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Community Member

NEWPTRs, NSEs and PSEs at same rate

Some of our 7200 VXR routers, connected to the same type of SDH-ADMs by OC3 POS-adapters, continously count NEWPTR events at (almost) the same rate as NSEs and PSEs:

sh contr pos4/0

POS4/0

SECTION

LOF = 0 LOS = 0 BIP(B1) = 0

LINE

AIS = 0 RDI = 0 FEBE = 0 BIP(B2) = 0

PATH

AIS = 0 RDI = 0 FEBE = 0 BIP(B3) = 0

PLM = 0 UNEQ = 0

LOP = 0 NEWPTR = 23643175 PSE = 23643174 NSE = 23643175

...

Does anyone know what could cause this?

My assumption is that these routers see concatenation indicators - although i don't know where they come from.

The only explanation i have is that they are generated in our providers SDH/Sonet ring (by concatenting VCs for diagnosis purposes etc.).

Is there a possibility to get a dump of a SDH frame from the router CLI in order to inspect the overheads?

2 REPLIES
Silver

Re: NEWPTRs, NSEs and PSEs at same rate

NSE/PSE (Negative/Positive Stuff Events) indicate that at some point along

the path, the payload on the STS3c was shifted to adjust for a timing

differences on the lower speed (OC-3) tributary and the higher-speed

(OC12-192) path. A NSE occurs when the incoming bitrate on the tributary is

too high for the read clock (the clock that reads data from an inbound

tributary to place the bitstream on the higher speed path) to process the

previous byte before the write clock fills the write buffer with the inbound

stream. Thus, it stuffs last byte received into a reserved position in the

LOH for negative stuffs, and adjusts the pointer values to reflect the the

change in position of the beginning of the SPE. The opposite is true if the

data is coming in to slow. It inserts dummy bits into the higher stream to

account for the "missing" bits because the inbound stream was too slow. To

summarize:

1) The LOH for each STS-3c contains two bytes (H1 & H2) that define the

location of the beginning of the SPE (the payload and the path overhead).

The first 4 bits in H1 are the New Data Flag bits and are used to detect a

malformed pointer value or an invalid pointer operation. Bits 5 and 6 are

reserved and set to 0. Bits 7-15 define the pointer value, which is any

number between 0 and 782. Note that the for concatenated signals, the

pointer vlaue is multiplied by the number of STS-1s concatenated (IE STS-3c,

12c, 48c, 192c, etc). This allows for 10 bit pointer values to be able to

address thousands of byte positions in the SONET frame. Finally, 5 bits of

the 10 are defined as decrement bits, and 5 as increment bits, in an

alternating fashion as such:

IDIDIDIDID

Under nominal operation, the payload (SPE) is somewhere offset from the

end of the LOH. The number of bytes offset from the H3 byte is the pointer

value.

If the incoming rate is too slow, n dummy bytes must be stuffed into the

STS-3n. In your case, it is an STS-3c and thus, three dummy bytes are

stuffed following the last of the three H3 bytes in the LOH. Remember,

STS-3c operates just like STS1 except times everything by three. As such,

the LTE inverts the I bits from their previous value to indicate a positive

stuff shall occur in the next frame. Then, the new pointer value is sent,

incremented by one. No change in this value can occur for the next three

frame. Any such change is regarded as a pointer violation and an LOP

condition is set.

If the rate comes in to the multiplexing equipment too fast, 3 bytes from

the STS-3c must be stuffed into the three H3 bytes in the LOH, and the

pointer value must be decremented by one. But first, the D bits are

inverted to indicate a negative stuff event is occurring. Then, the pointer

is adjusted, the D bits inverted back (inversion meands flip from 0 to 1 and

vice versa), and the pointer vlaue is decremented. Again, no change may

occur for three consecutive frames.

Finally, if there is any reason for the pointer value to change other

than for positive or negative stuff, the new pointer must be sent with the

NDF bits set to 1001. Again, this value cannot change for three consecutive

frames.

What you are seeing is a timing problem. If the routers are back-to-back,

set the clock source to internal on both of them. This sounds odd, but

there is a problem in the POS chipsets on PA-POS-OC3 cards such that this is

the only stable method. If they are through and ADM, check that your

carrier has the circuit optioned properly

Community Member

Re: NEWPTRs, NSEs and PSEs at same rate

Thank you for your really detailed explanation of the the Sonet/SDH pointers, the bit stuffing and the context when these mechanisms get applied.

But I knew these principles already.

My question was, what it means when all the 3 counters increase synchronously: with every newptr event I always get a NSE and PSE too!

This obviously can't mean a positive and negative stuffing and a pointer change due to another event at the same time.

But what does it mean then?

Our provider checked their equipment and confirmed that there is no synchronisation problem!

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