Multipoint Communications in a
Beyond
-
3G Internetwork
Elias C. Efstathiou & George C. Polyzos
Mobile Multimedia Laboratory
Department of Informatics
Athens University of Economics and Business
Athens 10434, Greece
polyzos@aueb.gr
http://mm.aueb.gr/
Tel.: +30 10 8203 650, Fax: +30 10 8203 686
polyzos@aueb.gr
2
Outline
Introduction
The Internet Beyond 3G
Mobile Multicast: High
-
level Issues
IP Multicast, Mobile IP and Cellular IP
Filters and Media Stream Quality
Combining IP Multicast and Mobility
IETF Mobile Multicast Approach
Extensions to the IETF Approach
Our Perspective
IGMP Mobility Support and IGMP Assumptions
Multicast Semantics and Mobility
Mobile Multicast Requirements
Cellular IP and Mobile Multicast
The Beyond
-
3G Environment
Conclusions
polyzos@aueb.gr
3
Introduction
-
The Internet Beyond 3G
Diverse network technologies
2.5G and 3G networks
700 million cellular subscribers today
2 billion expected in the 2006
-
2007 timeframe
Digital Video Broadcasting (DVB) networks
Terrestrial (DVB
-
T), Satellite (DVB
-
S) flavors
30 Mbps of shared downlink bandwidth
IEEE 802.11 networks
11 up to 54 Mbps in the ISM band
New business models emerging
Traditional wired access networks
Ethernet
PSTN, ISDN, DSL, Cable
polyzos@aueb.gr
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The Internet Beyond 3G (cont’d)
Goal: All
-
IP internetwork
IP
-
over
-
everything, IP
-
under
-
everything
Integrated services spanning network technologies
Audio, video, data
Unidirectional and bidirectional
Support for
Multipoint Communications
?
One
-
to
-
many, many
-
to
-
many
Support for
Mobility
?
Personal mobility
Network mobility (moving ships, trains, cars)
Our focus: The Mobile Multicast Problem
IP
-
based quasi
-
reliable mobile multipoint communications
assuming a fixed routing infrastructure (no ad hoc networks)
assuming IPv4, but taking IPv6 into account
polyzos@aueb.gr
5
Mobile Multicast: High
-
level Issues
IP Multicast
Easy for some technologies only
“Native” support in Ethernet and broadcast networks…
…but,
point
-
to
-
point links
in Cellular, PSTN/ISDN and DSL
Mobility
Not supported in the original Internet design
An IP address is a subnet and interface identifier but it’s also used in
packet routing
TCP connection identifiers include lower layer IP identifiers and do
not allow them to change
Answer: Mobile IP
One address for identification, another for routing
Hostile Wireless Environment
Higher BER challenges original TCP and IP assumptions
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IP Multicast
Many
-
to
-
many communication protocol
Host group service model
a receiving host may join and leave a
multicast group
at any time
all IP hosts can communicate unidirectionally with all group members
using only the group’s identifier
(its class D multicast address)
Routing packets and tracking membership
Global
and
Local
mechanisms respectively
Global Routing Mechanisms
Multicast routing protocols deliver a group’s packets to multicast
routers that have expressed interest in receiving packets for a
particular group
DVMRP, CBT, MOSPF, PIM
Graft
delay when a multicast router joins the
multicast tree
polyzos@aueb.gr
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IP Multicast (cont’d)
Local Membership Tracking Mechanisms
Multicast router: the “
interface”
between the local and the global
mechanism
Exposes aggregate list of groups all its hosts have joined
Protocols for membership tracking
IGMP (for IPv4) and MLD (for IPv6)
Soft
-
state principle
–
no explicit
LEAVE_GROUP
primitive
IGMP assumes link
-
level native broadcast
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Mobile IP (M
-
IP)
Allows internetwork host mobility in a manner
transparent to the transport layer
M
-
IP terminology
Mobile Host (MH)
Correspondent Host (CH)
Home Agent (HA)
Foreign Agent (FA)
Care
-
of Address (CoA
–
2 types: FA CoA and co
-
located CoA)
Tunneling (IP
-
in
-
IP encapsulation)
Registration with the HA needed
Soft
-
state principle, re
-
registrations required
Delays, lost packets
“Triangle routing” inefficiency
Solved in M
-
IPv6, which specifies that all CHs can make a CoA
-
to
-
home address binding and can also tunnel and de
-
tunnel packets
polyzos@aueb.gr
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Cellular IP (C
-
IP)
C
-
IP is a
micro
-
mobility
protocol
Unlike M
-
IP’s “slow” macro
-
mobility, C
-
IP assumes “fast” mobility
Needed because M
-
IP incurs delays
FA discovery time + Registration with FA + Registration with HA
M
-
IP can violate “the mobility assumption”
“total registration delay maybe more than the time a MH spends inside a cell
[controlled by one FA]”. No packets will be delivered
C
-
IP assumptions
Campus
-
wide, partially
-
overlapping micro
-
cells
Two
-
tier architecture: C
-
IP will rely on M
-
IP
Simpler than proposed “hierarchical FA M
-
IP schemes” (
Realistic
!)
C
-
IP gateway
M
-
IP FA
“interface” between the M
-
IP and C
-
IP routing infrastructures
Base stations
IP packet forwarders
Simple routing:
no tunneling
, resembles MAC bridge frame forwarding with
auto
-
learning
polyzos@aueb.gr
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Cellular IP Access Network
Mobile IP Internetwork
Correspondent Host
Home Agent
Foreign Agent and Cellular IP Gateway
BS1
BS4
BS3
Mobile Host
BS2
Cellular IP Network
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Filters and Media Stream Quality
Filters and transcoders
Absolutely necessary for mobile multicast
Help maintain a level of
Perceived Quality of Service (P
-
QoS)
“Smart” filters, “Simple” filters
Layered coding and
multi
-
resolution layered coding
A media stream is separated into more than one stream
Sub
-
streams can be transmitted in different multicast groups
Receivers “tune into” as many as possible
Filter mobility characteristics
Fixed
Usually located at the boundary between wired and wireless section
Mobile
In multicast trees, they can propagate upstream, closer to the source,
combine into one and serve many receivers in the same sub
-
tree
polyzos@aueb.gr
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Combining IP Multicast and Mobility
Mobile devices are fundamentally different
Limited battery life
have to avoid unnecessary operations
constant network traffic monitoring is impractical
Radio interface
cannot assume high bandwidth nor low BER
Handoffs
forced disconnections
Vertical and horizontal
TDMA and CDMA with power control
no link
-
level multicast yet
IPv4 address shortage
GPRS operators rely on NAT
NAT makes IP multicast more difficult
Cellular operators interpret “multicast” differently
Cell
-
limited usually
Not the IP
-
based multicast envisaged for the Beyond
-
3G Internet
polyzos@aueb.gr
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IETF Mobile Multicast Approach
RFC 3220 (Mobile IPv4) proposes two methods
(1) MIP
-
RS
–
“Remote subscription”
Assumption
: a multicast router exists in the visited subnet
MHs simply use IGMP and (re
-
)subscribe to any number of groups
Disadvantage 1
: delay, packet losses, tree rearrangement
Disadvantage 2
: “get
-
ahead” and “lag
-
behind” problems
(2) MIP
-
BT
–
“Bi
-
directional tunneled multicast”
Assumption 1
: the MH’s HA is a multicast router
IGMP requests are tunneled to the HA
The HA joins groups on MH’s behalf
Assumption 2
: MH must decapsulate the multicast packets sent
to it through the tunnel
-
even if it uses an FA for M
-
IP
decapsulation
Disadvantage 1
: potential packet duplication
Disadvantage 2
: potential
tunnel convergence
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Packet Duplication and Tunnel Convergence
FA
MH
MH
MH
MH
HA
HA
HA
FA
MH
MH
HA
Both visiting MHs belong to the same home network
and are members of the same multicast group but
because of tunneling the FA has no way of knowing this
Visiting MHs belong to different home networks but
they are members of the same multicast group causing
multiple HA
-
FA tunnels to carry the same datagrams
polyzos@aueb.gr
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Extensions to the IETF Approach
Mobile Multicast (MoM) Protocol
Based on MIP
-
BT
.
Key extension
: The
Designated Multicast Service
Provider
(DMSP)
A DMSP for a group is an HA chosen by a subnet’s FA out of the many that
may forward packets for a specific group there
FA chooses a DMSP and performs DMSP handoffs when needed
Solves tunnel convergence
Most cited alternative to MIP
-
BT and MIP
-
RS
V. Chikarmane et al., “Multicast Support for Mobile Hosts Using Mobile IP:
Design Issues and Proposed Architecture,”
ACM/Baltzer Mobile Networks and
Applications
, 3(4):365
-
379, Jan. 1999.
Mobile Multicast with Routing Optimization (MMROP)
Based on MIP
-
RS
.
Key extension
: The
Mobility Agent
(MA)
MAs route missing packets (via tunneling) to neighboring subnets
Tunnels need to be setup between FAs
Solves get
-
ahead problem
MMROP assumes packets are somehow numbered
J. Lai et al., “Mobile Multicast with Routing Optimization for Recipient Mobility,”
Proceedings IEEE ICC2001
, pp. 1340
-
1344, June 2001.
polyzos@aueb.gr
16
Extensions to the IETF Approach (cont’d)
Constraint Tree Migration Scheme (CTMS)
Improved version of the CBT multicast routing protocol
“automatically [migrates multicast trees] to better ones while maintaining the
QoS guarantees specified my mobile users”
Reduces packets losses due to reconfigurations and join delays
Difficult to deploy
Most multicast routers still run DVMRP
K. Chen et al., “CTMS: A novel constrained tree migration scheme for
multicast services in generic wireless systems,”
IEEE JSAC
, 19:1998
-
2014,
October 2001.
Multicast Scheme for Wireless Networks (MobiCast)
Based on MIP
-
RS
.
Key
-
extension
: The
Domain Foreign Agent
(DFA)
DFAs serve many small adjacent cells
Small cells are organized in one
Dynamic Virtual Macrocell
(DVM)
Similar to hierarchical FA M
-
IP and to our joint M
-
IP/C
-
IP solution
C. Tan and S. Pink, “MobiCast: A Multicast Scheme for Wireless Networks,”
ACM MONET
, 5(4):259
-
271, 2000.
polyzos@aueb.gr
17
IGMP Mobility Support & IGMP Assumptions
IGMP was designed with Ethernet in mind
IGMP is not suitable for routers with point
-
to
-
point links
IGMP queries have to be issued to each one of these links
Not everyone will hear responses…
… unless the router multi
-
unicasts them
More state information needed at the router
IGMP is not suitable for mobile hosts
Mobile hosts cannot constantly monitor network traffic
Mobile hosts should not be forced to resend unnecessary data
Solution
use explicit
JOIN_GROUP
and
LEAVE_GROUP
primitives
polyzos@aueb.gr
18
Multicast Semantics and Mobility
Multicast semantics require reexamination in the
presence of host mobility
Example: consider two Ethernet IP subnets X and Y
Some MHs from X are visiting Y and some MHs from Y are
visiting X
224.0.0.1 is the special IPv4 link
-
local all
-
hosts multicast group
A packet addressed to 224.0.0.1 is sent to X
–
what happens?
Packet is delivered only to hosts in subnet X regardless if they are
visitors or not
Packet is delivered only to hosts in subnet X that are not visitors
Packet is delivered to all X hosts irrespective of location
Answer: it depends on the originating service protocol
IPv6 will help: defines
link local
,
site local
and
organizational local
multicast scopes
polyzos@aueb.gr
19
Mobile Multicast Requirements
Significant vs non
-
significant moves
If a MH move causes the new subnet’s multicast router to subscribe
to new groups, the move is significant
Non
-
significant moves should have no effect on the global
mechanisms
Both types must appear similar from the user’s perspective
Multicast packet buffering
Buffer packets until when?
Disconnections due to
Handoffs
Physical layer problems
User intent
Mobile subnets
Deal with them as one logical entity
Roaming
Sophisticated authentication and pricing schemes are also required
polyzos@aueb.gr
20
Cellular IP and Mobile Multicast
Integrate efficient multicast mechanisms into C
-
IP
Use C
-
IP in conjunction with M
-
IP
Based on IETF’s C
-
IP and M
-
IP interoperability ideas
Scalability concerns
Similar to the MobiCast scheme
MobiCast DFA
C
-
IP gateway
MobiCast DVM
C
-
IP subnet
Based on MIP
-
RS
Closer to real
-
life network deployments
Campus
-
wide 802.11 internetworks
UMTS cells
DVB
-
T macrocells
MIP
-
BT tunneling not scalable
MHs should first exploit resources in their immediate environment
polyzos@aueb.gr
21
Cellular IP and Mobile Multicast (cont’d)
“Flat” address space in C
-
IP
Multicast addresses do not appear different from unicast addresses
Simple mapping of IP identifiers to forwarder ports
C
-
IP has keep
-
alive mechanisms similar to IGMP
Adapt the C
-
IP “route
-
update” packet mechanism
MHs send these packets but instead of using their own IP address in
the source field, they use the multicast group address instead
When, with C
-
IP forwarding, they reach the C
-
IP gateway, the
gateway (M
-
IP FA) may then subscribe to a group, if it’s not receiving
it already.
No need for IGMP. Reuse C
-
IP soft state mechanisms.
Multicast groups can be “virtual” C
-
IP hosts
C
-
IP forwarders should handle IP address
-
to
-
multiple ports mappings
C
-
IP gateway must be a multicast router
MHs use their IP stack in an “unconventional” way
Packet duplication only when paths towards receivers diverge!
polyzos@aueb.gr
22
Cellular IP and Mobile Multicast (cont’d)
Global Multicast Routing Protocol
224.1.2.3 transmission
source
Foreign Agent and Cellular IP Gateway
BS1
BS4
BS3
Mobile Host
BS2
Mobile Host
Mobile Host
The 3 MHs subscribe to 224.1.2.3 by
sending
route_update
with 224.1.2.3 as
the source IP address.
BSs update tables
accordingly for virtual MH “224.1.2.3”:
BS1
BS2
BS2
BS3 and BS4
BS3 and BS4 do link
-
local broadcast
The FA/CIP
-
GW grafts to new multicast
trees every time a
route_update
with a
new group arrives. IGMP
-
like soft
-
state
assured through C
-
IP mechanisms.
polyzos@aueb.gr
23
The Beyond
-
3G Environment
Many, superimposed, cellular technologies
Even if we ignore satellites…
DVB
-
T (1
-
100 Km) macrocells
DVB
-
T with 3G as the return channel
5
-
30 Mbps of shared bandwidth
3G neighborhood size cells
802.11 microcells
Devices with multiple interfaces
802.11 combined with DVB or GPRS
Mobile IP an accepted standard
M
-
IP support in devices and networks
Improved TCP versions
Filter and transcoding standards
polyzos@aueb.gr
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Conclusions
The Multipoint Communications Problem
Standard IETF protocols can solve it
IP multicast
Mobile IP
Cellular IP
The Environment Beyond
-
3G will be based on IP
Therefore, most of these IP
-
based solutions will be applicable
Future Research Areas in Mobile Multicast
Ad hoc networks
Strong reliability
Security
Roaming and pricing agreements
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