Section: Miscellaneous (7)
Updated: November 6, 1997
sap - Service Access Point specification
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 semantics):
- iso=1-8 bytes
- user=1-8 bytes
- 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
Basic mode ISO 1745
ITU-T Q.291 (Rec. I.441)
Extended LAPB, half-duplex (Rec. T.71)
LAN LLC (ISO/IEC 8802/2)
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 ...
- l2=iso7776 ...
ISO 7776 DTE-DTE
User-specified. information is an integer in the range 0 to 255.
For layer three, the following (again, mutually exclusive) possibilities
ITU-T X.233 | ISO/IEC 8473
ITU-T T.70 minimum network layer
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
- l3=iso8208 ...
- 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.
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
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 <firstname.lastname@example.org