10 Gigabit Ethernet WAN PHY

Transcription

1 White PAPER 10 Gigabit Ethernet WAN PHY Introduction The introduction of 10 Gigabit Ethernet (10 GbE) WAN PHY into the IP/Ethernet networking community has led to confusion over the applicability between 10 GbE WAN PHY and OC-192c/STM-64 interfaces. Both of these interfaces support transmission at 9.6 Gbps, support SONET/SDH framing, and can be connected to SONET/SDH ADM or DWDM gear. So what is the difference? The answer can be boiled down to two things: L2/L3 protocol support, and link diagnostic and maintenance capabilities. Support for Layer 2 and Layer 3 SONET/SDH interfaces deployed in routers have been designed to support Packet over SONET/SDH (POS) as defined in RFCs 1619, 1662 and Even though most IP packets originate from Ethernet networks as packet-only interfaces, support for transmission and switching of Ethernet frames on POS is explicitly excluded. POS interfaces actually strip off the Ethernet header and add their own link layer header, for example PPP or HDLC framing. This design aspect of POS interfaces has led to multiple efforts to carry Ethernet over SONET/SDH: ITU X.86 and T1X1 for OC-3 through OC-48, and 10 GbE WAN PHY for OC-192. While the cost difference between OC-192c POS and 10 GbE WAN PHY has created the perception that POS interfaces actually have greater functionality, this is a myth. By eliminating the need to re-encapsulate Ethernet into PPP, 10 GbE WAN PHY supports IP as well as direct transmission and switching of Ethernet frames more efficiently and cost effectively than OC-192 POS. Rich Diagnostic and Maintenance Capabilities The misperception exists that if you want rich diagnostic and maintenance capabilities across OC-192 links you need to buy OC-192 POS interfaces. The truth is that 10 GbE WAN PHY provides equivalent, and in some cases enhanced, diagnostic and maintenance functionality. The reason for the misperception lies in the methods used for the various functions. SONET approaches diagnostics from the perspective of managing a TDM link where all management information is carried outside of the TDM data. 10 GbE approaches the problem from a data link perspective where much of the diagnostic information is carried within the data frames. The 802.3ae standards body recognized this fact when designing the WAN PHY specification and included only the SONET diagnostic and maintenance functionality not already present in Ethernet. Figure 1. Framing overhead 2007 FORCE10 NETWORKS, INC. [ P AGE 1 OF 5 ]

2 Fault Management Functionality Ethernet Features TDM/SONET Equivalent Link availibilty, proper cable Link detect, interface up/down Loss of signal, signal fail Noisy link or faulty Tx/Rx Encoding error Coding/framing error Configuration mismatch of faulty Tx Giants, jabber NA (fixed frame length) Long links (collision), noisy link or faulty Tx/Rx Runts NA (fixed frame length) Noisy link or faulty Tx/Rx CRC B1, B2, B3, FEBE/REI, signal degrade Link quality NA (asynchronous, uses CRC) Errored seconds Noisy link or faulty Tx/Rx NA (no pointers) Loss of pointer Noisy link or faulty Tx/Rx NA (asynchronous, no clock) Loss of synch Remote alarm/defect Keep-alive AIS, RDI Fault protection/redundancy Link aggregation (LAG) APS (linear) Fault protection/redundancy NA (no ring topology) APS (UPSR/BLSR) Table 1. Fault management features As shown in Table 1, 10 GbE WAN PHY makes use of the SONET overhead bits to provide: Same diagnostics capability - Loss of signal - Framing errors/loss of frame - Coding violations (Line and Path RDI and Line and Path AIS) - Errored seconds - Severely errored seconds - Delay triggers (currently not supported in FTOS) - Loss of synchronization (not needed) Same error/performance monitoring - B1, B2, B3 - J0, J1 (J1 is currently not visible in the FTOS CLI) Same defect/alarms - FEBE - RDI - AIS Ethernet has built in mechanisms for detecting link state and frame errors so it does not need to rely on the SONET capabilities to provide this information even though it can use both Ethernet and SONET mechanisms for many features (Table 1). Much of the difference between SONET and Ethernet can be boiled down to the fact that SONET is synchronous, it relies on counting a specific number of clock cycles to identify the start of a frame, and Ethernet is asynchronous, frames may come at any time. The synchronization diagnostics in SONET, for the most part, do not apply in the Ethernet world. If the SONET link does lose synchronization, the Ethernet layer detects that the link is down without having to look at the SONET synchronization overhead bits. SONET APS and 10 GbE LAG One area of concern is 10 GbE WAN PHY s lack of support for SONET automatic protection switching (APS). In the POS world, support for APS was an interesting feature because there is no equivalent in the IP world. Nevertheless, APS on POS interfaces is significantly different from the APS supported on SONET add-drop multiplexers that must participate in a ring topology. POS interfaces only support Linear APS, or the ability to switch from a failed primary point-to-point connection to an idle backup FORCE10 NETWORKS, INC. [ P AGE 2 OF 5 ]

3 Protection Protection of Any Media The IEEE 802.3ae working group did not define Linear APS for 10 GbE WAN PHY because Ethernet already has a more generalized approach to handling this kind of link redundancy, 802.1ad Link aggregation (LAG). Unlike APS, since LAG operates at Layer 2, primary and backup links do not need to traverse the same Layer 1 physical media one link may be running 10 GbE LAN PHY over dark fiber and the backup link can be 10 GbE WAN PHY running over SONET or DWDM. This gives 10 GbE a major advantage over APS that only operates over SONET. N+1 Protection Another advantage of using LAG for protection switching is its ability to simultaneously protect multiple circuits. LAG incorporates load-balancing capabilities that enable up to 16 links to be combined into a single logical connection. Fast Failover Time Linear APS does have the advantage of 50 ms switchover time versus the approximately 100 ms it takes for LAG to detect a failed link and switch. In the voice world, 50 ms restoration of a SONET link that could be carrying anywhere from thousands to millions of revenue-generating telephone connections is imperative. A link failure that caused any connections to be dropped is a direct hit to the bottom line. In the data world the difference between 50 ms and 100 ms is like splitting hairs. In neither case will the link failure cause loss of IP sessions or connections Summary The myth that 10 GbE WAN PHY is a less capable version of OC-192 POS has been proven to be just a myth. With support for both switching of Ethernet frames and IP packets, 10 GbE WAN PHY offers greater flexibility in utilizing 10 Gbps links. The link diagnostic and management functionality of OC-192 POS has been incorporated into 10 GbE WAN PHY giving the latter equivalent capabilities. With the addition of LAG-based protection switching available on 10 GbE, the link protection capabilities and topology options surpass those available with SONET OC-192. Figure 2. Protection mechanisms in SONET and Ethernet 2007 FORCE10 NETWORKS, INC. [ P AGE 3 OF 5 ]

4 Appendix: WAN PHY Diagnostic CLI Command Example Force10#show controllers TenGigabitEthernet 6/0 Interface is TenGigabitEthernet 6/0 SECTION LOF = 0 LOS = 0 BIP(B1) = 0 LINE AIS = 0 RDI = 0 FEBE = 0 BIP(B2) = 0 PATH AIS = 0 RDI = 0 LOP = 0 FEBE = 0 BIP(B3) = 0 Active Defects: NONE Active Alarms: NONE Alarm reporting enabled for: B1-TCA LAIS LRDI B2-TCA B3-TCA Framing is SONET, AIS-shut is enabled Scramble-ATM is enabled, Down-when-looped is enabled Loopback is disabled, Clock source is line, Speed is Oc192 CRC is 32-bits, Flag C2 is 0x1a, Flag J0 is 0xcc, Flag S1S0 is 0x0 Appendix: Use of Overhead Bits in SONET and 10 GbE WAN PHY Byte Description OC-192c SONET 10 GbE WAN PHY A1 Framing Frame alignment Fixed: 0xF6 A2 Framing Frame alignment Fixed: 0x28 J0 Section trace User programmable section message Z0 Growth Undefined Unused: 0xCC B1 Section BIP-8 Bit interleave parity for section error monitoring of previous frame E1 Orderwire Optional 64kbps channel between STE Unused: zero F1 Section user channel Optional for data communication Unused: zero D1-3 Section DCC Optional for data communication Unused: zero Table 2. Section overhead 2007 FORCE10 NETWORKS, INC. [ P AGE 4 OF 5 ]

5 Byte Description OC-192c SONET 10 GbE WAN PHY H1, 2 Pointer byte Location of SPE in each STS relative to the pointer (in bytes). Also used for frequency justification. H3 Pointer action Used to adjust the fill of input buffers in case of negative Fixed: 0x00, pointer justification. Also used for frequency justification. no pointer action required B2 Line BIP-1536 Bit interleave parity for line error monitoring of previous frame K1 Linear APS Request (bits 1-4): specifies automatic protection switching request type Fixed: 0x0, no request or Ring APS (not used by WAN PHY) Channel (bits 5-8): channel to switch from Fixed: 0x1, working channel K2 Linear APS Channel (bits 1-4): channel to switch to Fixed: 0x0, working channel or Ring APS (not used by WAN PHY) Redundancy (bit 5): 1+1 or 1:n Fixed: Status (bits 6-8): indicates line AIS (111), line RDI (110), bi-directional (101), unidirectional (100), rest undefined Indicate line RDL, AIS or set to zero D4-12 Line OCC Optional for data communication Unused: zero S1 Synch Synchronization status Fixed: 0x0, no line synch required Z1, 2 Growth Undefined Unused: zero M1 FEBE Reports detected block errors (B2) to far end E2 Orderwire Optional 64kbps channel between LTE Unused: zero Table 3. Line overhead Byte Description OC-192c SONET 10 GbE WAN PHY J1 Path trace 16 J1 bytes in consecutive WIS frames make up a user programmable path message that repeats. First byte is 0x00 for no message. B3 Path BIP-8 Bit interleave parity for path error monitoring of previous frame C2 Path signal label Specifies payload type in SPE Fixed: 0x1A G1 Path status REI/FEBE (bits 1-4): reports detected block errors (B3) for far end RDI (bit 5): remote defect indicator F2 Path user channel Optional for user communication Unused: zero H4 Multiframe indicator Used for VT structured payload Unused: zero Z3, 4 Growth Undefined Unused: zero N1 TCM Optional tandem connection maintenance Unused: zero Table 4. Path overhead Force10 Networks, Inc. 350 Holger Way San Jose, CA USA PHONE FACSIMILE 2007 Force10 Networks, Inc. All rights reserved. Force10 Networks and E-Series are registered trademarks, and Force10, the Force10 logo, Reliable Business Networking, Force10 Reliable Networking, C-Series, P-Series, S-Series, EtherScale, TeraScale, FTOS, SFTOS, StarSupport and Hot Lock are trademarks of Force10 Networks, Inc. All other company names are trademarks of their respective holders. Information in this document is subject to change without notice. Certain features may not yet be generally available. Force10 Networks, Inc. assumes no responsibility for any errors that may appear in this document. WP v FORCE10 NETWORKS, INC. [ P AGE 5 OF 5 ]