Bits

8

7

6

5

4

3

2

1

Octets

Low layer compatibility Information element identifier

0

1

1

1

1

1

0

0

1

Length of the low layer compatibility contents

2

0/1 ext.

Coding standard

Information transfer capability

3

1 ext.

Negot.
indic.

0

0

0

0
Spare

0

0

3a*

1 ext.

Transfer mode

Information transfer rate

4

1 ext.

Rate multiplier

4.1*
(Note 1)

0/1 ext.

Layer 1 ident.

User information layer 1 protocol

5*

0

1

0/1 ext.

Synch./
asynch.

Negot.

User rate

5a*
(Note 2)

0/1 ext.

Intermediate rate

NIC on
Tx

NIC on
Rx

Flow control

Flow control

0
Spare

5b*
(Note 3)

0/1 ext.

Hdr/no
Hdr

Multiframe

Mode

Negot. LLI

Assignor/
Assign or ee

In-band negot.

0
Spare

5b*
(Note 4)

0/1 ext.

Number of stop bits

Number of data bits

Parity

5c*
(Note 2)

1 ext.

Duplex
mode

Modem type

5d*
(Note 2)

0/1 ext.

layer 2 ident.

User information layer 2 protocol

6*

1

0

0/1 ext.

Mode

Spare

Q.933 use

6a*
(Note 5)

0

0

0

1 ext.

User specified layer 2 protocol information

6a*
(Note 6)

1 ext.

Window size (k)

6b*
(Note 5)

0/1 ext.

layer 3 ident.

User information layer 3 protocol

7

1

1

1 ext.

Optional layer 3 protocol information

7a*
(Note 8)

0/1 ext.

Mode

Spare

7a*
(Note 7)

0

0

0

0

0

0/1 ext.

Spare

Default packet size

7b*
(Note 7)

0

0

0

1 ext.

Packet window size

7c*
(Note 7)

0 ext.

Spare

Additional layer 3 protocol information
(most significant bits)

7a*
(Note 9)

0

0

0

1 ext.

Spare

Additional layer 3 protocol information
(most significant bits)

7b*
(Note 9)

0

0

0

Coding standard (octet 3)

bits

7 6

0 0

CCITT standardized coding, as described below

0 1

ISO/IEC standard (Note 1)

1 0

National standard (Note 1)

1 1

Standard defined for the network (either public or private) present on the network side of the interface (Note 1)

Note 1 - These other coding standards should only be used only when the desired low layer compatibility cannot be represented by CCITT-standardized coding.

Information transfer capability (octet 3)

Bits

5 4 3 2 1

0 0 0 0 0

Speech

0 1 0 0 0

Unrestricted digital information

0 1 0 0 1

Restricted digital information

1 0 0 0 0

3.1 kHz audio

1 0 0 0 1

Unrestricted digital information with tones/announcements (Note 2)

1 1 0 0 0

Video

All other values are reserved.

Note 2 - Unrestricted digital information with tones/announcements (UDI-TA) is the new information transfer attribute value that had previously been named "7 kHz audio" in Recommendation Q.931 (1988).

Negotiation indicator (octet 3a)

Bits

7

0

Out-band negotiation not possible

1

Out-band negotiation possible

Note 3 - See Annex J for description of low layer compatibility negotiation.

Note 4 - When octet 3a is omitted, "out-band negotiation not possible" shall be assumed.

Transfer mode (octet 4)

Bits

7 6

0 0

Circuit mode

1 0

Packet-mode

All other values are reserved.

Information transfer rate (octet 4)

Bits

5 4 3 2 1

Circuit mode

Packet-mode

0 0 0 0 0

-

This code shall be used for all packet calls

1 0 0 0 0

64 kbit/s

-

1 0 0 0 1

2 × 64 kbit/s

-

1 0 0 1 1

384 kbit/s

-

1 0 1 0 1

1536 kbit/s

-

1 0 1 1 1

1920 kbit/s

-

1 1 0 0 0

Multirate (64 kbit/s base rate)

All other values are reserved.

Note 5 - When the information transfer rate 2 × 64 kbit/s is used the coding of octets 3 and 4 refer to both 64 kbit/s channels.

Note 6 - Additional attributes are defined in Table 4-17.

Rate multiplier (octet 4.1)

Coded as a binary representation of the multiplier to the base rate. The multiplier can take any value from 2 up to the maximum number of B-channels available on the interface.

User information layer 1 protocol (octet 5)

Bits

5 4 3 2 1

0 0 0 0 1

CCITT standardized rate adaption V.110 [7] and X.30 [8]. This implies the presence of octet 5a and optionally octets 5b, 5c and 5d as defined below.

0 0 0 1 0

Recommendation G.711 [10] m-law.

0 0 0 1 1

Recommendation G.711 A-law.

0 0 1 0 0

Recommendation G.721 [11] 32 kbit/s ADPCM and Recommendation I.460 [15].

0 0 1 0 1

Recommendations H.221 and H.242.

0 0 1 1 1

Non-ITU-T standardized rate adaption. This implies the presence of octet 5a and, optionally, octets 5b, 5c and 5d. The use of this code point indicates that the user rate specified in octet 5a is defined by the user. Additionally, octets 5b, 5c and 5d, if present, are defined consistent with the user specified rate adaption.

0 1 0 0 0

ITU-T standardized rate adaption V.120 [9]. This implies the presence of octets 5a and 5b as defined below, and optionally octets 5c and 5d.

0 1 0 0 1

ITU-T standardized rate adaption X.31 [14] HDLC flag stuffing.

All other values are reserved.

Note 7 - If the transfer mode is "circuit mode" and if the information transfer capability is "unrestricted digital information" or "Restricted digital information", and if a specific user information layer 1 protocol is to be identified to the addressed entity octet 5 shall be present. If the transfer mode is packet mode, octet 5 may be omitted.

Synchronous/Asynchronous (octet 5a)

Bit

7

0

Synchronous data

1

Asynchronous data

Note 8 - Octets 5b-5d may be omitted in the case of synchronous user rates.

Negotiation (octet 5a)

Bit

6

0

In-band negotiation not possible

1

In-band negotiation possible

Note 9 - See Recommendations V.110 [7], I.460 [15] and X.30 [8] or modem type recommendations.

User rate (octet 5a)

Bits

5 4 3 2 1

0 0 0 0 0

For I.460, rate is specified by bits 7, 6 of octet 5b, Intermediate rate.
For V.110 and X.30, rate is indicated by E-bits (synchronous data only) or may be negotiated in-band.
For V.120, rate is unspecified or may be negotiated in-band.

0 0 0 0 1

0.6 kbit/s Recommendations X.1 [17]

0 0 0 1 0

1.2 kbit/s

0 0 0 1 1

2.4 kbit/s Recommendations X.1

0 0 1 0 0

3.6 kbit/s

0 0 1 0 1

4.8 kbit/s Recommendations X.1

0 0 1 1 0

7.2 kbit/s

0 0 1 1 1

8 kbit/s Recommendation I.460

0 1 0 0 0

9.6 kbit/s Recommendations X.1

0 1 0 0 1

14.4 kbit/s

0 1 0 1 0

16 kbit/s Recommendation I.460

0 1 0 1 1

19.2 kbit/s

0 1 1 0 0

32 kbit/s Recommendation I.460

0 1 1 1 0

48 kbit/s Recommendations X.1

0 1 1 1 1

56 kbit/s

1 0 0 0 0

64 kbit/s Recommendation X.1

1 0 0 1 0

57.6 kbit/s Recommendation V.14 [88] extended

1 0 0 1 1

28.8 kbit/s Recommendation V.110 [89]

1 0 1 0 0

24 kbit/s Recommendation V.110 [89]

1 0 1 0 1

0.1345 kbit/s Recommendation X.1

1 0 1 1 0

0.100 kbit/s Recommendation X.1

1 0 1 1 1

0.075/1.2 kbit/s Recommendations X.1 (Note 10)

1 1 0 0 0

1.2/0.075 kbit/s Recommendations X.1 (Note 10)

1 1 0 0 1

0.050 kbit/s Recommendations X.1

1 1 0 1 0

0.075 kbit/s Recommendations X.1

1 1 0 1 1

0.110 kbit/s Recommendations X.1

1 1 1 0 0

0.150 kbit/s Recommendations X.1

1 1 1 0 1

0.200 kbit/s Recommendations X.1

1 1 1 1 0

0.300 kbit/s Recommendations X.1

1 1 1 1 1

12 kbit/s

All other values are reserved.

Note 10 - The first rate is the transmit rate in the forward direction of the call. The second rate is the transmit rate in the backward direction of the call.

Octet 5b for V.110 [7], I.460 [15] and X.30 [8] rate adaption

Intermediate rate (octet 5b)

Bits

7 6

0 0

Not used

0 1

8 kbit/s

1 0

16 kbit/s

1 1

32 kbit/s

Network independent clock (NIC) on transmission (Tx) (octet 5b) (Note 11)

Bit

5

0

Not required to send data with network independent clock

1

Required to send data with network independent clock

Note 11 - Refers to transmission in the forward direction of the call.

Note 12 - See Recommendations V.110, I.460 [15] and X.30.

Network independent clock (NIC) on reception (Rx) (octet 5b) (Note 13)

Bit

4

0

Cannot accept data with Network Independent Clock (i.e. sender does not support this optional procedure)

1

Can accept data with Network Independent Clock (i.e. sender does support this optional procedure)

Note 13 - Refers to transmission in the backward direction of the call.

Note 14 - See Recommendations V.110 [7], I.460 [15] and X.30 [8].

Flow control on transmission (Tx) (octet 5b) (Note 5)

Bit

3

0

Not required to send data with flow control mechanism

1

Required to send data with flow control mechanism

Note 15 - Refers to transmission in the forward direction of the call.

Note 16 - See Recommendations V.110, I.460 and X.30.

Flow control on reception (Rx) (octet 5b) (Note 17)

Bit

2

0

Cannot accept data with flow control mechanism (i.e. sender does not support this optional procedure)

1

Can accept data with flow control mechanism (i.e. sender does support this optional procedure)

Note 17 - Refers to transmission in the backward direction of the call.

Note 18 - See Recommendations V.110, I.460 and X.30.

Octet 5b for V.120 [9] Rate adaption

Rate adaption header/no header (octet 5b)

Bit

7

0

Rate adaption header not included

1

Rate adaption header included

Multiple frame establishment support in data link (octet 5b)

Bit

6

0

Multiple frame establishment not supported. Only UI frames allowed

1

Multiple frame establishment supported

Mode of operation (octet 5b)

Bit

5

0

Bit transparent mode of operation

1

Protocol sensitive mode of operation

Logical link identifier negotiation (octet 5b)

Bit

4

0

Default, LLI = 256 only

1

Full protocol negotiation (Note 19)

Note 19  - A connection over which protocol negotiation will be executed is indicated in bit 2 of octet 5b.

Assignor/assignee (octet 5b)

Bit

3

0

Message originator is "default assignee"

1

Message originator is "assignor only"

In-band/out-band negotiation (octet 5b)

Bit

2

0

Negotiation is done with USER INFORMATION messages on a temporary signalling connection

1

Negotiation is done in-band using logical link zero

Number of stop bits (octet 5c)

Bits

7 6

0 0

Not used

0 1

1 bit

1 0

1.5 bits

1 1

2 bits

Number of data bits excluding parity bit if present (octet 5c)

Bits

5 4

0 0

Not used

0 1

5 bits

1 0

7 bits

1 1

8 bits

Parity information (octet 5c)

Bits

3 2 1

0 0 0

Odd

0 1 0

Even

0 1 1

None

1 0 0

Forced to 0

1 0 1

Forced to 1

All other values are reserved.

Duplex mode (octet 5d)

Bit

7

0

Half duplex

1

Full duplex

Modem type (octet 5d)

Bits

6 5 4 3 2 1

0 0 0 0 0 0
through
0 0 0 1 0 1

National use

0 1 0 0 0 1

Recommendation V.21

0 1 0 0 1 0

Recommendation V.22

0 1 0 0 1 1

Recommendation V.22 bis

0 1 0 1 0 0

Recommendation V.23

0 1 0 1 0 1

Recommendation V.26

0 1 0 1 1 0

Recommendation V.26 bis

0 1 0 1 1 1

Recommendation V.26 ter

0 1 1 0 0 0

Recommendation V.27

0 1 1 0 0 1

Recommendation V.27 bis

0 1 1 0 1 0

Recommendation V.27 ter

0 1 1 0 1 1

Recommendation V.29

0 1 1 1 0 0

Recommendation V.32

0 1 1 1 1 0

Recommendation V.34 [90]

1 0 0 0 0 0
through
1 0 1 1 1 1

National use

1 1 0 0 0 0
through
1 1 1 1 1 1

User specified

All other values reserved.

User information layer 2 protocol (octet 6)

Bits

5 4 3 2 1

0 0 0 0 1

Basic mode ISO 1745 [36]

0 0 0 1 0

Recommendation Q.921 (I.441) [3] (Note 23)

0 0 1 1 0

Recommendation X.25 [5], link layer (Notes 20, 23)

0 1 1 1 1

Recommendation X.25 Multilink (Note 23)

0 1 0 0 0

Extended LAPB; for half duplex operation (T.71 [37])

0 1 0 0 1

HDLC ARM (ISO 4335) [38] (Note 23)

0 1 0 1 0

HDLC NRM (ISO 4335) (Note 23)

0 1 0 1 1

HDLC ABM (ISO 4335) (Note 23)

0 1 1 0 0

LAN logical link control (ISO 8802-2) [39]

0 1 1 0 1

Recommendation X.75 [40]. Single Link Procedure (SLP) (Note 23)

0 1 1 1 0

Recommendation Q.922 [ ] (Note 23)

0 1 1 1 1

Core aspects of Recommendation Q.922

1 0 0 0 0

User specified (Note 21)

1 0 0 0 1

ISO 7776 DTE-DTE operation (Notes 22, 23)

All other values are reserved.

Note 20 - This Recommendation is compatible with ISO 7776 DTE-DCE operation.

Note 21 - When this coding is included, octet 6a will include user coding for the user specified Layer 2 protocol.

Note 22 - This Standard is compatible with Recommendation X.75 modified by the application rules defined in Recommendation T.90.

Note 23 - When this coding is included, octets 6a and 6b with ITU-T encoding may be included.

Octet 6a for ITU-T codings

Mode of operation (octet 6a)

Bits

7 6

0 1

Normal mode of operation

1 0

Extended mode of operation

All other values are reserved.

Q.933 use (octet 6a)

Bits

2 1

0 0

For use when the coding defined in Recommendation Q.933 is not used

All other values are reserved.

Octet 6a for user protocol

User specified layer 2 protocol information (octet 6a)

The use and coding of octet 6a is according to user defined requirements.

Window size (k) (octet 6b)

Bits 7-1 binary coding of k parameter value in the range from 1 to 127.

User information layer 3 protocol (octet 7)

Bits

5 4 3 2 1

0 0 0 1 0

Recommendation Q.931/I.451

0 0 1 1 0

Recommendation X.25, packet layer (Note 25)

0 0 1 1 1

ISO/IEC 8208 [41] (X.25 packet level protocol for data terminal equipment) (Note 25)

0 1 0 0 0

ITU-T Rec. X.223 | ISO 8878 [81] (use of ISO/IEC 8208 [41] and Recommendation X.25 to provide the OSI-CONS) (Note 25)

0 1 0 0 1

ISO/IEC 8473 [43] (OSI connectionless mode protocol)

0 1 0 1 0

Recommendation T.70 [32] minimum network layer

0 1 0 1 1

ISO/IEC TR 9577 [82] (Protocol identification in the network layer) (Note 26)

1 0 0 0 0

User specified (Note 24)

All other values are reserved.

Note 24 - When this coding is included, octet 7a will included user coding for the user specified layer 3 protocol.

Note 25 - When this coding is included, octets 7a, 7b and 7c with ITU-T X.25, X.223 and ISO/IEC TR 9577 encoding may be included.

Note 26 – When this coding is included, octets 7a and 7b with ITU-T X.25, X.223 [96] and ISO/IEC TR 9577 encoding may be included.

Octet 7a, 7b and 7c X.25 packet layer, ISO/IEC 8208 and X.223 codings

Mode of operation (octet 7a)

Bits

7 6

0 1

Normal packet sequence numbering

1 0

Extended packet sequence numbering

All other values are reserved.

Default packet size (octet 7b)

Bits

4 3 2 1

0 1 0 0

Default packet size 16 octets

0 1 0 1

Default packet size 32 octets

0 1 1 0

Default packet size 64 octets

0 1 1 1

Default packet size 128 octets

1 0 0 0

Default packet size 256 octets

1 0 0 1

Default packet size 512 octets

1 0 1 0

Default packet size 1024 octets

1 0 1 1

Default packet size 2048 octets

1 1 0 0

Default packet size 4096 octets

All other values are reserved.

Packet window size (octet 7c)

Bits 7-1 binary coding of packet window size value in the range from 1 to 127.

Octet 7a for user protocol

User specified layer 3 protocol information (octet 7a)

The use and coding of octet 7a depends on user defined requirements

Octets 7a and 7b for ISO/IEC TR 9577 coding (Notes 26 and 27)

Bit 8 (ext.) set to 0 in octet 7a and set to 1 in octet 7b.

Bits 7 to 5 are spare (set to 0) in both octets.

7a

7b

Bits

Bits

4 3 2 1

4 3 2 1

1 1 0 0

1 1 0 0

1 1 0 0

1 1 1 1

Point-to-Point Protocol (RFC 1548)

All other values are reserved.

Note 27 – If the user information layer 3 protocol indicates "Network layer protocol identification", it may be included to identify the actual user information layer 3 protocol to the addressed entity (see Annex I). Any Network layer Protocol Identifier code defined in ISO/IEC TR 9577 [82] may be included. Octet 7c shall not be included.

LLC attributes

Additional attributes

Transfer mode

Information transfer capability

Structure

Configuration

Establishment

Symmetry

Circuit

Speech

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Circuit

Unrestricted data

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Circuit

Restricted data

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Circuit

3.1 kHz audio

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Circuit

Unrestricted data with tones/announcements

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Circuit

Video

8 kHz integrity

Point-to-point

Demand

Bi-directional symmetric

Packet

Unrestricted data

Service data unit integrity

Point-to-point

Demand

Bi-directional symmetric

NOTES

1. When the information transfer rate 2 × 64 kbit/s is used, 8 kHz integrity with Restricted Differential Time Delay (RDTD) is offered.

2. When multirate (64 kbit/s base rate) is indicated as the information transfer rate, Time Slot Sequence integrity shall be provided.