Network Working Group S. Guthery
Internet Draft S. Marks
Document: draft-guthery-tcp7816-00.txt Mobile-Mind
Expires: July, 2001 January, 2001
Category: Experimental
IP/TCP/UDP Header Compression for ISO 7816 Links
Status of this Memo
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Abstract
This document describes the transport of TCP and UDP packets over
the IP layer of ISO 7816 integrated circuit ("smart") cards with
particular attention to header compression.
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Table of Contents
Status of this Memo................................................1
Abstract...........................................................1
Table of Contents..................................................2
Overview...........................................................2
Conventions Used in this Document..................................2
Motivation.........................................................2
Header Compression on the Handset Link Layers......................3
RObust Header Compression (ROHC)...................................4
Van Jacobson Header Compression....................................5
Packet Type Indication.............................................5
Security Considerations............................................5
References.........................................................5
Author's Addresses.................................................8
Full Copyright Statement...........................................8
Overview
The Internet Draft "IP and ARP over ISO 7816" [7] describes the
transport of IP datagrams over the asynchronous, half-duplex link
layer protocols found on ISO 7816 compliant integrated circuit cards
(ICCs). This document describes the transport of TCP and UDP
packets on this network layer with particular attention to header
compression.
For the purpose of this document, a terminal together with all the
ICCs physically connected to it is taken to be a connected network
[3] wherein the terminal acts as the gateway router. A 3GPP mobile
telephone terminal with its ICC identity modules is an example of
such a connected network.
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 RFC-2119 [1].
A session is an interval of time that starts when the ICC is reset
and ends when either power is removed from the ICC or it is reset
again. For example, a session might be from when a mobile phone is
turned on and when is subsequently turned off or the time between
when a card is inserted into an ATM machine and it is subsequently
removed.
Motivation
Smart cards are tamper-resistant hardware security modules, usually
used for storing secret keys and performing cryptographic
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computations. Recently, there is a trend toward smart cards becoming
application platforms, thus turning them into trusted computing
bases.
Communication with smart cards today is based upon link layer
protocols such as T=0 [4] and T=1 [5] and the construction of
commands called Application Data Processing Units (APDUs) [6] for
accessing the services of the card. The ISO 7816 communication
channel is very efficiency sensitive. For contact cards it is a low
data rate channel and for contactless cards is open for only a short
period of time. In both situations transaction time is a critical
design metric.
Of particular interest are the smart cards in mobile telephones
called subscriber identity modules or SIMs. While they vary
slightly across mobile telephone technologies -- SIM for GSM, USIM
for 3GPP, R-UIM for 3GPP2 û they are essentially identical with
respect to available hardware resources and therefore design
considerations for supporting an Internet protocol stack.
Much work has been and continues to be devoted to the use of
Internet protocols on low-speed, error-prone channels such as those
found in mobile and wireless networks [8]. A key consideration of
this work is economical use of the transmission channel through
header compression [9-17]. The various header compression schemes
proposed over the years for various Internet protocols have been
synthesized in the RObust Header Compression (ROHC) effort [18].
Most of the work on mobile and wireless networks regards the handset
as the end-point of the mobile communication path. Because the
handset has ample computational resources (cycles and memory) is
typically willing to trade these resources for bandwidth efficiency.
An IP stack on the SIM has far fewer computational resources to work
with compared to the handset. As a result the code size and running
time of the compressors and decompressors are of as much interest as
the amount of bandwidth they save. Furthermore, the SIM is dealing
with a different physical link than the handset and perhaps a
different profile of Internet protocol usage.
Header Compression on the Handset Link Layers
The data link layer on the handset between the IP protocol stack and
the network will be PPP [25] for cdma2000, LLC [26] for 3GPP GPRS,
and PDCP [27] for UMTS. All of these standards call for header
compression to a greater or lesser degree of specificity. PDCP
mandates RFC 2507 [12] as one of the available options.
On one hand, one is motivated to use the same header compression
scheme(s) on the network link as on the SIM link. This would reduce
the amount of code on the handset and perhaps save decompression and
recompression steps for packets headed for the SIM. On the other
hand, the physical and traffic properties of the wireless channel
are vastly different than the same properties on the SIM channel so
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a wholly different header compression scheme on the SIM link is
justified.
RObust Header Compression (ROHC)
The requirements ROHC itself are listed in [19] and link layer
requirements imposed by ROHC are listed in [20]. From [20], the link
layer requirements are:
1. Lower layers MUST provide error detection for at least ROHC
headers.
2. It is RECOMMENDED that erroneous headers are passed up to the
decompressor instead of being discarded before the decompressor,
but in that case an indication that the header has errors MUST be
included to the decompressor together with the erroneous header.
3. Information about the received packet (with the compressed header)
length MUST be provided by the link layer.
4. The link layer MUST in some manner support varying header sizes
from 40 bytes (full RTP/UDP/IPv4 header) or 60 bytes (full
RTP/UDP/IPv6) down to 1 byte for the minimal compressed header.
5. The lower layers supporting ROHC MUST include mechanisms for
negotiating header compression parameters such as, CID usage
and/or header compression profiles. It is RECOMMENDED that the
lower layer have mechanisms that support re-negotiations of these
parameters.
6. It is RECOMMENDED that demultiplexing be done in the lower layers
supporting robust header compression.
7. If ROHC is used together with header compression schemes requiring
packet type identification at the link layer, e.g. [RFC2507,
RFC2508], or if ROHC is used on top of link layers where packet
type identifiers already are present, it is RECOMMENDED that one
(1) ROHC packet type identifier is supported on lower layers.
8. ROHC can handle packet duplication before the compressor but it is
RECOMMENDED that such packet duplications are avoided. Lower
layers MUST NOT duplicate packets on the path between ROHC
compressor and decompressor.
9. Lower layer MUST support transport of feedback packets from
decompressor to compressor if ROHC is to be used in O-mode or R-
mode. Lower layers MUST support transport of small stand-alone
feedback packets if piggybacking of feedback packets is not used.
The feedback packets from the decompressor SHOULD be delivered as
soon as possible to the compressor.
10. The lower layer MUST indicate to the header compressor that a
significant long event of consecutive packet loss has occurred.
The ISO 7816 link layer is taken to be error-free and continuously
available and thus satisfies 1, 2 and 10 by virtue of the nature of
the physical and data link layers. The proposed ISO 7816 IP [7]
satisfies 3, 4 and 8 by design. There is currently no provision to
satisfy 5 or 9 and 7 is not a considered possibility. Requirement 6
is problematic because there are many different multiplexing schemes
û most of them unused in practice û for communication with the SIM.
In the end full-bore ROHC as described in [18] is probably overly
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general and too resource demanding for use in ICCs in general and on
SIMs in particular.
Van Jacobson Header Compression
Since the physical link to the ICC is in fact a low-speed, low-loss
serial link, classic Van Jacobson header compression is a good
starting point for header compression for ISO 7816 links. The Van
Jacobson algorithm [9] can be coded in around 1K bytes for the
micro-processors in current ICCs and thus does not present an
unbearable code burden. It yields immediate returns and is widely
implemented.
The shortcomings of Van Jacobson compression are that it doesnÆt
include UDP or IPv6 headers and it doesnÆt comply fully with PDCP
which is RFC 2507. The IPv4 UDP header isnÆt worth either the code
space or the compute time on an ICC to compress. IPv6 will be used
on ICCs when the demand for static addresses for them exceeds the
IPv4 supply. Current work focuses on IPv4 stacks for ICCs.
Packet Type Indication
The ISO 7816 link layer must be able to indicate four Van Jacobson
packet types: TYPE_IP, TYPE_UNCOMPRESSED_TCP, TYPE_COMPRESSED_TCP
and TYPE_ERROR. The upper two bits of the second (INS) field of the
ISO 7816 link layer frame can be used for this purpose.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CLA = 0xFE |INS = Pkt Type | PP = 0x00 0x21 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | Length | IP Datagram à
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
INS Meaning
--- -------
0xFE TYPE_IP
0xBE TYPE_UNCOMPRESSED_TCP
0x7E TYPE_COMPRESSED_TCP
0x3E TYPE_ERROR
Security Considerations
Security issues are not discussed in this memo.
References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate requirement
Levels", BCP 14, RFC 2119, March 1997.
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3 Braden, R., "Requirements for Internet Hosts -- Communication
Layers," RFC 1122, October 1989.
4 ISO/IEC 7816-3 Identification cards - Integrated circuit(s) cards
with contacts - Part 3: Electronic signals and transmission
protocols, First edition, September 15, 1989.
5 ISO/IEC 7816-3 Identification cards - Integrated circuit(s) cards
with contacts - Part 3: Electronic signals and transmission
protocols. Amendment 1: Protocol type T=1, asynchronous half
duplex block transmission protocol. Amendment 1, December 1,
1992.
6 ISO/IEC 7816-4 Identification cards - Integrated circuit(s) cards
with contacts - Part 4: Interindustry commands for interchange.
7 Guthery, S. and S. Marks, "IP and ARP over ISO 7816," draft-
guthery-ip7816-01.txt, January, 2001.
8 Mitzel, D, "Overview of 2000 IAB Wireless Internetworking
Workshop", RFC 3002, December, 2000.
9 Jacobson, V., "Compressing TCP/IP Headers for Low-Speed Serial
Links", RFC 1144, February 1990.
10 Schryver, V., "PPP BSD Compression Protocol", RFC 1977, August,
1996.
11 Perkins, C., "Minimal Encapsulation within IP", RFC 2004, October
1996.
12 Degermark, M., B. Nordgren and S. Pink, "IP Header Compression",
RFC 2507, February, 1999.
13 Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP Headers for
Low-Speed Serial Links", RFC 2508, February 1999.
14 Engan, M., S. Casner, and C. Bormann, "IP Header Compression for
PPP", RFC 2509, February 1999.
15 Egan, M., S. Casner and C. Bormann, "IP Header Compression over
PPP", draft-koren-avt-crtp-ipcp-00.txt, November, 2000.
16 Casner, S., V. Jacobson, T. Koren, P. Ruddy, B. Thompson, A.
Tweeedly, D. Wing, J. Geevarghese, "Enhancements to IP/UDP/RTP
Header Compression", draft-ietf-avt-crtp-enhance-01.txt, July
2000.
17 Hiller, T. and P. McCann, "Good Enough Header COmpression
(GEHCO)", draft-hiller-rohc-gehco-00.txt, August, 2000.
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18 Bormann, C. et.al., "Robust Header Compression (ROHC)", draft-
ietf-rohc-rtp-06.txt, November, 2000.
19 Degermark, M., "Requirements for robust IP/UDP/RTP header
compression", draft-ietf-rohc-rtp-requirements-04.txt, December,
2000.
20 K. Svanbro, "Lower Layer Guidelines for Robust RTP/UDP/IP Header
Compression", draft-ietf-rohc-rtp-lower-layer-guidelines-00.txt,
October 2000.
21 Jonsson, L.-E., M. Degermark, H. Hannu, K. Svanbro, "RObust
Checksum-based header COmpression (ROCCO)", Internet Draft (work
in progress), June 2000.
22 Jonsson, L.-E., K. Svanbro and H. Hannu, "Profiles and Parameters
in ROHC", draft-jonsson-rohc-profiles-00.txt, August, 2000.
23 Liao, H.B., Q. Zhang, W. Zhu and Y.-Q. Zhang, "TCP-Aware RObust
Header Compression (TAROC)", draft-ietf-rohc-tcp-taroc-00.txt,
November, 2000.
24 Hannu, H., J. Christoffersson and K. Svanbro, "Application
signaling over cellular links", draft-hannu-rohc-signaling-
cellular-00.txt, November, 2000.
25 Telecommunications Industry Association, "Wireless IP Network
Standard", TIA/EIA/IS-835, June 2000.
26 European Telecommunications Standards Institute, "Mobile Station
- Serving GPRS Support Node (MS-SGSN); Logical Link Control (LLC)
layer specification", GSM 04.64.
27 European Telecommunications Standards Institute, "Packet Data
Convergence Protocol (PDCP) Specification", 3G TS 25.323.
28 European Telecommunications Standards Institute, "General Packet
Radio Service (GPRS); Service Description; Stage 3", GSM 03.60.
29 Lilley, Jermey, Jason Yang, Hari Balakrishnan, and Srinivasan
Seshan, "A Unified Header Compression Framework for Low-Bandwidth
Links", Proc. of the Sixth Annual ACM/IEEE International
Conference on Mobile Computing and Networking, August 2000.
(http://nms.lcs.mit.edu/software/headercompress)
1 RFC 2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
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Author's Addresses
Scott Guthery
Mobile-Mind
24 Church Street Phone: 1-617-926-6888
Watertown, MA USA Email: sguthery@mobile-mind.com
Scott Marks
Mobile-Mind
1808 Rolling Road Phone: 1-919-929-1436
Chapel Hill, NC USA Email: smarks@mobile-mind.com
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