Network Working Group Lars-Erik Jonsson, Ericsson
INTERNET-DRAFT Ghyslain Pelletier, Ericsson
Expires: August 23, 2001 Sweden
February 23, 2001
A Link-Layer Assisted ROHC Profile for IP/UDP/RTP
<draft-jonsson-rohc-lla-rtp-00.txt>
Status of this memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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 cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/lid-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This document is an individual submission to the IETF. Comments
should be directed to the authors.
Abstract
This document defines a ROHC profile for compression of IP/UDP/RTP
packets, utilizing functionality provided by the lower layer to
increase compression efficiency by completely eliminating the header
for most packets during normal operation. The profile is built as an
extension to the ROHC RTP profile [ROHC]. It defines additional
mechanisms needed in ROHC, states requirements on the lower layer to
guarantee transparency, and specifies general logic for compression
and decompression making use of this header-free packet.
Jonsson, Pelletier [Page 1]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
Table of contents
1. Introduction....................................................3
2. Terminology.....................................................5
3. Overview of the link-layer assisted profile.....................6
3.1. Providing packet type identification.....................6
3.2. Replacing the sequence number............................6
3.3. CRC replacement..........................................7
4. Additions and exceptions compared to ROHC RTP...................7
4.1. A no-header packet (NHP).................................7
4.2. A context check packet (CCP).............................8
4.3. Interface between compressor and lower layer.............9
4.4. Interface between lower layer and decompressor...........9
4.5. Periodic context verification...........................10
4.6. Feedback option RHP-REQUEST.............................10
4.7. Use of context identifiers..............................10
5. Implementation issues..........................................10
5.1. Implementation parameters and signals...................11
5.1.1. Implementation parameters at compressor........11
5.1.2. Implementation parameters at decompressor......12
5.2. Implementation structures...............................13
5.2.1. Compressor context.............................13
5.2.2. Decompressor context...........................13
5.3. Implementation over various link technologies...........13
6. IANA considerations............................................13
7. Security considerations........................................14
8. Acknowledgements...............................................14
9. References.....................................................14
10. Authors addresses..............................................15
Jonsson, Pelletier [Page 2]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
1. Introduction
Header compression is a technique used to compress and transparently
decompress the header information of a packet on a per-hop basis,
utilizing redundancy within individual packets and between
consecutive packets within a packet stream. Over the years, several
protocols [VJHC, IPHC] have been developed to compress the network
and transport protocol headers [IP, IPv6, UDP, TCP] and these schemes
have been successful at improving efficiency over many wired
bottleneck links, such as modem connections over telephone networks.
In addition to IP, UDP and TCP compression, an additional compression
scheme called Compressed RTP [CRTP] has been developed to further
improve compression efficiency for the case of real-time traffic
using the Real-time Transport Protocol [RTP].
The schemes mentioned above have all been designed taking into
account normal assumptions about link characteristics, which
traditionally have been based on wired links only. However, with an
increasing number of wireless links in the Internet paths, these
assumptions are not valid as general anymore. In wireless
environments, especially wide coverage cellular environments, the
error rates are relatively high to provide efficient usage of the
radio resources. For real-time traffic, which is more sensitive to
delays than to errors, this will be normal operating conditions over
links such as the 3rd generation cellular links and header
compression must therefore tolerate packet loss. However, with the
previously mentioned schemes, especially for real-time traffic
compressed by CRTP, high error rates have been shown to significantly
reduce header compression performance [CRTPC]. This problem was the
driving force for the creation of the RObust Header Compression
(ROHC) WG in the IETF.
The ROHC WG has developed a header compression framework on top of
which various profiles can be defined for different protocol sets, or
for different compression strategies. Because of the packet loss
robustness problems of CRTP and the demands of the cellular industry
for an efficient way of transporting voice over IP over wireless, the
main focus of ROHC has so far been on compression of IP/UDP/RTP
headers, which are generous in size, especially compared to the
payloads often carried by the packets with these headers.
ROHC RTP has become a very efficient, robust and capable compression
scheme, able to compress the headers down to a total size of one
octet only. Also, transparency is guaranteed to an extremely high
extent even when residual bit errors are present in compressed
headers delivered to the decompressor. The requirements for RTP
compression [RTP-REQ], defined by the WG before and during the
development process, has thus been fulfilled.
As mentioned above, the 3rd generation cellular systems, where IP
will be used end-to-end, has been one of the driving forces for ROHC
Jonsson, Pelletier [Page 3]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
RTP and the scheme has been designed to also suit new cellular air
interfaces, such as WCDMA, making even speech services possible with
an insignificantly lower spectrum efficiency than with existing one-
service circuit switched solutions. However, other existing air
interfaces such as GSM and IS-95 will be used in all-IP networks,
adding new implications to the header compression issue. These air
interfaces are less flexible with radio bearers optimized for
specific payload sizes. This means that not even a single octet of
header can be added without using the next higher fixed packet size
of the link and this is obviously very costly. For the already
deployed speech vocoders, the spectrum efficiency over these links
will thus be low compared to the existing circuit switched solutions.
To achieve high spectrum efficiency overall with any application,
more flexible air interfaces must be deployed and then the ROHC RTP
scheme will be excellent, as shown for WCDMA. For deployment reasons,
it is however important to also achieve efficiency with already
existing vocoders and air interfaces, such as GSM and IS-95, with
minimal effects on spectral efficiency.
This document defines a new link-layer assisted ROHC RTP profile
extending the ROHC RTP profile in [ROHC] (profile number 1). The
purpose of this new profile is to provide a header free packet format
that, for a certain application behavior, can replace a majority of
the regular 1-octet header ROHC RTP packets during normal operation,
while still being fully transparent and comply with all the
requirements of ROHC RTP [RTP-REQ]. For other applications,
compression will be carried out as with normal ROHC RTP. To
completely eliminate the header, all functionality normally provided
by the 1-octet header has to be provided by other means, typically by
utilizing functionality provided by the lower layer and sacrificing
efficiency for less frequently occurring larger header packets. The
latter is not a contradiction since the argument for eliminating the
last octet for most packets is not overall efficiency in general. It
is important to remember that the purpose of this profile is to
provide efficient matching of existing applications to existing link
technologies, not efficiency in general. The additional complexity
introduced by this profile, although minimized by a tight integration
with already existing ROHC functionality, implies that it should
therefore only be used to optimize performance of specific
applications over specific links.
When implementing this profile over various link technologies, care
must be taken to guarantee that all the functionality needed is
provided by ROHC and the lower layer together. Therefore, additional
standards-track documents should specify how to incorporate this
profile on top of various link technologies.
Jonsson, Pelletier [Page 4]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
2. Terminology
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 RFC 2119.
CCP Context Check Packet
CRC Cyclic Redundancy Check
LL Link Layer
MSB Most Significant Bit
NHP No Header Packet
ROHC Robust Header Compression
RHP ROHC Header Packet (either a CCP or a RRP packet)
RRP ROHC RTP Packet as defined in [ROHC, profile 1]
Link layer
Link layer in this document refers to the physical link layer.
Lower layer
Lower layer in this document refers to any entity implementing the
interface to ROHC as defined in section 4.3 and 4.4. It may, as an
example, refer to a sub-layer between the ROHC implementation and
the physical link layer used to adapt both implementations.
ROHC RTP
ROHC RTP in this document refers to the IP/UDP/RTP profile as
defined in [ROHC].
Jonsson, Pelletier [Page 5]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
3. Overview of the link-layer assisted profile
This ROHC IP/UDP/RTP profile is designed to be used over channels
that have been optimized for specific payload sizes and therefore
cannot efficiently accommodate header information to be transmitted
together with payloads corresponding to these optimal sizes.
The profile extends, thus also inherits all functionality from, the
ROCH RTP profile by defining some additional functionality and an
interface between the ROHC component towards the lower layer. By
putting additional requirements on the lower layer compared to [RTP-
LLG], it is possible for ROHC to infer the information needed to
maintain robust and transparent header compression even though the
headers are completely eliminated during most of the operation time.
Basically, what this profile does is to replace the smallest ROHC
header of one octet with a no-header format by providing the header
functionality by other means. The fields present in the one octet
ROHC RTP header for PT0 are the packet type identifier, the sequence
number and the CRC (optional in PT0 for Reliable mode). The
subsequent sections elaborate more on the replacement of the
functionality of these fields.
3.1. Providing packet type identification
All ROHC headers carry a packet type identifier, indicating to the
decompressor which context the compressed packet belongs to and how
it should be interpreted. This is a functionality that must be
provided by some means. ROHC RTP packets with header will still be
possible to distinguish between since they have this identifier, but
what must be provided is a mechanism to separate those packets with
header from the packets without header. This functionality MUST
therefore be provided by the lower layer in one way or another.
3.2. Replacing the sequence number
From the sending application, the RTP sequence number is increased by
one for each packet sent. The purpose of the sequence number is thus
to cope with packet reordering and packet loss. If reordering or loss
has occurred before the compression point, the compressor can easily
avoid problems by not allowing usage of a header-free packet.
However, the compressor can not in beforehand anticipate loss or
reordering that may occur between compressor and decompressor.
Therefore, the lower layer MUST guarantee in-order delivery and
provide an indication of packet loss over the link. This is basically
the same principle as VJ header compression [VJHC] relies on.
Note that guarantees for in-order delivery and packet loss indication
not only makes it possible to infer the sequence number information,
Jonsson, Pelletier [Page 6]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
it also supersedes the main functionality of the CRC, which normally
takes care of errors due to long losses and bit errors in the
compressed sequence number.
3.3. CRC replacement
All RRP packets carry a CRC calculated over the uncompressed header
(optional in PT0 for Reliable mode). This CRC is used by the
decompressor to verify that the decompressed header is correct. This
verification serves three purposes:
- Detection of longer losses than can be covered by the sequence
number LSBs (this applies to Unidirectional and Optimistic mode)
- Protection against failures caused by residual bit errors in the
compressed header
- Protection against faulty implementations or other causes of error
Since this profile defines a NHP packet without this CRC, care must
be taken to fulfill these purposes by other means. Detection of long
losses is already covered since the lower layer MUST provide
indication of all packet losses. Furthermore, the NHP packet has one
important advantage compared to RHP packets because residual bit
errors can not damage a header that is not even sent. It is thus
reasonable to assume that compression and decompression transparency
can be guaranteed even without a CRC in header-free packets. However,
to detect also unexpected errors and thereby provide transparency in
the ROHC class, periodical context checks SHOULD be performed.
4. Additions and exceptions compared to ROHC RTP
4.1. A no-header packet (NHP)
A no-header packet (NHP), thus a packet consisting only of a payload,
is defined and MAY be used instead of ROHC RTP packet type 0 (PT0)
when the sequence number has incremented with one from the previous
packet. Note that the requirement for using PT0 in the first place is
basically that all header fields must be unchanged or follow the
currently established change pattern. In addition, there are some
cases when NHP should not be used (see section 4.5).
Note that since the lower layer is responsible of separating NHP
packets from RHP packets, an indicated from the compressor to the
lower layer MUST be provided upon delivery of an NHP packet.
Jonsson, Pelletier [Page 7]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
4.2. A context check packet (CCP)
A Context Check Packet (CCP) is defined, which does not carry any
payload but, in addition to the packet type identifier, only a CRC
value. A CCP packet MAY be created by the compressor in addition to
the compressed packet and provided to the lower layer. Whether the
packet is sent over the link and delivered to the decompressor is not
decided by the compressor, but by the lower layer. The purpose of
this packet is to provide a useful packet that MAY be sent by a
synchronized physical link layer in the case when it must send
something on a regular basis, even if no compressed packet is
available. This is the format of the CCP packet:
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 1 1 1 1 0 0 1 | Packet type identifier
+---+---+---+---+---+---+---+---+
| R | CRC |
+---+---+---+---+---+---+---+---+
This packet is defined by one of the unused packet type identifiers
from ROHC RTP, carried in the first octet of the packet. As for any
ROHC packet, except NHP, the packet MAY begin with ROHC padding
and/or carry context identification. The (R)eserved bit MUST be set
to 0 in all CCP packets. The CRC is the 7-bits CRC over the original
uncompressed header as described in [ROHC section 5.9.2].
If the lower layer implementation makes use of the CCP feature, the
last CCP packet received from the compressor MUST always be used,
i.e. the CCP corresponding to the last data packet sent (NHP or RRP).
Accordingly, if a CCP packet is received by the decompressor, it MUST
be used as a context verification for the last packet decompressed
unless a packet loss indication was previously received. To
facilitate this verification, the 7-bit CRC MUST always be calculated
for all decompressed packets and saved in the decompressor context in
order to use the CCP. Upon CRC failure, actions MUST be taken as
specified in [ROHC, section 5.3.2.2.3].
Note that the usage of CCP is optional, depending on the link layer
this profile is implemented over. Whether it is used or not MUST
therefore be specified in the link layer implementation
specifications for this profile.
Jonsson, Pelletier [Page 8]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
4.3. Interface between compressor and the lower layer
This section defines the interface semantics between the compressor
and the lower layer, providing rules for packet delivery from the
compressor.
+-----------+-----+-----+-----+-----+-----+-----+-----+
| Interface | RRP | Seg | NHP | CCP | Seq | Seg | NHP |
| Parameter | | RRP | | | Num | Flg | Flg |
+-----------+-----+-----+-----+-----+-----+-----+-----+
| Case 1 | x | | x | x | x | | x |
+-----------+-----+-----+-----+-----+-----+-----+-----+
| Case 2 | | x | x | x | x | x | x |
+-----------+-----+-----+-----+-----+-----+-----+-----+
| Case 3 | x | | | x | | | |
+-----------+-----+-----+-----+-----+-----+-----+-----+
| Case 4 | | x | | x | | x | |
+-----------+-----+-----+-----+-----+-----+-----+-----+
Table 1: Data delivery from the compressor
As seen in table 1, four different delivery scenarios are possible.
Case 1 represent what needs to be delivered when the compressor
allows sending of an NHP packet, without any segmentation applied to
the corresponding RRP packet. Case 2 differs from case 1 in that a
segmented RRP is being delivered. Case 3 and case 4 shows the case
where a packet without header cannot be delivered.
If the compressor delivers a NHP packet to the lower layer, it MUST
also provide the RRP packet, a CCP packet, the Sequence Number and
the indication that a NHP packet MAY be used. Otherwise the RRP
packet MUST be delivered together with a CCP packet.
Furthermore, for the case where the RRP packet is delivered to the
lower layer as a segmented ROHC packet according to the rules in
chapter 5.5.1, an indication MUST be provided by the compressor.
4.4. Interface between lower layer and decompressor
The interface semantics between the lower layer and the decompressor
are defined here, and provide simple rules for the delivery of
received packets to the decompressor. The decompressor needs a way to
identify NHP packets from RHP packets. Also, when receiving packets
without headers, the decompressor needs a way to infer the sequencing
information to keep synchronization between received payload and the
sequence information of the decompressed headers. To achieve this,
the lower layer MUST provide the following to the decompressor:
- an indication of packet loss
- the received packets together with a indication whether the packet
received is an NHP or not
Jonsson, Pelletier [Page 9]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
4.5. Periodic context verification
As described in chapter 3.3, transparency is expected to be
guaranteed by the functionality provided by the lower layer. This
ROHC profile would therefore be at least as reliable as the older
header compression schemes [VJHC, IPHC, CRTP], which do not make use
of a header compression CRC. However, since ROHC RTP normally is
extremely safe to use from a transparency point of view, it would be
desirable if that also could be achieved with this profile. To
provide an additional guarantee for transparency and also catch non
expected errors, such as errors due to faulty implementations, it is
RECOMMENDED that RRP packets (with the CRC present also for Reliable
mode PT0 packets) be sent periodically, even when the normal logic
allows for NHP packets to be used.
Since a CCP packet serves the same purpose as a regular periodic
verification with RRP, indication of CCP transmission is beneficial
for the compressor, which can ignore some periodic RRP verifications.
4.6. Feedback option, RHP-REQUEST
The RHP-REQUEST option could be used by the decompressor to request
an RHP for context verification. This option should be used if only
NHP have been received for a long time and the context therefore has
not been verified recently. If the compressor receives a feedback
packet with this option, at least one RRP with CRC SHOULD be sent
immediately.
+---+---+---+---+---+---+---+---+
| Opt Type = 8 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
4.7. Use of context identifier
Since a NHP can not carry a context identifier (CID), there is a
restriction on how this profile may be used, related to context
identification. Independent of which CID size has been negotiated,
NHP packets can only be used for CID=0. If the decompressor receives
a NHP packet, it can only belong to CID=0.
5. Implementation issues
This document specifies mechanisms for the protocol and leaves
details on the use of these mechanisms to the implementers. This
chapter aims to provide guidelines, ideas and suggestions for
implementation of this profile.
Jonsson, Pelletier [Page 10]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
5.1. Implementation parameters and signals
As described in [ROHC, section 6.3], implementations uses parameters
to set up configuration information and to stipulate how a ROHC
implementation is to operate. The following are additions to the ones
used by ROHC RTP implementations, needed by this profile. Note that
if the PREFERRED_PACKET_SIZES parameters defined here are used, they
obsolete all PACKET_SIZE and PAYLOAD_SIZE parameters of ROHC RTP.
5.1.1. Implementation parameters at compressor
ALWAYS_PAD -- value: boolean
This parameter may be set by an external entity to specify to the
compressor that every RHP packet MUST be padded using the ROHC
padding.
The lower layer MUST provide a packet type identification. If no
field is available for this purpose from the protocol at the link
layer, then it is suggested to use a leading sequence to identify
RHP packets from NHP packets. Although the use of a leading
sequence is obviously not efficient since it sacrifices
efficiency for RHP packets, this leading sequence applies only to
packets with headers in order to favor the use of packets without
headers. If a leading sequence is desired for RHP identification,
the lower layer MAY use ROHC padding for this by setting the
ALWAYS_PAD parameter.
By default, this parameter is set to FALSE.
PREFERRED PACKET SIZES -- list of: SIZE -- value: integer (octets)
ONLY_NHP -- value: boolean
This parameter set governs which packet sizes that are preferred
by the lower layer. If this parameter set is used, all RHP
packets MUST be padded to fit the smallest possible of the
preferred sizes. If the unpadded packet size, or in the case of
ALWAYS_PAD being set the packet with minimal one octet padding,
is larger than the maximal preferred packet size, the compressor
has two options. It may either deliver this larger packet with an
arbitrary size or it may split the packet into several segments
using ROHC segmentation and pad each segment to one of the
preferred sizes. Which method to use depends on the value of the
LARGE_PACKETS_ALLOWED parameter below. NHP packets can only be
delivered to the lower layer if the payload size is part of the
preferred packet size set. Furthermore, if ONLY_NHP is set to
TRUE for any of the preferred packet sizes, that packet size is
only allowed to be used for NHP packets.
Jonsson, Pelletier [Page 11]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
By default, no preferred packet sizes are specified and when used
the default value of ONLY_NHP is FALSE for the specified sizes.
LARGE_PACKETS_ALLOWED -- value: boolean
This parameter may be set by an external entity to specify how to
handle packets that can not fit in any of the preferred packet
sizes specified. If set to TRUE, the compressor MUST deliver the
larger packet as it is and not use segmentation. If set to FALSE,
the ROHC segmentation scheme MUST be used to split the packet
into two or more segments and each segment MUST further be padded
to fit into any of the preferred packet sizes.
By default, this parameter is set to TRUE, which means that
segmentation is disabled.
VERIFICATION_PERIOD -- value: integer (octets)
This parameter may be set by an external entity to specify to the
compressor the minimum frequency for which a packet that
validates the context must be sent. This tells the compressor
that a packet containing a CRC field MUST be sent at least every
number of packets equals to this value. A value of 0 indicates
that no periodical verification are needed.
By default, this parameter is set to the value 1, which indicates
that packets with the CRC field MUST always be sent.
5.1.2. Implementation parameters at decompressor
NHP_PACKET -- value: boolean
This parameter informs the decompressor that the packet being
delivered is a NHP packet. The decompressor MUST accept this
packet type indicator from the lower layer. A lower layer MUST
set this indicator for every NHP packet delivered to true, and to
false for any other packet.
PACKET_LOST -- signal
This parameter indicates to the decompressor that a packet has
been lost on the link between the compressor and the
decompressor.
Jonsson, Pelletier [Page 12]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
5.2. Implementation structures
This section provides some explanatory material on data structures
specific to this profile that a ROHC implementation will have to
maintain in one form or another. What is listed here are additions
compared to ROHC RTP [ROHC section 6.5], imposed by this profile.
5.2.1. Compressor context
For the compressor context, this profile does not require any
additions to the data structures needed for ROHC RTP.
5.2.2. Decompressor context
An additional field MUST for all modes be kept in memory to store a
CRC value. The decompressor MUST calculate the CRC for every packet
header decompressed and always keep in one form or another the value
calculated for the last packet received.
CRC_PREVIOUS: CRC calculated from the decompressed header of the last
packet received
5.3. Implementation over various link technologies
This document provides the interface semantics and requirements
needed from the ROHC compressor and decompressor towards the link
layer to perform link-layer assisted header compression.
However, the document does not provide any link layer specific
operational information, except for some implementation suggestions.
Further details about how this profile should be implemented over
various link technologies must be described in additional standards
track documents, where specific characteristics of each link layer
can be taken into account to provide optimal usage of this profile.
These specifications MAY use a packet type bit pattern unused by this
profile to implement signaling on the lower layer. The pattern
available to a lower layer implementations is [1111101].
6. IANA considerations
A ROHC profile identifier must be reserved by the IANA for the
IP/UDP/RTP profile defined in this document. Since this additional
profile will be used concurrent to the ROHC IP/UDP/RTP profile in
[ROHC] and is part of the IETF standards track, an ordinary
identifier in the range from 4 to 127 should be reserved.
Jonsson, Pelletier [Page 13]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
7. Security considerations
The security considerations of ROHC RTP [ROHC section 7] apply also
to this document with one addition: in the case of a denial-of-
service attack scenario where an intruder inject bogus CCP packets
onto the link using random CRC values, the CRC check will fail for
incorrect reasons at the decompressor side. This would obviously
greatly reduce the advantages of ROHC and any extra efficiency
provided by this profile due to unnecessary context invalidation,
feedback messages and refresh packets. However, the same remarks
related to the presence of such an intruder applies.
8. Acknowledgements
The authors would like to thank Ulises Olvera-Hernandez and Francis
Lupien for valuable inputs.
9. References
[ROHC] C. Bormann, "Robust Header Compression (ROHC)", Internet
draft (work in progress), February 2001.
<draft-ietf-rohc-rtp-08.txt>
[VJHC] V. Jacobson, "Compressing TCP/IP Headers for Low-Speed
Serial Links", RFC 1144, February 1990.
[IPHC] M. Degermark, B. Nordgren, S. Pink, "IP Header
Compression", RFC 2507, February 1999.
[CRTP] S. Casner, V. Jacobson, "Compressing IP/UDP/RTP Headers
for Low-Speed Serial Links", RFC 2508, February 1999.
[CRTPC] M. Degermark, H. Hannu, L.-E. Jonsson, K. Svanbro,
"Evaluation of CRTP Performance over Cellular Radio
Networks", IEEE Personal Communications Magazine, Volume
7, number 4, pp. 20-25, August 2000.
[RTP-REQ] M. Degermark, "Requirements for IP/UDP/RTP Header
Compression", Internet draft (work in progress),
February 2001.
<draft-ietf-rohc-rtp-requirements-05.txt>
[RTP-LLG] K. Svanbro, "Lower Layer Guidelines for Robust
RTP/UDP/IP Header Compression", Internet draft (work in
progress), February 2001.
<draft-ietf-rohc-rtp-lower-layer-guidelines-01.txt>
[IP] J. Postel, "Internet Protocol", RFC 791, September 1981.
Jonsson, Pelletier [Page 14]
INTERNET-DRAFT A Link-Layer Assisted ROHC RTP February 23, 2001
[IPv6] S. Deering, R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[UDP] J. Postel, "User Datagram Protocol", RFC 768, August
1980.
[TCP] J. Postel, "Transmission Control Protocol", RFC 793,
September 1981.
[RTP] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications",
RFC 1889, January 1996.
10. Authors addresses
Lars-Erik Jonsson Tel: +46 920 20 21 07
Ericsson Erisoft AB Fax: +46 920 20 20 99
Box 920
SE-971 28 Lulea
Sweden EMail: lars-erik.jonsson@ericsson.com
Ghyslain Pelletier Tel: +46 920 20 24 32
Ericsson Erisoft AB Fax: +46 920 20 20 99
Box 920
SE-971 28 Lulea
Sweden EMail: ghyslain.pelletier@epl.ericsson.se
This Internet-Draft expires August 23, 2001.
Jonsson, Pelletier [Page 15]