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.

blli:l2=iso8802

Classical IP over ATM (RFC1577)

bhli:oui=0x0060D7,id=0x01000001,blli:l2=iso8802

Arequipa (RFC2170)

blli:l3=tr9577,ipi=snap,oui=0x00A03E,pid=0x0002

LAN Emulation

Werner Almesberger, EPFL LRC <werner.almesberger@lrc.di.epfl.ch>