\ \(em\ The data signalling rates of 600, 2400, 4800 and 9600\ bit/s are
also Recommendation\ X.1 user classes of service (see also
Recommendation\ X.30/I.461).
.LP
\fINote\ 2\fR
\ \(em\ In order to maintain compatibility with Recommendation\ X.30\ (I.461), the 600\ bit/s user rate E7 is coded to enable the 4\ \(mu\ 80\ bit multiframe
synchronization. To this end, E7 in the fourth 80\ bit frame is set to binary\ 0 (see \(sc\ 2.1.2.7 and Table\ 6a/V.110).
.LP
\fINote\ 3\fR
\ \(em\ C indicates the use of E4, E5 and E6 for the Transport of Network
Independent blocking information (see \(sc\ 5). These bits shall be set to ONE when unused.
.LP
\fINote\ 4\fR
\ \(em\ Synchronous rate information is carried by bits E1, E2 and E3 as
indicated. Asynchronous rate information must be provided with out\(hyof\(hyband
signalling (Layer 3 messages in the D\ channel) or with In Band Parameter
Exchange as described in Appendix\ 1.
.nr PS 9
.RT
.ad r
\fBTable 5/V.110 [T5.110], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 1
2.1.2.5
\fIRate negotiation\fR
.sp 9p
.RT
.PP
Negotiation of the synchronous rate may be appropriate in
interworking situations involving interconnections with modems on the PSTN
where the remote modem/DTE has the capability of operating at different
rates depending upon the conditions. It may also be appropriate in interconnections
for asynchronous transmission specified in \(sc\ 2.3 and accommodate split
rate
operation. The need for rate negotiation and the method is for further
study.
.RT
.sp 1P
.LP
2.1.2.6
\fIData bits\fR
.sp 9p
.RT
.PP
Data are conveyed in D bits, i.e., up to 48 bits per 80\(hybit frame. In
this Recommendation the octet boundaries of the user`s data stream are
not defined.
.RT
.sp 1P
.LP
2.1.2.7
\fIBit assignment\fR
.sp 9p
.RT
.PP
The adaptation of 600, 1200 and 2400 bit/s rates to the 8\ kbit/s
intermediate rate are shown in Tables\ 6a/V.110, 6b/V.110 and\ 6c/V.110,
respectively.
.PP
The adaptation of 7200 and 14\|400 bit/s rates to the 16 and 32\ kbit/s
intermediate rate, respectively, use the data bit assignments shown in
Table\ 6d/V.110.
.PP
The adaptation of 4800, 9600 and 19\|200 bit/s rates to the 8, 16 and 32\
kbit/s intermediate rate, respectively, use the data bit assignments shown
in Table\ 6e/V.110.
.PP
The adaptation of 12\|000 bit/s user rate to 32 kbit/s intermediate
rate use the data bit assignments shown in Table\ 6f/V.110.