Is 50 ms Restoration Necessary? Jeff Schallenberg Optical Systems Planning, Teleglobe jeff. schallenberg@teleglobe. com IEEE Bandwidth Management Workshop IX
Is 50 ms Restoration Necessary? Outline: l 1. Background l 2. 50 milliseconds in the Standards l 3. Laboratory Simulation of Brief Outages l 4. Conclusions
Is 50 ms Restoration Necessary? - Background l Stentor Network Long (4500 -km circumference) Matched -Node Ring* • One large SONET ring proves in over several smaller ones: • Fewer NEs and interfaces to buy • Less fiber-km (no crosslinks) • Theoretical availability is not significantly worse with longer fiber spans, even though there are more NEs and fiber in a single protection span • BUT the BLSR protocol is slowed by the long propagation time to and fro around the large ring • Matched Nodes using Drop-and-Continue on Protection also slow down intra-ring switching (like Extra Traffic) l The need to understand the REAL impact of brief outages Does operating outside the recommended 1200 -km ring circumference limit threaten any of the services riding in the SONET frames?
Is 50 ms Restoration Necessary? 50 milliseconds in the Standards l Telcordia General Recommendations, especially GR-499 CORE “Transport Systems Generic Requirements Common Requirements Criteria” l ANSI T 1. TR. 68 -2001 “Enhanced Network Survivability Performance” -Call-Dropping (All Circuit Switched Services ) -PL Disconnects -Potent ial Packet (X. 25) Disconnects -Potential Data Session Timeouts Outage Impac t -Potential Voiceband Disconnects (< 5%) -Affect Cell Rerouting Process -Trigger Changeover of CCS links -Service "Hit" (Reframes) Protection Switching Range 1 st Restoration Target Range 50 ms -May Drop Voiceband Calls Depending on Channel Bank Vintage 3 rd Restoration Target Range 2 nd Restoration Target Range 200 ms -Packet (X. 25) Disconnects -Data Session Timeout 4 th Restoration Target Range -Network Congestion Expected Social/ Business Impact s -Potentially FCC Reportable 6 th Restoration Target Range 5 th Restoration Target Range Outage Duration 2 s 10 s ~5 min ~30 min
Is 50 ms Restoration Necessary? 50 milliseconds in the Standards - continued From T 1. TR. 68 -2001: Examples of outage durations beyond which calls are abandoned, or other processes must be re-initiated (emphasis added): ·SNA: programmable timeout 1. 1 to 255 s ·X. 25: idle state condition timer settable 1 to 30 s ·ATM: cell rerouting process may be started within 200 ms, but could be longer in large or complex networks ·Old channel bank types (e. g. , D 1 A, D 1 D, D 2, D 3) exhibit carrier group alarm times of 300 milliseconds to 500 milliseconds. ·Voice circuit: possible false disconnect at downstream switch trunk interface with 150 ms on-hook supervisory signal state The TR further states “The time frame between 50 milliseconds to just under 200 milliseconds will have minimal impact to services. Any affected voiceband switched calls (voice or data) will have less than a 5% probability of being dropped. ”
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages l 1. The Telus Interruptor Switch – controlled “hits” with reed and optical switches Switches, pots - Adjust rate, duration Pushbutton - Start sequence Pin jacks - n/o, n/c reed relays with 100 - in series BNC Jacks for scope trigger + 6 VDC Reed Relay for Coaxial (DS-3) Optical Switch (OC-N)
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages 2. (a) Stentor Switching Lab – DMS-100 DS-0 SS 7 Links SSTP 0 SSTP 1 C-Links Interruptor Switch A-Links SDM 1 SDM 2 DS-1 Trunks • DS-0 hits <200 ms on a single link are not even detected • 200 ms < DS-0 hits < 1200 ms on a single link cause “excess control codes” alarms at receive end, but alarms clear immediately • TWO DS-0 HITS > 200 ms within 5 MINUTES on single link causes 60 s “Delayed” state where the link is OOS - but the alternate link is OK • To isolate a DMS (for 60 s) requires BOTH links to be hit TWICE IN 5 MINUTES by >200 ms Conclusion: SS 7 links are immune to MULTIPLE brief (<200 ms) interruptions and SINGLE moderate (>200 ms) hits
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages 2. (b) Stentor Switching Lab – DMS-100 DS-1 Trunks SSTP 0 SSTP 1 C-Links A-Links SDM 1 A-Links SDM 2 DS-1 Trunks Interruptor Switch • Single and multiple hits <2 s don’t affect a call. (Clicks and noise bursts are audible). • Hits >2 s cause DS-1 CGA, call is dropped, DS-1 trunk restores after 20 s Conclusion: The DS-1 voice trunk network is immune to brief (<2 s) hits
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages 3. Stentor Data Lab – 56 kb/s data service in DS-1 signal Data Test Set MTE Interruptor Switch DCS 1/0 MTE DS-0 Loopback 56/64 kb/s DS-1 • For DS-1 hits <2. 7 s, the 64 kb/s data stream recovers sync 20 -30 ms after hit clears. • However when the DS-1 is hit for >2. 7 s, data sync is not restored for 15 -20 s, depending on the particular Mega. Stream. Terminal Equipment (Newbridge and Tellabs were tested). A 4. 4 -s “hit” on the DS-1(actually 4, 1 -s hits) Switch drive Test set error output Is stretched by 20 s on the 56 kb/s data by the Tellabs 440 MTE Conclusion: DS-0 -based data services are immune to moderate (<2. 7 s) DS-1 hits
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages l 4. Stentor Data Lab – NTSC Video Codec over ATM/OC- 3 CCD Camera Colour Monitor 36150 NTSC Video OC-3 X 36150 NTSC Video • If OC-3 connector opened/replaced within 5 s (or so), the last frame is “frozen” by the codec until new data is received. • If the OC-3 outage is longer than a few seconds, the codec inserts a colour-bar test pattern. When OC-3 is restored, video returns immediately. Conclusion: Broadband services over ATM are immune to brief (<5 s) hits and are not “shut down” by longish (>5 s) interruptions
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages 5. Stentor Access Lab – VF signal over Access SONET OC-12 Interruptor Switch DS-1 Loopback FCOT Lockout W 5 ms/cm A 12 -ms hit recovers about 20 ms after fiber restores. VF 1000 Hz RFT C D S Storage Scope 10 s/cm >2 s hit on fiber causes DS-1 CGA, signal is lost for 20 s after fiber restores. Conclusion: there is no drastic stretching of brief (<2 s) fiber outages at tributary rates down to DS-0
Is 50 ms Restoration Necessary? Laboratory Simulation of Brief Outages 6. Bell Platforms and Architectures Lab – DS-1 AAL 1 over ATM and SONET OC-48 OC-12 OC-48 L L T OC-3 DS-3 PP 1 (Edge Switch) DS-1 AAL 1 NB 1 DS-3 A Interruptor Switch OC-48 Lockout (W) OC-12 OC-48 A A A NB 2 T OC-3 (Edge Switch) PP 2 (Core Switch) DS-1 Test Set • Outages <2. 5 s restored immediately on ATM switches, causing NO alarms on ATM interfaces • Outages >2. 5 s encountered the DS-1 CGA phenomenon, stretched for 34 s, caused PAIS alarms on Newbridge 2, RFI on Passport 1 Conclusion: The ATM Core and Edge networks are immune to brief (<2. 5 s) hits DS-1 AAL 1 Loopback
Is 50 ms Restoration Necessary? -. Conclusions No, not really! l Today’s network is quite resistant to brief outages l 200 ms outages would not jeopardize services (data, video, voice) l equipment design could be simplified l equipment costs could be reduced
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