| Re: Proposed Resolution for Issue 224/89 (and part of 146) | <– Date –> <– Thread –> |
From: Jim Murphy (jmurphy trapezenetworks.com)
|
|
| Date: Wed, 31 Jan 2007 14:45:53 -0800 (PST) | |
The rejection of this proposal for reasons of expediency makes little sense in light of recent history for the following reasons:
Firstly, I was asked by the working group chair to bring this proposal to this list at last week's interim meeting. The implication of the request was that indeed the proposal has merit and is worth the groups time to consider it.
Secondly, the expediency argument is a false economy. The working group members, both the supporters and the detractors have already invested their time considering the proposal through a productive dialog on this email list. As a result of this dialog, the proposal has been enhanced to address all the technical objections and a technically superior specification is now at hand. It seems shameful that after all technical issues have been addressed we now want to waste those efforts for the sake of expediency when in fact the work to include the proposal is comparatively small.
Finally, the expediency argument is further weekend by the fact that the proposed text is included in this email. I've included it as both clear text and a context diff.
Thanks,
Jim
--- Clear Text ---
4. CAPWAP Packet Formats
This section contains the CAPWAP protocol packet formats. A CAPWAP
protocol packet consists of one or more CAPWAP Transport Layer packet
headers followed by a CAPWAP message. The CAPWAP message can be either of
type Control or Data, where Control packets carry signaling, and Data
packets carry user payloads. The CAPWAP frame formats for CAPWAP
Data packets, and for DTLS encapsulated CAPWAP Data and Control
packets. See section Section 3.1 for more information on the use of
UDP.
The CAPWAP Control protocol includes two messages that are never protected by DTLS. These messages, called the Discovery Request and Discovery Response, need to be in the clear in order for the CAPWAP protocol to properly identify and process them. The format of these packets are as follows:
CAPWAP Control Packet (Discovery Request/Response):
+-------------------------------------------+
| IP | UDP | CAPWAP | Control | Message |
| Hdr | Hdr | Header | Header | Element(s) |
+-------------------------------------------+All other CAPWAP control protocol messages MUST be protected via the DTLS protocol, which ensures that the packets are both authenticated and encrypted. The format of these packets are as follows:
CAPWAP Control Packet (DTLS Security Required):
+--------------------------------------------------------------------+
| IP | UDP | CAPWAP | DTLS | CAPWAP | Control | Message | DTLS |
| Hdr | Hdr | DTLS Hdr | Hdr | Header | Header | Element(s) | Trlr |
+--------------------------------------------------------------------+
\----------- authenticated ------------/
\------------- encrypted -------------/The CAPWAP protocol allows optional encryption of the data frames, once again using the DTLS protocol. Whether or not the data frames are encrypted is a matter of policy, which is described in a later section of this specification. The format of these packets is as follows:
CAPWAP Plain Text Data Packet :
+--------------------------------+
| IP | UDP | CAPWAP | Wireless |
| Hdr | Hdr | Header | Payload |
+--------------------------------+ DTLS Secured CAPWAP Data Packet:
+--------------------------------------------------------+
| IP | UDP | CAPWAP | DTLS | CAPWAP | Wireless | DTLS |
| Hdr | Hdr | DTLS Hdr | Hdr | Hdr | Payload | Trlr |
+--------------------------------------------------------+
\----- authenticated -----/
\------- encrypted --------/ UDP: All CAPWAP packets are encapsulated within UDP. Section
Section 3.1 defines the specific UDP usage. CAPWAP DTLS Header: All DTLS encrypted CAPWAP protocol packets are
prefixed with the CAPWAP DTLS header. DTLS Header: The DTLS header provides authentication and encrytion
services to the CAPWAP payload it encapsulates. This protocol is
defined in RFC 4347 [9]. CAPWAP Header: All CAPWAP protocol packets use a common header that
immediately follows the UDP header. This header, is defined in
Section 4.3. Wireless Payload: A CAPWAP protocol packet that contains a wireless
payload is known as a data frame. The CAPWAP protocol does not
dictate the format of the wireless payload, which is defined by
the appropriate wireless standard. Additional information is in
Section 4.3. Control Header: The CAPWAP protocol includes a signalling component,
known as the CAPWAP control protocol. All CAPWAP control packets
include a Control Header, which is defined in Section 4.4.1. Message Elements: A CAPWAP Control packet includes one or more
message elements, which are found immediately following the
control header. These message elements are in a Type/Length/value
style header, defined in Section 4.5.4.1. CAPWAP Preamble
The CAPWAP preamble header common to all CAPWAP transport headers and
is used to identify the header type that immediately follows. The reason
for this header to is avoid needing to perform byte comparisons in order
to guess whether the frame is DTLS encrypted or not. It also provides an
extensibility framework that can be used to support additional transport
types. The format of the frame is as follows:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Version| Type |
+-+-+-+-+-+-+-+-+ Version: A 4 bit field which contains the version of CAPWAP used in
this packet. The value for this draft is zero (0). Payload Type: A 4 bit field which specifies the payload type that
follows the preamble header. The following values are supported: 0 - CAPWAP Header. If the packet is received on the data UDP port,
the CAPWAP stack MUST treat this as a clear text CAPWAP data
packet. If received on the control UDP port, the CAPWAP stack
MUST treat this as a clear text CAPWAP control packet. If the
control packet is not a Discovery Request or Response packet,
it is illegal and MUST be dropped. 1 - CAPWAP DTLS Header. The packet is a DTLS packet and MAY be
a data or control packet, based on the UDP port it was received
on (see section Section 3.1).4.2. CAPWAP DTLS Header
The CAPWAP DTLS header is used to identify the packet as a DTLS encrypted packet. The first eight bits includes the common CAPWAP preamble. The remaining 24 bits are padding to ensure 4 byte alignment.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CAPWAP Preamble| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ CAPWAP Preamble: See section 4.1. Payload Type is hard coded to 1 for
the CAPWAP DTLS Header.4.3. CAPWAP Header
All CAPWAP protocol messages are encapsulated using a common header format, regardless of the CAPWAP control or CAPWAP Data transport used to carry the messages. However, certain flags are not applicable for a given transport. Refer to the specific transport section in order to determine which flags are valid.
Note that the optional fields defined in this section MUST be present in the precise order shown below.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |CAPWAP Preamble| HLEN | RID | WBID |T|F|L|W|M|K|Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fragment ID | Frag Offset |Rsvd | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (optional) Radio MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (optional) Wireless Specific Information | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
CAPWAP Preamble: See section 4.1. Payload type is hardcoded to 0.
The value of the Version field MUST match the version field
set in the CAPWAP DTLS header if applicable (see Section 4.2).
The reason for this duplicate field is to avoid any possible
tampering of the version field in the CAPWAP DTLS header which
is not encrypted or authenticated. HLEN: A 5 bit field containing the length of the CAPWAP transport
header in 4 byte words (Similar to IP header length). This length
includes the optional headers. RID: A 5 bit field which contains the Radio ID number for this
packet. WTPs with multiple radios but a single MAC Address range
use this field to indicate which radio is associated with the
packet.---- Context Diffs ----
*** draft-ietf-capwap-protocol-specification-04.txt 2007-01-31 11:22:23.000000000 -0800
--- preamble-mods.txt 2007-01-31 12:06:59.000000000 -0800
***************
*** 1908,1915 ****
4. CAPWAP Packet Formats
This section contains the CAPWAP protocol packet formats. A CAPWAP
! protocol packet consists of a CAPWAP Transport Layer packet header
! followed by a CAPWAP message. The CAPWAP message can be either of
type Control or Data, where Control packets carry signaling, and Data
packets carry user payloads. The CAPWAP frame formats for CAPWAP
Data packets, and for DTLS encapsulated CAPWAP Data and Control
--- 1908,1915 ----
4. CAPWAP Packet FormatsThis section contains the CAPWAP protocol packet formats. A CAPWAP
! protocol packet consists of one or more CAPWAP Transport Layer packet
! headers followed by a CAPWAP message. The CAPWAP message can be either of
type Control or Data, where Control packets carry signaling, and Data
packets carry user payloads. The CAPWAP frame formats for CAPWAP
Data packets, and for DTLS encapsulated CAPWAP Data and Control
***************
*** 1923,1944 ****
packets are as follows:
CAPWAP Control Packet (Discovery Request/Response): ! +---------------------------------------------------+ ! | IP | UDP | CAPWAP |CAPWAP | Control | Message | ! | Hdr | Hdr | p-amble|Header | Header | Element(s) | ! +---------------------------------------------------+
All other CAPWAP control protocol messages MUST be protected via the
DTLS protocol, which ensures that the packets are both authenticated
and encrypted. The format of these packets are as follows:CAPWAP Control Packet (DTLS Security Required): ! +------------------------------------------------------------------+ ! | IP | UDP | CAPWAP | DTLS | CAPWAP | Control | Message | DTLS | ! | Hdr | Hdr | p-amble| Hdr | Header | Header | Element(s) | Trlr | ! +------------------------------------------------------------------+ ! \----------- authenticated ------------/ ! \------------- encrypted -------------/
The CAPWAP protocol allows optional encryption of the data frames,
once again using the DTLS protocol. Whether or not the data frames
--- 1923,1944 ----
packets are as follows:CAPWAP Control Packet (Discovery Request/Response): ! +-------------------------------------------+ ! | IP | UDP | CAPWAP | Control | Message | ! | Hdr | Hdr | Header | Header | Element(s) | ! +-------------------------------------------+
All other CAPWAP control protocol messages MUST be protected via the
DTLS protocol, which ensures that the packets are both authenticated
and encrypted. The format of these packets are as follows:CAPWAP Control Packet (DTLS Security Required): ! +--------------------------------------------------------------------+ ! | IP | UDP | CAPWAP | DTLS | CAPWAP | Control | Message | DTLS | ! | Hdr | Hdr | DTLS Hdr | Hdr | Header | Header | Element(s) | Trlr | ! +--------------------------------------------------------------------+ ! \----------- authenticated ------------/ ! \------------- encrypted -------------/
The CAPWAP protocol allows optional encryption of the data frames,
once again using the DTLS protocol. Whether or not the data frames
***************
*** 1962,1986 ****
CAPWAP Plain Text Data Packet : ! +-----------------------------------------+ ! | IP | UDP | CAPWAP | CAPWAP | Wireless | ! | Hdr | Hdr | p-amble| Header | Payload | ! +-----------------------------------------+
DTLS Secured CAPWAP Data Packet: ! +------------------------------------------------------+ ! | IP | UDP | CAPWAP | DTLS | CAPWAP | Wireless | DTLS | ! | Hdr | Hdr | p-amble| Hdr | Hdr | Payload | Trlr | ! +------------------------------------------------------+ ! \----- authenticated -----/ ! \------- encrypted --------/
UDP: All CAPWAP packets are encapsulated within UDP. Section
Section 3.1 defines the specific UDP usage.! CAPWAP preamble: All CAPWAP protocol packets are prefixed with the ! preable header, which is used to identify the frame type that ! follows. This header, is defined in Section 4.1.
DTLS Header: The DTLS header provides authentication and encrytion
services to the CAPWAP payload it encapsulates. This protocol is
--- 1962,1985 ----
CAPWAP Plain Text Data Packet : ! +--------------------------------+ ! | IP | UDP | CAPWAP | Wireless | ! | Hdr | Hdr | Header | Payload | ! +--------------------------------+
DTLS Secured CAPWAP Data Packet: ! +--------------------------------------------------------+ ! | IP | UDP | CAPWAP | DTLS | CAPWAP | Wireless | DTLS | ! | Hdr | Hdr | DTLS Hdr | Hdr | Hdr | Payload | Trlr | ! +--------------------------------------------------------+ ! \----- authenticated -----/ ! \------- encrypted --------/
UDP: All CAPWAP packets are encapsulated within UDP. Section
Section 3.1 defines the specific UDP usage.! CAPWAP DTLS Header: All DTLS encrypted CAPWAP protocol packets are ! prefixed with the CAPWAP DTLS header.
DTLS Header: The DTLS header provides authentication and encrytion
services to the CAPWAP payload it encapsulates. This protocol is
***************
*** 1988,1994 **** CAPWAP Header: All CAPWAP protocol packets use a common header that
immediately follows the UDP header. This header, is defined in
! Section 4.2. Wireless Payload: A CAPWAP protocol packet that contains a wireless
payload is known as a data frame. The CAPWAP protocol does not
--- 1987,1993 ---- CAPWAP Header: All CAPWAP protocol packets use a common header that
immediately follows the UDP header. This header, is defined in
! Section 4.3. Wireless Payload: A CAPWAP protocol packet that contains a wireless
payload is known as a data frame. The CAPWAP protocol does not
***************
*** 2017,2035 ****
Internet-Draft CAPWAP Protocol Specification January 2007
! 4.1. CAPWAP preamble
! The CAPWAP preamble header is used to help identify the payload type ! that immediately follows. The reason for this header to is avoid ! needing the perform byte comparisons in order to guess whether the ! frame is DTLS encrypted or not. The format of the frame is as ! follows: ! ! 0 1 2 3 ! 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! |Version| Type | Reserved | ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version: A 4 bit field which contains the version of CAPWAP used in
this packet. The value for this draft is zero (0).
--- 2016,2035 ----
Internet-Draft CAPWAP Protocol Specification January 2007
! 4.1. CAPWAP Preamble
! The CAPWAP preamble header common to all CAPWAP transport headers and
! is used to identify the header type that immediately follows. The reason
! for this header to is avoid needing to perform byte comparisons in order
! to guess whether the frame is DTLS encrypted or not. It also provides an
! extensibility framework that can be used to support additional transport
! types. The format of the frame is as follows:
!
! 0
! 0 1 2 3 4 5 6 7
! +-+-+-+-+-+-+-+-+
! |Version| Type |
! +-+-+-+-+-+-+-+-+
Version: A 4 bit field which contains the version of CAPWAP used in
this packet. The value for this draft is zero (0).
***************
*** 2037,2060 ****
Payload Type: A 4 bit field which specifies the payload type that
follows the preamble header. The following values are supported:! 0 - Clear text. If the packet is received on the data UDP port,
the CAPWAP stack MUST treat this as a clear text CAPWAP data
packet. If received on the control UDP port, the CAPWAP stack
MUST treat this as a clear text CAPWAP control packet. If the
control packet is not a Discovery Request or Response packet,
! it is illegal and MUST be dropped.! 1 - DTLS Payload. The packet is either a DTLS packet and MAY be
a data or control packet, based on the UDP port it was received
on (see section Section 3.1).! Reserved: The 24-bit field is reserved for future use. All ! implementations complying with this protocol MUST set to zero any ! bits that are reserved in the version of the protocol supported by ! that implementation. Receivers MUST ignore all bits not defined ! for the version of the protocol they support.
! 4.2. CAPWAP Header
All CAPWAP protocol messages are encapsulated using a common header
format, regardless of the CAPWAP control or CAPWAP Data transport
--- 2037,2069 ----
Payload Type: A 4 bit field which specifies the payload type that
follows the preamble header. The following values are supported:! 0 - CAPWAP Header. If the packet is received on the data UDP port,
the CAPWAP stack MUST treat this as a clear text CAPWAP data
packet. If received on the control UDP port, the CAPWAP stack
MUST treat this as a clear text CAPWAP control packet. If the
control packet is not a Discovery Request or Response packet,
! it is illegal and MUST be dropped.! 1 - CAPWAP DTLS Header. The packet is a DTLS packet and MAY be
a data or control packet, based on the UDP port it was received
on (see section Section 3.1).! 4.2. CAPWAP DTLS Header
! The CAPWAP DTLS header is used to identify the packet as a DTLS ! encrypted packet. The first eight bits includes the common CAPWAP ! preamble. The remaining 24 bits are padding to ensure 4 byte alignment. ! ! 0 1 2 3 ! 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! |CAPWAP Preamble| Reserved | ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! ! CAPWAP Preamble: See section 4.1. Payload Type is hard coded to 1 for ! the CAPWAP DTLS Header. ! ! 4.3. CAPWAP Header
All CAPWAP protocol messages are encapsulated using a common header
format, regardless of the CAPWAP control or CAPWAP Data transport
***************
*** 2076,2082 ****
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! |Version| RID | HLEN | WBID |T|F|L|W|M|K| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment ID | Frag Offset |Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
--- 2085,2091 ----
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! |CAPWAP Preamble| HLEN | RID | WBID |T|F|L|W|M|K|Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment ID | Frag Offset |Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
***************
*** 2087,2108 ****
| Payload .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+! Version: A 4 bit field which contains the version of CAPWAP used in ! this packet. The value of this field MUST match the version field ! set in the CAPWAP preamble header (see Section 4.1). The reason ! for this duplicate field is to avoid any possible tampering of the ! version field in the preamble header which is not encrypted or ! authenticated.
RID: A 5 bit field which contains the Radio ID number for this
packet. WTPs with multiple radios but a single MAC Address range
use this field to indicate which radio is associated with the
packet.- HLEN: A 5 bit field containing the length of the CAPWAP transport
- header in 4 byte words (Similar to IP header length). This length
- includes the optional headers.
-
WBID: A 5 bit field which is the wireless binding identifier. The
identifier will indicate the type of wireless packet type
associated with the radio. The following values are defined:
--- 2096,2117 ----
| Payload .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+! CAPWAP Preamble: See section 4.1. Payload type is hardcoded to 0. ! The value of the Version field MUST match the version field ! set in the CAPWAP DTLS header if applicable (see Section 4.2). ! The reason for this duplicate field is to avoid any possible ! tampering of the version field in the CAPWAP DTLS header which ! is not encrypted or authenticated. ! ! HLEN: A 5 bit field containing the length of the CAPWAP transport ! header in 4 byte words (Similar to IP header length). This length ! includes the optional headers.
RID: A 5 bit field which contains the Radio ID number for this
packet. WTPs with multiple radios but a single MAC Address range
use this field to indicate which radio is associated with the
packet. WBID: A 5 bit field which is the wireless binding identifier. The
identifier will indicate the type of wireless packet type
associated with the radio. The following values are defined:
Margaret Wasserman wrote:
<chair hat=off>
I agree with the proposal to add this item to the wish list for consideration in a possible later version of CAPWAP.
Margaret
</chair>
On Jan 30, 2007, at 6:44 PM, Pat Calhoun (pacalhou) wrote:
I agree with Abhijit. Yes, it has taken us three years to get to this point and we need to be focused on what's broken in the protocol vs. wish lists. I would propose we add this to the wish list for the next version of CAPWAP.
Pat Calhoun CTO, Wireless Networking Business Unit Cisco Systems
From: Abhijit Choudhury [mailto:abhijit10425 [at] yahoo.com]
Sent: Monday, January 29, 2007 9:08 PM
To: Sudhanshu; capwap [at] frascone.com
Subject: Re: [Capwap] Proposed Resolution for Issue 224/89 (and part of 146)
Hi Sudhanshu, Please see my responses in-line,.
Thanks, Abhijit
----- Original Message ----
From: Sudhanshu <sudhanshu.ietf [at] gmail.com>
To: Abhijit Choudhury <abhijit [at] ieee.org>; capwap [at] frascone.com
Sent: Monday, January 29, 2007 7:39:16 PM
Subject: RE: [Capwap] Proposed Resolution for Issue 224/89 (and part of 146)
Abhijit,
Don’t hang on to your calculation of 32 bit per packet in 1G pipe line.
CAPWAP is not designed only for the Greenfield deployments. And there will be lots of a/b/g APs which will be supporting CAPWAP, if it ever became a popular standard.
There will be hardly any AP with real 1G throughput any time soon. Most of them will be supporting max ~ 2xx mbps. And overhead has to be calculated on 2xx Mbps.
[Abhijit] The 1G link I referred to was the link between the WTP and AC. The up-link of WTPs will be
gradually changing over to 10/100/1000 MACs as Gig interfaces on L2/L3 switches become
ubiquitous. In that case, no matter what your WTP throughput, the
CAPWAP encapsulated packet will be transmitted by the WTP towards the AC at 1G rate. The special
packet format is reducing the header by 32 bits, which means 32ns is being optimized away on this link.
You have to justify that that amount of time is worth adding additional code in the data path.
Not every architecture/every system will support the pure pipe line processing. And in that case, 4 byte DMA back-n-forth may be unnecessary overhead on memory bandwidth and processing both in AP and Switch
[Abhijit] Typically DMA is done on chunks of data. Packet descriptors are often allocated for 32, 64 or 128 bytes at a time.
It is not clear that reducing your packet length by 4 bytes will make much of a difference in storage or
DMA bandwidth.
CAPWAP is not designed for the LAN environment only. In that case 1G bandwidth is a luxury, even in today’s world.
[Abhijit] Agreed. But you have to look at where the primary use of CAPWAP is going to be.
If you to look back and review why after 3+ years, we still don’t have a standard, everybody may have their own opinion. But in the best interest of moving forward, let’s looks for the consensus.
[Abhijit] That is the goal of this mailing list - creating consensus. All I am saying is that there are
bigger issues to be finalized before we start discussing optimizations.
_Suds
From: Abhijit Choudhury [mailto:abhijit10425 [at] yahoo.com]
Sent: Sunday, January 28, 2007 10:50 PM
To: capwap [at] frascone.com
Subject: Re: [Capwap] Proposed Resolution for Issue 224/89 (and part of 146)
Folks,
I'm sure there are many more optimizations that can be
made in the spec. It's been close to three years since
this WG started, and we still don't have a spec out.
Meanwhile, the WLAN industry has been impatiently waiting
for this standard. It can be argued that if this spec
is not ratified soon it might lose its relevance.
At this point in time, as a group, we need to
focus on fixing items that need fixing because they
are broken. We cannot afford to spend time
debating "nice-to-have"s and changing perfectly working
items in the spec because we want to make some minor
optimizations.
If the packet format in the current spec is broken, we
should surely fix it. If 32 bits on a 1Gig link
is all that is being optimized by this new packet
format and additional code in the data path, I'd argue
that this is not what this WG should be spending its time on.
There are a whole bunch of decisions that need to be made
before this spec can be sent out for last call. We need to
focus on those items and get this spec out asap.
.
Thanks,
Abhijit
-----Original Message-----
From: Jim Murphy [mailto:jmurphy [at] trapezenetworks.com]
Sent: Friday, January 26, 2007 11:57 PM
To: Bob O'Hara (boohara)
Cc: capwap [at] frascone.com
Subject: Re: [Capwap] Proposed Resolution for Issue 224/89 (and part of
146)
Bob,
I see no reason why this optimization can not be used in the control channel as well. If so, then the concerns about the data and control channel having to be exactly the same are eliminated with the added benefit of improved performance in each case.
That said, I think we could improve the format a bit based on feedback from Sudhanshu and some new observations based on the idea of packet header overlay.
The basic idea is that Version and Type fields are what is needed for the "preamble" and exist for every type of packet. However, only 8 bits are required. We then define the DTLS shim and CAPWAP Header to include the preamble. The resulting format is something like this:
CAPWAP Preamble 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |Version| Type | +-+-+-+-+-+-+-+-+
Version: A 4 bit field which contains the version of CAPWAP used in
this packet. The value for this draft is zero (0).
Payload Type: A 4 bit field which specifies the payload type that
follows the preamble header. Unsupported values MUST be silently
dropped. The following values are supported:
0 - Clear text. If the packet is received on the data UDP port,
the CAPWAP stack MUST treat this as a clear text CAPWAP data
packet. If received on the control UDP port, the CAPWAP stack
MUST treat this as a clear text CAPWAP control packet. If the
control packet is not a Discovery Request or Response packet,
it is illegal and MUST be dropped.
1 - DTLS Payload. The packet is either a DTLS packet and MAY be
a data or control packet, based on the UDP port it was
received
on (see section Section 3.1).
CAPWAP DTLS shim:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Or, said slightly differently:
CAPWAP DTLS shim:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preamble | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For the header we then have the following:
CAPWAP Header:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Type | HLEN | RID | WBID |T|F|L|W|M|K|Flags|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment ID | Frag Offset | Rsvd
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note, Version/Type are the CAPWAP preamble.
Essentially, what we have created a de-multiplexing scheme that has the
following properties:
- Its performance characteristics are no worse than those of the -04 preamble. In fact, demuxing directly off the preamble type is very attractive from a performance perspective. - It does not waste 32 bits in the clear path case. - It works equally well for the data path and the control path so it is a universal solution. - It provides for a powerful extensibility feature that will enhance the longevity of the protocol.
Other notes:
- I have transposed RID and HLEN to give the hint of a TLV structure.
I think this is a useful concept that we should support in the
protocol.
- I belive the F and L flags could be moved to the Rsvd area of the
fragmentation super frame as suggested by David Perkins. This opens
up some more flag space in the first super frame.
Thanks,
Jim
Bob O'Hara (boohara) wrote:It's always fun to be part of an exercise to optimize somethinguntilit can't be optimized any further, and let's be clear about it.Thatis what we are doing here. The current preamble, common to both
control and data packets, works. What is being proposed is to make
the data packet preamble as short as possible, by reducing itssize by 32 bits.This comes at the cost of having the control and data packet formats diverge.
Let me propose some reasons for keeping the preamble of the control and data packets the same as they were.
1. A DTLS-protected packet, either control or data, is handledexactly
the same way to produce the decrypted CAPWAP payload. Thisdecryptedpayload can then be passed to software for processing (eithercontrolorprocessing.
data) or can be passed to fast path hardware for data pathACs.2. 32 bits take exactly 32ns to transmit at a gigabit per second, which is likely to be the predominant connection for both WTPs andbugs to discover and fix.Optimizing the protocol to save these 32ns is a foolish economy. Is there a dire cost that we encounter, in order to send these bits?
3. Having two different CAPWAP preambles doubles the cost of development of this portion of the protocol (particularly if the CAPWAP header cracking is done in hardware), doubles the hardware necessary to process this portion of the packet (perhaps even that necessary to process the entire packet), and doubles the number ofCAPWAPI believe these practical reasons outweigh the reasons presented for making the change to the header.
-Bob
-----Original Message----- From: Jim Murphy [mailto:jmurphy [at] trapezenetworks.com] Sent: Thursday, January 25, 2007 12:19 AM To: capwap [at] frascone.com Subject: Re: [Capwap] Proposed Resolution for Issue 224/89 (and part of 146)
Please consider the following alternative proposal to optimize the
data channel when no DTLS encryption is present. With this proposal,
CAPWAP data channels running in the clear will not require the2 3preamble. However, CAPWAP data channels running DTLS must have the CAPWAP preamble.
The CAPWAP preamble is modified as follows:
[...]
0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 78 9 0
2 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Type | Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [...] P: Must be 1. Indicates that this is a CAPWAP preamble. [...]
The CAPWAP Header is modified as follows:
[...]
0 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 78 9 0
1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| RID | HLEN | WBID |T|F|L|W|M|K| Flags |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [...] P: Must be 0. Indicates that this is a CAPWAP preamble. [...]
The basic idea is to overlay the CAPWAP preamble and the first
32 bits of the CAPWAP Header. Note the intentional overlap of the
Version field and the P bit. Essentially the P bit is a typeindicator
that indicates the type of super field present. A 1 indicates aCAPWAP
preamble, a 0 indicates the first 32 bits of the CAPWAP Header.
Any data packet on a clear (unencrypted) data channel looks asfollows
Specifically(to illustrate the use of the P bit):
CAPWAP Plain Text Data Packet: +--------------------------------+ | IP | UDP | CAPWAP | Wireless | | Hdr | Hdr | Header | Payload | | | | P=0 | | +--------------------------------+
Any data packet on an encrypted data channel or a DTLS session establishment packet looks as follows:
DTLS Secured CAPWAP Data Packet: +------------------------------------------------------+ | IP | UDP | CAPWAP | DTLS | CAPWAP | Wireless | DTLS | | Hdr | Hdr | p-amble| Hdr | Hdr | Payload | Trlr | | | | P=1 | | | | | +------------------------------------------------------+ \----- authenticated -----/ \------- encrypted --------/
A switching entity need only check the CAPWAP Version and then the P bit to determine if the CAPWAP packet needs DTLS processing. If the P but is not set, the switching entity may immediately assume only a CAPWAP header and commences de-encapsulation and possible reassembly processing.
This proposal serves the following purposes:
- The CAPWAP preamble is present only when really needed.to identify CAPWAP packet attributes outside of the DTLSencrypted/convey aauthenticated area when DTLS is used.
- Eliminates the waste of 32 bits of header information toDTLSsingle bit of information when in the clear.
- Allows for the continued use of the CAPWAP preamble for other purposes, such as DTLS session de-multiplexing to deal with the issue of QoS reordering. (see earlier email from Mani - The QoSfactor)
Please let me know if you have any questions.
Thanks,
Jim
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- Re: Proposed Resolution for Issue 224/89 (and part of 146), (continued)
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Sudhanshu, January 29 2007
-
Re: Proposed Resolution for Issue 224/89 (and part of 146) Abhijit Choudhury, January 29 2007
-
Re: Proposed Resolution for Issue 224/89 (and part of 146) Pat Calhoun (pacalhou), January 30 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Margaret Wasserman, January 30 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Jim Murphy, January 31 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Margaret Wasserman, February 1 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Sudhanshu, February 1 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Margaret Wasserman, February 1 2007
- Re: Proposed Resolution for Issue 224/89 (and part of 146) Puneet Agarwal, February 1 2007
-
Re: Proposed Resolution for Issue 224/89 (and part of 146) Pat Calhoun (pacalhou), January 30 2007
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