less of an electromagnetic compatibility challenge than a cellular phone because of the product’s much lower transmit signal level.
Security and unique identity
Plantronics 1.9GHz DECT product compliance with privacy and confidentiality regulations
The products each are HIPAA compliant and Sarbanes-Oxley (2002) sec. 404 compliant. This statement is based on the compliance of the encryption measures incorporated in the product with the requirements of USA regulation 45 CFR 164.312(a)(2)(iv).
Members of the Plantronics 1.9GHz DECT wireless headset product family provide excellent security against eavesdropping. The casual eavesdropper listening to the radio channel will hear only a buzzing sound since the audio is digitally coded and encrypted. The products avoid two users sharing the same channel and timeslot under normal circumstances because units automatically chose the best available channel, and will change channels automatically if the channel in use experiences interference from another user. In the event of operation in a high-density system where no other better channel and timeslot is available, two users near each other and sharing the same channel and timeslot will experience occasional mutes of the receive or transmit audio and occasional audio distortion artifacts, rather than intercepted audio.
The protection against deliberate eavesdropping is through user authentication and 64-bit true digital encryption of voice data according to the standard algorithm if EN 300 175-7. A description of the public portion of this encryption algorithm is available through the website of the European Telecommunications Standards Institute (ETSI). Individuals and organizations having a credentialed need for more detail regarding the encryption scheme should contact Plantronics Engineering through the Technical Assistance Center. The Plantronics 1.9GHz DECT products and the DECT standard in general are considered secure enough for commercial applications requiring voice privacy. This assurance is based on the 64-bit digital encryption of speech and the internationally-recognized and standardized encryption algorithm used.
Members of this product family use fixed-rate adaptive frequency hopping during idle-locked state, which is when the base and the headset are in range but audio is not enabled. This was done to ensure that the base and headset are compensating for changes in the radio signal spectrum due to other users and the presence of interferers, and thus to improve the reliability of the link, but it has the effect of adding a layer of security. The hop sequence is random, on the basis of the physical environment. 1.9GHz DECT product family members use aperiodic adaptive frequency hopping when an audio link is enabled, for the same reason. The system is aperiodic because in this mode rather than changing channels at a fixed interval of time, the system hops channels whenever there is another user sharing the same channel and producing interference. In an environment with many users, this adds a layer of security because users change channels from time to time, rather than staying in a fixed channel. This adaptive approach offers improved security relative to other systems which use a single, common and fixed hop sequence for frequency hopping.
Understanding pairing of base and headset units
The headsets and bases are paired uniquely. The communications protocol permits audio exchange only between a headset and a base that are paired. The user can subscribe a new headset to an existing base to create a new pairing, or an existing headset can be subscribed to a new base, but a base can be paired with only one headset at a time, and a headset can be paired with only one base at a time. When a new pairing is established, the old pairing is lost.
Each base and headset unit has a unique identity. A headset will link only to a base that has the identity that the headset is expecting, and a base will link only to a headset that has the identity that the base is expecting. The process of initially pairing a base and a headset to create the expected identifiers in each end of the link is called subscription. A base and a headset can each be subscribed to only one headset or base, respectively. If a new headset is subscribed to a base, the old headset is automatically unsubscribed, whether it is in the area or not.
If a second headset is subscribed to a base that is already subscribed to a first headset using the process described in the User Guide, the first headset will commence flashing its Talk LED about three times per second continuously, to indicate loss of subscription, and the establishment of a clear audio link through that headset will no longer be possible. See the subscription directions in the User Guide to perform re-subscription, in the event a headset has been unpaired from a base.
Pairing and multi-shift usage options
Some members of the Plantronics 1.9GHz DECT product family support a fast subscription process that facilitates rapid headset/base pairing. This feature allows multiple individuals each with a personally-assigned headset to use a single base and lifter at, for example, a three-shift 24/7 help-desk. Users retain their personal headset, and pair their headset to a commonly-used base unit at the start of their shift, automatically unpairing the headset of the user from the previous shift in the process. The fast pairing process is discussed in detail in the “Multi-Shift Pairing” section of the User Guide, if supported by the model in question.
Multi-shift usage with individual separate bases without daily pairing is also supported for low-user-density installations by means of daisy-chaining full base/headset systems, so long as full lifter function is not desired. Each base in this product family has a telephone input port that connects to the telephone in place of the telephone’s handset./ Each base also has a handset output port to which the telephone’s handset is then connected (in a single-user applications), for occasions when the user wants to use the handset instead of the wireless headset. In a multi-unit installation a base’s telephone input port can plug into another base’s handset output port in place of the telephone handset. A large number of bases can be connected in this manner to a single telephone; the first base in the chain has its telephone input port connected to the telephone in place of the telephone’s handset, then each succeeding base in the chain has its telephone input port connected to the handset output port of the preceding unit. The first unit in the chain (starting at the telephone) which has an active audio link receives the audio, as the audio is then switched within that base away from that base’s handset output port, so only one headset can be used at a time in such a multi-base system. In this multiple-base configuration it is not possible to have bases share a single lifter, though; only the last base in the chain can be used to connect to the lifter, if audio is to be routed properly to all bases.
The limit to the number of bases that can be connected to a single telephone is constrained by the power-line buzz in the audio induced by stray capacitance and the local common-mode voltage between the telephone and the local AC mains ground at the installation site. Individual installation will vary in the degree to which this is an issue. The multiple bases in such a daisy-chained system must also each be counted against the budget for total user density permitted in an area; accordingly, only a few daisy-chained systems in an area can be used, and range will be in-office only.
Some issues that may arise during pairing have to do with the timing of each step of the process.
- Pairing of a new headset must start with the audio link between the base and the previously-paired headset inactive. If the previously-paired headset has live audio with the base when pairing with the new headset is initiated, the pairing process may not proceed to completion properly with the old headset cleanly unpaired and the new headset paired.
- Progress in the pairing process is indicated by LEDs on the base and on both the new headset and the previously-paired headset. The red LED on the face of the base flashes to indicate that it is ready to pair. The green Talk LED on the new headset turns on continuously when the new headset is attempting to pair. When pairing of the new headset completes, the Talk LED on the new headset does out and stays out. At this point the previously-paired headset starts flashing its Talk LED at a rate of three times per second, since it has been unpaired.
- The new headset may take some time to complete the pairing process, particularly in a high-density installation. The new headset will not respond properly to control inputs (button presses or lifting out of the charging cradle) until the new headset’s Talk LED goes dark at the completion of the pairing process; providing control inputs on the new headset or the previously-paired headset prior to the completion of the pairing process for the new headset may cause the pairing process to terminate abnormally.
The battery used in the headset is a single Lithium-polymer cell. It offers all-days (10 hours) talk time on a three-hour charge, and half-day talk time on a 1-hour charge. The battery and charger system are designed to resist wear out of the battery; for many users, the battery will last the life of the product. The battery does not exhibit memory effect so best battery life is obtained by keeping the headset docked on the base when not in use.
The headset may run the battery down in a few days when the headset is out of range of the base unit. If the headset has a fully discharged battery, it must be docked for at least a few minutes to charge before use; one hour docking is recommended prior to use if the battery is completely discharged.
Battery state indications
Fully discharged - pressing the Talk button on the headset results in no response in the headset; no beeps from the earpiece, and no activity on the Talk indicator LED on the headset. Docking the headset in this state is necessary to charge it. The system will not subscribe or enter Talk mode for several minutes, until the battery charges somewhat.
Nearly discharged - pressing the Talk button on the headset results in the error tone (three beeps in the headset earpiece) and the unit does not enter Talk mode. A background beep (lower frequency) every 10 seconds is present, indicating that the battery is low. The system may not subscribe, or the system may subscribe if the headset is docked but may still not enter Talk mode, or the system may subscribe and enter Talk mode when docked but may not link after the headset is undocked, or the system may link but then go unlinked a few minutes after docking.
Normal - pressing the Talk button causes the system to enter the Talk mode. The system can be subscribed docked or undocked, and will link undocked or docked.
The headset battery will charge enough in a few minutes of docked charging to operate normally, at least for a few minutes.
Charger state indications
- When the charger in the base is charging the headset, the amber charge LED on the face of the base flashes once per second. This charging takes place about three hours to complete, for a completely discharged battery.
- After the charger has completed charging the battery, the amber LED switches from flashing to continuously one.
- If there is a fault in the battery, or the headset is not seated properly when docked, that amber charge LED will flash at a rapid rate. Try redocking the headset; if the problem continues then the battery needs to be replaced.
All products in the 1.9GHz family use a dynamic speaker. Various microphone type and positioning options are offered by individual models. Best audio quality is obtained if a particular product is chosen that is suitable for the level of ambient noise; noise-canceling capability often offers better transmit audio quality in a noisy area, and binaural capability may be attractive to users desiring best receive audio intelligibility when the usage area is noisy.
The audio processing is 32k ADPCM, telephony bandwidth. Listen volume adjustment is provided on the headset, with larger (centering) listen volume adjustment possible using the 1234 volume switch on the back of the base. Talk volume is adjusted using the up/down arrow buttons on the back of the base. Larger (centering) talk volume adjustment is possible using the ABCD switch on the underside of the base. Speech transmissions may be fully muted using the Mute control on the headset.
Plantronics 1.9GHz DECT products operate in the 1920 – 1930 MHz (1.9GHz) UPCS/LE-PCS band; all equipment approved for this band must implement a spectrum-sharing etiquette that minimizes mutual interference. The products do not generally suffer interference from systems that use other bands; the products are compatible with Bluetooth, LANs, and with 802.11a, 802.11b and 802.11g systems under normal circumstances. The products also will normally operate in an area where other 1.9GHz DECT products are in use, as the spectrum is generally shared on a non-interfering basis.
If the base or headset are placed within a few inches of a cellular phone, the system may experience interference. Reposition the cellular phone or the base or headset to increase the separation if this problem occurs.
For some installations the user may hear distorted sidetone. They hear their own speaking voice in the headset as they speak, and the audio sounds harsh or rattley. This usually occurs if the talk volume level is too high, or if there is a telephone compatibility adjustment that is not correct. If distorted sidetone occurs, the user should adjust the headset’s listen (receive) volume level to normal (where the “centered” beep is heard as the receive volume adjustment in the headset is adjusted up or down”, and should adjust the telephone’s listen volume to be centered. Then adjust the talk volume level downward using the Speak Volume Fine Tune up/down buttons on the back of the base until the distortion in the sidetone disappears. If the talk volume adjustment is already at or near the low end of the adjust range, change the Speak Volume Master slide-switch on the bottom of the base to the next lower letter; from D to C, C to B, or B to A, and adjust the Speak Volume Fine Tune up/down buttons for somewhat reduced talk level relative to the original loudness. Be aware that not all Telephone Configuration Dial tumbler positions will work with all Speak Volume Master slide-switch positions. For example, tumble position 1 may work with slide position B but not with slide position C. Most systems for which distorted sidetone is a problem will perform properly with one to three step of reduced transmit volume, adjusting the Speak Volume Fine Tune up/down button on the back of the base. After setting the talk audio level, readjust the headset listen (receive) volume to a comfortable level.
If distorted sidetone persists with reducing the talk (transmit) audio level, try changing the Telephone Configuration Dial tumbler setting to another position. Often several positions will appear to work but the audio will be distorted in one of the positions.
Be aware that the systems use an echo canceller which takes a few second to compensate for gain changes when the product level is adjusted; distorted sidetone may persist for a few seconds after the adjustment of transmit gain.
Range and user-density
Range for normal in-office use is as much as 100 feet, for an installation with only a few units in place. The effective limit to range is set by audio artifacts introduced by the weak signal. The system reduces the volume level when operating near the edge of range, to improve subjective audio quality. Range can be reduced within a building by the obstruction or interior walls, or by the presence of other systems using the UPCS/LE-PCS (1.9 GHz DECT) band, or by the presence of a large number of similar units in use in the immediate area.
Guidelines on planning a density site
The products can be used in a high-density application within certain limitations, if there are barriers such as cubicle walls preventing line-of-sight between individual users while in talk mode. The system automatically senses the presence of other users and will reduce coverage area if there are too many other users to permit good audio performance at a long range. In a high-density environment the system becomes a short-range in-office system. The level of density at which this effect begins to occur depends on how much time all users in an area spend with their systems in talk mode, and how far away the users are from each other. The general rule to follow is that in an office layout with cubicle walls high enough to prevent line-of-sight when users are seated, if there are more than 30 users talking at the same time and within 100 feet of each other, the system will be in-cubicle only. If there are fewer than 15 users within 100 feet, or with less than full-time usage, then the coverage area will be larger. IN a density-limited environment coverage may be limited by loss of audio (random muting), or by audio distortion artifacts increasing as the user walks away from the base. The worst-case for this coverage limit will occur when a user is distant from their own base but close to other users’ bases or headsets.
In a high-density application the headset may take some time to reestablish connectivity with the base when the user returns to the coverage area after having been out of range. It normally takes a few seconds for the headset to find the base’s signal as the user enters the coverage area, but this process can take a minute or so in a high-density application. To the user this effect appears as inability to enter talk mode until the user has been in the coverage area for a minute or so.
In most environments, even for high-density, users in a cubicle grid with walls high enough to prevent line-of-sight with other users while the system is in use will probably get clear audio within their own cubicle. Users will both receive and be a source of interference if they leave their work area while a call is in progress. For the users in a higher-density application, a dense open floorplan without cubicle walls, acceptable audio quality may not be achieved if there are more than 30 users within view. Achievable density for all installations is dependent on the building layout, and on other environmental factors. Experience with such products has taught that often performance in a high-density application is satisfactory even for a very large number of users, several hundred on a building floor, as long as there is sufficient physical separation of the radio signals from different users. This separation can be attained by cubicle walls, by hardwalls, or in some cases by physical distance. An open-plan layout (no cubicle walls or hardwalls) with more than about 30 users of 1.9GHz unity within line of sight of each other will, however, probably not offer acceptable audio quality for most users even at short range from base to headset.
In high-density applications it is important not to have other UPCS/LE-PCS or 1.9GHz DECT products in use in the area. Even though such systems are required by the conditions of regulatory approval for the UPCS band to automatically choose channels of operation in such a way as to minimize mutual interference, interference ultimately limits density. Interference may come from systems well outside the coverage area, as the range for interference is greater than the coverage range.
1.0GHz DECT over/underlay with CS50 systems for simultaneous density and roaming
The 1.9GHz DECT product family members operate in a different radio band than does the CS50. The CS50 uses 902 – 928 MHz, so the CS50 and 1.9GHz DECT products each do not mutually interfere with products of the other type. Accordingly, adding CS50s to a 1.9GHz DECT installed base, or vice versa, does not degrade performance in either system. This can allow high-density CS50 installation to coexist physically in the same area as a high-density 1.9GHz DECT system, offering a net greater density, or it can allow a low-density CS50 or 1.9GHz DECT system to coexist physically with a high-density system of the opposite type. If a customer desires to have both long-range and high density service within an area, the mass of users can be offered 1.9GHz DECT product family units, and a few CS50 units can be installed for supervisory staff or those with unique roaming requirements. As long as the number of CS50 units within a geographical area is limited, the CS50 users can roam. The 1.9GHz DECT product users, with a unity on every desk (for example) are limited in roaming range, but the CS50 users are not so constrained. A typical such installation in a cubicle environment would have a 1.9GHz DECT unit on every desk offering performance as noted previously in the discussion of high-density installations, while up to 30 users of CS50 systems could be present in the “long range area”, each roaming to the full range offered a CS50 system in a low-density application, limited only by the signal strength loss with distance rather than by interference from other users. For such a system, the high-density installation portion should be based on 1.9GHz DECT units, and the long-range portion should be CS50-based, as the CS50 has a longer native range.
Products within the 1.9GHz DECT product family share the same band, and so such units count equally towards total attainable density irrespective of type within the 1.9GHz DECT product family.
Accurately predicting the effective range and region of susceptibility to interference for individual environments and building layouts is of sufficient complexity as to be beyond the scope of this discussion. The preceding information is provided as a reference for system planning, and performance of individual installations may vary.