Transcript Title Subtitle

16ng BOF
IETF-64 Meeting
Vancouver, November 7th 2005
802.16 Convergence Sublayer Selection for
IPv4 and IPv6 transport
Overview & Issues
Jeff Mandin ([email protected])
Overview
 The fundamental issues in creating a specification for IP transport over
802.16 are:



Determination of the IP subnetwork model
selection of a 802.16 “Convergence Sublayer type”
specification of how to set up the “classifier tables” in the convergence sublayer
 The 802.3/ethernet convergence sublayer type is the obvious
choice for IP transport




Clean and simple solution
By providing generic L2 services, full support for IPv4 and IPv6 are
automatically available
Compatible with host and router IPv4/v6 stacks
Header Suppression/Compression, Broadcast control mechanisms can
reduce the 802.3 overhead to almost zero; Proxy ND for powersaving
 IETF includes the expertise relevant for proper standardization of
IPv4 / IPv6 over IEEE 802.16


Nov 7, 2005
16ng charter should be broadened to include IPv4 over .16
Should standardize a generic 802.3/Eth CS solution for IP
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Convergence Sublayer – why and what
 802.16 does not support any kind of “native” application
access to its MAC:
o Native access would expose the 802.16 Common Part
Sublayer to the higher-layer application
o With native access, it would be necessary for (eg.) an IP
router layer to maintain information about individual
unidirectional (and possibly multicast) 802.16 MAC
connections
o This would be unwieldy, and also force applications to
include 802.16-media-specific processing
 Instead, the 802.16 MAC provides a logical layer (ie. the CS) to
“converge” the 802.16 MAC to a well-known interface type
Nov 7, 2005
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Convergence Sublayer Operation
Higher Layer Entity (e.g. Host IP or Ethernet Layer)
SDU
Classifier
CID #1
CID #2
CID #N
Convergence
Sub Layer
PHS
PHS
Scheme:
PHS
SDU + CID
MAC Common Part Sub Layer
Nov 7, 2005
 Classification
— SDUs are assigned to
MAC Connections based
on data fields only
— MAC connection has a
particular destination and
QoS parameter set
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Convergence Sublayer Types
 The full list of CS types from 802.16-2004:
 No CS (behaviour is not defined)
 IPv4
 IPv6
 802.3/ethernet
 802.1Q/VLAN
 IPv4 over 802.3/ethernet
 IPv6 over 802.3/ethernet
 IPv4 over 802.1Q/VLAN
 IPv6 over 802.1Q/VLAN
 ATM
 For the purposes of the IP transport discussion, we
may group the CS types ie.
 802.3/Ethernet-based (ie. including 802.1Q types)
 IPv4/IPv6
 ATM CS has garnered little interest, so we disregard it
Nov 7, 2005
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Airlink resource conservation with
802.3/Ethernet CS
•
Repetitive 802.3 header can be
suppressed/compressed so as to reduce payload
overhead
•
802.16 Payload Header Suppression (PHS) feature replaces 802.3
header with 1 byte PHS Index
•
802.16e includes Robust Header Compression ( ROHC )
functionality – can reduce the overhead to 0 bytes
•
Selective broadcast filtering prevents unnecessary
control traffic
•
Proxy ARP/ND to prevent waking up devices that are in
sleep mode
Nov 7, 2005
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Selecting the IP Subnetwork model
 What should constitute a “link” or “subnet” from the IP
perspective when a host or gateway is connected to an
802.16 point-to-multipoint network? Some options:
a) Can view the PMP network as a collection of point-to-point links
b) Can create an “emulated broadcast network” at layer 2 which the IP
layer then regards as a regular IEEE 802-style broadcast network
 NBMA model seems to be not relevant - as NBMA
networks support direct communication between leaf
nodes (which 802.16 does not)
 point-to-point model is disadvantaged by lack of
support in 802.16 for PPP or similar mechanism
 Most (perhaps all) proposals to date use the emulated
broadcast network model
Nov 7, 2005
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Summary of CS features
Eth CS
IPv4/v6 CS
Upper Edge
Service
Interface
Standard (looks
like 802.3 driver)
Non-standard (IPv4/v6 datagram
interface is neither L2 nor L3)
Downlink
Classification
Classifies
Classifies packets to wireless
packets to
wireless MAC
connections using
L2 addresses with L3/L4 fields
available for QoS
differentiation
MAC connections using IP
addresses
Trivially
compatible with
existing stacks
Requires stateful network
monitoring, since IP addresses are
assigned with DHCP or other
dynamic mechanisms
Unsolved problems with IPv6
autoconfig
Nov 7, 2005
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Summary of CS features (cont.)
Eth CS
Airlink format
IPv4/v6 CS
Payload includes
Payload carries IP
802.3 header – so
uplink packets can be
addressed to a
specific IP Router/MIP
Foreign Agent
datagrams only
There can be
beyond link endpoints
multiple nodes at
subscriber side
(identified by MAC
addr)
So air link is pointto-point
No L2 addressability
No control plane
transport
802.3 format can
carry control plane
protocols (ARP,
802.1x)
Nov 7, 2005
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Summary of CS features (cont.)
Eth CS
Airlink overhead
Nov 7, 2005
IPv4/v6 CS
Compression and
No L2 overhead, but
Proxy techniques can
remove almost all
overhead
no L2 capabilities
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Even point-to-point
service would require
manual configuration
- since there is no
control plane support
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Postscript: Status of IP transport work in
Wimax Forum

2 approaches being developed in parallel in Network Working
Group:
a) Broadcast network emulation based on 802.3/Ethernet Convergence
Sublayer types (for IPv4 and IPv6)
- supports optional PPPoE mode of operation
b) Approach based on IPv4 Convergence Sublayer type (ie. Raw IP datagrams
as the 802.16 payload)
- Minimal details in NWG spec currently, eg. no description of how to
perform IP address resolution

Wimax Forum Network Working Group is committed to supporting
both these approaches in its end-to-end architecture

Wimax Forum Profiles group (MTG) is currently considering
whether to endorse one particular approach or mandate support of
both (despite the fact that both these approaches remain largely
unpublished “work-in-progress”).

The problem of IPv4/IPv6 support in 802.16 can benefit from IETF
expertise and standardization
Nov 7, 2005
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Thank you
Nov 7, 2005
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Appendix
Example of broadcast network emulation
with Eth CS
Gateway
IP router
MAC Bridge
filters
Backhaul
Base Station Unit
802.16
MAC and PHY
LAN Broadcast
Connection
(Classifier
ff:ff:ff:ff:ff:ff)
Uplink
connection
bundle
Downlink unicast
connection bundle
(provisioned classifiers
include
host MAC address)
All
Connections
are 802.3 CS
802.16 MAC and PHY
SAP
Host (ie. laptop, VoIP phone, etc.) with host MAC
address (yy:yy:yy:yy:yy:yy)
Subscriber Station Unit
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Impact of a Particular Convergence Sublayer
Use of a particular CS type determines 3 things:
1. SDU Interface presented to the higher-layer application (ie.
802.3/ethernet CS carries 802.3-format frames and
presents and 802.3 style interface; ATM CS carries ATM
cells and presents and ATM interface)
2. Downlink classification mechanism ie. which fields in the
SDU can be used to associate transmit-direction data to an
outbound downlink MAC connection (eg. IPv6-overethernet allows fields from the 802.3, IPv6, or layer 4
headers to be used to assign an SDU to a connection)
3. Format of data transmitted over the 802.16 air interface.
(eg. with IPv6 CS the IPv6 header appears directly in the
PDU payload cf. 802.16-2004 section 5.2)
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Evaluation of the Convergence Sublayer
types
Our method is to evaluate the 3 feature areas of the CS type ie.
1. SDU Interface
2. Downlink classification mechanism
3. Format of data transmitted on airlink
… for suitability with the the 2 IP subnetwork models that we
determined to be appropriate ie.
1. IEEE 802-style broadcast network emulation
2. Point-to-point service
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Criterion 1: Upper-layer SDU interface
 802.3/Eth CS types

Supports broadcast network service (by providing an 802.3/ethernet-style
upper interface) as well as point-to-point service (via PPPoE)

From IP layer, the 802.16 network simply looks like a LAN
 IPv4 and IPv6 CS types

The IPv4 and IPv6 CS types are perplexing - because they do not
“converge” to any L2 or L3 interface
 What would be the data service provided by an IPv4/IPv6 CS interface?
 Some people have incorrectly inferred that the IPv4 and IPv6 CS types are
intended to enable the Convergence Sublayer to implement a routing
function. But CS functionality (ie. classification table) is too weak to
implement routing
 What IP layer (host or router) generates IP datagrams without also
generating L2 (ie. ethernet, PPP, or proprietary) control packets and
prepended headers?
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Criterion 2: Downlink Classification Scheme
(with 802.3/Eth CS)
 For 802.3/Eth CS-based broadcast network service, the
Convergence Sublayer will perform downlink classification
according to the destination MAC address of the transmitted SDU
(ie. perform simple MAC bridging)
 Network management therefore configures classifiers statically in the
BS and MS immediately after the MS enters the network
in mobility enabled 802.16e – these classifiers remain applicable across
handovers as they are based on unchanging L2 address
 Classifiers may use additional 802.3, IP, or layer 4 parameters for classof-service and prioritization purposes
 The destination MAC address of 802.3 frames received over the uplink
may be used at the BS side for forwarding the 802.3 frame to an IP
Gateway or Mobile IPv4 FA (ie. when the IP gateway is not colocated
with the BS)
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Criterion 2: Downlink Classification Scheme
(with 802.3/Eth CS)
 For 802.3/Eth CS-based PPPoE service, the
Convergence Sublayer will perform downlink
classification according to the destination MAC
address of the SDU and also 802.1D fields if present
 802.16 doesn’t know how to look inside the PPP frame
 The destination MAC address of SDUs received over
the uplink will be used for forwarding the 802.3 frame to
the PPP RAS
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Criterion 2: Downlink Classification Scheme
(with IPv4/IPv6 CS)
 IPv4/IPv6 CS classification is cumbersome for supporting traffic
in a broadcast network because:



Nov 7, 2005
IP Hosts and gateways on broadcast networks transmit various types of
“layer 2.5 traffic” which rely on a MAC address for correct forwarding.
IPv4/IPv6 CS cannot forward these correctly eg.:
 DHCPOFFER, DHCPNAK (sent to nodes that have no destination IP)
 Disrupts subscriber station initialization (familiar to handheld
users already)
With IPv4/IPv6 CS, it’s necessary for network management to perform
stateful monitoring of IP address assignment in the network (ie. DHCP
address assignment / release / lease expiration / reboot events etc.) and
configure IPv4/v6 header-based classifiers in response
Stateful monitoring of traffic and maintenance of IP address state is
complex and offers many opportunities for lack of synchronization (eg.
when DHCPACK is lost over the air).
Each classifier modification requires a 3-way MAC signaling exchange
Mobile IP registration latency is lengthened by the need for classifier
change after acquisition of a new colocated IP address
No simple way to set up the classifiers in the case of IPv6
autoconfiguration
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Criterion 2: Downlink Classification Scheme
(with IPv4/IPv6 CS)
 IPv4/IPv6 CS classification is adequate to support
point-to-point traffic provided that the IP endpoint
parameters have been configured by an out-of-band
mechanism
 Eg. manually
 This is because IPv4/IPv6 CS does not facilitate
classification of PPP control messages or similar
endpoint provisioning schemes
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Criterion 3: Format for data transmission
over 802.16 airlink (with IPv4/IPv6 CS)
 The IPv4/IPv6 CS types only carry IP datagrams as payloads
 As such, there is no L2 header that could provide information on
the next-hop node. Consequently, with IPv4/IPv6 CS we have no
support for basic components of IP support on broadcast
networks ie.:

IP Gateways (ie. routers), and ICMP-redirect among them

Mobile IP Foreign Agents
 As well, the data format cannot accommodate ARP (for IPv4) as
there is no ethertype field
 However, the IPv4/IPv6 CS data transmission format can carry
point-to-point traffic provided that the IP endpoint parameters
have been configured by an out-of-band mechanism

Nov 7, 2005
Eg. manually
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Criterion 3: Format for data transmission
over 802.16 airlink (with 802.3/Eth CS)
 With 802.3 CS, the 802.3 frame is carried in the 802.16 airlink
payload

Transparent support for 802 broadcast network data and for PPPoE
 Performance enhancements for wireless environment

Use of 802.16 Payload Header Suppression (shrink the 802.3 header
overhead to a single byte)

ROHC (802.16e) can potentially eliminate the entire 802.3 overhead

Also: Proxy ARP and broadcast filtering to reduce broadcasts
 Consequently: any repetitive headers are compressed away, but
not truncated

Nov 7, 2005
Truncation of the 802.3 header would cause loss of the ability to specify
address multiple gateways, FAs, endpoints; loss of ability to transport
ARP for IPv4 or 802.1x for authorization of multiple clients.
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