Network Working Group J. Jurski Internet Draft Technical University of Gdansk Document: draft-jurski-pppext-iphc-01.txt September 2006 Expires: March 2007 Obsoletes: 3544 Category: Informational IP Header Compression over PPP Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March, 21 2007. Copyright Notice Copyright (C) The Internet Society (2006). All Rights Reserved. Jurski Expires - March 2007 [Page 1] Internet-draft IP Header Compression over PPP September 2006 Abstract This document extends RFC 3544 (which extended its predecessor, RFC 2509) by specifying additional negotiation options to PPP Control Protocols for IPv4 and IPv6 (see RFC 1332, RFC 2472). The negotiation options specified in RFC 2509 defined an all-or-nothing strategy for applying header compression: peers were assumed to support compression for any combination of headers. RFC 3544 refined that strategy to make it possible to negotiate header compression for only TCP or only non-TCP packets. The current document further refines the strategy by also making it possible to negotiate header compression for only particular combinations of headers or header types. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Table of Contents 1. Introduction..................................................3 2. Configuration Option..........................................4 2.1 Configuration Option Format..............................5 2.2 RTP-Compression Suboption................................7 2.3 Enhanced RTP-Compression Suboption.......................8 2.4 Negotiating Header Compression for only TCP or only non-TCP Packets..........................................9 2.5 Disabling Particular Header Compression Types...........10 2.5.1 Limitations for Differential TCP Compression..........11 2.5.2 Limitations for non-differential TCP Compression......13 2.5.3 Limitations for non-TCP Compression...................15 3. Multiple Network Control Protocols...........................17 3.1 Sharing Context Identifier Space........................17 4. Demultiplexing of Datagrams..................................17 5. Changes from Previous RFCs and Motivation....................19 5.1 Changes from Previous RFCs..............................19 5.2 Motivation..............................................19 6. References...................................................21 6.1 Normative References....................................21 6.2 Informative References..................................21 7. IANA Considerations..........................................22 8. Security Considerations......................................23 Acknowledgments.................................................23 Author's Address................................................24 Intellectual Property Statement.................................24 Full Copyright Statement........................................24 Jurski Expires - March 2007 [Page 2] Internet-draft IP Header Compression over PPP September 2006 1. Introduction The IP Header Compression (IPHC) defined in [RFC2507] may be used for compression of both IPv4 and IPv6 datagrams or packets encapsulated with multiple IP headers. IPHC is also capable of compressing both TCP and UDP transport protocol headers. The IP/UDP/RTP header compression defined in [RFC2508] and [RFC3545] fits within the framework defined by IPHC so that it may also be applied to both IPv4 and IPv6 packets. In order to establish compression of IP datagrams sent over a PPP link each end of the link must agree on a set of configuration parameters for the compression. The process of negotiating link parameters for network layer protocols is handled in PPP by a family of network control protocols (NCPs). Since there are separate NCPs for IPv4 and IPv6, this document defines configuration options to be used in both NCPs to negotiate parameters for the compression scheme. This document obsoletes RFC 2509 and RFC 3544, adding new suboptions to the IP header compression configuration option. By using these new suboptions, the decompressor can request that the use of compression for particular header types or combinations of headers in the datagram is disabled. IPHC relies on the link layer's ability to indicate the types of datagrams carried in the link layer frames. In this document nine new types for the PPP Data Link Layer Protocol Field are defined along with their meaning. In general, header compression schemes that use delta encoding of compressed packets require that the lower layer does not reorder packets between compressor and decompressor. IPHC uses delta encoding of compressed packets for TCP and RTP. The IPHC specification [RFC2507] includes methods that allow link layers that may reorder packets to be used with IPHC. Since PPP does not reorder packets these mechanisms are disabled by default. When using reordering mechanisms such as multiclass multilink PPP [RFC2686], care must be taken so that packets that share the same compression context are not reordered. Jurski Expires - March 2007 [Page 3] Internet-draft IP Header Compression over PPP September 2006 2. Configuration Option This document specifies a new compression protocol value for the IPCP IP-Compression-Protocol option as specified in [RFC1332]. The new value and the associated option format are described in section 2.1. The option format is structured to allow future extensions to the IPHC scheme. NOTE: The specification of link and network layer parameter negotiation for PPP [RFC1661], [RFC1331], [RFC1332] does not prohibit multiple instances of one configuration option but states that the specification of a configuration option must explicitly allow multiple instances. [RFC3241] updates RFC 1332 by explicitly allowing the sending of multiple instances of the IP- Compression-Protocol configuration option, each with a different value for IP-Compression-Protocol. Each type of compression protocol may independently establish its own parameters. NOTE: [RFC1332] is not explicit about whether the option negotiates the capabilities of the receiver or of the sender. In keeping with current practice, we assume that the option describes the capabilities of the decompressor (receiving side) of the peer that sends the Config-Req. Jurski Expires - March 2007 [Page 4] Internet-draft IP Header Compression over PPP September 2006 2.1 Configuration Option Format Both the network control protocol for IPv4, IPCP [RFC1332] and the IPv6 NCP, IPV6CP [RFC2472] may be used to negotiate IP Header Compression parameters for their respective protocols. The format of the configuration option is the same for both IPCP and IPV6CP. Description This NCP configuration option is used to negotiate parameters for IP Header Compression. Successful negotiation of parameters enables the use of Protocol Identifiers FULL_HEADER, COMPRESSED_TCP, COMPRESSED_TCP_NODELTA, COMPRESSED_NON_TCP and CONTEXT_STATE as specified in [RFC2507]. The option format is summarized below. The fields are transmitted from left to right. 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | IP-Compression-Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TCP_SPACE | NON_TCP_SPACE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | F_MAX_PERIOD | F_MAX_TIME | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAX_HEADER | suboptions... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 2 Length >= 14 The length may be increased if the presence of additional parameters is indicated by additional suboptions. IP-Compression-Protocol 0061 (hex) TCP_SPACE The TCP_SPACE field is two octets and indicates the maximum value of a context identifier in the space of context identifiers allocated for TCP. Suggested value: 15 TCP_SPACE must be at least 0 and at most 255 (the value 0 implies having one context). Jurski Expires - March 2007 [Page 5] Internet-draft IP Header Compression over PPP September 2006 NON_TCP_SPACE The NON_TCP_SPACE field is two octets and indicates the maximum value of a context identifier in the space of context identifiers allocated for non-TCP. These context identifiers are carried in COMPRESSED_NON_TCP, COMPRESSED_UDP and COMPRESSED_RTP packet headers. Suggested value: 15 NON_TCP_SPACE must be at least 0 and at most 65535 (the value 0 implies having one context). F_MAX_PERIOD Maximum interval between full headers. No more than F_MAX_PERIOD COMPRESSED_NON_TCP headers may be sent between FULL_HEADER headers. Suggested value: 256 A value of zero implies infinity, i.e. there is no limit to the number of consecutive COMPRESSED_NON_TCP headers. F_MAX_TIME Maximum time interval between full headers. COMPRESSED_NON_TCP headers may not be sent more than F_MAX_TIME seconds after sending the last FULL_HEADER header. Suggested value: 5 seconds A value of zero implies infinity. MAX_HEADER The largest header size in octets that may be compressed. Suggested value: 168 octets The value of MAX_HEADER should be large enough so that at least the outer network layer header can be compressed. To increase compression efficiency MAX_HEADER should be set to a value large enough to cover common combinations of network and transport layer headers. Jurski Expires - March 2007 [Page 6] Internet-draft IP Header Compression over PPP September 2006 suboptions The suboptions field consists of zero or more suboptions. Each suboption consists of a type field, a length field and zero or more parameter octets, as defined by the suboption type. The value of the length field indicates the length of the suboption in its entirety, including the lengths of the type and length fields. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Parameters... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2 RTP-Compression Suboption The RTP-Compression suboption is included in the NCP IP-Compression- Protocol option for IPHC if IP/UDP/RTP compression is to be enabled. Inclusion of the RTP-Compression suboption enables use of additional Protocol Identifiers COMPRESSED_RTP and COMPRESSED_UDP along with additional forms of CONTEXT_STATE as specified in [RFC2508]. Description Enable use of Protocol Identifiers COMPRESSED_RTP, COMPRESSED_UDP and CONTEXT_STATE as specified in [RFC2508]. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 Length 2 Jurski Expires - March 2007 [Page 7] Internet-draft IP Header Compression over PPP September 2006 2.3 Enhanced RTP-Compression Suboption To use the enhanced RTP header compression defined in [RFC3545], a new sub-option 2 is added. Sub-option 2 is negotiated instead of, not in addition to, sub-option 1. Description Enable use of Protocol Identifiers COMPRESSED_RTP and CONTEXT_STATE as specified in [RFC2508]. In addition, enable use of [RFC3545] compliant compression including the use of Protocol Identifier COMPRESSED_UDP with additional flags and use of the C flag with the FULL_HEADER Protocol Identifier to indicate use of HDRCKSUM with COMPRESSED_RTP and COMPRESSED_UDP packets. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 2 Length 2 Jurski Expires - March 2007 [Page 8] Internet-draft IP Header Compression over PPP September 2006 2.4 Negotiating Header Compression for only TCP or only non-TCP Packets In RFC 2509 it was not possible to negotiate only TCP header compression or only non-TCP header compression because a value of 0 in the TCP_SPACE or the NON_TCP_SPACE fields actually means that 1 context is negotiated. A new suboption 3 is added to allow specifying that the number of contexts for TCP_SPACE or NON_TCP_SPACE is zero, disabling use of the corresponding compression. Description Enable header compression for only TCP or only non-TCP packets. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Parameter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 3 Length 3 Parameter The parameter is 1 byte with one of the following values: 1 = the number of contexts for TCP_SPACE is 0 2 = the number of contexts for NON_TCP_SPACE is 0 This suboption overrides the values that were previously assigned to TCP_SPACE and NON_TCP_SPACE in the IP Header Compression option. If suboption 3 is included multiple times with parameter 1 and 2, compression is disabled for all packets. Jurski Expires - March 2007 [Page 9] Internet-draft IP Header Compression over PPP September 2006 2.5 Disabling Particular Header Compression Types According to RFC 2509, the peers compressed and decompressed all combinations of headers. Therefore, it was not possible to disable compression for a particular header type or a combination of headers. For example, even nodes that only supported IPv4 had to support IPv6 header compression because it was impossible to specify that IPv6 headers shall not be compressed. Three new suboptions 4, 5, and 6 are added to make it possible for a decompressor to specify which particular types of headers or their combinations MUST NOT be compressed by a compressor. Separate sets of limitations are defined in the following subsections for differential TCP, non-differential TCP, and non-TCP compression methods. However, the compression limitations specified in these suboptions should be used with care. Indiscriminate use of these limitations may lead to suboptimal compression, or even no compression. General purpose systems SHOULD normally request no limitation and use the full compression functionality defined in RFC 2509. The decompressor MAY only be configured to request limited compression if there is no benefit from a particular header compression type. For each system, advantages and disadvantages must be carefully examined (see discussion in section 5.2), including scenarios when the compressor may not fully support all combinations of flags specified in this suboption. Although new implementations of the compressor are expected to support this suboption, there are many older systems that do not support it. The decompressor SHOULD agree on the full RFC 2509 compression if it receives a request from an older peer (compressor). Note that flag A of suboption 4 and flag B of suboption 5 overlap with suboption 3 with parameter 1. For this reason, in order to avoid a suboptimal NCP negotiation exchange, peers SHOULD use suboption 3 with parameter 1 to completely disable TCP compression, instead of setting both flags A and B in suboption 4 and 5. Accordingly, peers implementing suboptions 4 and 5 SHALL also understand suboption 3. Jurski Expires - March 2007 [Page 10] Internet-draft IP Header Compression over PPP September 2006 2.5.1 Limitations for Differential TCP Compression This suboption defines limitations that apply for the differential encoding compression method only. Description Disable differential TCP header compression for a particular compression method(s), header type(s), or header combination(s). 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |A B C D E F G| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 4 Length = 4 Flags (ABCDEFG) This field is a set of bit-flags that specify limitations. A flag set refers to a particular limitation: A: TCP differential encoding method shall not be used at all ([RFC2507], Section 7.12.1); if this flag is set, the remaining flags are irrelevant (MUST be set to zero by the sender and ignored by the receiver) B: Unused – MUST be set to zero by the sender and ignored by the receiver C: IPv4 header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv4 headers are not compressed and break the compression chain of headers); if this flag is set for IPv6 Control Protocol, IPv4 header compression is completely disabled (see Section 3 for explanation) D: IPv6 base header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv6 headers are not compressed and break the compression chain of headers); if this flag is set for IP Control Protocol, IPv6 header compression is completely disabled (see Section 3 for explanation) Jurski Expires - March 2007 [Page 11] Internet-draft IP Header Compression over PPP September 2006 E: IPv4 header for a fragment or with options shall not be compressed ([RFC2507], Section 7.13, point b); this flag is irrelevant if IPv4 header compression is completely disabled F: IPv6 extension headers shall not be compressed ([RFC2507], Sections from 7.1 to 7.10); this flag is irrelevant if IPv6 header compression is completely disabled G: minimal encapsulation header shall not be compressed ([RFC2507], Section 7.14) Reserved MUST be set to zero by the sender and ignored by the receiver. This suboption SHOULD NOT be included in an NCP message if suboption 3 with parameter 1 is included. If this suboption is included multiple times, the sum of all the limitations applies (logical-or on all flags). Jurski Expires - March 2007 [Page 12] Internet-draft IP Header Compression over PPP September 2006 2.5.2 Limitations for non-differential TCP Compression This suboption defines limitations that apply for the non-differential encoding compression method only. Description Disable non-differential TCP header compression for a particular compression method(s), header type(s), or header combination(s). 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |A B C D E F G| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 5 Length = 4 Flags (ABCDEFG) This field is a set of bit-flags that specify limitations. A flag set refers to a particular limitation: A: Unused – MUST be set to zero by the sender and ignored by the receiver B: TCP non-differential encoding method shall not be used ([RFC2507], Section 7.12.2); if this flag is set, the remaining flags are irrelevant (MUST be set to zero by the sender and ignored by the receiver) C: IPv4 header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv4 headers are not compressed and break the compression chain of headers); if this flag is set for IPv6 Control Protocol, IPv4 header compression is completely disabled (see Section 3 for explanation) D: IPv6 base header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv6 headers are not compressed and break the compression chain of headers); if this flag is set for IP Control Protocol, IPv6 header compression is completely disabled (see Section 3 for explanation) Jurski Expires - March 2007 [Page 13] Internet-draft IP Header Compression over PPP September 2006 E: IPv4 header for a fragment or with options shall not be compressed ([RFC2507], Section 7.13, point b); this flag is irrelevant if IPv4 header compression is completely disabled F: IPv6 extension headers shall not be compressed ([RFC2507], Sections from 7.1 to 7.10); this flag is irrelevant if IPv6 header compression is completely disabled G: minimal encapsulation header shall not be compressed ([RFC2507], Section 7.14) Reserved MUST be set to zero by the sender and ignored by the receiver. This suboption SHOULD NOT be included in an NCP message if suboption 3 with parameter 1 is included. If this suboption is included multiple times, the sum of all the limitations applies (logical-or on all flags). Jurski Expires - March 2007 [Page 14] Internet-draft IP Header Compression over PPP September 2006 2.5.3 Limitations for non-TCP Compression This suboption defines limitations that apply for the non-TCP compression method only. Description Disable non-TCP header compression for a particular compression method(s), header type(s), or header combination(s). 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |A B C D E F G H I J K| Reserved| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 6 Length = 4 Flags (ABCDEFGHIJK) This field is a set of bit-flags that specify limitations. A flag set refers to a particular limitation: A: Unused – MUST be set to zero by the sender and ignored by the receiver B: Unused – MUST be set to zero by the sender and ignored by the receiver C: IPv4 header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv4 headers are not compressed and break the compression chain of headers); if this flag is set for IPv6 Control Protocol, IPv4 header compression is completely disabled (see Section 3 for explanation) D: IPv6 base header can be compressed only if it is the first header in the compression chain (i.e. tunneled IPv6 headers are not compressed and break the compression chain of headers); if this flag is set for IP Control Protocol, IPv6 header compression is completely disabled (see Section 3 for explanation) Jurski Expires - March 2007 [Page 15] Internet-draft IP Header Compression over PPP September 2006 E: IPv4 header for a fragment or with options shall not be compressed ([RFC2507], Section 7.13, point b); this flag is irrelevant if IPv4 header compression is completely disabled F: IPv6 extension headers shall not be compressed ([RFC2507], Sections from 7.1 to 7.10); this flag is irrelevant if IPv6 header compression is completely disabled G: minimal encapsulation header shall not be compressed ([RFC2507], Section 7.14) H: UDP headers with non-zero UDP checksum shall not be compressed ([RFC2507], Section 7.11); note that the checksum cannot be zero with IPv6 I: the compressed chain of headers must include a compressed UDP or a compressed RTP header; if the compressible chain of headers does not include a UDP or RTP header, the whole chain cannot be compressed J: the compressed chain of headers must include a compressed RTP header; if the compressible chain of headers does not include a RTP header, the whole chain cannot be compressed; this flag is irrelevant if flag I is set; this flag MUST be set to zero by the sender and ignored by the receiver if RTP compression is not enabled (with use of suboption 1 or 2 as specified in Section 2.2 or 2.3, respectively) K: RTP headers with non-empty CSRC list shall not be compressed ([RFC2508], Section 3.3.2); this flag MUST be set to zero by the sender and ignored by the receiver if RTP compression is not enabled Reserved MUST be set to zero by the sender and ignored by the receiver. This suboption SHOULD NOT be included in an NCP message if suboption 3 with parameter 2 is included. If this suboption is included multiple times, the sum of all the limitations applies (logical-or on all flags). Jurski Expires - March 2007 [Page 16] Internet-draft IP Header Compression over PPP September 2006 3. Multiple Network Control Protocols The IPHC protocol is able to compress both IPv4 and IPv6 datagrams. Both IPCP and IPV6CP are able to negotiate option parameter values for IPHC. These values apply to the compression of packets where the outer header is an IPv4 header and an IPv6 header, respectively. 3.1 Sharing Context Identifier Space For the compression and decompression of IPv4 and IPv6 datagram headers the context identifier space is shared. While the parameter values are independently negotiated, sharing the context identifier spaces becomes more complex when the parameter values differ. Since the compressed packets share context identifier space, the compression engine must allocate context identifiers out of a common pool; for compressed packets, the decompressor has to examine the context state to determine what parameters to use for decompression. Context identifier spaces are not shared between TCP and non- TCP/UDP/RTP. Doing so would require additional mechanisms to ensure that no error can occur when switching from using a context identifier for TCP to non-TCP. 4. Demultiplexing of Datagrams The IPHC specification [RFC2507] defines four header formats for different types of compressed headers. They are compressed TCP, compressed TCP with no delta encoding, compressed non-TCP with 8 bit CID and compressed non-TCP with 16 bit CID. The two non-TCP formats may be distinguished by their contents so both may use the same link-level identifier. A fifth header format, the full header is distinct from a regular header in that it carries additional information to establish shared context between the compressor and decompressor. The specification of IP/UDP/RTP Header Compression [RFC2508] defines four additional formats of compressed headers. They are for compressed UDP and compressed RTP (on top of UDP), both with either 8- or 16-bit CIDs. In addition, there is an explicit error message from the decompressor to the compressor. The link layer must be able to indicate these header formats with distinct values. Nine PPP Data Link Layer Protocol Field values are specified below. Jurski Expires - March 2007 [Page 17] Internet-draft IP Header Compression over PPP September 2006 FULL_HEADER The frame contains a full header as specified in [RFC2508] Section 3.3.1. This is the same as the FULL_HEADER specified in [RFC2507] Section 5.3. Value: 0061 (hex) COMPRESSED_TCP The frame contains a datagram with a compressed header with the format as specified in [RFC2507] Section 6a. Value: 0063 (hex) COMPRESSED_TCP_NODELTA The frame contains a datagram with a compressed header with the format as specified in [RFC2507] Section 6b. Value: 2063 (hex) COMPRESSED_NON_TCP The frame contains a datagram with a compressed header with the format as specified in either Section 6c or Section 6d of [RFC2507]. Value: 0065 (hex) COMPRESSED_RTP_8 The frame contains a datagram with a compressed header with the format as specified in [RFC2508] Section 3.3.2, using 8-bit CIDs. Value: 0069 (hex) COMPRESSED_RTP_16 The frame contains a datagram with a compressed header with the format as specified in [RFC2508] Section 3.3.2, using 16-bit CIDs. Value: 2069 (hex) COMPRESSED_UDP_8 The frame contains a datagram with a compressed header with the format as specified in [RFC2508] Section 3.3.3 or as specified in [RFC3545] Section 2.1, using 8-bit CIDs. Value: 0067 (hex) COMPRESSED_UDP_16 The frame contains a datagram with a compressed header with the format as specified in [RFC2508] Section 3.3.3 or as specified in [RFC3545] Section 2.1, using 16-bit CIDs. Value: 2067 (hex) CONTEXT_STATE The frame is a link-level message sent from the decompressor to the compressor as specified in [RFC2508] Section 3.3.5. Value: 2065 (hex) Jurski Expires - March 2007 [Page 18] Internet-draft IP Header Compression over PPP September 2006 5. Changes from Previous RFCs and Motivation 5.1 Changes from Previous RFCs Most of this document is identical to RFC 3544 and RFC 2509. The new suboptions are only defined in Section 2.5. Note that the new suboptions (defined in RFC 3544 and in this document) modify the stopping criteria specified in [RFC2507] in Section 7. This can be considered as adding a new subpoint "c)" to the list in the first paragraph of Section 7 in [RFC2507]. This new point would specify that the compressible chain of headers would be additionally limited by the new suboptions. 5.2 Motivation There is always a need to efficiently use system resources, such as link capacity, processing power, and memory. These resources are usually limited. IPHC makes efficient use of link capacity at the expense of additional processing power and memory. It requires the peers to be able to decompress (not necessarily compress) all combinations of headers, using all algorithms defined in [RFC2507]. This is a good solution for general purpose equipment, such as Internet routers. There are, however, specific applications that do not benefit from most of the functionality offered by IPHC (in other words, such applications may waste their resources). For example, equipment that transports mainly VoIP data encapsulated in IP/UDP/RTP headers and only rarely expects other types of packets could make the most efficient use of available resources by using compression for only IP/UDP/RTP headers. In this manner, it could support more IP/UDP/RTP compression contexts improving overall compression efficiency. This would come at the cost of not supporting compression for other combinations of headers, but the assumption is that other combinations are not needed in this case (or they are very rare). This document makes it possible. Note that, while the compressor could use heuristics to determine the most efficient way to compress flows, the decompressor may be in a much better position to know the expected traffic type and resource limitations. For example, a compressor (at a service provider) that supports a variety of customers is unable to predict the type of traffic carried for a specific customer, while the decompressor at the customer's site often knows the expected traffic precisely. Similarly, if the decompressor can decompress only, for example, either 1000 TCP flows with the non-differential compression method or just 500 TCP flows with the differential compression method, and the Jurski Expires - March 2007 [Page 19] Internet-draft IP Header Compression over PPP September 2006 expectation is that there will be 1000 flows, it may be more beneficial to ask the compressor to use only the non-differential compression. This could potentially limit per-flow compression efficiency but improve the overall compression efficiency. Note also that there is no way of making dynamic adjustments in the negotiated values for IPHC protocol, because the decompressor is always expected to correctly handle incoming traffic according to the negotiated parameters. However, a request for these new suboptions by a decompressor might cause inefficient use of the available link capacity. Especially because many compressors do not support these new suboptions and may not support it in the future. Therefore, the decompressor shall only request limited compression if it does not benefit from a particular header compression type. And for this reason, the new suboptions are designed backward-compatible, so that peers that do not support the new suboptions can interoperate with peers that support them by using the full functionality defined in RFC 2509. It may seem that CPU speed or memory size limitations are ephemeral issues nowadays and such savings are worthless. The author of this document believes that even if memory and processing power are cheap, there is still a desire to make a more efficient use of them simply because the resources are limited. Mobile equipment (which must be lightweight), satellite systems (which cannot be upgraded during their lifetime), or even high-capacity high-speed media gateways carrying thousands of compressible connections (which require gigabytes of memory for IPHC) are good examples of systems that could benefit from the new extensions. The benefits will not only include memory and processing power savings but also improved overall compression efficiency. This is a good reason to add the new suboptions to the protocol. The author is aware that the new suboptions represent an additional cost to the community that implements and tests this protocol. There are however more and more specialized applications that could greatly benefit from these new suboptions. Moreover, by controlling the trade-off between compression efficiency and resource usage, proposed extensions make the protocol more flexible and suitable in more various usage scenarios. This may also be beneficial for reasons which cannot be seen directly. For example, instead of supporting full compression for 500 users one can provide a limited compression to 1000 users, thus supporting all users with equal capabilities. Jurski Expires - March 2007 [Page 20] Internet-draft IP Header Compression over PPP September 2006 6. References 6.1 Normative References [RFC1144] Jacobson, V., "Compressing TCP/IP Headers for low-speed serial links", RFC 1144, February 1990. [RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol (IPCP)", RFC 1332, May 1992. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2472] Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC 2472, December 1998. [RFC2507] Degermark, M., Nordgren, B. and S. Pink, "Header Compression for IP", RFC 2507, February 1999. [RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP Headers for Low-Speed Serial Links", RFC 2508, February 1999. [RFC3241] Bormann, C., "Robust Header Compression (ROHC) over PPP", RFC 3241, April 2002. [RFC3545] Koren, T., Casner, S., Geevarghese, J., Thompson, B. and P. Ruddy, "Enhanced Compressed RTP (CRTP) for Links with High Delay, Packet Loss and Reordering", RFC 3545, July 2003. 6.2 Informative References [RFC1661] Simpson, W., Ed., "The Point-To-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2686] Bormann, C., "The Multi-Class Extension to Multi-Link PPP", RFC 2686, September 1999. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003. Jurski Expires - March 2007 [Page 21] Internet-draft IP Header Compression over PPP September 2006 7. IANA Considerations This document does not require any additional allocations from existing namespaces in the IANA Point-to-Point Protocol Field Assignments registry. However, there are three namespaces that were defined by RFC 1332, RFC 2472, and RFC 2509 but not created in the registry. Those three namespaces, described below, have been added to the PPP registry. This document specifies two additional allocations in the third one. Section 3.2 of RFC 1332 specifies an IP-Compression-Protocol Configuration Option for the PPP IP Control Protocol and defines one value for the IP-Compression-Protocol type field in that option. An IANA registry has been created to allocate additional values for that type field. As stated in RFC 1332, the values for the IP-Compression-Protocol type field are always the same as the (primary) PPP DLL Protocol Number assigned to packets of the particular compression protocol. Assignment of additional IP- Compression-Protocol type values is through the IETF consensus procedure as specified in [RFC2434]. Section 4.2 of RFC 2472 specifies an IPv6-Compression-Protocol Configuration Option for the PPP IPv6 Control Protocol and defines one value for the IPv6-Compression-Protocol type field in that option. An IANA registry has been created to allocate additional values for that type field. The IPv6-Compression-Protocol Configuration Option has the same structure as the IP-Compression- Protocol Configuration Option defined in RFC 1332, but the set of values defined for the type field may be different. As stated in RFC 2472, the values for the IPv6-Compression-Protocol type field are always the same as the (primary) PPP DLL Protocol Number assigned to packets of the particular compression protocol. Assignment of additional IPv6-Compression-Protocol type values is through the IETF consensus procedure as specified in [RFC2434]. Section 2.1 of RFC 2509 (repeated in RFC 3544) specifies an additional type value to be registered for both the IP-Compression- Protocol Configuration Option and the IPv6-Compression-Protocol Configuration Option to indicate use of the "IP Header Compression" protocol. The specification of that type value is repeated in Section 2.1 of this document which obsoletes RFC 3544. In conjunction with the additional type value, the format for the variable-length option is specified. The format includes a suboption field that may contain one or more suboptions. Each suboption begins with a suboption type value. An IANA registry has been created for the suboption type values; and is titled, "IP Header Compression Configuration Option Suboption Types". Jurski Expires - March 2007 [Page 22] Internet-draft IP Header Compression over PPP September 2006 Section 2.2 of RFC 2509 (repeated in this document) defines one suboption type. Sections 2.3 and 2.4 of RFC 3544 (repeated in this document) define two additional suboption types. Section 2.5 of this document defines three additional suboption types. It is expected that the number of additional suboptions that will need to be defined is small. Therefore, anyone wishing to define new suboptions is required to produce a revision of this document to be vetted through the normal Internet Standards process, as specified in [RFC2434]. RFC 2509 also defines nine PPP Data Link Layer Protocol Field values which are already listed in the IANA registry of Point-to-Point Protocol Field Assignments. Section 4 of this document repeats the specification of those values without change. 8. Security Considerations Negotiation of the option defined here imposes no additional security considerations beyond those that otherwise apply to PPP [RFC1661]. The use of header compression can, in rare cases, cause the misdelivery of packets. If necessary, confidentiality of packet contents should be assured by encryption. Encryption applied at the IP layer (e.g., using IPSEC mechanisms) precludes header compression of the encrypted headers, though compression of the outer IP header and authentication/security headers is still possible as described in [RFC2507]. For RTP packets, full header compression is possible if the RTP payload is encrypted by itself without encrypting the UDP or RTP headers, as described in [RFC3550]. This method is appropriate when the UDP and RTP header information need not be kept confidential. Acknowledgments The author would like to thank particularly to Piotr Uminski for his contribution to this document and to James Carlson and Carsten Bormann for their critical comments regarding the new suboptions. Mathias Engan, Stephen L. Casner, Carsten Bormann, and Tmima Koren are the authors of RFC 2509 and RFC 3544 documents, of which this document is a revision. Jurski Expires - March 2007 [Page 23] Internet-draft IP Header Compression over PPP September 2006 Author's Address Janusz Jurski Technical University of Gdansk ul. Narutowicza 11/12 80-952 Gdansk Poland Email: jjurski@eti.pg.gda.pl Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the ISOC's procedures with respect to rights in ISOC Documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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