Overview of Reliable Multicast Protocols

The table below is not meant to be exhaustive but rather to set the context and framework for presentations and ensuing discussion:

protocol (authors) reliability semantics session? Participant structure knowledge of participants? ACK/NAK

SRM (LBL et al.) reliable no local recovery groups via wb session msgs NAK, receiver reliable

rmtp (Bell Labs) reliable yes, with late join hierarchy of regions, DR's optional, may be known window of pkts ACK/NAK'ed

MTP-2 (TU Bremen) also RCF1301 reliable, totally ordered atomic deliver yes, w/ explicit join master, producer, consumer known NAK(?)

RAMP (TASC) RFC1458 reliable yes w/ late join none known NAK w/ selective ACK (sender and rcvr reliable

TMTP (Kentucky) reliable no tree-based, via ring search no restricted NAK's, NAK suppression, periodic ACKs

log-based (stanford) reliable no logging hierarchy estimated NAK w/ statistical ACK

LORAX (UCSC) stable, reliable no(?) tree-based parent/child hierarchical ACKs

sce (Ga Tech) reliable, weak ordering yes, no late join no known ACK, sender-reliable

HORUS (cornell) reliable up to total ordering membership microprotocol tree possible with PARCLD via membership NAK at lowest level

RMP (NASA

/UC Berkeley) reliable up to totally ordered explicit membership peers, full members, clients via membership ACK w/ NAK, fully stable

NTE (M. Handley) reliable no local recovery via session pkts triggered NAKs with randomization

Some comments made during the discussion at workshop included:

need to include something in above taxonomy about flow control
need to include something in above taxonomy about stability (who gets to release packet) and the issue of notification (who knows when something is delivered correctly)
are re-tranmissions multicast or unicast (either, both) in the above and who controls this decision?

Observations:

many protocols proposed and implemented
essentially two classes of reliability semantics
- 100% data reliable with or without …..
- ordering and causality
protocols differ widely in design
- logical structure of communication pathways (ring versus tree versus none)
- group membership mechanisms and assumptions
- receiver-reliable versus sender reliable
- ACK/NAK
and the application for which they were designed

Up to main page for reliable multicast session.