Order Issuer 

•     Want reliable communication of any length message
1. Tell packet-person "come back into room".

Wait for acknowedgement.

Order taker

1. Accept order.
2. Do order

Packetizing Person

• Want from lower level:  Packets that always get thru correctly
• Offer higher level:  Full length messages.

1. Accept message.  Append the word "eend" to the message
2. Hand first undelivered word to error checking person.
3. Wait for ack
4. If more words, go to step #2.
5. Tell Order issuer that message was delivered.

Go to step 1

Assembly person

1. Accept each packet from error checker.
2. If you see word "eend", 
1. Hand all packets accept the "eend" to the order taker.
2. Throw away "eend" packet.
3. Go to step 1

Error checking person

• Want from lower level:  Packets that maybe get thru
• Offer higher level:  Packets that always get thru and are correct.

1. Accept packet
2. Append the number of letters onto the packet.  For instance, if the packet is "also" you make the packet be "also4".
3. Give packet to yeller.
4. If no ack within 30 seconds, go to step 3.
5. Tell packetizing person that packet was delievered.
6. Go to step 1

Error Checking person

1. Accept packet from listener
2. If number matches packet length,
1. Tell listener to say "O.K."
2. Hand packet to assembly person
3. Go to step 1

Yeller

• Want from lower level:  Quiet room in which to yell
• Offer higher level:  Packets that may or may not get thru

1. Yell (gently) each letter or digit in the packet.
2. If here OK, tell error checker OK
3. Go to step 1

Listener

1. Write down each letter or digit you here.  Hand list to error-cheker.
2. If you get a command to say "OK", then do so.
3. Go to step 1