Multipoint Communications in a Beyond-3G Internetwork

greydullNetworking and Communications

Oct 30, 2013 (3 years and 7 months ago)

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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

4

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


polyzos@aueb.gr

6

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

7

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


polyzos@aueb.gr

8

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

9

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

10

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

polyzos@aueb.gr

11

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

12

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

13

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

polyzos@aueb.gr

14

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

15

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

24

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