The Low layer compatibility information element is transferred transparently by an ISDN between the call originating entity (e.g. the calling user) and the addressed entity.
If low layer compatibility negotiation is allowed by the network, the Low layer compatibility information element is also passed transparently from the addressed entity to originating entity.
The maximum length of this information element is 18 octets.
NOTE - Some networks conforming to Recommendation Q.931 (1988) may support a maximum information element length of only 16 octets.
8 7 6 5 4 3 2 1
1 0 1 1 1 1 1 0 0 = 7C
2 length max 18
3 0/1 ext b b a a a a a
3a 1 ext b1 0 0 0 0 0 0
4 1 ext d d c c c c c
4.1 1 ext e e e e e e e
5 0/1 ext 0 1 f f f f f
5a 0/1 ext i h g g g g g
5b 0/1 ext n n m l k j 0
5b 0/1 ext t s r q p o 0
5c 0/1 ext w w v v u u u
5d 1 ext y x x x x x x
6 0/1 ext 1 0 p2 p2 p2 p2 p2
6a 0/1 ext d1 d1 0 0 0 c1 c1
6a 1 ext i2 i2 i2 i2 i2 i2 i2
6b 1 ext ws ws ws ws ws ws ws
7 0/1 ext 1 1 p3 p3 p3 p3 p3
7a 0/1 ext e1 e1 0 0 0 0 0
7a 1 ext i3 i3 i3 i3 i3 i3 i3
7b 0/1 ext 0 0 0 ps ps ps ps
7c 1 ext pw pw pw pw pw pw pw
ext=1 last octet
ext=0 the octet continues through the last octet
A kovetkezo fieldek azonosak a Bearer capability informacios elem
megfelelo fieldjeivel.
a) Information transfer capability (octet 3)
b) Coding standard (octet 3)
c) Information transfer rate (octet 4)
d) Transfer mode (octet 4)
e) Rate multiplier (octet 4.1)
f) User information layer 1 protocol (octet 5)
g) User rate (octet 5a)
h) Negotiation (octet 5a)
i) Synchronous/Asynchronous (octet 5a)
j) Flow control on reception (Rx) (octet 5b) (Note 7)
k) Flow control on transmission (Tx) (octet 5b) (Note 5)
l) Network independent clock (NIC) on reception (Rx) (octet 5b) (Note 3)
m) Network independent clock (NIC) on transmission (Tx) (octet 5b) (Note 1)
n) Intermediate rate (octet 5b)
o) In-band/out-band negotiation (octet 5b)
p) Assignor/assignee (octet 5b)
q) Logical link identifier negotiation (octet 5b)
r) Mode of operation (octet 5b)
s) Multiple frame establishment support in data link (octet 5b)
t) Rate adaption header/no header (octet 5b)
u) Parity information (Octet 5c)
v) Number of data bits excluding parity Bit if present (octet 5c)
w) Number of stop bits (octet 5c)
x) Modem type (octet 5d)
y) Mode duplex (octet 5d)
NOTES:
1 This octet is required if octet 4 indicates multirate (64 kbit/s base rate). Otherwise, it shall not be present.
2 This octet may be present if octet 3 indicates unrestricted digital information and octet 5 indicates either of the CCITT standardized rate adaptions V.110 and X.30 or V.120 [9]. It may also be present if octet 3 indicates 3.1 kHz audio and octet
cates G.711.
3 This octet is significant only if octet 5 indicates CCITT standardized rate adaption (V.110 [7] and X.30 [8]).
4 This octet is significant only if octet 5 indicates CCITT standardized rate adaption V.120 [9].
5 This octet may be present only if octet 6 indicates certain acknowledged mode HDLC elements of procedure as indicated in Table 4-16.
6 This octet may be present only if octet 6 indicates user specified layer 2 protocol.
7 This octet may be present only if octet 7 indicates a layer 3 protocol based on CCITT X.25 | ISO/IEC 8208 or CCITT Rec. X.223 | ISO 8878 as indicated in Table 4-16.
8 This octet may be present only if octet 7 indicates user specified layer 3 protocol.
b1) 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.
b2) 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 4)
0 0 1 1 0 Recommendation X.25 [5], link layer (Notes 1, 4)
0 1 1 1 1 Recommendation X.25 Multilink (Note 4)
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 4)
0 1 0 1 0 HDLC NRM (ISO 4335) (Note 4)
0 1 0 1 1 HDLC ABM (ISO 4335) (Note 4)
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 4)
0 1 1 1 0 Recommendation Q.922 [ ] (Note 4)
0 1 1 1 1 Core aspects of Recommendation Q.922
1 0 0 0 0 User specified (Note 2)
1 0 0 0 1 ISO 7776 DTE-DTE operation (Notes 3, 4)
All other values are reserved.
NOTES
1 This Recommendation is compatible with ISO 7776 DTE-DCE operation.
2 When this coding is included, octet 6a will include user coding for the user specified Layer 2 protocol.
3 This Standard is compatible with Recommendation X.75 modified by the application rules defined in Recommendation T.90.
4 When this coding is included, octets 6a and 6b with CCITT encoding may be included.
d1) 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.
c1) 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
i2) User specified layer 2 protocol information (octet 6a)
The use and coding of octet 6a is according to user defined requirements.
ws) Window size (k) (octet 6b)
Bits 7-1 binary coding of k parameter value in the range from 1 to 127.
p3) 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 2)
0 0 1 1 1 ISO/IEC 8208 [41] (X.25 packet level protocol for data terminal equipment) (Note 2)
0 1 0 0 0 CCITT Rec. X.223 | ISO 8878 [81] (use of ISO/IEC 8208 [41] and Recommendation X.25 to provide the OSI-CONS) (Note 2)
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)
1 0 0 0 0 User specified (Note 1)
All other values are reserved.
NOTE 1 – When this coding is included, octet 7a will included user coding for the user specified layer 3 protocol.
NOTE 2 – When this coding is included, octets 7a, 7b and 7c with CCITT encoding may be included.
Octet 7a for CCITT codings
e1) 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.
Octet 7a for user protocol
i3) User specified layer 3 protocol information (octet 7a)
The use and coding of octet 7a depends on user defined requirements.
ps) 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.
pw) Packet window size (octet 7c)
Bits 7-1 binary coding of packet window size value in the range from 1 to 127.
TABLE 4-17/Q.931
Low layer compatibility attributes
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.