Setting the Standards with Dr. Yaakov Stein

In this edition of "Setting the Standards" we will review the proceedings of the SG15 study group of the I hope you will find it useful and informative, and we appreciate your feedback.

Between February 6 and 17, Study Group 15 (SG15) of the ITU-T met in the ITU headquarters in Geneva. SG15 is responsible for "transport network infrastructures," including DSL, optical fiber (both physical layer and SONET/SDH protocols), and access networks. SG15 develops most of the "G" series of ITU Recommendations, in addition to a few Recommendations in the "I," "Q," "X," and "V" series. Some SG15 Recommendations have alternative titles in the "Y" series.

 

A significant number of new documents were "consented" by the Study Group plenary at this meeting, thus completing the first stage towards their publication as official ITU Recommendations. Of these, several are of particular interest to RAD. G.8261 (formerly G.pactiming) deals with timing distribution over packet switched networks. Alon Geva from the Digital Signal Processing R&D department was actively involved in the development of this Recommendation. The long awaited VDSL2 standard entitled G.993.2 was also consented, ushering in a new era in high bandwidth copper access. A trio of Recommendations on "transport MPLS" were sent for consent: T-MPLS architecture G.8110.1, T-MPLS hierarchy G.8112, and the T-MPLS equipment specification G.8121.

 

Other consented documents include: G.8001 (formerly G.vcoeth) "Terms and definitions for Ethernet Frames over Transport (EoT)"; G.8031 (formerly Y.17ethps) "Ethernet protection switching"; and G.8601 (formerly G.asm) "Architecture of service management in multi-bearer, multi-carrier environment." In addition, a large number of amendments to in-force Recommendations were also consented.

 

G.8261 deals with synchronization aspects of packet networks, in particular with requirements for synchronization when transporting TDM over Ethernet. It thus directly impacts RAD’s TDMoIP technology, specifying allowed budgets for jitter and wander when recovering TDM clocks using adaptive clock techniques such as those used in RAD’s IPmux line and RJ-020 and RJ021 TDMoIP ASICs. G.8261 contains an appendix with guidelines for testing TDMoIP clock recovery implementations, including specific test cases.

 

G.993.2 specifies VDSL2 (Very high speed Digital Subscriber Lines 2), the fastest DSL technology to date. VDSL2 supports asymmetric and symmetric transmission at bidirectional rates of up to 200 Mbps, using bandwidth of up to 30 MHz. Like ADSL, G.993.2 utilizes discrete multi-tone (DMT) modulation, but it mandates support for Trellis coding. Due to the limited reach of the technology, it is expected that the main application will be within buildings or street cabinets located in close proximity to the customer premises. The annexes of G.993.2 include band plans and power spectral density (PSD) masks that enable VDSL2 to be employed in various geographical locations.

 

MPLS was developed by the IETF in order to accelerate routers in core IP networks. For several years the ITU has been interested in adapting MPLS to make it a "carrier class" network functioning according to recognized architectural principles. The result is "Transport MPLS" (T-MPLS), which is a purely connection-oriented subset of MPLS (in contradistinction to IETF MPLS, which is hybird connectionless/connection-oriented) which prohibits certain MPLS optimizations such as penultimate hop popping (PHP), merging, and equal cost multi-path (ECMP) load balancing. Y.1711 OAM and Y.1720 protection switching are mandated. An appendix to G.8110.1 and the basic signal structure in G.8112 detail the functioning of MPLS pseudowires, referring to Recommendations Y.1411 through Y.1415 previously developed by SG13.