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A Western Electric 400G line card for 1A2 key systems
Northern Telecom World Line Card NT6X17BA, circa 1995

A line card or digital line card is a modular electronic circuit designed to fit on a separate printed circuit board (PCB) and interface with a telecommunications access network.[1]

A line card typically interfaces with a twisted pair cable of a plain old telephone service (POTS) local loop to the public switched telephone network (PSTN). Telephone line cards perform multiple tasks, such as analog-to-digital and digital-to-analog conversion of voice, off-hook detection, ring supervision, line integrity tests, and other BORSCHT functions. In some telephone exchange designs, the line cards generate ringing current and decode DTMF signals. The line card in a subscriber loop carrier is called a subscriber line interface card (SLIC).[2][3]

A line card can terminate a line supporting voice POTS service, ISDN service, DSL service, or proprietary ones. Some line cards are capable of terminating more than one type of service.[3]

Since an access network element is usually intended to interface many users (typically a few thousand), some exchanges have multiple line terminations per card. Likewise, one network element can have many line cards.

See also

[edit]

References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Line card

View on Grokipedia
from Grokipedia
A line card has two primary meanings in different contexts. In telecommunications and networking, it is a modular (PCB) that serves as an interface in equipment such as routers, switches, multiplexers, or exchanges, providing transmitting and receiving ports to connect to local area networks (LANs), wide area networks (WANs), or subscriber lines. In systems, it typically handles the termination of circuits like (POTS) lines via twisted-pair cables, performing essential functions known as BORSCHT—battery feed, overvoltage protection, ringing, supervision (off-hook detection), (analog-to-digital conversion), hybrid (two-to-four wire conversion), and testing. These cards are hot-swappable in high-end modular , allowing and maintenance without system downtime, and they support a range of interfaces from analog voice to high-speed digital Ethernet or connections for modern and IP/MPLS services. Line cards differ from fixed ports in smaller devices, where interface circuitry is integrated directly into the , and from network interface cards (NICs) in end-user computers, as they are designed for carrier-grade, high-density environments. In contemporary networks, they enable line-rate forwarding, (QoS), and integration with (SDN) architectures, evolving to support triple-play (voice, video, data) and beyond. In and , a is a concise or that lists the products, services, or manufacturers offered by a or , serving as to highlight offerings to potential customers.

Telecommunications and networking

Definition

A is a modular board (PCB) that interfaces between a network device, such as a router, switch, or access , and external communication lines in and networking systems. It serves as the primary point of connection for transmitting and receiving signals, converting between digital and analog formats where necessary to enable communication over various media like twisted-pair cables or optical fibers. In chassis-based architectures, the line card functions as a hot-swappable, pluggable module that handles operations at the physical and data link layers (Layers 1 and 2 of the OSI model) for specific interface types, such as Ethernet, SONET/SDH, or T1/E1 lines. This design distinguishes line cards from fixed interfaces, emphasizing modularity for easy replacement, scalability to support high port densities, and flexibility in upgrading without disrupting the entire system. As a key termination point, the line card connects subscriber lines or network trunks to broader access networks, including the (PSTN) or wide area networks (WAN), thereby aggregating and routing traffic efficiently in carrier-grade environments. For instance, in traditional setups, it may briefly incorporate functions to manage battery feed, ringing, and signaling for analog connections.

Functions

Line cards in telecommunications systems primarily handle signal conversion and interfacing between analog subscriber lines and digital network cores. A core function is analog-to-digital (A/D) conversion, which digitizes incoming voice or data signals from the two-wire subscriber loop for processing in digital switches, and digital-to-analog (D/A) conversion, which reconstructs analog signals for transmission to the subscriber. These conversions ensure compatibility between traditional analog and modern digital infrastructure. The operational roles of line cards are often encapsulated in the functions, an denoting the essential processes performed by subscriber line interface circuits (SLICs) within the line card. Battery feed supplies a nominal DC voltage, typically -48 V, to the subscriber line to power the set and maintain loop current during calls. Overvoltage protection safeguards the line card against transient high voltages from events like strikes, often using isolation techniques to limit exposure up to 1 kV. Ringing generates an AC signal, such as 20 Hz at 80 V RMS, applied via a to activate the subscriber's ringer and alert the user to an incoming call. monitors line status by detecting changes in loop current or voltage, identifying on-hook/off-hook transitions to manage call states. The performs A/D and D/A encoding/decoding of voice signals at rates like 64 kbps using mu-law or A-law companding for (PCM) integration with the digital network. Hybrid functionality transforms the bidirectional two-wire line into unidirectional four-wire paths, balancing impedance to isolate transmit and receive signals and suppress . Testing enables diagnostic access, such as switching the line for metallic loop tests to verify continuity and signal quality. Beyond , line cards manage specific signaling tasks, including off-hook detection, which senses loop closure when the handset is lifted to initiate call setup, integrated within supervision circuits. Ring supervision monitors current during ringing to detect answer and trip the ring signal automatically upon off-hook. Line integrity testing assesses loop resistance, , and to ensure reliable transmission, often through automated metallic or longitudinal balance measurements. DTMF decoding interprets dual-tone multi-frequency signals generated by key presses for digit collection during dialing, while generation produces these tones for or automated systems. In core routers, line cards extend these roles to high-speed data networking by performing , where ingress engines classify and route packets based on IP or MPLS labels at rates up to hundreds of Gbps. regulates flows using queuing mechanisms like deficit round-robin and shaping to prioritize classes of service and prevent congestion. Interface protocol termination handles Layer 1/2 framing and for standards such as Ethernet or /SDH, enabling seamless integration with diverse physical media. Error handling and diagnostics on line cards include monitoring packet errors, bit errors, and performance metrics, with loopback testing routing signals back to the source interface to isolate faults in transmission paths without external equipment. These capabilities ensure rapid fault detection and maintain network reliability.

Components and architecture

A line card in and networking typically comprises several key hardware components that enable interface and capabilities. Central to analog line handling are Subscriber Line Interface Circuits (SLICs), which provide the electrical interface between the network and subscriber lines, managing functions such as battery feed, ringing, and for voice or DSL connections. Optical and electrical transceivers serve as the interfaces, converting signals between electrical and optical formats to support high-speed data transmission over fiber or copper media, often using pluggable modules like SFP or QSFP for flexibility. Application-Specific Integrated Circuits () handle core tasks, including , , and protocol handling, optimizing performance through custom silicon designs tailored to networking demands. The architecture of a line card emphasizes seamless integration with the router or switch via a shared , which facilitates high-bandwidth interconnections through fabric interfaces that enable data exchange between line cards and control modules. Power distribution is managed through dedicated voltage rails from the power shelves, ensuring stable supply to components like and transceivers while incorporating regulators for efficient DC-DC conversion. Cooling mechanisms, such as integrated fans and heat sinks within the , dissipate heat generated by high-density processing, with airflow directed across line cards to maintain operational temperatures. Line cards adopt a to enhance deployability and upgradability, featuring form factors such as full-size cards occupying a complete slot or half-height variants for denser configurations, alongside SFP-based modules that allow swaps without card replacement. These designs incorporate hot-pluggable Field-Replaceable Units (FRUs), enabling insertion or removal during live operation to minimize in carrier environments. Internally, line cards are built on printed circuit boards (PCBs) that host edge connectors for backplane , along with voltage regulators to step down chassis-supplied power for sensitive ICs. Protection circuits, including surge suppressors and transient voltage suppressors, safeguard against electrical faults like lightning-induced surges on subscriber lines. Scalability is achieved through multi-port configurations on a single card, allowing aggregation of numerous interfaces; for instance, Cisco's 12000 Series supports 16-port OC-3 setups for high-density /SDH deployments.

Types and applications

Line cards in networks are categorized based on their deployment in access, core, or aggregation layers, each tailored to specific transmission media and protocols. In access networks, (POTS) or analog line cards facilitate connections to (PSTN) loops, supporting traditional voice services over copper lines. DSL line cards enable broadband internet delivery, such as Asymmetric Digital Subscriber Line (ADSL) and Very-high-bit-rate Digital Subscriber Line (VDSL), by modulating data over existing telephone wires to provide high-speed access for residential and small business users. ISDN line cards handle digital voice and data transmission, utilizing Basic Rate Interface (BRI) or Primary Rate Interface (PRI) to support integrated services like simultaneous telephony and low-speed data at rates up to 144 kbps for BRI. Core and aggregation line cards focus on high-capacity fiber-optic transport. Optical line cards, often incorporating Dense Wavelength Division Multiplexing (DWDM), transport 100G Ethernet signals over long-haul fiber spans, achieving capacities up to 9.6 Tbps per card in coherent optics configurations for backbone networks. Ethernet line cards provide scalable interfaces for (LAN) and (WAN) aggregation, featuring ports at 10 Gbps, 40 Gbps, or 100 Gbps to handle in metro and regional networks. These line cards find applications in various equipment for edge and transport roles. In routers like the 12000 series, they enable edge routing by processing high-volume traffic at network boundaries, supporting for service provider backbones. Switches such as the PTX series utilize line cards for packet transport, combining Engines with Ethernet interfaces to deliver terabit-scale throughput in core platforms. Subscriber loop carriers employ access-oriented line cards, such as those in Access Multiplexers (DSLAMs), to aggregate telco access signals from end-user loops into higher-speed uplinks. Hybrid or multi-service line cards integrate multiple protocols on a single module to support converged services. These cards accommodate mixed voice and data traffic, for instance, combining / broadband with voice-over-POTS or ISDN interfaces to streamline deployment in access nodes. Modern trends emphasize and integrations, driving line cards toward higher port densities and multi-rate support. For example, advancements enable 36 x 400 ports per card in intelligent IP routers, facilitating low-latency edge processing for 5G-Advanced (5G-A) networks with enhanced connectivity and AI-driven optimization. As of 2025, developments in 800G Ethernet are enabling even higher capacities, with initial deployments in AI-driven data centers and core networks.

History and development

The origins of line cards in telecommunications trace back to the mid-20th century, but their modular form gained prominence in the 1970s and 1980s within telephone key systems and central office switches. The Western Electric 1A2 Key Telephone System, introduced in 1964 and widely deployed through the 1970s, utilized compact printed circuit line cards such as the 400-type series (e.g., 400D for central office/PBX line service) to interface multiple subscriber lines with key telephones, enabling efficient scaling for small businesses. These early cards handled analog signaling functions like ringing and supervision, often incorporating discrete components or early integrated circuits, and were driven by the need for cost-effective expansion in response to growing demand for multi-line service. By the 1980s, the transition from analog to digital networks accelerated with the adoption of pulse-code modulation (PCM) in switches like Northern Telecom's DMS-100 (launched 1976), where line cards began integrating coder-decoders (CODECs) for 64 kbit/s DS0 channels, laying the groundwork for higher-density deployments. In the , line cards evolved significantly to support digital services like Integrated Services Digital Network (ISDN) and early (DSL) technologies, reflecting the push toward integrated voice and data over existing copper infrastructure. Northern Telecom's platform incorporated digital line cards for ISDN basic rate interfaces, enabling simultaneous voice and 128 kbit/s data transmission, while advancements in subscriber line interface circuits (SLICs) reduced component counts and improved efficiency. A landmark example was Alcatel's A1000 Asymmetric Subscriber Access (ASAM) in 1997, which featured DSL line cards delivering multi-megabit downstream speeds for broadband internet trials, marking a shift from circuit-switched to packet-oriented access. This era's innovations were propelled by semiconductor progress, allowing system-on-chip designs that combined analog front-ends with digital processing, and the rising demand for data services amid ISDN's global rollout in the late 1980s and early . The 2000s saw line cards pivot toward core IP networking in routers, emphasizing modularity and high-speed interfaces to accommodate the internet boom. Cisco's 12000 Series Gigabit Switch Router, introduced in 1997 and expanded through the 2000s, featured line cards supporting OC-3 (155 Mbit/s) and DS3 (45 Mbit/s) interfaces for SONET/SDH transport, enabling scalable backbone connectivity for emerging IP traffic. This period's key driver was the rise of IP networks, supplanting traditional TDM hierarchies with packet switching, which necessitated pluggable line cards for easy upgrades and higher port densities in carrier environments. Modularity became central, allowing operators to mix interface types without full system overhauls. Post-2010 developments focused on ultra-high-speed optical line cards for data centers and emerging infrastructure, supporting 100 Gbit/s and beyond to handle explosive bandwidth growth. ' PTX Series Packet Transport Routers, launched in 2011, introduced 100G line cards using coherent for long-haul transport, optimizing for low-latency IP/MPLS cores in cloud-scale networks. These advancements were fueled by the analog-to-digital legacy's full realization in all-optical systems, combined with IP dominance and 's fronthaul requirements, where modular designs now integrate DSP-based forwarding for terabit-scale scalability.

Business and sales

Definition and purpose

In the context of business and , a line card is a concise printed or that lists the products, descriptions, and specifications offered by a , , or manufacturer's representative. It serves as a high-level overview of a business's product lines, often used by third-party sellers such as value-added resellers (VARs) or to communicate their portfolio to potential clients. Unlike more detailed resources, a line card focuses on essential highlights, typically spanning 1-2 pages, to provide quick accessibility during interactions. The primary purpose of a line card is to act as a "menu" of offerings for potential clients, enabling sales teams to deliver rapid overviews in settings like pitches, trade shows, or partnership discussions. It facilitates product comparisons by including key details such as specifications and manufacturers, helping buyers assess options and costs without overwhelming depth. In B2B environments, line cards originated as tools for distributors and representatives to showcase carried lines, evolving from simple lists to structured collateral that underscores supplier relationships. Line cards are particularly common in industries like , (IT), and distribution, where they highlight portfolios without requiring full catalogs. They differ from comprehensive catalogs by emphasizing brevity and strategic summaries over exhaustive technical or pricing data, making them ideal for initial engagements. Key benefits include building client awareness of available solutions, supporting through efficient demonstrations, and differentiating a by illustrating its broad market reach and partnerships in competitive sectors.

Typical contents

A typical business line card serves as a compact tool that outlines a company's offerings, often in a single- or double-sided format, to facilitate quick reference during client interactions. Core elements generally include the company for branding, full contact information such as phone numbers, addresses, and URLs, and a categorized list of products or services grouped by industry, type, or function. Product or service listings typically feature brief descriptions highlighting key features, along with essential specifications like capabilities, dimensions, or performance metrics where relevant, without overwhelming detail. For distributors, these lists often incorporate manufacturer logos and names to demonstrate partnerships and supply chain breadth. Value propositions, such as certifications (e.g., ISO standards) or unique benefits like short lead times and customization options, are commonly emphasized to differentiate the offerings. Visual aids enhance readability and appeal, including high-quality images or icons representing products, icons for service categories, and clean layouts with white space, columns, and color accents to guide the viewer's eye. The front side usually focuses on an overview with branding, a , and high-level summaries, while the back provides detailed listings organized into sections for clarity. In manufacturing contexts, line cards often list industrial products like valves, gauges, or components with specs such as types and ratings, alongside supplier details to validate reach. For IT services, they highlight bundles of software, hardware, or managed solutions, including capabilities like integration or cybersecurity features, tailored to demonstrate comprehensive support. Customization is key, with content adapted to the —for instance, including more technical specifications and diagrams for engineers, or high-level benefits and case studies for executives—to align with contexts where the line card reinforces the company's role in addressing client needs.

Design and best practices

Effective line cards in and are designed to be concise documents, typically limited to one or two pages in PDF or digital formats, to ensure quick consumption by distributors, partners, or prospects during meetings or events. Clean layouts with generous white space promote readability, while high-quality product images or icons visually represent offerings without cluttering the page. Consistent branding elements, such as company logos, color schemes, and , reinforce professional identity and align with broader materials. Best practices emphasize scannability to capture attention in brief interactions, achieved through bullet points for product descriptions, bold headings for categories, and hierarchical text to guide the eye from key benefits to details. Incorporating calls-to-action, like "Contact us for custom quotes" or QR codes linking to full catalogs, drives immediate follow-up. Regular updates—at least annually or with major product changes—keep the content relevant, reflecting new offerings and preventing that could undermine trust. Tools for creation include professional software like for precise layouts and custom graphics, ideal for print-ready versions used at trade shows. For quicker digital iterations, platforms like offer user-friendly templates that support easy customization and export to shareable PDFs or interactive online formats via or websites. Digital line cards excel in remote sharing and analytics tracking, whereas printed ones provide tangible impact in face-to-face networking. Common pitfalls include overloading pages with dense text or excessive specifications, which reduces engagement as prospects scan for value in seconds; instead, focus on benefits over . Outdated information risks eroding credibility, so implement version controls during updates. Generic content without unique selling points fails to differentiate from competitors, and neglecting mobile optimization in digital formats can hinder on devices used in the field. Ensure designs pass basic readability tests across screens and prints. In , well-designed line cards have driven partnerships by integrating brief success stories, such as reduced lead times through featured products, leading to stronger alignments as noted in sales collateral analyses. For example, firms emphasizing customer outcomes in their line cards reported higher engagement in industry guides, facilitating deals by clearly demonstrating value.

References

  1. https://www.pcmag.com/encyclopedia/term/line-card
  2. https://www.techtarget.com/searchitchannel/definition/line-card
  3. https://www.cisco.com/c/en/us/products/collateral/routers/asr-9000-series-aggregation-services-routers/data_sheet_c78-501338.html
  4. https://www.windmillstrategy.com/a-guide-to-manufacturing-sales-and-marketing-collateral-sell-sheets-data-sheets-line-cards/
  5. https://www.cisco.com/c/en/us/td/docs/routers/crs/ec/system/description/lccecsysdescbook/lccecsysdesccards.html
  6. https://www.juniper.net/documentation/us/en/hardware/ptx10004/topics/topic-map/ptx10004-line-card-components.html
  7. https://www.renesas.com/en/document/apn/an549-hc-5502x4x-telephone-subscriber-line-interface-circuits
  8. https://www.cisco.com/c/en/us/td/docs/iosxr/crs/hardware-install/crs-1/4-slot/system-description/b-crs-crs1-4-slot-line-card-chassis-system-description/b-crs-crs1-4-slot-line-card-chassis-system-description_chapter_0101.pdf
  9. https://www.ti.com/lit/pdf/snla133
  10. https://www.juniper.net/documentation/us/en/hardware/qfx10008/topics/topic-map/qfx10000-line-cards.html
  11. https://www.juniper.net/content/dam/www/assets/datasheets/us/en/switches/ex8200-ethernet-line-cards.pdf
  12. https://www.cisco.com/c/en/us/td/docs/routers/crs/ec/system/description/lccecsysdescbook/lccecsysdesccooling.html
  13. https://www.cisco.com/en/US/docs/routers/crs/crs1/16_slot/site_planning/requirements/guide/sitplch3.html
  14. https://www.networkhardwares.com/products/juniper-ex9200-6qs-juniper-ex9200-6qs-line-card
  15. https://www.littelfuse.com/assetdocs/littelfuse-designing-surge-and-power-fault-protection-circuits-for-solid-state-subscriber-line-interfaces-application-note?assetguid=76cdf886-ea46-45a4-bd4e-cf7b3571840b
  16. https://www.cisco.com/c/en/us/products/interfaces-modules/12000-series-16-port-oc-3c-stm-1c-pos-sdh-line-card/index.html
  17. https://www.broadcom.com/news/broadcom-introduces-industrys-first-800g-ai-ethernet-nic
  18. https://www.telephonecollectors.info/index.php/browse/catalogs-manuals-educational-docs-by-company/western-electric-bell-system/publications-and-educational-documents-by-date/blr/11644-70oct-blr-p259-advances-in-the1a2-key-telephone-system/file
  19. https://www.eetimes.com/evolution-of-the-line-card-part-1/
  20. https://www.edn.com/evolution-of-the-line-card-part-2/
  21. https://ethw.org/Milestones:Asymmetric_Digital_Subscriber_Line_%28ADSL%29_Enabling_Broadband_Internet%2C_1993-1997
  22. https://www.nbcnews.com/id/wbna5053279
  23. https://www.edn.com/evolution-of-the-line-card-part-iii/
  24. https://www.lightwaveonline.com/network-design/article/16660577/ptx-series-packet-transport-switch-starts-juniper-networks-down-packet-optical-transport-path
  25. https://fitsmallbusiness.com/wholesale-line-sheet/
  26. https://www.daniellealexanderdesign.com/blog/the-dos-and-donts-of-line-cards-where-manufacturing-deals-begin
  27. https://www.gushwork.ai/blog/line-cards-manufacturing-sales-collateral
  28. https://www.linkedin.com/pulse/how-create-line-card-your-business-nadia-mcdannels-gp4ff
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