idnits 2.17.1 draft-ietf-p2psip-service-discovery-10.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 313 has weird spacing: '...ExtType type...' -- The document date (February 2, 2014) is 3737 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '0' on line 280 -- Looks like a reference, but probably isn't: '7' on line 280 -- Looks like a reference, but probably isn't: '8' on line 280 -- Looks like a reference, but probably isn't: '15' on line 280 == Outdated reference: A later version (-09) exists of draft-ietf-p2psip-concepts-05 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 P2PSIP Working Group J. Maenpaa 3 Internet-Draft G. Camarillo 4 Intended status: Standards Track Ericsson 5 Expires: August 6, 2014 February 2, 2014 7 Service Discovery Usage for REsource LOcation And Discovery (RELOAD) 8 draft-ietf-p2psip-service-discovery-10.txt 10 Abstract 12 REsource LOcation and Discovery (RELOAD) does not define a generic 13 service discovery mechanism as a part of the base protocol. This 14 document defines how the Recursive Distributed Rendezvous (ReDiR) 15 service discovery mechanism used in OpenDHT can be applied to RELOAD 16 overlays to provide a generic service discovery mechanism. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on August 6, 2014. 35 Copyright Notice 37 Copyright (c) 2014 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. Introduction to ReDiR . . . . . . . . . . . . . . . . . . . . 5 55 4. Using ReDiR in a RELOAD Overlay Instance . . . . . . . . . . 8 56 4.1. Data Structure . . . . . . . . . . . . . . . . . . . . . 8 57 4.2. Selecting the Starting Level . . . . . . . . . . . . . . 9 58 4.3. Service Provider Registration . . . . . . . . . . . . . . 10 59 4.4. Refreshing Registrations . . . . . . . . . . . . . . . . 11 60 4.5. Service Lookups . . . . . . . . . . . . . . . . . . . . . 11 61 4.6. Removing Registrations . . . . . . . . . . . . . . . . . 13 62 5. Access Control Rules . . . . . . . . . . . . . . . . . . . . 13 63 6. REDIR Kind Definition . . . . . . . . . . . . . . . . . . . . 13 64 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14 65 7.1. Service Registration . . . . . . . . . . . . . . . . . . 14 66 7.2. Service Lookup . . . . . . . . . . . . . . . . . . . . . 16 67 8. Overlay Configuration Document Extension . . . . . . . . . . 17 68 9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 69 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 70 10.1. Access Control Policies . . . . . . . . . . . . . . . . 17 71 10.2. Data Kind-ID . . . . . . . . . . . . . . . . . . . . . . 17 72 10.3. ReDiR Namespaces . . . . . . . . . . . . . . . . . . . . 18 73 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 74 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 75 12.1. Normative References . . . . . . . . . . . . . . . . . . 18 76 12.2. Informative References . . . . . . . . . . . . . . . . . 19 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 79 1. Introduction 81 REsource LOcation And Discovery (RELOAD) [I-D.ietf-p2psip-base] is a 82 peer-to-peer signaling protocol that can be used to maintain an 83 overlay network, and to store data in and retrieve data from the 84 overlay. Although RELOAD defines a Traversal Using Relays around 85 Network Address Translation (TURN) specific service discovery 86 mechanism, it does not define a generic service discovery mechanism 87 as a part of the base protocol. This document defines how the 88 Recursive Distributed Rendezvous (ReDiR) service discovery mechanism 89 [Redir] used in OpenDHT can be applied to RELOAD overlays. 91 In a Peer-to-Peer (P2P) overlay network such as a RELOAD Overlay 92 Instance, the peers forming the overlay share their resources in 93 order to provide the service the system has been designed to provide. 94 The peers in the overlay both provide services to other peers and 95 request services from other peers. Examples of possible services 96 peers in a RELOAD Overlay Instance can offer to each other include a 97 TURN relay service, a voice mail service, a gateway location service, 98 and a transcoding service. Typically, only a small subset of the 99 peers participating in the system are providers of a given service. 100 A peer that wishes to use a particular service faces the problem of 101 finding peers that are providing that service from the Overlay 102 Instance. 104 A naive way to perform service discovery is to store the Node-IDs of 105 all nodes providing a particular service under a well-known key k. 106 The limitation of this approach is that it scales linearly with the 107 number of nodes that provide the service. The problem is two-fold: 108 the node n that is responsible for service s identified by key k may 109 end up storing a large number of Node-IDs and most importantly, may 110 also become overloaded since all service lookup requests for service 111 s will need to be answered by node n. An efficient service discovery 112 mechanism does not overload the nodes storing pointers to service 113 providers. In addition, the mechanism must ensure that the load of 114 providing a given service is distributed evenly among the nodes 115 providing the service. 117 ReDiR implements service discovery by building a tree structure of 118 the service providers that provide a particular service. The tree 119 structure is stored into the RELOAD Overlay Instance using RELOAD 120 Store and Fetch requests. Each service provided in the Overlay 121 Instance has its own tree. The nodes in a ReDiR tree contain 122 pointers to service providers. During service discovery, a peer 123 wishing to use a given service fetches ReDiR tree nodes one-by-one 124 from the RELOAD Overlay Instance until it finds a service provider 125 responsible for its Node-ID. It has been proved that ReDiR can find 126 a service provider using only a constant number of Fetch operations 127 [Redir]. 129 2. Terminology 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 133 document are to be interpreted as described in RFC 2119 [RFC2119]. 135 This document uses the terminology and definitions from the Concepts 136 and Terminology for Peer to Peer SIP [I-D.ietf-p2psip-concepts] 137 draft. 139 DHT: Distributed Hash Tables (DHTs) are a class of decentralized 140 distributed systems that provide a lookup service similar to a 141 regular hash table. Given a key, any peer participating in the 142 system can retrieve the value associated with that key. The 143 responsibility for maintaining the mapping from keys to values is 144 distributed among the peers. 146 H(x): Refers to a hash function (e.g., SHA-1) calculated over the 147 value x. 149 I(lvl,k): An interval at level lvl in the ReDiR tree that encloses 150 key k. As an example, I(5,10) refers to an interval at level 5 in 151 the ReDiR tree within whose range key 10 falls. 153 n.id: Refers to the RELOAD Node-ID of node n. 155 Namespace: An arbitrary identifier that identifies a service 156 provided in the RELOAD Overlay Instance. Examples of potential 157 namespaces include "voice-mail" and "turn-relay". The namespace 158 is an UTF-8 text string. 160 numBitsInNodeId: Refers to the number of bits in a RELOAD Node-ID. 161 This value is used in the equations for calculating the ranges of 162 intervals that ReDiR tree nodes are responsible for. 164 ReDiR tree: A tree structure of the nodes that provide a particular 165 service. The nodes embed the ReDiR tree into the RELOAD Overlay 166 Instance using RELOAD Store and Fetch requests. Each tree node in 167 the ReDiR tree belongs to some level in the tree. The root node 168 of the ReDiR tree is located at level 0 of the ReDiR tree. The 169 child nodes of the root node are located at level 1. The children 170 of the tree nodes at level 1 are located at level 2, and so forth. 171 The ReDiR tree has a branching factor b. At every level lvl in the 172 ReDiR tree, there is room for a maximum of b^lvl tree nodes. Each 173 tree node in the ReDiR tree is uniquely identified by a pair 174 (lvl,j), where lvl is a level in the ReDiR tree and j is the 175 position of the tree node (from the left) at that level. 177 Successor: The successor of identifier k in namespace ns is the node 178 belonging to the namespace ns whose identifier most immediately 179 follows the identifier k. 181 3. Introduction to ReDiR 183 Recursive Distributed Rendezvous (ReDiR) [Redir] does not require new 184 functionality from the RELOAD base protocol. This is possible since 185 ReDiR interacts with the RELOAD Overlay Instance by simply storing 186 and fetching data, that is, using RELOAD Store and Fetch requests. 187 ReDiR creates a tree structure of the service providers of a 188 particular service and stores it into the RELOAD Overlay Instance 189 using the Store and Fetch requests. ReDiR service lookups require a 190 logarithmic number of Fetch operations. Further, if information from 191 past service lookups is used to determine the optimal level in the 192 ReDiR tree from which to start new service lookups, an average 193 service lookup can typically finish after a constant number of Fetch 194 operations assuming that Node-IDs are distributed uniformly at 195 random. 197 In ReDiR, each service provided in the overlay is identified by an 198 identifier, called the namespace. All service providers of a given 199 service store their information under the namespace of that service. 200 Peers wishing to use a service perform lookups within the namespace 201 of the service. The result of a ReDiR lookup for an identifier k in 202 namespace ns is a RedirServiceProvider structure (see Section 4.1) of 203 a service provider that belongs to ns and whose Node-ID is the 204 closest successor of identifier k in the namespace. 206 Each tree node in the ReDiR tree contains a dictionary of 207 RedirServiceProvider entries of peers providing a particular service. 208 Each tree node in the ReDiR tree also belongs to some level in the 209 tree. The root node of the ReDiR tree is located at level 0. The 210 child nodes of the root node are located at level 1 of the ReDiR 211 tree. The children of the tree nodes at level 1 are located at level 212 2, and so forth. The ReDiR tree has a branching factor, whose value 213 is determined by a new element in the RELOAD overlay configuration 214 document, called branching-factor. At every level lvl in the ReDiR 215 tree, there is room for a maximum of branching-factor^lvl tree nodes. 216 As an example, in a tree whose branching-factor is 2, the second 217 level can contain up to 4 tree nodes (note that a given level may 218 contain less than the maximum number of tree nodes since empty tree 219 nodes are not stored). Each tree node in the ReDiR tree is uniquely 220 identified by a pair (lvl,j), where lvl is a level in the ReDiR tree 221 and j is the position of the tree node (from the left) at that level. 223 As an example, the pair (2,3) identifies the 3rd tree node from the 224 left at level 2. 226 The ReDiR tree is stored into the RELOAD Overlay Instance tree node 227 by tree node, by storing the values of tree node (level,j) under a 228 key created by taking a hash over the concatenation of the namespace, 229 level, and j, that is, as H(namespace,level,j). As an example, the 230 root of the tree for a voice mail service is stored at H("voice- 231 mail",0,0). Each node (level,j) in the ReDiR tree contains b 232 intervals of the DHT's identifier space as follows: 234 [2^numBitsInNodeID*b^(-level)*(j+(b'/b)), 235 2^numBitsInNodeID*b^(-level)*(j+((b'+1)/b))), for 0<=b'; 315 opaque namespace<0..2^16-1>; 316 uint16 level; 317 uint16 node; 318 uint16 length; 320 select (type) { 321 /* This type may be extended */ 322 } extension; 324 } RedirServiceProvider; 326 The contents of the RedirServiceProvider Resource Record are as 327 follows: 329 type 331 The type of an extension to the RedirServiceProvider Resource 332 Record. Unknown types are allowed. 334 destination_list 336 A list of IDs through which a message is to be routed to reach the 337 service provider. The destination list consists of a sequence of 338 Destination values. The contents of the Destination structure are 339 as defined in RELOAD base [I-D.ietf-p2psip-base]. 341 namespace 342 An opaque UTF-8 encoded string containing the namespace. 344 level 346 The level in the ReDiR tree. 348 node 350 The position of the node storing this RedirServiceProvider record 351 at the current level in the ReDiR tree. 353 length 355 The length of the rest of the Resource Record. 357 extension 359 An extension value. The RedirServiceProvider Resource Record can 360 be extended to include for instance service or service provider 361 specific information. 363 4.2. Selecting the Starting Level 365 Before registering as a service provider or performing a service 366 lookup, a peer needs to determine the starting level Lstart for the 367 registration or lookup operation in the ReDiR tree. It is 368 RECOMMENDED that Lstart is set to 2. In subsequent registrations, 369 Lstart MAY, as an optimization, be set to the lowest level at which a 370 registration operation has last completed. 372 In the case of subsequent service lookups, nodes MAY, as an 373 optimization, record the levels at which the last 16 service lookups 374 completed and take Lstart to be the mode of those depths. 376 4.3. Service Provider Registration 378 A node MUST use the following procedure to register as a service 379 provider in the RELOAD Overlay Instance: 381 1. A node n with Node-ID n.id wishing to register as a service 382 provider starts from a starting level Lstart (see Section 4.2 for 383 the details on selecting the starting level). Therefore, node n 384 sets the current level to level=Lstart. 386 2. Node n MUST send a RELOAD Fetch request to fetch the contents of 387 the tree node responsible for I(level,n.id). An interval I(l,k) 388 is the interval at level l in the ReDiR tree that includes key k. 389 The fetch MUST be a wildcard fetch. 391 3. Node n MUST send a RELOAD Store request to add its 392 RedirServiceProvider entry to the dictionary stored in the tree 393 node responsible for I(level,n.id). Note that node n always 394 stores its RedirServiceProvider entry, regardless of the contents 395 of the dictionary. 397 4. If node n's Node-ID (n.id) is the lowest or highest Node-ID 398 stored in the tree node responsible for I(Lstart,n.id), node n 399 MUST reduce the current level by one (i.e., set level=level-1) 400 and continue up the ReDiR tree towards the root level (level 0), 401 repeating the steps 2 and 3 above. Node n MUST continue in this 402 way until it reaches either the root of the tree or a level at 403 which n.id is not the lowest or highest Node-ID in the interval 404 I(level,n.id). 406 5. Node n MUST also perform a downward walk in the ReDiR tree, 407 during which it goes through the tree nodes responsible for 408 intervals I(Lstart,n.id), I(Lstart+1,n.id), I(Lstart+2,n.id), 409 etc. At each step, node n MUST fetch the responsible tree node, 410 and store its RedirServiceProvider record in that tree node if 411 n.id is the lowest or highest Node-ID in its interval. Node n 412 MUST end this downward walk as soon as it reaches a level l at 413 which it is the only service provider in its interval I(l,n.id). 415 Note that above, when we refer to 'the tree node responsible for 416 I(l,k)', we mean the entire tree node (that is, all the intervals 417 within the tree node) responsible for interval I(l,k). In contrast, 418 I(l,k) refers to a specific interval within a tree node. 420 4.4. Refreshing Registrations 422 All state in the ReDiR tree is soft. Therefore, a service provider 423 needs to periodically repeat the registration process to refresh its 424 RedirServiceProvider Resource Record. If a record expires, it MUST 425 be dropped from the dictionary by the peer storing the tree node. 426 Deciding an appropriate lifetime for the RedirServiceProvider 427 Resource Records is up to each service provider. Every service 428 provider MUST repeat the entire registration process periodically 429 until it leaves the RELOAD Overlay Instance. 431 Note that no new mechanisms are needed to keep track of the remaining 432 lifetime of RedirServiceProvider records. The 'storage_time' and 433 'lifetime' fields of RELOAD's StoredData structure can be used for 434 this purpose in the usual way. 436 4.5. Service Lookups 438 The purpose of a service lookup for identifier k in namespace ns is 439 to find the node that is a part of ns and whose identifier most 440 immediately follows (i.e., is the closest successor of) the 441 identifier k. 443 A service lookup operation resembles the service registration 444 operation described in Section 4.3. Service lookups start from a 445 given starting level level=Lstart in the ReDiR tree (see Section 4.2 446 for the details on selecting the starting level). At each step, a 447 node n wishing to discover a service provider MUST fetch the tree 448 node responsible for the interval I(level,n.id) that encloses the 449 search key n.id at the current level using a RELOAD Fetch request. 450 Having fetched the tree node, node n MUST determine the next action 451 to carry out as follows: 453 1. If there is no successor of node n present in the just fetched 454 ReDiR tree node (note: within the entire tree and not only within 455 the current interval) responsible for I(level,n.id), then the 456 successor of node n must be present in a larger segment of the 457 identifier space (i.e., further up in the ReDiR tree where each 458 interval and tree node covers a larger range of the identifier 459 space). Therefore, node n MUST reduce the current level by one 460 to level=level-1 and carry out a new Fetch operation for the tree 461 node responsible for n.id at that level. The fetched tree node 462 is then analyzed and the next action determined by checking 463 conditions 1-3. 465 2. If n.id is neither the lowest nor the highest Node-ID within the 466 interval (note: within the interval, not within the entire tree 467 node) I(level,n.id), n MUST next check the tree node responsible 468 for n.id at the next level down the tree. Thus, node n MUST 469 increase the level by one to level=level+1 and carry out a new 470 Fetch operation at that level. The fetched tree node is then 471 analyzed and the next action determined by checking conditions 472 1-3. 474 3. If neither of the conditions above holds, meaning that there is a 475 successor s of n.id present in the just fetched ReDiR tree node 476 and n.id is the highest or lowest Node-ID in its interval, the 477 service lookup has finished successfully and s must be the 478 closest successor of n.id in the ReDiR tree. 480 Note that above, when we refer to 'the tree node responsible for 481 interval I(l,k)', we mean the entire tree node (that is, all the 482 intervals within the tree node) responsible for interval I(l,k). In 483 contrast, I(l,k) refers to a specific interval within a tree node. 485 Note also that there may be some cases in which no successor can be 486 found from the ReDiR tree. An example is a situation in which all of 487 the service providers stored in the ReDiR tree have a Node-ID smaller 488 than identifier k. In this case, the upward walk of the service 489 lookup will reach the root of the tree without encountering a 490 successor. An appropriate strategy in this case is to pick one of 491 the RedirServiceProvider entries stored in the dictionary of the root 492 node at random. 494 Since RedirServiceProvider records are expiring and registrations are 495 being refreshed periodically, there can be certain rare situations in 496 which a service lookup may fail even if there is a valid successor 497 present in the ReDiR tree. An example is a case in which a ReDiR 498 tree node is fetched just after a RedirServiceProvider entry of the 499 only successor of k present in the tree node has expired and just 500 before a Store request that has been sent to refresh the entry 501 reaches the peer storing the tree node. In this rather unlikely 502 scenario, the successor that should have been present in the tree 503 node is temporarily missing. Thus, the service lookup will fail and 504 needs to be carried out again. 506 To recover from the kinds of situations described above, a ReDiR 507 implementation MAY choose to use the optimization described next. 508 The ReDiR implementation MAY implement a local temporary cache that 509 is maintained for the duration of a service lookup operation in a 510 RELOAD node. The temporary cache is used to store all 511 RedirServiceProvider entries that have been fetched during the upward 512 and downward walks of a service lookup operation. Should it happen 513 that a service lookup operation fails due to the downward walk 514 reaching a level that does not contain a successor, the cache is 515 searched for successors of the search key. If there are successors 516 present in the cache, the closest one of them is selected as the 517 service provider. 519 4.6. Removing Registrations 521 Before leaving the RELOAD Overlay Instance, a service provider MUST 522 remove the RedirServiceProvider records it has stored by storing 523 exists=False values in their place, as described in 524 [I-D.ietf-p2psip-base]. 526 5. Access Control Rules 528 As specified in RELOAD base [I-D.ietf-p2psip-base], every kind which 529 is storable in an overlay must be associated with an access control 530 policy. This policy defines whether a request from a given node to 531 operate on a given value should succeed or fail. Usages can define 532 any access control rules they choose, including publicly writable 533 values. 535 ReDiR requires an access control policy that allows multiple nodes in 536 the overlay read and write access to the ReDiR tree nodes stored in 537 the overlay. Therefore, none of the access control policies 538 specified in RELOAD base [I-D.ietf-p2psip-base] is sufficient. 540 This document defines a new access control policy, called NODE-ID- 541 MATCH. In this policy, a given value MUST be written and overwritten 542 only if the the request is signed with a key associated with a 543 certificate whose Node-ID is equal to the dictionary key. In 544 addition, provided that exists=TRUE, the Node-ID MUST belong to one 545 of the intervals associated with the tree node (the number of 546 intervals each tree node has is determined by the branching-factor 547 parameter). Finally, provided that exists=TRUE, 548 H(namespace,level,node), where namespace, level, and node are taken 549 from the RedirServiceProvider structure being stored, MUST be equal 550 to the Resource-ID for the resource. The NODE-ID-MATCH policy may 551 only be used with dictionary types. 553 6. REDIR Kind Definition 555 This section defines the REDIR kind. 557 Name 559 REDIR 561 Kind IDs 562 The Resource Name for the REDIR Kind-ID is created by 563 concatenating three pieces of information: namespace, level, and 564 node number. Namespace is an opaque UTF-8 encoded string 565 identifying a service, such as "turn-server". Level is an integer 566 specifying a level in the ReDiR tree. Node number is an integer 567 identifying a ReDiR tree node at a specific level. The data 568 stored is a RedirServiceProvider structure that was defined in 569 Section 4.1. 571 Data Model 573 The data model for the REDIR Kind-ID is dictionary. The 574 dictionary key is the Node-ID of the service provider. 576 Access Control 578 The access control policy for the REDIR kind is the NODE-ID-MATCH 579 policy that was defined in Section 5. 581 7. Examples 583 7.1. Service Registration 585 Figure 4 shows an example of a ReDiR tree containing information 586 about four different service providers whose Node-IDs are 2, 3, 4, 587 and 7. In the example, numBitsInNodeID=4. Initially, the ReDiR tree 588 is empty; Figure 4 shows the state of the tree at the point when all 589 the service providers have registered. 591 Level 0 ____2_3___4_____7_|__________________ 592 | | 593 Level 1 ____2_3_|_4_____7 ________|________ 594 | | | | 595 Level 2 ___|2_3 4__|__7 ___|___ ___|___ 596 | | | | | | | | 597 Level 3 _|_ _|3 _|_ _|_ _|_ _|_ _|_ _|_ 599 Figure 4: Example of a ReDiR tree 601 First, peer 2 whose Node-ID is 2 joins the namespace. Since this is 602 the first registration peer 2 performs, peer 2 sets the starting 603 level Lstart to 2, as was described in Section 4.2. Also all other 604 peers in this example will start from level 2. First, peer 2 fetches 605 the contents of the tree node associated with interval I(2,2) from 606 the RELOAD Overlay Instance. This tree node is the first tree node 607 from the left at Level 2 since key 2 is associated with the second 608 interval of the first tree node. Peer 2 also stores its 609 RedirServiceProvider record in that tree node. Since peer 2's Node- 610 ID is the only Node-ID stored in the tree node (i.e., peer 2's Node- 611 ID fulfills the condition in Section 4.3 that it is the numerically 612 lowest or highest among the keys stored in the node), peer 2 613 continues up the tree. In fact, peer 2 continues up in the tree all 614 the way to the root inserting its own Node-ID in all levels since the 615 tree is empty (which means that peer 2's Node-ID always fulfills the 616 condition that it is the numerically lowest or highest Node-ID in the 617 interval I(level, 2) during the upward walk). As described in 618 Section 4.3, peer 2 also walks down the tree. The downward walk peer 619 2 does ends at level 2 since peer 2 is the only node in its interval 620 at that level. 622 The next peer to join the namespace is peer 3, whose Node-ID is 3. 623 Peer 3 starts from level 2. At that level, peer 3 stores its 624 RedirServiceProvider entry in the same interval I(2,3) that already 625 contains the RedirServiceProvider entry of peer 2. Interval I(2,3), 626 that is, the interval at Level 2 enclosing key 3, is associated with 627 the right hand side interval of the first tree node. Since peer 3 628 has the numerically highest Node-ID in the tree node associated with 629 I(2,3), peer 3 continues up the tree. Peer 3 stores its 630 RedirServiceProvider record also at levels 1 and 0 since its Node-ID 631 is numerically highest among the Node-IDs stored in the intervals to 632 which its own Node-ID belongs. Peer 3 also does a downward walk 633 which starts from level 2 (i.e., the starting level). Since peer 3 634 is not the only node in interval I(2,3), it continues down the tree 635 to level 3. The downward walk ends at this level since peer 3 is the 636 only service provider in the interval I(3,3). 638 The third peer to join the namespace is peer 7, whose Node-ID is 7. 639 Like the two earlier peers, also peer 7 starts from level 2 because 640 this is the first registration it performs. Peer 7 stores its 641 RedirServiceProvider record at level 2. At level 1, peer 7 has the 642 numerically highest (and lowest) Node-ID in its interval I(1,7) 643 (because it is the only node in interval I(1,7); peers 2 and 3 are 644 stored in the same tree node but in a different interval) and 645 therefore it stores its Node-ID in the tree node associated with that 646 interval. Peer 7 also has the numerically highest Node-ID in the 647 interval I(0,7) associated with its Node-ID at level 0. Finally, 648 peer 7 performs a downward walk, which ends at level 2 because peer 7 649 is the only node in its interval at that level. 651 The final peer to join the ReDiR tree is peer 4, whose Node-ID is 4. 652 Peer 4 starts by storing its RedirServiceProvider record at level 2. 653 Since it has the numerically lowest Node-ID in the tree node 654 associated with interval I(2,4), it continues up in the tree to level 655 1. At level 1, peer 4 stores its record in the tree node associated 656 with interval I(1,4) because it has the numerically lowest Node-ID in 657 that interval. Next, peer 4 continues to the root level, at which it 658 stores its RedirServiceProvider record and finishes the upward walk 659 since the root level was reached. Peer 4 also does a downward walk 660 starting from level 2. The downward walk stops at level 2 because 661 peer 4 is the only peer in the interval I(2,4). 663 7.2. Service Lookup 665 This subsection gives an example of peer 5 whose Node-ID is 5 666 performing a service lookup operation in the ReDiR tree shown in 667 Figure 4. This is the first service lookup peer 5 carries out and 668 thus the service lookup starts from the default starting level 2. As 669 the first action, peer 5 fetches the tree node corresponding to the 670 interval I(2,5) from the starting level. This interval maps to the 671 second tree node from the left at level 2 since that tree node is 672 responsible for the interval (third interval from left) to which 673 Node-ID 5 falls at level 2. Having fetched the tree node, peer 5 674 checks its contents. First, there is a successor, peer 7, present in 675 the tree node. Therefore, condition 1 of Section 4.5 is false and 676 there is no need to perform an upward walk. Second, Node-ID 5 is the 677 highest Node-ID in its interval, so condition 2 of Section 4.5 is 678 also false and there is no need to perform a downward walk. Thus, 679 the service lookup finishes at level 2 since Node-ID 7 is the closest 680 successor of peer 5. 682 Note that the service lookup procedure would be slightly different if 683 peer 5 used level 3 as the starting level. Peer 5 might use this 684 starting level for instance if it has already carried out service 685 lookups in the past and follows the heuristic in Section 4.2 to 686 select the starting level. In this case, peer 5's first action is to 687 fetch the tree node at level 3 that is responsible for I(3,5). Thus, 688 peer 5 fetches the third tree node from the left. Since this tree 689 node is empty, peer 5 decreases the current level by one to 2 and 690 thus continues up in the tree. The next action peer 5 performs is 691 identical to the single action in the previous example of fetching 692 the node associated with I(2,5) from level 2. Thus, the service 693 lookup finishes at level 2. 695 8. Overlay Configuration Document Extension 697 This document extends the RELOAD overlay configuration document by 698 adding a new element "branching-factor" inside the new "REDIR" kind 699 element: 701 redir:branching-factor: The branching factor of the ReDir tree. The 702 default value is 10. 704 This new element is formally defined as follows: 706 namespace redir = "urn:ietf:params:xml:ns:p2p:service-discovery" 708 parameter &= element redir:branching-factor { xsd:unsignedInt } 710 The 'redir' namespace is added into the element 711 in the overlay configuration file. 713 9. Security Considerations 715 There are no new security considerations introduced in this document. 716 The security considerations of RELOAD [I-D.ietf-p2psip-base] apply. 718 10. IANA Considerations 720 10.1. Access Control Policies 722 This document introduces one additional access control policy to the 723 "RELOAD Access Control Policy" Registry: 725 NODE-ID-MATCH 727 This access control policy was described in Section 5. 729 10.2. Data Kind-ID 731 This document introduces one additional data Kind-ID to the "RELOAD 732 Data Kind-ID" Registry: 734 +--------------+------------+----------+ 735 | Kind | Kind-ID | RFC | 736 +--------------+------------+----------+ 737 | REDIR | 104 | RFC-AAAA | 738 +--------------+------------+----------+ 740 This Kind-ID was defined in Section 6. 742 Note to RFC Editor: please replace AAAA with the RFC number for this 743 specification. 745 10.3. ReDiR Namespaces 747 IANA SHALL create a "ReDiR Namespaces" Registry. Entries in this 748 registry are strings denoting ReDiR namespace values. The initial 749 contents of this registry are: 751 +----------------+----------+ 752 | Namespace | RFC | 753 +----------------+----------+ 754 | turn-server | RFC-AAAA | 755 +----------------+----------+ 757 The namespace 'turn-server' is used by nodes that wish to register as 758 providers of a TURN relay service in the RELOAD overlay and by nodes 759 that wish to discover providers of a TURN relay service from the 760 RELOAD overlay. 762 Note to RFC Editor: please replace AAAA with the RFC number for this 763 specification. 765 11. Acknowledgments 767 The authors would like to thank Marc Petit-Huguenin, Joscha 768 Schneider, and Carlos Bernardos for their comments on the document. 770 12. References 772 12.1. Normative References 774 [I-D.ietf-p2psip-base] 775 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 776 H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) 777 Base Protocol", draft-ietf-p2psip-base-26 (work in 778 progress), February 2013. 780 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 781 Requirement Levels", BCP 14, RFC 2119, March 1997. 783 12.2. Informative References 785 [I-D.ietf-p2psip-concepts] 786 Bryan, D., Matthews, P., Shim, E., Willis, D., and S. 787 Dawkins, "Concepts and Terminology for Peer to Peer SIP", 788 draft-ietf-p2psip-concepts-05 (work in progress), July 789 2013. 791 [Redir] Rhea, S., Godfrey, P., Karp, B., Kubiatowicz, J., 792 Ratnasamy, S., Shenker, S., Stoica, I., and H. Yu, "Open 793 DHT: A Public DHT Service and Its Uses", October 2005. 795 Authors' Addresses 797 Jouni Maenpaa 798 Ericsson 799 Hirsalantie 11 800 Jorvas 02420 801 Finland 803 Email: Jouni.Maenpaa@ericsson.com 805 Gonzalo Camarillo 806 Ericsson 807 Hirsalantie 11 808 Jorvas 02420 809 Finland 811 Email: Gonzalo.Camarillo@ericsson.com