On Demand Mobility ManagementActilityIstanbulTurkeyalper.yegin@actility.comIntel CorporationPetah TikvaIsraeldanny.moses@intel.comSamsungSuwonSouth Koreakisuk.kweon@samsung.comSamsungSuwonSouth Koreajs81.lee@samsung.comSamsungSuwonSouth Koreashin02.park@samsung.comSungkyunkwan UniversitySuwonSouth Koreaseiljeon@skku.eduDMM Working GroupApplications differ with respect to whether they need IP session
continuity and/or IP address reachability. The network providing the
same type of service to any mobile host and any application running on
the host yields inefficiencies. This document describes a solution for
taking the application needs into account in selectively providing IP
session continuity and IP address reachability on a per-socket
basis.In the context of Mobile IP ,
following two attributes are defined for the IP service provided to the
mobile hosts:IP session continuity: The ability to maintain an ongoing IP session
by keeping the same local end-point IP address throughout the session
despite the mobile host changing its point of attachment within the IP
network topology. The IP address of the host may change between two
independent IP sessions, but that does not jeopardize the IP session
continuity. IP session continuity is essential for mobile hosts to
maintain ongoing flows without any interruption.IP address reachability: The ability to maintain the same IP address
for an extended period of time. The IP address stays the same across
independent IP sessions, and even in the absence of any IP session. The
IP address may be published in a long-term registry (e.g., DNS), and it
is made available for serving incoming (e.g., TCP) connections. IP
address reachability is essential for mobile hosts to use
specific/published IP addresses.Mobile IP is designed to provide both IP session continuity and IP
address reachability to mobile hosts. Architectures utilizing these
protocols (e.g., 3GPP, 3GPP2, WIMAX) ensure that any mobile host
attached to the compliant networks can enjoy these benefits. Any
application running on these mobile hosts is subjected to the same
treatment with respect to the IP session continuity and IP address
reachability.It should be noted that in reality not every application may need
those benefits. IP address reachability is required for applications
running as servers (e.g., a web server running on the mobile host). But,
a typical client application (e.g., web browser) does not necessarily
require IP address reachability. Similarly, IP session continuity is not
required for all types of applications either. Applications performing
brief communication (e.g., DNS client) can survive without having IP
session continuity support.Achieving IP session continuity and IP address reachability by using
Mobile IP incurs some cost. Mobile IP protocol forces the mobile host's
IP traffic to traverse a centrally-located router (Home Agent, HA),
which incurs additional transmission latency and use of additional
network resources, adds to the network CAPEX and OPEX, and decreases the
reliability of the network due to the introduction of a single point of
failure . Therefore, IP
session continuity and IP address reachability should be be provided
only when needed.Furthermore, when an application needs session continuity, it may be
able to satisfy that need by using a solution above the IP layer, such
as MPTCP , SIP mobility , or an application-layer mobility solution. Those
higher-layer solutions are not subject to the same issues that arise
with the use of Mobile IP since they can utilize the most direct data
path between the end-points. But, if Mobile IP is being applied to the
mobile host, those higher-layer protocols are rendered useless because
their operation is inhibited by the Mobile IP. Since Mobile IP ensures
that the IP address of the mobile host remains fixed (despite the location
and movement of the mobile host), the higher-layer protocols never
detect the IP-layer change and never engage in mobility management.This document proposes a solution for the applications running on the
mobile host to indicate whether they need IP session continuity or IP
address reachability. The network protocol stack on the mobile host, in
conjunction with the network infrastructure, would provide the required
type of IP service. It is for the benefit of both the users and the
network operators not to engage an extra level of service unless it is
absolutely necessary. So it is expected that applications and networks
compliant with this specification would utilize this solution to use
network resources more efficiently.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in . Three types of IP addresses are defined with respect to the
mobility management.- Fixed IP Address A Fixed IP address is an address with a guarantee to be valid for a
very long time, regardless of whether it is being used in any packet
to/from the mobile host, or whether or not the mobile host is
connected to the network, or whether it moves from one
point-of-attachment to another (with a different subnet or IP prefix)
while it is connected.Fixed IP addresses are required by applications that need both IP
session continuity and IP address reachability.- Session-lasting IP AddressA session-lasting IP address is an address with a guarantee to be
valid throughout the IP session(s) for which it was requested. It is
guaranteed to be valid even after the mobile host had moved from one
point-of-attachment to another (with a different subnet or IP
prefix).Session-lasting IP addresses are required by applications that need
IP session continuity but do not need IP address reachability.- Non-persistent IP AddressThis type of IP address provides neither IP session continuity nor
IP address reachability. The IP address is obtained from the serving
IP gateway and it is not maintained across gateway changes. In other
words, the IP address may be released and replaced by a new IP address
when the IP gateway changes due to the movement of the mobile
host.Applications running as servers at a published IP address require a
Fixed IP Address. Long-standing applications (e.g., an SSH session)
may also require this type of address. Enterprise applications that
connect to an enterprise network via virtual LAN require a Fixed IP
Address.Applications with short-lived transient IP sessions can use
Session-lasting IP Addresses. For example: Web browsers.Applications with very short IP sessions, such as DNS clients and
instant messengers, can utilize Non-persistent IP Addresses. Even
though they could very well use Fixed or Session-lasting IP
Addresses, the transmission latency would be minimized when a
Non-persistent IP Addresses are used.The network creates the desired guarantee (Fixed, Session-lasting
or Non-persistent) by either assigning the address prefix
(as part of a stateless address generation process), or by assigning
an IP address (as part of a stateful IP address generation).The exact mechanism of prefix or address assignment is outside the
scope of this specification.The IP address type selection is made on a per-socket granularity.
Different parts of the same application may have different needs. For
example, control-plane of an application may require a Fixed IP
Address in order to stay reachable, whereas data-plane of the same
application may be satisfied with a Session-lasting IP Address.At any point in time, a mobile host may have a combination of IP
addresses configured. Zero or more Non-persistent, zero or more
Session-lasting, and zero or more Fixed IP addresses may be configured
on the IP stack of the host. The combination may be as a result of the
host policy, application demand, or a mix of the two.When an application requires a specific type of IP address and such
address is not already configured on the host, the IP stack shall
attempt to configure one. For example, a host may not always have a
Session-lasting IP address available. When an application requests
one, the IP stack shall make an attempt to configure one by issuing a
request to the network (see section
for more details). If the operation fails, the IP stack shall
fail the associated socket request. If successful, a Session-lasting
IP Address gets configured on the mobile host. If another socket
requests a Session-lasting IP address at a later time, the same IP
address may be served to that socket as well. When the last socket
using the same configured IP address is closed, the IP address may be
released or kept for future applications that may be launched and
require a Session-lasting IP address.In some cases it might be preferable for the mobile host to request
a new Session-lasting IP address for a new opening of an IP session
(even though one was already assigned to the mobile host by the
network and might be in use in a different, already active IP
session). It is outside the scope of this specification to define
criteria for selecting to use available addresses or choose to request
new ones. It supports both alternatives (and any combination).It is outside the scope of this specification to define how the
host requests a specific type of address (Fixed, Session-lasting or
Non-persistent) and how the network indicates the type of address in
its advertisement of IP prefixes or addresses (or in its reply to a
request).The following are matters of policy, which may be dictated by the
host itself, the network operator, or the system architecture
standard: - The initial set of IP addresses configured on the host at boot
time.- Permission to grant various types of IP addresses to a requesting
application.- Determination of a default address type when an application does
not make any explicit indication, whether it already supports the
required API or it is just a legacy application.The selection of the address type is conveyed from the applications
to the IP stack in order to influence the source address selection
algorithm .The current source address selection algorithm operates on the
available set of IP addresses, when selecting an address. According to
the proposed solution, if the requested IP address type is not
available at the time of the request, the IP stack shall make an
attempt to configure one such IP address. The selected IP address
shall be compliant with the requested IP address type, whether it is
selected among available addresses or dynamically configured. In the
absence of a matching type (because it is not available and not
configurable on demand), the source address selection algorithm shall
return an empty set.A Socket API-based interface for enabling applications to influence
the source address selection algorithm is described in . That specification defines IPV6_ADDR_PREFERENCES
option at the IPPROTO_IPV6 level. That option can be used with
setsockopt() and getsockopt() calls to set and get address selection
preferences.Furthermore, that RFC also specifies two flags that relate to IP
mobility management: IPV6_PREFER_SRC_HOME and IPV6_PREFER_SRC_COA.
These flags are used for influencing the source address selection to
prefer either a Home Address or a Care-of Address.Unfortunately, these flags do not satisfy the aforementioned needs
due to the following reasons:- Current flags indicate a "preference" whereas there is a need for
indicating "requirement". Source address selection algorithm does not
have to produce an IP address compliant with the "preference" , but it
has to produce an IP address compliant with the "requirement". - Current flags influence the selection made among available IP
addresses. The new flags force the IP stack to configure a compliant
IP address if none is available at the time of the request.- The Home vs. Care-of Address distinction is not sufficient to
capture the three different types of IP addresses described in Section
2.1.The following new flags are defined in this document and they shall
be used with Socket API in compliance with :IPV6_REQUIRE_FIXED_IP /* Require a Fixed IP address as source */IPV6_REQUIRE_SESSION_LASTING_IP /* Require a Session-lasting IP
address as source */IPV6_REQUIRE_NON_PERSISTENT_IP /* Require a Non-persistent IP
address as source */Only one of these flags may be set on the same socket. If an
application attempts to set more than one flag, the most recent
setting will be the one in effect. When any of these new flags is used, the IPV6_PREFER_SRC_HOME
and IPV6_PREFER_SRC_COA flags, if used, shall be ignored.These new flags are used with setsockopt()/getsockopt(),
getaddrinfo(), and inet6_is_srcaddr() functions . Similar to the setsockopt()/getsockopt() calls,
the getaddrinfo() call shall also trigger configuration of the required
IP address type, if one is not already available. When the new flags
are used with getaddrinfo() and the triggered configuration fails, the
getaddrinfo() call shall ignore that failure (i.e., not return an
error code to indicate that failure). Only the setsockopt() shall
return an error when configuration of the requested IP address type
fails.When the IP stack is required to use a source IP address of a
specified type, it can perform one of the following: It can use an
existing address (if it has one), or it can create a new one from an
existing prefix of the desired type. If the host does not already
have an IPv6 prefix of the specific type, it can request one from the
network.Using an existing address from an existing prefix is faster but
might yield a less optimal route (if a hand-off event occurred since its
configuration), on the other hand, acquiring a new IP prefix from the
network may take some time (due to signaling exchange with the
network) and may fail due to network policies.An additional new flag - ON_NET flag - enables the application to
direct the IP stack whether to use a preconfigured source IP address
(if exists) or to request a new IPv6 prefix from the current serving
network and configure a new IP address:IPV6_REQUIRE_SRC_ON_NET /* Set IP stack address allocation behavior
*/If set, the IP stack will request a new IPv6 prefix of the desired
type from the current serving network and configure a new source IP address.
If reset, the IP stack will use a preconfigured one if exists. If there is no
preconfigured IP address of the desired type, the IP stack will request a IPv6
prefix from the current serving network (regardless of whether this flag is set
or not).The ON_NET flag must be used together with one of the 3 flags defined
above. If ON_NET flag is used without any of these flags, it must be
ignored. If the ON_NET flag is not used, the IP stack is free to either
use an existing IP address (if preconfigured) or access the network to
configure a new one (the decision is left to implementation).The following new error codes are also defined in the document and
will be used in the Socket API in compliance with .EAI_REQUIREDIPNOTSUPPORTED /* The network does not support the
ability to request that specific IP address type */EAI_REQUIREDIPFAILED /* The network could not assign that specific
IP address type */The following example shows the code for creating a Stream socket (TCP)
with a Session-Lasting source IP address: Backwards compatibility support is required by the following 3 types
of entities: - The Applications on the mobile host- The IP stack in the mobile host- The network infrastructure Legacy applications that do not support the new flags will use the
legacy API to the IP stack and will not enjoy On-Demand Mobility
feature. Applications using the new flags must be aware that they may be
executed in environments that do not support the On-Demand Mobility
feature. Such environments may include legacy IP stack in the mobile
host, legacy network infrastructure, or both. In either case, the API
will return an error code and the invoking applications must respond
with using legacy calls without the On-Demand Mobility feature. New IP stacks must continue to support all legacy operations. If an
application does not use On-Demand Mobility feature, the IP stack must
respond in a legacy manner. If the network infrastructure supports On-Demand Mobility feature,
the IP stack should follow the application request: If the application
requests a specific address type, the stack should forward this
request to the network. If the application does not request an address
type, the IP stack must not request an address type and leave it to
the network's default behavior to choose the type of the allocated IP
prefix. If an IP prefix was already allocated to the host, the IP
stack uses it and may not request a new one from the network. The network infrastructure may or may not support the On-Demand
Mobility feature. How the IP stack on the host and the network
infrastructure behave in case of a compatibility issue is outside the
scope of this API specification. The following list summarizes the new constants definitions discussed
in this memo: The setting of certain IP address type on a given socket may be
restricted to privileged applications. For example, a Fixed IP Address
may be provided as a premium service and only certain applications may
be allowed to use them. Setting and enforcement of such privileges are
outside the scope of this document.This document has no IANA considerations.This document was merged with .
We would like to acknowledge the contribution of the following people to that document as
well:We would like to thank Alexandru Petrescu, Jouni Korhonen, Sri Gundavelli,
Dave Dolson and Lorenzo Colitti for their valuable comments and suggestions
on this work.