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Operators’ Options in choosing TDM/Packet based transport equipment

In my last post, I had explained that it would be bandwidth in-efficient to carry TDM over Ethernet/IP links; today I came across an interesting white paper by Heavy Reading which indirectly does point to this fact and argues that it is better and efficient to keep TDM traffic completely over TDM network. The white paper can be found at

The white paper focuses on metro aggregation area and argues that in the foreseeable future, transport in this area ought to be “All Native” i.e. TDM carried as TDM transport and Packet in its native form most likely as MPLS-TP (All within one network element). It elaborates that it is still a far cry to have an All IP transport considering that the nature of traffic in today’s network is mostly mixed; that majority of revenue still comes from TDM circuits and most importantly considerable investments have already been done in TDM equipment by incumbent operators that they would like to protect.  The paper points out that majority of products are either optimized for TDM or IP but not for both. The best approach, thus the paper maintains, would be to have the All-Native transport supported by one network element that carries both kinds of transports in what is called as P-OTS (Packet Optical Transport System). The P-OTS system is also called “Hybrid” network element by some vendors. According to Heavy reading predictions, by 2016 even though the majority of the traffic will be IP but the major revenues will still come from circuit switched traffic.

My take on this is that any investment into transport network element for metro area needs to be evaluated carefully by operators considering the following options:

  • Incumbent operators who have already invested in TDM equipment would like to protect their investments. To meet their growing packet needs, they would rather invest additionally in pure packet platform and have two platforms to support both their TDM and Packet needs instead of forklift upgrades to make way for hybrid platforms. This is especially true about sites which have TDM installations already. Nevertheless, such Operators must be cognizant of the long term OPEX of keeping two types equipment for the different traffic types.
  • Incumbent Operators who would like to expand to NEW sites would find investment in hybrid equipment a better alternative rather than buying two different gears to support their TDM/hybrid needs. Investment in hybrid would protect their investment when they will transition to complete packet architecture in future.
  • Greenfield operators going to install new equipment would find investment in hybrid equipment much better if they carry mixed traffic. However if the nature of services offered by the greenfield operator are completely IP based ( for example Internet and IPTV), it would be wise for the operator to invest only in pure packet based equipment which would be much cheaper in terms of CAPEX and OPEX.

Therefore, in my view, there is no one answer to what is the best type of transport equipment for metro operators. It depends on what the operator already has installed; is it doing expansion on existing sites or adding new sites and of course, on what kind of services the operator will be offering.

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6 years ago

Very informative article.

All operators these days deploying MPLS-TP ( TDMoIP or Circuit Emulation, with Packet boards) or Pure IP boxes.

Hybrid box deployments, are very rare.

Need more clarity and discussion on this

Faisal Khan
Faisal Khan
6 years ago
Reply to  Vikram

Thanks Vikram, By Hybrid box I mean OTN switch that can accept both TDM and IP interfaces. I can understand that owing to predominant IP traffic it would make sense for operators to go for MPLS-TP or Seam MPLS solutions instead of OTN switch.


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