urv.olsr.message.generator
Class HelloMessageGenerator
java.lang.Object
urv.olsr.message.generator.HelloMessageGenerator
public class HelloMessageGenerator
- extends java.lang.Object
This involves transmitting the Link Set, the Neighbor Set and the MPR
Set. In principle, a HELLO message serves three independent tasks:
- link sensing
- neighbor detection
- MPR selection signaling
Three tasks are all are based on periodic information exchange within
a nodes neighborhood, and serve the common purpose of "local topology
discovery". A HELLO message is therefore generated based on the
information stored in the Local Link Set, the Neighbor Set and the
MPR Set from the local link information base.
A node must perform link sensing on each interface, in order to
detect links between the interface and neighbor interfaces.
Furthermore, a node must advertise its entire symmetric 1-hop
neighborhood on each interface in order to perform neighbor
detection. Hence, for a given interface, a HELLO message will
contain a list of links on that interface (with associated link
types), as well as a list of the entire neighborhood (with an
associated neighbor types).
The Vtime field is set such that it corresponds to the value of the
node's NEIGHB_HOLD_TIME parameter. The Htime field is set such that
it corresponds to the value of the node's HELLO_INTERVAL parameter
(see section 18.3).
The Willingness field is set such that it corresponds to the node's
willingness to forward traffic on behalf of other nodes (see section
18.8). A node MUST advertise the same willingness on all interfaces.
The lists of addresses declared in a HELLO message is a list of
neighbor interface addresses computed as follows:
For each tuple in the Link Set, where L_local_iface_addr is the
interface where the HELLO is to be transmitted, and where L_time >=
current time (i.e., not expired), L_neighbor_iface_addr is advertised
with:
1 The Link Type set according to the following:
1.1 if L_SYM_time >= current time (not expired)
Link Type = SYM_LINK
1.2 Otherwise, if L_ASYM_time >= current time (not expired)
AND
L_SYM_time < current time (expired)
Link Type = ASYM_LINK
1.3 Otherwise, if L_ASYM_time < current time (expired) AND
L_SYM_time < current time (expired)
Link Type = LOST_LINK
2 The Neighbor Type is set according to the following:
2.1 If the main address, corresponding to
L_neighbor_iface_addr, is included in the MPR set:
Neighbor Type = MPR_NEIGH
2.2 Otherwise, if the main address, corresponding to
L_neighbor_iface_addr, is included in the neighbor set:
2.2.1
if N_status == SYM
Neighbor Type = SYM_NEIGH
2.2.2
Otherwise, if N_status == NOT_SYM
Neighbor Type = NOT_NEIGH
For each tuple in the Neighbor Set, for which no
L_neighbor_iface_addr from an associated link tuple has been
advertised by the previous algorithm, N_neighbor_main_addr is
advertised with:
- Link Type = UNSPEC_LINK,
- Neighbor Type set as described in step 2 above
For a node with a single OLSR interface, the main address is simply
the address of the OLSR interface, i.e., for a node with a single
OLSR interface the main address, corresponding to
L_neighbor_iface_addr is simply L_neighbor_iface_addr.
A HELLO message can be partial (e.g., due to message size
limitations, imposed by the network), the rule being the following,
on each interface: each link and each neighbor node MUST be cited at
least once within a predetermined refreshing period,
REFRESH_INTERVAL. To keep track of fast connectivity changes, a
HELLO message must be sent at least every HELLO_INTERVAL period,
smaller than or equal to REFRESH_INTERVAL.
Notice that for limiting the impact from loss of control messages, it
is desirable that a message (plus the generic packet header) can fit
into a single MAC frame.
- Author:
- Gerard Paris Aixala
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
HelloMessageGenerator
public HelloMessageGenerator(OLSRMessageSender messageSender,
NeighborTable table,
OLSRPacketFactory olsrPacketFactory)
generateAndSend
public void generateAndSend()