Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1999-02-11
2004-10-19
Rao, Seema S. (Department: 2666)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
Reexamination Certificate
active
06807194
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a radio terminal station apparatus for an SDH network, particularly to a method of selecting an operation clock in a radio terminal station apparatus for an SDH communication connected to a wired transmission line or a wireless transmission line.
(ii) Description of the Related Art
SDH (Synchronous Digital Hierarchy) is a standard established for standardizing synchronous networks, and its details are regulated by ITU-T or the like.
FIG. 6
is a view showing the structure of an STM-1 frame in an SDH frame structure. The STM-1 frame consists of an SOH (Section Over Head) consisting of a frame synchronization, a parity of a transmission line, a transmission line for maintenance data and so on, an AU pointer for indicating the head of a data signal sequence when changing clocks, a payload that is a data signal sequence, and so on.
Besides, an S1 byte in the SOH is defined for transmitting a quality that is the quality of a clock in a synchronous network. The quality indicated by the S1 byte is defined by ITU-TG.707 or the like. By extracting the quality Q from the S1 byte in the SOH, the quality of the clock of a transmission line can be known.
FIG. 7
shows an example of the contents of this quality Q.
Besides, in the SDH network, synchronization of the whole of the network is necessary for keeping the quality of the network high, and the clock source that is the origin of the synchronous network becomes important. For this reason, there is a case that, in addition to a primary clock supply source of the highest quality, a secondary clock source is provided for use when a trouble arises on this primary clock source and it can not be used, and the primary and secondary clock sources are switched over with the quality in the S
1
byte. At this time, for the secondary clock, a clock source of a lower quality than the primary clock is mostly employed for an economical reason or the like.
Further, each NE (Network Element: synchronous terminal station apparatus) mostly has an internal clock source that is used when either of the primary and secondary clock sources can not be used. Besides, in apparatus for transmitting data signal sequences including SDH frames, there are transmission terminal station apparatus that make communications through wired transmission lines such as optical cables and radio terminal station apparatus that are connected to such transmission terminal station apparatus and make communications through wireless transmission lines.
FIG. 8
shows an example in which an SDH network is built with such transmission and radio terminal station apparatus. In
FIG. 8
, NE
1
, NE
2
, NE
7
and NE
10
denote transmission terminal station apparatus, and NE
3
, NE
4
, NE
5
, NE
6
, NE
8
and NE
9
do radio terminal station apparatus. U
1
denotes a primary clock source that is the origin of an ordinary SDH synchronous network, and U
2
does a secondary clock source.
Besides, it is the example in which the network construction branches into two directions at the wired transmission lines from NE
4
to NE
5
and NE
8
. Further, each of SYS
1
and
2
has a set of up-link or down-link data signal sequences including SDH frames, and MUX denotes a multiplexer, and DMR does a digital microwave radio equipment. As understood from
FIG. 8
, in a wireless transmission line, data signal sequences of plural system are transmitted and received through a single antenna in general, so the network never branches at the wireless line.
By the way, although it was above described that, when the SDH network is constructed, the whole of the network is synchronized, and a case that a trouble arises on the clock of the origin of synchronization, or the like is dealt with by switching over, at this time, if opposed apparatus are synchronized with line clocks from opposite directions, respectively, a loop is generated in the clock synchronization construction, as a result, the network synchronization construction breaks. This operation is called timing loop. For preventing this operation, in the S
1
byte indicating the clock quality, as shown in
FIG. 7
, “Don't use for sync” of Q=F is defined, and the line clock of the route on which Q=F is detected is not used as the clock in the apparatus.
A conventional radio or transmission terminal station apparatus has clock selection means in which a process of a flowchart shown in
FIG. 9A
or
9
B is carried out as a method of determining a quality to insert.
FIG. 9A
shows a flowchart used when the transmission directions of the whole system are the same like radio terminal station apparatus. In this flowchart, when the clock in the apparatus is generated from a line clock, Q=F on the qualities to multiplex on all systems in which the direction of multiplexing the qualities is opposite to the line clock that was the origin of the clock in the apparatus.
FIG. 9B
shows a flowchart used in a transmission terminal station apparatus or the like, wherein, in case that the clock in the apparatus is generated from a line clock, Q=F is multiplexed only when the direction of multiplexing the qualities is opposite to the line clock that was the origin of the clock in the apparatus and the system is the same route.
Next, operations of the SDH network constructed with conventional radio terminal station apparatus having the process flowchart of
FIG. 9A
will be described with reference to
FIGS. 10A and 10B
. In
FIGS. 10A and 10B
,
FIG. 10A
shows synchronization of clocks in a stationary state. In this
FIG. 10A
, line clocks of both routes of (NE
1
→NE
2
→NE
3
→NE
4
) and (NE
1
→NE
2
→NE
5
→NE
6
) all are synchronized with the output clock of U
1
. Here, (NE
1
→NE
2
) denotes direction of clock signal transmitted from NE
1
to NE
2
. All of multiplexed qualities of routes of (NE
4
→NE
3
→NE
2
→NE
1
) and (NE
6
÷NE
5
→NE
2
→NE
1
), which are in the opposite directions of the above routes, are Q=F. P denotes a priority showing the degree of priority, and shows information on the degree of priority assigned to each clock of the input port part of SYS
1
and
2
or the like of each apparatus, respectively.
Here, as shown in
FIG. 10B
, supposing a case that a trouble or the like arises on the output clock of U
1
and it can not be used, all line clocks of route of (NE
4
→NE
3
→SYS
1
of NE
2
→NE
1
) are synchronized with the secondary clock of U
2
. However, in NE
2
, because the line clock from NE
3
becomes the clock in the apparatus, the quality sent out from SYS
2
of NE
2
to NE
5
becomes the quality of Q=F for inhibiting a timing loop. Thereupon, in NE
5
, because the quality from the SYS
2
of NE
2
is Q=F, it can not be used as the clock in the apparatus and it operates with the internal clock of the highest quality in the apparatus. Accordingly, NE
6
is also synchronized with the internal clock of NE
5
, and NE
5
and NE
6
operate separately from the conventional synchronous network.
Successively, operations of the SDH network constructed with conventional radio terminal station apparatus having the process flowchart of FIG.
9
A and conventional transmission terminal station apparatus having the process flowchart of
FIG. 9B
will be described with reference to
FIGS. 11A
to
11
D.
FIG. 11A
shows synchronization of clocks in a stationary state. In
FIG. 11A
, all line clocks of route of (NE
1
→NE
2
→NE
3
) are synchronized with the output clock of U
1
, and all multiplexed qualities of route of (NE
3
→NE
2
→NE
1
), which are in the opposite direction of the above route, are Q=F.
In this state, like
FIG. 11B
, supposing a case that a trouble arises on the output of U
1
, because the clock having the highest quality in NE
1
is the internal clock, line clocks of route (NE
1
→NE
2
→NE
3
) are once synchronized with the internal clock of NE
1
. Thereupon, in NE
3
, because the clock having th
Harper Kevin C.
NEC Corporation
Rao Seema S.
Young & Thompson
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