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All drawings appearing in this Recommendation have been done in Autocad.
Recommendation Q.512
EXCHANGE INTERFACES FOR SUBSCRIBER ACCESS
1 General
This Recommendation applies to digital local and combined exchanges for
telephony in Integrated Digital Networks (IDN) and mixed (analogue/digital)
networks, and also to local and combined exchanges in Integrated Services Digital
Networks (ISDN). The field of application of this Recommendation is more fully
defined in Recommendation Q.500.
2 Scope of Recommendation
Exchange interfaces for subscriber access that have been considered are
described, and illustrated in Figure 1/Q.512 and Table 1/Q.512, but it is not
intended to specify every interface. Other interfaces are for further study
(e.g., those for dynamic multiplexed basic rate access, broadband access, etc.).
FIGURE 1/Q.512 - T1108841-88
TABLE 1/Q.512
Interface references
Access type Interface Paragra Related Related OAM Application to
/referenc ph physical Recs. connect
e points Recs.
Basic access V1 3.2 (Note 1) G.960 (Note 1) ISDN basic
digital section I.603 access
(2B + D)
Generic digital V2 3.3 None Digital network
section equipment,
supporting any
combination of
access types
Generic V3 3.4 G.703 G.706 I.604 Digital
subscriber G.704 (Note 3) subscriber
access (Note 2) G.705 equipment
digital section
Digital access
Fascicle VI.5 - Rec. Q.512 PAGE1
link (Static V4 3.5 G.706 A multiple of
multiplex) I.605 ISDN basic
accesses
Generic analogue Z 4.1 None (Note None Analogue
subscriber 4) subscriber lines
access
Note 1 - Recommendation G.961 specifies the characteristics of a digital transmission
system on metallic local lines which may form part of the basic access digital selection.
Note 2 - In the case of ISDN access this is the primary rate access digital section.
Note 3 - Only in the case of ISDN application, G.706 and I.604 are recommended.
Note 4 - Characteristics other than those defined in Recommendations Q.551 to Q.554 are
not subject of CCITT Recommendation.
This Recommendation is not intended to define any transmission system,
network or subscriber equipment in or connected to, a digital exchange via these
interfaces. Therefore only the characteristics of the interfaces are described.
Digital exchange interfaces for subscriber access are defined at the V
reference point which is the boundary between the ET and the digital access
section or link. These interfaces are designated interface V and are defined to
allow flexibility of implementation for different exchange and transmission
equipment realizations. However, a physical interface will not be specified for
all subscriber access types identified (see Figure 1/Q.512).
In this Recommendation, a digital section is defined as the whole of the
means of digital transmission of a digital signal of specified rate between two
consecutive reference points. A digital link comprises one or more digital
sections and may include either a multiplexer or concentrator, but not switching.
3 Characteristics of digital exchange interfaces for subscriber
access
3.1 General
As an objective, the characteristics of digital interfaces on the
subscriber side of the exchange should be aligned with the characteristics of
ISDN user/network access structures (Recommendation I.411).
However in many countries, digital access arrangements not structured
according to ISDN principles are used, e.g., to ensure compatibility with
existing networks and services and it is expected that these arrangements will
continue to be used for several years. Only certain characteristics of these
arrangements are the subject of CCITT Recommendations.
3.2 Interface V1
3.2.1 General
Interface V1 may be used at the V1 reference point to connect to an ISDN
basic access digital section for the provision of a single basic access. The
characteristics of the basic access digital section are defined in Recommendation
G.960 and the characteristics and parameters of a digital transmission system
which may form part of the digital section for the ISDN basic rate access are
given in Recommendation G.961.
3.2.2 Functional characteristics
The functional description is illustrated in Figure 2/Q.512 and the
following functional requirements are defined:
1) (2B + D) channels
To provide the bidirectional transmission capability for two B channels
and one 16 kbit/s D channel as described in Recommendation I.412.
2) Bit timing
To provide bit (signal element) timing to enable the digital section to
recover information from the aggregate bit stream.
3) Frame timing
To provide frame timing to enable digital section and ET to recover the
time division multiplexed channels.
4) CV1 channel
The CV1 channel provides, for each direction of
transmission, the capability to transfer management
functions required for the digital section as specified in
Recommendations G.960 and I.603. The CV1 channel may carry
one or more functional links. These functions include
activation from network side, activation from network side,
activation request from a digital section, deactivation
from ET side, operation and maintenance signals.
PAGE2 Fascicle VI.5 - Rec. Q.512
5) Power feed
This function provides for remote power feeding for the
digital section and possibly terminal equipment. This
function is optional.
3.2.3 Electrical characteristics
The electrical characteristics of interface V1 are not subject to CCITT
Recommendations.
3.2.4 Channel types, channel allocation and signalling
The channel types associated with interface V1 include two B channels and
one D channel as defined at the user network interface in Recommendation I.412.
In addition, the CV1 channel is required to support the operational and
maintenance functions.
The channel allocation is not subject to CCITT Recommendations.
The D channel signalling procedures are defined in the Q.920 and
Q.930-Series Recommendations.
Figure 2/Q.512 - T1107731-88
3.3 Interface V2
3.3.1 General
Interface V2 is a generic digital interface used to connect remote or
local digital network equipment via a first or second order digital section. This
network equipment may support any combination of analogue, digital and ISDN
subscriber access. The characteristics of this interface may not be structured
according to the ISDN principles.
3.3.2 Functional characteristics
The functional characteristics depend on the specific application of the
V2 interface. These are not generally subject to CCITT Recommendations.
3.3.3 Electrical characteristics
The electrical characteristics of interface V2 are described in
Recommendation G.703.
The basic frame structure at interface V2 should be identical to that of
the first or second order rate multiplexes described in Recommendations G.704 and
G.705.
3.3.4 Channel types, channel allocation and signalling
The channel types, channel allocation and signalling depends on the
specific application of the V2 interface. These are not generally subject to
CCITT Recommendations.
3.4 Interface V3
3.4.1 General
Interface V3 is a digital interface used to connect digital subscriber
equipment (e.g., PABX) via a generic digital subscriber section. The
characteristics of this interface may not be structured according to the ISDN
principles. In this case, only the electrical characteristics defined in S 3.4.2
are recommended. However, in the case of ISDN where interface V3 is used to
connect a primary rate access digital section for the provision of a single
primary rate access, all of the following characteristics apply.
3.4.2 Functional characteristics
The use of the Cyclic Redundancy Check (CRC) procedures described in
Recommendations G.704 and G.706 is recommended. The information on the status of
the CRC processing shall be passed across the V3 interface. The maintenance
procedures are defined in Recommendation I.604.
3.4.3 Electrical characteristics
The electrical characteristics of interface V3 are described in
Recommendation G.703.
The frame structure at interface V3 should be identical to that described
in Recommendations G.704 and G.705.
3.4.4 Channel types, channel allocation and signalling
The channel types and allocation associated with interface V3 are 30 B + 1
D at 2048 kbit/s or 23 B + 1 D at 1544 kbit/s as described in Recommendation
I.431.
The channel allocation should also consider that:
a) when the signalling for the B channels in one primary rate structure is
carried by the D channel in another primary rate structure, the channel
timeslot normally used for signalling may be used to provide an
additional B channel;
Fascicle VI.5 - Rec. Q.512 PAGE1
b) at interface V3 the designated number of B channels is always present
within the multiplexed channel structure, but one or more of the B
channels may not be used in any given application.
The D channel signalling procedures are defined in the Q.920 and
Q.930-Series Recommendations.
3.5 Interface V4
3.5.1 General
Interface V4 is a digital interface used to connect a digital access link
which includes a static multiplexer supporting several basic access digital
sections. The local digital multiplexer application is considered to be a subset
of the remote digital multiplexer application.
3.5.2 Functional characteristics
The functional description is illustrated in Figure 3/Q.512 and the
following functional requirements are defined:
- m x (2 B + D + CV1): to provide the bidirectional transmission
capability for the B, and D, CV1 channels from each basic rate access
section.
- Timing: to provide the necessary timing information for bit
transmission, frame synchronization and subscriber line
synchronization.
- Operations and maintenance: to provide the transmission capability to
carry the operation and maintenance signals of the digital link and the
basic access muldex as defined in I.605.
Figure 3/Q.512 - T1106942-88
The use of the Cyclic Redundancy Check (CRC) procedures described in
Recommendations G.704 and G.706 are recommended. The information on the status of
the CRC processing shall be passed across the V4 interface.
3.5.3 Electrical characteristics
The electrical characteristics of interface V4 are described in
Recommendation G.703.
The basic frame structure at interface V4 should be identical to that of
the first order multiplexes described in Recommendations G.704 and G.705.
3.5.4 Channel types, channel allocation and signalling
3.5.4.1 General
The V4 interface is composed of a number of individual ISDN basic rate
access digital sections, as described in S 3.2.
The channel allocation at interface V4 is defined within a first order
structure using a static multiplexing principle as follows:
3.5.4.2 Static multiplexed at 2048 kbit/s
3.5.4.2.1 Channel allocation
In this case 12 basic access channels are multiplexed in a static manner
using fixed allocation of the channels. Figure 4/Q.512 illustrates the channel
allocation for 2048 kbit/s, where 24 channel timeslots are used by B1 and B2
channels and 6 channel timeslots are used by the D and CV1 channels of the 12
basic accesses.
The CV1 and D channels of two basic accesses are multiplexed into one
channel timeslot. Five contiguous channel timeslots are occupied by two basic
accesses each consisting of B1 + B2 + D + CV1 channels.
Channel timeslot 0 is used for frame alignment including the application
of CRC4 according to Recommendation G.704. Additionally, the alarm handling
facilities of channel timeslot 0 are used for maintenance of the primary link as
described in Recommendation I.605.
According to the channel allocation shown in Figure 4/Q.512, the CV1
channels are located in timeslots 5, 10, 15, 21, 26 and 31. These represent 8
bits, namely two bits for each of the D and CV1 channels of two basic accesses.
Channel timeslot No. Contents
0 Frame alignment signal/Remote service
alarm indication. (See Recommendation
G.704)
1 B1,1
2 B2,1
3 B1,2
4 B2,2
5 D1, CV11, D2, CV12
6 B1,5
7 B2,5
PAGE2 Fascicle VI.5 - Rec. Q.512
8 B1,6
9 B2,6
10 D5, CV15, D6, CV16
11 B1,9
12 B2,9
13 B1,10
14 B2,10
15 D9, CV19, D10, CV110
16 Not used
17 B1,3
18 B2,3
19 B1,4
20 B2,4
21 D3, CV13, D4, CV14
22 B1,7
23 B2,7
24
Fascicle VI.5 - Rec. Q.512 PAGE1
B1,8
25 B2,8
26 D7, CV17, D8, CV18
27 B1,11
28 B2,11
29 B1,12
30 B2,12
31 D11, CV111, D12, CV112
B1,i B1 channel of basic access i
B2,i B2 channel of basic access i
Di D channel of basic access i
CV1i Control CV1 channel of basic access i
FIGURE 4/Q.512
Channel allocation at the V4 interface for 2048 kbit/s
3.5.4.2.2 CV1 channel structure
To facilitate separate treatment of bundles of two basic accesses,
represented by five 64 kbit/s channels, multi-frame alignment should be performed
individually for each bundle. The relevant overhead information should be
contained in the CV1 channels. CV1 channel structure is for further study.
The D channel signalling procedures are defined in the Q.920 and
Q.930-Series Recommendations.
3.5.4.3 Static multiplexed 1544 kbit/s
For further study.
4 Characteristics of analogue exchange interface for subscriber
access
4.1 Interface Z
Interface Z is a generic analogue interface defined at the exchange side
of an analogue subscriber line used to connect subscriber equipment (e.g., single
telephone set or PABX).
It is recognized that the characteristics of analogue interfaces
(generally designated Z interface) vary considerably from country to country and
therefore it is not intended that those interfaces be the subject of CCITT
Recommendations beyond those aspects covered in Recommendations Q.551/552.
5 Combined digital and analogue interface for subscriber access
In the evolution towards an ISDN, user network accesses may exist which
have a combination of both analogue and digital interfaces.
This type of interface is not presently considered to be a matter for
CCITT Recommendations.
PAGE2 Fascicle VI.5 - Rec. Q.512
