16ng Working Group S. Madanapalli
Internet-Draft Ordyn Technologies
Intended status: Standards Track Soohong D. Park
Expires: August 28, 2008 Samsung Electronics
S. Chakrabarti
IP Infusion
February 25, 2008
Transmission of IPv4 packets over IEEE 802.16's IP Convergence Sublayer
draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-02.txt
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Copyright (C) The IETF Trust (2008).
Abstract
IEEE 802.16 is an air interface specification for wireless broadband
access. IEEE 802.16 has specified multiple service specific
convergence sublayers (Asynchronous Transfer Mode Convergence
Sublayer (ATM CS) and Packet Convergence Sublayer (Packet CS) are the
two main service specific convergence sublayers) for transmitting
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upper layer protocols. The packet CS is used for the transport of
all packet-based protocols such as Internet Protocol (IP), IEEE 802.3
(Ethernet) and IEEE 802.1Q (VLAN). The IP specific part of the
Packet CS enables the transport of IPv4 packets directly over the
IEEE 802.16 MAC.
This document specifies the frame format, the Maximum Transmission
Unit (MTU) and address assignment procedures for transmitting IPv4
packets over IP Convergence Sublayer of the IEEE 802.16.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Typical Network Architecture for IPv4 over IEEE 802.16 . . . . 3
4. Frame Format for IPv4 Packets . . . . . . . . . . . . . . . . 4
5. Maximum Transmission Unit . . . . . . . . . . . . . . . . . . 5
6. Subnet Model and IPv4 Address Assignment . . . . . . . . . . . 6
7. Address Resolution Protocol . . . . . . . . . . . . . . . . . 6
8. IP Multicast Address Mapping . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
12.1. Normative References . . . . . . . . . . . . . . . . . . 7
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Multiple Convergence Layers - Impact on Subnet
Model . . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix B. Sending and Receiving IPv4 Packets . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
IEEE 802.16 [11] is a connection oriented access technology for the
last mile. The IEEE 802.16 specification includes the PHY and MAC
details. The MAC includes various convergence sublayers (CS) for
transmitting higher layer packets. IPv4 packets can be carried over
the IEEE 802.16 specified air interface via:
1. IP-specific part of the Packet CS or
2. IEEE 802.3-specific part of the Packet CS
The scope of this specification is limited to the operation of IPv4
over the IP-specific part of the packet CS (referred to as "IPv4 CS"
or simply "IP CS" in this document).
The mobile station (MS)/host is attached to an access router via a
base station (BS). The MS and the BS are connected via the IEEE
802.16 air interface at the link and physical layers. The IPv4 link
from the MS terminates at an access router that may be a part of the
BS or an entity beyond the BS. The base station is a layer 2 entity
(from the perspective of the IPv4 link between the MS and access
router (AR)) and relays the IPv4 packets between the AR and the MS
via a point-to-point connection over the air interface.
This document specifies a method for encapsulating and transmitting
IPv4 [2] packets over IP CS of IEEE 802.16. This document also
specifies the MTU and address assignment method for the IEEE 802.16
based networks using IP CS.
This document also mentions about ARP (Address Resolution Protocol)
and Multicast Address Mapping whose operation is similar to any other
point-to-point link model.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1].
2. Terminology
The terminology in this document is based on the definitions in [10].
3. Typical Network Architecture for IPv4 over IEEE 802.16
In a network that utilizes the IEEE 802.16 air interface, each MS is
attached to an Access Router (AR) through a Base Station (BS), a
layer 2 entity. The AR can be an integral part of the BS or the AR
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could be an entity beyond the BS within the access network. IPv4
packets between the MS and BS are carried over a point-to-point MAC
transport connection which has a unique connection identifier (CID).
The packets between BS and AR are carried using L2 tunnel (typically
GRE tunnel) so that MS and AR are seen as layer 3 peer entities. At
least one L2 tunnel is required for each MS, so that IP packets can
be sent to MSs before they acquire IP addresses. The figure below
illustrates the network architecture.
+-----+ CID1 +------+ +-----------+
| MS1 |----------+| BS |----------| AR |-----Internet
+-----+ / +------+ +-----------+
. / ____________
. CIDn / ()__________()
+-----+ / L2 Tunnel
| MSn |-----/
+-----+
Figure 1: Typical Network Architecture for IPv4 over IEEE 802.16
The above network model serves as an example and is shown to
illustrate the point to point link between the MS and the AR. The L2
tunnel is not required if BS and AR are integrated into a single box.
4. Frame Format for IPv4 Packets
IPv4 packets are transmitted in Generic IEEE 802.16 MAC frames as
shown in the following figure.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|H|E| TYPE |R|C|EKS|R|LEN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LEN LSB | CID MSB |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CID LSB | HCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 |
+- -+
| header |
+- -+
| and |
+- -+
/ payload /
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CRC (optional) |
+-+-+-+-+-+-+-+-+
Figure 2: IEEE 802.16 MAC Frame Format for IPv4 Packets
H: Header Type (1 bit). Shall be set to zero indicating that it
is a Generic MAC PDU.
E: Encryption Control. 0 = Payload is not encrypted; 1 = Payload
is encrypted.
R: Reserved. Shall be set to zero.
C: CRC Indicator. 1 = CRC is included, 0 = 1 No CRC is included
EKS: Encryption Key Sequence
LEN: The Length in bytes of the MAC PDU including the MAC header
and the CRC if present (11 bits)
CID: Connection Identifier (16 bits)
HCS: Header Check Sequence (8 bits)
CRC: An optional 8-bit field. CRC appended to the PDU after
encryption.
TYPE: This field indicates the subheaders (Mesh subheader,
Fragmentation Subheader, Packing subheader etc and special payload
types (ARQ) present in the message payload
5. Maximum Transmission Unit
The MTU value for IPv4 packets on an IEEE 802.16 link is
configurable. The default MTU for IPv4 packets over an IEEE 802.16
link SHOULD be 1400 bytes. This default value accommodates for the
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overhead of the GRE tunnel used to transport IPv4 packets between the
BS and AR and the 6-byte IEEE 802.16 MAC header over the air
interface.
The Length parameter of IEEE 802.16 MAC frame has a size of 11 bits.
Hence the total PDU size is 2048 bytes. The IPv4 payload can be a
maximum value of 2038 bytes ( Total PDU size (2048) - (MAC Header (6)
+ CRC (4)), which is the maximum possible MTU. The IPv4 payload size
can vary and can be either greater or less than the default value.
The MTU value of the MS can be configured via Path MTU Discovery [6],
Packetization layer path MTU discovery [7], DHCP MTU option [8] or
static configuration of each MS.
6. Subnet Model and IPv4 Address Assignment
The Subnet Model recommended for IPv4 over IEEE 802.16 using IP CS is
based on point-to-point link between MS and AR, hence each MS shall
be on different IP subnet. The point-to-point link between MS and AR
is achieved using a set of IEEE 802.16 MAC connections (identified by
CIDs) and at least an L2 tunnel (usually GRE tunnel) per MS between
BS and AR. If the AR is co-located with the BS then the set of IEEE
802.16 MAC connections between the MS and BS/AR represent the
point-to- point connection.
DHCP [4] SHOULD be used for assigning IPv4 address for the MSs. DHCP
messages are transported over IEEE 802.16 MAC transported connection
to and from the AR. In case DHCP server does not reside in AR, the
AR SHOULD implement DHCP relay Agent [5].
7. Address Resolution Protocol
The IP CS does not allow for transmission of ARP [3] packets,
accordingly, other mechanisms for address resolution must be used.
In a point-to-point link model, address resolution may not be needed.
8. IP Multicast Address Mapping
IPv4 multicast packets are carried over the point-to-point link
between the AR and the MS (via the BS). The IPv4 multicast packets
are classified normally at the IP CS if the IEEE 802.16 MAC
connection has been setup with a multicast IP address as a
classification parameter for the destination IP address.
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9. Security Considerations
This document specifies transmission of IPv4 packets over IEEE 802.16
networks with IPv4 Convergence Sublayer and does not introduce any
new vulnerabilities to IPv4 specifications or operation. The
security of the IEEE 802.16 air interface is the subject of [11]. In
addition, the security issues of the network architecture spanning
beyond the IEEE 802.16 base stations is the subject of the documents
defining such architectures, such as WiMAX Network Architecture [12].
10. IANA Considerations
This document has no actions for IANA.
11. Acknowledgements
The authors would like to acknowledge the contributions of Bernard
Aboba, Dave Thaler, Jari Arkko, Gabriel Montenegro, Bachet Sarikaya,
Basavaraj Patil, Paolo Narvaez, and Bruno Sousa for their review and
comments.
12. References
12.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[3] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[5] Wimer, W., "Clarifications and Extensions for the Bootstrap
Protocol", RFC 1542, October 1993.
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12.2. Informative References
[6] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[7] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[8] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[9] Aboba, B., Davies, E., and D. Thaler, "Multiple Encapsulation
Methods Considered Harmful", RFC 4840, April 2007.
[10] Jee, J., "IP over 802.16 Problem Statement and Goals",
December 2007, <http://www.ietf.org/internet-drafts/
draft-ietf-16ng-ps-goals-04.txt>.
[11] "IEEE 802.16e, IEEE standard for Local and metropolitan area
networks, Part 16:Air Interface for fixed and Mobile broadband
wireless access systems", October 2005.
[12] "WiMAX End-to-End Network Systems Architecture Stage 2-3
Release 1.2, http://www.wimaxforum.org/technology/documents",
January 2008.
Appendix A. Multiple Convergence Layers - Impact on Subnet Model
Two different MSs using two different convergence sublayers (e.g. an
MS using Ethernet CS only and another MS using IP CS only) cannot
communicate at data link layer and requires interworking at IP layer.
For this reason, these two nodes must be configured to be on two
different subnets. For more information refer [9].
Appendix B. Sending and Receiving IPv4 Packets
IEEE 802.16 MAC is a point-to-multipoint connection oriented air-
interface, and the process of sending and receiving of IPv4 packets
is different from multicast capable shared medium technologies like
Ethernet.
Before any packets being transmitted, IEEE 802.16 transport
connection must be established. This connection consists of IEEE
802.16 MAC transport connection between MS and BS and an L2 tunnel
between BS and AR. This IEEE 802.16 transport connection provides a
point-to-point link between MS and AR. all the packets originated at
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the MS always reach AR before being transmitted to the final
destination.
IPv4 packets are carried directly in the payload of IEEE 802.16
frames when the IPv4 CS is used. IPv4 CS classifies the packet based
on upper layer (IP and transport layers)header fields to put the
packet on one of the available connections identified by the CID.
The classifiers for the IPv4 CS are source and destination IPv4
addresses, source and destinations ports, Type-of-Service and IP
protocol field. The CS may employ Packet Header Suppression (PHS)
after the classification.
The BS tunnels the packet that has been received on a particular MAC
connection to the AR. BS reconstructs the payload header if the PHS
is in use before the packet is tunneled to the AR. Similarly the
packets received on a tunnel interface from the AR, would be mapped
to a particular CID using IPv4 classification mechanism.
AR performs normal routing for the packets that it receives and
forwards the packet based on its forwarding table. However the DHCP
relay agent in the AR, MUST maintain the tunnel interface on which it
receives DHCP requests, so that it can relay the DHCP responses to
the correct MS. One way of doing this is to have a mapping between
MAC address and Tunnel Identifier.
Authors' Addresses
Syam Madanapalli
Ordyn Technologies
1st Floor, Creator Building, ITPL
Bangalore - 560066
India
Email: smadanapalli@gmail.com
Soohong Daniel Park
Samsung Electronics
416 Maetan-3dong, Yeongtong-gu
Suwon 442-742
Korea
Email: soohong.park@samsung.com
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Samita Chakrabarti
IP Infusion
125 South Market Street, 9th Floor
San Jose, CA
USA
Email: samitac2@gmail.com
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