Repository for the NWCRG meeting materials (agenda, presentations, minutes) used during IETF meetings and Interim meetings. Related Internet-drafts are accessible from the NWCRG datatracker web site.
Note that, in addition to this repository:
- meeting material is always uploaded at [https://datatracker.ietf.org/meeting/materials/] prior to each IETF meetings;
- past meeting material for all IETF/IRTF groups is archived at [https://www.ietf.org/how/meetings/past/];
- past meeting material related to NWCRG is easily accessible at [https://datatracker.ietf.org/rg/nwcrg/meetings/].
- we're not at PHY-layer, we are above in the protocol stack and potential bit errors have either been fixed or the packet dropped
"Decoding consists in using redundancy (i.e., using "repair packets") to recover from packet losses"
- it's essentially a matter of linear combination and linear system resolution (e.g., via basic Gaussian elimination)
- details (e.g., computations in a certain Finite Field) can be complex, but mastering them is not required
- block: segment the packet flow into blocks and apply FEC encoding per block, independently
- sliding window: an encoding window slides progressively over the packet flow, the encoder computes a linear combination of packets in this encoding window
"With large independant data objects, block codes are great, with streams of real-time data that have time correlation, sliding window codes are preferable"
- ... because splitting the application flow into blocks delays the moment when "repair packets" can be generated!
- code performance also depends on the type of losses (independant, uniform losses versus correlated, bursty losses)
- usually called FEC
- usually called Network Coding (NC)
- trivial example where a network equipment could reduce traffic (it sends a single "P1 XOR P2" packet (using multicast or broadcast) instead of sending both P1 and P2):
Alice Wireless router Bob
| --P1--> | |
| | <--P2-- |
| <--P1 XOR P2--- | ---P1 XOR P2--> | (multicast or broadcast)
| | |
recover P2 Recover P1
- only stupid persons will further overload a congested network with even more redundant traffic in the hope it may help!