IP Header Compression over PPP
draft-engan-ip-compress-02
The information below is for an old version of the document that is already published as an RFC.
| Document | Type | RFC Internet-Draft (pppext WG) | |
|---|---|---|---|
| Authors | Carsten Bormann , Stephen L. Casner , Mathias Engan | ||
| Last updated | 2013-03-02 (Latest revision 1997-12-23) | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text htmlized pdfized bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | RFC 2509 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-engan-ip-compress-02
Internet Engineering Task Force IPng, ISSLL and AVT Working Groups
INTERNET-DRAFT Mathias Engan
draft-engan-ip-compress-02.txt CDT/Lulea University of Technology
S. Casner
Precept Software
C. Bormann
Universitaet Bremen TZI
December 17, 1997
Expires: 6/98
IP Header Compression over PPP
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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Distribution of this document is unlimited.
Abstract
This document describes an option for negotiating the use of
header compression on IP datagrams transmitted over the Point-to-
Point Protocol [RFC1661]. It defines extensions to the PPP Control
Protocols for IPv4 and IPv6 [RFC1332, RFC2023]. Header compression
may be applied to IPv4 and IPv6 datagrams in combination with TCP,
UDP and RTP transport protocols as specified in [IPHC] and [CRTP].
[Note to IANA, to be removed before publication: The PPP protocol
type assignments suggested in this document were selected from those
unassigned in ftp://ftp.isi.edu/in-notes/iana/assignments/ppp-numbers
on December 7, 1997. These selections were presented to the PPPEXT
working group at IETF in Washington, DC on December 9, 1997 and were
approved as being in the appropriate ranges for this protocol.]
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1. Introduction
The IP Header Compression (IPHC) defined in [IPHC] 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 [CRTP] 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 param-
eters 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.
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 [IPHC]
includes methods that allow link layers that may reorder packets to
be used with IPHC. Since PPP does not reorder packets these mechan-
isms are disabled by default. When using reordering mechanisms such
as multiclass multilink PPP [MCML], care must be taken so that pack-
ets that share the same compression context are not reordered.
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 parame-
ter 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. From the
current specification of the IPCP IP-Compression-Protocol
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configuration option [RFC1332, p 6] it follows that it can
only be used to select a single compression protocol at any
given time.
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.
2.1. Configuration Option Format
Both the network control protocol for IPv4, IPCP [RFC1332] and the IPv6
NCP, IPV6CP [RFC2023] may be used to negotiate IP Header Compression
parameters for their respective protocols. The format of the configura-
tion option is the same for both IPCP and IPV6CP.
Description
This NCP configuration option is used to negotiate parameters for
IP Header Compression. 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 parame-
ters is indicated by additional suboptions.
IP-Compression-Protocol
0061 (hex)
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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).
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
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compression efficiency MAX_HEADER should be set to a value large
enough to cover common combinations of network and transport layer
headers.
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.
After successful negotiation of parameters for IP Header Compression
the use of Protocol Identifiers FULL_HEADER, COMPRESSED_TCP,
COMPRESSED_TCP_NODELTA and COMPRESSED_NON_TCP is enabled, regardless
of the prescence of an RTP-Compression suboption.
Description
Enable use of Protocol Identifiers COMPRESSED_RTP, COMPRESSED_UDP
and CONTEXT_STATE as specified in [CRTP].
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1
Length
2
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3. Multiple Network Control Protocols
The IPHC protocol is able to compress both IPv6 and IPv4 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 compres-
sion 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 identif-
ier for TCP to non-TCP.
4. Demultiplexing of Datagrams
The IPHC specification [IPHC] defines four header formats for dif-
ferent 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 informa-
tion to establish shared context between the compressor and
decompressor.
The specification of IP/UDP/RTP Header Compression [CRTP] 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.
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FULL_HEADER
The frame contains a full header as specified in [CRTP] Section
3.3.1. This is the same as the FULL_HEADER specified in [IPHC]
Section 5.3.
Value: 0061 (hex)
COMPRESSED_TCP
The frame contains a datagram with a compressed header with the
format as specified in [IPHC] Section 6a.
Value: 0063 (hex)
COMPRESSED_TCP_NODELTA
The frame contains a datagram with a compressed header with the
format as specified in [IPHC] 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 [IPHC].
Value: 0065 (hex)
COMPRESSED_RTP_8
The frame contains a datagram with a compressed header with the
format as specified in [CRTP] 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 [CRTP] 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 [CRTP] Section 3.3.3, 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 [CRTP] Section 3.3.3, 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 [CRTP] Section 3.3.5.
Value: 2065 (hex)
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5. References
[CRTP] Casner, S., Jacobson, V., "Compressing IP/UDP/RTP Headers
for Low-Speed Serial Links", Internet-Draft
draft-ietf-avt-crtp (work in progress), November 21, 1997,
expires May 1998.
[IPHC] Degermark, M., Nordgren, B., Pink, S., "Header Compression
for IP", Internet-Draft draft-degermark-ipv6-hc (work in
progress), November 18, 1997, expires May 1998.
[RFC2023] Haskin, E., Allan, E., "IP Version 6 over PPP", RFC 2023,
October 1996.
[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.
[RFC1889] Schulzrinne, H., Casner, S., Frederick, R., and Jacobson,
V., "RTP: A Transport Protocol for real-time applica-
tions", RFC 1889, January 1996.
[RFC1661] Simpson, W., ed., "The Point-To-Point Protocol (PPP)",
RFC 1661, July 1994.
[MCML] Bormann, C., "The Multi-Class Extension to Multi-Link
PPP", Internet-Draft draft-ietf-issll-isslow-mcml (work in
progress), May 1997, expires November 1997.
6. 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 mis-
delivery 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
[IPHC]. 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 [RFC1889]. This method is appropriate when
the UDP and RTP header information need not be kept confidential.
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7. Authors' Addresses
Mathias Engan
CDT/Dept of Computer Communication
Lulea University of Technology
S-971 87 Lulea, Sweden
Phone: +46 920 72288
Mobile: +46 70 522 8109
Fax: +46 920 72801
EMail: engan@cdt.luth.se
Stephen L. Casner
Precept Software, Inc.
1072 Arastradero Road
Palo Alto, CA 94304
United States
EMail: casner@precept.com
Carsten Bormann
Universitaet Bremen FB3 TZI
Postfach 330440
D-28334 Bremen, GERMANY
EMail: cabo@tzi.uni-bremen.de
Phone: +49.421.218-7024
Fax: +49.421.218-7000
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