RE: [Asterisk-Users] T1-PRI deployment questions...
I have been on vacation so didn't jump in earlier. Some of what I say here has been gone over earlier in this thread but I will repeat the results as a summery. AMI is not lossy, but it is almost always used in conjunction with a ones density technique called bit7. Bit7 will change bit 7 to a 1 when a word (8 bits) are all zeros. In North America when someone says AMI they really mean AMI with bit7. PRI ISDN will not work on an AMI (with bit7) T1. When validating ones density B8ZS does introduce errors but in such a way that the far end will know that they are errors and remove them. The only reasonable choice for PRI ISDN is B8ZS Robbed bit signaling uses bit 8 of each word of every 6th frame for signaling. This does not introduce errors on the line but it does make those bits unavailable for data. Usually data services assumes that the 8th bit of every work of every frame are not available so that you have 7 of each 8 bit word. That makes 56Kbit/s of 64Kbit/s of bandwidth available. PRI ISDN does not use Robbed bit signaling. Instead it uses the D channel. Slips are caused by a timing problem and have nothing to do with AMI or B8ZS. Framing of either SF (D4) or ESF can be used on a T1 regardless of the line coding. (some mistakenly believe that B8ZS must be used with ESF and AMI must be used with SF) ESF is preferred because more robust performance monitoring is possible while the T1 is in service. Don Pobanz Ps. For a while the group I worked with back at the phone company was known as 'T1s are us' so I should be familiar with this stuff. ;) ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
Re: [Asterisk-Users] T1-PRI deployment questions...
PRI is shorthand for Primary Rate Interface ISDN BRI is Basic Rate Interface ISDN John Harragin wrote: Thanks to everyone for all the info... One more question. Until now, I had succesfully avoided isdn throughout my computer career... other than having the notion that it was a fairly troublesome line with data rates several times faster than pots. So far from ACC (my pri vendor) my T1-PRI must be b8zs/esf. On the form I have to fill out most of the pri enteries are listed under ISDN/PRI so I'm not really sure which questions are particular to pri. My usage will 23 voice (with an occational fax) plus the d channel. What is the relationship between pri isdn - is it considered isdn? If so, what do I need to know about that? John -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Don Pobanz Sent: Monday, June 02, 2003 9:42 AM To: '[EMAIL PROTECTED]' Subject: RE: [Asterisk-Users] T1-PRI deployment questions... I have been on vacation so didn't jump in earlier. Some of what I say here has been gone over earlier in this thread but I will repeat the results as a summery. AMI is not lossy, but it is almost always used in conjunction with a ones density technique called bit7. Bit7 will change bit 7 to a 1 when a word (8 bits) are all zeros. In North America when someone says AMI they really mean AMI with bit7. PRI ISDN will not work on an AMI (with bit7) T1. When validating ones density B8ZS does introduce errors but in such a way that the far end will know that they are errors and remove them. The only reasonable choice for PRI ISDN is B8ZS Robbed bit signaling uses bit 8 of each word of every 6th frame for signaling. This does not introduce errors on the line but it does make those bits unavailable for data. Usually data services assumes that the 8th bit of every work of every frame are not available so that you have 7 of each 8 bit word. That makes 56Kbit/s of 64Kbit/s of bandwidth available. PRI ISDN does not use Robbed bit signaling. Instead it uses the D channel. Slips are caused by a timing problem and have nothing to do with AMI or B8ZS. Framing of either SF (D4) or ESF can be used on a T1 regardless of the line coding. (some mistakenly believe that B8ZS must be used with ESF and AMI must be used with SF) ESF is preferred because more robust performance monitoring is possible while the T1 is in service. Don Pobanz Ps. For a while the group I worked with back at the phone company was known as 'T1s are us' so I should be familiar with this stuff. ;) ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users This e-mail was scanned and found clean by Monroe-Woodbury CSD Antivirus. This e-mail was scanned and found clean by Monroe-Woodbury CSD Antivirus. ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
Re: [Asterisk-Users] T1-PRI deployment questions...
On Thu, 2003-05-29 at 10:04, John Harragin wrote: I am ordering T1-PRI service from local service provider and have a few questions. Is there framing and coding considerations (or is it all one standard), if so what is best? How are calls routed based on DIDs - are these just dtmf tones passed after the call is picked up and treated as normal exten= definitions? I'll answer this since I just had mine installed and went through this. Signalling comes in just a few options at the base level and is specific to the T1 transport. Your options are ESF or D4 for framing, and AMI or B8ZS for error detection. Your PRI rides on top of the T1 transport. In the PRI your DIDs are passed as part of the call setup in Q.931 packets on the D channel. Specifically you will place all your incoming PRI lines into a context in extentions.conf and then you will make extensions with the incoming phone numbers or part there of if your telco provider isn't sending the whole called number. In these extension deffinitions you can redirect the calls to either the appropriate IVR menu, or an internal extention. -- Steven Critchfield [EMAIL PROTECTED] ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
RE: [Asterisk-Users] T1-PRI deployment questions...
B8ZS/ESF I believe is the usual for a PRI DID calls in asterisk are routed just like dtmf dialed extensions, but there are not DTMF tones passed. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Harragin Sent: Thursday, May 29, 2003 11:05 AM To: Asterisk Subject: [Asterisk-Users] T1-PRI deployment questions... I am ordering T1-PRI service from local service provider and have a few questions. Is there framing and coding considerations (or is it all one standard), if so what is best? How are calls routed based on DIDs - are these just dtmf tones passed after the call is picked up and treated as normal exten= definitions? John This e-mail was scanned and found clean by Monroe-Woodbury CSD Antivirus. ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
RE: [Asterisk-Users] T1-PRI deployment questions...
On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: B8ZS is required for PRI. It's a digital service and can not handle the loss of data required for AMI. I wasn't aware that AMI lost data. AMI just inverts polarity on the line for every other 1. B8ZS does the same thing but intentionally introduces errors on the line to maintain 1's density. Neither one is lossy. On Thu, 29 May 2003, Joe Antkowiak wrote: B8ZS/ESF I believe is the usual for a PRI DID calls in asterisk are routed just like dtmf dialed extensions, but there are not DTMF tones passed. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Harragin Sent: Thursday, May 29, 2003 11:05 AM To: Asterisk Subject: [Asterisk-Users] T1-PRI deployment questions... I am ordering T1-PRI service from local service provider and have a few questions. Is there framing and coding considerations (or is it all one standard), if so what is best? How are calls routed based on DIDs - are these just dtmf tones passed after the call is picked up and treated as normal exten= definitions? John This e-mail was scanned and found clean by Monroe-Woodbury CSD Antivirus. ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users -- Steven Critchfield [EMAIL PROTECTED] ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
RE: [Asterisk-Users] T1-PRI deployment questions...
On 29 May 2003, Steven Critchfield wrote: On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: B8ZS is required for PRI. It's a digital service and can not handle the loss of data required for AMI. I wasn't aware that AMI lost data. AMI just inverts polarity on the line for every other 1. B8ZS does the same thing but intentionally introduces errors on the line to maintain 1's density. Neither one is lossy. AMI is lossy. When the ones density in the signal is too low, AMI will insert ones to ensure that the far end does not lose sync. C. ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
RE: [Asterisk-Users] T1-PRI deployment questions...
On Thu, 2003-05-29 at 15:06, Charles E. Youse wrote: On 29 May 2003, Steven Critchfield wrote: On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: B8ZS is required for PRI. It's a digital service and can not handle the loss of data required for AMI. I wasn't aware that AMI lost data. AMI just inverts polarity on the line for every other 1. B8ZS does the same thing but intentionally introduces errors on the line to maintain 1's density. Neither one is lossy. AMI is lossy. When the ones density in the signal is too low, AMI will insert ones to ensure that the far end does not lose sync. As I understand it, AMI is not lossy but will may cause problems due to not maintaining 1's density. 1's density is used to make sure both sides are synced up properly. B8ZS is AMI except that it introduces bipolar violoations to make sure the line doesn't stay in an off state for too long. So B8ZS intentionally throws errors on the line in a known manner so as to make sure each side is in sync, but AMI does not care if the line goes all 0's for a while. I still haven't been able to dig up any documentation to back up that AMI is lossy, just maybe prone to errors via slips. -- Steven Critchfield [EMAIL PROTECTED] ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
RE: [Asterisk-Users] T1-PRI deployment questions...
On Thu, 2003-05-29 at 15:46, Steven Critchfield wrote: On Thu, 2003-05-29 at 15:06, Charles E. Youse wrote: On 29 May 2003, Steven Critchfield wrote: On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: B8ZS is required for PRI. It's a digital service and can not handle the loss of data required for AMI. I wasn't aware that AMI lost data. AMI just inverts polarity on the line for every other 1. B8ZS does the same thing but intentionally introduces errors on the line to maintain 1's density. Neither one is lossy. AMI is lossy. When the ones density in the signal is too low, AMI will insert ones to ensure that the far end does not lose sync. As I understand it, AMI is not lossy but will may cause problems due to not maintaining 1's density. 1's density is used to make sure both sides are synced up properly. B8ZS is AMI except that it introduces bipolar violoations to make sure the line doesn't stay in an off state for too long. So B8ZS intentionally throws errors on the line in a known manner so as to make sure each side is in sync, but AMI does not care if the line goes all 0's for a while. I still haven't been able to dig up any documentation to back up that AMI is lossy, just maybe prone to errors via slips. I still can't find any reference to AMI being lossy, and can't find any comments that show where a AMI circuit would introduce 1's to maintain 1's density. After reading a page describing test patterns and why they use certain test patterns, it makes sense why AMI might not be usable for a PRI though. http://www.electrodata.com/testpat.htm In a PRI, since the signalling is in the D channel, and the consecutive B channels could be completely clear, you could run into times with more than 15 consecutive zeros. Although I need to do more looking at how D4 or ESF lays on top of a T1 signal. Anyways, with more than 15 consectuives zeros you no longer are within ANSI spec. On a RBS circuit it would be less likely to fall too far out of spec using AMI. -- Steven Critchfield [EMAIL PROTECTED] ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
Re: [Asterisk-Users] T1-PRI deployment questions...
Steven Critchfield wrote: On Thu, 2003-05-29 at 15:46, Steven Critchfield wrote: On Thu, 2003-05-29 at 15:06, Charles E. Youse wrote: On 29 May 2003, Steven Critchfield wrote: On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: B8ZS is required for PRI. It's a digital service and can not handle the loss of data required for AMI. I wasn't aware that AMI lost data. AMI just inverts polarity on the line for every other 1. B8ZS does the same thing but intentionally introduces errors on the line to maintain 1's density. Neither one is lossy. AMI is lossy. When the ones density in the signal is too low, AMI will insert ones to ensure that the far end does not lose sync. As I understand it, AMI is not lossy but will may cause problems due to not maintaining 1's density. 1's density is used to make sure both sides are synced up properly. B8ZS is AMI except that it introduces bipolar violoations to make sure the line doesn't stay in an off state for too long. So B8ZS intentionally throws errors on the line in a known manner so as to make sure each side is in sync, but AMI does not care if the line goes all 0's for a while. I still haven't been able to dig up any documentation to back up that AMI is lossy, just maybe prone to errors via slips. I still can't find any reference to AMI being lossy, and can't find any comments that show where a AMI circuit would introduce 1's to maintain 1's density. After reading a page describing test patterns and why they use certain test patterns, it makes sense why AMI might not be usable for a PRI though. http://www.electrodata.com/testpat.htm In a PRI, since the signalling is in the D channel, and the consecutive B channels could be completely clear, you could run into times with more than 15 consecutive zeros. Although I need to do more looking at how D4 or ESF lays on top of a T1 signal. Anyways, with more than 15 consectuives zeros you no longer are within ANSI spec. On a RBS circuit it would be less likely to fall too far out of spec using AMI. You are right, Steve. AMI isn't lossy. It stands for alternate mark inversion. It simply forces more transitions into the stream to ensure good sync at the receiver. With the way old T1s worked this was good enough to ensure sync., as the content of these T1s was always voice, and not completely arbitrary. With ISDN, or other data applications, which carry completely arbitrary content as well as voice, you really need a more robust sync scheme. This caused changes in both E1s and T1s. E1s got CRC4 to ensure robust frame sync. T1s got 8BZS to ensure robust bit sync. An ISDN T1 *should* be using 8BZS, but isn't always. Similarly, an ISDN E1 *should* be using CRC4 framing, but some countries insist on the older flakier framing mechanism for some odd reason. I think the confusion about lossy T1s probably relates to the robbed bit signalling that is generally used on non-ISDN T1s. This does, of course, lose a little of the 64kbps channel in a rather PITA way. Regards, Steve ___ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
