eoc state transitions

The following shall govern state changes as shown in Figures 18 and 19.

1) The protocol state changes are performed based on received messages. At the ATU-C, received messages are responses from the ATU-R to messages sent from the ATU-C. Depending on the ATU-C receiver protocol state, the ATU-C transmitter message set may be restricted. It is left up to the ATU-C transmitter to organize and send a sequence of message such that the right response from the ATU-R is achieved based on the receiver protocol state machines.

2) (#"message" = N) is true if and only if the previously received N messages are identical (i.e. all 13 bits equal) and properly addressed (i.e. having ATU-R address). (#"message" = 1) means the most recently received message is different (in at least 1 out of 13 bits) from the immediately preceding message and is properly addressed.

3) Moving to another state (based on the message received) shall be considered first, then the (same or new) state shall be executed. At the ATU-R, execution of commands in the Idle state shall be as described in 8.3 (invoking latching, unlatching or self test).

4) All the eoc messages with bit 5 set to 1b shall be considered as received messages and cause

an eoc response message at the ATU-R. Other eoc messages shall not cause a change of state in the eoc state machine and shall not cause an eoc response message at the ATU-R. The responses allowed from the ATU-R fall into three categories:

1) message/echo-response protocol states: Idle State and EXE State; 2) message/Unable-to-Comply-response protocol state: UTC State;

3) message/data-response protocol states: Data Read States and Data Write States; 4) (Data Read States includes Pre-Read, Data Read odd and Data Read even states)

(Data Write State includes Pre-Write, Data Write odd and Data Write even states).

Autonomous messages do not effect the eoc protocol states. The reception of the DGASP message at the ATU-C may however cause a reset at the ATU-C leading to an eoc state change at the ATU-C (e.g. to Idle State).

The eoc protocol shall enter the Message/Echo-response protocol state (Idle State) when the ATUs transition from the initialization and training sequence to steady state transmission. In order to cause the desired action in the ATU-R, the ATU-C shall repeat the message (without exceeding the limit of outstanding messages) until it receives three identical consecutive eoc message echoes from the ATU-R. This completes the command and response protocol, but the ATU-C may continue to send the same message thereafter. The command and response protocol for that message must be completed before a new message (containing a new command), which may induce a different protocol state in the ATU-R, may be issued.

At the ATU-R, depending on the state it is in, various restricted sets of eoc messages shall be acceptable. These sets shall be as shown in Table 16. Reception of other, inapplicable, messages shall result in an Unable to Comply (UTC) response to the ATU-C.

Table 16/G.992.2 – eoc messages acceptable at the ATU-R ATU-R state eoc messages acceptable at the ATU-R

Idle All messages acceptable

UTC All messages acceptable

Data pre-read Read NEXT odd RTN HOLD

Data read odd, even NEXT odd NEXT even RTN HOLD

Data pre-write WRITE DATA odd EOD

Data write odd, even DATA odd DATA even EOD

8.4.2.1 Message/Echo-response protocol state

This state is identical to the Idle state shown in Figures 18 and 19. To initiate an action at the ATU-R, the ATU-C shall begin sending eoc messages with the Data/opcode set to 1b and with the

appropriate message opcode in the information field.

The ATU-R shall initiate action when, and only when, three identical, consecutive, and properly addressed eoc frames that contain a message recognized by the ATU-R have been received. The ATU-R shall respond to all received messages. The response shall be an echo of the received ADSL eoc message. The combination of the ATU-C sending an ADSL eoc frame and the ATU-R echoing the frame back comprises the Message/Echo-response protocol state.

For the ATU-C to confirm correct reception of the message by the ATU-R, the message/echo-response ADSL eoc protocol state is repeated until the ATU-C receives three identical and consecutive echoes. This serves as an implicit acknowledgement to the ATU-C that the ATU-R has correctly received the transmitted message and is acting on it. This completes the Message/Echo-response protocol state.

The ATU-C continuously sends the activating message after the receipt of the three valid echoes, or alternatively, it may switch to sending the "Hold State" message. If the message was one of the latching commands, then the ATU-R shall maintain the commanded condition until the ATU-C issues the appropriate command that ends the specific latched condition or until the ATU-C issues the "Return to Normal" command (at which time all latched conditions in the ATU-R shall be terminated).

8.4.2.2 Message/Unable-to-Comply response protocol state

When the ATU-R does not support a message that it has received three times identically and consecutively, it shall respond with the Unable to Comply (UTC) ADSL eoc response message with its own address in lieu of a third identical and consecutive echo. In this manner the ATU-R will switch to the message/UTC-response protocol state.

The transmission by the ATU-R and reception by the ATU-C of three identical, consecutive, properly-addressed Unable to Comply messages constitutes notification to the ATU-C that the ATU-R does not support the requested function, at which time the ATU-C may abandon its attempt.

8.4.2.3 Data Read State

To read data from the ATU-R, the ATU-C shall issue a bidirectional READ eoc message to the ATU-R that specifies the register to be read.

INFORMATION field of the "Next Byte" echo message. The ATU-C continues to send the "Next Byte" message and the ATU-R continues to respond with the "Next Byte" echo message containing the first byte of data in the INFORMATION field until the ATU-C has received at least three consecutive, identical and properly addressed data frames with bit 4 set to indicate "odd byte".

If there are more data to be read, the ATU-C shall request the second byte of data by sending "Next Byte" messages with bit 4 set to 0b ("even byte"), repeating the procedure defined above for reading

the first byte from the register.

The procedure using the "Next Byte" message continues for the third and all subsequent bytes with the value of bit 4 toggling from "odd byte" to "even byte" or vice versa, on each succeeding byte. Each time bit 4 is toggled, the ATU-R echoes for two correct frames, and starts sending the data frame on the third reception. The process ends only when all data in the register has been read.

To continue reading data, once the ATU-R is in the Data Read odd or even State, the only message that the ATU-C is allowed to send is the "Next Byte" message with bit 4 toggling. To end the data read state abnormally, the ATU-C sends either "Hold State" or "Return to Normal", depending on whether any latched states are to be retained. If the ATU-R receives any other message three times consecutively, identically and properly addressed while it is in Data Read odd or even State, it shall go into the UTC State.

If, after all bytes have been read from the ATU-R register, the ATU-C continues to send the "Next Byte" message with bit 4 toggled, then the ATU-R shall send an "End of Data" message (with bit 3 set to 1_b indicating opcode) beginning with the third such reception.

For the ATU-C, the data read state ends either when the ATU-C has received the last requested data byte three times consecutively, identically and properly addressed, or when the ATU-C has received three consecutive, identical and properly addressed "End of Data" messages with bit 3 set to 1b. The

ATU-C shall then switch itself and the ATU-R over to the Idle State with the "Hold State" or "Return to Normal" message, and the ATU-R shall release the register and leave the Data Read State after receiving three identical, consecutive and properly addressed "Hold State" or "Return to Normal" messages.

8.4.2.4 Data Write State

To write data to the ATU-R's memory, the ATU-C shall issue a bidirectional WRITE eoc message to the ATU-R that specifies the register to be written. When the ATU-R acknowledges with three consecutive, identical and properly addressed echo messages, the ATU-C sends the first byte of data by transmitting the DATA eoc message. The ATU-R shall acknowledge the receipt of the byte with an echo of the message. After the ATU-C is satisfied with three identical, consecutive and properly addressed echo responses, it shall start sending the next byte of data. Each time the ATU-C receives at least three identical and consecutive correct data echo responses, it shall switch to sending the next byte of data. It shall also toggle the "odd/even" bit accordingly. The ATU-C shall end the Data Write State with the EOD eoc message indicating to the ATU-R to return to the Idle State.

To continue writing data, once the ATU-R is in the Data Write odd or even State, the only message that the ATU-C is allowed to send is the DATA eoc message. If the ATU-R receives any other message three times consecutively, identically and properly addressed while it is in Data Write state, it shall go into the UTC state.

If, after all bytes have been written to the ATU-R register, the ATU-C continues to send a next byte of data, then the ATU-R shall send an EOD eoc message beginning with the third such reception.