Subject: [rohc] Multipoint Robust Compression for MANET

From: [email-masked]
Date: Mon, 05 Apr 2004 22:16:47 +0000

I'm designing a MANET system suitable for handheld and 
automobile portable radios that can operate on the move with 
link rages greater than 1 km. We will be adding IPv6 to the 
system so header compression has become a necessity as the 
network generally achieves less than 100kbps on links. In 
order to maximize bandwidth efficiency we are using broadcast 
and multicast traffic (multipoint traffic) to our neighbor 
nodes. I propose that we either create an extension to ROHC 
for multipoint links or come up with a method to efficiently 
use the current version in multipoint MANETS. I have been in 
contact with representatives from Effnet and Procito who are 
interested in designing the compression scheme.  I have 
included a problem statement that defines the issues that I 
think need to be addressed and suggest that the ROHC group 
take this up as a new action item.
 
Please let me know what you think, and if the we can address 
this problem within the working group. 
 
Thank you,

David Green
SRI International
EMail: [email-masked]

> David,
> 
> Please reformat and submit the document as an Internet-Draft.
> 
> Thanks!
> /Lars-Erik, ROHC chair
> 
> 
> > -----Original Message-----
> > From: [email-masked] [mailto:[email-masked]]On Behalf Of
> > [email-masked]
> > Sent: den 30 mars 2004 00:06
> > To: [email-masked]
> > Subject: [rohc] Multipoint Robust Compression for MANET
> > 
> > 
> > I'm designing a MANET system suitable for handheld and 
> > automobile portable radios that can operate on the move with 
> > link rages greater than 1 km. We will be adding IPv6 to the 
> > system so header compression has become a necessity as the 
> > network generally achieves less than 100kbps on links. In 
> > order to maximize bandwidth efficiency we are using broadcast 
> > and multicast traffic (multipoint traffic) to our neighbor 
> > nodes. I propose that we either create an extension to ROHC 
> > for multipoint links or come up with a method to efficiently 
> > use the current version in multipoint MANETS. I have been in 
> > contact with representatives from Effnet and Procito who are 
> > interested in designing the compression scheme.  I have 
> > included a problem statement that defines the issues that I 
> > think need to be addressed and suggest that the ROHC group 
> > take this up as a new action item.
> > 
> > Please let me know what you think, and if the we can address 
> > this problem within the working group. 
> > 
> > Thank you,
> > 
> >    David Green
> >    SRI International
> >    EMail: [email-masked]
> > 
> 
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   ROHC Working Group                                                   
   Internet Draft                                              D. Green 
   Document: draft-ietf-green-ROHC-multipoint-        SRI International 
   MANET.01.txt 
   Expires: October 2004                                     April 2004 

                 Problem Statement: RObust Header Compression (ROHC) 
                      in Multipoint Mobile Adhoc NEtwork (MANET) 
                   <draft-ietf-green-ROHC-multipoint-MANET.01.txt> 

Status of this Memo 
    
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026 [1].  
    
   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. 

Abstract 
    
   This problem statement document poses the issues that need to be 
   addressed to optimize ROHC for a Mobile Adhoc NEtwork (MANET) 
   containing point-to-multipoint (broadcast and multicast) messages 
   sent across ad-hoc radio network topologies. 

    

 
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             Problem Statement: ROHC in Multipoint MANET  April 20044 

Table of Contents 
    
   1. Introduction...................................................2 
   2. Network Design Requirements....................................2 
      2.1 Multipoint Network General Approach........................3 
      2.2 MANET General Issues.......................................3 
      2.3 MANET Data-Link Layer Considerations.......................4 
      2.4 MANET Network Layer considerations.........................5 
      2.5 Unique IPv6 considerations.................................5 
   3. Combining MANET and ROHC - Specific Challenges.................5 
   4. Security Considerations........................................5 
   References........................................................6 
   Acknowledgments...................................................7 
   Author's Addresses................................................7 

1. Introduction 
    
   RFC 3509 [2], entitled "RObust Header Compression (ROHC): Framework 
   and four profiles: RTP, UDP, ESP, and uncompressed" gives a good 
   overview of the requirements for IPv4 and IPv6 header compression in 
   wireless networks. It describes the various issues and requirements 
   that need to be addressed in such a network, and has led to the 
   development of a number of extensions to the base protocol [3] [4] 
   [5] [6]. 
    
   These protocols specifically address networks in which the only, or 
   the primary, communication vehicle is a point-to-point radio link 
   with significant error rates, and long round-trip times. In ad hoc 
   radio networks containing or contained within larger IP networks, 
   many of the capabilities of ROHC are desirable and arguably 
   necessary, but for maximum efficiency additional extensions need to 
   be made for point-to-multipoint traffic such as broadcast and 
   multicast traffic. 
    
   This document poses the issues that need to be addressed to make ROHC 
   work well in a network containing both traditional point-to-point 
   (cellular) and point to multipoint (MANET) radio network topologies. 
    
2. Network Design Requirements 
    
   In the portions of networks linked by MANET capable radios, the radio 
   frequency (RF) physical medium is error prone (10^-3 error rates are 
   common), data rate limited (288kbps or less for long range 1km+ 
   mobile data radios), and high delay (10s to 100s of milliseconds per 
   hop) medium when compared to wired networks. When networks are 
   operating on the move, terrain masking, foliage scattering, and the 

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             Problem Statement: ROHC in Multipoint MANET  April 20044 

   changing propagation distances between nodes all exacerbate packet 
   errors, network outages, router topology changes, and delays.  
    
   Due to the ad-hoc nature of MANET architectures, the radio system is 
   inherently a broadcast medium where all neighbor radios may receive 
   the transmission of any transmitting radio if they are within the RF 
   range of the transmitter. Given the inherent broadcast nature of the 
   RF medium, MANET radios may transmit point-to-point style (unicast) 
   messages to single neighbors (and other neighbors discard the 
   transmissions not meant for them), point-to-multipoint (multicast) 
   messages to groups of neighbors (neighbors in the multipoint group 
   listen to the message while neighbors not in the group discard the 
   message), or point-to-all (broadcast) messages which are received and 
   processed by all neighbors. These capabilities enable radios to 
   service Internet Protocol unicast, multicast, and broadcast style 
   messages.  Since messaging applications attached to MANETs often need 
   to send messages to multiple destinations within the MANET, multicast 
   and broadcast messages are used heavily as they consume less data 
   bandwidth than transmitting multiple point-to-point unicast messages. 
     
   MANET networks have the same RF medium characteristics of high error 
   rates, severely limited data rates, and high delay that the ROHC base 
   specification addresses via robust Window-based LSB encoding. MANET 
   networks differ from the current extensions for ROHC since they must 
   service, broadcast and multicast messages in addition to unicast 
   point-to-point messages. Since the RF physical medium characteristics 
   are well addressed by ROHC, and only the capability to efficiently 
   support multicast and broadcast transmissions may not supported, we 
   reason that ROHC may properly support multicast and broadcast links 
   with little or no modification. 
    
2.1 Multipoint Network General Approach 
    
   A node sending a broadcast or multicast message needs a method to 
   check and see if the message recipients correspond to current layer 
   1-2 (single hop) neighbors, and a method to look into a compression 
   context table to determine if a full header needs to be sent or what 
   level of compression may be used. Current unidirectional-mode (u-
   mode) compression can support multipoint data dissemination, but 
   higher levels of compression may be gained through feedback 
   mechanisms if the mechanisms do not cause excessive overhead.  
   Compression on point to multipoint links will probably have a lower 
   average efficiency when compared to point-to-point links, but a 
   properly designed scheme should significantly lower IP overhead for 
   IPv4 and v6 and result in a net savings. 
    
2.2 MANET General Issues 
    
   RFC 2501 [3], in section 3, lists a number of important points about 

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             Problem Statement: ROHC in Multipoint MANET  April 20044 

   MANET networks. They have dynamic topologies, which is to say that a 
   system's list of neighboring hosts and routers changes from time to 
   time. They are often bandwidth-constrained, both because the medium 
   is shared with other nodes and because of limitations of the 
   technology. They are also often power-constrained - a man portable 
   MANET system carried by a person is running on its battery, and the 
   simple act of transmission can be a major power drain. They also 
   enjoy limited security: even if locked in a room, their radio 
   transmissions can be a beacon identifying their location or giving 
   away information about the frequency and RF waveform with which they 
   transmit.  
    
   From the perspective of adapting an existing header compression 
   protocol, these MANET characteristics have specific implications. If 
   transmissions consume power & bandwidth while potentially 
   compromising security, unnecessary transmission is something to be 
   avoided. As a result, if there are several ways that a peer might 
   establish compression context (using multicast and broadcast to 
   exchange compression context information to multiple neighbors 
   simultaneously, piggybacking compression on messages for neighbor 
   discovery or routing information exchange, etc.), selecting the one 
   that uses the least power and bandwidth will have the least impact - 
   at least less impact than allowing duplicates. If the network is 
   bandwidth-constrained, limiting transmissions also preserves 
   bandwidth for other uses, and compressing data in ways that maximize 
   available bandwidth is extremely helpful. Security threats need to be 
   actively addressed, and in regions of rapid network change, or during 
   periods of rapid network change, the transmission and computation 
   loads need to be minimized. These issues are often deemed unimportant 
   in protocols designed for fixed usage. 
    
2.3 MANET Data-Link Layer Considerations 
    
   MANET capable radios may be based on common commercial technology 
   such as 802.11, emergency service or military radios, or other 
   technologies. Despite the variations in radio technology, the radios 
   are usually built using a small set of link-layer technologies. Link 
   layer assisted schemes will vary between radios, or in the case of 
   JTRS and other software defined radios; they will vary as the 
   software defined waveform changes. 
    
   General similarities of most MANET Radios: 
   *Data Link (Logical Link Control sub layer) Protocols such as ARP, 
   RARP, RDISC are common and may be leveraged by multipoint ROHC 
     
   General differences between most MANET Radios: 
   *Channel access protocols vary between CSMA, CDMA, TDMA, and hybrid 
   schemes  

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             Problem Statement: ROHC in Multipoint MANET  April 20044 

   *MAC Frame Formats often vary 
    
2.4 MANET Network Layer considerations 
   *MANETS operate on many different experimental routing protocols 
   (AODV, OLSR, TBRPF, OSPF with MANET extensions, and others) since 
   there is no IETF standards-track MANET protocol 
    
   *MANET protocols that maintain active neighbor lists may provide the 
   neighbor state information needed to check against multipoint 
   recipients to determine if a compression context is established. 
    
2.5 Unique IPv6 considerations  
   *For information on IPv6 reference [7] 
   *Larger addresses make header compression a more urgent need 
   *Automatic address reassignment via autodiscovery and 
   autoconfiguration could impact header compression 
   *IPv6 neighbor discovery (neighbor solicitation and 
   advertisement)(RFC 2461) [8] could be an enabling mechanism to gather 
   information on neighbors 

3. Combining MANET and ROHC - Specific Challenges 
 
   *Determining if messages require broadcast or multicast support 
   *Determining/discovering neighbors to establish compression contexts  
   *Method for crosschecking multicast message recipients against 
   neighbor tables 
   *U-mode probably will work for a low level of compression 
   *To get higher efficiency, we might need to redesign the feedback 
   logic for bi-directional modes to handle multipoint links without 
   generating collisions or congestion in dense networks  
   *Impairment considerations for multipoint links 
   *Method for context repair for multipoint links 

4. Security Considerations 
    
   As a problem statement, this note imposes no new security 
   requirements on MANET networks that are not known from RFC 2501 [3]. 
   Those problems can, however, be extreme. RFC 2501's 
   Security Considerations read: 
       
      “Mobile wireless networks are generally more prone to physical 
      security threats than are fixed, hardwired networks. Existing 
      link-level security techniques (e.g. encryption) are often 
      applied within wireless networks to reduce these threats. Absent 
      link-level encryption, at the network layer, the most pressing 
      issue is one of inter-router authentication prior to the exchange 
      of network control information.  Several levels of authentication 

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             Problem Statement: ROHC in Multipoint MANET  April 20044 

      ranging from no security (always an option) and       simple 
      shared-key approaches, to full public key infrastructure-based 
      authentication mechanisms will be explored by the group.  As an 
      adjunct to the working groups efforts, several optional 
      authentication modes may be standardized for use in MANETs.” 
    
   Note, however, that the issues that routing in a wireless network are 
   very vulnerable to attack, and appropriate security issues need to be 
   taken seriously. 

    
References 

   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP 
      9, RFC 2026, October 1996. 
    
   2  Bormann, C., Burmeister, C., Degermark, M., Fukushima, H., Hannu, 
      H., Jonsson, L-E., Hakenberg, R., Koren, T.,Le, K., Liu, Z., 
      Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T., Yoshimura, 
      T. and H. Zheng, "Robust Header Compression (ROHC): Framework and 
      four profiles: RTP, UDP, ESP, and uncompressed", RFC 3095, July 
      2001. 
    
   3  Degermark, M., "Requirements for IP/UDP/RTP Header Compression", 
      RFC 3096, July 2001. 
    
   4  Jonsson, L-E., "RObust Header Compression (ROHC): Requirements and 
      Assumptions for 0-byte IP/UDP/RTP Compression", RFC 3243, April 
      2002. 
    
   5  C. Bormann, "Robust Header Compression (ROHC) over PPP", RFC 3241, 
      April 2002. 
    
   6  Jonsson, L. and G. Pelletier, "RObust Header Compression (ROHC): A 
      compression profile for IP", Internet draft (work in progress), 
      October 2003, <draft-ietf-rohc-ip- only-05.txt> 
    
   7  Deering, S. and R. Hinden, "Internet Protocol, Version (IPv6) 
      Specification", RFC 2460, December 1998. 
    
   8  Narten, T., Nordmark, E., Simpson, W., and Daydreamer, "Neighbor 
      Discovery for Ipv6", RFC 2461, December 1998 

 
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             Problem Statement: ROHC in Multipoint MANET  April 20044 

   Portions of this document in its current state have been taken 
   directly from http://www.ietf.org/Draft-Statements/draft-baker-manet-
   ospf-problem-statement-00.txt  as this document relates to creating 
   an OSPF-MANET routing protocol and many general considerations in 
   Baker's problem statement overlap with considerations for developing 
   a MANET compression protocol. 

Acknowledgments 
    
   Initial comments were received from Tommy Lundemo, Jesus Arango, Fred 
   Templin, and Pete Sholander to help define this problem. 

Author's Addresses 
    
   David Green 
   SRI International 
   333 Ravenswood Ave 
   Menlo Park, California  94025 USA 
   Phone: +1-732-532-6715 
   Fax:   +1-732-427-2065 
   EMail: [email-masked] 

 
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