Transcript
Always On / Dynamic ISDN (AO/DI) Turn-up and Maintenance
Application Note 69
DA-5 3
Q.921 Q.921 Q.921 Q.921 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP
:Control field: : Type ............................................... I : Send Sequence Number, N(S)................... 80 : Poll/final bit ...................................... 0 :-------------- X.25 layer 3 ------------------:General Field Information: : Q/A-bit............................................ 0 : D-bit ............................................... 0 : Modulo-bits ....................................... 01 (modulo 8) :Channel ............................................... 1 : Logical Group Number............................. 0 <- D PPP ID = 1 Call-Req BAP 20 G 15:37:37115 : Logical Channel Number .......................... 1 -> D 16 21 r RR - 81 4 G 15:37:37131 :Packet type .......................................... DATA -> D 16 21 c I 80 81 1 RR 5 7 G 15:37:37143 :Send Sequence Number, P(s) ....................... ->0 D PPP ID = 1 Call-Resp BAP 23 G 15:37:37191 :Receive Sequence Number, P(r) .................... <-0 D 16 21 c I 81 82 1 RR 3 7 G 15:37:37224 : More data (M bit) ................................ <-0 D 0 65 c SABME p 3 G 15:37:37246 :-------------- Point-to-Point Protocol --------> D 0 65 r UA f 3 G 15:37:37253 :PPP header ............ FF 03 <- D 0 65 c I 0 0 08 02 SETUP 35 G 15:37:37279 :Protocol code ......... Not compressed Channel: Any Calling: 8050258 Called: 8095100 :Protocol ............... BAP (C02D) <- DMLP SEQ= 33 Begin & End VJC 26 G 15:37:37420 :BAP Code.............. Call-Req. -> DMLP SEQ= 28 Begin & End VJC 20 G 15:37:37543 :Identifier ............. 1 -> D 0 65 c I 0 1 08 02 f CALL PROC. 11 G15:37:37592 :BAP length ............ 9 Channel: B1 : <- DMLP SEQ= 34 Begin & End CP 132 G 15:37:37608 :Option 01 ............. Lg = 5 -> D 0 65 c I 1 1 08 02 f ALERTING 8 G 15:37:37701 :(Link-Type) -> DMLP SEQ= 29 Begin & End VJC 22 G 15:37:37794 : Hex.value ............ 00 40 1D <- D 16 21 c I 85 86 1 RR 5 7 G 15:37:37811 : Speed (Kbps)......... 64 -> D 0 65 c I 2 1 08 02 f CONNECT 26 G 15:37:37821 : Type .................. ISDN Connected: 8095100 : Type .................. Analog <- D 0 65 c I 1 3 08 02 CONNECT ACK. 8 G 15:37:37832 : Type .................. Switched Dig. <- B1PPP ID = 1 Config-Req LCP 29 G 15:37:37845 : Type .................. ISDN data/voice -> B1PPP ID = 1 Config-Req LCP 38 G 15:37:37856 <- B1PPP
ID = 1
Config-Rej
LCP
12 G 15:37:37860
Summary This Application Note describes the many advantages brought by the new AO/DI (Always On / Dynamic ISDN) service and explains why the use of a suitable protocol analyzer is required for its turn-up and maintenance. Today the DA-5 is the only analyzer on the market capable of simultaneously analyzing all of the protocols implemented by AO/DI in the D and B channels. This ability is mandatory for solving problems of performance and excessive communication costs that frequently occur with dynamic bandwidth allocation.
Application Note 69
Introduction One of the main concerns with remote access is longduration connection, which may result in overloaded telephone networks and access concentrators. To offer full-time connection to end-users while retaining existing infrastructures, the VIA (Vendors ISDN Association) has implemented various mature technologies to set up an innovative service: AO/DI (Always On/Dynamic ISDN). The service uses the packet switch capability of the Dchannel to offer an ‘Always On’ connection between the user and the service provider. This 9.6 kbps connection rate is sufficient for applications such as e-mail notification, news feeds, push services or credit card verification.
When the activity decreases, the B channels are automatically released and the communication continues on the D channel. This new full-feature WAN service requires a ‘ubiquitous’ analysis solution to help during trials and operation.
Telcos
Customer premises Central Office ISDN CO
Public Switched Telephone Network
Point of Presence
BRI
End user
X.25
Service providers
B channel only established when additional bandwidth is needed
When additional bandwidth is necessary, for instance to download a Web page, one or both B channels are opened and used instead of the packet connection.
X.25 logical channel (the « Always on » link)
Figure 1: AO/DI concept
AO/DI: a win/win/win technology AO/DI provides numerous advantages as compared with traditional methods that use only circuit connections. This will push worldwide adoption of AO/DI quite soon:
• For end-users Web surfers and telecommuters can remain connected to a remote LAN or be notified of incoming e-mail in real time while keeping B channels available for voice or fax traffic. This solution results in lower communication costs.
• For telcos The X.25 packets in the D channel are handled by the packet handler and routed toward an X.25 network without crossing the switch. This optimizes the utilization of the switched network infrastructure and eliminates the potential congestion problems for voice calls.
• For service providers and IT managers As the primary link, X.25 enables service providers to support more customers with the same amount of network resources (B channels).
How does it work? An X.25 connection is made with the service provider. This constitutes the famous ‘Always On’ link. Data is then encapsulated in the multilink PPP protocol and sent over the X.25 virtual channel. When additional bandwidth is needed, one or two B channels are added to the multilink PPP bundle. As soon as a B channel is opened, only BAP control packets are sent over the X.25 channel to control the allocation and de-allocation of the B channels. In the B channels, the X.25 encapsulation is not used, which allows almost 64 kbps to be reached on each B channel.
The multilink bundle includes the X.25 logical channel (which is the primary link) as well as the additional B channels opened only when needed.
BAP/BACP
TCP/IP (Data)
PPP/MLP
PPP
Q.931
PPP
PPP
Channel B1
Channel B2
X.25
Q.921
D Channel
Q.931: ISDN signaling layer 3 Q.921: LAPD (layer 2) PPP/MLP: Point to Point protocol with the multilink option BAP/BACP: Bandwidth Allocation Protocol/Bandwidth Allocation Control Protocol
Figure 2: AO/DI protocol stack
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Application Note 69
A complex technology to be provided and maintained AO/DI is a smart but complex technology: • Different channels used simultaneously • Two very different types of network involved: circuit switched telephone network and packet switched network • Several complex protocols (ISDN signaling, X.25, PPP/MLP, BAP/BACP, TCP/IP) that must work in harmony to deliver the service • A different protocol encapsulation over D and B • Dynamic allocation of the bandwidth Due to a potential incompatibility between equipment from different vendors (this is a new technology) or a CPE configuration error, many problems may occur during CPE installation, service provisioning and maintenance. Indeed, AO/DI is not a plug-and-play
technology and requires the following parameters: • For X.25: address, packet size, window, number of logical channels, TEI, etc. • For ISDN: ISDN protocol, TEI, SPID and addresses for the different B channels, etc. • For the correct allocation of the B channels (depends on the implementation): bandwidth allocation strategy, thresholds to set up and clear the calls, etc. • For the security: ID, password, etc. • For IP: address, mask Incorrect parameter tuning may result in a total failure, performance problems (B channel never allocated) or excessive communication costs (for example, B channels used/open too long or always nailed up).
WG DA-5: the right troubleshooting tool for AO/DI Because this technology is so complex, troubleshooting AO/DI requires a protocol analyzer able to analyze traffic in the different channels in real time and simultaneously (D + 2B), with a complete decode of all protocols involved. In the D channel: • ISDN signaling • X.25 • PPP and multilink PPP (MLP) encapsulated in X.25 • BAP/BACP • TCP/IP • Authentication protocols like PAP and CHAP. In the 2 B channels: • PPP and multilink PPP • BAP/BACP • TCP/IP carried into PPP/MLP • Authentication protocols like PAP and CHAP.
Q.921 Q.921 Q.921 Q.921 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 X.25 PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP PPP
:Control field: : Type ............................................... I : Send Sequence Number, N(S)................... 80 : Poll/final bit ...................................... 0 :-------------- X.25 layer 3 ------------------:General Field Information: : Q/A-bit............................................ 0 : D-bit ............................................... 0 : Modulo-bits ....................................... 01 (modulo 8) :Channel ............................................... 1 : Logical Group Number............................. 0 : Logical Channel Number .......................... 1 :Packet type .......................................... DATA :Send Sequence Number, P(s) ....................... 0 :Receive Sequence Number, P(r) .................... 0 : More data (M bit) ................................ 0 :-------------- Point-to-Point Protocol -------:PPP header ............ FF 03 :Protocol code ......... Not compressed :Protocol ............... BAP (C02D) :BAP Code.............. Call-Req. :Identifier ............. 1 :BAP length ............ 9 : :Option 01 ............. Lg = 5 :(Link-Type) : Hex.value ............ 00 40 1D : Speed (Kbps) ......... 64 : Type .................. ISDN : Type .................. Analog : Type .................. Switched Dig. : Type .................. ISDN data/voice
The DA-5 is a unique, robust and compact analyzer specifically designed for the field that offers all these decodes simultaneously. With the DA-5, the user can troubleshoot all kinds of problems whatever their source: ISDN signaling, X.25, PPP, etc. Frames are decoded in real time and can be stored on the PC hard disk, enabling very long duration captures. The possibility to analyze frames from the different channels in a single window display facilitates understanding of the different synchronization problems that may occur. The DA-5 supports most of the ISDN protocol variants and can be used at any ISDN BRI interface: S, T or U when used jointly with the ISDN U-interface monitor WG IUM-10.
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Application Note 69
To learn more about it: http://www.via-isdn.org/ http://always.sonnet.com/ http://isdn.wg.com/ For further information, consult the technical datasheets for WG DA-5 and WG IUM-10. WG DA-5 BN 7517/10 http://www.wg.com/products/ium10/ium10.html WG IUM-10 BN 7534/10 http://www.wg.com/products/da5/da5.html IMK-50 package Contains one DA-5 and one IUM-10
BN 7534/82
Carrying bag for IUM-10 and DA-5
BN 7534/90.05
IMK-50: DA-5 with U monitoring option
Your contacts: Brazil Wandel & Goltermann Instrumentacao Ltda. & Cia. Av. Eng. Luis Carlos Berrini, 936-9. andar 04571-000 Sao Paulo, SP Brazil Tel. +55-11 5505 3266 Fax +55-11 5505 1598
China Wandel & Goltermann Pty. Ltd. Beijing Office Suite 1902 Ever Bright Building 6, Fu Xing Men Wai Da Jie Beijing 100045 People's Republic of China Tel. +86-10-6856 1034 Australia Fax +86-10-6856 1031 Wandel & Goltermann Pty. Ltd. Singapore P. O. Box 419 World Trade Centre Wandel & Goltermann Melbourne, Victoria 3005 Singapore Pty Ltd Australia 51 Goldhill Plaza #20-05 Tel. +61-3-9690 6700 Singapore 308900 Tel. +65-356-3246 Fax +65-356-3247
Subject to change without notice – Order number E 04.99/D2/69prov Printed in France
United Kingdom Wandel & Goltermann Sales Ltd. Portland House, Aldermaston Park Aldermaston, Berkshire RG7 4HR England Tel. +44-1189 409200 Fax +44-1189 409210 e-mail:
[email protected]
For other countries (not listed) please contact: Wandel & Goltermann GmbH&Co. Elektronische Meßtechnik Marketing International Postfach 12 62 D-72795 Eningen u.A. Allemagne Tel. +49-7121-86 16 16 Fax +49-7121-86 13 33 e-mail:
[email protected]
http://www.wg.com USA Wandel & Goltermann, Inc. P. O. Box 13585 Research Triangle Park, NC 27709-3585 USA Tel. +1-919-941-5730 Fax +1-919-941-5751
1999
