sap - Service Access Point specification
The text2sap and sap2text functions use the format
described in this man page. Because all standard ATM tools on Linux use
those functions to convert to or from the textual representation of SAP
specifications, they expect them in the same format too.
The SAP is divided into two parts: the broadband high layer
information (BHLI) and the broadband low layer information
(BLLI). A SAP can contain one, both, or none of them. In the latter case,
the SAP is usually considered as a wildcard SAP, i.e. a SAP that is
compatible with any other SAP.
Each part begins with its name (bhli or blli),
followed by a colon and a (non-empty) list of attributes, which are of the
form attribute=value. Some attributes have
sub-attributes, which follow them. Everything that isn't separated by a
colon or an equal sign is separated by a comma.
Values which are a number of bytes are specified as the
corresponding sequence of pairs of hex digits. The sequence can be
optionally prefixed with 0x. Values with are integers in a given
range can be specified in decimal (no prefix), octal (0 prefix), and
hexadecimal (0x prefix).
The following, mutually exclusive attributes are allowed in the
bhli part (see the corresponding ATM Forum and ITU documents for the
semantics):
- iso=1-8 bytes
- ISO
- user=1-8 bytes
- User-specific
- hlp=4 bytes
- High layer profile. Note that this attribute only exists on UNI 3.0.
text2sap only recognizes it if your system is configured to accept
UNI 3.0 message formats.
- oui=3 bytes,id=4 bytes
- Vendor-specific application identifier
The structure of the bhli part is more complex. It
distinguishes three layers, l1, l2, and l3, of which
the first one is presently unsupported. For layer two, the following
(mutually exclusive) possibilities exist:
- l2=iso1745
- Basic mode ISO 1745
- l2=q291
- ITU-T Q.291 (Rec. I.441)
- l2=lapb
- Extended LAPB, half-duplex (Rec. T.71)
- l2=iso8802
- LAN LLC (ISO/IEC 8802/2)
- l2=x75
- ITU-T X.75, SLP
- l2=x25_ll ...
- ITU-T X.25, link layer. This attribute and the following attributes
through l2=iso7776 can optionally be followed by one or more of the
following sub-attributes: mode=mode (mode of operation,
either norm or ext), and window=window size
(window size in k, 1-127).
- l2=x25_ml ...
- ITU-T X.25, multilink
- l2=hdlc_arm ...
- HDLC ARM (ISO/IEC 4335)
- l2=hdlc_nrm ...
- HDLC NRM (ISO/IEC 4335)
- l2=hdlc_abm ...
- HDLC ABM (ISO/IEC 4335)
- l2=q992 ...
- ITU-T Q.922
- l2=iso7776 ...
- ISO 7776 DTE-DTE
- l2=user,info=information
- User-specified. information is an integer in the range 0 to
255.
For layer three, the following (again, mutually exclusive)
possibilities exist:
- l3=iso8473
- ITU-T X.233 | ISO/IEC 8473
- l3=t70
- ITU-T T.70 minimum network layer
- l3=h321
- ITU-T Recommendation H.321
- l3=x25 ...
- ITU-T X.25, packet layer. This attribute and the following attributes
through l3=x223 can optionally be followed by one or more of the
following sub-attributes: mode=mode (see above),
size=default packet size (4-12, corresponding to
16-4096), window=window size (see above).
- l3=iso8208 ...
- ISO/IEC 8208
- l3=x223 ...
- ITU-T X.223 | ISO/IEC 8878
- l3=tr9577,ipi=identifier ...
- ISO/IEC TR 9577. identifier is the initial protocol identifier in
the range 0-255. For SNAP (0x80), the keyword snap can be used, and
the following sub-attributes have to be specified: oui=3
bytes, and pid=2 bytes.
- l2=user,info=information
- User-specified, see above.
- l3=h310 ...
- ITU-T Recommendation H.310. The sub-attribute term=type
(terminal type, rx, tx, or rxtx) is recognized. If
present, it enables the two additional sub-attributes
fw_mpx=capability (forward multiplexing capability,
ts, ts_fec, ps, ps_fec, or h221) and
bw_mpx=capability. Both are optional.
Note that commas must never follow colons or other commas. Also,
whitespace is not allowed inside a SAP specification. SAP specifications are
case-insensitive. On input, items must be written in exactly the order used
in this document.
Werner Almesberger, EPFL LRC
<werner.almesberger@lrc.di.epfl.ch>