RE: Simple solution to terminate the discussion about SONET versus SDH

[Heiles Juergen <Juergen.Heiles@icn.siemens.de>]

I wanted to add some clarifications to my "YES", but Steve did it first.

Both SONET and SDH have Options like the 16 or 64 byte trace for the J1. SDH defines the 16 byte trace as a must when crossing international borders or operator domains, if not mutual agreed otherwise by the involved operators and it allows the 64 byte trace within national networks and operator domains.
Also the "SONET enhanced RDI" is described as an option for SDH in an Appendix of G.707.
 
If you want to have interworking even within a "SDH or SONET network" you have to consider these options. A general selection between SDH and SONET doesn't help at all.

Regards

Juergen

> -----Original Message-----
> From: Stephen Trowbridge [mailto:sjtrowbridge@lucent.com]
> Sent: Tuesday, February 26, 2002 4:22 PM
> To: Mannie, Eric
> Cc: 'Heiles Juergen'; 'mvissers@lucent.com'; Wijnen, Bert (Bert);
> 'vijay@umbc.edu'; ccamp-wg; 'sob@harvard.edu'; 'Kireeti Kompella'
> Subject: Re: Simple solution to terminate the discussion about SONET
> versus SDH
> 
> 
> Eric,
> I don't think you ask quite the right question.
> The right question is:
> Can all frame structures which are common to SONET and SDH be 
> interconnected,
> and do they interoperate? This is what we care about from the 
> viewpoint of
> establishing switched connections.
> The answer to this is YES.
> 
> Are they fully identical from all points of view? As Juergen 
> says, this is the
> tricky question, as the answer of "No" might mislead some 
> into thinking that
> these signals cannot be interconnected between SONET and SDH. 
> This is not
> the case.
> 
> For those who care, some of the key differences are as 
> follows. Note that these
> do NOT affect the ability to interconnect these signals 
> (although sometimes there
> are rules about HOW to interconnect them).
> 
> SS bits - In the past, this was an issue in the high order 
> pointers. SDH sent
> and expected "10", for SONET these bits were unspecified. 
> This problem was corrected
> a few years ago by requiring that ALL equipment send "10" and 
> ignore the incoming
> bits. Note that even prior to aligning the standards, a great 
> deal of the older
> equipment followed this strategy as VC-4s and STS-3cs were 
> interconnected long
> before the standards alignment.
> 
> Trace identifier - For J1, within SONET, a 64 byte format is 
> normally used. For SDH,
> a 16 byte format is normally used. SONET specifies that in 
> the case that the far end
> is SDH, a 16 byte format should be used to allow 
> interworking. For J2, this is normally
> used in SDH and not normally in SONET. Interworking is 
> acheived by having the SDH end
> ignore the incoming trace identifier (a required capability 
> in the standards).
> 
> RDI - SONET uses some extra bits that are reserved in SDH to 
> further classify far end
> alarms (called ENHANCED RDI). This provides no obstacle to 
> interworking: The SONET
> side will not be able to provide a more detailed 
> classification of SDH end alarms (it
> does know there is a far end alarm). The SDH end ignores the 
> extra bits. The Enhanced
> RDI feature only operates if both ends are SONET.
> 
> BIP - The coding for BIP is identical. The way degrade is 
> detected is different.
> SONET generally uses a Poisson algorithm to declare degrade 
> and SDH normally uses
> a bursty error detection algorithm. This provides no obstacle 
> to interconnect - the
> criteria for declaring dDEG is just slightly different. Also, 
> SONET provides an
> EXC alarm for BER > 10^-3 which does not appear in SDH. This 
> also does not prevent
> interconnect - you just have an alarm which can be declared 
> at one end and not the
> other.
> 
> These are the major differences (besides the fact that SONET 
> and SDH tend to have
> different names for identical things- This is just a 
> US/Europe language issue).
> Regards,
> Steve
> 
> "Mannie, Eric" wrote:
> > 
> > Dear All,
> > 
> > There is an easy way to stop definitively this discussion 
> based on technical
> > facts:
> > 
> > Stephen, Juergen and Maarten, please tell us: today, are the frame
> > structures and all the bytes in the SDH and SONET overhead 
> completely
> > identical, used and interpreted in the same way, is the 
> monitoring exactly
> > the same ? In particular, if I provision and operate an SDH 
> circuit/LSP is
> > this fully identical to a SONET circuit/LSP from *all* 
> point of views ?
> > 
> > PLEASE ANSWER BY YES OR NO ONLY. Other explanations are not 
> needed at this
> > stage.
> > 
> > If the answer is yes: SONET is totally identical to SDH.
> > If the answer is no: SONET is not the same as SDH.
> > 
> > I think that without that answer we cannot take any 
> *technical* decision on
> > this mailing list and at the IETF.
> > 
> > Thanks to answer.
> > 
> > Kind regards,
> > 
> > Eric
> > 
> > ps: feel free to forward this e-mail to any ITU-T mailing list if a
> > confirmation is needed.
>