--- 1/draft-ietf-ipsecme-iptfs-02.txt 2020-11-15 12:13:12.475941322 -0800 +++ 2/draft-ietf-ipsecme-iptfs-03.txt 2020-11-15 12:13:12.535942840 -0800 @@ -1,44 +1,44 @@ Network Working Group C. Hopps Internet-Draft LabN Consulting, L.L.C. -Intended status: Standards Track September 30, 2020 -Expires: April 3, 2021 +Intended status: Standards Track November 15, 2020 +Expires: May 19, 2021 IP Traffic Flow Security - draft-ietf-ipsecme-iptfs-02 + draft-ietf-ipsecme-iptfs-03 Abstract This document describes a mechanism to enhance IPsec traffic flow security by adding traffic flow confidentiality to encrypted IP encapsulated traffic. Traffic flow confidentiality is provided by obscuring the size and frequency of IP traffic using a fixed-sized, constant-send-rate IPsec tunnel. The solution allows for congestion - control as well. + control as well as non-constant send-rate usage. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on April 3, 2021. + This Internet-Draft will expire on May 19, 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -54,80 +54,80 @@ 1.1. Terminology & Concepts . . . . . . . . . . . . . . . . . 3 2. The IP-TFS Tunnel . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Tunnel Content . . . . . . . . . . . . . . . . . . . . . 4 2.2. IPTFS_PROTOCOL Payload Content . . . . . . . . . . . . . 4 2.2.1. Data Blocks . . . . . . . . . . . . . . . . . . . . . 5 2.2.2. No Implicit End Padding Required . . . . . . . . . . 6 2.2.3. Fragmentation, Sequence Numbers and All-Pad Payloads 6 2.2.4. Empty Payload . . . . . . . . . . . . . . . . . . . . 6 2.2.5. IP Header Value Mapping . . . . . . . . . . . . . . . 7 2.3. Exclusive SA Use . . . . . . . . . . . . . . . . . . . . 7 - 2.4. Zero-Conf Receive-Side Operation On The SA. . . . . . . . 7 - 2.5. Modes of Operation . . . . . . . . . . . . . . . . . . . 7 - 2.5.1. Non-Congestion Controlled Mode . . . . . . . . . . . 8 - 2.5.2. Congestion Controlled Mode . . . . . . . . . . . . . 8 + 2.4. Modes of Operation . . . . . . . . . . . . . . . . . . . 7 + 2.4.1. Non-Congestion Controlled Mode . . . . . . . . . . . 7 + 2.4.2. Congestion Controlled Mode . . . . . . . . . . . . . 8 3. Congestion Information . . . . . . . . . . . . . . . . . . . 9 3.1. ECN Support . . . . . . . . . . . . . . . . . . . . . . . 10 - 4. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 10 - 4.1. Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 10 + 4. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 11 + 4.1. Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Fixed Packet Size . . . . . . . . . . . . . . . . . . . . 11 4.3. Congestion Control . . . . . . . . . . . . . . . . . . . 11 5. IKEv2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.1. USE_TFS Notification Message . . . . . . . . . . . . . . 11 6. Packet and Data Formats . . . . . . . . . . . . . . . . . . . 12 6.1. IP-TFS Payload . . . . . . . . . . . . . . . . . . . . . 12 6.1.1. Non-Congestion Control IPTFS_PROTOCOL Payload Format 12 6.1.2. Congestion Control IPTFS_PROTOCOL Payload Format . . 13 - 6.1.3. Data Blocks . . . . . . . . . . . . . . . . . . . . . 14 - 6.1.4. IKEv2 USE_IPTFS Notification Message . . . . . . . . 16 - 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 - 7.1. IPTFS_PROTOCOL Type . . . . . . . . . . . . . . . . . . . 17 - 7.2. IPTFS_PROTOCOL Sub-Type Registry . . . . . . . . . . . . 17 - 7.3. USE_IPTFS Notify Message Status Type . . . . . . . . . . 17 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 - 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 - 9.1. Normative References . . . . . . . . . . . . . . . . . . 18 - 9.2. Informative References . . . . . . . . . . . . . . . . . 18 - Appendix A. Example Of An Encapsulated IP Packet Flow . . . . . 20 - Appendix B. A Send and Loss Event Rate Calculation . . . . . . . 21 - Appendix C. Comparisons of IP-TFS . . . . . . . . . . . . . . . 21 - C.1. Comparing Overhead . . . . . . . . . . . . . . . . . . . 21 - C.1.1. IP-TFS Overhead . . . . . . . . . . . . . . . . . . . 21 - C.1.2. ESP with Padding Overhead . . . . . . . . . . . . . . 22 - - C.2. Overhead Comparison . . . . . . . . . . . . . . . . . . . 23 - C.3. Comparing Available Bandwidth . . . . . . . . . . . . . . 23 - C.3.1. Ethernet . . . . . . . . . . . . . . . . . . . . . . 24 - Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 26 - Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 26 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26 + 6.1.3. Data Blocks . . . . . . . . . . . . . . . . . . . . . 15 + 6.1.4. IKEv2 USE_IPTFS Notification Message . . . . . . . . 17 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 + 7.1. IPTFS_PROTOCOL Type . . . . . . . . . . . . . . . . . . . 18 + 7.2. IPTFS_PROTOCOL Sub-Type Registry . . . . . . . . . . . . 18 + 7.3. USE_IPTFS Notify Message Status Type . . . . . . . . . . 18 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 19 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 + 9.1. Normative References . . . . . . . . . . . . . . . . . . 19 + 9.2. Informative References . . . . . . . . . . . . . . . . . 19 + Appendix A. Example Of An Encapsulated IP Packet Flow . . . . . 21 + Appendix B. A Send and Loss Event Rate Calculation . . . . . . . 22 + Appendix C. Comparisons of IP-TFS . . . . . . . . . . . . . . . 22 + C.1. Comparing Overhead . . . . . . . . . . . . . . . . . . . 22 + C.1.1. IP-TFS Overhead . . . . . . . . . . . . . . . . . . . 22 + C.1.2. ESP with Padding Overhead . . . . . . . . . . . . . . 23 + C.2. Overhead Comparison . . . . . . . . . . . . . . . . . . . 24 + C.3. Comparing Available Bandwidth . . . . . . . . . . . . . . 25 + C.3.1. Ethernet . . . . . . . . . . . . . . . . . . . . . . 25 + Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 27 + Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 27 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 27 1. Introduction Traffic Analysis ([RFC4301], [AppCrypt]) is the act of extracting information about data being sent through a network. While one may directly obscure the data through the use of encryption [RFC4303], the traffic pattern itself exposes information due to variations in it's shape and timing ([I-D.iab-wire-image], [AppCrypt]). Hiding the size and frequency of traffic is referred to as Traffic Flow Confidentiality (TFC) per [RFC4303]. [RFC4303] provides for TFC by allowing padding to be added to encrypted IP packets and allowing for transmission of all-pad packets (indicated using protocol 59). This method has the major limitation that it can significantly under-utilize the available bandwidth. The IP-TFS solution provides for full TFC without the aforementioned bandwidth limitation. This is accomplished by using a constant-send- rate IPsec [RFC4303] tunnel with fixed-sized encapsulating packets; however, these fixed-sized packets can contain partial, whole or - multiple IP packets to maximize the bandwidth of the tunnel. + multiple IP packets to maximize the bandwidth of the tunnel. A non- + constant send-rate is allowed, but the confidentiality properties of + its use are outside the scope of this document. For a comparison of the overhead of IP-TFS with the RFC4303 prescribed TFC solution see Appendix C. Additionally, IP-TFS provides for dealing with network congestion [RFC2914]. This is important for when the IP-TFS user is not in full control of the domain through which the IP-TFS tunnel path flows. 1.1. Terminology & Concepts @@ -171,27 +171,27 @@ packet can be sent per encapsulating packet. In order to maximize bandwidth IP-TFS breaks this one-to-one association. IP-TFS aggregates as well as fragments the inner IP traffic flow into fixed-sized encapsulating IPsec tunnel packets. Padding is only added to the the tunnel packets if there is no data available to be sent at the time of tunnel packet transmission, or if fragmentation has been disabled by the receiver. This is accomplished using a new Encapsulating Security Payload (ESP, - [RFC4303]) type which is identified by the IP protocol number - IPTFS_PROTOCOL (TBD1). + [RFC4303]) type which is identified by the number IPTFS_PROTOCOL + (Section 6.1). 2.2. IPTFS_PROTOCOL Payload Content The IPTFS_PROTOCOL payload content defined in this document is - comprised of a 4 or 16 octet header followed by either a partial, a + comprised of a 4 or 24 octet header followed by either a partial, a full or multiple partial or full data blocks. The following diagram illustrates this IPTFS_PROTOCOL payload within the ESP packet. See Section 6.1 for the exact formats of the IPTFS_PROTOCOL payload. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outer Encapsulating Header ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ESP Header... . +---------------------------------------------------------------+ | ... : BlockOffset | @@ -306,53 +306,46 @@ It is not the intention of this specification to allow for mixed use of an IP-TFS enabled SA. In other words, an SA that has IP-TFS enabled is exclusively for IP-TFS use and MUST NOT have non-IP-TFS payloads such as IP (IP protocol 4), TCP transport (IP protocol 6), or ESP pad packets (protocol 59) intermixed with non-empty IP-TFS (IP protocol TBD1) payloads. While it's possible to envision making the algorithm work in the presence of sequence number skips in the IP-TFS payload stream, the added complexity is not deemed worthwhile. Other IPsec uses can configure and use their own SAs. -2.4. Zero-Conf Receive-Side Operation On The SA. - - Receive-side operation of IP-TFS does not require any per-SA - configuration on the receiver; as such, an IP-TFS implementation - SHOULD support the option of switching to IP-TFS receive-side - operation on receipt of the first IP-TFS payload. - -2.5. Modes of Operation +2.4. Modes of Operation Just as with normal IPsec/ESP tunnels, IP-TFS tunnels are unidirectional. Bidirectional IP-TFS functionality is achieved by setting up 2 IP-TFS tunnels, one in either direction. An IP-TFS tunnel can operate in 2 modes, a non-congestion controlled mode and congestion controlled mode. -2.5.1. Non-Congestion Controlled Mode +2.4.1. Non-Congestion Controlled Mode In the non-congestion controlled mode IP-TFS sends fixed-sized packets at a constant rate. The packet send rate is constant and is not automatically adjusted regardless of any network congestion (e.g., packet loss). For similar reasons as given in [RFC7510] the non-congestion controlled mode should only be used where the user has full administrative control over the path the tunnel will take. This is required so the user can guarantee the bandwidth and also be sure as to not be negatively affecting network congestion [RFC2914]. In this case packet loss should be reported to the administrator (e.g., via syslog, YANG notification, SNMP traps, etc) so that any failures due to a lack of bandwidth can be corrected. -2.5.2. Congestion Controlled Mode +2.4.2. Congestion Controlled Mode With the congestion controlled mode, IP-TFS adapts to network congestion by lowering the packet send rate to accommodate the congestion, as well as raising the rate when congestion subsides. Since overhead is per packet, by allowing for maximal fixed-size packets and varying the send rate transport overhead is minimized. The output of the congestion control algorithm will adjust the rate at which the ingress sends packets. While this document does not require a specific congestion control algorithm, best current @@ -374,39 +367,41 @@ receiver and from the sender, at least once per RTT. Prior to establishing an RTT the information SHOULD be sent constantly from the sender and the receiver so that an RTT estimate can be established. The lack of receiving this information over multiple consecutive RTT intervals should be considered a congestion event that causes the sender to adjust it's sending rate lower. For example, [RFC4342] calls this the "no feedback timeout" and it is equal to 4 RTT intervals. When a "no feedback timeout" has occurred [RFC4342] halves the sending rate. - An implementation could choose to always include the congestion + An implementation MAY choose to always include the congestion information in it's IP-TFS payload header if sending on an IP-TFS enabled SA. Since IP-TFS normally will operate with a large packet size, the congestion information should represent a small portion of - the available tunnel bandwidth. + the available tunnel bandwidth. An implementation choosing to always + send the data MAY also choose to only update the "LossEventRate" and + "RTT" header field values it sends every "RTT" though. When an implementation is choosing a congestion control algorithm (or a selection of algorithms) one should remember that IP-TFS is not providing for reliable delivery of IP traffic, and so per packet ACKs are not required and are not provided. It's worth noting that the variable send-rate of a congestion controlled IP-TFS tunnel, is not private; however, this send-rate is being driven by network congestion, and as long as the encapsulated (inner) traffic flow shape and timing are not directly affecting the (outer) network congestion, the variations in the tunnel rate will not weaken the provided inner traffic flow confidentiality. -2.5.2.1. Circuit Breakers +2.4.2.1. Circuit Breakers In additional to congestion control, implementations MAY choose to define and implement circuit breakers [RFC8084] as a recovery method of last resort. Enabling circuit breakers is also a reason a user may wish to enable congestion information reports even when using the non-congestion controlled mode of operation. The definition of circuit breakers are outside the scope of this document. 3. Congestion Information @@ -418,28 +413,47 @@ paired SA back to the sender (this is always the case when the tunnel was created using IKEv2). If the SA back to the sender is a non-IP- TFS enabled SA then an IPTFS_PROTOCOL empty payload (i.e., header only) is used to convey the information. In order to calculate a loss event rate compatible with [RFC5348], the receiver needs to have a round-trip time estimate. Thus the sender communicates this estimate in the "RTT" header field. On startup this value will be zero as no RTT estimate is yet known. - In order to allow the sender to calculate the "RTT" value, the - receiver communicates the last sequence number it has seen to the - sender in the "LastSeqNum" header field. In addition to the - "LastSeqNum" value, the receiver sends an estimate of the amount of - time between receiving the "LastSeqNum" packet and transmitting the - "LastSeqNum" value back to the sender in the congestion information. - It places this time estimate in the "Delay" header field along with - the "LastSeqNum". + In order for the sender to estimate it's "RTT" value, the sender + places a timestamp value in the "TVal" header field. On first + receipt of this "TVal", the receiver records the new "TVal" value + along with the time it arrived locally, subsequent receipt of the + same "TVal" MUST not update the recorded time. When the receiver + sends it's CC header it places this latest recorded value in the + "TEcho" header field, along with 2 delay values, "Echo Delay" and + "Transmit Delay". The "Echo Delay" value is the time delta from the + recorded arrival time of "TVal" and the current clock in + microseconds. The second value, "Transmit Delay", is the receiver's + current transmission delay on the tunnel (i.e., the average time + between sending packets on it's half of the IP-TFS tunnel). When the + sender receives back it's "TVal" in the "TEcho" header field it + calculates 2 RTT estimates. The first is the actual delay found by + subtracting the "TEcho" value from it's current clock and then + subtracting "Echo Delay" as well. The second RTT estimate is found + by adding the received "Transmit Delay" header value to the senders + own transmission delay (i.e., the average time between sending + packets on it's half of the IP-TFS tunnel). The larger of these 2 + RTT estimates SHOULD be used as the "RTT" value. The two estimates + are required to handle different combinations of faster or slow + tunnel packet paths with fast or slow fixed tunnel rates. Choosing + the larger of the two values guarantees that the "RTT" is never + considered faster than the aggregate transmission delay based on the + IP-TFS tunnel rate (the second estimate), as well as never being + considered faster than the actual RTT along the tunnel packet path + (the first estimate). The receiver also calculates, and communicates in the "LossEventRate" header field, the loss event rate for use by the sender. This is slightly different from [RFC4342] which periodically sends all the loss interval data back to the sender so that it can do the calculation. See Appendix B for a suggested way to calculate the loss event rate value. Initially this value will be zero (indicating no loss) until enough data has been collected by the receiver to update it. @@ -517,23 +531,25 @@ initiator, by deleting the child SA if the now established non-IP-TFS operation is unacceptable). The notification type and payload flag values are defined in Section 6.1.4. 6. Packet and Data Formats 6.1. IP-TFS Payload - An IP-TFS payload is identified by the IP protocol number - IPTFS_PROTOCOL (TBD1). The first octet of this payload indicates the - format of the remaining payload data. + ESP Payload Type: 0x5 + + An IP-TFS payload is identified by the ESP payload type + IPTFS_PROTOCOL which has the value 0x5. The first octet of this + payload indicates the format of the remaining payload data. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+-+-+- | Sub-type | ... +-+-+-+-+-+-+-+-+-+-+- Sub-type: An 8 bit value indicating the payload format. This specification defines 2 payload sub-types. These payload @@ -570,77 +586,93 @@ "DataBlocks" data (i.e., it does not count subsequent packets non-"DataBlocks" octets). DataBlocks: Variable number of octets that begins with the start of a data block, or the continuation of a previous data block, followed by zero or more additional data blocks. 6.1.2. Congestion Control IPTFS_PROTOCOL Payload Format - The congestion control IPTFS_PROTOCOL payload is comprised of a 16 + The congestion control IPTFS_PROTOCOL payload is comprised of a 24 octet header followed by a variable amount of "DataBlocks" data as shown below. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-type (1) | Reserved |E| BlockOffset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | RTT | Delay | - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LossEventRate | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | LastSeqNum | + | RTT | Echo Delay ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ... Echo Delay | Transmit Delay | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | TVal | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | TEcho | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DataBlocks ... +-+-+-+-+-+-+-+-+-+-+- Sub-type: An octet indicating the payload format. For this congestion control format, the value is 1. Reserved: A 7 bit field set to 0 on generation, and ignored on receipt. E: A 1 bit value if set indicates that Congestion Experienced (CE) ECN bits were received and used in deriving the reported "LossEventRate". BlockOffset: The same value as the non-congestion controlled payload format value. - RTT: - A 16 bit value specifying the sender's current round-trip time - estimate in milliseconds. The value MAY be zero prior to the - sender having calculated a round-trip time estimate. The value - SHOULD be set to zero on non-IP-TFS enabled SAs. - - Delay: - A 16 bit value specifying the delay in milliseconds incurred - between the receiver receiving the "LastSeqNum" packet and the - sending of this acknowledgement of it. - LossEventRate: A 32 bit value specifying the inverse of the current loss event rate as calculated by the receiver. A value of zero indicates no loss. Otherwise the loss event rate is "1/LossEventRate". - LastSeqNum: - A 32 bit value containing the lower 32 bits of the largest - sequence number last received. This is the latest in the sequence - not necessarily the most recent (in the case of re-ordering of - packets it may be less recent). When determining largest and 64 - bit extended sequence numbers are in use, the upper 32 bits should - be used during the comparison. + RTT: + A 22 bit value specifying the sender's current round-trip time + estimate in microseconds. The value MAY be zero prior to the + sender having calculated a round-trip time estimate. The value + SHOULD be set to zero on non-IP-TFS enabled SAs. If the value is + equal to or larger than "0x3FFFFF" it MUST be set to "0x3FFFFF". + + Echo Delay: + + A 21 bit value specifying the delay in microseconds incurred + between the receiver first receiving the "TVal" value which it is + sending back in "TEcho". If the value is equal to or larger than + "0x1FFFFF" it MUST be set to "0x1FFFFF". + + Transmit Delay: + A 21 bit value specifying the transmission delay in microseconds. + This is the fixed (or average) delay on the receiver between it + sending packets on the IPTFS tunnel. If the value is equal to or + larger than "0x1FFFFF" it MUST be set to "0x1FFFFF". + + TVal: + An opaque 32 bit value that will be echoed back by the receiver in + later packets in the "TEcho" field, along with a "Delay" value of + how long that echo took. + + TEcho: + The opaque 32 bit value from a received packet's "TVal" field. + The received "TVal" is placed in "TEcho" along with a "Delay" + value indicating how long it has been since receiving the "TVal" + value. DataBlocks: Variable number of octets that begins with the start of a data block, or the continuation of a previous data block, followed by zero or more additional data blocks. For the special case of sending congestion control information on an non-IP-TFS enabled SA this value MUST be empty (i.e., be zero octets long). 6.1.3. Data Blocks @@ -799,21 +831,21 @@ 8. Security Considerations This document describes a mechanism to add Traffic Flow Confidentiality to IP traffic. Use of this mechanism is expected to increase the security of the traffic being transported. Other than the additional security afforded by using this mechanism, IP-TFS utilizes the security protocols [RFC4303] and [RFC7296] and so their security considerations apply to IP-TFS as well. - As noted previously in Section 2.5.2, for TFC to be fully maintained + As noted previously in Section 2.4.2, for TFC to be fully maintained the encapsulated traffic flow should not be affecting network congestion in a predictable way, and if it would be then non- congestion controlled mode use should be considered instead. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, @@ -933,44 +965,49 @@ at the IP data block immediately following the IP-TFS header. The following packet ESP2s "BlockOffset" points inward 100 octets to the start of the 60 octet data block. The third encapsulating packet ESP3 contains the middle portion of the 4000 octet data block so the offset points past its end and into the forth encapsulating packet. The fourth packet ESP4s offset is 1400 pointing at the padding which follows the completion of the continued 4000 octet packet. Appendix B. A Send and Loss Event Rate Calculation - The current best practice indicates that congestion control should be + The current best practice indicates that congestion control SHOULD be done in a TCP friendly way. A TCP friendly congestion control algorithm is described in [RFC5348]. For this IP-TFS use case (as with [RFC4342]) the (fixed) packet size is used as the segment size - for the algorithm. The formula for the send rate is then as follows: + for the algorithm. The main formula in the algorithm for the send + rate is then as follows: 1 - X_Pps = ----------------------------------------------- + X = ----------------------------------------------- R * (sqrt(2*p/3) + 12*sqrt(3*p/8)*p*(1+32*p^2)) - Where "X_Pps" is the send rate in packets per second, "R" is the - round trip time estimate and "p" is the loss event rate (the inverse - of which is provided by the receiver). + Where "X" is the send rate in packets per second, "R" is the round + trip time estimate and "p" is the loss event rate (the inverse of + which is provided by the receiver). - The IP-TFS receiver, having the RTT estimate from the sender MAY use - the same method as described in [RFC4342] to collect the loss - intervals and calculate the loss event rate value using the weighted - average as indicated. The receiver communicates the inverse of this - value back to the sender in the IPTFS_PROTOCOL payload header field - "LossEventRate". + In addition the algorithm in [RFC5348] also uses an "X_recv" value + (the receiver's receive rate). For IP-TFS one MAY set this value + according to the sender's current tunnel send-rate ("X"). + + The IP-TFS receiver, having the RTT estimate from the sender can use + the same method as described in [RFC5348] and [RFC4342] to collect + the loss intervals and calculate the loss event rate value using the + weighted average as indicated. The receiver communicates the inverse + of this value back to the sender in the IPTFS_PROTOCOL payload header + field "LossEventRate". The IP-TFS sender now has both the "R" and "p" values and can - calculate the correct sending rate ("X_Pps"). If following [RFC5348] - the sender SHOULD also use the slow start mechanism described therein + calculate the correct sending rate. If following [RFC5348] the + sender SHOULD also use the slow start mechanism described therein when the IP-TFS SA is first established. Appendix C. Comparisons of IP-TFS C.1. Comparing Overhead C.1.1. IP-TFS Overhead The overhead of IP-TFS is 40 bytes per outer packet. Therefore the octet overhead per inner packet is 40 divided by the number of outer