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Re: [HSSG] Yet another topic for consideration - bit parallel

Title: Yet another topic for consideration - bit parallel



Regarding your question on serial implementations:


The state of the art, as far as I know, on higher speed serial transmission modules which are commercially available today, is 40 Gb/s (see OC-768 ports on core routers).


A typical device of this type, used for relatively short distances, has an SFI-5 interface (OIF spec) which is 16 x 2.5 Gb/s with the proper de-skew mechanisms on the system side, connecting on a PCB to a SONET framer (or in principle could connect to an Ethernet MAC chip). On the optical side it is 40 Gb/s serial.


Inside such modules you will typically find Silicon-Germanium (SiGe)  Serializer and Deserializer chips which have a 40 Gb/s electrical interface. The serial 40 Gb/s Tx electrical signal drives an optical modulator (e.g. Electro-Absorption-Modulator or EAM) and hence generates the serial optical bit stream at 40 Gb/s. The 40 Gb/s optical Rx signal goes into a PIN diode which connects electrically to a preamplifier or directly into the Deserializer.


Modules of this type usually run with NRZ data. Some of these modules can run as high as 43 Gb/s which allows the application of Forward Error Correction techniques prior to the SFI-5 interface on the system side (which becomes 16 x 2.7 Gb/s) and thus adding 3 – 6 dB to the link budget (depending on the type of FEC used).


The market inputs we received in the pre-CFI phase indicated strong preference for HSSG to go higher than 40Gb/s. If that input will stay consistent in the next few months we will have to go to “multiple lanes” (Physical Link Aggregation). The question is how many lanes and at what speed....






From: Kevern, James D [mailto:james.kevern@xxxxxxxxxxxxxxxxxxx]
Sent: Wednesday, August 02, 2006 10:05 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: [HSSG] Yet another topic for consideration - bit parallel


Along with a previous suggestion that we become more educated on the problems associated with n x 10G LAG implementations, I, for one, would like to better understand the concerns regarding what I'll call bit parallel vs serial implementations.  There was an earlier post indicating MAC implementations might be in the order of 64 wide, maybe even 128.  So at the one extreme, one could envision a parallel connection 64 wide, at the other extreme is time division multiplexing this down to a single serial stream.  Note, that for this discusion, it does not matter whether the parallel paths are accomplished by individual cables, individual fibers in one cable, different wavelengths on a single fiber, or even individual traces on a backplane.  As has been mentioned, there are various possibilities in between the extremes, such as 10x 10 Gig, N x M, etc.

There are, of course, the obvious cost and reliability issues of number of sources, detectors, fibers, connectors, space constraints, etc.  But what about performance issues such as latency and throughput.  How would bit parallel differ from LAG?  Are there other issues as well?

This is a specific case of what could be considered a broader topic related to how we organize our work.  In addition to, as Menachem suggested, prioritizing application spaces, perhaps building a knowledge foundation, whether through postings here, tutorial presentations, links to web sites, etc. could be an early part of the effort.


Jim Kevern
Principal Engineer - Applications
Fiber Optics Business Unit
tyco / Electronics

( phone: 717-986-5701
2 fax: 717-986-5449
: e-mail : james.kevern@xxxxxxxxxxxxxxxxxxx

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