Transcript Multipoint Communications in a Beyond

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
[email protected]
http://mm.aueb.gr/
Tel.: +30 10 8203 650, Fax: +30 10 8203 686
Outline
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Introduction
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IP Multicast, Mobile IP and Cellular IP
Filters and Media Stream Quality
Combining IP Multicast and Mobility
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IETF Mobile Multicast Approach
Extensions to the IETF Approach
Our Perspective
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The Internet Beyond 3G
Mobile Multicast: High-level Issues
IGMP Mobility Support and IGMP Assumptions
Multicast Semantics and Mobility
Mobile Multicast Requirements
Cellular IP and Mobile Multicast
The Beyond-3G Environment
Conclusions
[email protected]
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Introduction - The Internet Beyond 3G
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Diverse network technologies
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2.5G and 3G networks
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Digital Video Broadcasting (DVB) networks
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Terrestrial (DVB-T), Satellite (DVB-S) flavors
30 Mbps of shared downlink bandwidth
IEEE 802.11 networks
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700 million cellular subscribers today
2 billion expected in the 2006-2007 timeframe
11 up to 54 Mbps in the ISM band
New business models emerging
Traditional wired access networks
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[email protected]
Ethernet
PSTN, ISDN, DSL, Cable
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The Internet Beyond 3G (cont’d)
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Goal: All-IP internetwork
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IP-over-everything, IP-under-everything
Integrated services spanning network technologies
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Support for Multipoint Communications?
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One-to-many, many-to-many
Support for Mobility?
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Audio, video, data
Unidirectional and bidirectional
Personal mobility
Network mobility (moving ships, trains, cars)
Our focus: The Mobile Multicast Problem
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IP-based quasi-reliable mobile multipoint communications
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assuming a fixed routing infrastructure (no ad hoc networks)
assuming IPv4, but taking IPv6 into account
[email protected]
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Mobile Multicast: High-level Issues
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IP Multicast
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Easy for some technologies only
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Mobility
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Not supported in the original Internet design
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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
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“Native” support in Ethernet and broadcast networks…
…but, point-to-point links in Cellular, PSTN/ISDN and DSL
One address for identification, another for routing
Hostile Wireless Environment
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[email protected]
Higher BER challenges original TCP and IP assumptions
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IP Multicast
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Many-to-many communication protocol
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Host group service model
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Routing packets and tracking membership
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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)
Global and Local mechanisms respectively
Global Routing Mechanisms
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Multicast routing protocols deliver a group’s packets to multicast
routers that have expressed interest in receiving packets for a
particular group
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DVMRP, CBT, MOSPF, PIM
Graft delay when a multicast router joins the multicast tree
[email protected]
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IP Multicast (cont’d)
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Local Membership Tracking Mechanisms
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Multicast router: the “interface” between the local and the global
mechanism
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Protocols for membership tracking
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Exposes aggregate list of groups all its hosts have joined
IGMP (for IPv4) and MLD (for IPv6)
Soft-state principle – no explicit LEAVE_GROUP primitive
IGMP assumes link-level native broadcast
[email protected]
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Mobile IP (M-IP)
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Allows internetwork host mobility in a manner
transparent to the transport layer
M-IP terminology
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Registration with the HA needed
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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)
Soft-state principle, re-registrations required
Delays, lost packets
“Triangle routing” inefficiency
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Solved in M-IPv6, which specifies that all CHs can make a CoA-tohome address binding and can also tunnel and de-tunnel packets
[email protected]
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Cellular IP (C-IP)
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C-IP is a micro-mobility protocol
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Unlike M-IP’s “slow” macro-mobility, C-IP assumes “fast” mobility
Needed because M-IP incurs delays
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M-IP can violate “the mobility assumption”
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FA discovery time + Registration with FA + Registration with HA
“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
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Campus-wide, partially-overlapping micro-cells
Two-tier architecture: C-IP will rely on M-IP
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C-IP gateway  M-IP FA
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Simpler than proposed “hierarchical FA M-IP schemes” (Realistic!)
“interface” between the M-IP and C-IP routing infrastructures
Base stations  IP packet forwarders
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Simple routing: no tunneling, resembles MAC bridge frame forwarding with
auto-learning
[email protected]
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Cellular IP Access Network
Correspondent Host
Mobile IP Internetwork
Home Agent
Foreign Agent and Cellular IP Gateway
Cellular IP Network
BS1
BS2
BS4
BS3
Mobile Host
[email protected]
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Filters and Media Stream Quality
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Filters and transcoders
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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
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A media stream is separated into more than one stream
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Sub-streams can be transmitted in different multicast groups
Receivers “tune into” as many as possible
Filter mobility characteristics
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Fixed
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Usually located at the boundary between wired and wireless section
Mobile
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In multicast trees, they can propagate upstream, closer to the source,
combine into one and serve many receivers in the same sub-tree
[email protected]
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Combining IP Multicast and Mobility
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Mobile devices are fundamentally different
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Limited battery life  have to avoid unnecessary operations
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Radio interface  cannot assume high bandwidth nor low BER
Handoffs  forced disconnections
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Vertical and horizontal
TDMA and CDMA with power control  no link-level multicast yet
IPv4 address shortage
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GPRS operators rely on NAT
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constant network traffic monitoring is impractical
NAT makes IP multicast more difficult
Cellular operators interpret “multicast” differently
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Cell-limited usually
Not the IP-based multicast envisaged for the Beyond-3G Internet
[email protected]
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IETF Mobile Multicast Approach
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RFC 3220 (Mobile IPv4) proposes two methods
(1) MIP-RS – “Remote subscription”
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Assumption: a multicast router exists in the visited subnet
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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”
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Assumption 1: the MH’s HA is a multicast router
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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
[email protected]
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Packet Duplication and Tunnel Convergence
HA
HA
FA
FA
MH
MH
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
[email protected]
HA
HA
MH
MH
MH
MH
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
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Extensions to the IETF Approach
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Mobile Multicast (MoM) Protocol
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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)
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[email protected]
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.
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Extensions to the IETF Approach (cont’d)
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Constraint Tree Migration Scheme (CTMS)
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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
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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)
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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.
[email protected]
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IGMP Mobility Support & IGMP Assumptions
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IGMP was designed with Ethernet in mind
IGMP is not suitable for routers with point-to-point links
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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
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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
[email protected]
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Multicast Semantics and Mobility
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Multicast semantics require reexamination in the
presence of host mobility
Example: consider two Ethernet IP subnets X and Y
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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?
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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
[email protected]
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Mobile Multicast Requirements
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Significant vs non-significant moves
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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
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Buffer packets until when?
Disconnections due to
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Mobile subnets
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Handoffs
Physical layer problems
User intent
Deal with them as one logical entity
Roaming
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Sophisticated authentication and pricing schemes are also required
[email protected]
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Cellular IP and Mobile Multicast
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Integrate efficient multicast mechanisms into C-IP
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Similar to the MobiCast scheme
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Use C-IP in conjunction with M-IP
Based on IETF’s C-IP and M-IP interoperability ideas
Scalability concerns
MobiCast DFA  C-IP gateway
MobiCast DVM  C-IP subnet
Based on MIP-RS
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Closer to real-life network deployments
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Campus-wide 802.11 internetworks
UMTS cells
DVB-T macrocells
MIP-BT tunneling not scalable
MHs should first exploit resources in their immediate environment
[email protected]
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Cellular IP and Mobile Multicast (cont’d)
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“Flat” address space in C-IP
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C-IP has keep-alive mechanisms similar to IGMP
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Multicast addresses do not appear different from unicast addresses
Simple mapping of IP identifiers to forwarder ports
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
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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!
[email protected]
21
Cellular IP and Mobile Multicast (cont’d)
224.1.2.3 transmission
source
Global Multicast Routing Protocol
Foreign Agent and Cellular IP Gateway
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
BS1
BS2
BS4
Mobile Host
BS3
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.
[email protected]
Mobile Host
Mobile Host
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The Beyond-3G Environment
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Many, superimposed, cellular technologies
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Even if we ignore satellites…
DVB-T (1-100 Km) macrocells
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802.11 combined with DVB or GPRS
Mobile IP an accepted standard
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3G neighborhood size cells
802.11 microcells
Devices with multiple interfaces
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DVB-T with 3G as the return channel
5-30 Mbps of shared bandwidth
M-IP support in devices and networks
Improved TCP versions
Filter and transcoding standards
[email protected]
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Conclusions
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The Multipoint Communications Problem
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Standard IETF protocols can solve it
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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
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Ad hoc networks
Strong reliability
Security
Roaming and pricing agreements
[email protected]
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