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PSIRP Architectural Components Part 1

PSIRP Architectural Components Part 1. Walter Wong NomadicLab & HIIT 08.02.2010. Outline. Identifiers Algorithmic IDs Node Internal Architecture Helper Functions Rendezvous System. Background – IP-based Identifier. Network Layer Identifier IP address Topological identifier

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PSIRP Architectural Components Part 1

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  1. PSIRP Architectural Components Part 1 Walter Wong NomadicLab & HIIT 08.02.2010

  2. Outline • Identifiers • Algorithmic IDs • Node Internal Architecture • Helper Functions • Rendezvous System

  3. Background – IP-based Identifier • Network Layer Identifier • IP address • Topological identifier • Refers to a specific location in the network • Transport Layer Identifier • Also IP address (IPsrc/dst, portsrc/dst, protocol) • Identifies end-hosts in the Internet

  4. Application Transport Network Link Physical IP Semantic Overload Problem Socket 174.180.23/24 IP 128.17.11.22 200.201.11/24

  5. IP-based Identification – Problems • Entangle host location with identification • Host-centric approach • Content can’t be addressed alone • Sub-part of a URL • Ex. www.unicamp.br/main/courses/index.html • Identified as part of connection parameters • Ex. TCP sequence number • Limited naming system • Hinders new features, ex., mobility, multicast • Users can’t express their interest in data regardless of location

  6. PSIRP Identifiers – Motivation • Express user interests • WWW • users are interested in documents regardless of their location • Currently users express an interest (what) and it is translated to a place (where) • Publish/subscribe • Users express their interest on data • Data is asynchronously delivered to users

  7. PSIRP Identifiers • Application Level Identifier (AId) • Rendezvous Identifier (RId) • Scope Identifier (SId) • Forwarding Identifier (FId) • Algorithmic Identifier (AlgId)

  8. Application Level Identifier (AId) • Application level identification • Based application requirements • Easiness to route, easiness to resolve, randomness, etc • Can be any namespace • Flat labels • Structured names (FQDN) • Global Unique Identifier (GUID) • Electronic Numbering (ENUM)

  9. Rendezvous Identifier (RId) • PSIRP network level identifier • Uniquely identifies a piece of information • 256-bit identifier (SHA-256 hash over the data) • Goal: identify the interest between publishers and subscribers in the rendezvous system

  10. Rendezvous Identifier (Rid) Doesn’t subscribe RIdnut Interest! Rendezvous Point Bingo Publish RIdnut Deliver data Nut Subscribe RIdnut Scrat

  11. Scope Identifier (Sid) • Also PSIRP network identifier with 256 bits length • Goal: aggregate a set of Rids into one group (scope) • Represents a collection of whatever information that Rids represents • Scope = implicit context of a set of Rids • Photo album has a Sid and each photo has a Rid • Also • Access control • Metadata control operations

  12. Scope Identifier (Sid) RidA Sidpublic_album Sidfamily_album RidB RidC

  13. Forwarding ID • 256-bit long network identifier • Goal: identify path segments in the forwarding path • Difference: • Sid/Rid used in the rendezvous system (slow path) • Fid used in the forwarding fabric (fast path) • Can be aggregated in Bloom filters

  14. Forwarding ID FId12 FId22 FId21 FId11 FId31 Rendezvous 1 Rendezvous 2 FId12 FId21 FId22 FId11 FId13 David Bloom-filter FIdA Bob Clark

  15. Forwarding ID • Source controlled packet soft state • Topology manager creates the Bloom filter • + stateless • - requires constant updates from the rendezvous to identify new subscribers • - recycle Fids after un-subscription • In-network state • Fid switching state in the forwarding nodes • + Identifies just initial Fid • - state in the switches

  16. Algorithmic Identifiers (AIgIds) • Special class of identifiers • Information collection concept • group semantically similar information items • Goal: automatic generation of IDs for different pieces of information • Allow elaborate tests with the identifier

  17. Algorithmic Identifiers • Allows relationship tests on each ID: • Ordering: precedence (does an identifier precede another one?) • Composition: does an ID belong to another ID (e.g. a chunk ID belongs to a file ID) • Completeness: do we have all the identifiers composing another information object?

  18. Algorithmic IDs • Applications • Automatic deriving identifiers for information fragments • Calculating the next identifier for a sequence • Deducing the identifier

  19. Subscription Management Subscribe comics algID Billy Comics Part 2 Comics part 1 ID2 ID1 ID5 ID6 ID3 ID4 Comics Part 5 Comics Part 6 Comics Part 4 Comics Part 3

  20. Forwarding State Aggregation RVS FId21 FId22 FIdB RVS FId12 David FId11 FId11 FId13 FId13 RVS FId31 FId32 FId31 FId32 FIdC FIdC FIdA FIdA Bloom-filter Clark Bob

  21. Re-encoding the same publication AlgIDhigh_resolution IDA IDB IDC Publication ID2 Publisher AlgIDlow_resolution ID1

  22. Return Path (legacy client-server model) RVS Subscribe(algIdA) Publish(algIdA) Clark Bob Publish(hash(algIdA)) Subscribe(hash(algIdA)) Hey Clark, let’s have a beer after work! Okee dokee, Bob!

  23. Sequence Numbering RVS Subscribe(algId) Publish(algId) ID3 ID3 ID2 ID2 ID1 ID1 ID1 = hash(algId) ID2 = hash(ID1) Beth Alice ID3 = hash(ID2)

  24. Algorithmic IDs – Other scenarios • Error control • generate error messages identified with IDs derived from the error ID • Reliability • different algIds can be generated to receive error messages • Announcements • prior to a data publication, publishers announce in the algId channel, informing possible subscribers that data will be published in the related algId

  25. Algorithmic ID – General design • Direct Acyclic Graph • Identifiers are related to each other by functions • Sorting algorithms • Ordering the identifiers • Trees are generated by consecutive application of one-way functions • Sequences can be expressed as the recursive application of a singular function • Reverse function to walk in both directions

  26. Algorithmic IDs – Example A B = f(A,1) C = f(A,2) D = f(C,1) B,1 C,2 C = f-1(F,3) A = f-1(C,2) D,1 E,2 F,3 G,1 H,1

  27. Node Internal Architecture • Blackboard Approach • Communication model for sharing memory objects through the network • Uses Memory Object Service • Simple unreliable page service • Simple memory object service

  28. Unreliable Page Service • Simple unreliable page service • Pages can be mapped to packet level transmissions using PageIDs • Allows for identifying and caching individual packets within the network • There is one PageID for each Fid Memory Pages PageIDA PageIDB PageIDC PageIDD PageIDE

  29. Memory Object Service • Works on the page service • Supports larger data files (over one memory page) • Supports update on memory objects Memory Object Memory Pages PageIDA MOA PageIDB PageIDC PageIDD PageIDE

  30. Memory Object Creation & Publication Blackboard Memory Object Publisher 1. Publisher requests a meta-publication and a memory object 2. Memory service returns a memory object with the meta attached 3. Publisher fills the data in the memory object 4. Publisher creates a Rid for the memory object. It can be republished as many times as he needs with equal or different tags

  31. Memory Object Subscription • Subscriber subscribers to the MO-Rid • Subscriber receives an event stream • File descriptor which can be read with select • Whenever the publisher publishes some data, the subscriber will be notified and will receive a new memory object representing the corresponding version of the object

  32. Node Internals – Networking • Nodes • Local input queues, with one Fid for each queue • Local output queues, with one Fid for each queue • Sender-helper sends the packet identified with the interfaces Fid • Network-receiver receives packets from the network

  33. Node Internal Architecture Application Publish call Node Internal - Networking Sender Helper Output queue 1 (FId1) Output queue 2 (FId2) Input queue 1 (FId3) Network Receiver Input queue 1 (FId4)

  34. Node Internal Architecture Application Subscribe call Node Internal - Networking Sender Helper Output queue 1 (FId1) Output queue 2 (FId2) Memory Object Input queue 1 (FId3) Network Receiver Input queue 1 (FId4)

  35. Memory Object Segmentation • Packetiser helper • handles memory objects larger than a packet size • Partitions objects into a set of packets • At each local output places, whenever there is a new object, the packetiser chunks the data and places each of them in the correct output queue scope • There is no memory copy, just a new mapping of the object in the scope directory

  36. Memory Object Segmentation Local Blackboard Packetiser De-packetiser Output Places Input Places M D0 D1 D2 Input Queue Output Queue Network M D0 D1 D2

  37. Helper Functions • Not core network service • Not traditional applications • Actually, it is a set of functions providing additional features for the system • “Helps the system!” • PSIRP has three categories: • Network Management Functions • Remote Service Functions • Host Centric Functions

  38. Network Management Functions • Network Management & Information gathering • Information gathering for better planning and management • Increase performance • In PSIRP, network management functions can subscribe to the link state, receiving information as it becomes available

  39. Network Management Functions – Example • Current Internet • SNMP/ICMP • GET/SET/TRAP directives • Managed systems generate asynchronous messages to notify new events

  40. Network Management Functions – Unified Link Layer API (ULLA) • Closely resembles publish/subscribe • Introduces an interface to collect information from the link layer • Link aware applications express their interests by specifying link conditions • Notifications can be asynchronous or periodic • ULLA can be the base for the helper function which subscribes to the link conditions and wait for updates

  41. Remote Service Functions • Segmentation function • Helps in the segmentation decision • Extracts data from link layer, such as MTU, and provides parameters for the fragmentation • Merger function • Merges partitioned data to get the original publication

  42. Remote Service Functions • Forwarding Error Correction/Content protection • Error correction in the transmission • Recover received data without retransmissions • Send redundant data together • Ex. Reed Solomon Block Code (N, K) • N-K symbol redundancy • After receiving any K symbols out of N, the receiver is able to decode the original data

  43. FEC Parameters • Currently, the FEC parameters are statically set, degrading the performance • Inaccuracy in the estimation of the underlying channel state, resulting in inefficient bandwidth usage • FEC helper can subscribe to the channel conditions in order to generate better parameters

  44. Remote Service Functions • Content re-encoding • Scenario: heterogeneous subscribers requesting the same video but with different resolution • Content provider can’t attend the demand • Content provider asks for remote helper functions located closer to the subscribers to perform the translation

  45. Application-specific Caches • Content caching • Offers the same interface as the original content provider (transparent) • Applications can select from which cache to retrieve data • content providers may instruct caches to serve content on their behalf • subscribers can receive data from the closest caches, saving network resources

  46. Host Service Functions • Transport and other middle network services • PSIRP offers shared blackboard for distributed applications using the network • Analysis and debugging purposes • Ping, traceroute, tcpdump, wireshark • PSIRP context • Transport component for rate control and reliability algorithm for point-to-point delivery

  47. Rendezvous System • Meeting point of interests between publishers and subscribers • Requirements • Scalability (Internet scale) • Efficiency in operation • Deployability (gradual deployment and stakeholders incentives)

  48. Rendezvous Network • Composed of Rendezvous Nodes (RNs) • Organized as a BGP-like inter-domain hierarchy • Collection of RNs from multiple cooperative ASes • Rendezvous points (RPs) • logical meeting points of interests between publishers and subscribers • one rendezvous point for each Sid/Rid pair

  49. Rendezvous Network Interconnection • Some approaches • Central entity managing signaling reachability: lack of incentives, trust, competition • Multiple entities: providers compete for global reachability coverage • Fully distributed mechanism: rendezvous networks self-organize to interconnect without any third party infrastructure

  50. Rendezvous Network Connection • Canon DHT • Hierarchical DHT • Maintains local communication within its domain • Caching in the sub-domain exit between levels in the DHT

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