Bits and Bytes of Computer Networking (Week 1)

the most common data link layer is?

the Ethernet

a physical layer device that allows for connections from many computers at once.

A hub

what is a preamble?

A preamble is 8 bytes or 64 bits long and can itself be split into two sections.

What charge will a standard copper network cable carry?

A standard copper network cable, once connected to devices on both ends, will carry a constant electrical charge.

Similarities and differences of Hubs and Switches

A switch is very similar to a hub since you can connect many devices to it so they can communicate. The difference is that while a hub is a layer one (physical layer device), a switch is a layer two (data link device).

are the most common form of networking cable. They're made up of multiple pairs of copper wires inside a plastic insulator.

Copper cables

The purpose of the most common type of router found in the office and home are?

The purpose of these routers is mainly just to take traffic originating from inside the home or office LAN and to forward it along to the ISP, (Internet service provider).

A router

- A router is a device that knows how to forward data between independent networks. - a router operates at layer 3, a network layer.

Explain CSMA/CD

CSMA/CD is used to determine when the communications channels are clear and when the device is free to transmit data.

what connects different devices to each other, allowing data to be transmitted over them.

Cables

Data packets at the Ethernet level are known as ? Explain

Ethernet frames. An Ethernet frame is a highly structured collection of information presented in a specific order.

Ethernet itself only reports on data integrity. It doesn't perform data recovery.

Ethernet itself only reports on data integrity. It doesn't perform data recovery.

What is the most common network layer protocol.

Internet Protocol (IP)

a process called simplex communication is.

a process called simplex communication is unidirectional. e.g a baby monitor

Just like a switch can inspect Ethernet data to determine where to send things, what can a router inspect?

a router can inspect IP data to determine where to send things.

Twisted pair network cables are terminated with a plug that takes the individual internal wires and exposes them. The most common plug is known as

an RJ45, or Registered Jack 45.

Why Cat 5e cables have mostly replaced those older Cat 5 cables

because their internals reduces crosstalk.

a data payload of an Ethernet frame.

- A payload in networking terms is the actual data being transported, which is everything that isn't a header. - The data payload of a traditional Ethernet frame can be anywhere from 46 to 1500 bytes long. - This contains all of the data from higher layers such as the IP, transport, and application layers that are actually being transmitted.

Diff btw Copper and Fiber Cables

- Copper uses electrical voltages, - fiber cables use pulses of light to represent the ones and zeros of the underlying data.

What is Crosstalk?

- Crosstalk is when an electrical pulse on one wire is accidentally detected on another wire. - The receiving end isn't able to understand the data causing a network error.

Pros and Cons of Fiber cables

- Fiber is even sometimes used specifically in environments where there's a lot of electromagnetic interference from outside sources because this can impact data being sent across copper wires. - Fiber cables can generally transport data quicker than copper cables can, - Fiber cables are much more expensive and fragile. - Fiber can also transport data over much longer distances than copper can without suffering potential data loss.

Following that data we have what's known as

- Frame Check Sequence. - This is a 4-byte or 32-bit number that represents a checksum value for the entire frame. - This checksum value is calculated by performing what's known as a cyclical redundancy check against the frame

In a hub device, there is a thing called "A collision domain" explain.

A collision domain, is a network segment where only one device can communicate at a time. If multiple systems try sending data at the same time, the electrical pulses sent across the cable can interfere with each other.

one device to transmit data to one other device and the transmission is always meant for just one receiving address. This is what's known as?

A unicast

How does CSMA/CD works?

If there's no data currently being transmitted on the network segment, a node will feel free to send data. If it turns out that two or more computers end up trying to send data at the same time, the computers detect this collision and stop sending data.

The differences in how the twisted pairs are arranged inside these cables can:

can drastically alter how quickly data can be sent across them and how resistant these signals are to outside interference.

Most network cables used today can be split into two categories namely?

copper and fiber.

Once traffic is at the ISP, a way more sophisticated type of router takes over called?

core routers

Network ports are

generally directly attached to the devices that make up a computer network.

Almost all sections of an Ethernet frame are mandatory and most of them have a fixed size. The first part of an Ethernet frame is known as ?

preamble.

The first three octets of a MAC address are known as?

the organizationally unique identifier or OUI. (These are assigned to individual hardware manufacturers by the IEEE or the Institute of Electrical and Electronics Engineers.)

The protocol most commonly used in the fourth layer, the transport layer is known as?

TCP or Transmission Control Protocol.

How can the last three octets of MAC address be assigned?

The last three octets of MAC address can be assigned in any way that the manufacturer would like with the condition that they only assign each possible address once to keep all MAC addresses globally unique.

It represents the physical devices that interconnect computers. This includes the specifications for the networking cables and the connectors that join devices together along with specifications describing how signals are sent over these connections.

The physical layer

consists of devices and means of transmitting bits across computer networks.

The physical layer

Preamble 2nd part (1 BYTES)

This last byte in the preamble is known as the SFD or start frame delimiter. This signals to a receiving device that the preamble is over and that the actual frame contents will now follow.

How VLAN is used

- Any frame with a VLAN tag will only be delivered out of a switch interface configured to relay that specific tag. - This way you can have a single physical network that operates like it's multiple LANs - VLANs are usually used to segregate different forms of traffic.

How does the sending device communicates binary data across these copper wires

by changing the voltage between two ranges.

The way networking cables ensure that duplex communication is possible is by?

by reserving one or two pairs for communicating in one direction. They then use the other one or two pairs for communicating in the other direction. (FULL DUPLEX)

Explain a MAC address

. A MAC address is a globally unique identifier attached to an individual network interface.

Duplex communication is?

Duplex communication is the concept that information can flow in both directions across the cable. e.g a phone call

If there's something wrong with the connection, you might see a network link degrade and report itself as operating as

Half-duplex means that, while communication is possible in each direction, only one device can be communicating at a time.

are the primary devices used to connect computers on a single network, usually referred to as a LAN, or local area network.

Hubs and switches

How many bits number is a MAC address

It's a 48-bit number normally represented by six groupings of two hexadecimal numbers. hexadecimal is a way to represent numbers using 16 digits. MAC referenced a group of numbers by using octet.

VLAN, virtual LAN

It's a technique that lets you have multiple logical LANs operating on the same physical equipment. (4 bytes)

Explain what happens when a device gets ready to send an Internet frame.

When a device gets ready to send an Internet frame, it collects all the information, like the destination and originating MAC addresses, the data payload, and so on. Then it performs a CRC against that data and attaches the resulting checksum number as the frame check sequence at the end of the frame. This data is then sent across a link and received at the other end.

What does Line Coding allows?

- It allows devices on either end of a link to understand that an electrical charge in a certain state is a zero, and in another state is a one. - Through these seemingly simple techniques, modern networks are capable of moving 10 billion ones and zeros across a single network cable every second.

Ones and zeros are sent across those network cables through a process called modulation. What is Modulation?

- Modulation is a way of varying the voltage of this charge moving across the cable. - When used for computer networks, this kind of modulation is more specifically known as line coding.

Do other transfer protocols also use IP to get around?

- Other transfer protocols also use IP to get around, including a protocol known as UDP or User Datagram Protocol. - The big difference between the two is that TCP provides mechanisms to ensure that data is reliably delivered while UDP does not.

Explain the Link and Activity LED

- The link LED will be lit when a cable is properly connected to two devices that are both powered on. - The activity LED will flash when data is actively transmitted across the cable.

the fifth layer is known as the application layer.

- There are lots of different protocols at this layer, and they are application-specific. - Protocols used to allow you to browse the web or send receive email are some common ones. - The protocols at play in the application layer will be most familiar to you, since they are ones you probably interacted with directly before even if you didn't realize it.

A standard cat six cable has how many wires?

- A standard cat six cable has eight wires consisting of four twisted pairs inside a single jacket. - Exactly how many pairs are actually in use depends on the transmission technology being used. - But in all modern forms of networking, it's important to know that these cables allow for duplex communication.

Cat 6 cables

- Cat 6 cables, following even more strict specifications to avoid crosstalk, making those cables more expensive. - Cat 6 cables can transfer data faster and more reliably than Cat 5e cables can, but because of their internal arrangement, they have a shorter maximum distance when used at higher speeds

The protocol most widely used to send data across individual links is known as

- Ethernet. Ethernet and the data link layer provide a means for software at higher levels of the stack to send and receive data.

At the Ethernet level, this is done by looking at a special bit in the destination MAC address. what happens if the destination is set to zero?

- If the least significant bit in the first octet of a destination address is set to zero, it means that the Ethernet frame is intended for only the destination address. - This means it would be sent to all devices on the collision domain, but only actually received and processed by the intended destination. (Unicast)

About the core router

- core routers form the backbone of the Internet and are directly responsible for how we send and receive data all over the Internet every single day. - Core ISP routers don't just handle a lot more traffic than a home or small office router, they also have to deal with much more complexity in making decisions about where to send traffic. - A core router usually has many different connections to many other routers.

The second primary form of networking cable is known as?

- fiber or fiber-optic cables. - Fiber cables contain individual optical fibers, which are tiny tubes made out of glass about the width of a human hair. - These tubes of glass can transport beams of light.

Most network ports have two small LEDs.

- the Link LED - the activity LED.

Diff btw the network and transport layer

- the network layer, in our case IP, is responsible for getting data from one node to another. - Also, the transport layer, mostly TCP and UDP, is responsible for ensuring that data gets to the right applications running on those nodes.

What can the Switch do?

- the switch can actually inspect the contents of the Ethernet protocol data being sent around the network. - Determine which system the data is intended for and then only send that data to that one system. This reduces or even completely eliminates the size of collision domains on the network.

A MAC address is split into how many sections?

2 sections.

A bit

A bit is the smallest representation of data that a computer can understand. It's a one or a zero.

The third type of Ethernet transmission is known as

A broadcast. - An Ethernet broadcast is sent to every single device on a LAN. - This is accomplished by using a special destination known as a broadcast address. - The Ethernet broadcast address is all Fs. - Ethernet broadcasts are used so that devices can learn more about each other.

Internetwork meaning

A collection of networks connected together through routers is an internetwork, the most famous of these being the Internet.

What is a Cyclical Redundancy Check (CRC)

A cyclical redundancy check (CRC), is an important concept for data integrity and is used all over computing, not just network transmissions.

A data packet

A data packet is an all-encompassing term that represents any single set of binary data being sent across a network link. The term data packet isn't tied to any specific layer or technology. It just represents a concept. One set of data being sent from point A to Point B.

A multicast frame

A multicast frame is similarly set to all devices on the local network signal. What's different is that it will be accepted or discarded by each device depending on criteria aside from their own hardware MAC address. Network interfaces can be configured to accept lists of configured multicast addresses for these sort of communication.

Routers share data with each other via a protocol known?

BGP, or border gateway protocol, that lets them learn about the most optimal paths to forward traffic.

The most common forms of copper twisted-pair cables used in networking are?

Category 5, Category 5e, and Category 6 cables.

How does the Ethernet uses MAC addresses?

Ethernet uses MAC addresses to ensure that the data it sends has both an address for the machine that sent the transmission, as well as the one that the transmission was intended for. In this way, even on a network segment, acting as a single collision domain, each node on that network knows when traffic is intended for it.

What solved the problem of collisions domain

Ethernet, as a protocol, solved this problem by using a technique known as Carrier Sense Multiple Access with Collision Detection. CSMA/CD.

If the checksum computed by the receiving end doesn't match the checksum what happens?.

If the checksum computed by the receiving end doesn't match the checksum in the frame check sequence field, the data is thrown out. This is because some amount of data must have been lost or corrupted during transmission.

If the least significant bit in the first octet of a destination address is set to one?

If the least significant bit in the first octet of a destination address is set to one, it means you're dealing with a multicast frame.

What follows the Start Frame Delimiter on the Ethernet frame?

Immediately following the start frame delimiter, comes the destination MAC address. (6 bytes) This is the hardware address of the intended recipient

where else is a network port connected instead of directly to a device.

Instead, there might be network ports mounted on a wall or underneath your desk. These ports are generally connected to the network via cables, run through the walls that eventually end at a patch panel.

A network cable with an RJ45 plug can connect to an

RJ45 network port.

What does the Router store that contains information?

Routers store internal tables containing information about how to route traffic between lots of different networks all over the world.

the primary reason hubs are fairly rare is because?

The collision domain causes these systems to have to wait for a quiet period before they try sending their data again. It really slows down network communications and is the primary reason hubs are fairly rare.

Preamble 1st part (7 BYTES)

The first seven bytes are a series of alternating ones and zeros. These act partially as a buffer between frames and can also be used by the network interfaces to synchronize internal clocks they use, to regulate the speed at which they send data.

Analogy of the five layer

The physical layer is the delivery truck and the roads. The data link layer is how the delivery trucks get from one intersection to the next over and over. The network layer identifies which roads need to be taken to get from address A to address B. The transport layer ensures that delivery driver knows how to knock on your door to tell you your package has arrived. And the application layer is the contents of the package itself.

Anytime you perform a CRC against a set of data, you should end up with the same checksum number. Why is it included in the Ethernet frame?

The reason it's included in the Ethernet frame is so that the receiving network interface can infer if it received uncorrupted data.

Some sources will call this layer the network interface or the network access layer. At this layer, we introduce our first protocols. the data link layer is responsible for defining a common way of interpreting these signals, so network devices can communicate.

The second layer is known as the data link layer.

Twisted pair

These pairs act as a single conduit for information, and their twisted nature helps protect against electromagnetic interference and crosstalk from neighboring pairs.

Difference between datalink and the network layer

While the data link layer is responsible for getting data across a single link, the network layer is responsible for getting data delivered across a collection of networks.

instead of the EtherType field, you could also find what's known?

as a VLAN header. It indicates that the frame itself is what's called a VLAN frame. If a VLAN header is present, the EtherType field follows it.

Since we don't have numerals to represent any individual digit larger than nine, how does hexadecimal numbers represent 10 to 15?

hexadecimal numbers employed the letters A, B, C, D, E, and F to represent the numbers 10, 11, 12, 13, 14, and 15.

The next part of an Ethernet frame after Source MAC Address is?

is called the EtherType field. It's 16 bits long and used to describe the protocol of the contents of the frame.

When a network segment is a collision domain, it means that all devices on that segment.....

receive all communication across the entire segment. This means we need a way to identify which node the transmission was actually meant for. This is where the media access control address or MAC address comes into play.

What. follows the Destination address or destination MAC add?

the Source MAC Address, or where the frame originated from. (6 bytes)

It's this layer that allows different networks to communicate with each other through devices known as routers.

the network layer is also sometimes called the Internet layer. (The third layer)

What is the layer that sorts out which client and server programs are supposed to get that data called?

the transport layer (fourth layer)

The most common type of cabling used for connecting computing devices is known as?

twisted pair.