INTERNET-DRAFT Zach D. Shelby
Petri Mähönen
University of Oulu
Dionisios Gatzounas
Intracom
Alessandro Inzerilli
Ville Typpö
VTT Electronics
June 2001
Cellular IP Route Optimization
<draft-shelby-cip-routeoptimization-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document introduces a technique for intra-domain route
optimization. This is applicable to both the Cellular IP [1] and
Cellular IPv6 [2] proposals. Appendix A is included showing text
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changes required to apply this to [2].
1. Introduction
Traffic between mobile hosts within a wireless access IP network is
an important consideration for the application of the CIP protocol.
Currently in [1] and [2] there is a requirement that traffic must
always be routed through the CIP gateway. This is to retain routing
cache consistency.
In order to optimize the performance of these networks, a route
optimization method is proposed here which is applicable to both Cel-
lular IP and Cellular IPv6. No new entities are added, and soft
state routing is maintained throughout. The optimization function is
transparent to mobile hosts.
A performance review of the technique is presented in [3]. The code
can be downloaded from [4] for Linux. Simulation code for OPNET may
be available in the future. The basic performance result is as fol-
lows (simulated). The number of hops taken on routes is less and the
end-to-end delay of traffic across the network is lower. The perfor-
mance gains rise as the percentage of intra-domain traffic is
increased.
1.1. Applicability
Applicable to all CIP and CIPv6 networks where Intra-domain traffic
between mobile hosts is common and a multi-level hierarchy of routers
is used.
1.2. New Architectural Entities
None.
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1.3. Terminology
Crossover node
Any node that maintains multiple downlink interfaces.
Optimizing CIP node
Closest common node between two Mobile Hosts used to perform the
route optimization.
Optimization teardown packet
Packet sent in order to clear route optimization upon handoff. Sent
from both downlink and uplink.
Proxy route-update packet
A control packet sent from an optimizing CIP node uplink towards the
Gateway on behalf of a mobile host. The address of the mobile host
is encoded in the Route Optimization control information field.
Route Optimization
Service performed by CIP node so that traffic takes the shortest
route possible between two Mobile Hosts within the same CIP network.
This traffic does not need to traverse the gateway.
2. Specification
The requirement for routing all uplink traffic through the gateway,
regardless of destination address is required for protocol con-
sistency in CIP. However, in networks with a high level of intra-
domain traffic, this can be a performance & congestion problem. In
this document an optional uplink route optimization is proposed. This
would be implemented only for active mobile hosts and in possible
crossover nodes since any crossover node can potentially be the
optimizing node between two communicating mobile hosts. Only one
crossover node at any time performs route optimization for a single
pair of communicating mobile hosts in the same Cellular IP network.
Crossover nodes add a 6th criteria in their routing cache; The Tear-
down Optimization (TO) flag. This TO flag is unset by default.
When a crossover node receives a data packet from a downlink inter-
face, it checks the downlink route cache for a mapping that
corresponds to the packet's destination address. If a mapping is
found without the Teardown-Optimization (TO) flag set, then route
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optimization is performed and the packet is relayed to the
corresponding downlink interface. At the same time, a proxy route-
update packet is sent to the gateway. The route optimization control
field is added containing the IP address of the mobile host optimiza-
tion is being performed for. While optimization is being performed,
proxy route-update packets are sent uplink at a rate just faster than
the route timeout. Uplink nodes then use this proxy route-update
packet's route optimization control field to update route caches.
When other traffic from that MH is forwarded uplink, this resets the
timer for sending the next proxy route-update. If no optimization is
performed during one route-timeout period, then the sending of proxy
update packets ceases (optimization ends).
When an active mobile host performs a handoff to a new BS, it first
must transmit an optimization teardown packet to the current BS. This
packet does not erase the cache entry for this mobile host at each
optimizing node. It only sets the TO flag of mappings making the
mobile host "unavailable" to receive route-optimized data. Therefore,
data can no longer be optimized to this host, but will be normally
forwarded uplink. Upon receiving the optimization teardown packet,
the optimizing node ceases to send proxy update packets for the
corresponding mobile host.
If this optimization teardown packet was lost on the wireless chan-
nel, it would create a black out time of one route-timeout for the
optimized traffic. To avoid this, an extra optimization teardown
packet is also sent by the uplink crossover node of the old and new
base stations. This is detailed in Appendix A: section 2.3.
3. Security Considerations
The use of a proxy route-update message requires a security relation-
ship between crossover nodes and the gateway. This is because update
packets must be authenticated. This relationship is not problematic
since both nodes are under a single administration.
This draft imposes no other security concerns beyond that mentioned
in [1] and [2].
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Appendix A. Text changes to CIPv6 I-D [2]
(1.4 Protocol Overview)
Paragraph 3:
By default all IP packets transmitted by a mobile host are routed
from the Base Station to the Gateway by hop-by-hop shortest path
routing, regardless of the destination address. However, with route
optimization being performed, IP traffic between two mobile hosts in
the same CIP network is routed through the optimizing CIP node.
(2.2 Routing)
Paragraph 1:
Packets transmitted by mobile hosts are routed to the Gateway using
shortest path hop-by-hop routing. However, if these packets are des-
tined for another active mobile host in the same CIP network then
routing is performed through the optimizing CIP node. Cellular IP
nodes monitor these passing data packets and use them to create and
update Route Cache mappings. These map mobile host IP addresses to
Downlink neighbors of the Cellular IP node. Packets addressed to the
mobile host are routed along the reverse path, on a hop-by-hop basis,
by these Route Cache mappings.
(2.3 Handoff)
Handoff is initiated by the mobile host. As an active mobile host
approaches a new Base Station, it transmits a route-update packet and
redirects its packets from the old to the new Base Station. It
transmits also a route optimization teardown packet to the old Base
Station. This packet will be routed uplink towards the gateway and
will set the TO flag of corresponding mappings at each optimizing
node, thus making the mobile host "unavailable" to receive any
route-optimized data. The route-update packet will configure Route
Caches along the way from the new Base Station to the Gateway. (The
paths leading to the old and new Base Stations may overlap. In nodes
where the two paths coincide, the route-update packet simply
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refreshes the old mapping and the handoff remains unnoticed.) In a
node which is a crossover point between the old and new BSs there
will already be an older cache entry for this MH on another inter-
face. This older cache entry is removed and if the TO flag is not set
(probably the teardown optimization sent through the old BS was lost)
another route optimization teardown packet is sent downlink on that
interface. This packet will be routed downlink following the MH's old
cache mappings that have not yet been expired and will set the TO
flag at each optimizing node. This assures that optimization is
correctly ended upon handoff.
An idle mobile host, moving to a new Base Station, transmits a
paging-update packet only if the new Base Station is in a new Paging
Area. During handoffs between Base Stations within the same Paging
Area idle mobile hosts may remain silent, as paging is performed
within the entire Paging Area.
(3.3.2. Route-Update packet)
The following control option must be added:
Route Optimization
IP address of Mobile Host which route optimization is
being performed for.
(3.3.5. Proxy route-update packet)
A proxy route-update packet is an IPv6 packet with a Hop-by-Hop
Options extension header where
- the source address is the IP address of the sending optimizing CIP node;
- the destination address is the Gateway; and
- the Hop-by-Hop option is of proxy route-update type.
The option of the proxy route-update packet carries control informa-
tion in the same format as the route-update packet. The Route Optimi-
zation control information field carries the address of the mobile
host which route optimization is being performed for. The S and I
flags must be 0 for proxy route-update packets.
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(3.3.6. Route optimization teardown packet)
A route optimization teardown packet is an IPv6 packet with a Hop-
by-Hop Options extension header where the Hop-by-Hop option is of
route optimization teardown type.
If it is sent by a mobile host (uplink direction)
- the source address is the IP address of the sending mobile host; and
- the destination address is the Gateway;
However, if it is sent by a node (downlink direction)
- the source address is the address of the sending node; and
- the destination address is the IP address of the mobile host that route
optimization teardown is being performed for.
The payload of the route optimization teardown packet carries control
information in the same format as the route-update packet. The S, and
I flags must be 0 for route optimization teardown packets. This
packet is processed only by optimizing nodes.
(3.6.2 Uplink Routing)
Paragraphs 1 and 2: A packet arriving at a node from one of its Down-
link neighbors is assumed to be coming from a mobile host. The
packet is first used to update the node's Route and Paging Caches and
is then forwarded to the node's Uplink neighbor. However, if the node
is a crossover node, the route cache is searched for a mapping that
corresponds to packet's destination address.
To update the Caches, the node reads the packet type, port number and
the source IP address. Paging-update packets update the Paging Cache
only. Route-update packets update both Route and Paging Caches. Data
packets only refresh the soft state of both caches, but do not change
it. Both types of caches consist of
{ IPv6 address, interface, MAC address, expiration time, timestamp }
5-tuples, called mappings. The Route Cache of crossover nodes con-
tain an additional field being the Teardown Optimization (TO) flag.
This TO flag is unset by default and is set each time a route optimi-
zation teardown packet is received on either the uplink or downlink
interface. The IPv6 address is the address of the mobile host the
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mapping corresponds to. The interface and the MAC address denote the
Downlink neighbor toward the mobile host. The timestamp field con-
tains the timestamp of the control packet that has established the
mapping.
Two additional paragraphs are needed before the last sentence: When a
route-update packet arrives on a different downlink interface than
that is in its mapping, a route optimization teardown packet is first
sent on the interface that corresponds to the "old" mapping and then
the caches are updated.
When a route optimization teardown packet arrives on a downlink
interface of an optimizing node then the authentication is first
validated. For valid packets the node searches its Route Cache for a
mapping that corresponds to packet's source address. If a mapping is
found the TO flag is set.
(3.6.3 Downlink Routing)
An additional paragraph is needed at the end:
A route optimization teardown packet arriving at the uplink interface
of an optimizing CIP node sets the TO flag of the mapping that
corresponds to packet's destination address. Then the packet is for-
warded to the corresponding downlink interface. The CIP gateway is
exempt from this function.
References
[1] "Cellular IP," A. T. Campbell, J. Gomez, C-Y. Wan, S. Kim, Z.
Turanyi, A. Valko, Work in Progress, <draft-ietf-mobileip-
cellularip-00>, January 2000.
[2] "Cellular IPv6," Z. D. Shelby, D. Gatzounas, A. T. Campbell, C-Y. Wan
Turanyi, A. , Work in Progress, <draft-shelby-seamoby
cellularipv6-00>, November 2000.
[3] "Route Optimization for Cellular IP networks" D. Gatzounas A. Malataras,
C. Chrisanthakopoulos, Z. Shelby, A. Inzerilli, IPCN' 2001, May 2001.
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[4] "Cellular IPv6 homepage" WINE project, <http://cipv6.intranet.gr>, June 2001.
Authors' Addresses
Zach D. Shelby, Dr. Petri Mähönen
University of Oil
Center for Wireless Communications
PO Box 4500
90014 Oil, Finland
phone: +358 40 779 6297
email: zach.shelby@ee.oulu.fi
Dionisios D. Gatzounas
INTRACOM S.A.
Development Programmes Department
Panepistimiou 254
26443 Patras
GREECE
phone: +30 61 465168
fax: +30 61 465070
email: dgat@intracom.gr
Ville Typpö, Alessandro Inzerilli
Technical Research Center of Finland
Wireless Internet Laboratory
Kaitoväylä 1
FIN-90571 Oil, Finland
phone: +358 8 551 2164
fax : +358 8 551 2320
email: ville.typpo@vtt.fi
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Table of Contents
1. Introduction ................................................... 2
1.1. Applicability ................................................ 2
1.2. New Architectural Entities ................................... 2
1.3. Terminology .................................................. 3
2. Specification .................................................. 3
3. Security Considerations ........................................ 4
Appendix A. Text changes to CIPv6 I-D [2] ......................... 5
(1.4 Protocol Overview) ........................................... 5
(2.2 Routing) ..................................................... 5
(2.3 Handoff) ..................................................... 5
(3.3.2. Route-Update packet) ...................................... 6
(3.3.5. Proxy route-update packet) ................................ 6
(3.3.6. Route optimization teardown packet) ....................... 7
(3.6.2 Uplink Routing) ............................................ 7
(3.6.3 Downlink Routing) .......................................... 8
References ........................................................ 8
Authors' Addresses ................................................ 9
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