Contiguous+concatenation

Contiguous concatenation The technique of contiguous concatenation makes it possible to transmit signals at a higher rate than would otherwise be the case. Victoria can carry out generation and analysis at these higher rates in both SDH and SONET hierarchies.

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Contiguous concatenation Contiguous concatenation

Some of today’s technologies such as ATM require payloads of up to 600 Mbit/s, while the system used to transport different signals of this type synchronously is usually either SDH or SONET. This creates a problem since neither of these systems defines containers that are optimized for the transport of tributary signals occupying bandwidths greater than the usual VC-4 or STS-3c SPE1 capacity. For this reason, in order to transmit signals requiring these bandwidths, the contiguous concatenation mechanism is used. With Victoria, it is possible to generate and analyze STM-4/OC-12 frames at bit rates of 622 Mbit/s.

CONTIGUOUS

CONCATENATION The basic principle of contiguous concatenation involves joining four consecutive VC-4 containers together to form a single STM-4/OC-12 structure that provides a bit rate of 622 Mbit/s. The resulting STM4/OC-12 frame carries one virtual container instead of four VC-4s with their bytes interleaved, thus guaranteeing the integrity of the signal transported. The virtual container formed by concatenation is called VC-4-4c/STS12c SPE and is made up of one column for the path overhead (POH), three columns of fixed-stuff and 1040 columns for the C-4-4c container (actual payload capacity in SONET), which has a capacity of 600 Mbit/s. J1

...

B3 C2 G1 F2

VVC-4-4c C-4-Xc Fixed Stuff

H4 3x9 bytes F3 K3 N1 X -1 VC-4-4c VC -4-Xc POH

... 4X x 260 bytes

T1518490-95

ATM Cell

53 octets

Figure

1.

1

Mapping of ATM cells in VC-4-4c

SPE: Synchronous Payload Envelope

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Contiguous concatenation The pointer in concatenation

THE

POINTER IN CONCATENATION The pointers of the concatenated AU-4 take the fixed values “1001” in bits 1 to 4, bits 5 and 6 are unspecified and there are ten ones in bits 7 to 16. The concatenation indicator in these pointers is intended to show that they perform the same functions as the first AU-4 of the AU-4-4c (STS-3c SPE plus the corresponding pointers in SONET). This first pointer contains three bytes: H1, H2 and H3. Bits 1 to 4 of these bytes contain the New Data Flag (NDF) and bits 7 to 16 represent a binary number between 0 and 782, which must be multiplied by 12 for STM-4 to locate the point in the frame where the VC4-4c container begins. (The same mechanism is valid for SONET).The VC-4-4c is nested in the STM frame and the pointer value is updated. In order to keep the VC-4 containers contiguous, positive justification (the adding of stuffing bytes) is used when the VC-4 is too slow compared to the STM-1 signal, and negative justification (moving the payload forward in order to have an extra space given by H3 bytes) when the VC-4 is too fast. VC -4-4c 10

+

1040

11

J1 B3 C2 G1 F2 H4 F3 K3

Fixed stuff

NDF POH

N1

N I D

H1 Y Y H2 1 1 H3 H3 H3

Figure

2

H3

H2

H1 N N N N 1 0

I

D

I

D

I

D I

D I

Pointer value (10 bits)

D Possibility of negative justification

: New Data Flag (NDF) bit : increasing bit : decreasing bit

NDF activated:

Y: 1011SS11 (SS bits not specified)

Possibility of positive justification

1

0

0

1

NDF deactivated :

0

1

1

0

1: 11111111

Inside the pointer bytes

The pointer of the STM-4 frames follows a logical multiplexing process whereby parts of the pointers are multiplexed byte by byte. Victoria lets you work at 622Mbit/s in SDH and SONET with VC-4-4c or STS-12c SPE or by mapping up to the STM-4/OC-12 frame. This makes it possible to perform a range of tests over 622 Mbit/s, such as transparency tests over bulk-loaded C-4-4c/STS-12c SPE payload capacity and overhead channels. Likewise, mux/demux tests, pointer actions/sequences, detection/insertion of errors and alarms or the

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programming/visualization of overheads can all be carried out at 622 Mbit/s. STM -0 (SO N ET STS-1)

STM -1 (SO N ET STS-3c)

STM -4

H1

H2 3 bytes

H1

Y

Figure

3

Y

H2

H1

.......

Y

1

1

H3

3 bytes

3 bytes

(SO N ET O C -12)

Figure

x 3 frames

H3

Y

12 bytes

H2

H3

H3

x 4 frames

3 bytes

1

....... 12 bytes

1

H3

H 3 ....... H 3 12 bytes

Pointers in STM/STS frames

4

Multiplexing up to STM-4 with Victoria

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