DLEP Control Plane Based Pause Extension

Three data items are defined by this extension. The Queue Parameters Data Item is used by a modem to provide information on the DSCPs it uses in forwarding. The Pause Data Item is used by a modem to indicate when a router should cease sending packets and the Restart Data Item is used by a modem to indicate when a router can resume sending packets.

The Queue Parameters Data Item is used by a modem to indicate DSCP values that may be independently paused. This data item MUST be included in a Session Initialization Response Message that also contains the Control Plane Pause Extension Type Value in the Extensions Supported Data Item. Updates to these parameters MAY be sent by a modem by including the data item in Session Update Messages. The Queue Parameters Data Item identifies DSCPs based on groups of logical queues. The number of logical queues is variable as is the number of DSCPs associated with each queue. A queue size (in bytes) is provided for informational purposes. An implementation that does not support DSCPs would indicate 1 queue with 0 DSCPs, and the number of bytes that may be in its associated link transmit queue. The format of the Queue Parameters Data Item is:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data Item Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num Queues | Scale | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Num DSCPs Q0(0)| Queue Size Q0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num DSCPs Q1 | Queue Size Q1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num DSCPs Q2 | Queue Size Q2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : ... : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num DSCPs Qn | Queue Size Qn | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DS Field Q1 | DS Field Q1 | DS Field Q1 | DS Field Q2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : ... | DS Field Qn | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ TBA2 Variable Per Length is the number of octets in the data item, excluding the Type and Length fields. An 8-bit unsigned integer indicating the number of queues represented in the data item. This field MUST contain a value of at least one (1). Note that this number is one larger than the largest queue index value included in the data item. An 4-bit unsigned integer indicating the scale used in the Queue Size fields. The valid values are:

Value Scale ------------ 0 B - Bytes (Octets) 1 KB - Kilobytes (B/1024) 2 MB - Megabytes (KB/1024) 3 GB - Gigabytes (MB/1024) MUST be set to zero by the sender (a modem) and ignored by the receiver (a router). An 8-bit unsigned integer indicating the number of DSCPs associated with the indexed queue. Other than the special case covered in the next paragraph, this field MUST contain a value of at least one (1). Queue indexes start at zero (0) and the maximum queue index "Qn" is one less than the value carried in the Num Queues field. Queue indexes are implicit in the position in the data item. Queue index zero "Q0" is a special case. It is used for any traffic that does not carry a DSCP value represented in the data item. Therefore the value of the Queue index zero field, "Num DSCPs Q0", field MUST be zero (0). A 24-bit unsigned integer representing the size, in the octet scale indicated by the Scale field, of the queue supporting traffic with the DSCPs associated with the queue index. The data item contains a sequence of 8 bit DS Fields. The position in the sequence identifies the associated queue index. The number of DS Fields present should equal the sum of all Num DSCPs field values. The DS Field structure is the same as .

0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | DSCP | CU | +---+---+---+---+---+---+---+---+ DSCP: differentiated services codepoint CU: currently unused, MUST be zero

The Pause Data Item is used by a modem to indicate to its peer that traffic is to be suppressed. An example of when a modem might send this data item is when an internal queue length exceeds a particular threshold. A modem may indicate that traffic is to be suppressed on a device wide or destination specific basis. An example of when a modem might use device wide indications is when output queues are shared across all destinations, and destination specific might be used when per destination queuing is used. To indicate that suppression applies to all destinations, a modem MAY send the Pause Data Item in a Session Update Message. To indicate that suppression applies to a particular destination a modem MAY send the Pause Data Item in a Destination Update Message. Each Pause Data Item identifies the traffic to be suppressed by the Queue Index defined by , which in turn indicates a set of traffic identified by DSCPs. The special value of 255 is used to indicate that all traffic is to be suppressed. While there is no restriction on the number of Messages containing Pause Data Item that may be sent by a modem, a modem SHOULD include multiple queue indexes in the same message when possible. A router which receives the Pause Data Item MUST cease sending the identified traffic to the modem. This may of course translate into the router's queues exceeding their own thresholds. The format of the Pause Data Item is:

The Restart Data Item is used by a modem to indicate to its peer that transmission of previously suppressed traffic may be resumed. An example of when a modem might send this data item is when an internal queue length drops below a particular threshold. The sending of this data item parallels the Pause Data Item, see the previous section, and follows the same rules. This includes that to indicate that transmission can resume to all destinations, a modem MAY send the Restart Data Item in a Session Update Message. It also includes that to indicate that transmission can resume to a particular destination a modem MAY send the Pause Restart Item in a Destination Update Message. Finally, the same rules apply to queue indexes. A router which receives the Restart Data Item SHOULD resume transmission of the identified traffic to the modem. The format of the Restart Data Item matches the Pause Data Item and is: