[net2-wg] beginnings of the link estimation protocol TEP

[Omprakash Gnawali]

A compilation of different aspects of the link estimation protocol
that needs to be specified.

Thanks.

- om_p

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SLEEP: Simple Link Estimation Extension Protocol

Assumptions

- the data link frame has a single-hop source field.
- the data link layer provides broadcast address.

SLEEP is used to compute bi-directional link quality to the
neighbors. It computes bi-directional link quality in two steps:
in-bound link quality estimation and link quality exchange.

In-bound Link Quality Estimation

Each SLEEP frame has a sequence number. SLEEP frames are transmitted
to the broadcast address. Nodes in the vicinity receive the frame and
compute the in-bound link quality from the node identified by the link
source address by using the sequence number in the SLEEP frame. The
set of sequence numbers received from a particular node over time is
used to compute the link quality.

Link Quality Exchange

To compute bi-directional link quality, in-bound link quality must be
exchanged among the neighbors. SLEEP appends a footer consisting of
the tuple (neighborid, inbound link quality) to the frame. When a node
receives the SLEEP frame and finds its id in one of the tuples, the
node can use the second element of that tuple as its outbound link
quality to the neighbor identified by the data link source address. If
the neighbor table has more entries than what will fit in a single
SLEEP frame, a node should use round robin to broadcast inbound link
quality for all the entries in the neighbor table.

Link Metric

Extra ETX (EETX) is used as the link metric.


SLEEP Frame:

A SLEEP frame has link estimation header, the payload, and a footer
with the neighbor entries as shown in this diagram:

   -----------------------------------------------------
  | Link Estimation | Payload | Entry | Entry | Entry | ...
  |     Header      |         |   1   |   2   |   3   |
   -----------------------------------------------------


Header format:
                           1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |nentry | rsrvd |      seqno      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Field definitions:

nentry - number of neighbor entries in the footer
seqno - link estimation sequence number.
rsrvd - reserved

Entry format:
                           1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             neighbor            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     metric    |
      +-+-+-+-+-+-+-+-+

Field definitions:

neighbor: the address of the neighbor
metric: inbound link quality from the neighbor

The byte offset of the first entry can be computed as:
frame size - nentry * 3


- om_p