idnits 2.17.1 draft-ietf-manet-dlep-credit-flow-control-09.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 -- The document date (24 October 2021) is 887 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-11) exists of draft-ietf-manet-dlep-traffic-classification-06 == Outdated reference: A later version (-16) exists of draft-ietf-manet-dlep-da-credit-extension-12 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Cheng 3 Internet-Draft D. Wiggins 4 Intended status: Standards Track MIT Lincoln Laboratory 5 Expires: 27 April 2022 L. Berger 6 LabN Consulting, L.L.C. 7 S. Ratliff 8 24 October 2021 10 DLEP Credit-Based Flow Control Messages and Data Items 11 draft-ietf-manet-dlep-credit-flow-control-09 13 Abstract 15 This document defines new Dynamic Link Exchange Protocol (DLEP) Data 16 Items that are used to support credit-based flow control. Credit 17 window control is used to regulate when data may be sent to an 18 associated virtual or physical queue. The Data Items are defined in 19 an extensible and reusable fashion. Their use will be mandated in 20 other documents defining specific DLEP extensions. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on 27 April 2022. 39 Copyright Notice 41 Copyright (c) 2021 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 46 license-info) in effect on the date of publication of this document. 47 Please review these documents carefully, as they describe your rights 48 and restrictions with respect to this document. Code Components 49 extracted from this document must include Simplified BSD License text 50 as described in Section 4.e of the Trust Legal Provisions and are 51 provided without warranty as described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Credit Window Control . . . . . . . . . . . . . . . . . . . . 3 58 2.1. Data Plane Considerations . . . . . . . . . . . . . . . . 5 59 2.2. Credit Window Messages . . . . . . . . . . . . . . . . . 5 60 2.2.1. Credit Control Message . . . . . . . . . . . . . . . 6 61 2.2.2. Credit Control Response Message . . . . . . . . . . . 6 62 2.3. Credit Window Control Data Items . . . . . . . . . . . . 7 63 2.3.1. Credit Window Initialization . . . . . . . . . . . . 7 64 2.3.2. Credit Window Association . . . . . . . . . . . . . . 9 65 2.3.3. Credit Window Grant . . . . . . . . . . . . . . . . . 10 66 2.3.4. Credit Window Status . . . . . . . . . . . . . . . . 12 67 2.3.5. Credit Window Request . . . . . . . . . . . . . . . . 13 68 2.4. Management Considerations . . . . . . . . . . . . . . . . 15 69 3. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 15 70 4. Security Considerations . . . . . . . . . . . . . . . . . . . 15 71 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 72 5.1. Message Values . . . . . . . . . . . . . . . . . . . . . 15 73 5.2. Data Item Values . . . . . . . . . . . . . . . . . . . . 16 74 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 75 6.1. Normative References . . . . . . . . . . . . . . . . . . 16 76 6.2. Informative References . . . . . . . . . . . . . . . . . 17 77 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 17 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 80 1. Introduction 82 The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175]. 83 It provides the exchange of link related control information between 84 DLEP peers. DLEP peers are comprised of a modem and a router. DLEP 85 defines a base set of mechanisms as well as support for possible 86 extensions. DLEP defines Data Items which are sets of information 87 that can be reused in DLEP messaging. The base DLEP specification 88 does not include any flow identification beyond DLEP endpoints nor 89 flow control capability. There are various flow control techniques 90 theoretically possible with DLEP. For example, a credit-window 91 scheme for destination-specific flow control which provides aggregate 92 flow control for both modem and routers has been proposed in 93 [I-D.ietf-manet-credit-window], and a control plane pause based 94 mechanism is defined in [RFC8651]. 96 This document defines DLEP Data Items and Messages which provide a 97 flow control mechanism for traffic sent from a router to a modem. 98 Flow control is provided using one or more logical "Credit Windows", 99 each of which will typically be supported by an associated virtual or 100 physical queue. A router will use traffic flow classification 101 information provided by the modem, as defined in 102 [I-D.ietf-manet-dlep-traffic-classification], to identify which 103 traffic is associated with each credit window. In this case, a flow 104 is identified based on information found in a data plane header and 105 one or more matches are associated with a single flow. (For general 106 background on traffic classification see [RFC2475] Section 2.3.) 107 Credit windows may be shared or dedicated on a per flow basis. The 108 Data Items are structured to allow for reuse of the defined credit 109 window based flow control with different traffic classification 110 techniques. 112 Note that this document defines common Messages, Data Items and 113 mechanisms that are reusable. They are expected to be required by 114 DLEP extensions defined in other documents such as found in 115 [I-D.ietf-manet-dlep-da-credit-extension]. 117 This document supports credit window control by introducing two new 118 DLEP messages in Section 2.2, and five new DLEP Data Items in 119 Section 2.3. 121 1.1. Key Words 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 125 "OPTIONAL" in this document are to be interpreted as described in BCP 126 14 [RFC2119] [RFC8174] when, and only when, they appear in all 127 capitals, as shown here. 129 2. Credit Window Control 131 This section defines additions to DLEP used in credit based flow 132 control. Two new messages and five Data Items are defined to support 133 credit window control. The use of credit window control impacts the 134 data plane. 136 The credit window control mechanisms defined in this document support 137 credit based flow control of traffic sent from a router to a modem. 138 The mapping of specific flows of traffic to a particular credit 139 window is based on the Traffic Classification Data Item defined in 140 [I-D.ietf-manet-dlep-traffic-classification]. Both types of DLEP 141 endpoints, i.e., a router and a modem, negotiate the use of this 142 extension during session initialization, e.g., see 143 [I-D.ietf-manet-dlep-da-credit-extension]. When using credit 144 windows, data traffic is only allowed to be sent by the router to the 145 modem when there are credits available. 147 Credits are managed on a per logical "Credit Window" basis. Each 148 credit window can be thought of as corresponding to a queue within a 149 modem. Credit windows may be shared across, or dedicated to, 150 destinations and data plane identifiers, e.g., DSCPs, at a 151 granularity that is appropriate for a modem's implementation and its 152 attached transmission technology. As defined below, there is a 153 direct one-for-one mapping of credit windows to flows as identified 154 by Flow Identifiers (FIDs) carried within the Traffic Classification 155 Data Item. Modems pass to the router information on their credit 156 windows and FIDs prior to a router being able to send data when an 157 extension requiring the use of credit window control is used. In 158 addition to the traffic classification information associated with an 159 FID, modems provide an initial credit window size, as well as the 160 maximum size of the logical queue associated with each credit window. 161 The maximum size is included for informative and potential future 162 uses. 164 Modems provide an initial credit window size at the time of "Credit 165 Window Initialization". Such initialization can take place during 166 session initiation or any point thereafter. It can also take place 167 when rate information changes. Additional "Credit Grants", i.e., 168 increments to Credit Window size, are provided using a Destination Up 169 or the new "Credit Control" Message. A router provides its view of 170 the Credit Window, which is known as "Status", in Destination Up 171 Response and the new "Credit Control Response" Messages. Routers can 172 also request credits using the new "Credit Control" Message. 174 When modems provide credits to a router, they will need to take into 175 account any overhead of their attached transmission technology and 176 map it into the credit semantics defined in this document. In 177 particular, the credit window is defined below to include per frame 178 (packet) MAC headers, and this may not match the actual overhead of 179 the modem attached transmission technology. In that case a direct 180 mapping, or an approximation will need to be made by the modem to 181 provide appropriate credit values. 183 Actual flows of traffic are mapped to credit windows based on flow 184 identification information provided by modems in the Traffic 185 Classification Data item defined in 186 [I-D.ietf-manet-dlep-traffic-classification]. This data item 187 supports traffic classification on a per destination or more fine 188 grain level. Routers use the combination of the DLEP identified 189 destination and flow information associated with a credit window in 190 order to match traffic they send to specific credit windows. 192 When a destination becomes reachable, a modem "associates" 193 (identifies) the appropriate traffic classification information via 194 the Traffic Class. Identifier (TID) to be used for traffic sent by 195 the router to that destination. As defined, each credit window has a 196 corresponding FID. This means that the use of FIDs, TIDs and the 197 association of a TID to a DLEP destination enables a modem to share 198 or dedicate resources as needed to match the specifics of its 199 implementation and its attached transmission technology. 201 The defined credit window control has similar objectives as the 202 control found in [I-D.ietf-manet-credit-window]. One notable 203 difference from that credit control is that in this document, credits 204 are never provided by the router to the modem. 206 2.1. Data Plane Considerations 208 When credit windowing is used, a router MUST NOT send data traffic to 209 a modem for forwarding when there are no credits available in the 210 associated Credit Window. This document defines credit windows in 211 octets. A credit window value MUST be larger than the number of 212 octets contained in a packet, including any MAC overhead (e.g., 213 framing, headers and trailers) used between the router and the modem, 214 in order for the router to send the packet to a modem for forwarding. 215 The credit window is decremented by the number of sent octets. 217 A router MUST identify the credit window associated with traffic sent 218 to a modem based on the traffic classification information provided 219 in the Data Items defined in this document. 221 2.2. Credit Window Messages 223 Two new messages are defined in support for credit window control: 224 the Credit Control and the Credit Control Response Message. Sending 225 and receiving both message types is REQUIRED to support the credit 226 window control defined in this document. 228 2.2.1. Credit Control Message 230 Credit Control Messages are sent by modems and routers. Each sender 231 is only permitted to have one message outstanding at one time. That 232 is, a sender (i.e., modem or router) MUST NOT send a second or any 233 subsequent Credit Control Message until a Credit Control Response 234 Message is received from its peer (i.e., router or modem). 236 Credit Control Messages are sent by modems to provide credit window 237 increases. Modems send credit increases when there is transmission 238 or local queue availability that exceeds the credit window value 239 previously provided to the router. Modems will need to balance the 240 load generated by sending and processing frequent credit window 241 increases against a router having data traffic available to send, but 242 no credits available. 244 Credit Control Messages MAY be sent by routers to request credits and 245 provide window status. Routers will need to balance the load 246 generated by sending and processing frequent credit window requests 247 against having data traffic available to send, but no credits 248 available. 250 The Message Type value in the DLEP Message Header is set to TBA2. 252 A message sent by a modem, MUST contain one or more Credit Window 253 Grant Data Items as defined below in Section 2.3.3. A router 254 receiving this message MUST respond with a Credit Control Response 255 Message. 257 A message sent by a router, MUST contain one or more Credit Window 258 Request Data Items defined below in Section 2.3.5 and SHOULD contain 259 a Credit Window Status Data Item, defined in Section 2.3.4, 260 corresponding to each credit window request. A modem receiving this 261 message MUST respond with a Credit Control Response Message based on 262 the received message and Data Item and the processing defined below, 263 which will typically result in credit window increments being 264 provided. 266 Specific processing associated with each Credit Data Item is provided 267 below. 269 2.2.2. Credit Control Response Message 271 Credit Control Response Messages are sent by routers to report the 272 current Credit Window for a destination. A message sent by a router, 273 MUST contain one or more Credit Window Status Data Items as defined 274 below in Section 2.3.4. Specific receive processing associated with 275 the Credit Window Status Data Item is provided below. 277 Credit Control Response Messages sent by modems MUST contain one or 278 more Credit Window Grant Data Items. A Data Item for every Credit 279 Window Request Data Item contained in the corresponding Credit 280 Control Message received by the modem MUST be included. Each Credit 281 Grant Data Item MAY provide zero or more additional credits based on 282 the modem's transmission or local queue availability. Specific 283 receive processing associated with each Grant Data Item is provided 284 below. 286 The Message Type value in the DLEP Message Header is set to TBA3. 288 2.3. Credit Window Control Data Items 290 Five new Data Items are defined to support credit window control. 291 The Credit Window Initialization Data Item is used by a modem to 292 identify a credit window and set its size. The Credit Window 293 Association Data Item is used by a modem to identify which traffic 294 classification identifiers (flows) should be used when sending 295 traffic to a particular DLEP identified destination. The Credit 296 Window Grant is used by a modem to provide additional credits to a 297 router. The Credit Window Request is used by a router to request 298 additional credits. The Credit Window Status is used to advertise 299 the sender's view of number of available credits for state 300 synchronization purposes. 302 Any errors or inconsistencies encountered in parsing Data Items are 303 handled in the same fashion as any other data item parsing error 304 encountered in DLEP, see [RFC8175]. In particular, the node parsing 305 the Data Item MUST terminate the session with a Status Data Item 306 indicating Invalid Data. 308 2.3.1. Credit Window Initialization 310 The Credit Window Initialization Data Item is used by a modem to 311 identify a credit window and set its size. This Data Item SHOULD be 312 included in any Session Initialization Response Message that also 313 indicates support for an extension that requires support for the 314 credit window control mechanisms defined in this document, e.g., see 315 [I-D.ietf-manet-dlep-da-credit-extension]. Updates to previously 316 identified credit windows or new credit windows MAY be sent by a 317 modem by including the Data Item in Session Update Messages. More 318 than one data item MAY be included in a message to provide 319 information on multiple credit windows. 321 The Credit Window Initialization Data Item identifies a credit window 322 using a Flow Identifier, or FID. It also provides the size of the 323 identified credit window. Finally, a queue size (in bytes) is 324 provided for informational purposes. Note that to be used, a FID 325 must be defined within a Traffic Classification Data Item and the 326 associated TID must be provided via a Credit Window Association Data 327 Item. 329 The format of the Credit Window Initialization Data Item is: 331 0 1 2 3 332 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | Data Item Type | Length (16) | 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 | Flow Identifier (FID) | Reserved | 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | Credit Value : 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 : Credit Value | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 | Scale | Credit Window Size | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 Data Item Type: 346 TBA4 348 Length: 349 16 351 Per [RFC8175] Length is the number of octets in the Data Item. It 352 MUST be equal to sixteen (16). 354 Flow Identifier (FID): 355 A flow identifier as defined by the Traffic Classification Data 356 Item. The FID also uniquely identifies a credit window. 358 Reserved: 359 MUST be set to zero by the sender (a modem) and ignored by the 360 receiver (a router). 362 Credit Value: 363 A 64-bit unsigned integer representing the credits, in octets, to 364 be applied to the Credit Window. This value includes MAC headers 365 as seen on the link between the modem and router. 367 Scale: 368 An 8-bit unsigned integer indicating the scale used in the Credit 369 Window Size field. The valid values are: 371 Value Scale 372 ------------ 373 0 B - Bytes (Octets) 374 1 KB - Kilobytes (B/1024) 375 2 MB - Megabytes (KB/1024) 376 3 GB - Gigabytes (MB/1024) 378 Credit Window Size: 379 A 24-bit unsigned integer representing the maximum size, in the 380 octet scale indicated by the Scale field, of the associated credit 381 window. 383 A router that receives a Credit Window Initialization Data Item MUST 384 ensure that the FID field value has been provided by the modem in a 385 Traffic Classification Data Item carried in either the current or a 386 previous message. If the FID cannot be found the router SHOULD 387 report or log this information. Note that no traffic will be 388 associated with the credit window in this case. After FID 389 validation, the router MUST locate the credit window that is 390 associated with the FID indicated in each received Data Item. If no 391 associated credit window is found, the router MUST initialize a new 392 credit window using the values carried in the Data Item. When an 393 associated credit window is found, the router MUST update the credit 394 window and associated data plane state using the values carried in 395 the Data Item. It is worth noting, that such updates can result in a 396 credit window size being reduced, for example, due to a transmission 397 rate change on the modem. 399 2.3.2. Credit Window Association 401 The Credit Window Association Data Item is used by a modem to 402 associate traffic classification information with a destination. The 403 traffic classification information is identified using a TID value 404 that has previously been sent by the modem or is listed in a Traffic 405 Classification Data Item carried in the same message as the Data 406 Item. 408 A single Credit Window Association Data Item MUST be included in all 409 Destination Up and Destination Update Messages sent by a modem when 410 the credit window control defined in this document is used. Note 411 that a TID will not be used unless it is listed in a Credit Window 412 Association Data Item. 414 The format of the Credit Window Association Data Item is: 416 0 1 2 3 417 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 419 | Data Item Type | Length (2) | 420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 421 |Traffic Class. Identifier (TID)| 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 424 Data Item Type: 425 TBA5 427 Length: 428 2 430 Per [RFC8175] Length is the number of octets in the Data Item. It 431 MUST be equal to two (2). 433 Traffic Classification Identifier (TID): 434 A 16-bit unsigned integer identifying a traffic classification set 435 that has been identified in a Traffic Classification Data Item, 436 see [I-D.ietf-manet-dlep-traffic-classification]. 438 A router that receives the Credit Window Association Data Item MUST 439 locate the traffic classification information indicated by the 440 received TID. If no corresponding information can be located, the 441 Data Item MUST be treated as an error as described above. Once the 442 traffic classification information is located, it MUST be associated 443 with the destination and the router MUST ensure that any data plane 444 state, see Section 2.1, that is associated with the TID and its 445 corresponding FIDs is updated as needed. 447 2.3.3. Credit Window Grant 449 The Credit Window Grant Data Item is used by a modem to provide 450 credits to a router. One or more Credit Window Grant Data Items MAY 451 be carried in the DLEP Destination Up, Destination Announce Response, 452 Destination Update, Credit Control Messages, and Credit Control 453 Response Messages. Multiple Credit Window Grant Data Items in a 454 single message are used to indicate different credit values for 455 different credit windows. In all message types, this Data Item 456 provides an additional number of octets to be added to the indicated 457 credit window. Credit windows are identified using FID values that 458 have been previously been sent by the modem or are listed in a Credit 459 Window Initialization Data Item carried in the same message as the 460 Data Item. 462 The format of the Credit Window Grant Data Item is: 464 0 1 2 3 465 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 467 | Data Item Type | Length (12) | 468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 469 | Flow Identifier (FID) | Reserved | 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | Additional Credits : 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 : Additional Credits | 474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 Data Item Type: 477 TBA6 479 Length: 480 12 482 Per [RFC8175], Length is the number of octets in the Data Item. 483 It MUST be equal to twelve (12). 485 Flow Identifier (FID): 486 A flow identifier as defined by the Traffic Classification Data 487 Item. The FID also uniquely identifies a credit window. 489 Reserved: 490 MUST be set to zero by the sender and ignored by the receiver. 492 Additional Credit: 493 A 64-bit unsigned integer representing the credits, in octets, to 494 be added to the Credit Window. This value includes MAC headers as 495 seen on the link between the modem and router. A value of zero 496 indicates that no additional credits are being provided. 498 When receiving this Data Item, a router MUST identify the credit 499 window indicated by the FID. If the FID is not known to the router, 500 it SHOULD report or log this information and discard the Data Item. 501 It is important to note that while this Data Item can be received in 502 a destination specific message, credit windows are managed 503 independently from the destination identified in the message carrying 504 this Data Item, and the indicated FID MAY even be disjoint from the 505 identified destination. 507 Once the credit window is identified, the credit window size MUST be 508 increased by the value contained in the Additional Credits field. If 509 the increase results in a window overflow, i.e., the size of the 510 credit window after the increase is smaller than the original credit 511 window size, the Credit Window must be set to its maximum 512 (0xFFFFFFFFFFFFFFFF). 514 No response is sent by the router to a modem after processing a 515 Credit Window Grant Data Item received in a Credit Control Response 516 Message. In other cases, the receiving router MUST send a Credit 517 Window Status Data Item or items reflecting the resulting Credit 518 Window value of the updated credit window. When the Credit Grant 519 Data Item is received in a Destination Up Message, the Credit Window 520 Status Data Item(s) MUST be sent in the corresponding Destination Up 521 Response Message. Otherwise, a Credit Control Message MUST be sent. 523 2.3.4. Credit Window Status 525 The Credit Window Status Data Item is used by a router to report the 526 current credit window size to its peer modem. One or more Credit 527 Window Status Data Items MAY be carried in a Destination Up Response 528 Message or a Credit Control Response Message. As discussed above, 529 the Destination Up Response Message is used when the Data Item is 530 sent in response to a Destination Up Message, and the Credit Control 531 Response Message is sent in response to a Credit Control Message. 532 Multiple Credit Window Status Data Items in a single message are used 533 to indicate different sizes of different credit windows. Similar to 534 the Credit Window Grant, credit windows are identified using FID 535 values that have been previously been sent by the modem. 537 The format of the Credit Window Status Data Item is: 539 0 1 2 3 540 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 | Data Item Type | Length (12) | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 | Flow Identifier (FID) | Reserved | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 | Current Credit Window Size : 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 : Current Credit Window Size | 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 Data Item Type: 552 TBA7 554 Length: 556 12 558 Per [RFC8175] Length is the number of octets in the Data Item. It 559 MUST be equal to twelve (12). 561 Flow Identifier (FID): 562 A flow identifier as defined by the Traffic Classification Data 563 Item. The FID also uniquely identifies a credit window. 565 Reserved: 566 MUST be set to zero by the sender and ignored by the receiver. 568 Current Credit Window Size: 569 A 64-bit unsigned integer, indicating the current number of 570 credits, in octets, available for the router to send to the modem. 571 This is referred to as the Modem Receive Window in 572 [I-D.ietf-manet-credit-window]. 574 When receiving this Data Item, a modem MUST identify the credit 575 window indicated by the FID. If the FID is not known to the modem, 576 it SHOULD report or log this information and discard the Data Item. 577 As with the Credit Window Grant Data Item, the FID MAY be unrelated 578 to the Destination indicated in the message carrying the Data Item. 580 Once the credit window is identified, the modem SHOULD check the 581 received Current Credit Window Size field value against the 582 outstanding credit window's available credits at the time the most 583 recent Credit Window Initialization or Grant Data Item associated 584 with the indicated FID was sent. If the values significantly differ, 585 i.e., greater than can be accounted for based on observed data 586 frames, then the modem SHOULD send a Credit Window Initialization 587 Data Item to reset the associated credit window size to the modem's 588 current view of the available credits. As defined above, Credit 589 Window Initialization Data Items are sent in Session Update Messages. 590 When multiple Data Items need to be sent, they SHOULD be combined 591 into a single message when possible. Alternatively, and also in 592 cases where there are small differences, the modem MAY adjust the 593 values sent in Credit Window Grant Data Items to account for the 594 reported Credit Window. 596 2.3.5. Credit Window Request 598 The Credit Window Request Data Item is used by a router to request 599 additional credits for particular credit windows. Credit Window 600 Request Data Items are carried in Credit Control Messages, and one or 601 more Credit Window Request Data Items MAY be present in a message. 603 Credit windows are identified using a FID as defined above in 604 Section 2.3.1. Multiple FIDs MAY be present to allow for the case 605 where the router identifies that credits are needed in multiple 606 credit windows. A special FID value, as defined below, is used to 607 indicate that a credit request is being made across all queues. 609 The format of the Credit Window Request Data Item is: 611 0 1 2 3 612 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | Data Item Type | Length | 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 | Flow Identifier (FID) | ... : 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 : ... | Flow Identifier (FID) | 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 Data Item Type: 622 TBA8 624 Length: 625 Variable 627 Per [RFC8175] Length is the number of octets in the Data Item, 628 excluding the Type and Length fields. It will equal the number of 629 FID fields carried in the Data Item times 2 and MUST be at least 630 2. 632 Flow Identifier (FID): 633 A flow identifier as defined by the Traffic Classification Data 634 Item. The FID also uniquely identifies a credit window. The 635 special value of 0xFFFF indicates that the request applies to all 636 FIDs. Note that when the special value is included, all other FID 637 values included in the Data Item are redundant as the special 638 value indicates all FIDs. 640 A modem receiving this Data Item MUST provide a Credit Increment for 641 the indicated credit windows via Credit Window Grant Data Items 642 carried in a new Credit Control Message. Multiple values and queue 643 indexes SHOULD be combined into a single Credit Control Message when 644 possible. Unknown FID values SHOULD be reported or logged and then 645 ignored by the modem. 647 2.4. Management Considerations 649 This section provides several network management guidelines to 650 implementations supporting the credit window mechanisms defined in 651 this document. 653 Modems MAY support the configuration of the number of credit windows 654 (queues) to advertise to a router. 656 Routers may have limits on the number of queues that they can support 657 and, perhaps, even limits in supported credit window combinations, 658 e.g., if per destination queues can even be supported at all. When 659 modem-provided credit window information exceeds the capabilities of 660 a router, the router MAY use a subset of the provided credit windows. 661 Alternatively, a router MAY reset the session and indicate that the 662 extension is not supported. In either case, the mismatch of 663 capabilities SHOULD be reported to the user via normal network 664 management mechanisms, e.g., user interface or error logging. 666 3. Compatibility 668 The messages and data items defined in this document will only be 669 used when extensions require their use. 671 4. Security Considerations 673 This document introduces credit window control and flow mechanisms to 674 DLEP. These mechanisms do not inherently introduce any additional 675 vulnerabilities above those documented in [RFC8175]. The approach 676 taken to Security in that document applies equally to the mechanism 677 defined in this document. 679 5. IANA Considerations 681 This document requests the assignment of several values by IANA. All 682 assignments are to registries defined by [RFC8175]. 684 5.1. Message Values 686 This document requests 2 new assignments to the DLEP Message Registry 687 named "Message Values" in the range with the "Specification Required" 688 policy. The requested values are as follows: 690 +===========+=========================+ 691 | Type Code | Description | 692 +===========+=========================+ 693 | TBA2 | Credit Control | 694 +-----------+-------------------------+ 695 | TBA3 | Credit Control Response | 696 +-----------+-------------------------+ 698 Table 1: Requested Message Values 700 5.2. Data Item Values 702 This document requests the following new assignments to the DLEP Data 703 Item Registry named "Data Item Type Values" in the range with the 704 "Specification Required" policy. The requested values are as 705 follows: 707 +===========+==============================+ 708 | Type Code | Description | 709 +===========+==============================+ 710 | TBA4 | Credit Window Initialization | 711 +-----------+------------------------------+ 712 | TBA5 | Credit Window Association | 713 +-----------+------------------------------+ 714 | TBA6 | Credit Window Grant | 715 +-----------+------------------------------+ 716 | TBA7 | Credit Window Status | 717 +-----------+------------------------------+ 718 | TBA8 | Credit Window Request | 719 +-----------+------------------------------+ 721 Table 2: Requested Data Item Values 723 6. References 725 6.1. Normative References 727 [I-D.ietf-manet-dlep-traffic-classification] 728 Cheng, B., Wiggins, D., and L. Berger, "DLEP Traffic 729 Classification Data Item", Work in Progress, Internet- 730 Draft, draft-ietf-manet-dlep-traffic-classification-06, 29 731 July 2021, . 734 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 735 Requirement Levels", BCP 14, RFC 2119, 736 DOI 10.17487/RFC2119, March 1997, 737 . 739 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 740 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 741 May 2017, . 743 [RFC8175] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B. 744 Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175, 745 DOI 10.17487/RFC8175, June 2017, 746 . 748 6.2. Informative References 750 [I-D.ietf-manet-credit-window] 751 Ratliff, S., "Credit Windowing extension for DLEP", Work 752 in Progress, Internet-Draft, draft-ietf-manet-credit- 753 window-07, 13 November 2016, 754 . 757 [I-D.ietf-manet-dlep-da-credit-extension] 758 Cheng, B., Wiggins, D., and L. Berger, "DLEP DiffServ 759 Aware Credit Window Extension", Work in Progress, 760 Internet-Draft, draft-ietf-manet-dlep-da-credit-extension- 761 12, 29 July 2021, . 764 [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., 765 and W. Weiss, "An Architecture for Differentiated 766 Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, 767 . 769 [RFC8651] Cheng, B., Wiggins, D., and L. Berger, Ed., "Dynamic Link 770 Exchange Protocol (DLEP) Control-Plane-Based Pause 771 Extension", RFC 8651, DOI 10.17487/RFC8651, October 2019, 772 . 774 Appendix A. Acknowledgments 776 We mourn the loss of Stan Ratliff who passed away on October 22, 777 2019. His guidance, leadership and personal contributions were 778 critical in the development of this work and DLEP as a whole. His 779 leadership and friendship shall be missed. 781 Many useful comments were received from contributors to the MANET 782 working group, notably Rick Taylor. This document was derived from 783 [I-D.ietf-manet-dlep-da-credit-extension] as a result of discussions 784 at IETF101. 786 Authors' Addresses 788 Bow-Nan Cheng 789 MIT Lincoln Laboratory 790 Massachusetts Institute of Technology 791 244 Wood Street 792 Lexington 794 Email: bcheng@ll.mit.edu 796 David Wiggins 797 MIT Lincoln Laboratory 798 Massachusetts Institute of Technology 799 244 Wood Street 800 Lexington 802 Email: David.Wiggins@ll.mit.edu 804 Lou Berger 805 LabN Consulting, L.L.C. 807 Email: lberger@labn.net 809 Stan Ratliff