802.16 Convergence Sublayer Selection for IPv4 and IPv6 transport Overview & Issues Jeff Mandin ([email protected]) 16ng BOF IETF-64 Meeting.

802.16 Convergence Sublayer Selection for IPv4 and IPv6 transportOverview & Issues

Jeff Mandin ([email protected])

16ng BOFIETF-64 Meeting

Vancouver, November 7th 2005

2 draft-mandin-ip-over-80216-ethcs-00.Nov 7, 2005

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 16ng charter should be broadened to include IPv4 over .16 Should standardize a generic 802.3/Eth CS solution for IP


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


Convergence Sublayer Operation

Higher Layer Entity (e.g. Host IP or Ethernet Layer)

Classifier

CID #1 CID #2 CID #N

PHS PHS PHS

SDU

MAC Common Part Sub Layer

SDU + CID

ConvergenceSub Layer

Classification Scheme:—SDUs are assigned to

MAC Connections based on data fields only

—MAC connection has a particular destination and QoS parameter set


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


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


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


Summary of CS features

Eth CS IPv4/v6 CSUpper Edge Service Interface

Standard (looks like 802.3 driver)

Trivially compatible with existing stacks

Non-standard (IPv4/v6 datagram interface is neither L2 nor L3)

Downlink Classification

Classifies packets to wireless MAC connections using L2 addresses - with L3/L4 fields available for QoS differentiation

Classifies packets to wireless MAC connections using IP addresses

Requires stateful network monitoring, since IP addresses are assigned with DHCP or other dynamic mechanisms

Unsolved problems with IPv6 autoconfig


Summary of CS features (cont.)

Eth CS IPv4/v6 CSAirlink format Payload includes

802.3 header – so uplink packets can be addressed to a specific IP Router/MIP Foreign Agent

There can be multiple nodes at subscriber side (identified by MAC addr)

802.3 format can carry control plane protocols (ARP, 802.1x)

Payload carries IP datagrams only

So air link is point-to-point

No L2 addressability beyond link endpoints

No control plane transport


Summary of CS features (cont.)

Eth CS IPv4/v6 CSAirlink overhead Compression and

Proxy techniques can remove almost all overhead

No L2 overhead, but no L2 capabilities

Even point-to-point service would require manual configuration - since there is no control plane support


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


Thank you

Appendix


Example of broadcast network emulation with Eth CS

Gateway

Subscriber Station Unit

Base Station Unit

MAC Bridge

filters

802.16MAC and PHY

802.16 MAC and PHY

Downlink unicastconnection bundle

(provisioned classifiersinclude

host MAC address)

Uplinkconnection

bundle

LAN BroadcastConnection(Classifier

ff:ff:ff:ff:ff:ff)

IP router

AllConnectionsare 802.3 CS

Host (ie. laptop, VoIP phone, etc.) with host MACaddress (yy:yy:yy:yy:yy:yy)

SAP

Backhaul


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-over-ethernet 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)


Evaluation of the Convergence Sublayer types

Our method is to evaluate the 3 feature areas of the CS type ie.

1. SDU Interface2. Downlink classification mechanism3. 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


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?


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 class-of-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)


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


Criterion 2: Downlink Classification Scheme (with IPv4/IPv6 CS)

IPv4/IPv6 CS classification is cumbersome for supporting traffic in a broadcast network because: 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 exchangeMobile 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


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


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 Eg. manually


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 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.

802.16 Convergence Sublayer Selection for IPv4 and IPv6 transport Overview & Issues Jeff Mandin ([email protected]) 16ng BOF IETF-64 Meeting.

Documents

ip slide

ip perspective

ethernet ipv4

ip transport clean

ip router layer

ip transport discussion

convergence sublayer

ethernet ipv6