RFC 3421 (rfc3421) - Page 2 of 8

Select and Sort Extensions for the Service Location Protocol (SLP)

Alternative Format: Original Text Document
< Previous
Next >
RFC 3421           Select and Sort Extensions for SLP      November 2002


   Using the Select extension, a UA can opt for finding just a few (not
   necessarily all) matching services, which is useful if the UA uses a
   low-bandwidth channel.  Using the Sort extension, a UA can ask the
   DA/SA to sort matching URL entries, which helps the UA to choose a
   service from multiple candidates.  Sorting by the server is more
   efficient than sorting by the client since for sorting purposes, the
   former does not need to pass the attributes of matching URLs to the
   client.  Furthermore, using the Select and Sort extensions together
   can facilitate discovering the best match, such as finding a service
   that has the maximum speed or the minimum load, or has a speed
   closest to a reference value.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted according to in BCP 14, RFC 2119
   [RFC 2119].

2. Select Extension

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Select Extension ID = 0x4002  |  Next Extension Offset (NEO)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | NEO, cont'd   |      Number of URL Entries    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1. Select Extension

   The format of the Select extension is shown in Figure 1.  A UA uses
   this extension in a Service Request (SrvRqst) to limit the maximum
   number (say, n) of URL entries to be returned.  When a DA/SA receives
   a SrvRqst with a Select extension, it MUST use a Select extension in
   the corresponding SrvRply to indicate the total number (say, m) of
   matching URL entries if the DA/SA supports this extension, otherwise
   the DA/SA MUST set the error code in the corresponding SrvRply to
   OPTION_NOT_UNDERSTOOD [RFC 2608].  If n
< Previous
Next >