Proper understanding of
"bbr" <[email protected]> Mon, 1 Jan 2007 12:54:00 -0500
| Newsgroups | gmane.ietf.rddp |
|---|---|
| Organization | Lamprey Networks |
| Message-ID | <200701011254837.SM05976@i6000bbr> |
This is a multi-part message in MIME format. --===============1963363504== Content-Type: multipart/alternative; boundary="----=_NextPart_000_003D_01C72DA3.E85F7E40" This is a multi-part message in MIME format. ------=_NextPart_000_003D_01C72DA3.E85F7E40 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Folks, I'm looking at the changes in MPA from draft 02 (against which the conformance suite was written) to draft 08. I would like to understand how to take the following text from page 25 (clause 6). "To detect the start of the FPDU unambiguously one of the following MUST be used: 1: In an ordered TCP stream, the ULPDU Length field in the current FPDU when FPDU has a valid CRC, can be used to identify the beginning of the next FPDU. 2: For optimized MPA/TCP receivers that support out of order reception of FPDUs (see section 4.3 MPA Markers on page 15) a Marker can always be used to locate the beginning of an FPDU (in FPDUs with valid CRCs). Since the location of the Marker is known in the octet stream (sequence number space), the Marker can always be found. 3: Having found an FPDU by means of a Marker, an optimized MPA/TCP receiver can find following contiguous FPDUs by using the ULPDU Length fields (from FPDUs with valid CRCs) to establish the next FPDU boundary." Question: Is an implementation allowed to use the marker, as described below, to "unambiguously" detect the start of a FPDU? Condition under which marker was received: 1. Markers being used (negotiated on) 2. Large FPDU being sent which consumes three TCP segments (not desired but allowed) 3. Second TCP segment lost 4. Marker located in third TCP segment Issue: In item two above it would appear that the implementation would have to validate the FPDU in which the marker is received (perform CRC check) before it can use it. However, since a portion of the FPDU is missing this would not be possible to do. Therefore a conformant device MUST NOT use this marker to detect the start of the FPDU. Is this the correct understanding of this requirement? Barry Reinhold (603) 868-8411 [email protected] ------=_NextPart_000_003D_01C72DA3.E85F7E40 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable <html xmlns:v=3D"urn:schemas-microsoft-com:vml" = xmlns:o=3D"urn:schemas-microsoft-com:office:office" = xmlns:w=3D"urn:schemas-microsoft-com:office:word" = xmlns=3D"http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv=3DContent-Type content=3D"text/html; = charset=3Dus-ascii"> <meta name=3DGenerator content=3D"Microsoft Word 11 (filtered medium)"> <style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {margin:0in; margin-bottom:.0001pt; font-size:12.0pt; font-family:"Times New Roman";} a:link, span.MsoHyperlink {color:blue; text-decoration:underline;} a:visited, span.MsoHyperlinkFollowed {color:purple; text-decoration:underline;} p.MsoAutoSig, li.MsoAutoSig, div.MsoAutoSig {margin:0in; margin-bottom:.0001pt; font-size:12.0pt; font-family:"Times New Roman";} span.EmailStyle17 {mso-style-type:personal-compose; font-family:Arial; color:windowtext;} p.Default, li.Default, div.Default {margin:0in; margin-bottom:.0001pt; text-autospace:none; font-size:12.0pt; font-family:"Courier New"; color:black;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in;} div.Section1 {page:Section1;} /* List Definitions */ @list l0 {mso-list-id:1271469048; mso-list-type:hybrid; mso-list-template-ids:633232126 67698703 67698713 67698715 67698703 = 67698713 67698715 67698703 67698713 67698715;} @list l0:level1 {mso-level-tab-stop:.5in; mso-level-number-position:left; text-indent:-.25in;} ol {margin-bottom:0in;} ul {margin-bottom:0in;} --> </style> <!--[if gte mso 9]><xml> <o:shapedefaults v:ext=3D"edit" spidmax=3D"1026" /> </xml><![endif]--><!--[if gte mso 9]><xml> <o:shapelayout v:ext=3D"edit"> <o:idmap v:ext=3D"edit" data=3D"1" /> </o:shapelayout></xml><![endif]--> </head> <body lang=3DEN-US link=3Dblue vlink=3Dpurple> <div class=3DSection1> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'>Folks,<o:p></o:p></span></font></p> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'><o:p> </o:p></span></font></p> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'>I’m looking at the changes in MPA from draft 02 (against which the conformance suite was written) to draft 08. I would = like to understand how to take the following text from page 25 (clause = 6).<o:p></o:p></span></font></p> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'><o:p> </o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>“To detect the start of the FPDU = unambiguously one of the following <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>MUST be used: <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>1: In an ordered TCP stream, the ULPDU Length = field in the current <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>FPDU when FPDU has a valid CRC, can be used = to identify the <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>beginning of the next FPDU. = <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>2: For optimized MPA/TCP receivers that = support out of order <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>reception of FPDUs (see section 4.3 MPA = Markers on page 15) a <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Marker can always be used to locate the = beginning of an FPDU (in <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>FPDUs with valid CRCs). Since the location of = the Marker is <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>known in the octet stream (sequence number = space), the Marker can <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>always be found. = <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>3: Having found an FPDU by means of a Marker, = an optimized MPA/TCP <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>receiver can find following contiguous FPDUs = by using the ULPDU <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Length fields (from FPDUs with valid CRCs) to establish the next <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>FPDU boundary.” = <o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'><o:p> </o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Question: Is an implementation allowed to use = the marker, as described below, to “unambiguously” detect the = start of a FPDU?<o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'><o:p> </o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Condition under which marker was = received:<o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'><o:p> </o:p></span></font></p> <p class=3DDefault = style=3D'margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 = lfo1'><![if !supportLists]><font size=3D2 color=3Dblack face=3D"Courier New"><span = style=3D'font-size:10.0pt'><span style=3D'mso-list:Ignore'>1.<font size=3D1 face=3D"Times New = Roman"><span style=3D'font:7.0pt "Times New Roman"'> = </span></font></span></span></font><![endif]><font size=3D2><span style=3D'font-size:10.0pt'>Markers being used (negotiated = on)<o:p></o:p></span></font></p> <p class=3DDefault = style=3D'margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 = lfo1'><![if !supportLists]><font size=3D2 color=3Dblack face=3D"Courier New"><span = style=3D'font-size:10.0pt'><span style=3D'mso-list:Ignore'>2.<font size=3D1 face=3D"Times New = Roman"><span style=3D'font:7.0pt "Times New Roman"'> = </span></font></span></span></font><![endif]><font size=3D2><span style=3D'font-size:10.0pt'>Large FPDU being sent which = consumes three TCP segments (not desired but = allowed)<o:p></o:p></span></font></p> <p class=3DDefault = style=3D'margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 = lfo1'><![if !supportLists]><font size=3D2 color=3Dblack face=3D"Courier New"><span = style=3D'font-size:10.0pt'><span style=3D'mso-list:Ignore'>3.<font size=3D1 face=3D"Times New = Roman"><span style=3D'font:7.0pt "Times New Roman"'> = </span></font></span></span></font><![endif]><font size=3D2><span style=3D'font-size:10.0pt'>Second TCP segment = lost<o:p></o:p></span></font></p> <p class=3DDefault = style=3D'margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 = lfo1'><![if !supportLists]><font size=3D2 color=3Dblack face=3D"Courier New"><span = style=3D'font-size:10.0pt'><span style=3D'mso-list:Ignore'>4.<font size=3D1 face=3D"Times New = Roman"><span style=3D'font:7.0pt "Times New Roman"'> = </span></font></span></span></font><![endif]><font size=3D2><span style=3D'font-size:10.0pt'>Marker located in third TCP = segment<o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'><o:p> </o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Issue: In item two above it would appear that = the implementation would have to validate the FPDU in which the marker is = received (perform CRC check) before it can use it. However, since a portion of the FPDU is = missing this would not be possible to do. Therefore a conformant device MUST NOT = use this marker to detect the start of the = FPDU.<o:p></o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'><o:p> </o:p></span></font></p> <p class=3DDefault><font size=3D2 color=3Dblack face=3D"Courier = New"><span style=3D'font-size:10.0pt'>Is this the correct understanding of this = requirement?<o:p></o:p></span></font></p> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'><o:p> </o:p></span></font></p> <p class=3DMsoNormal><font size=3D2 face=3DArial><span = style=3D'font-size:10.0pt; font-family:Arial'><o:p> </o:p></span></font></p> <p class=3DMsoAutoSig><font size=3D3 face=3D"Times New Roman"><span = style=3D'font-size: 12.0pt'>Barry Reinhold<o:p></o:p></span></font></p> <p class=3DMsoAutoSig><font size=3D3 face=3D"Times New Roman"><span = style=3D'font-size: 12.0pt'>(603) 868-8411<o:p></o:p></span></font></p> <p class=3DMsoAutoSig><font size=3D3 face=3D"Times New Roman"><span = style=3D'font-size: 12.0pt'><a = href=3D"mailto:[email protected]">[email protected]</a><o:p><= /o:p></span></font></p> <p class=3DMsoNormal><font size=3D3 face=3D"Times New Roman"><span = style=3D'font-size: 12.0pt'><o:p> </o:p></span></font></p> </div> </body> </html> ------=_NextPart_000_003D_01C72DA3.E85F7E40-- --===============1963363504== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ rddp mailing list [email protected] https://www1.ietf.org/mailman/listinfo/rddp --===============1963363504==--