Introduction to 2.hcna-hntd--Transmission media

In addition to the communication device itself, the communication network includes the transmission media connected to these devices, such as coaxial cable (mainly used for CCTV, obsolete), twisted pair and fiber optics. Different transmission media have different characteristics, these characteristics directly affect the communication of many aspects, such as line coding, transmission speed and transmission distance.

Learning Goals:

1. Learn about some common transport media (identify media types, etc.)
2. Understanding the basic concepts of conflict domains and duplex patterns

Here are two hosts, host A and B, two hosts through physical media interconnection, like two people to through the air this medium to speak, this air is the transmission medium.
For the network, the most important transmission medium is the physical medium.

The following describes the common transport media:

For CCTV, there are two standards, one coarse and one fine, coarse transmission distance, thin transmission distance short. Features: Low bandwidth, conflicting
Coaxial cable is an early-use transmission medium, the standard of coaxial cable is divided into two kinds, 10base2 and 10base5. Both of these standards support a 10Mbps transmission rate, with a maximum transmission distance of 185 meters and 500 meters respectively. General attaining, 10BASE2 coaxial cable using BNC connector, 10BASE5 coaxial cable using n-type connector.
Now, the 10Mbps transmission rate has not met the current enterprise network requirements, so coaxial cable in the current enterprise network is rarely used.
10base5 and 10base2 are the early two Ethernet standards, both of which use coaxial cables as transmission media. 10BASE5 and 10BASE2 use coaxial cable diameters of 9.5mm and 5mm respectively, so the former is also known as the thick cable, the latter is also known as the thin cable. In general, the 10BASE5 coaxial cable uses the N-type connector, and the 10BASE2 coaxial cable uses the BNC connector. Both the 10BASE5 and 10BASE2 support 10Mbps transmission rates, with a maximum effective transmission distance of 500 m and 185 m respectively.
At present, these two kinds of Ethernet have been basically eliminated, and the enterprise network almost no longer use them.

In order to avoid electromagnetic interference, the use of twisted-pair form.
The non-coaxial cable has a lower manufacturing and deployment cost than a twisted pair (Twisted pair) and is therefore widely used in the enterprise network. Twisted pair can be divided into shielded twisted pair (shielded Twisted PAIR,STP) and unshielded twisted pair (unshielded Twisted PAIR,UTP). Shielded twisted-pair wires have a metal shielding layer between the twisted pair of insulated envelopes, which shields the electromagnetic interference. There are many types of twisted pair, and the transmission rates supported by different types of twisted pair are generally not the same. For example, the Class 3 twisted pair supports a 10Mbps transfer rate, the 5 class twisted pair supports a 100Mbps transfer rate, meets the Fast Ethernet standard, and the Ultra 5 twisted pair and higher level twisted pair support Gigabit Ethernet transmission. The twisted pair uses the RJ-45 connector to connect to the network device. In order to ensure that the terminal can properly collect anticipation data, the pins in the RJ-45 connector must be arranged in a certain line order.
568b--Orange White-orange-green white-blue-blue white-green-brown white-brown
1 3 rounds 2 6 receive

The optical signal is transmitted, singlemode (only one optical signal is transmitted), multimode (multi-signal). Short multimode distances (dispersion of the light, attenuation is severe). Multimode suitable for internal network transmission, single mode for long-distance transmission. The cost of single mode is expensive.
Twisted-pair and coaxial cables use electrical signals when transmitting data, while optical signals are used to transmit data. The transmission rates supported by the fiber include 10mbps,100mbps,1gbps, 10Gbps, or even higher. According to the optical fiber transmission optical signal mode, the fiber can be divided into single mode fiber and multimode fiber. Single Mode optical fiber can only transmit one pattern of light, there is no die colors dispersion, so it is suitable for long-distance transmission. Multimode optical fibers allow different modes of light to be transmitted on a single fiber, and because of the large modulus colors, the signal pulse broadening is serious, so multimode fiber is mainly used for short distance transmission in local area network. There are many types of fiber optic connectors, commonly used connectors include ST,FC,SC,LC connectors.

Two models, the serial interface, are used on the WAN line.
Now, RS-232 has gradually been the new standard canceled, such as FireWire, USB, new products and equipment have been widely used USB standard
Conflict domain:
Signal collisions may occur in a shared network

Assuming that host a sends packets, and host C just sends the packets, there is a conflict and a packet loss.
Both devices are in a shared network, on a shared device, in the same conflict domain.
is a 10BASE5 Ethernet, each host is using the same coaxial cable to communicate with no other host, so the coaxial cable here is also known as shared media, the corresponding network is called a shared media network, or simply a shared network. In a shared network, when different hosts anticipation to send data at the same time, there is a problem of signal conflict, and the method of solving this problem is generally using carrier-based multi-access/collision detection (Carrier sense multiple access/collision Detection).

Duplex is the kind of telephone we call, but also to listen, but also to say.
Simplex is the walkie-talkie kind, either listen, or say.
In which the single-worker conflict treatment method is usually used CSMA/CD (carrier monitoring multiplexing with collision detection technology)
Working principle is: before sending data to listen to whether the channel is idle, if idle, send data immediately. If the channel is busy, it waits for a period of time until the transmission of the information in the channel ends and then sends the data, and if two or more nodes are sent at the end of the last message, then the request is determined as a conflict. If you hear a conflict, stop sending data immediately, wait for a random time, and try again.
The principle of simple summary for: First listen to the post, the side of the sound, the conflict stopped, random delay after the re-hair

In half-duplex mode, both parties that share physical media must use the CSMA/CD mechanism to avoid
Conflict-free. For example, the communication mode of 10BASE5 Ethernet must be half-duplex mode.
In full-duplex mode, both sides of the communication can simultaneously implement two-way communication, which does not create a conflict and therefore does not require the use of the CSMA/CD mechanism. For example, the 10BASE-T Ethernet communication mode can be a full-duplex mode.
The duplex mode of the two devices connected on the same physical link must be consistent.

Summarize:
1. What kind of transmission media is used when Gigabit Ethernet is deployed in the enterprise network?
A: Gigabit Ethernet transmissions must use over 5 standard and above twisted pair, or use gigabit and higher grade fiber.
2. What is the conflict domain?
A: A conflict domain is a collection of all nodes that are transported in two directions by sharing physical media. When a host in the same conflict domain sends data at the same time, the data may collide before it reaches the destination.
3. What is the role of CSMA/CD?
A: CSMA/CD is a mechanism for detecting and avoiding conflicts on a shared network. CSMA/CD's work process is as follows:
1) The device continuously detects the status of the shared line. If the line is idle, data can be sent, and if the line is not idle, it waits.
2) If another device sends data at the same time, the data sent by the two devices will inevitably conflict, resulting in chaotic signal on the line.
3) The terminal device detects this conflict and immediately stops sending its own data.
4) The terminal device sends a series of interference pulses, and then waits for a period of time before the data is sent.

Introduction to 2.hcna-hntd--Transmission media