Context Transfer, Handoff Candidate Discovery, and Dormant Mode Host Alerting (seamoby)

Last Modified: 2004-06-08


Pat Calhoun <>
James Kempf <>

Transport Area Director(s):

Allison Mankin <>
Jon Peterson <>

Transport Area Advisor:

Allison Mankin <>

Technical Advisor(s):

Basavaraj Patil <>
Pekka Savola <>
Antti Tuominen <>

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Description of Working Group:

During the fast handoff discussions within the Mobile IP WG, a need for
a new protocol was identified that would allow state information to be
transferred between edge mobility devices. Examples of state
that could be useful to transfer is AAA information, security context,
QOS properties assigned to the user, Robust Header Compression
information, etc.

Further, Standards Defining Organizations (SDOs) that work on wireless,
such as 3GPP, 3GPP2, IEEE and others, are hoping that the IETF will be
able to provide a set of protocols that will enable them to provide
real-time services over an IP infrastructure, and, along with Mobile
IP, SeaMoby is expected to provide such protocols. Furthermore, the
protocols developed by the Seamoby Working Group must allow for
real-time services to work with minimal disruption across heterogeneous
wireless, and wired, technologies.

It is expected that SDOs working on wireless technologies will provide
their input into the WG during the requirements gathering and protocol
design phase.

In addition to Context Transfer, the working group has identified two
more technologies that are important for use as tools for providing
real-time services over IP wireless infrastructure:  Handoff Candidate
Discovery and Dormant Mode Host Alerting (aka "IP paging"). Another
technology, micro-mobility, in which routing occurs without the Mobile
IP address change, was determined by WG discussions to require
research; it has been removed by the present rechartering and the topic
has been addressed to the IRTF Routing Research Group. The present
charter (revised from its original form) is to define and then possibly
develop the three technologies.  The WG will ensure that its
deliverables are compatible with the Mobile IP Working Group's mobility
management technology.

Context Transfer

There are a large number of IP access networks that support mobility of
hosts. For example, wireless Personal Area Networks (PANs) and LANs,
satellite and cellular WANs. The nature of this roaming is such that
communication path to the host changes frequently, and rapidly. In many
situations, the chage of communications path includes a change in
communications media between the host and access networking, including
changes from a wireless to a wired connection and changes between
wireless technologies even under common administration.

Although the protocol used to actively re-direct the IP packet flows
during a change in a mobile's point of attachment is handled by the
Mobile IP WG, there is a need for preserving the context of its active
IP flows. The IP flow context that might be useful to transfer could
include, but not be limited to security context, policy, QOS (diffserv
or intserv as needed) header compression, and accounting/AAA

The SeaMoby Working group will analyze the requirements and tradeoffs
for the goal of transferring context information from a mobile's old
access to the new access device. Depending on the results of the
requirements analysis, the SeaMoby WG will develop a protocol (or start
from an existing protocol such as Contract Net Protocol (CNP) or the
IEEE's 802.11f) to transfer the context information for a session.

Handoff Candidate Discovery

Second, while the Mobile IP Working Group in particular is developing
protocols to provide "fast handoff" solutions, the mechanisms
currently under development assume that a set of candidates has
already been chosen and and that handoff should be initiated to all of
them. However, the selection of suitable candidates is not part of the
Mobile IP WG's overall scope.  The Seamoby Working Group has
documented that "seamless" handoffs can best be achieved by
considering multiple handoff candidates and selecting one or more of
them as targets for context transfer. This problem is within scope of
Seamoby. Specifically, Seamoby will define the work in a problem
statement, and if needed, will define the requirements and the
protocol for a handoff candidate discovery protocol, which could be
used with any mobility management protocol.

Dormant Mode Host Alerting

Third, the Working Group will define the requirements for Dormant Mode
Host Alerting (DMHA) at the IP layer (also known as IP Paging) in
networks, and a protocol will be developed to tackle this problem. DMHA
is typically used in networks that support mobile devices that
periodically enter dormant mode to reduce power consumption. DMHA
network devices to track a mobile that has moved from its last point of
attachment, while in dormant mode, allowing the mobile's packets to be

All work produced by the Working Group will support both IPv4 and IPv6,
will follow the congestion control principles in RFC2914 (BCP41), and
will undergo a security review prior to WG last call. Protocols
developed will be accompanied by MIBs.

The Working Group will coordinate closely with the aaa, mobileip, pilc,
and rohc working groups.

Goals and Milestones:

Done    Submit I-D on Layer 3 Paging Requirements & Needs assesment
Done    Submit revised charter to IESG with any changes needed especially with respect to the micro-mobility evaluation
Done    Submit I-D on Dormant Mode Host Alerting Requirements to IESG for consideration as Informational
Done    Submit Inter Access Point Context Transfer Problem Statement to IESG
Done    Submit Handoff Candidate Discovery Problem Statement to IESG
Done    Submit Inter Access Point Context Transfer Protocol Requirements to IESG for consideration as Informational
Done    Inter Access Point Context Transfer Protocol to IESG for consideration as a Proposed Standard
Done    Handoff Discovery Protocol to IESG for consideration as a Proposed Standard

No Current Internet-Drafts

Request For Comments:

Dormant Mode Host Alerting ('IP Paging') Problem Statement (RFC 3132) (34985 bytes)
Requirements and Functional Architecture for an IP Mobile Node Alerting Protocol (RFC 3154) (31534 bytes)
Problem Description: Reasons For Performing Context Transfers Between Nodes in an IP Access Network (RFC 3374) (28245 bytes)
Mobility Related Terminology (RFC 3753) (0 bytes)
Candidate Access Router Discovery (CARD) (RFC 4066) (116733 bytes)
Context Transfer Protocol (CXTP) (RFC 4067) (77718 bytes)
Instructions for Seamoby Experimental Protocol IANA Allocations (RFC 4065) (16179 bytes)