CS-590F - Jitesh R. Nair BREADCRUMB FORWARDING SERVICE A synthesis of PGM and EXPRESS to improve and...
-
Upload
dustin-harmon -
Category
Documents
-
view
212 -
download
0
Transcript of CS-590F - Jitesh R. Nair BREADCRUMB FORWARDING SERVICE A synthesis of PGM and EXPRESS to improve and...
CS-590F - Jitesh R. Nair
BREADCRUMB FORWARDING SERVICE
A synthesis of PGM and EXPRESS to improve and simplify global IP multicast
Authors: Koichi Yano, Steven McCanne
Presenter: Jitesh R. Nair
CS-590F - Jitesh R. Nair
INTRODUCTION
Problems in Multicasting
• Viable interdomain multicast routing protocol yet to be developed
• Dealing with packet drops – can impact indeterminate subsets of the reciever group
CS-590F - Jitesh R. Nair
BreadCrumb Forwarding Service [BCFS]
• A single source request based multicast service – advocates a model where a multicast tree is rooted at a single source and receivers explicitly indicate that source when subscribing to a multicast channel
• Abandons the anonymity of the Class D group address
CS-590F - Jitesh R. Nair
LABEL
Uses an abstract “Label” to identify a particular request with respect to some source
(Source, Label) identifies forwarding paths
Label is generated by transport protocol
LABEL Identifier of request
CS-590F - Jitesh R. Nair
BASIC SETUP MECHANISM
• REQUEST messages, issued for some piece of data.
• Drops “breadcrumbs” along the path to the source.
• The breadcrumbs in turn guide the REPLY message from the source back to all requesting receivers.
Each breadcrumb identified by (S,L) pair
CS-590F - Jitesh R. Nair
TEARDOWN AND SUPPRESSION
LEVEL A number that each breadcrumb carries. Also carried by REQUEST and REPLY messages.
Depending on LEVEL number
• Messages sent to source are suppressed• Breadcrumb state at the router is torn down
CS-590F - Jitesh R. Nair
SEQUENCE OF EVENTS
REQUEST – A receiver sends a request packet with a label and a level
SETUP – A router that receives a request message maintains state for forwarding links and the level associated with the label
SUPPRESSION – The router forwards the request message toward the source if the label in the request message is new for that router or the level number is larger than the highest level being maintained.
REPLY – A source in response to the request message, sends the requested data together with the label embedded in the request message and a level number to be torn down.
FORWARDING – A router directs a reply message to the links that are associated with the label.
TEARDOWN – The router removes the forwarding state of the link associated with the label, if the reply message includes a level number that is larger than the level maintained by the router.
CS-590F - Jitesh R. Nair
ROUTER BEHAVIOUR
• Maintain “breadcrumb state” tied to a particular label
• Does not store copy of message• Stores level number• Stores directed link list – (link from
which the REQUEST message came)
CS-590F - Jitesh R. Nair
HOW DOES LABEL AND LEVEL FIT IN ?
A REQUEST packet arrives at the router from the receiver
If pair (S,L) is new for the router•Make a new entry for this pair•Note the link from which this REQUEST came•Couple the level number to the link •Forward the message upstream towards the source
If pair (S,L) is already present in the router• Explore the list of forwarding links• If link not present then add this to the directed link list with
level number• If link present, then update the level number if the REQUEST
had higher level number.• If level of the request message is greater than any level
number stored, then forward the message towards the source, else suppress the message.
CS-590F - Jitesh R. Nair
Level: Control Suppression
From author’s websitehttp://www.cs.berkeley.edu/~yano/pubs/retreat-sum99/sld009.htm
CS-590F - Jitesh R. Nair
Level: Control Teardown
From author’s websitehttp://www.cs.berkeley.edu/~yano/pubs/retreat-sum99/sld010.htm
CS-590F - Jitesh R. Nair
So far we have talked about “LABELS” and “LEVELS”. How exactly will they be used ?
APPLICATIONS
FEC based loss recovery
LABEL – Block numberLEVEL – Number of packets lost
• Source can tell maximum lost number in a block
• As many requested packets arrive at receivers for a Block
CS-590F - Jitesh R. Nair
RAINBOW ON BCFS
RAINBOW – ReliAble multicast by INdividual Bandwidth adaptation using windOW
• TCP friendly congestion control on top of BCFS
• Source need not manage state on a per-receiver basis
• Concept of Digital Fountain – [ A digital fountain
approach to reliable distribution of bulk data – Byers et al. ]
CS-590F - Jitesh R. Nair
RAINBOW
Individual TCP-like window control• Data transmission triggered by arrival of breadcrumbs at
sender
Transmission request by BCF messages• Receiver sends transmission request as a BCF REQUEST• LABELS – denote window size.• TRQ with same LABEL are aggregated• Can be considered akin to “ACK” in a TCP scheme
Simple request by Digital fountain source• Can respond to each TRQ by sending one packet after
another, which includes the same label as TRQ
CS-590F - Jitesh R. Nair
Simulation: Scenario 1
From author’s websitehttp://www.cs.berkeley.edu/~yano/pubs/retreat-sum99/sld023.htm
CS-590F - Jitesh R. Nair
Simulation: Scenario 2
From author’s websitehttp://www.cs.berkeley.edu/~yano/pubs/retreat-sum99/sld026.htm