BREADCRUMB FORWARDING SERVICE

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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
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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

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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

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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
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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

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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

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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.
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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)

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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.

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Level Control Suppression
From authors website http//www.cs.berkeley.edu/
yano/pubs/retreat-sum99/sld009.htm
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Level Control Teardown
From authors website http//www.cs.berkeley.edu/
yano/pubs/retreat-sum99/sld010.htm
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APPLICATIONS
So far we have talked about LABELS and
LEVELS. How exactly will they be used ?
FEC based loss recovery
LABEL Block number LEVEL Number of packets
lost

• Source can tell maximum lost number in a block
• As many requested packets arrive at receivers for
  a Block

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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.

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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

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Simulation Scenario 1
From authors website http//www.cs.berkeley.edu/
yano/pubs/retreat-sum99/sld023.htm
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Simulation Scenario 2
From authors website http//www.cs.berkeley.edu/
yano/pubs/retreat-sum99/sld026.htm