Cisco Catalyst PON Series White Paper

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Cisco Catalyst PON Series

White paper

Cisco public


Contents

Introduction 3

Cisco Catalyst PON Series 4

Cisco Catalyst PON OLTs 4

Cisco Catalyst PON ONTs 5

Cisco Catalyst PON Manager 6

Optical Distribution Network (ODN) 7

Passive optical splitter 7

Splitting level design 7

Centralized split design 8

Distributed split (cascaded) design 8

Splitting ratio 9

Cisco Catalyst PON optics 10

Optical power loss 10

Cisco Catalyst PON Type B protection 12

Packet walks 13

Summary 15


Introduction

A passive optical network (PON) is a point-to-multipoint architecture that uses a single strand of single-mode

fiber and unpowered optical splitters to deliver voice, video, and data to several users (or devices). PONs use

passive splitters in the optical distribution network (ODN), enabling one single feeding fiber from the provider’s

central location to serve multiple homes and offices.

The Cisco® Catalyst® PON Series offers a competitive network solution with high performance, simple

management, and easy maintenance. Moreover, the Catalyst PON Series can help organizations simplify

complexity, optimize IT, and reduce operational costs by providing 2.5 Gbps of downstream bandwidth and

1.25 Gbps of upstream bandwidth.

The three main network components of the Cisco Catalyst PON Series are the Optical Line Terminal (OLT), the

passive optical splitter, and the Optical Network Terminal (ONT). The OLT can be used in the core layer, and the

ONT can be used in the access layer.

Figure 1.

Active Ethernet network vs. passive optical network

By using passive optical splitters, the Cisco Catalyst PON Series can substitute for the distribution switching

layer, present in traditional active Ethernet architectures, and reduce the amount of infrastructure required.

Each fiber optic cable can be shared by up to 128 ONTs, minimizing the amount of fiber cabling required.

Although multiple users share the same PON, the Cisco Catalyst PON Series provides Quality-of-Service (QoS)

mechanisms that help ensure that the traffic is correctly prioritized.


Cisco Catalyst PON Series

Figure 2.

Cisco Catalyst PON infrastructure

Cisco Catalyst PON OLTs

The Cisco Catalyst PON OLT is a centralized 1-Rack-Unit (1RU) access point for the entire LAN, capable of

serving many users and devices. It has market-leading capacity: up to 108 Gbps switching capacity, up to 95

Mpps forwarding capacity, and a maximum reach of up to 20 km (12.5 miles) to ONTs. Two Cisco Catalyst PON

OLT models are currently available, one with 8 ports (CGP-OLT-8T) and one with 16 ports (CGP-OLT-16T), to

support all types of deployments: hospitality, healthcare, public sector, and commercial buildings.

The Cisco Catalyst PON OLT enables organizations to achieve:

● Lower operational costs (savings in power, floor space, and centralized management)

● Long-term value with a fixed architecture over generations of PONs

● Secure communication with a fiber-based infrastructure

Table 1. Cisco Catalyst PON OLTs

CGP-OLT-8T CGP-OLT-16T

OLT model

PON ports 8 Gigabit-capable PON (GPON) ports 16 GPON ports

Ethernet uplink ports 4x 1G combo ports

(Copper/SFP optical) and 2x 10G SFP+ ports

4 x 1G combo ports

(Copper/SFP optical) and 2 x 10G SFP+ ports

Optical connectivity SC/APC SC/APC

Endpoints 1024 2056


Cisco Catalyst PON ONTs

Cisco Catalyst PON ONTs are the user access points controlled by the OLT and can deliver superior services

with Gigabit bandwidth to every user. The ONTs can provide access options to connect to high-speed internet,

Wi-Fi, video, POTS, CCTV, and CATV.

There are five ONT models, providing a wide range of 1G fanless deployment options, including data, POTS,

CATV, and Wi-Fi. All are managed by the Cisco Catalyst PON Manager.

● 1x 1G PoE+ (CGP-ONT-1P)*

● 4x 1G PoE+ (CGP-ONT-4P)

● 4x 1G PoE+, 2x POTS (CGP-ONT-4PV)

● 4x 1G PoE+, 2x POTS, 1x CATV (CGP-ONT-4PVC)

● 4x 1G, 2x POTS, 1x CATV, 2.4 GHz/5 GHz Wi-Fi (CGP-ONT-4TVCW)*

* Available Q1 2021

Table 2. Cisco Catalyst PON ONTs

Desktop ONT model PON POTS ports CATV ports

CGP-ONT-1P

1 PoE+ – –

CGP-ONT-4P

4 PoE+ – –

CGP-ONT-4PV

4 PoE+ 2 (RJ11) –

CGP-ONT-4PVC

4 PoE+ 2 (RJ11) 1 coax

Wireless ONT PON ports POTS ports CATV ports

CGP-ONT-4TVCW

4 2 (RJ11) 1 coax


Cisco Catalyst PON Manager

Cisco Catalyst PON Manager is used for remote centralized network management of Cisco Catalyst PON OLT

and ONT devices. The integrated network management system includes a fully graphical interface that is easy

to operate and use.

Figure 3.

Cisco Catalyst PON Manager

Cisco Catalyst PON Manager uses a client/server structure. That is, a server connects with several clients in the

Cisco Catalyst PON Manager. The PON Manager server provides network nodes (OLT or ONT) with data

processing and storage functions. Users can operate and maintain network nodes via the PON Manager client.

The following figure shows the Cisco Catalyst PON Manager hardware architecture.


Figure 4.

Cisco Catalyst PON Manager architecture

For more information on Cisco Catalyst PON Manager, please visit:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst_pon/overview_guide/b-cisco-catalyst-pon-

manager-overview-guide/overview_guide.html

Optical Distribution Network (ODN)

The ODN is located between the OLT and ONTs, connecting one OLT and multiple ONTs to provide

bidirectional optical signal transmission. The ODN is composed of passive optical components, such as optical

fiber cables and passive optical splitters.

Figure 5.

ODN overview

Passive optical splitter

The passive optical splitter is a major component of the PON that splits the fiber and its signal. A passive optical

splitter does not require power input or climate control to operate.

A signal from the OLT is sent along the single-strand fiber cable. When the signal reaches the passive optical

splitter, it is split into multiple outputs. The common split ratios are 1:2, 1:4, 1:8, 1:16, 1:32, and 1:64. Although

the Cisco Catalyst PON Series can support up to a 1:128 ratio, Cisco’s recommendation is to use only up to a

1:64 ratio.

Although the operation of the splitter is very simple, its splitting level and ratio designs need to be considered

when designing a PON network.

Splitting level design

The PON splitting may be achieved by centralized splitting (one level) or by cascaded splitting (two levels or

more).

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst_pon/overview_guide/b-cisco-catalyst-pon-manager-overview-guide/overview_guide.html

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst_pon/overview_guide/b-cisco-catalyst-pon-manager-overview-guide/overview_guide.html


Centralized split design

Centralized splitting uses a single-stage splitter in a central hub to provide flexibility in PON management. This

design requires more fiber cables from the splitter to the user locations, but it has the advantage of an easily

accessed testing point.

In a centralized design, the splitter is directly connected via a single fiber to an OLT in the central office. On the

other side of the splitter, 32 fibers are connected to 32 homes using ONTs if a 1:32 or 2:32 splitter is used.

Figure 6.

Centralized optical split design

Table 3. Centralized splitting advantages and disadvantages

Advantages Disadvantages

Better OLT utilization More distribution fiber

Future-ready and flexible PON design Higher CapEx

Easy monitoring and maintenance

Distributed split (cascaded) design

A distributed split (cascaded) design uses multiple splitters in a series to accomplish the overall desired split

ratio. For example, it would use a 1:4 splitter and 1:8 splitters as two splitting levels. This distributed design can

reduce the amount of fiber in the distribution network. However, this design generally has poorer OLT port

utilization, compared to a centralized split architecture.

In the scenario shown in the figure below, the OLT from the central office is connected to a 1:4 splitter. Each of

the four fibers leaving the stage 1 splitter is directed to a 1:8 stage 2 splitter. There will be total of 32 fibers

(4x8) reaching 32 locations.


Figure 7.

Distributed optical split design

Table 4. Distributed splitting advantages and disadvantages

Advantages Disadvantages

Lower CapEx More actives and more splitters

Less flexible network

Complex monitoring and maintenance

Splitting ratio

The most common optical splitter deployed in a PON is a splitter with a 1:N or 2:N splitting ratio, where N is the

number of output ports. Different splitting ratios will provide different network performance as well as a different

distance between OLT and ONT.

For the highest-capacity bandwidth, connecting a few ONTs to a single PON port could provide a 20-km (12.5-

mile) distance with the full bandwidth of the PON port. Each PON port can provide 2.488 Gbps downstream and

1.244 Gbps upstream.

For the highest capacity of users, a splitter with a 1:128 ratio connected to a PON port could provide 128

clients with equal bandwidth of about 19 Mbps download and 9 Mbps upload when the clients are all within a

range of 8 km (5 miles).


Cisco Catalyst PON optics

The Cisco Catalyst PON Series supports Class C+ optics to support the maximum acceptable optical power

loss. Class C+ optics can provide a longer reach of 20 km (12.5 miles) with most splitter ratios and can support

a maximum optical loss of -32 dB. Optical power loss of all the ONTs must be within this maximum loss range.

Table 5. PON optic classes

Optical module

OLT ONT Maximum system optical loss (dB)

Transmitted optical power (dbm)

Receiving sensitivity (dB)

Transmitted optical power (dbm)

Receiving sensitivity (dB)

Min Max Min Max Downstream Upstream

Class B+ 1.5 5 -28 0.5 5 -27 28 28

Class C+ 3 7 -32 0.5 5 -30 32 32

Optical power loss

Attenuation is the most important factor in designing a GPON. Knowledge of the following sources of

attenuation and calculation of the optical power level (dBm) is required in designing the PON.

● Upstream length loss (1310 nm): ~0.42 dB per km

● Downstream length loss (1490 nm): ~0.3 dB per km

● Splices loss: ~0.1 dB per splice

● Connectors loss: ~0.3 dB per connector

● Splitter loss: See the table below.

Table 6. Loss calculation per splitter type

Splitter type Loss value (dB)

1×2 3.9

1×4 7.2

1×8 10.5

1×16 13.8

1×32 17.1

1×64 20.1

1×128 23.7

Here is a sample calculation of upstream and downstream optical power loss based on the topology shown in

the figure below. The distance between OLT and ONT is 13 km. Total optical power loss needs to be less than

the maximum supported optical power loss.


Figure 8.

Sample topology for optical power loss calculation

Table 7. Downstream calculation

Source Loss of optical power calculation Loss in dB

Length 0.3 dB x 8 km + 0.3 dB x 5 km -3.9 dB

Splices 0.1 dB x 2 splices -0.2 dB

Connectors 0.3 dB x 4 connectors -1.2 dB

Splitter 17.1 dB for 1:32 splitter -17.1 dB

3 dB (reserve for margin ) -25.4 dB


Table 8. Upstream calculation

Source Loss of optical power calculation Loss in dB

Length 0.42 dB x 8 km + 0.4 2dB x 5 km -5.46 dB

Splices 0.1 dB x 2 splices -0.2 dB

Connectors 0.3 dB x 4 connectors -1.2 dB

Splitter 17.1 dB for 1:32 splitter -17.1 dB

3 dB (reserve for margin ) -26.96 dB

Both the upstream and downstream signals are within the acceptable range of maximum optical loss of 32 dB

with Class C+ optics.

Cisco Catalyst PON Type B protection

When a fault occurs on the Cisco Catalyst OLT port or fiber cable, services can be switched to the functional

optical fiber.

The following figure shows a GPON Type B protection network. The protection covers the active and standby

PON ports on the OLT, and the active and standby optical fibers.

Figure 9.

GPON Type B protection

If the optical fiber connected to the active port is broken or no upstream optical signals are received because

the active port has malfunctioned, the standby port can detect and will handle the traffic.


Packet walks

Downstream traffic

Figure 10.

PON downstream traffic

1. OLT sends Ethernet frames to the GPON service processing module within the OLT based on

configured mapping rules between upstream data ports and OLT uplink ports.

2. GPON service processing module then encapsulates the Ethernet frames into GPON Encapsulation

Method (GEM) Packet Data Units (PDUs) for downstream transmission using a PON port.

3. GPON Transmission Convergence (GTC) frames containing GEM PDUs are broadcast to all ONTs

connected to the PON port.

4. ONT filters the received data according to the GEM port ID contained in the GEM PDU header and

retains only the data belonging to the GEM ports of this ONT.

5. ONT decapsulates the data to Ethernet frames and sends them to end users using ONT data ports.


Upstream traffic

Figure 11.

PON upstream traffic

1. ONT sends Ethernet frames to GEM ports based on configured mapping rules between ONT data

ports and GEM ports.

2. GEM ports encapsulate the Ethernet frames into GEM PDUs and add these PDUs to transmission

container (T-CONT) queues based on mapping rules between GEM ports and T-CONT queues.

3. T-CONT queues use time slots for upstream transmission to send GEM PDUs to the OLT.

4. OLT receives the GEM PDUs and obtains Ethernet frames from them.

5. OLT sends Ethernet frames from a specified uplink port based on mapping rules between upstream

data ports and OLT uplink ports.


Summary

Catalyst PON Series switches are the industry’s all-optical solution with differentiated resiliency and progressive

architecture for cost-effective optical network access.

Cisco Catalyst PON OLT products are compact, high-density network aggregation devices, meeting the

requirements of ITU-T G.984 and relative GPON standards, with high access capacity, carrier-class reliability,

and powerful security functions.

Cisco Catalyst PON ONT products provide access for comprehensive services, including high-speed internet,

video, VoIP, CCTV, and CATV to subscribers in FTTx applications with powerful interoperability and stability.

Cisco Catalyst PON Series switches make refreshing your passive optical network easy. With enterprise-grade

features such as power and uplink redundancy, PoE+, and sensitivity to cost and ease of operations, the Cisco

Catalyst PON Series gives you what you need today with the confidence that your investment is protected with

future innovations to come.

Printed in USA C11-744796-00 03/21

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