physics

PAROLI

PAROLI is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PAROLI rather than just read about it. In short: PAROLI is a proprietary protocol used inside a multi-shelf Carrier Routing System from Cisco and stands for "parallel optical link." Paroli usage It is used to connect the line-cards in a so-called line-card chassis with the switching fabric in a switch-fabric chassis. As the traffic between these kinds of chassis is comparable with the data that flows over a backplane in a single-shelf system the required bandwidth…

Key takeaways

PAROLI belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PAROLI to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PAROLI from memory before moving on to harder problems.

Reference excerpt

PAROLI is a proprietary protocol used inside a multi-shelf Carrier Routing System from Cisco and stands for "parallel optical link."

Paroli usage It is used to connect the line-cards in a so-called line-card chassis with the switching fabric in a switch-fabric chassis. As the traffic between these kinds of chassis is comparable with the data that flows over a backplane in a single-shelf system the required bandwidth is very high and as is the need for reliability the shelves are interconnected using several fibre optic cables. As this protocol/feature is only used in multi-shelf Cisco-CRS systems you will only find it in IOS XR the special high performance version of Cisco IOS. There are basically two types of multi-shelf CRS systems:

single switch-fabric chassis and two line-card chassis two switch-fabric chassis and two line-card chassis four switch-fabric chassis and two line-card chassis The second option allows for the most fault-tolerant system in a CRS system: although a single shelf switch-fabric allows for redundancy on most levels (power. fans, management-cards, switch-cards etc.), a multi-shelf system based on two switch-fabric cards and (at least) two line-card chassis will continue to run even when one of the switch-fabric shelves is completely down. The four SCC/2 LCC also gives optimal availability and reliability without the loss of any throughput in case that a switch fabric module fails.

Distance between shelves Although the different shelves of a multi-shelf routing system will often be placed directly next to each other the PAROLI system allows for some distance between the shelves. If you want to place the different shelves in different rooms (e.g. in a system with two switch-fabris chassis have one of these chassis with 50% of the line-card chassis in dataroom 1 and the rest of the system in room 2 so that even when there is fire in one room the system will continue to work) it is possible as long as the length of the fibre-optic cables doesn't exceed 100 meters (328 feet). This will also allow you to move individual shelves of the system

Interconnecting shelves All traffic coming in into a multi-shelf CRS system will come in via an interface of a line card on a line-card shelf. The traffic is then sent to the switch-fabric shelf where the packet is processed and based on the destination (and of course system-configuration) the data is then sent to the outgoing interface on a line-card in a line-card shelf. The inter shelf communication links will therefore process the same kind of data-volumes as a backplane will normally carry in any single-shelf router. To allow these speeds via external fibre optic cabling Cisco designed special modules to make this possible. For a multi-shelf system you need three kind of connections between the line-card chassis and the switch-fabric chassis:

1:Management cabling 2:Controller cabling 3:Fabric cabling

Management cabling The management, alarm and external clock cabling is to allow management of the different shelves in the system. There are different type of management and clock signalling options. At least one management cabling is required and in general that will be the RP Ethernet connection.

Console cabling: initial configuration of the route processor (RP) of a shelf a multi-shelf system is done via the console port. The Ethernet management port will only become operational after configuring it with a terminal connected to a console port. Initial configuration of a shelf is done via the console port of a RP. The console port of the 22 (switch fabric shelf) or 2 port (line card shelf) SCGE card (see below) cannot be used to configure a new system. If you want all console ports of each RP connected you can use a terminal server AUX port: provides remote out of band access to the RP, similar to the console port, but is meant for remote access via a modem Management Ethernet port:This will be the main means of configuring and managing the system after initial configuration. In general the Ethernet ports of each RP in the system will be connected to an out-of-band Ethernet LAN so you keep control over the system even when the CSR wouldn't be able to route any data. If the CSR is installed at the same location as the configuration system you will probably use a dedicated Ethernet LAN. If the CSR is in a different location you will probably connect this (configuration) management (V)LAN with your NOC via a network connection that doesn't use the CRS to route the data (or you have a fall-back method such as ISDN access to the local management LAN) Alarm-Out cabling: You can use the external alarm-out circuits to raise alarms with the power modules External network clocking: If you use an external clock to synchronize your network components you can 'feed' this clock into all shelves.

Controller cabling For the controller cabling Cisco have created a special module for use in the fabric card chassis: the 22 port Shelf Controller Gigabit Ethernet module the SC-GE-22. And on the LCC's you use the two Ethernet interfaces provided with the two RP's in each chassis. In a single SFC with two LCC you will install both SC-GE-22 modules in the single SFC and each interface of the RP connect twice to the single SFC. In a 2 x 2 setup one GE port of each RP connects to one SFC and the other GE port connects to the other SFC. In a four SFC setup the first RP connects to SFC 1 and 3 while the other RP of that shelf connects to SFC 2 and 4. To allow for redundancy you will connect each ethernetport0 interface of each RP to a port on the first FC-FE-22 and each interface 1 to the second SC-FE-22. And to allow for communication between the two Sc-FE-22 modules (creating a mesh-network) you connect port 22 of each SC-FE-22 to each other. In a dual SFC each SC-FE-22 has a direct (full mesh) link to all 3 other SC-FE-22 and in a 4 SFC system you also create a full-mesh network between all FC-FE-22 modules. This cabling means that for a one SFC and two LCC you will need 8+1 Ethernet cables for network control, in a dual SFC you will need 14 cables (8xSC-LC + 6 LCC mesh) and in a 4 SFC-2 LCC you need 8 LC cables and 28 SFC-SFC mesh cables.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with PAROLI

Start with the simplest possible case. Write down what PAROLI claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PAROLI before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PAROLI ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PAROLI

In research: PAROLI appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PAROLI in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PAROLI is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cisco products, Fiber-optic communications, Link protocols, so understanding it makes those chapters shorter.
In everyday life: Look for PAROLI outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “PAROLI” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study PAROLI in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PAROLI means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PAROLI out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PAROLI in simple terms?

PAROLI is a proprietary protocol used inside a multi-shelf Carrier Routing System from Cisco and stands for "parallel optical link." Paroli usage It is used to connect the line-cards in a so-called line-card chassis with the switching fabric in a switch-fabric chassis. As the traffic between these…

Why does PAROLI matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PAROLI?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PAROLI.