This is in reply to comments we received from Behcet and Suresh regarding the three types of addresses define in the draft. Suresh commented that the ‘Fixed IP address’ is not necessary and application only require to select
Sustained or Nomadic IP addresses and Behcet commented that the ‘Sustained IP address’ is not needed and not well define due to the fact that the draft does not define how to identify the end of an IP session (will be discussed in a separate email).
We have gave more thought to these types and concluded that the definitions in the spec were confusing. We are providing new text in the new version, hoping they are more clear.
We re-evaluated whether to stay with the definition of three IP address types or move to a two IP address type scheme and eventually concluded that it is better to stay with the three type alternative. We hope that the better
text in the new draft version will clarify and here are some additional inputs:
Nomadic IP address (or in its new name: Non-persistent IP address):
Clearly this type is useful for all applications that do not require any IP session continuity guarantee from the network and wish to avoid the overhead introduced by the network as part of that guarantee (inefficient routes,
Sustained IP address (or in its new name: Session-lasting IP address):
This is our accurate definition for the IP session continuity service that some application require and is similar to what is provided today by default, by mobile operators via GTP or PMIP. Basically, current implementations
provide a guarantee for the source IP address to be valid throughout the time the mobile host is connected to the mobile network.
We concluded that mobile hosts do not really require such a guarantee. It is sufficient to require a guarantee of the IP address availability while there is/are an IP session(s) using this IP address and hence the more accurate
definition. Furthermore, some WG members have shown cases in DMM where it is more efficient for applications to request a new Session-lasting IP address when launched rather than using an existing one that was allocated to the mobile host in the past. This
is due to possible movement of the mobile host to a LAN which is being served by a mobility anchor that is different from the one that was used when the older Session-lasting IP address was assigned to the mobile host.
Fixed IP address (no renaming …):
We believe that this is where our original text was the most unclear leading to the confusion on the mailing list and the comments from the flour. A Fixed IP address is guaranteed by the network to Always be valid, even if the
mobile host is not utilizing any IP sessions, or has been disconnected from the network for some time. This is a special service that mobile network operators provide for a premium charge, for servers, VPNs , secured content and other applications. With this
IP address type the network operator provide IP address reachability in addition to IP session continuity, and mobile hosts may register these addresses in DNS infrastructure for name resolution.
Clearly, most mobile hosts do not require Fixed IP addresses and their owners will not pay the premium cost for this service, but still, it is a service that mobile operators provide and this is enough proof for us to acknowledge
its need. Please see some examples from
providing this service (which is called: Static IP address)
Alper and Danny