4. Monitor Functions

4a. Network I/O drivers

4a1. Input

4a1a. Input message from IMP.

4a1b. Do error checking on message.

4a1b1. Verify checksum,

4a1b2. Send "message recieved" aknowledgement over control link if aknowledge mode is in effect.

4a1c. (trans)character translation

4a1c1. There is a strong possibility that the character translation may be done in the IMP.

4a1c2. This needs to be explored further with BBN.

4a1c3. There are two main considerations

4a1c3a. Should the translation be done by table or algorithm?

4a1c3a1. Initially it seems as though the best way to go is table.

4a1c3b. How should we decide which messages should be translated, i.e. is it desirable to not translate everything (YES!!) and by what means can we use to differentiate?

4a1d. Decode header, and pass message to correct recipient as identified by source, and link.

4a2. Output

4a2a. Build header

4a2b. Character translation

4a2b1. See remarks under the section on output translation (trans).

4a2c. Create checksum

4a2d. Check status of link

4a2d1. If there has not been a RFNM since the last message transmitted out the link, wait for it.

4a2e. Transmit message to IMP

4a2f. If aknowledge mode is in effect,wait for

4a2f1. RFNM from destination IMP.

4a2f2. Response from destination HOST over control line 0.

4b. Network status

4b1. Maintain status of other HOSTs on network

4b1a. If an IMP is down, then his HOST is considered to be down.

4b2. Maintain status of control lines.

4b3. Answer status queries from other HOSTs.

4b4. Inform other HOSTs as to status of primary and auxilliary links on an interrupt basis.

4b5. Inform other HOSTs as to status of programs using primary and secondary links