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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. INTRODUCTION. Problems in Multicasting Viable interdomain multicast routing protocol yet to be developed

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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


  • 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


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


  • 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


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


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


  • 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


  • 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 website

CS-590F - Jitesh R. Nair

Level: Control Teardown

From author’s website

CS-590F - Jitesh R. Nair


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

CS-590F - Jitesh R. Nair


  • 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


  • 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 website

Simulation: Scenario 2

From author’s website

CS-590F - Jitesh R. Nair