Re: [tcmtf] Improved version (v8) of the TCM-TF charter draft

"Jose Saldana" <> Thu, 21 November 2013 16:57 UTC

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From: "Jose Saldana" <>
To: "'Reinaldo Penno \(repenno\)'" <>, <>, <>, <>
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Date: Thu, 21 Nov 2013 17:56:52 +0100
Organization: Universidad de Zaragoza
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Cc: 'Martin Stiemerling' <>, 'Spencer Dawkins' <>
Subject: Re: [tcmtf] Improved version (v8) of the TCM-TF charter draft
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Hi, Reinaldo and Lars. Thank you very much for your comments. I will build a
new version of the charter in the next days.

Just a question about the scenarios. As agreed yesterday, we should limit to
scenarios with more than a single L3 hop. If there is a single L3 hop,
header compression (ROHC/ ECRTP / IPHC, depending on the protocols
implemented by the two optimizers) will suffice.

In some scenarios the number of hops is clear:
- in an air-to-ground connection there is a single hop. Not interesting for
- in a pair of appliances creating a tunnel between two offices  of a
company, there are a number of hops. Interesting for TCM-TF

But what happens if a scenario may involve one, two or more L3 hops? This
will  happen in a "community network": you can create a tunnel just to
connect a village with the Internet (one hop), or to connect a village with
another village, which is the one really connected to the Internet (more
than one hop). See a paper about the topology of these networks here

Perhaps we should take this into account when thinking about the "TCM-TF
negotiation". Suppose there are two TCM-optimizers that want to create an
optimized tunnel. During the negotiation they SHOULD check if the number of
L3 hops between them is 1. In that case, they can avoid the tunnel, and also
the multiplexing (and multiplexing delay in turn). This could be seen as a
particular case of TCM-TF:

- Compression layer: ROHC
- Multiplexing layer: send every single packet. No need for PPPMux
- Tunneling layer: no tunnel

So perhaps we should also consider the "no multiplexing" and "no tunneling"
options in the protocol stack, in order to cover these cases.

What do you think?


> -----Mensaje original-----
> De: Reinaldo Penno (repenno) []
> Enviado el: miércoles, 20 de noviembre de 2013 19:41
> Para:;;
> CC: Martin Stiemerling; 'Spencer Dawkins'
> Asunto: Re: [tcmtf] Improved version (v8) of the TCM-TF charter draft
> Hi,
> Some comments:
> * Put somewhere more explicitly the problem statement. If we are doing
> this to save bandwidth, then I suggest saying so in one bullet instead of
> being lost inside a huge paragraph.
> * Number 5: "So the first objective of this group². Then number 6 "As a
> objective, a document..². There are two first objectives with different
> descriptions. Are these the same document or different documents?
> * "The document will present a list of available traffic classification
> which can be used for identification of the service or application to
which a
> particular flow belongs². My first reaction would be to not try to list
> available classification methods since it will get into implementation
> details. And what if traffic is e2e encrypted? Given the whole
> thing should we we can expect this to happen? How would you know a flow
> is candidate or suitable for compression?
> * I wonder if some of the possible scenarios really apply. It seems we are
> throwing everything to see what sticks.  Example: Journalist covering the
> cycling competition do not need write their report real time. And if they
> need to do a interview, it seems to be working well right now, HD and
> everything.
> * "- an agreement between two network operators could allow them to
> compress a number of flows they are exchanging between a pair of Internet
> Routers². Not sure compressing flows between peering routers is a good
> use-case.
> On 11/20/13, 3:13 AM, "Jose Saldana" <> wrote:
> >TCM-TF charter draft v8
> >
> >Description of Working Group
> >
> >1. In the last years we are witnessing the raise of new real-time
> >services that use the Internet for the delivery of interactive
> >multimedia
> >applications: VoIP, videoconferencing, telemedicine, video vigilance,
> >online gaming, etc. Due to the need of interactivity, many of these
> >services use small packets (some tens of bytes), since they have to
> >send frequent updates between the extremes of the communication. In
> >addition, some other services also send small packets, but 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, and it becomes even
> >higher when IPv6 is used, since the basic
> >IPv6
> >header is twice the size of the IPv4 one.
> >
> >2. The efficiency cannot be increased by the inclusion of a higher
> >number of samples in a single packet, since this would harm the delay
> >requirements of the service. But there exist some scenarios in which a
> >number of flows share the same path. In this case, packets belonging to
> >different flows can be grouped together, adding a small multiplexing
> >delay as a counterpart of bandwidth saving. This delay will have to be
> >maintained under some threshold in order to grant the delay
> >requirements. Some examples of the scenarios where grouping packets is
> >possible are:
> >
> >- aggregation networks of a network operator;
> >- an end-to-end tunnel between appliances located in two different
> >offices of the same company;
> >- the access connection of an Internet Café including a high number of
> >VoIP/gaming flows;
> >- an agreement between two network operators could allow them to
> >compress a number of flows they are exchanging between a pair of
> >Internet Routers;
> >- a wireless Internet connection shared by a number of people in a
> >place with low Internet penetration
> >- a community network, in which a number of people in the same
> >geographical place share their connections in a cooperative way
> >- a satellite connection used for collecting the data of a high number
> >of sensors.
> >- a satellite connection used for providing connectivity in a
> >non-connected area during a short period of time (e.g. journalists
> >covering the arrival of a mountain stage of a cycling competition).
> >- an air-to-ground connection providing Internet connectivity to the
> >passengers of an aircraft, multiplexing a number of simultaneous VoIP
> >flows.
> >The same can be applied between a cruise ship and a satellite.
> >
> >3. VoIP using RTP is a clear example of a real-time service using small
> >packets with high overhead. In order to improve efficiency, RFC4170
> >(TCRTP)
> >defined a method for grouping packets when a number of flows share a
> >path, considering three different layers: header compression by means
> >of ECRTP; multiplexing by means of PPPMux; tunneling by means of
> L2TPv3.
> >
> >4. However, in the last years, emerging real-time services which do not
> >use UDP/RTP have become popular: some of them use UDP. In addition,
> new
> >header compression methods have been defined (ROHC). So there is a
> need
> >of widening the scope of RFC4170 in order to consider not only UDP/RTP
> >but also other protocols. The same structure of three layers will be
> >considered:
> >
> >- Header compression: Taking into account that real-time applications
> >use different headers (RTP/UDP, UDP), different protocols can be used:
> >no compression, ECRTP, IPHC and ROHC.
> >- Multiplexing: If a number of flows share a path between an origin and
> >a destination, a TCM-optimizer (called TCM-ingress optimizer) can build
> >a bigger multiplexed packet in which a number of payloads share a
> >common header. Another TCM-optimizer (called TCM-egress optimizer) is
> >then necessary at the end of the common path, so as to rebuild the
> >packets as they were originally sent. PPPMux will be the main option.
> >Other ones are not discarded.
> >- Tunneling will be used to send the multiplexed packets end-to-end.
> >The options in this layer are L2TP, GRE and MPLS.
> >
> >5. So the first objective of this group is to specify the protocol
> >stack for tunneling, compressing and multiplexing traffic flows
> >(TCM-TF). Since standard protocols are being used at each layer, the
> >signaling methods of those protocols will be used. Interactions with
> >the Working Groups and Areas in which these protocols are developed can
> >be expected. However, the development of new compressing,
> multiplexing
> >or tunneling protocols is not an objective of this Working Group. In
> >addition, since the current RFC
> >4170
> >would be considered as one of the options, this RFC could be obsoleted.
> >
> >6. As a first objective, a document (TCM-TF - reference model) will
> >define the different options which can be used at each layer. Specific
> >problems caused by the interaction between layers will have to be
> >issued, and suitable extensions may have to be added to the involved
> protocols.
> >
> >7. If a pair of ingress/egress optimizers want to establish a TCM-TF
> >session, they have first to use a mechanism to negotiate which concrete
> >option would they use in each layer: header compression, multiplexing
> >and tunneling. This will depend on the protocols that each extreme
> >implements at each level, and in the scenario. So another document
> >(TCM-TF - negotiation
> >protocol) will include:
> >
> >- a mechanism to setup/release a TCM-TF session between an ingress and
> >an egress-optimizer, also including:
> >- a negotiation mechanism to decide the options to use at each layer
> >(header compression, multiplexing and tunneling) between an ingress and
> >an egress-optimizer,
> >
> >8. As a counterpart of the bandwidth saving, TCM-TF may add some delay
> >and jitter. This is not a problem for the services which are not
> >sensitive to delay. However, regarding delay-sensitive services, the
> >Working Group will also develop a document (TCM-TF - recommendations)
> >with useful recommendations in order to decide which packet flows can
> >or can not be multiplexed and how. The document will present a list of
> >available traffic classification methods which can be used for
> >identification of the service or application to which a particular flow
> >belongs, as well as recommendations of the maximum delay and jitter to
> >be added depending of the identified service or application. The
> >eventual impact of multiplexing on protocol dynamics (e.g. the loss of
> >a multiplexed packet, MTU-related
> >issues) will also have to be addressed.
> >
> >9. The working group may identify additional deliverables that are
> >necessary/useful, e.g., a mechanism for a TCM-ingress optimizer to
> >discover an egress optimizer, and vice versa. The working group would
> >re-charter to add them before working on them.
> >
> >10. In addition, specific uses of TCM-TF, such as in wireless and
> >satellite scenarios, could be considered, and it might be studied
> >whether modifications or extensions are required on the protocol. The
> >working group would re-charter to work on those
> >modifications/extensions.
> >
> >11. Interactions with other Working Groups can be expected, since
> >TCM-TF uses already defined protocols for compression, multiplexing and
> >tunneling (ROHC, PPPMux, MPLS, GRE, L2TP).
> >
> >
> >Goals and Milestones
> >
> >Specification of TCM-TF  reference model.
> >
> >Specification of TCM-TF negotiation protocol.
> >
> >Specification of TCM-TF recommendations of using existing traffic
> >classification methods, maximum delay and jitter to add, depending on
> >the service.
> >
> >
> >Current version of Document (TCM-TF - reference model):
> >
> >
> >Current version of Document (TCM-TF - recommendations):
> >
> >
> >
> >
> >Best regards,
> >
> >Jose
> >
> >
> >_______________________________________________
> >tcmtf mailing list
> >
> >