Network Components

Let's learn about the components needed to build and use a network

Reference: [Book] Network Introduction for IT Engineers

1. Network Interface Card (NIC)

• The official name for what is commonly called a LAN card is Network Interface Card (NIC)

  • Besides NIC, it is also called Network Card or Network Interface Controller

• NIC is a hardware device for connecting a computer to a network

Main Roles of NIC

• Serialization

  • The Network Interface Card converts electrical signals to data signal form or data signal form to electrical signal form

  • On the external cable of the NIC, data is transmitted in electrical signal form, and this mutual conversion process is called serialization

• MAC Address

  • The Network Interface Card has a MAC address

  • If the destination address of a received packet is not its own MAC address, it discards the packet; if it is its own address, it forwards it so it can be processed within the system

• Flow Control

  • In Packet-based networks, various communications use a single channel, so new data may not be received because of ongoing data processing

    • To prevent data loss in such situations, when data cannot be received, a request to stop communication can be sent to the other party, and this process is called flow control

Multifunction NIC

• Ethernet is not the only network transmission technology used

  • The Fibre Channel standard exists for SAN (Storage Area Network) configurations connecting Storage and servers,

  • The iSCSI protocol exists for configuring storage networks over Ethernet

  • InfiniBand technology is also used in HPC (High Performance Computing) networks that implement high-performance clustering by linking multiple servers, like supercomputers

• Recently, these various protocols have been transitioning to Ethernet-based,

  • But these various protocols are still used in some networks

  • Network cards that support and accelerate these special networks are also being used

2. Cable and Connector

• While the use of wireless connections from laptops, smartphones, and tablets for Internet access is increasing, wired connections are still used when high-reliability communication is needed, such as connecting to company networks or connecting servers to the network

  • The first network connection point to consider for such connections is the cable

• Cables come in 3 types: Twisted Pair, Coaxial cable, and Fiber-optic cable

  • To correctly select the right cable for the desired environment, you need to know the basic elements and standards that make up the cable

2-1. Ethernet Network Standards

• Currently popular Ethernet standards are Gigabit Ethernet and 10 Gigabit Ethernet

  • General terminals like PCs use Gigabit Ethernet, while terminals like data center servers primarily use Gigabit or 10 Gigabit Ethernet

  • When connecting servers and switches with 10 Gigabit Ethernet, switches use 40 Gigabit or 100 Gigabit Ethernet to secure uplink bandwidth for connections with upstream switches

• Ethernet is further subdivided into multiple standards by cable type, encoder type, etc., but 3 standards are most commonly used

  1. 1,000BASE-T/10GBASE-T

     • Gigabit Ethernet standard using Twisted pair cable

  2. 1,000BASE-SX/10GBASE-SR

     • Uses Multi-mode optical cable and can transmit over relatively short distances

  3. 1,000BASE-LX/10GBASE-LR

     • Uses Single-mode optical cable and can transmit over relatively long distances

Explaining the meaning of each nomenclature using 1,000BASE-T, one of the Gigabit Ethernet standards,

• The number 1,000 at the front indicates speed

  • If the front number is 1,000, it is a network that can communicate at 1,000Mbps speed

• The middle characters refer to the type of channel

  • BASE indicates single-channel communication,

  • BROAD indicates multi-channel communication

• The last characters indicate the cable type

  • The T character indicates Twisted Pair cable

  • The optical signal and transceiver type change based on the last character

2-2. Cable and Connector Structure

• Cables are physically divided into several elements like cable body, connector, and transceiver

  • The cable body is divided into Twisted Pair, coaxial, and optical cables

  • The connector and transceiver types also change depending on the cable body type

• For Twisted Pair Cable, the connector and body are configured as one, and there is often no separate transceiver

• Optical cables need to support various speeds and distances, so the transceiver, connector, and cable are often separated

2-3. Cable - Twisted Pair Cable

• The most commonly used cable is the Twisted Pair cable

• Twisted Pair cables use RJ-45 connectors that are attached to the cable body and cannot be separated

• Plugging it into a LAN port on a computer or server connects it to the network

• Types of Twisted Pair cables

  • STP (Shielded Twisted Pair) cable with mesh-type shield

  • FTP (Foil Twisted Pair) cable with foil-type shield

  • UTP (Unshielded Twisted Pair) cable without shield

• Cables with shields on each twisted pair and cables with an overall cable protection shield may use STP/FTP combinations

  • STP/FTP has each pair shielded with foil and an overall cable protection shield

    • This can effectively block both internal interference and external interference!

• Twisted Pair cable grades

  • Twisted Pair cables are graded by category

  • The most commonly used cable is the category 5E cable

    • It is a common cable supporting 1G speeds and is suitable for connecting general terminals like desktops and laptops,

    • But not suitable when high bandwidth like data centers needs to be supported

2-4. Cable - Coaxial Cable

• Coaxial cables are the same type as the thick black cables used to connect cable TV

• In the past they were also used in LAN sections, but since they are hard to handle and expensive, they are rarely used and have only been used for cable TV and Internet connections

  • However, recently for 10G or higher high-speed connections, DAC (Direct Attach Copper) cables with integrated transceivers are widely used, which are a type of coaxial cable

2-5. Cable - Optical Cable

• Optical cables generally have higher reliability than other copper wires (UTP, coaxial) and can communicate over longer distances, so they are primarily used for communication between network devices that require high bandwidth or need to communicate over long distances

• Cables need to be protected from attenuation caused by resistance and interference from surrounding magnetic fields, and optical cables based on optical signals are relatively free from such attenuation and interference

• Optical cables are divided into 2 types: Single mode and Multi mode

  • Single mode

    • The cable thickness is very thin to support long-distance communication, and laser is used as the light source

      • Lasers have the property of traveling straight without dispersing over long distances compared to other light

    • Called single mode because a single laser signal passes through a thin transmission path

    • Single mode with a small reflection angle can transmit over much longer distances

    • Single mode cables are yellow

  • Multi mode

    • Uses a relatively thicker cable compared to single mode and uses LED as the light source

      • LED light sources are easier to implement than lasers, so both multi mode cables and transceivers are cheaper than single mode

    • Called multi mode because multiple light sources are transmitted through a wide optical transmission path

    • Multi mode cables are orange (1G) and sky blue (10G)

2-6. Connector

• The connector is the end part of the cable that connects to network devices or network cards

• Twisted Pair cables use RJ-45 connectors, but optical cables have various connectors

  • Optical cables primarily use LC connectors, and SC connectors are partially used

  • When using optical cables for servers, the connector type must be communicated to the network administrator when requesting network connections to ensure the appropriate cable is used

2-7. Transceiver

• Transceivers convert external signals into electrical signals inside the computer

• In the past when transceivers were not separately distinguished, different network devices or NICs had to be purchased to satisfy various Ethernet standards and cables

  • To solve the problem of having to replace network devices and NICs when cables changed, and to allow the mixed use of different diverse network standards, transceivers are used

• Among transceivers, GBIC is the name of the initially developed module, and subsequent upper standards like SFP and SFP+ were released, but

  • Generally, all transceivers are collectively referred to as GBIC

• To be precise,

  • GBIC (GigaBit Interface Converter) is an interface that can connect SC type connectors

    • SC type connectors are mainly used for optical cables

  • SFP (Small Form-Factor Pluggable) can connect LC type connectors

• Without Transceivers, using dedicated interfaces would require purchasing different network devices or NICs for each length and speed, but

  • By only changing the Transceiver, communication length and speed can be adjusted, so most recently produced network devices and NICs support transceivers

3. Hub

• Hub is a device that operates at Layer 1 (Physical Layer), the same as cable

• Hub regenerates electrical signals that weaken with distance, and as the term HUB implies, is used to connect multiple devices

• Hub simply sends incoming signals to all ports, causing all terminals connected to the network to compete, resulting in problems of reduced overall network performance

  • Infinite packet loops can occur, paralyzing the entire network, and various failure causes like loops mean that hubs are rarely used today

4. Switch

• Switch, like Hub, is a Layer 2 (Data Link Layer) device that connects multiple devices and mediates communication

• Switch performs both the role of a Hub and mediating communication, so it is also called a Switching Hub

• Hub simply regenerates electrical signals and sends them to all ports except the source,

  • But Switch, unlike Hub, can understand MAC addresses, identify the location of the destination MAC address, and send electrical signals only to the port where the correct destination is connected

    • ex) When servers A, B, C, D exist and A needs to communicate with C,

      • Hub sends electrical signals to all ports B, C, D except the source port when A sends a signal,

      • Switch sends electrical signals only to C

        • B and D are completely unaffected by this communication and can simultaneously perform other communications

• Hub works like a walkie-talkie that cannot send and receive simultaneously and operates in only one direction,

• Switch works like a telephone that can send and receive simultaneously

5. Router

• As network sizes grew and the need to communicate with networks in distant areas increased, routers became necessary

• Router operates at Layer 3 (Network Layer) of the OSI 7 layers and converts to protocols that can communicate over long distances

• Router controls broadcast and multicast to prevent unnecessary packets from being transmitted to remote locations, and discards communications to unclear addresses

  • It designates paths so packets are transmitted in the correct direction and forwards packets through the optimal path

    • In other words, the router's role is to verify the network address and then designate the path

• Recently, it is difficult for general users to encounter Router devices, but L3 Switches and home routers (shared routers) that perform similar roles to routers can be easily found

6. Load Balancer

• Generally, Load Balancers operate at Layer 4 (Transport Layer) of the OSI 7 layers

• Layer 7 Load Balancers that understand and operate based on application protocol characteristics at the application layer are separately called ADC (Application Delivery Controller)

• Network devices called L4 Switches are also a type of load balancer, referring to devices that have multiple ports like a switch while performing the load balancer role

• Load Balancers can check Layer 4 port addresses while simultaneously changing IP addresses

• The service where Load Balancers are most commonly used is Web

  • When you want to scale up a web server, place a load balancer in front of the web servers and increase the number of web servers

    • The load balancer holds the representative IP, and the load balancer changes the destination IP address of packets to send them to each web server

  • Using this principle, multiple web servers operate simultaneously to improve service performance

  • Even if some web servers have problems, it helps recover service quickly

    • For these functions, load balancers have capabilities like service health check and high-volume session processing in addition to IP translation!

7. Security Devices (Firewall/IPS)

• While most network devices focus on accurate information delivery,

  • Security devices focus on properly controlling information and defending against attacks

• Various security devices are used according to the defense purpose and the location where they are installed

• Generally, the most well-known security device is the Firewall

  • Firewalls operate at Layer 4 (Transport Layer) of the OSI 7 layers, checking Layer 3 and 4 information of packets passing through,

  • And comparing packets against policies to either discard or forward them

8. Others (Modem/Home Router)

8-1. Home Router (Shared Router)

• The home router used in nearly every household or small business is a device that combines Layer 2 switch, Layer 3 router, and Layer 4 NAT and firewall functions in one place

• The inside of a home router is divided into Switch section, Wireless section, and Router section circuits

  • It looks like a single device on the outside, but internally it is a complex device broadly divided into switch, wireless AP, and Router

8-2. Modem

• A Modem is a device that converts between technologies because short-distance communication technology and long-distance communication technology are different

• Both the LAN (Local Area Network) port and WAN (Wide Area Network) port of a home router cannot send data farther than 100m over regular Ethernet, so a separate modem is needed to convert to long-distance communication technology

• Various types of modems are used depending on the carrier network type and technology

  • For gigabit Internet, mostly FTTH (Fiber To The Home) modems are used,

  • For coaxial cable Internet, Cable modems,

  • For telephone lines, ADSL (Asymmetric Digital Subscriber Line) modems or VDSL (Very high bit-rate Digital Subscriber Line) modems are used