Synchrounous Optical network

CHAPTER V

SYNCHROUNOUS OPTICAL NETWORK

5.1 INTRODUCTION

Fiber Span Layout Demand Distribution, Fiber Network User Service Survivability and Optical network Demand Bundling using Digital Signal 3 (DS3) forming are discussed in the previous chapters. In continuation to that the present chapter describes Synchronous Optical Network [SONET] which is an integrated approach of the above three.

Starting from the SONET Characteristics, Frank J.Effen Berger [19], discussed the survivability of SONET in hubbing architecture. However the case study considered only simple networks in which single period candidate network architecture was implemented and 20% throughput is obtained as shown Fig. 5.1 and table 5.1.

The present work determines SONET in Point-to-Point architecture. In this multi-period candidate network architecture is implemented. It also facilitates the parameters like the network distribution, restoration capacities and cumulative demand in an integrated approach.

5.2 SONET INTEGRATED APPROACH

The simulations in SONET comprises of Point-to-Point architecture with diverse protection and Ring Architecture. This type of architecture is very useful in the study of survivability in broadband services. This provides the implementation of multiperiod candidate survivable analysis, which facilitates the network component connectivity at all the Digital Signal Levels.

Further the SONET is extended to include multi network demands, which may be called Multiperiod Synchronous Optical Network Survivability (MSONS). This can be used to estimate the various parameters like link connections, node locations, corresponding signal level transformation and end-to-end multi year demands. It can also be extended further to calculate the automatic restoration facility and physically diverse routing regarding working and protection fiber.

SONET data rates are simple and capable to implement different survivable network architectures. Network survivability has become a part of SONET network requirements because high speed SONET system failure is not affordable.

Tradeoffs among different restoration architectures have naturally resulted in a hierarchical restoration model for service protection, which is depicted in Fig.5.2. It consists of ring/route DP, DCS, and mesh restoration parameters [37].

These parameters are implemented by using the SONET survivable architecture. It consists of Point-to-Point/Hubbing with APS (Automatic Protection Switching), SHR's (Self-Healing Rings) and reconfigurable DCS (Digital Cross connectivity System) mesh network architectures.

5.2.1 NETWORK GROWTH ASSUMPTIONS

1. Use of point-to-point systems to carry point-to-point demands until the Hubbing/DP and/or ring architecture become economical to carry remaining demands.

2. The mixed use of Hubbing/DP and ring architectures carry the remaining demands.

3. If the Hubbing/DP structure is used as startup architecture, it is used throughout the entire planning period.

4. If the SHR architecture is used as the startup architecture, it is used until its capacity is exhausted. The remaining demand is carried by either another SHR or Hubbing/DP architecture until further capacity is exhausted or the end of the planning period is reached.

These assumptions result in the accommodated growth demand and are shown in the Fig.5.3. The planning model requires selecting an architecture base year one and the appropriating growth strategies in the N-th year [42]. Thus, the total network over a planning period is minimized. Fig.5.4 depicts a structured view of the multiplex performance design model for selecting appropriate survivable network architectures and the planning period.

The model is further described, based on the following additional assumptions.

1. The topology allows the ring to be built.

2. Incremental demand on any fiber span in any year is not greater than the maximum line rate considered in the Hubbing/DP option.

3. Similarly, the incremental demand on any ring in any year is not greater than the maximum line rate considered in the ring option.

The total demand can be estimated by SONET Planning Period model. In this total demand between each pair of buildings increases each year, thus, the considered demand is the incremental demand. The model's objective is to minimize the economy impact of network development over N years, while ensuring that sufficient fibers and equipment are installed in the network to accommodate the growth demand. Next, the high speed SHR architecture is considered, and the resulting solution is compared with the one obtained by using the Hubbing/DP architecture. To maintain 100 percent survivability, 1:1 /DP architecture is assumed.

5.2.2 MULTI-PERIOD ARCHITECTURAL SELECTION and CAPACITY

ASSIGNMENT MODEL

The design of SONET Multi-period capacity calculation determines the demands, optical carriers, Routes and protection schemes which are described for different fiber network planning periods as shown in Fig.5.5.

The Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) are a set of related standards for synchronous data transmission over fiber optic networks. They are often used for framing and synchronization at the physical layer as shown in the flow chart in the Fig.5.6 and the program is given in Appendix - D. SONET/SDH and can be used in an ATM or non-ATM environment. Packet over SONET/SDH (POS) maps IP datagram's into the SONET frame payload using Point-to-Point Protocol (PPP). In the ATM environment, connections to SONET/SDH lines can be via multi-mode.

The candidate survivable network architecture considered here includes the ring architecture, the fiber hub bed architecture with DP, and the point-to-point architecture with DP.

This model evaluates the best combination of available architectures and associated capacities that can be deployed in a survivable manner over a planning period (for example, five years). As discussed earlier, the major limitation of deploying the SHRs for the interoffice network application is the capacity exhaust problem. Two types of planning methods are used to address this problem: worst case planning and multi-period transition planning. Worst case planning considers the sum of the given multi-year demand and plans it as a single-year case. In this type of planning, ring exhaust is not a concern because the network can always be engineered to meet the demand requirement.

However, this method is usually more expensive than the multi-period transition planning model because the latter method can design the network based on a transition path. For example, the network for using multiple SHRs could be higher than the path restoration of using the traditional 1:1/DP approach in a growth scenario. Thus, accounting for growth is crucial for SONET network planning when the SHRs architectures are used.

Therefore, a multi-year planning model is used to ensure that the right architecture is chosen at the right time in the candidate area to minimize the total network over a planning period. Given a candidate ring area for analysis, the model is divided into three sub modules. The first part gives a method for determining how the point-to-point systems are to be built. The second part is used to solve the fiber optic network capacity expansion problem through Hubbing/DP architecture over a planning period. The third part describes an algorithm for solving the capacity expansion problem using a combination of SHR and Hubbing/DP architectures [43].

The algorithm first creates a root and then tries the Hubbing/DP option and the three line rate options for rings. The capacity is assumed to be made available at the beginning of the period. If the algorithm starts from the DP option, it uses the same option to carry demands to the last planning year using the capacity expansion design algorithm.

For each ring option, the system carries the demand to the period in which the capacity is exhausted. For example, the OC-48 ring capacity will be exhausted after the second year. Thus, a child node is created from the root for the OC-48 ring at the second year. An interval period is created for each line rate that starts from the current period and continues to the year that begins the period in which the capacity is exhausted. For example, the initial interval period for the OC-48 system is between the first and second years. The algorithm computes the survivability for each selected line rate option over the interval period obtained and inserts the demands into the queue Q.
The node is computed which is based on the demand-routing algorithm and the model used. The node computations in Q are then sorted in increasing order, and the lowest node is placed in the beginning of Q. The program stops when the minimum-performance node is at the end of the planning period [47]. The capacity arrangements for the Hubbing/DP spans installed in the beginning of the second year are obtained by using the capacity expansion algorithm. In most practical applications i.e., a 10-year planning period is chosen with five options. They are (i)DP option with OC-3, OC-12, OC-24, (ii) OC-48; (iii) four ring options, (iv)OC-3 ring, OC-12 ring, OC-24 ring, and (v) OC-48 ring.

5.3 NUMERICAL RESULTS

SONET multiperiod capacity expansion algorithm is implemented by using input parameters such as connectivity pattern, DS3 traffic requirement demands in table 5.2. And the output parameters such as incremental demand connectivities are as shown in table 5.3 respectively. The demands assumption is at random.

In the previous work Frank J.Effen Berger et.al. Group worked the the SONET single period survivability implementation in 1 X 5 node connectivity only in Hubbing Span Architecture and obtained 20% throughput.

Thus throughput performance of planning period model of SONET multi-period capacity expansion algorithm achieved is 87% as compared with the earlier work.

5.4 DISCUSSIONS

The SONET Hubbing Network Architecture was proposed by Frank J.Effen Berger for a single user point & single period demand. It established the node-to-node configuration for a simple network. The survivability of the network in a given Hubbing span Architecture cannot be used from a multi user point of view.

A new Architecture proposed, i.e. MultiPeriod Synchronous Optical Network Survivability (MSONS) overcomes the limitations of Hubbing Span Architecture. This architecture assures satisfactory survivability parameter estimations for multi-node-to-node connectivity and multi-period planning of complex networks. The MSONS algorithm mainly deals with the automatic restoration in the event of single facility, and also physically diverse routing of working and protection fiber. These networks provide the flexibility to add nodes and allow the add/drop of DS3s/DS1s and future broadband services.

Survivability parameters of SONET in the Physical Layer Module have been analyzed in this chapter, and the procedure is extended to compute the Logical Layer parameters of the optical networks described in the next chapter

Table 5.1 Physical Layer Network

Span No.

Source, Destination

Working Path

Protection Path

1

(1,2)

1-2

1-3-2

2

(1,3)

1-3

1-4-3

3

(1,4)

1-4

1-3-4

Table 5.2 INPUT TABLE FOR SONET MULTI-PERIOD CAPACITY

EXPANSION

S.NO.

NETWORK CONNECTIVITY

DS3 TRAFFIC

CAPACITY

1

1-2, 1-3

40,70

250

2

2-1

40

250

3

3-1,3-4,3-5,3-6,3-7

70,40,40,56,7

100 170 150 180 100

4

4-3

40

170

5

5-3,5-8,5-9,5-10,5-11

40,40,40,56,98

150 260 200 220 255

6

6-3

56

180

7

7-3

7

100

8

8-5

40

260

9

9-5

40

200

10

10-5

56

220

11

11-5

98

255

Table 5.3 OUTPUT TABLE SONET MULTI-PERIOD CAPACITY EXPANSION

Sorted List of Demands in Ascending Order:

100

100

100

100

100

150

150

170

170

180

200

200

200

220

220

250

250

255

255

260

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