Moby Dick Consolidated System Integration Plan

D0103v1.doc Version 1 6.7.2003
Since MTNM module is in user space and FHO module is in kernel space, as specified before, to
exchange messages between them we deployed the character device technology. The character device is a
special device which allows the communication between user space and kernel space; figure 17 depicts
the behaviour of FHO module.
USERSPACE
MTNM
KERNELSPACE
FHO
START_FHO
L2_REQ
-Sending Router Soll. Proxy
-Receiving Proxy Router Adv
-Sending Fast Binding Update
-Receiving Fast Binding Ack
Configuring
Layer 2 handover
L2_ACK
-Fast Handover Execution
FHO_ACK
Figure 17: User space/Kernel space communication
The Fast Handover Module waits for the START_FHO message from the MTNM in order to trigger the
fast handover mechanism (independently if the handover was triggered automatically or manually). Once
the fast handover trigger is received, the message flow depicted in figure 18 is executed.
According to what is specified in previous sections, the module performs two main tasks:
• on the oldAR when the Router Solicitation Proxy message is received FHO module recovers
AAAC context from AAAC Attendant and sends it, as data attached in the Handover Initiate
message, to the newAR. In parallel a request for QoS availability is send to QoS attendant.
• on the newAR, once the Handover Initiate message has been handled, FHO module waits for a
response from QoS attendant about resource availability: in case of positive answer it relies the
AAAC context to the AAAC attendant, otherwise this step is just skipped. In both conditions an
Handover Acknowledgement is send back to the oldAR in order to inform the MN (MTNM)
about the possibility or not to perform handover.
Mobile IPv6 messages exchanged between MN-oldAR-newAR are realized via new types of ICMP
messages, which are created by the Fast Handover Module and sent via ‘standard’ IPv6 kernel functions
(i.e., interface Fast Handover Module and IPv6 stack). .
The “layer 2” handover is triggered via the interface with MTNM module (i.e. character device); the
messages L2_req (layer 2 handover request) and L2_ack (layer 2 handover acknowledgement) are
exchanged between MTNM module and FHO module after receiving the message Fast Binding
Acknowledgement on the MN.
The last message (FHO_ACK) informs MTNM module about the result of the handover: if all the steps
described are well performed the returned status is safe, otherwise, if the handover is not possible, (e.g. a
lack of resources on the new link) MTNM will try to use another technology (if available) or to access
another link.
D0103v1.doc 34 / 168