Understanding Infrared Speed

The Infrared Data Association (IrDA) has developed four transfer rate (“speed”) standards for short- range infrared data transmission:

SIR* (Serial Infrared): 115.2Kbps, which is broadly adopted in mobile phones and many portable devices. MIR (Medium Infrared): 1.152Mbps, which is rarely adopted. FIR (Fast Infrared): 4Mbps, which is adopted in laptops and digital cameras and some Pocket PC PDAs. VFIR (Very Fast Infrared): 16Mbps, which is supported by Windows XP.

*[Note: SIR includes baud rate from 300 to 115200. Clarinet implements 9600, 57600 and 115200 baud.]

Two systems involve in the infrared communication will negotiate the speed during the establishing stage and automatically adopt the highest speed both can support.

Devices Using IrDA Infrared

Most notebook computers and handheld devices have an infrared port making it easy and convenient to exchange information. IrDA has been implemented in all notebooks using Windows 95/98/Me/2000/XP. For the past several years the FIR standard is inherent in notebooks using these versions of Windows. Windows XP goes further and has support for VFIR, which notebook manufacturers will soon migrate to. Apple Macintosh notebooks and notebooks using Linux also support FIR and have the additional IrDA protocol known as "IrLAN" which essentially is a virtual Network Interface card but uses the infrared port as the point of network access.

Most handheld devices running the Palm OS and PocketPC (PPC) OS have support only for SIR although this will soon change in favor of faster infrared FIR speeds for such devices as Compaq iPAQ's H36xx/37xx series providing Clarinet’s iPAQ FIR driver is installed (see Clarinet's website at: www.clarinetsys.com). NEC's Pocket Gear PG5000 and MobilePro P300 have just been released with FIR enabled at the point that this document was written. Later in this document we will present methods for software and hardware engineers and network administrators to increase infrared performance and throughput at the design and planning level.

Benefits of Using Infrared

Infrared is a mature and stable technology that has been around for many years and is on most portable devices whereas Bluetooth (Radio Frequency) has not taken hold as yet and is not included in any of the above operating systems. IrDA infrared is secure as it is purposely limited at one meter line-of-sight and thirty degrees cone. Keeping in shorter distance, infrared uses very little power, which is an important factor to consider when it comes to handheld devices. The cost of using infrared is minimal (IR transceiver module is less than $2) whereas Bluetooth is expensive (chipset is at $20 range). Bluetooth 1Mbps is shared amongst users whereas infrared offers dedicated connectivity -- up to 4Mbps when using Clarinet Systems' infrared networking technology.

Note: There are various infrared technologies on the market are not IrDA compliant. "Diffused IR", although not being able to penetrate a solid object can avoid line-of-sight limitations and reach other infrared enabled devices at a distance. High power infrared beams transfer high-speed data from 45Mbps to 10Gbps and are installed between buildings within a few miles for security protection or toll stations with high accuracy. The trade-off of these technologies versus IrDA's IR protocol is the high cost and great power consumption.

Infrared Performance Consideration for PDA Applications The performance of infrared LAN access and network synchronization depends upon the following factors:

1. PDA CPU speed

2. Infrared speed

3. Synchronization software

4. Application program design

5. Network infrastructure

With these factors in mind a small file transfer or data synch may take a few to tens of seconds or, if data is in megabytes, it may take up to several minutes or longer on current SIR enabled palm-sized PDA devices. With the future implementation of FIR as the standard port in PDAs these factors will not be a major concern. For now, there are ways to improve infrared throughput :

1. CPU Speed. Newer versions of Palm PDAs have a 33Mhz CPU instead of 16Mhz delivering for better performance but still far slower than PPC. However, most PocketPC devices have a powerful CPU, which delivers great IR performance. PPC with 206Mhz CPU performs IR transfer 5 times faster than current Palm devices.

2. Infrared speed. Giving enough CPU power, infrared speed represents the most critical factor impacting IR performance. Since the majority of infrared speed implemented in Palm and PocketPC devices today is SIR, the file size has to be relatively small in order to transmit data in a few seconds or in the tens of seconds -- which is especially true for Palm devices. Clarinet's FIR driver offers speeds at least 8 times faster than SIR. If it is possible, users should consider buying PDAs with FIR capability such as Compaq iPAQ's 36xx/37xx with Clarinet’s FIR driver or NEC’s PocketPC offering (see above).

For a 500 Kbytes file transfer

* Compaq ships iPAQ 3600/3700 with FIR hardware, but with only SIR driver.

** Palm device shipped with SIR only.

1. Synchronization software. Synchronization software such as HotSync, HotSync server, AvantGo, EXTDConnect, Synchrologic, Aether Systems' ScoutSync server and others implement different schemes and techniques for providing synchronization that directly impacts performance. Some synchronization software and application programs implement a lot of connection assurance, which is required for RF (802.11 or cellular) but is not necessary for infrared because infrared is already a secure connection -- as if actually being physically wired. For instance, the SSL (Secure Sockets Layer) feature in AvantGo is not needed for IR connection, which if not used, would result in a 30% performance increase. Some synchronization software are far more optimized than the others, therefore, synchronization time could vary dramatically depending on which software is selected.

2. Application program design. Application program design impacts sync time too. For instance, some applications may copy the entire data exchange between PDA devices and the server during each and every sync rather than just synching the data that has changed -- this increases sync time substantially. Given the speed limitation of PDAs today, the application should sync only data that has been modified. With some programming effort, Clarinet Systems' OBEX functionality in its EthIR LAN and EthIR STAR line can improve network throughput 2-3 times over a conventional TCP/IP/PPP connection.

3. Network infrastructure. Normal network infrastructure and traffic is usually not a factor in supporting hundreds of PDA connections simultaneously. However, in many situations, incorrect subnet partitioning, wrong IP address assigning, improperly planning router setup, and jamming caused by high traffic broadcasting does happen -- these will have a major impact in the PDAs network performance. If the synchronization has to go through the Internet, then the sync time could be affected even more depending on the Internet's traffic load.

Infrared Performance Improvement for PDA Manufacturers

Linux, Mac, EPOC, and all of the Microsoft's OS including PocketPC support both SIR and FIR in its IrDA protocol stack. Although Palm supports SIR, it has not delivered FIR capability yet so it is difficult to prove if Palm OS can support the FIR protocol. The IrDA protocol stack supposedly is independent of SIR and FIR -- it is the device's infrared driver that determines whether it is going to use the SIR or FIR transfer rate. Therefore, it is very likely Palm OS supports both. Palm’s licensee should confirm with Palm before incorporating FIR circuitry.

In order to support FIR, the manufacturers need to develop an FIR device driver. A good FIR driver can perform two times faster than a driver that is not efficiently coded. To gain performance, the driver should use smaller turn around time -- 1ms -- and a maximum packet window size of 7 as specified in IrDA specs.

Since the IrDA protocol is a reliable link, Windows 2000 and XP increase IR performance further by implementing IrNET, an optimized PPP protocol at packet level. Clarinet’s IR products support IrNET. Some vendors may have had plans to implement IrNET to gain performance and, thereby, saving battery power.

Infrared Performance for PDA users

On current PDAs FIR delivers a data rate at least 8 times faster than SIR. Users looking for a new PDA should select one with FIR capabilities as outlined at the beginning of this document. Everyone should urge PDA manufacturers to implement FIR for their newer version of PDA devices.