cumulative should not exceed 255.
AGI and AII max lengths are restricted by their respective
types which has to be approved by expert review and registered by IANA.
Check out http://www.iana.org/assignments/pwe3-parameters
So far max AII len is 35 for AII type 4 and max AGI len is 8.
hope this helps..
himanshu
-----Original Message-----
From: l2vpn-bounces at ietf.org on behalf of venkatesan mahalingam
Sent: Sat 4/18/2009 4:02 PM
To: mpls at ietf.org; l2vpn at ietf.org; l2vpn-request at ietf.org
Subject: Doubt on PW info. length format
Hi All,Please help me in understanding the encoding of Gen FEC Id element,
PW info length is one byte length in FEC element format.
As per RFC-4447 standard, we need to store the length of AGI, SAII and
TAII length into this one byte PW info length.
If all are max length say 255.
then we are getting (255+255+255) => 765.
How can we accomadate this value in one byte length PW info length field?
For your reference I've attached the RFC contents,
5.3.2. Encoding the Generalized ID FEC Element
FEC element type 0x81 is used. The FEC element is encoded as
follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Gen PWid (0x81)|C| PW Type |PW info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This document does not specify the AII and AGI type field values;
specification of the type field values to be used for a particular
application is part of the specification of that application. IANA
has assigned these values using the method defined in the [IANA
<http://tools.ietf.org/html/rfc4447#ref-IANA>]
document.
The SAII, TAII, and AGI are simply carried as octet strings. The
length byte specifies the size of the Value field. The null string
can be sent by setting the length byte to 0. If a particular
application does not need all three of these sub-elements, it MUST
send all the sub-elements but set the length to 0 for the unused
sub-elements.
The PW information length field contains the *length of the SAII,
TAII, and AGI, combined in octets*. If this value is 0, then it
references all PWs using the specified grouping ID. In this case,
there are no other FEC element fields (AGI, SAII, etc.) present, nor
any interface parameters TLVs.