1. 802.16 Convergence Sublayer Selection for IPv4 and IPv6 transport Overview & Issues Jeff Mandin (jeff@streetwaves-networks.com) 16ng BOF IETF-64 Meeting Vancouver, November 7th 2005

2. 1 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

3. 2 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Convergence Sublayer – why and what  802.16 does not support any kind of “native” application access to its MAC: oNative access would expose the 802.16 Common Part Sublayer to the higher-layer application oWith 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 oThis 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

4. 3 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Convergence Sublayer Operation ã Classification Scheme: —SDUs are assigned to MAC Connections based on data fields only —MAC connection has a particular destination and QoS parameter set

5. 4 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

6. 5 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

7. 6 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

8. 7 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Summary of CS features Eth CSIPv4/v6 CS Upper 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

9. 8 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Summary of CS features (cont.) Eth CSIPv4/v6 CS Airlink 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

10. 9 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Summary of CS features (cont.) Eth CSIPv4/v6 CS Airlink 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

11. 10 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

12. 11 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Thank you

13. Appendix

14. 13 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 Example of broadcast network emulation with Eth CS

15. 14 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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)

16. 15 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

17. 16 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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?

18. 17 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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)

19. 18 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

20. 19 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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 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

21. 20 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

22. 21 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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

23. 22 draft-mandin-ip-over-80216-ethcs-00. Nov 7, 2005 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.