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Versions: 00 01 02 03 04 05 06 07 08 09 10                              
Transport Area Working Group                                  J. Saldana
Internet-Draft                                    University of Zaragoza
Obsoletes: 4170 (if approved)                                    D. Wing
Intended status: Best Current Practice                     Cisco Systems
Expires: January 12, 2014                           J. Fernandez Navajas
                                                  University of Zaragoza
                                                          Muthu. Perumal
                                                           Cisco Systems
                                                       F. Pascual Blanco
                                                          Telefonica I+D
                                                           July 11, 2013


        Tunneling Compressed Multiplexed Traffic Flows (TCM-TF)
                      draft-saldana-tsvwg-tcmtf-05

Abstract

   Tunneling Compressed and Multiplexed Traffic Flows (TCM-TF) is a
   method for improving the bandwidth utilization of network segments
   that carry multiple flows in parallel sharing a common path.  The
   method combines standard protocols for header compression,
   multiplexing, and tunneling over a network path for the purpose of
   reducing the bandwidth used when multiple flows are carried over that
   path.  The amount of packets per second can also be reduced.

   This document describes the TCM-TF framework and the different
   options which can be used for each layer (header compression,
   multiplexing and tunneling).

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 12, 2014.





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Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Bandwidth efficiency of flows sending small packets . . .   3
       1.2.1.  Real-time applications using RTP  . . . . . . . . . .   3
       1.2.2.  Real-time applications not using RTP  . . . . . . . .   4
       1.2.3.  Other applications generating small packets . . . . .   4
       1.2.4.  Optimization of small-packet flows  . . . . . . . . .   5
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Scenarios of application  . . . . . . . . . . . . . . . .   6
       1.4.1.  Residential scenario  . . . . . . . . . . . . . . . .   6
       1.4.2.  Corporate environments  . . . . . . . . . . . . . . .   7
       1.4.3.  Machine to Machine (M2M) scenario . . . . . . . . . .   8
     1.5.  Potential beneficiaries of TCM optimization . . . . . . .   9
     1.6.  Current Standard  . . . . . . . . . . . . . . . . . . . .   9
     1.7.  Improved Standard Proposal  . . . . . . . . . . . . . . .  10
   2.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .  11
     2.1.  Models of implementation  . . . . . . . . . . . . . . . .  11
     2.2.  Choice of the compressing protocol  . . . . . . . . . . .  12
       2.2.1.  Context Synchronization in ECRTP  . . . . . . . . . .  13
       2.2.2.  Context Synchronization in ROHC . . . . . . . . . . .  14
     2.3.  Multiplexing  . . . . . . . . . . . . . . . . . . . . . .  14
     2.4.  Tunneling . . . . . . . . . . . . . . . . . . . . . . . .  15
       2.4.1.  Tunneling schemes over IP: L2TP and GRE . . . . . . .  15
       2.4.2.  MPLS tunneling  . . . . . . . . . . . . . . . . . . .  15
     2.5.  Encapsulation Formats . . . . . . . . . . . . . . . . . .  15
   3.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .  17
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction




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   This document describes a way to combine existing protocols for
   header compression, multiplexing and tunneling to save bandwidth for
   applications that generate long-term flows of small packets.

1.1.  Requirements Language

   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 [RFC2119].

1.2.  Bandwidth efficiency of flows sending small packets

   The interactivity demands of some real-time services (VoIP,
   videoconferencing, telemedicine, video vigilance, online gaming,
   etc.) require a traffic profile consisting of high rates of small
   packets, which are necessary in order to transmit frequent updates
   between the two extremes of the communication.  These services also
   demand small network delays.  In addition, some other services also
   use small packets, although they are not delay-sensitive (e.g.,
   instant messaging, M2M packets sending collected data in sensor
   networks using wireless or satellite scenarios).  For both the delay-
   sensitive and delay-insensitive applications, their small data
   payloads incur significant overhead.

   When a number of flows based on small packets (small-packet flows)
   share the same path, bandwidth can be saved by multiplexing packets
   belonging to different flows.  If a transmission queue has not
   already been formed but multiplexing is desired, it is necessary to
   add a multiplexing delay, which has to be maintained under some
   threshold if the service presents tight delay requirements.

1.2.1.  Real-time applications using RTP

   The first design of the Internet did not include any mechanism
   capable of guaranteeing an upper bound for delivery delay, taking
   into account that the first deployed services were e-mail, file
   transfer, etc., in which delay is not critical.  RTP [RTP] was first
   defined in 1996 in order to permit the delivery of real-time
   contents.  Nowadays, although there are a variety of protocols used
   for signaling real-time flows (SIP [SIP], H.323, etc.), RTP has
   become the standard par excellence for the delivery of real-time
   content.

   RTP was designed to work over UDP datagrams.  This implies that an
   IPv4 packet carrying real-time information has to include 40 bytes of
   headers: 20 for IPv4 header, 8 for UDP, and 12 for RTP.  This
   overhead is significant, taking into account that many real-time
   services send very small payloads.  It becomes even more significant



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   with IPv6 packets, as the basic IPv6 header is twice the size of the
   IPv4 header.  Table 1 illustrates the overhead problem of VoIP for
   two different codecs.

   +--------------------------------+----------------------------------+
   |              IPv4              |               IPv6               |
   +--------------------------------+----------------------------------+
   | IPv4+UDP+RTP: 40 bytes header  |  IPv6+UDP+RTP: 60 bytes header   |
   | G.711 at 20 ms packetization:  |  G.711 at 20 ms packetization:   |
   |      25% header overhead       |      37.5% header overhead       |
   | G.729 at 20 ms packetization:  |  G.729 at 20 ms packetization:   |
   |      200% header overhead      |       300% header overhead       |
   +--------------------------------+----------------------------------+

               Table 1: Efficiency of different voice codecs

1.2.2.  Real-time applications not using RTP

   At the same time, there are many real-time applications that do not
   use RTP.  Some of them send UDP (but not RTP) packets, e.g., First
   Person Shooter (FPS) online games, for which latency is very
   critical.

   There is also another kind of applications which have been reported
   as real-time using TCP: MMORPGs (Massively Multiplayer Online Role
   Playing Games), which in some cases have millions of players,
   thousands of them sharing the same virtual world.  They use TCP
   packets to send the player commands to the server, and also to send
   to the player's application the characteristics and situation of
   other gamers' avatars.  These games do not have the same
   interactivity of FPSs, but the quickness and the movements of the
   players are important, and can decide if they win or lose a fight.

   Finally, there is also another fact which has to be taken into
   account: TCP is getting used for media delivery.  For many reasons,
   such as avoiding firewalls, the standard RTP/UDP/IP protocol stack is
   substituted in many cases by FLV/HTTP/TCP/IP (FLash Video [FLV]).

1.2.3.  Other applications generating small packets

   Other applications without delay constraints are also becoming
   popular (e.g., instant messaging, M2M packets sending collected data
   in sensor networks using wireless or satellite scenarios).  The
   number of wireless M2M (machine-to-machine) connections is steady
   growing since a few years, and a share of these is being used for
   delay-intolerant applications, e.g., industrial SCADA (Supervisory
   Control And Data Acquisition), power plant monitoring, smart grids,
   asset tracking.



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1.2.4.  Optimization of small-packet flows

   In order to mitigate the bad network efficiency of flows using small
   packets, the multiplexing of a number of payloads into a single
   packet can be considered as a solution.  For example, if a single
   VoIP flow is considered, the number of samples included in a packet
   can be increased, but at the cost of adding new packetization delays.

   When a number of flows share the same path between an origin and a
   destination, a multiplexer can build a bigger packet in which a
   number of payloads share a common header.  A demultiplexer is
   necessary at the end of the common path, so as to rebuild the packets
   as they were originally sent, making multiplexing a transparent
   process for the extremes of the flow.

   In addition, the headers of the original packets can be compressed to
   save more bandwidth, using some of the already existing header
   compression standards ([cRTP], [ECRTP], [IPHC], [ROHC]).  When
   different headers are compressed together, tunneling can be used to
   relieve intermediate routers from the decompression and compression
   processing.

   If only one stream is tunneled and compressed, then little bandwidth
   savings will be obtained.  In contrast, multiplexing is helpful to
   amortize the overhead of the tunnel header over many payloads.  The
   obtained savings grow with the number of flows optimized together.

1.3.  Terminology

   This document uses a number of terms to refer to the roles played by
   the entities using TCM-TF.

   o  native packet

   A packet sent by an application, belonging to a flow that can be
   optimized by means of TCM-TF.

   o  native flow

   A flow of native packets.  It can be considered a "small-packet flow"
   when the vast majority of the generated packets present a low
   payload-to-header ratio.

   o  TCM packet

   A packet including a number of multiplexed and header-compressed
   native ones, and also a tunneling header.




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   o  TCM flow

   A flow of TCM packets, including a number of optimized native flows.

   o  TCM optimizer

   The host where TCM optimization is deployed.  It corresponds to both
   the ingress and the egress of the tunnel transporting the compressed
   and multiplexed packets.

   If the optimizer compresses headers, multiplexes packets and creates
   the tunnel, it behaves as a "TCM-ingress optimizer", or "TCM-IO".  It
   takes native packets or flows and "optimizes" them.

   If it extracts packets from the tunnel, demultiplexes packets and
   decompresses headers, it behaves as a "TCM-egress optimizer", or
   "TCM-EO".  The TCM-egress optimizer takes a TCM flow and "rebuilds"
   the native packets as they were originally sent.

   o  TCM-TF session

   The relationship between a pair of TCM optimizers exchanging TCM
   packets.

   o  policy manager

   A network entity which makes the decisions about TCM-TF parameters:
   multiplexing period to be used, flows to be optimized together,
   depending on their IP addresses, ports, etc.  It is connected with a
   number of TCM-TF optimizers, and orchestrates the optimization that
   takes place between them.

1.4.  Scenarios of application

   Different scenarios of application can be considered for the
   tunneling, compressing and multiplexing solution:

1.4.1.  Residential scenario

   If we consider the residential users of a real-time interactive
   application (e.g., VoIP, an online game generating small packets) in
   a town or a district, a TCM optimizing module can be included in
   network devices, in order to group packets with the same destination.
   Depending on the number of users of the application, the packets
   could be grouped at different levels in DSL fixed network scenarios,
   at gateway level in LTE mobile network scenarios or even in other ISP
   edge routers.  TCM-TF may also be applied for fiber residential
   accesses, and in 2G/3G mobile networks.  This would reduce bandwidth



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   requirements in the provider aggregation network, and in the network
   connection of the application provider, thus resulting in savings for
   both actors.

   In this scenario, agreements between different companies can be
   established in order to save bandwidth and to reduce packets per
   second.  For example, a service provider (e.g., an online gaming
   company) could be allowed to place a TCM optimizer in the aggregation
   network of an ISP, being able to optimize all the flows of a game or
   service.  Another TCM optimizer would rebuild these packets once they
   arrive to the network of the provider.

   At the same time, the ISP would implement TCM-TF capabilities within
   its own MPLS network in order to optimize internal network resources:
   optimizing modules could be embedded in the Label Edge Routers of the
   network.  In that scenario MPLS would be the "tunneling" layer, being
   the tunnels the paths defined by the MPLS labels and avoiding the use
   of other tunneling protocols.

   Finally, some networks use cRTP [cRTP] on their access links.  This
   gives bandwidth savings on the access link, but as a counterpart it
   consumes considerable CPU resources on the aggregation router.  In
   these cases, by means of TCM, instead of only saving bandwidth on the
   access link, it could also be saved across the core, and on the far-
   end access link, all without the CPU impact on the aggregation
   router.

1.4.2.  Corporate environments

   End users can also optimize traffic end-to-end from network borders.
   As an example, we can consider the case of an enterprise with a
   number of distributed central offices, in which an appliance could be
   placed next to the access router, being able to optimize traffic
   flows with a shared origin and destination.  Thus, a number of remote
   desktop sessions to the same server could be optimized, or a number
   of VoIP calls between two offices could also require less bandwidth
   and fewer packets per second.

   Another example of an end user collaborating in traffic optimization
   could be an Internet cafe, which is suitable of having many users of
   the same application (e.g., a game) sharing the same access link.
   Internet cafes are very popular in countries with relatively low
   access speeds in households, where home computer penetration is
   usually low as well.  In many of these countries, bandwidth can
   become a serious limitation for this kind of business, so TCM-TF
   savings may become critical for their viability.





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   Satellite communication links that often manage the bandwidth by
   limiting the transmission rate, measured in packets per second (pps),
   to and from the satellite.  Applications like VoIP that generate a
   large number of small packets can easily fill the maximum number of
   pps slots, limiting the throughput across such links.  As an example,
   a G.729a voice call generates 50 pps at 20 ms packetization time.  If
   the satellite transmission allows 1,500 pps, the number of
   simultaneous voice calls is limited to 30.  This results in poor
   utilization of the satellite link's bandwidth as well as places a low
   bound on the number of voice calls that can utilize the link
   simultaneously.  TCM optimization of small packets into one packet
   for transmission would improve the efficiency.  Satellite links would
   also find it useful to multiplex and compress small TCP packets into
   one packet.  This could be especially interesting for compressing TCP
   ACKs.

   Desktop or application sharing where the traffic from the server to
   the client typically consists of the delta of screen updates.  Also,
   the standard for remote desktop sharing emerging for WebRTC in the
   RTCWEB Working Group is: {something}/SCTP/UDP (Stream Control
   Transmission Protocol [SCTP]).  In this scenario, SCTP/UDP could be
   used in other cases: chatting, file sharing and applications related
   to WebRTC peers.  There could be hundreds of clients at a site
   talking to a server located at a datacenter over a WAN.  Compressing,
   multiplexing and tunneling this traffic could save WAN bandwidth and
   potentially improve latency.

1.4.3.  Machine to Machine (M2M) scenario

   In a M2M/SCADA (Supervisory Control And Data Acquisition) context,
   TCM optimization can be applied when a satellite link is used for
   collecting the data of a number of sensors.  M2M terminals are
   normally equipped with sensing devices which can interface to
   proximity sensor networks through wireless connections.  The terminal
   can send the collected sensing data using a satellite link connecting
   to a satellite gateway, which in turn will forward the M2M/SCADA data
   to the to the processing and control center through Internet.  The
   size of typical M2M application transaction depends on the specific
   service and it may vary from a minimum of 20 bytes (e.g., tracking
   and metering in private security) to about 1,000 bytes (e.g., video-
   surveillance).  In this context, TCM-TF concepts can be also applied
   to allow a more efficient use of the available satellite link
   capacity, matching the requirements demanded by some M2M services.
   If the case of large sensor deployments is considered, where
   proximity sensor networks transmit data through different satellite
   terminals, the use of compression algorithms already available in
   current satellite systems to reduce the overhead introduced by TCP or
   UDP and IPv6 protocols is certainly desirable.  In addition to this,



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   tunneling and multiplexing functions available from TCM-TF allows
   extending compression functionality throughout the rest the network,
   to eventually reach the processing and control centers.

1.5.  Potential beneficiaries of TCM optimization

   In conclusion, a standard able to compress headers, multiplex a
   number of packets and send them together using a tunnel, can benefit
   various stakeholders:

   o  network operators can compress traffic flows sharing a common
      network segment;

   o  ISPs;

   o  developers of VoIP systems can include this option in their
      solutions;

   o  service providers, who can achieve bandwidth savings in their
      supporting infrastructures.

   Other fact that has to be taken into account is that the technique
   not only saves bandwidth but also reduces the number of packets per
   second, which sometimes can be a bottleneck for a satellite link or
   even for a network router.

1.6.  Current Standard

   The current standard [TCRTP] defines a way to reduce bandwidth and
   pps of RTP traffic, by combining three different standard protocols:

   o  Regarding compression, [ECRTP] is the selected option.

   o  Multiplexing is accomplished using PPP Multiplexing [PPP-MUX]

   o  Tunneling is accomplished by using L2TP (Layer 2 Tunneling
      Protocol [L2TPv3]).

   The three layers are combined as shown in the Figure 1:












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                 RTP/UDP/IP
                    |
                    |         ----------------------------
                    |
                  ECRTP             compressing layer
                    |
                    |         ----------------------------
                    |
                  PPPMUX            multiplexing layer
                    |
                    |         ----------------------------
                    |
                  L2TP              tunneling layer
                    |
                    |         ----------------------------
                    |
                   IP

                                 Figure 1

1.7.  Improved Standard Proposal

   In contrast to the current standard [TCRTP], TCM-TF allows other
   header compression protocols in addition to RTP/UDP, since services
   based on small packets also use by bare UDP or TCP, as shown in
   Figure 2:

       TCP/IP   UDP/IP  RTP/UDP/IP
            \     |     /
             \    |    /                  ------------------------------
              \   |   /
   Nothing or ROHC or ECRTP or IPHC          header compressing layer
                  |
                  |                       ------------------------------
                  |
      PPPMUX or other mux protocols             multiplexing layer
                  |
                 / \                      ------------------------------
                /   \
               /     \
      GRE or L2TP     \                           tunneling layer
             |        MPLS
             |                            ------------------------------
             IP

                                 Figure 2





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   Each of the three layers is considered as independent of the other
   two, i.e. different combinations of protocols can be implemented
   according to the new proposal:

   o  Regarding compression, a number of options can be considered: as
      different standards are able to compress different headers
      ([cRTP], [ECRTP], [IPHC], [ROHC]).  The one to be used could be
      selected depending on the traffic to compress and the concrete
      scenario (packet loss percentage, delay, etc.).  It also exists
      the possibility of having a null header compression, in the case
      of wanting to avoid traffic compression, taking into account the
      need of storing a context for every flow and the problems of
      context desynchronization in certain scenarios.  Although non
      shown in Figure 2, ESP (Encapsulating Security Payload [ESP])
      headers can also be compressed.

   o  Multiplexing is also accomplished using PPP Multiplexing
      [PPP-MUX].  Nevertheless, other multiplexing protocols can also be
      considered.

   o  Tunneling is accomplished by using L2TP (Layer 2 Tunneling
      Protocol [L2TPv3]) over IP, GRE (Generic Routing Encapsulation
      [GRE]) over IP, or MPLS (Multiprotocol Label Switching
      Architecture [MPLS]).

   It can be observed that TCRTP [TCRTP] is included as an option in
   TCM-TF, combining [ECRTP], [PPP-MUX] and [L2TPv3].

   Payload compression schemes could also be used, but they are not the
   aim of this document.

2.  Protocol Operation

   This section describes how to combine protocols belonging to trhee
   layers (compressing, multiplexing, and tunneling), in order to save
   bandwidth for the considered flows.

2.1.  Models of implementation

   TCM-TF can be implemented in different ways.  The most
   straightforward is to implement it in the devices terminating the
   flows (these devices can be e.g., voice gateways, or proxies grouping
   a number of flows):








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                       [ending device]---[ending device]
                                       ^
                                       |
                                  TCM-TF over IP

                                 Figure 3

   Another way TCM-TF can be implemented is with an external
   concentration device.  This device could be placed at strategic
   places in the network and could dynamically create and destroy TCM-TF
   sessions without the participation of the endpoints that generate the
   flows (Figure 4).

     [ending device]\                                   /[ending device]
     [ending device]---[concentrator]---[concentrator]---[ending device]
     [ending device]/                                   \[ending device]
                     ^                ^                ^
                     |                |                |
                  Native IP      TCM-TF over IP      Native IP

                                 Figure 4

   A number of already compressed flows can also be merged in a tunnel
   using a concentrator in order to increase the number of flows in a
   tunnel (Figure 5):

     [ending device]\                                   /[ending device]
     [ending device]---[concentrator]---[concentrator]---[ending device]
     [ending device]/                                   \[ending device]
                     ^                ^                ^
                     |                |                |
                Compressed        TCM-TF over IP    Compressed

                                 Figure 5

2.2.  Choice of the compressing protocol

   There are different protocols that can be used for compressing IP
   flows:

   o  IPHC (IP Header Compression [IPHC]) permits the compression of TCP
      /IP, UDP/IP and ESP/IP headers.  It has a low implementation
      complexity.  On the other hand, the resynchronization of the
      context can be slow over long RTT links.  It should be used in
      scenarios presenting very low packet loss percentage.

   o  cRTP (compressed RTP [cRTP]) works the same way as IPHC, but is
      also able to compress RTP headers.  The link layer transport is



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      not specified, but typically PPP is used.  For cRTP to compress
      headers, it must be implemented on each PPP link.  A lot of
      context is required to successfully run cRTP, and memory and
      processing requirements are high, especially if multiple hops must
      implement cRTP to save bandwidth on each of the hops.  At higher
      line rates, cRTP's processor consumption becomes prohibitively
      expensive. cRTP is not suitable over long-delay WAN links commonly
      used when tunneling, as proposed by this document.  To avoid the
      per-hop expense of cRTP, a simplistic solution is to use cRTP with
      L2TP to achieve end-to-end cRTP.  However, cRTP is only suitable
      for links with low delay and low loss.  Thus, if multiple router
      hops are involved, cRTP's expectation of low delay and low loss
      can no longer be met.  Furthermore, packets can arrive out of
      order.

   o  ECRTP (Enhanced Compressed RTP [ECRTP]) is an extension of cRTP
      [cRTP] that provides tolerance to packet loss and packet
      reordering between compressor and decompressor.  Thus, ECRTP
      should be used instead of cRTP when possible (e.g., the two TCM
      optimizers implementing ECRTP).

   o  ROHC (RObust Header Compression [ROHC]) is able to compress TCP/
      IP, UDP/IP, ESP/IP and RTP/UDP/IP headers.  It is a robust scheme
      developed for header compression over links with high bit error
      rate, such as wireless ones.  It incorporates mechanisms for quick
      resynchronization of the context.  It includes an improved
      encoding scheme for compressing the header fields that change
      dynamically.  Its main drawback is that it requires significantly
      more processing and memory resources than the ones necessary for
      IPHC or ECRTP.

   This standard does not determine which of the existing protocols has
   to be used for the compressing layer.  The decision will depend on
   the scenario, and will mainly be determined by the packet loss
   probability, RTT, and the availability of memory and processing
   resources.  The standard is also suitable to include other
   compressing schemes that may be further developed.

2.2.1.  Context Synchronization in ECRTP

   When the compressor receives an RTP packet that has an unpredicted
   change in the RTP header, the compressor should send a COMPRESSED_UDP
   packet (described in [ECRTP]) to synchronize the ECRTP decompressor
   state.  The COMPRESSED_UDP packet updates the RTP context in the
   decompressor.






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   To ensure delivery of updates of context variables, COMPRESSED_UDP
   packets should be delivered using the robust operation described in
   [ECRTP].

   Because the "twice" algorithm described in [ECRTP] relies on UDP
   checksums, the IP stack on the RTP transmitter should transmit UDP
   checksums.  If UDP checksums are not used, the ECRTP compressor
   should use the cRTP Header checksum described in [ECRTP].

2.2.2.  Context Synchronization in ROHC

   ROHC [ROHC] includes a more complex mechanism in order to maintain
   context synchronization.  It has different operation modes and
   defines compressor states which change depending on link behavior.

2.3.  Multiplexing

   Header compressing algorithms require a layer two protocol that
   allows identifying different protocols.  PPP [PPP] is suited for
   this, although other multiplexing protocols can also be used for this
   layer of TCM-TF.

   When header compression is used inside a tunnel, it reduces the size
   of the headers of the IP packets carried in the tunnel.  However, the
   tunnel itself has overhead due to its IP header and the tunnel header
   (the information necessary to identify the tunneled payload).

   By multiplexing multiple small payloads in a single tunneled packet,
   reasonable bandwidth efficiency can be achieved, since the tunnel
   overhead is shared by multiple packets belonging to the flows active
   between the source and destination of an L2TP tunnel.  The packet
   size of the flows has to be small in order to permit good bandwidth
   savings.

   If the source and destination of the tunnel are the same as the
   source and destination of the compressing protocol sessions, then the
   source and destination must have multiple active small-packet flows
   to get any benefit from multiplexing.

   Because of this, TCM-TF is mostly useful for applications where many
   small-packet flows run between a pair of hosts.  The number of
   simultaneous sessions required to reduce the header overhead to the
   desired level depends on the average payload size, and also on the
   size of the tunnel header.  A smaller tunnel header will result in
   fewer simultaneous sessions being required to produce adequate
   bandwidth efficiencies.





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2.4.  Tunneling

   Different tunneling schemes can be used for sending end to end the
   compressed payloads.

2.4.1.  Tunneling schemes over IP: L2TP and GRE

   L2TP tunnels should be used to tunnel the compressed payloads end to
   end.  L2TP includes methods for tunneling messages used in PPP
   session establishment, such as NCP (Network Control Protocol).  This
   allows [IPCP-HC] to negotiate ECRTP compression/decompression
   parameters.

   Other tunneling schemes, such as GRE [GRE] may also be used to
   implement the tunneling layer of TCM-TF.

2.4.2.  MPLS tunneling

   In some scenarios, mainly in operator's core networks, the use of
   MPLS is widely deployed as data transport method.  The adoption of
   MPLS as tunneling layer in this proposal intends to natively adapt
   TCM-TF to those transport networks.

   In the same way that layer 3 tunnels, MPLS paths, identified by MPLS
   labels, established between Label Edge Routers (LSRs), could be used
   to transport the compressed payloads within an MPLS network.  This
   way, multiplexing layer must be placed over MPLS layer.  Note that,
   in this case, layer 3 tunnel headers do not have to be used, with the
   consequent data efficiency improvement.

2.5.  Encapsulation Formats

   The packet format for a packet compressed is:

                      +------------+-----------------------+
                      |            |                       |
                      |   Compr    |                       |
                      |   Header   |      Data             |
                      |            |                       |
                      |            |                       |
                      +------------+-----------------------+

                                 Figure 6

   The packet format of a multiplexed PPP packet as defined by [PPP-MUX]
   is:





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         +-------+---+------+-------+-----+   +---+------+-------+-----+
         | Mux   |P L|      |       |     |   |P L|      |       |     |
         | PPP   |F X|Len1  |  PPP  |     |   |F X|LenN  |  PPP  |     |
         | Prot. |F T|      | Prot. |Info1| ~ |F T|      | Prot. |InfoN|
         | Field |          | Field1|     |   |          |FieldN |     |
         | (1)   |1-2 octets| (0-2) |     |   |1-2 octets| (0-2) |     |
         +-------+----------+-------+-----+   +----------+-------+-----+

                                 Figure 7

   The combined format used for TCM-TF with a single payload is all of
   the above packets concatenated.  Here is an example with one payload,
   using L2TP or GRE tunneling:

             +------+------+-------+----------+-------+--------+----+
             | IP   |Tunnel| Mux   |P L|      |       |        |    |
             |header|header| PPP   |F X|Len1  |  PPP  | Compr  |    |
             | (20) |      | Proto |F T|      | Proto | header |Data|
             |      |      | Field |          | Field1|        |    |
             |      |      | (1)   |1-2 octets| (0-2) |        |    |
             +------+------+-------+----------+-------+--------+----+
                    |<------------- IP payload -------------------->|
                                   |<-------- Mux payload --------->|

                                 Figure 8

   If the tunneling technology is MPLS, then the scheme would be:

                 +------+-------+----------+-------+--------+----+
                 |MPLS  | Mux   |P L|      |       |        |    |
                 |header| PPP   |F X|Len1  |  PPP  | Compr  |    |
                 |      | Proto |F T|      | Proto | header |Data|
                 |      | Field |          | Field1|        |    |
                 |      | (1)   |1-2 octets| (0-2) |        |    |
                -+------+-------+----------+-------+--------+----+
                        |<---------- MPLS payload -------------->|
                                |<-------- Mux payload --------->|

                                 Figure 9

   If the tunnel contains multiplexed traffic, multiple "PPPMux
   payload"s are transmitted in one IP packet.









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3.  Contributing Authors

   Gonzalo Camarillo
   Ericsson
   Advanced Signalling Research Lab.
   FIN-02420 Jorvas
   Finland

   Email: Gonzalo.Camarillo@ericsson.com


   Michael A. Ramalho
   Cisco Systems, Inc.
   8000 Hawkins Road
   Sarasota, FL 34241-9300
   US

   Phone: +1.732.832.9723
   Email: mramalho@cisco.com


   Jose Ruiz Mas
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   50018 Zaragoza
   Spain

   Phone: +34 976762158
   Email: jruiz@unizar.es


   Diego Lopez Garcia
   Telefonica I+D
   Ramon de la cruz 84
   28006 Madrid
   Spain

   Phone: +34 913129041
   Email: diego@tid.es


   David Florez Rodriguez
   Telefonica I+D
   Ramon de la cruz 84
   28006 Madrid
   Spain

   Phone: +34 91312884



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   Email: dflorez@tid.es


   Manuel Nunez Sanz
   Telefonica I+D
   Ramon de la cruz 84
   28006 Madrid
   Spain

   Phone: +34 913128821
   Email: mns@tid.es


   Juan Antonio Castell Lucia
   Telefonica I+D
   Ramon de la cruz 84
   28006 Madrid
   Spain

   Phone: +34 913129157
   Email: jacl@tid.es


   Mirko Suznjevic
   University of Zagreb
   Faculty of Electrical Engineering and Computing, Unska 3
   10000 Zagreb
   Croatia

   Phone: +385 1 6129 755
   Email: mirko.suznjevic@fer.hr


4.  Acknowledgements

5.  IANA Considerations

   This memo includes no request to IANA.

6.  Security Considerations

   The most straightforward option for securing a number of non-secured
   flows sharing a path is by the use of IPsec [IPsec], when TCM using
   an IP tunnel is employed.  Instead of adding a security header to the
   packets of each native flow, and then compressing and multiplexing
   them, a single IPsec tunnel can be used in order to secure all the
   flows together, thus achieving a higher efficiency.  This use of
   IPsec protects the packets only within the transport network between



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   tunnel ingress and egress and therefore does not provide end-to-end
   authentication or encryption.  In some cases , e.g., where the end
   points are trusted, this model may be appropriate.

   When a number of already secured flows including ESP [ESP] headers
   are optimized by means of TCM, and the addition of further security
   is not necessary, their ESP/IP headers can still be compressed using
   suitable algorithms [RFC5225], in order to improve the efficiency.
   This header compression does not change the end-to-end security
   model.

   Future versions of this document will consider whether some TCM-TF
   mechanisms could be potentially exploited in order to deploy or
   amplify DoS attacks against network infrastructure.  Solutions will
   be provided if potential attacks are identified.

7.  Normative References

   [ECRTP]    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, 2003.

   [ESP]      Kent, S., "IP Encapsulating Security Payload ", RFC 4303,
              2005.

   [FLV]      ISO/IEC, "FLV and F4V File Format Specification", 14496-12
              MPEG-4 Part 12, 2008.

   [GRE]      Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              2000.

   [I.363.2]  ITU-T, "B-ISDN ATM Adaptation layer specification: Type 2
              AAL", I. 363.2, 1997.

   [IPCP-HC]  Engan, M., Casner, S., Bormann, C., and T. Koren, "IP
              Header Compression over PPP", RFC 3544, 2003.

   [IPHC]     Degermark, M., Nordgren, B., and S. Pink, "IP Header
              Compression", RFC 2580, 1999.

   [IPsec]    Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [L2TPv3]   Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
              Protocol - Version 3 (L2TPv3)", RFC 3931, 2005.





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   [MPLS]     Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [PPP-MUX]  Pazhyannur, R., Ali, I., and C. Fox, "PPP Multiplexing",
              RFC 3153, 2001.

   [PPP]      Simpson, W., "The Point-to-Point Protocol (PPP)", RFC
              1661, 1994.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5225]  Pelletier, G. and K. Sandlund, "RObust Header Compression
              Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and
              UDP-Lite ", RFC 5225, April 2008.

   [ROHC]     Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795, 2010.

   [RTP]      Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", RFC 3550, 2003.

   [SCTP]     Stewart, Ed., R., "Stream Control Transmission Protocol",
              RFC 4960, 2007.

   [SIP]      Rosenberg, J., Schulzrinne, H., Camarillo, G., and et.
              al., "SIP: Session Initiation Protocol", RFC 3261, 2005.

   [TCRTP]    Thomson, B., Koren, T., and D. Wing, "Tunneling
              Multiplexed Compressed RTP (TCRTP)", RFC 4170, 2005.

   [cRTP]     Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
              Headers for Low-Speed Serial Links", RFC 2508, 1999.

Authors' Addresses

   Jose Saldana
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   Zaragoza  50018
   Spain

   Phone: +34 976 762 698
   Email: jsaldana@unizar.es






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   Dan Wing
   Cisco Systems
   771 Alder Drive
   San Jose, CA  95035
   US

   Phone: +44 7889 488 335
   Email: dwing@cisco.com


   Julian Fernandez Navajas
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   Zaragoza  50018
   Spain

   Phone: +34 976 761 963
   Email: navajas@unizar.es


   Muthu Arul Mozhi Perumal
   Cisco Systems
   Cessna Business Park
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Phone: +91 9449288768
   Email: mperumal@cisco.com


   Fernando Pascual Blanco
   Telefonica I+D
   Ramon de la Cruz 84
   Madrid  28006
   Spain

   Phone: +34 913128779
   Email: fpb@tid.es












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