IEEE 802.21 MEDIA INDEPENDENT HANDOVER
DCN:21-09-0043-02
Title: Responses to 802.21c PAR comments
Date Submitted: March 11, 2009
Presented at IEEE 802.21 session #31 in Vancouver
Authors or Source(s): James Han, Junghoon Jee, H Anthony Chan
Abstract: Responses to comments received from the different IEEE
802 working groups on the 802.21c PAR and 5C.
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IEEE 802.21 presentation release statements
•
This document has been prepared to assist the IEEE 802.21
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•
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The IEEE 802.16 Working Group has reviewed the draft P802.21c PAR and offers the following comments.
• In general, we appreciate the exemplary quality of this document.
• We do have one concern. Namely, we believe that, with the amendment, the scope of IEEE Std 802.21 would be expanded enough to make the title of the standard obsolete. Therefore, we suggest that the PAR propose to rename IEEE Std 802.21. Our suggestion is the following: “IEEE Media
Independent Handover and Multi-Radio Services.” We believe that this title would provide for additional future amendments, without a title change, should interest develop in other multi-radio services.
– We thank you for your comments, which are excellent. There will indeed be more services which can be built above 802.21 beyond handover such as multi-radio power management.
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General comment:
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If you are managing Watts, then measure Watts.
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Power consumption is not generally available from Radio interfaces, so it is not meaningful to manage power control using measurements that are not available. (802.2 LLC does not expose power consumption).
– Each technology defines its own power saving mechanisms to reduce its own power consumption. MRPM will not change the power saving mechanisms defined by that technology.
Therefore, MRPM ’ s approach is based on existing power saving modes and does not need to measure Watts. MRPM will provide the mechanism to manage and coordinate multi-radios in the device and their networks to save power.
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Multiple Radio Power Management does not belong in 802.21.
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Handover control is not the same as Power management
– We think that 802.16’s comments, “Our suggestion is the following: “IEEE Media Independent Handover and Multi-
Radio Services. We believe that this title would provide for additional future amendments” are excellent and as a matter of fact, there will be more services which can be built above
802.21 beyond handover such as multi-radio power management.
•
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Power management in a client is truly an implementation issue not a standardization issue
– We do not eliminate the ability of the client to manage power.
MRPM extends this ability through network support of additional power saving options.
– Current standards have defined various power saving modes for power management. Without such standards, the network and the device from different vendors cannot achieve today’s talk time and standby time. MRPM is built above these power saving modes in their respective standards to coordinate and manage multi-radio power.
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The 5C provide insufficient justification for starting this project.
– We have added the following to section 17.5.1a Multiple vendors and numerous users in the revised 5C: “Multi-radio devices have already experienced battery life problems.”
– In addition, the need for the project is in Section 5.5 of the
PAR.
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The stated objective for the PAR is as follows:
"The purpose of this amendment is to enhance the user experience by extending the battery operating life of multi-radio mobile devices"
In reading the PAR/5C (in particular Clause 5.5 & Clause
17.5.4) the text suggests that the power improvement only applies to multi-radio devices while only 1 radio is active.
The problem with focusing on saving power by choosing 1 radio over another is that it implies that the device may only use 1 radio at a time for all applications running on the dual mode device.
Several points are worth raising about this issue:
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• Comment 1: * Many dual radio devices operate today with both radios active. Saving power while BOTH radios are active is a major concern. However, this PAR ignores this use case by suggesting that the solution to the power save problem is to deactivate or disable the secondary radio. The PAR should not suggest a solution to the dual-radio device power save problem is to deactivate the secondary radio.
– We agree and the 4th paragraph in section 17.5.4 has been amended into: Radios that are not in service in a mobile multiradio device may be turned off or put into a lower power state.
Should traffic be sent to one of the turned off radios then it is desirable that the mobile client be notified of that traffic on an active radio. Upon such notification, the mobile client may turn on the target radio.
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• The proposed PAR suggests having the .21 "system" enable a mechanism to switch between radios rather than enabling both radios at the same time. It would seem that the .21 is forcing itself into the data path of applications to ensure only one radio is active at a time. It is not clear that this is practical and scalable. The PAR needs to focus on saving power without requiring devices switching between radios coordinated by the
.21 system. The PAR also suggests that the .21 will become the entity that chooses the "right" network/radio. This is inappropriate for a IEEE technology to create such a system.
– The MRPM is not an entity to choose the right network itself.
MRPM will define mechanisms for multi-radio power management and coordination. The defined mechanisms can be utilized by a network selection entity in choosing the right network.
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• It is not clear how a .21 system knows what is the best power saving option for each radio technology so in a practical sense what terms are defined in the PAR for saving power other than shutting down radios?
• MRPM coordinates and manages multi-radio power management through network support. It turns unused radios into lower power states. It enables an off radio to be awakened through a different radio.
• It is not clear that the PAR is focused on the right problem to saving power with dual radios active.
– We already answered that more than one radios may be in service. However MRPM cannot provide power saving if all radios need to be in service.
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Comments to section 8.1
• PAR language 8.1: “2. Enable the optimal power configuration of different radios in a multi-radio mobile device: whether radio is “on,” “off-available,” or “off-do-not-disturb.”
• Comments: There are more variations on power saving than these three “configurations”, none of which are “optimal”.
– We thank you for your comment and have revised the above sentence into:
– 2. Enable the power configuration of different radios in a multiradio mobile device to reduce power consumption: whether radio is “on,” “off-available,” “off-do-not-disturb,” or in other states.
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Comments to section 8.1
• PAR language 8.1: “3. Enable power management through coordination across multiple networks of different radios, taking into account the power management functions in individual radios and networks and QoS requirements.”
• Comments: You cannot put license-exempt bands in the same power regime as licensed bands, as the reliability of management communication is vastly different. Changing the radio’s modulation and coding scheme has as large an effect on power consumption as changing sleep strategy.
– We are not trying to change the existing modulations and coding schemes. Our purpose is to manage and coordinate the multi-radio device (either radios in licensed-exempt bands or licensed bands) to reduce power consumption
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Comments to section 8.1
• PAR language 8.1: “3.1 Keep an energy efficient radio “on” for receiving notification of incoming service.”
• Comments: not just energy efficient, but also able to receive and communicate reliably. One also needs to know the power consumption per service per radio in order to choose among radios for a requested service.
– The optimization goal can include reliability and power consumption or their weighted combinations.
We revise this sentence in section 8.1 to:
– 3.1 Keep an energy efficient and reliable radio “on” for receiving notification of incoming service.
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•
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Comments to section 17.5.1 Broad Market Potential
• 5C language a) Broad sets of applicability: “One major bottleneck in the implementation of multi-mode terminals for any application area is the overall power management mechanism for different radios, each with its own mechanism. We expect multi-radio devices to depend on 802.21 services that should be extended to improve the power efficiency of multiradio mobile devices.”
• Comments: Power management mechanisms are specific to device types and services, not radio interfaces. The claim than an 802.21 API would allow better power management than current schemes is not supported by any reference in these 5C.
– Power management includes many aspects, such as, radio communication, display, services, background light, etc. The power management of multiradio device investigated here focuses on multiple radio communication issues. It will reduce the power consumption caused by multiple radios’ communication.
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Comments to section 17.5.1 Broad Market Potential
• 5C language c) Balanced costs (LAN versus attached stations).: “Multiradio equipment is accepted as having balanced costs. The addition of multiradio power management capabilities will not increase the costs of devices significantly.”
• Comments: It would increase the message traffic between radio types, without proven benefit.
– The control signaling traffic will increase slightly for the specific radio. The gain is in power consumption reduction in the other radios. There are published papers showing the net gain such as.
• Shih, E., Bahl P., and Sinclair, M.J., “Wake on Wireless: an event driven energy saving strategy for battery operated devices,” in Proc. ACM Int. Conf. Mobile
Computing and Networking, 2002.
• Agarwal, Y., Schurgers C., and Gupta R., “Dynamic Power Management using On
Demand Paging for Networked Embedded Systems,” in Proc. of Asia-South Pacific
Design Automation Conference (ASPDAC), 2005.
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Comments to section 17.5.2 Compatibility
• 5C language: “Consideration will be made to ensure compatibility with the IEEE 802.21 and IEEE 802 wireless architectural models.”
• Comments: The IEEE 802 O&A does not provide management plane standardization for power consumption. Name the IEEE
802 radio standards that expose power consumption measurands today, and relates those measurands to traffic streams.
– As mentioned before, MRPM will not change the power saving mechanisms defined by each individual radio technology and its approach is based on existing power saving modes. MRPM does not need to do power measurements.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “The ability to save power has been proven in various wireless access technologies such as IEEE 802.11 power saving mode, IEEE
802.16e idle mode and sleep mode, and cellular power saving modes in
3GPP/2.”
• Comments: No two are the same, and each trades latency for power saving.
There is nothing in the management interfaces of 802.11 that reveal the power consumed in transmission, in frame reception, in idle or in sleeping.
Regardless of 802.21’s technical algorithms, no power consumption measurand input equals a psychic management scheme..
– It is true that no two are the same. This is the reason why we need MRPM to manage and coordinate multiple radios to reduce the power consumption.
The measurements are not the necessary condition for power reduction approach in MRPM. Each technology already worked out the relative power consumption for various power saving modes. The MRPM can use these information to develop efficient power saving approaches.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “The ability to locate and page a single-radio mobile device in dormant mode is also a proven and tested technology in various networks such as 3GPP/2.”
• Comments: This observation has nothing to do with the technical feasibility of multi-radio power management of unlicensed band radios, which do no paging.
– It is true that there is no paging in unlicensed band radios. But there are power-saving modes: such as PS mode and extended
PS mode. The MRPM does not only deal with radios with paging, but also deal with unlicensed-band radios without paging.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “Methods of coordinating the operating modes of multiple independent radio interfaces as well as comparing the relative energy consumption of those radio interfaces can be defined as extensions of IEEE
802.21 which is an extensible protocol and which supports multiple radio interfaces.”
• Comments: 802.21 is not chartered to define power consumption metrics for streams in radios defined in other standards, nor to request interfaces that provide that information, nor to control power consumption. Without changing the management interfaces of unlicensed radios, no methods of power consumption coordination are technically feasible.
– The power consumption measurements are not a necessary condition for
MRPM as mentioned before.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “All but one radio in a mobile multi-radio device may be turned off to save power. Should traffic be sent to one of the turned off radios then it is desirable that the mobile client be notified of that traffic on its active radio. Upon such notification, the mobile client may either turn on the target radio or route the traffic over the currently active interface. The correct choice depends on the anticipated traffic, the performance characteristics of the radios, and on a policy. Regardless, an
MRPM entity must coordinate with an entity in each radio’s network in order to update its routing information to reflect the current interface power modes. This operation is similar to the Mobile IP routing update normally required by mobile nodes. Mobile IP is an established routing protocol and a similar update mechanism and demonstrates the feasibility of this approach.”
• Comments: This observation ignores the cost of maintaining and communicating traffic over each of the radios, as all but one may be turned off. This text does not acknowledge the fact that multi-radio power management costs more energy to perform than single radio power management does. Balancing traffic among sleeping radios is not technically feasible without changing the management interfaces of unlicensed radios.
 (Response in next slide)
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– The specific radio traffic will increase slightly for the other radios due to the small amount of control signaling. However, we can expect more gain in power consumption reduction.
• MRPM needs to know the power saving status of unlicensed radios but does not need to change the management interface.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “IEEE 802.11 supports a power saving mode that is effective when confronted with isochronous traffic flows. “Always on” applications and bulk data transfers reduce the effectiveness of the 802.11 power save mechanism. Because of its high data rates, 802.11 is also an economical choice when a host needs to transfer large volumes of data. These observations have been noted in the literature with several suggestions that a cross-layer power savings can be obtained by intermittently running the radio interface at full speed and otherwise leaving it turned off. Access network entities such as Intermediate-TCP have been proposed to facilitate this sort of periodic power operation and their effectiveness has been demonstrated in actual implementations.”
• Comments: This observation is a judgment, as some want two-second sleep time to be supported by access points. There is no provision in the 802.11 standard for access points to start isochronous traffic flows for sleeping stations. This operation is not technically feasible without changing the management interfaces of unlicensed radios.
 (Response in next slide)
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 We agree with your comment and have deleted this paragraph.
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Comments to section 17.5.4 Technical Feasibility
• 5C language: “There may be a tradeoff between the service availability of always-on connectivity and battery life. Yet existing platform- and network-specific power managers that operate independently without considering the overall power consumption of a multi-radio mobile device may result in shortened battery operation life, which according to user experience is contradictory to a reliable service. This project to enhance battery life is trying to enhance such user experience. In addition, no specific new hardware technology is introduced, so hardware reliability should not be an issue.”
• Comments: 802.21 has not provided anything that shows a general power management algorithm would work as well as those currently employed by manufacturers of multi-radio devices. Until 802.21 posts some white paper or analysis that shows what improvement is possible, the technical feasibility is unknown.
 (Response in next slide)
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 Currently multi-radio devices have already experienced battery life problem and are using proprietary protocol to solve the problem.
 802.21 provides Information service, event service, and command service for heterogeneous networks. MRPM coordinates and manages multi-radio power using these services.
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Comments to section 17.5.5 Economic Feasibility
• 5C language: “Sections of this work simply represent an incremental cost in enhancing the baseline implementation of IEEE 802.21. Additional costs will be incurred owing to facilitating network coordination. Where coordination with core network entities is required, the capital and operational costs should be similar to that of installing Mobile IP servers. Where coordination between the mobile device and access network is required, the capital and operational costs will be similar to that of installing an operating system utility at an access point.”
• Comments: These statements do not account for the operating costs of communicating power consumption to an 802.21 management mechanism, and taking direction from it. By definition, such traffic is in addition to normal operation.
 First, the amount of traffics and messages are relatively very small in addition to normal operation. Second, the extra power consumption related to the additional traffics and messages is much less than the power consumption to make the extra radio “on”.
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Comments to section 17.5.5 Economic Feasibility
• 5C language: “IEEE 802.21 is uniquely positioned to provide a coordinating role in radio power management. IEEE 802.21 already provides a uniform set of services that work across heterogeneous networks. ”
• Comments: 802.21 required the 802.11u amendment to create new elements in the
802.11 MAC and expose them to 802.21. This PAR does not provide energy management hooks in 802.11 at all, and without them, this PAR does not provide any value to 802.11.
– The power consumption measurements are not a necessary condition for MRPM as mentioned before. The energy management hooks in 802.11 are not needed. The
MRPM manages and coordinate multiple radios to achieve the reduction of power consumption. It does not try to reduce power consumption within 802.11. Therefore, the power measurements within 802.11 are not necessary.
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