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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
The following, mutually exclusive attributes are allowed in the bhli
part (see the corresponding ATM Forum and ITU documents for the
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)
Basic mode ISO 1745
ITU-T Q.291 (Rec. I.441)
Extended LAPB, half-duplex (Rec. T.71)
LAN LLC (ISO/IEC 8802/2)
l2=x75 ITU-T X.75, SLP
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).
ITU-T X.25, multilink
HDLC ARM (ISO/IEC 4335)
HDLC NRM (ISO/IEC 4335)
HDLC ABM (ISO/IEC 4335)
ISO 7776 DTE-DTE
User-specified. information is an integer in the range 0 to 255.
For layer three, the following (again, mutually exclusive)
ITU-T X.233 | ISO/IEC 8473
l3=t70 ITU-T T.70 minimum network layer
ITU-T Recommendation H.321
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).
ITU-T X.223 | ISO/IEC 8878
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.
User-specified, see above.
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.
Classical IP over ATM (RFC1577)
Werner Almesberger, EPFL LRC <email@example.com>