general node and the management node

Do you know OTN ODUk Shared Protection Ring

Network survivability reflects the network in case of failure, Able to maintain the service capability, the survival mechanisms of the network, topology, available resources, coordination mechanisms for survivability has a significant impact. In terms of the transport network, SDH  survivability as one of the most distinctive part, to lay the basis of SDH transmission technology position has achieved a lot, but its mechanism of survival of the next generation transmission network has also been – optical transport network ( OTN) eclectic, as an important cornerstone of its survivability. Currently ITU-T is stepping up development G.808.1 (general linear protection switching), G.808.2 (common ring network protection switching), G.873.1 (linear optical transport network protection), G.873.2 (Optical Transport network based on ODUk Shared protection ring) four main recommendations to plan OTN survivability.
Following the main reference of ITU-T G.873.2, here to analyze ODUk shared protection ring mechanism. And discus the huawei ODUK SPRing features.
OTN ring network protection features
(1) optical transport network ring protection switching is based on the subnet of each ODUk, or ring up and down on the business connection between the ODUk series, rather than on ODUk the “aggregation” (as in the SDH multiplex section shared protection ring). It should be noted is that each has their own ODUk automatic protection protocol (APS);
(2) optical transmission ring network protection scheme has good adaptability, because even the other physical network topology, you can also learn a logical ring network virtual
(3) switching only occurs in the end node, such a requirement for the following reasons: 1) simplify the structure; 2) shorten the switching time; 3) avoid the path length may be increased to twice the loop length caused additional damage.
(4) all of the distal ring to allow proximal switching and switching. Used to protect the proximal signal in the ring and work on the same side, while the distal is the opposite. To show that, in the G.709 OTN defined, even when the work and the protection of ODUk coexist in the same fiber, but also allows only the proximal switching.
(5) no longer have 2 / 4 fiber structural difference. For a particular cross-section, its working or
protection path may be located in different or coexist in the same optical fiber, although this will affect the survival of their size, but will not affect its structure and switching.
(6) OTN ring all up and down the normal course of business by the signals or additional signals of nodes. Normal course of business through multiple cross-section of the signal can, because the intermediate nodes may be used for the upper and lower protection signal or dual nodes up and down between the completion of multiple business functions.
OTN protection from the above features can be seen, although the OTN, SDH ring protection relative to the ring protection is concerned, made some changes, but essentially no difference, but considering that a comprehensive and more abstract.

Requirements of the APS protocol OTN
(1) 50 m s switching time requirements of the ring structure and status with the following: Number of nodes on the ring doe s not exceed 31;
The ring length of not more than 1200 km;
(2) ring protection capacity is shared not lead to the occurrence of false connections. However, the SDH m ultiplex section shared protection ring and the SONET Line protection ring using the APS protocol based on bit stream to complete the switching of the exper ience, to achieve the
50ms switchover is challenging. If you are using a relatively simple addition of the A PS protocol
based on bit stream to achieve 50m s sw itching time requirements from the protocol should be designed at all level s of the following: There is no additional traffic, so ring switching can be divide d into two main Steps to complete, that is, when demand information distributed to the ring, the establishment of the node to the end of the bridge. Waves propagating in the fiber, about to be 5 nanoseconds per meter, so 1200km long one-way ring comm unication needs 6 ms time, two-way switching occurs w hen the propagation time of 12ms is required.
SDH / SONET A PS agreement of only three in a row received the same bytes K1 and K2 bytes be
treated as valid. To 125μs cycle frame de sign, which requires time to take 375μs. Consider a buffer of time, so that each node se nd and receive A PS news at least 0.5ms delay, 16 node s, in the case of two-way sw itching, which receive a total time of 16m s.
The remaining 22ms switching time to the near failure of the switching node to complete the
action. G.709 use d by APS and SDH / SONET is different for different TCM, which uses a single multi-frame algorithm to distinguish APS message is valid, for 2.5 Gbit / s rate signal, the worst case, the agreement As long as the receiving time 392μs, the higher the rate of the signal, but also shorten the time of the relative (OTN different speed grades, fixed frame length, which SDH/SONET different). Although not a physical layer of the “laws” restrict the development of new agreements, to change the existing signaling mec hanisms to meet the requirements of 50m s, but the development costs and complexity encourage people to still choose a relatively simple bit-stream based APS protocol. Because in terms of protection for ODUk, after all, we already have a frame of APS based on the use of overhead bytes

There are three types of APS news
(1) the state requests
Wait to restore (WTR): This is a switching of the state has maintained that the state can only be the end of the timer, which can not be any end of the current command or conditions.
(2) switching request
As is usually used to indicate command (forced or manual switching) or defect (signal failure or signal degradation), and work need to be switched to the protection of the signal channel. The request because the switching or ring switchi ng segments generated in the distal or proximal.
(3) status messages, including:
Information on status messa ges. Used to inform the proximal distal node switching
Information or, conversely, it is usually not request information;
Active messages. Protection channel is used to indicate the robustness of the transmission of these messages will affect the switching decision, for example, when the proximal protection fails, the use of distal protection switching.
The APS protocol OTN content
OTN frame structure used for the APS ODUk four bytes, shown in Figure . Since the A PS channe ls for different leve ls of TCM, or a different structure a nd signaling, APS protocol in accordance with

Table1 the value o fmulti-frame indicator is designed to re-frame structure.

Request S Res Requestedchannel Bridgedchannel Statuschannel

APS signaling format

MFAS APS/PCC
xxxxx000 ODUkchannel
xxxxx001 TCM1
xxxxx010 TCM2
xxxxx011 TCM3
xxxxx100 TCM4
xxxxx101 TCM5
xxxxx110 TCM6

Allows the use of different monitor inglevel so fthere spective frame structure o fthe complex

APS

First four bits used to indicate the type of APS request

Request Meaning
1111 LockoutProtection*
1110 SignalFailProtection*
1101 ForcedSwitch
1100 SignalFail
1011 SignalDegradeProtection*
1010 SignalDegrade
0110 ManualSwitch
0101 WaittoRestoreProtection*
0100 WaittoRestore
0011 Exercise*
0010 ReverseRequest
0000 NoRequest

APS request type

 

APS bytes in the other domains of meaning:

S: 1,switching request me ssage request or status, 0 state information; N: 1, proximal request / status messages, 0 means

Distal request (in addition to the dual node interconnection of circum stances, can request and
Deduce the meaning of S-bit)
Requested Channel: request to switch to the protection c hannel, said channe l number; Bridged Channel: bridging the protection channe l, said the actual cha nnel number;
Status Channel: only for status messages, indicating that the request does not directly affect the channel is involved in the message or the bridge to the channel number.
Huawei ODUk SPRING features

The ODUk SPRing protection applies to ring networks and thus requires the support of a network protection protocol. The protection adopts dual-ended switching m ode, name ly, whe n the receive end of the working channel fails, both the receive and transmit ends of the w orking channel are switched to the protection cha nnel s.
The node configured with the ODUk SPRing protection is classified into the general node and the management node

 

general node and the management node

 

If all protection cha nnel s of the ring network are passthrough cross-connections, their performance cannot be accurately detected. In this case, t he protection fails. Hence, a management node must be specified. After the management node is specified, the system automatically deletes the bidirectional cross-connection between the east and west protection channels of the protection group that corresponds to the management node. In the mean time, the system tri-fed one of the add/drop ser vices at the node. One of the three channels of trisected services is fed to the normal w orking channel; the other two of the three channe ls of trisected services are respectivel y broadcasted to the west and east protection channel s. As a result, the protection channe ls also bear services
The management node is considered as an example to describe the realization of the SPRing protection
Because the protection ring status should detect by TU (only TU can process pretection level’s
ODUk PM) so here have to set the management node.
• In the transmit direction: The c lient ser vices to be protected are input through the tributary board, cross -connected to the east working line board, and then dually fed to the east and west protection line boards. In this way, the working signals and protection signals are separated. After that, the working signals and protection signals are respectively transmitted over the w orking and protect ion c hannel s.

• In the receive direction, whe n the operating is normal, only the cross-connection of the working channel is enable d; that of the protection c hannel is disabled. Whe n the working channel is faulty, disconnect the cross-connection of the w orking c hannel at the receive end. Hence, the cross -connection of the protection channe l that corresponds to the west line board is available, and the service s are operating in the protection channel.

• When the working channel is restored, because the protection is revertive, the service signals are switched back the cross-c onnection that corresponds to the originally specifie d line board

Conclusion
As can be seen from the above analysis, OTN ring network protection mechanisms of Inherited SDH ring protection mechanism in the most characteristic elements, such as 50 ms Protection switching time. Meanwhile, according to the optical transmission network for future special Point, made important improvements, such as no longer distinguish between the 2 / 4 fiber; A PS signaling The m ulti-frame structure to 4 Byte pass, failure to use the channel number and positioning Not the node number. Want to see is, in order to run cross domain network operators to effectively Protection, OTN is defined up to six, and can be cascaded, nested, cross-TCM, stack monitoring, and 3 R regeneration point s in the section provide d between the monitoring of the word Day SM, between the user network interface to provide end to end connection monitoring byte PM, etc., OTN of this structure on the one hand significantly improve its survivability, It also increased the difficulty of its protection mechanisms.

 

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