IrLAP – Infrared Link Access Protocol

ByMary Hsieh and Peggy Shen

Points that will be addressed

The services that IrLAP providesThe assumptions that are made about the environment when the protocol is executedThe vocabulary of messages used to implement the protocolThe encoding of the messagesThe procedures

Intro – Bit and Byte Ordering

Datagram formBinary formHex formMultiple Byte Form

Note: Half Duplex

Intro (background info) – OSI and TCP/IP Models

OSI ModelApplication

PresentationSession

TransportNetwork

Data LinkPhysical

TCP/IP ModelApplication

TransportInternet

Host-to-Network

Services – Definition

RequestIndicationResponseConfirm

Upper Layer Upper Layer

IrLAP Layer IrLAP Layer

Request IndicationResponse

Confirm

Packets transferring

Data Link Services – (Continued)

Discovery Services Discover what devices are ready or

compatible

Address Conflict Services Resolves device address conflict issues

Unit Data Services Unreliable, connectionless way to send

data, usually through broadcasting

Connection Oriented Service

Connect ServicesSniffing ServicesData ServicesStatus ServicesReset ServicesDisconnect Services

Example: IrLAP_service.request(Handle)

Environment and Operational Characteristics - Configurations

Point to point, point to multipointHalf duplexHidden nodesNarrow infrared cone (15 degree half angle)Synchronize transmission speedNo collision detection

Data Link States and Modes

Connection state Has a connection

Contention state Waiting for a connection

Modes NRM – Normal Response Mode NDM – Normal Disconnect Mode

Frame Structure

To determine where the frame begins and endsTo determine whether the frame is intended for that stationTo determine what actions to perform with the information receivedTo detect the occurrence of transmission errors in received framesTo acknowledge its receipt of frames to the transmitting station

Example of a Packet

A normal packet

Elements of the IrLAP Frame

Address Field – 8 bits ( least significant bit is the command/response identifier bit)Control Field U – unnumbered S - supervisory I - Information

Information Field Must be a multiple of 8 bits

IrLAP Description of Procedures

Steps to Connect, Transfer, and Disconnect

Conclusion

What may be useful for our project We can use the broadcast command to send

out signal We know what the packets look like, so we

can use the oscilloscope to see what they look like in analog form

If we can’t use the IrDA port to transmit and receive signals through the skin, we could at least use it to transmit data that has been collected

Conclusion - Continued

What would impede our project Half Duplex – if data cannot move in both

directions at the same time, it may be difficult to send signals and get them back in a timely fashion

Start/End Header – if we send a signal to the skin, the skin would not be able to generate a packet with headers that tells the IrDA port to get ready for data reception

Bit Representation – it would be hard for us to control what is sent out in bits, etc.

Conclusion - Continued

Therefore, we have concluded that we cannot use the IrDA port to do what we would like it to do. We would need a separate piece of hardware between the PDA and the laser diode to do the job.

Bibliography

http://www.irda.org/standards/specificationsoldest.asp