Decoding the Dot: A Deep Dive into Barcode Label Printer Electronics - Extended Section 20 |
Subtitle: Communication Interfaces - Ethernet and TCP/IP Networking |
Introductory Summary (Extended Section 20 Preview) |
In the previous section, we explored USB communication - the direct, point-to-point connection between a printer and a single host computer. But in many modern workplaces - warehouses, factories, retail stores, and shipping centers - printers are not connected to one computer. They are connected to a network, where they can receive print jobs from multiple computers, be monitored remotely, and even be updated with new firmware over the internet. This is the domain of Ethernet and TCP/IP networking. This chapter is devoted entirely to the Ethernet interface in barcode printers. We will explain what Ethernet is, why it is used in printers, and how it is implemented. We will cover the hardware: the Ethernet controller (MAC), the physical layer transceiver (PHY), the magnetic RJ45 connector, and the isolation transformers. We will explore the software: the TCP/IP stack, the network protocols (DHCP, DNS, HTTP, and LPR), and the printer's built-in web server. We will look at real-world designs from major companies: Texas Instruments' Ethernet MAC integrated into the Sitara processor, Microchip's ENC28J60 SPI-to-Ethernet controller for low-cost designs, WIZnet's W5500 hardwired TCP/IP controller, STMicroelectronics' Ethernet MAC with DMA support, and Realtek's RTL8201 PHY used in many printers. We will also discuss the network configuration, the security considerations, and the remote management features. By the end, you will understand how a printer can be a fully-fledged network citizen, and you will appreciate the engineering that makes it possible to print from anywhere in the world. |
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Chapter 1: The Problem - Printing in a Networked World |
A barcode printer in a warehouse is not sitting next to a single computer. It is on a network, connected to a warehouse management system, a shipping system, and maybe a dozen handheld terminals. The printer must receive print jobs from any of these sources. It must also report its status - paper out, ribbon out, head open, or jammed - to a central monitoring system. The printer must be managed remotely - its firmware updated, its configuration changed, and its logs reviewed - without a technician having to visit it. The Ethernet interface, combined with the TCP/IP networking protocols, makes all of this possible. Ethernet provides the physical connection, and TCP/IP provides the communication protocol. |
Design Example: Networked Printing in a Shipping Center |
A shipping center uses 20 barcode printers, each connected to the network. The printers receive print jobs from a central server. The server sends the label data to the appropriate printer based on the shipping lane. The printers report their status to the server. If a printer runs out of paper, the server sends an alert to the operator. The center uses Ethernet to connect all the printers and the server. |
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Chapter 2: What Is Ethernet- The Physical Layer |
Ethernet is a family of networking technologies that define the physical and data link layers of the network. The most common Ethernet standard for printers is 10/100Base-TX, which supports 10 Mbps and 100 Mbps speeds. The physical medium is a twisted-pair cable with RJ45 connectors. The cable has four pairs of wires, but 10/100Base-TX uses only two pairs: one for transmitting and one for receiving. The cable is typically Category 5 (CAT5) or higher. The maximum cable length is 100 meters. The Ethernet physical layer is defined by the IEEE 802.3 standard. |
Design Example: 100Base-TX in Zebra Printers |
Zebra's ZT600 series uses 100Base-TX Ethernet. The manufacturer chose 100Base-TX because it provides a fast and reliable connection. The manufacturer also supports 10 Mbps for compatibility with older networks. |
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Chapter 3: The Ethernet MAC - The Media Access Controller |
The MAC (Media Access Controller) is the hardware that controls the access to the Ethernet medium. The MAC is responsible for the framing, the addressing, and the error detection. The MAC generates the Ethernet frame - a packet that includes the destination MAC address, the source MAC address, the type/length, the payload, and the CRC (Cyclic Redundancy Check). The MAC also controls the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) - the protocol that allows multiple devices to share the same medium. The MAC is typically integrated into the CPU or into a separate Ethernet controller. |
Design Example: MAC in TI Sitara |
The Texas Instruments Sitara AM335x processor has an integrated Ethernet MAC. The MAC supports 10/100/1000 Mbps. The MAC has a built-in DMA engine that can transfer the data directly to the memory. In a design from a European printer manufacturer, the Sitara's MAC is used for the Ethernet interface. The manufacturer chose the Sitara because of its integrated MAC and its powerful CPU. |
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Chapter 4: The Ethernet PHY - The Physical Layer Transceiver |
The PHY (Physical Layer Transceiver) is the hardware that converts the digital signals from the MAC to the analog signals that are transmitted over the cable. The PHY also converts the received analog signals to the digital signals for the MAC. The PHY handles the line coding, the clock recovery, and the auto-negotiation. The PHY is typically a separate IC that connects to the MAC via an MII (Media Independent Interface) or an RMII (Reduced Media Independent Interface). The PHY is a critical component of the Ethernet interface. |
Design Example: PHY in Realtek RTL8201 |
The Realtek RTL8201 is a popular 10/100Base-TX PHY. The RTL8201 supports the MII and the RMII interfaces. The RTL8201 also supports the auto-negotiation - the process by which the PHY negotiates the speed and the duplex mode with the link partner. In a design from a Taiwanese printer manufacturer, the RTL8201 is used with a CPU that has an integrated MAC. The manufacturer chose the RTL8201 because it is inexpensive and readily available. |
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Chapter 5: The Magnetic RJ45 Connector - The Isolation Transformer |
The RJ45 connector is the physical connector for the Ethernet cable. The RJ45 connector has eight pins. The 10/100Base-TX uses pins 1, 2 (transmit), and 3, 6 (receive). The RJ45 connector is typically integrated with the isolation transformers - the magnetic components that provide the galvanic isolation between the printer and the network. The isolation transformers prevent the DC currents and the voltage spikes from damaging the printer. The RJ45 connector also includes the LEDs for the link and the activity indicators. The magnetic RJ45 connector is a modular component that simplifies the design. |
Design Example: Magnetic RJ45 in Brother Printers |
Brother's printer uses a magnetic RJ45 connector with integrated isolation transformers. The connector is a standard part from Pulse Electronics. The manufacturer chose the magnetic RJ45 because it simplifies the design and provides the required isolation. |
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Chapter 6: The MII Interface - Connecting the MAC and the PHY |
The MII (Media Independent Interface) is a standard interface that connects the MAC to the PHY. The MII has 16 pins. The MII includes the transmit data (TXD), the transmit clock (TX_CLK), the transmit enable (TX_EN), the receive data (RXD), the receive clock (RX_CLK), the receive data valid (RX_DV), the carrier sense (CRS), and the collision (COL). The MII is a parallel interface that operates at 25 MHz for 100 Mbps and 2.5 MHz for 10 Mbps. The MII is a reliable and flexible interface, but it requires many pins. The RMII (Reduced MII) is a simpler interface that uses fewer pins (11 pins). The RMII operates at 50 MHz for both 10 and 100 Mbps. |
Design Example: RMII in Sato Printers |
Sato's printer uses the RMII interface to connect the MAC to the PHY. The manufacturer chose the RMII because it uses fewer pins than the MII, which simplifies the PCB layout. |
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Chapter 7: The Auto-Negotiation - A Smart Handshake |
The auto-negotiation is a feature of the Ethernet PHY that allows the device to negotiate the speed and the duplex mode with the link partner. The auto-negotiation is a process that sends a series of pulses (the fast link pulses) to the link partner. The pulses contain the capabilities of the device - the supported speeds, the duplex modes, and the flow control. The link partner responds with its capabilities. The two devices then select the highest common speed and the duplex mode. The auto-negotiation is a critical feature that ensures the interoperability. |
Design Example: Auto-Negotiation in Zebra Printers |
Zebra's printer supports the auto-negotiation. The manufacturer chose the auto-negotiation to ensure the printer works with any network switch. |
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Chapter 8: The TCP/IP Stack - The Network Protocol |
The TCP/IP stack is the software that implements the network protocols. The TCP/IP stack includes the IP (Internet Protocol), the TCP (Transmission Control Protocol), and the UDP (User Datagram Protocol). The IP is responsible for the addressing and the routing. The TCP is a reliable, connection-oriented protocol that ensures the data is delivered correctly. The UDP is a connectionless protocol that is used for the simple messages. The TCP/IP stack is a complex software library. The TCP/IP stack is typically provided by the operating system (e.g., Linux) or by a dedicated TCP/IP library (e.g., lwIP). The TCP/IP stack is a critical part of the network communication. |
Design Example: lwIP in Honeywell Printers |
Honeywell's printer uses the lwIP (lightweight IP) TCP/IP stack. The lwIP is a small, open-source TCP/IP stack that is designed for the embedded systems. The manufacturer chose the lwIP because it is small, efficient, and well-documented. |
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Chapter 9: The IP Address - The Printer's Identity on the Network |
The IP address is a unique identifier that identifies the printer on the network. The IP address is a 32-bit number that is typically written in the dotted-decimal notation (e.g., 192.168.1.100). The IP address can be assigned statically (fixed) or dynamically (via DHCP). The IP address is a critical configuration parameter. The printer must have a valid IP address to communicate on the network. |
Design Example: DHCP in Brother Printers |
Brother's printer supports DHCP (Dynamic Host Configuration Protocol). The printer obtains its IP address, the subnet mask, the default gateway, and the DNS server from the DHCP server. The manufacturer chose the DHCP because it simplifies the network configuration. |
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Chapter 10: The DHCP - Automatic Configuration |
The DHCP (Dynamic Host Configuration Protocol) is a protocol that automatically assigns the IP address and the other configuration parameters to the devices on the network. The printer sends a DHCP request to the network. The DHCP server responds with an IP address. The DHCP simplifies the network configuration, especially in large networks. |
Design Example: DHCP in Sato Printers |
Sato's printer uses the DHCP to obtain its IP address. The manufacturer chose the DHCP because it simplifies the network setup for the user. |
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Chapter 11: The DNS - Name Resolution |
The DNS (Domain Name System) is a protocol that translates the domain names (e.g., printer1.example.com) to the IP addresses. The DNS is used to locate the printers and the servers on the network. The DNS is a critical part of the network infrastructure. |
Design Example: DNS in Zebra Printers |
Zebra's printer uses the DNS to resolve the server names. The printer can send the print jobs to a server by name, rather than by the IP address. The manufacturer chose the DNS because it makes the configuration more flexible. |
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Chapter 12: The HTTP - A Web Server in the Printer |
The HTTP (Hypertext Transfer Protocol) is the protocol that is used for the web browsing. Many printers have a built-in web server that provides a web interface. The web interface allows the user to configure the printer, to monitor the status, and to view the logs. The web interface is a convenient and powerful management tool. |
Design Example: Web Server in Brother Printers |
Brother's printer has a built-in web server. The user can open a web browser and type the printer's IP address. The web page shows the printer's status, the configuration, and the print queue. The manufacturer chose the web server because it provides a simple and universal management interface. |
Chapter 13: The LPR - A Standard Printing Protocol |
The LPR (Line Printer Daemon) is a standard printing protocol that is used on the Unix and the Linux systems. The LPR uses the TCP port 515. The LPR sends the print job to the printer. The printer receives the job and prints it. The LPR is a simple and reliable protocol. |
Design Example: LPR in Sato Printers |
Sato's printer supports the LPR protocol. The manufacturer chose the LPR because it is a standard protocol that is supported by many host systems. |
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Chapter 14: The IPP - A Modern Printing Protocol |
The IPP (Internet Printing Protocol) is a modern printing protocol that uses the HTTP. The IPP is a more advanced protocol than the LPR. The IPP supports the authentication, the encryption, and the job management. The IPP is used in the Windows, the Mac, and the Linux systems. |
Design Example: IPP in Zebra Printers |
Zebra's printer supports the IPP. The manufacturer chose the IPP because it provides a secure and feature-rich printing protocol. |
Chapter 15: The SNMP - A Network Management Protocol |
The SNMP (Simple Network Management Protocol) is a protocol that is used for the network management. The SNMP allows the network administrator to monitor the printer's status - the paper level, the ribbon level, the temperature, and the error status. The SNMP is a critical tool for the large-scale printer deployments. |
Design Example: SNMP in Brother Printers |
Brother's printer supports the SNMP. The network administrator can use the SNMP to monitor the printer's status from the central management console. The manufacturer chose the SNMP because it is a standard network management protocol. |
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Chapter 16: The Telnet - A Command-Line Interface |
The Telnet is a protocol that provides a command-line interface to the printer. The user can connect to the printer with the Telnet client and send the commands. The Telnet interface is a powerful tool for the advanced users and the technicians. |
Design Example: Telnet in Sato Printers |
Sato's printer supports the Telnet. The technician can use the Telnet to configure the printer and to diagnose the problems. The manufacturer chose the Telnet because it provides a powerful and flexible management tool. |
Chapter 17: The SSH - A Secure Command-Line Interface |
The SSH (Secure Shell) is a secure version of the Telnet. The SSH encrypts the communication, protecting it from the eavesdropping. The SSH is a more secure alternative to the Telnet. The SSH is used in the printers that require the secure management. |
Design Example: SSH in Zebra Printers |
Zebra's printer supports the SSH. The manufacturer chose the SSH because it provides a secure command-line interface. |
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Chapter 18: The FTP - A File Transfer Protocol |
The FTP (File Transfer Protocol) is a protocol that is used for the file transfer. The FTP can be used to upload the firmware and the font files to the printer. The FTP is a simple and reliable file transfer protocol. |
Design Example: FTP in Brother Printers |
Brother's printer supports the FTP. The user can upload the new firmware to the printer via the FTP. The manufacturer chose the FTP because it is a standard file transfer protocol. |
Chapter 19: The TFTP - A Simple File Transfer |
The TFTP (Trivial File Transfer Protocol) is a simpler version of the FTP. The TFTP is used for the firmware updates and the configuration backups. The TFTP is a simple and lightweight protocol. |
Design Example: TFTP in Sato Printers |
Sato's printer supports the TFTP. The technician can use the TFTP to update the firmware. The manufacturer chose the TFTP because it is simple and lightweight. |
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Chapter 20: The NTP - Network Time Protocol |
The NTP (Network Time Protocol) is a protocol that synchronizes the printer's clock with a network time server. The NTP ensures that the printer's time is accurate. The accurate time is important for the logging and the scheduling. |
Design Example: NTP in Zebra Printers |
Zebra's printer supports the NTP. The printer synchronizes its clock with the NTP server. The manufacturer chose the NTP because it ensures the accurate time. |
Chapter 21: The Web Services - A Modern API |
Some printers support the web services - a modern API that allows the applications to interact with the printer over the HTTP. The web services use the SOAP (Simple Object Access Protocol) or the REST (Representational State Transfer) protocols. The web services provide a flexible and powerful programming interface. |
Design Example: Web Services in Brother Printers |
Brother's printer supports the web services. The developer can use the web services to send the print jobs, to check the status, and to configure the printer. The manufacturer chose the web services because they provide a modern and flexible API. |
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Chapter 22: The Ethernet Cable - The Connection Medium |
The Ethernet cable is the physical connection between the printer and the network. The cable is a twisted-pair cable with RJ45 connectors. The cable is typically CAT5e or CAT6. The cable length is limited to 100 meters. The cable must be shielded or unshielded, depending on the environment. The cable is a critical part of the Ethernet interface. |
Design Example: Ethernet Cable in Sato Printers |
Sato's printer uses a standard CAT5e Ethernet cable. The manufacturer tested the cable with a 100-meter length and found the signals to be clean. |
Chapter 23: The Network Switch - A Central Hub |
The network switch is a central hub that connects multiple devices on the network. The printer is connected to the network switch. The switch forwards the data between the devices. The switch is a critical component of the network infrastructure. |
Design Example: Switch in Zebra Printers |
Zebra's printer is connected to a network switch. The manufacturer tested the printer with different switches and found it to be compatible. |
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Chapter 24: The Network Security - A Critical Concern |
The network security is a critical concern for the network printers. The printer must be protected from the unauthorized access. The security measures include the password protection, the encryption (SSL/TLS), and the access control lists (ACLs). The security measures prevent the data from being intercepted and the printer from being compromised. |
Design Example: Security in Brother Printers |
Brother's printer supports the password protection and the SSL/TLS encryption. The manufacturer chose the security features to protect the printer from the unauthorized access. |
Chapter 25: The Firewall - A Network Protection |
The firewall is a network device that filters the traffic. The firewall can be used to block the unauthorized access to the printer. The firewall is a critical security component. |
Design Example: Firewall in Sato Printers |
Sato's printer is used behind a firewall. The firewall blocks the unauthorized access to the printer. The manufacturer recommended using a firewall to protect the printer. |
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Chapter 26: The VLAN - A Virtual Network |
The VLAN (Virtual LAN) is a virtual network that separates the traffic. The VLAN can be used to isolate the printer traffic from the other network traffic. The VLAN is a security and management feature. |
Design Example: VLAN in Zebra Printers |
Zebra's printer supports the VLAN. The manufacturer chose the VLAN to separate the printer traffic. |
Chapter 27: The MAC Address - A Unique Hardware Identifier |
The MAC address is a unique identifier that is assigned to the Ethernet interface. The MAC address is a 48-bit number that is written in the hexadecimal format (e.g., 00:1A:2B:3C:4D:5E). The MAC address is used at the data link layer. The MAC address is a critical identifier for the network communication. |
Design Example: MAC Address in Brother Printers |
Brother's printer has a unique MAC address that is assigned at the factory. The manufacturer chose to use a unique MAC address to identify the printer on the network. |
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Chapter 28: The IP Conflict - A Network Problem |
The IP conflict is a network problem that occurs when two devices on the same network have the same IP address. The IP conflict causes the communication errors. The IP conflict is prevented by using the DHCP, which automatically assigns the unique IP addresses. |
Design Example: IP Conflict in Sato Printers |
Sato's printer uses the DHCP to avoid the IP conflict. The manufacturer chose the DHCP to prevent the IP conflicts. |
Chapter 29: The Network Diagnostics - A Troubleshooting Tool |
The network diagnostics are a set of tools that help the technician to troubleshoot the network problems. The diagnostics include the ping, the traceroute, and the ARP (Address Resolution Protocol). The diagnostics are a critical tool for the network troubleshooting. |
Design Example: Ping in Zebra Printers |
Zebra's printer supports the ping command. The technician can use the ping to test the network connectivity. The manufacturer chose the ping because it is a simple and effective diagnostic tool. |
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Chapter 30: The Power over Ethernet - A Convenient Feature |
The Power over Ethernet (PoE) is a feature that allows the printer to be powered over the Ethernet cable. The PoE eliminates the need for a separate power supply. The PoE simplifies the installation. The PoE is defined by the IEEE 802.3af and 802.3at standards. |
Design Example: PoE in Brother Printers |
Brother's printer supports the PoE. The manufacturer chose the PoE because it simplifies the installation. The printer can be powered from the network switch. |
Chapter 31: The Wake-on-LAN - A Remote Power-On |
The Wake-on-LAN (WoL) is a feature that allows the printer to be powered on remotely. The WoL is a network protocol that sends a magic packet to the printer. The printer detects the magic packet and turns on. The WoL is a convenient feature for the remote management. |
Design Example: WoL in Sato Printers |
Sato's printer supports the Wake-on-LAN. The manufacturer chose the WoL to allow the remote power-on. |
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Chapter 32: The Firmware Update - A Remote Upgrade |
The firmware update can be done remotely over the network. The new firmware is uploaded to the printer via the FTP, the TFTP, or the web interface. The remote update simplifies the maintenance. |
Design Example: Remote Update in Zebra Printers |
Zebra's printer supports the remote firmware update. The technician can upload the new firmware via the web interface. The manufacturer chose the remote update to simplify the maintenance. |
Chapter 33: The Print Queue - A Job Management |
The print queue is a list of the print jobs that are waiting to be printed. The print queue can be managed remotely - the user can view the queue, cancel the jobs, and reorder the jobs. The print queue is a critical feature for the network printing. |
Design Example: Print Queue in Brother Printers |
Brother's printer has a print queue that can be viewed via the web interface. The manufacturer chose the web interface for the queue management. |
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Chapter 34: The Logging - A Diagnostic Tool |
The printer logs the events - the print jobs, the errors, and the status changes. The logs are stored in the printer's memory. The logs can be viewed remotely via the web interface or the SNMP. The logs are a valuable diagnostic tool. |
Design Example: Logging in Sato Printers |
Sato's printer logs the events. The logs can be viewed via the web interface. The manufacturer chose the logging to simplify the troubleshooting. |
Chapter 35: The System Integration - A Complete Network System |
We have now covered the Ethernet interface and the TCP/IP networking. Let us put it all together. The Ethernet connector provides the physical connection. The PHY and the MAC provide the data link layer. The TCP/IP stack provides the network protocols. The web server, the LPR, the SNMP, and the other services provide the application layer. The Ethernet interface is a complete network system. |
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Chapter 36: The Future of Network Printing - The Internet of Things |
The future of network printing is the Internet of Things (IoT). The printers will be connected to the internet and will be managed from the cloud. The printers will also be able to send the alerts and the status updates to the cloud. The IoT will make the printers more intelligent and easier to manage. |
Chapter 37: The Cloud Printing - A New Paradigm |
The cloud printing is a new paradigm where the print jobs are sent to the printer via the cloud. The cloud printing allows the users to print from anywhere. The cloud printing simplifies the printing infrastructure. |
Chapter 38: The Future - Smarter and More Connected |
The future of the printer communication lies in the smarter and more connected solutions. The future printers will have a built-in web server, a cloud connection, and a remote management. The future printers will be more intelligent, more secure, and easier to use. |
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Detailed Summary - Tying It All Together |
We have now completed our comprehensive exploration of the Ethernet interface and the TCP/IP networking in barcode printers. We began by understanding the problem: the printer needs to connect to a network to receive the print jobs from multiple sources, to report its status, and to be managed remotely. We learned about the Ethernet physical layer - the RJ45 connector, the twisted-pair cable, the PHY, and the MAC. We saw how the PHY and the MAC are connected via the MII or the RMII interfaces. |
We explored the TCP/IP stack - the IP, the TCP, and the UDP. We discussed the IP address, the DHCP, and the DNS. We examined the application layer protocols - the HTTP (web server), the LPR, the IPP, the SNMP, the Telnet, the SSH, and the FTP. We saw how these protocols provide the management, the printing, and the file transfer capabilities. |
We looked at the practical aspects: the auto-negotiation, the cable, the network switch, the firewall, and the VLAN. We discussed the security measures - the password protection, the encryption, and the access control lists. We examined the network diagnostics - the ping, the traceroute, and the ARP. |
We explored the advanced features: the Power over Ethernet (PoE), the Wake-on-LAN (WoL), the remote firmware update, the print queue management, and the logging. We considered the future of network printing - the Internet of Things (IoT) and the cloud printing. |
The overarching lesson is that the Ethernet interface is not just a physical connection - it is a complete network system that includes the hardware, the firmware, and the software. A well-designed Ethernet interface makes the printer a full-fledged network citizen - it can receive the print jobs from multiple sources, it can report its status, and it can be managed remotely. A poorly designed interface causes the communication errors, the network problems, and the management difficulties. Understanding the Ethernet interface and the TCP/IP networking is essential for any engineer who wants to design a modern, networked barcode printer, and this chapter has provided that understanding from the basic principles of the Ethernet PHY to the advanced techniques of the cloud printing. |
End of Extended Section 20 |
cs@easiersoft.com