55 

 

CHAPTER 5

BANDWIDTH UTILIZATION AND PACKET LOSS RATE

ANALYSIS IN NEXT GENERATION SONET METRO SYSTEMS 

5.1. INTRODUCTION

This chapter provides a systematic approach for determining the best of three

emerging network technologies, such as next-generation SONET/SDH, RPR (Resilient

Packet Rings) and OBS (Optical burst switching ). In this chapter, we compared the

performance of above said technologies, such as the number of required wavelengths,

bandwidth utilization, distribution of delay variation and packet loss rate.

5.1.1. Ethernet over SONET

To routine the SONET/SDH transport infrastructure, many techniques are

proposed including the GFP, VC and the LCAS. VCAT and LCAS provide the

improvement in bandwidth efficiently for data transport. Ethernet over SONET/SDH

combines with GFP and allow the Service Provider to operate its SONET/SDH.

A number of proprietary encapsulation methods has been used to transport

IP/Ethernet over SONET/SDH, before EoS apparatus vendors. ATM is a very efficient

switching and multiplexing technology. ATM requires speed with SONET/SDH but the

ATM “cell tax” of 5 byte header and it has a heavy software burden.

The multiple ports are encapsulated over ML - PPP links when IP traffic derives

to an Ethernet port is encapsulated over a PPP link. The PPP traffic method is used to

transport over the SONET/SDH payload by using an HDLC framing and the other data

services over SONET VCAT and LCAS [141 ─144].

56 

 

In this chapter, we used a two - fiber ring network model which is the most familiar

architecture in MAN to compare the data transmission ability. The analytical and

numerical modeling techniques are applied to compare the network performance for all

technologies in terms of delay and delay variation, and the number of required

wavelengths and to investigate the impact of traffic demands.

5.2. SCHEMATIC OF NETWORK MODEL FOR COMPARISON

As the ring is the familiar topology in MAN, we have used a two-fiber ring

network as the topology model in our research, which has been shown in Fig. 5.1.

There are four nodes (RN) in the ring and the two fibers between each two

adjacent RNs can make the ring either unidirectional or bidirectional. The number of

wavelengths in the fibers is undetermined, and it will be decided by the requirement of

each technology for the same traffic model. The data transfer rate of each wavelength is

2.5 Gbit/s.

Fig. 5.1 The Different Network Model

57 

 

The distance from each RN to its adjacent node is same as 50 km. That is to say,

according to the transmission speed of the optical signals in fibers which is only 5 µs/km,

the transmission delay from one RN to its adjacent node will be 250 µs. Also, there are 3

independent Packet Generator and Receivers (PGR) coupled to each RN. PGR is used to

generate the various background traffics. It is also used to constant Bit Rate (CBR) flow,

Dynamic Bit Rate (DBR) flow and Self-similar flow to the other three RNs as

illuminated in Fig. 5.1.

Network strategy is based on the requirement of the background traffic. While, as

the self-similar traffic could not be measured accurately, we design the network

according to the max average traffic of CBR flow. The detailed definition is: the max

average bit rate of the traffic generated by each PGR could be 2.5 Gbit/s.

The number of RNs in the ring 4

The number of fibers in the ring 2

The distance between two adjacent RNs and the

transmission delay in fibers

50 km/250 us

The number of PGRs for each RN 1

The max average traffic from one PGR to another 2.5 Gbit/s

The max average input traffic of one RN 7.5 gbit/s

The max average input traffic of the whole network 30 Gbit/s

Table 5.1. Parameters Used in Networks

Therefore, the max average input bit rate of one RN is 7.5 Gbit/s. and the one of the

whole network is 30 Gbit/s. In summary, all the parameters mentioned above have been

displayed in Table 5.1.

58 

 

5.3. SONET/SDH NETWORK

Next-generation SONET/SDH has made a countless development on data transfer

compared with the traditional SONET/SDH. As there are two protection-switched modes

(1+1 protection mode and 1:1 protection mode) for Private protection in SONET/SDH

network, we have designed two network models to simulate these two different modes.

The distribution of wavelengths has been shown in Fig. 5.2.

Fig. 5.2. Distribution of time - Slot in NG - SONET/SDH

As is shown in Fig. 5.2, for the 1+1 protection mode, to meet the requirements of the

traffic from the upper layer, there should be a private wavelength between each two

nodes. While, on account of the scheme of bidirectional transmitting and selective

59 

 

receiving, both ringlets would carry the traffic synchronously. Therefore, 12 wavelengths

must be presented at each ringlet. On the contrary, for the 1:1 protection mode, as the

wavelengths could be shared as is shown in Fig.5. 2, we will only use 6 wavelengths to

carry these traffics on one ringlet.

When the packets arrive at a RN, they would queue up there waiting to be transmitted

by SONET/SDH frames, which are transmitted by the RN periodically every other 125

µs. Since the frames would go through O/E and E/O conversions and add and drop the

packets, the whole delay must be longer than 125 µs which is only caused by E/O

conversation. The reading and writing processing delay is based on the clock of the

equipment, and based on the investigation of the processing ability of the existing

technologies, the extra 125 µs delay for processing should be appropriate.

5.4. RPR NETWORK

For RPR network, to match the requirements we defined before, only two wavelengths

in each fiber have already been enough. One possible distribution of bandwidth has been

shown in fig.5.3.

60 

 

Fig. 5.3 Distribution of Bandwidth

As Fig. 5.3 shows, spatial reuse makes RPR network more efficient, which only

use total four wavelengths to carry the same traffic. As the node feeds the ring with the

client traffic and the traffic that it has to forward from upstream nodes to downstream

nodes, two approaches are presented to schedule these different traffic streams: a “store-

and-forward” approach and a “cut - through” approach [143].

In addition, one issue should be illustrated is the processing delay of a RPR node.

Since RPR is known as a Layer 2 protocol, and in our comparison, we build the RPR

network on the SONET/SDH ring, that is, the delay at the RN will include not only the

time of O/E/O conversions which will take 125 µs, but also the time of the processing by

Lay 2. Therefore, the extra 250 µs for the processing delay should be appropriate.

5.5. OBS RING NETWORK

The fixed and tunable semiconductor lasers, tunable optical filters, fixed and

tunable receivers, wavelength conversion devices, wavelength division multiplexers and

61 

 

demultiplexers, and add drop routing elements are the hardware components for multi

wavelength communication system. The four basic techniques has been used for the

implementation of multi wavelength networks. These are the following. Fixed

transmitters and fixed receivers (FTFR), tunable transmitters and fixed receivers (TTFR),

fixed transmitters and tunable receivers (FTTR), and tunable transmitters and tunable

receivers (TTTR) are. The number of wavelength channels available to be inserted in the

fiber amplifier's gain is determined by the window Laser wavelength line width and

wavelength channel separation. With each channel corresponding to a CDMA code, an

OCDMA network can be viewed as a multiple - channel system. Each OCDMA node is

furnished with a transceiver for data transmission and detection. The encodes or decodes

messages are used with the right code. Both fixed and tunable semiconductor lasers or

laser arrays are critical components for the multi wavelength networks. Based on whether

the nodal transceiver is tunable or not, OCDMA nodes can be classified into four

categories:

a. FTFR: fixed transmitter and fixed receiver

b. TTFR: tunable transmitter and fixed receiver

c. FTTR: Fixed transmitter and tunable receiver

d. TTTR: tunable transmitter and tunable receiver

For OBS ring network, some new protocols have already been presented, such as

Token Access protocol [145], Dest – Resv - Free protocol [146], advanced Token Access

protocol [147] and so on. For all these protocols, the one which is based on token seems

to be able to get better performances [145]. Therefore, two mode of OBS ring based on

token have been considered in our comparison, one is Fixed Transmitter and Tunable

Receiver (FTTR) mode based on the ODD (Only Destination Delay) [145] protocol and

the another is Tunable Transmitter and Fixed Receiver (TTFR) mode based on the OSD

(Only Source Delay) protocol.

62 

 

For both FTTR and TTFR models, if we want to transmit the traffic as we defined

before, three transmitters and three receivers which have the data transmitting or

receiving rate of 2.5 should be designed on each RN. Therefore, as one of the transmitter

and the receiver would be fixed to the local ring node in these two protocols, at least 13

wavelengths should be designed on the ring, one for control channel which would

transfer tokens and control packets, the others for the data transfer. Hence, as the network

model has two fibers and the token ring is unidirectional, we design each fiber with 7

wavelengths including one control channel and six data channel. Moreover, based on that

design, we can use the control channel in one fiber transfer tokens, and the one in the

other fiber transfer the headers of each burst.

In addition, we have designed another bidirectional OBS ring based on the scheme of

wavelength grouping [148], and we have named it WG - OBS ring. The detailed structure

of the WG - OBS node has been shown in Fig. 5.4.

Fig. 5.4. The Schematic of WG - OBS Ring Node

63 

 

In Fig 5.4, we can see that the ring totally needs 6 wavelengths, two for control

channel of each direction, and four for data channels. When the packets from PRGs arrive

at the RN, it will be queue up there until the max assembly time up or the max burst

length reached. The routing scheme adopts OSPF protocol, which will first choose the

ringlet for transmission. Then, for the wavelength reservation, according to the

wavelength grouping, the RN will try to reserve the corresponding wavelength at first,

and reserve the other one if the first try is failed. Moreover, if neither of the wavelengths

is available, it will delay the transmission of the burst and only use the corresponding

wavelength until it is available.

Offset time

Min burst Max burst Max assembly

length (bits) length (bits) time (s)

Token OBS

FTTR 10 µs 512 U -

Token OBS

TTFR 10 µs 512 U -

WG-OBS n*10 µs 512 500000 0.0005

Table 5.2 Predefined Parameters of the OBS Network Mode

64 

 

For all the modes of OBS ring network, there are several parameters must be discussed

before hand, such as the offset time, the max and min burst size, the max assembly time

and so on. All of them have been shown in Table 5.2.

Number of

data

Queue

Network

mode Direction

Processing

delay Buffer

wavelengths

size (MB)

NG-

1+1

mode 24 Bidirectional n*125µs 64

SONET/

SDH

1:1

mode 12 Bidirectional n*125µs 64

RPR

CT 4 Bidirectional n*250µs 64

SF 4 Bidirectional n*250µs 64

FTTR 12 unidirectional 10µs 64

OBS TTFR 12 unidirectional 10µs 64

WG 4 Bidirectional n*10µs 64

Table 5.3 summary of the predefined parameters for each network mode

65 

 

In Table 5.2, as the network modes of FTTR and TTFR don’t need wavelength

conversations, the offset time of them are only used to the tuning delay of the transmitter

or receiver. Therefore, 10 µs would be enough according to [149]. The definition of the

max burst length and the max assembly time for WG-OBS are based on a great deal of

simulation with the traffic we defined before, and this parameters could make the packet

loss rate of this network so low that it is only 0.2% even at the condition of 90% load

with the dynamic traffic (which has been defined at the following section) in the whole

network. And the max burst length for token OBS is according to the discussion in [145].

In summary, all the parameters of these 7 network modes we defined before have been

shown in Table 5.3.

5.6. NUMERICAL SIMULATION FOR BANDWIDTH UTILIZATION

Simple quantative methodologies have been proposed to define the width

requirements in unidirectional and bidirectional. the total traffic on that ring is given by

the following formula, for a unidirectional ring having a uniform traffic demand between

nodes

[q * (q - 1)/2] *D

Here q is the number of nodes. The traffic demand between the nodes is D. The same

equations are used for the bidirectional rings. In a bidirectional ring with uniform traffic

demand the capacity required for each span can be shown to be

[(q * q) - 1)/4] * D rings with odd number of nodes

[(q*q)/4] *D + q/2 rings with even number of nodes and an odd amount of uniform

traffic

[(q * q)/4] * D rings with even number of nodes and an even amount of uniform traffic

66 

 

Fig.5.5. Applications Configuration

Fig.5. 6. Database Access Table

67 

 

Fig.5.7. Telnet Session Table

Fig.5.8. Profiles Configuration

68 

 

Fig.5.9. SONET DCC Network

Two dissimilar types of traffics dynamic traffic and the self-similar traffic are studied

in detail. The traffic through a fixed uniform - distribution packet length from 512 bits to

12144 bits is so called dynamic traffic. A variably exponential-distributed packet inter-

arrival time with mean from 2.61µs to 25.5µs is called self-similar traffic. The numerical

simulation of the bandwidth utilization and the average Edge – to - Edge delay from

RN_A to RN_C of each network model have been shown in Fig. 5.10 and Fig. 5.11

respectively. The self-similar traffic with a fixed uniform-distributed packet length from

512 bits to 12144 bits is reported. We also showed a variably pare to - distributed packet

inter-arrival time with different locations and shapes. The difference of the input rate with

the self-similar traffics at each node in our comparison has been shown in Fig. 5.12. The

distributions of the Edge – to - Edge delay from RN_A to RN_C and the packet loss rate

for each network model with the self-similar traffics have been shown in Fig. 5.13 and

Fig. 5.14 respectively.

69 

 

Fig.5.10. Bandwidth Utilization for the Dynamic Traffic

Fig.5.11. Average Delay for the Dynamic Traffic

70 

 

Fig. 5.12. Distribution of the Input Rate

Fig. 5.13. Distribution of the ETE Delay from RN_A to RN_C

71 

 

Fig. 5.14. Distribution of Packet Loss Rate With Self-Similar Traffic

From Fig. 5.10, we revealed that with the same traffic, WG - OBS network can get the

maximum bandwidth utilization and some tools like NG - SONET/SDH and token - OBS

with FTTR and TTFR could not match 50 percent of bandwidth utilization even when the

traffic load is 100 %.

Delay variation control is essential to ensure proper transport of TDM services

over an RPR ring. Control can be achieved by synchronizing the nodes on the RPR ring

by a common timing source as shown in fig.5.10. Fig. 5.2 showed some wavelengths in

NG - SONET/SDH, which is not useable in both 1+1 and 1:1 mode that makes the NG -

SONET/SDH less efficient.

There are two factors that make OBS’s bandwidth utilization small. Another is

FTTR mode, where the token cannot be released ahead of schedule as the TTFR mode.

none of RNs on the ring unable to send any data when the token is sending from one RN

to another, Hence, when the transmission time of the token is increasing, the bandwidth

utilization of FTTR mode also decreases.

72 

 

Network mode

NG-SONET/SDH RPR OBS

1+1 1:1 mode CT SF FTTR TTFR WG-

OBS

Average ET delay(s)

.04 .04 .02 .03 .05 .045 .015

Average Throughput (%)

95.4 96.6 98.56 98.22 100 100 97.13

Bandwidth Utilization (%)

37.34 74.11 85.56 86.12 36.6 37.8 70.15

Average packet Loss ratio (%)

2.8 2.8 0 0 0 0 6.8

Table 5.4. Simulation Results of Network Models With a Self-Similar Traffic

In Fig. 5.11, we showed that the WG - OBS network model has the marginal ETE

delay among all of them. For the NG - SONET/SDH case, it is designed to meet the

initial requirements of TDM services, the transmission delay is invariable. Both FTTR

and TTFR of OBS network model can transfer the data only when they held the TOKEN

and the transmission delay is much larger than the other technologies.

It is clear from Fig. 5.11 that the average Edge – to - Edge delay when the

network load is 20 % is less than that when the network load is 40 %. In Fig. 5.13 we

showed that the distribution of the Edge-to-Edge delays from RN_A to RN_C in each

network model with self-similar traffic. From it, we can see that in the NG -SONET/SDH

network models, the Edge – to - Edge delay of the most packets is nearly 60 ms. Fig.

5.13 shows that the average Edge – to - Edge delay of the WG - OBS network model is

the shortest among these three networks because the most packets have been delayed less

than 1ms.

73 

 

The distributions of packet loss rate in each network have been shown in Fig. 5.14. It is

also seen that all networks have some packet losses.

It is showed that NG - SONET delivers performance gains over traditional

SONET, it remains subservient to OBS-JET from a delay perspective and subservient to

WR-OBS from a loss perspective. This is because NG-SONET lacks a flexible and

dynamic bandwidth allocation scheme that can adapt to data traffic and as a result, edge

traffic incurs significant queueing delays, which lead to data loss.

5.7. DISCUSSIONS

For NG - SONET/SDH networks, the packet loss is mainly caused by the buffer

overflowing. In spite of the fact, for WG - OBS network, all the packet loss is caused by

the resource competitions. Moreover, the packet loss is based on a burst which consists of

many packets from the PRGs, the average packet loss rate is much higher than the other

networks [150].