public class RSVPTEHelloMessage extends RSVPMessage
5. Hello Extension
The RSVP Hello extension enables RSVP nodes to detect when a
neighboring node is not reachable. The mechanism provides node to
node failure detection. When such a failure is detected it is
handled much the same as a link layer communication failure. This
mechanism is intended to be used when notification of link layer
failures is not available and unnumbered links are not used, or when
the failure detection mechanisms provided by the link layer are not
sufficient for timely node failure detection.
It should be noted that node failure detection is not the same as a
link failure detection mechanism, particularly in the case of
multiple parallel unnumbered links.
The Hello extension is specifically designed so that one side can use
the mechanism while the other side does not. Neighbor failure
detection may be initiated at any time. This includes when neighbors
first learn about each other, or just when neighbors are sharing Resv
or Path state.
The Hello extension is composed of a Hello message, a HELLO REQUEST
object and a HELLO ACK object. Hello processing between two
neighbors supports independent selection of, typically configured,
failure detection intervals. Each neighbor can autonomously issue
HELLO REQUEST objects. Each request is answered by an
acknowledgment. Hello Messages also contain enough information so
that one neighbor can suppress issuing hello requests and still
perform neighbor failure detection. A Hello message may be included
as a sub-message within a bundle message.
Neighbor failure detection is accomplished by collecting and storing
a neighbor's "instance" value. If a change in value is seen or if
the neighbor is not properly reporting the locally advertised value,
then the neighbor is presumed to have reset. When a neighbor's value
is seen to change or when communication is lost with a neighbor, then
the instance value advertised to that neighbor is also changed. The
HELLO objects provide a mechanism for polling for and providing an
instance value. A poll request also includes the sender's instance
value. This allows the receiver of a poll to optionally treat the
poll as an implicit poll response. This optional handling is an
optimization that can reduce the total number of polls and responses
processed by a pair of neighbors. In all cases, when both sides
support the optimization the result will be only one set of polls and
responses per failure detection interval. Depending on selected
intervals, the same benefit can occur even when only one neighbor
supports the optimization.
5.1. Hello Message Format
Hello Messages are always sent between two RSVP neighbors. The IP
source address is the IP address of the sending node. The IP
destination address is the IP address of the neighbor node.
The HELLO mechanism is intended for use between immediate neighbors.
When HELLO messages are being the exchanged between immediate
neighbors, the IP TTL field of all outgoing HELLO messages SHOULD be
set to 1.
The Hello message has a Msg Type of 20. The Hello message format is
as follows:
bytes, flags, length, msgType, reserved, rsvpChecksum, sendTTL, vers| Constructor and Description |
|---|
RSVPTEHelloMessage()
Constructor to be used when a new RSVP-TE Hello Message wanted to be sent
|
RSVPTEHelloMessage(byte[] bytes,
int length)
Constructor to be used when an RSVP-TE Hello Message wanted to be decoded
|
| Modifier and Type | Method and Description |
|---|---|
void |
decode()
|
void |
encode()
|
void |
encodeHeader()
RSVP Common Header
0 1 2 3
+-------------+-------------+-------------+-------------+
| Vers | Flags| Msg Type | RSVP Checksum |
+-------------+-------------+-------------+-------------+
| Send_TTL | (Reserved) | RSVP Length |
+-------------+-------------+-------------+-------------+
The fields in the common header are as follows:
Vers: 4 bits
Protocol version number.
|
calculateChecksum, decodeHeader, getBytes, getFlags, getLength, getMsgLength, getMsgType, getMsgType, getReserved, getRsvpChecksum, getSendTTL, getVers, setBytes, setFlags, setLength, setMsgType, setReserved, setRsvpChecksum, setSendTTL, setVerspublic RSVPTEHelloMessage()
public RSVPTEHelloMessage(byte[] bytes,
int length)
bytes - length - public void encodeHeader()
RSVP Common Header 0 1 2 3 +-------------+-------------+-------------+-------------+ | Vers | Flags| Msg Type | RSVP Checksum | +-------------+-------------+-------------+-------------+ | Send_TTL | (Reserved) | RSVP Length | +-------------+-------------+-------------+-------------+ The fields in the common header are as follows: Vers: 4 bits Protocol version number. This is version 1. Flags: 4 bits 0x01-0x08: Reserved No flag bits are defined yet. Msg Type: 8 bits 20 = Hello RSVP Checksum: 16 bits The one's complement of the one's complement sum of the message, with the checksum field replaced by zero for the purpose of computing the checksum. An all-zero value means that no checksum was transmitted. Send_TTL: 8 bits The IP TTL value with which the message was sent. RSVP Length: 16 bits The total length of this RSVP message in bytes, including the common header and the variable-length objects that follow.
encodeHeader in class RSVPMessagepublic void encode()
throws RSVPProtocolViolationException
encode in interface RSVPElementencode in class RSVPMessageRSVPProtocolViolationExceptionpublic void decode()
throws RSVPProtocolViolationException
decode in class RSVPMessageRSVPProtocolViolationExceptionCopyright © 2016. All rights reserved.