Local Area Networks (LAN)

Local Area Networks exist to serve applications. The cables, switches, and access points we've studied are means to an end—enabling people and systems to communicate, share resources, and accomplish work. Understanding LAN applications helps network professionals design infrastructure that meets actual business needs rather than arbitrary technical specifications.

LAN applications span a remarkable range—from simple file sharing to real-time financial trading systems, from basic printing to immersive video conferencing, from centralized backups to distributed computing clusters. Each application has unique requirements for bandwidth, latency, reliability, and security. A network that excels at bulk file transfers might fail miserably for voice communications if designed without understanding these requirements.

This page explores the major categories of LAN applications, their technical requirements, and the network design considerations each demands.

File sharing was the original driving force behind LAN development. The ability to access shared files without physical media exchange remains fundamental to organizational productivity.

Server-Based File Sharing:

Centralized file servers provide:

• Organized storage: Hierarchical folder structures with consistent naming
• Access control: Permissions based on user identity and group membership
• Data protection: Centralized backup, RAID storage, replication
• Auditing: Logs of who accessed what files and when

Common File Sharing Protocols:

SMB (Server Message Block):

SMB is the dominant file sharing protocol in enterprise environments:

• SMB1: Original version, deprecated due to security vulnerabilities (WannaCry exploit)
• SMB2: Improved efficiency with larger reads/writes, pipelining, compounding
• SMB3: Encryption, multi-channel, transparent failover, RDMA support

Performance Considerations:

• Sequential access: Large file transfers benefit from high throughput
• Random access: Database-like workloads need low latency
• Metadata operations: Many small files stress directory services
• Concurrency: Multiple users accessing same files requires careful locking

Network Requirements:

Modern Approaches:

• DFS (Distributed File System): Namespace aggregation across multiple servers
• File sync services: OneDrive, SharePoint providing cloud-integrated access
• Object storage: S3-compatible storage for large-scale unstructured data

Network printing enables shared access to printing resources, reducing costs and improving management compared to direct-connected printers.

Print Architecture Components:

1. Network Printers:

• Direct network connection via Ethernet or Wi-Fi
• Built-in print server functionality
• Support multiple protocols (IPP, LPD, RAW/JetDirect)
• Web-based management interfaces

2. Print Servers:

• Centralize print queue management
• Handle driver distribution
• Provide accounting and auditing
• Enable location-based printing

3. Print Clients:

• Submit jobs to print queues
• Use network or locally-installed drivers
• May require specific protocols based on environment

Print Protocols:

Enterprise Print Management:

Pull Printing (Secure Print Release):

• Jobs held in central queue until user authenticates at printer
• Prevents sensitive documents sitting in output trays
• Enables print-anywhere (release job at any printer)
• Commercial solutions: PaperCut, Equitrac, uniFLOW

Print Tracking and Accounting:

• Track usage by user, department, cost center
• Implement quotas and chargeback
• Identify waste and optimization opportunities

Network Requirements for Printing:

Printing is surprisingly network-intensive:

• Complex documents (graphics, high-resolution images) can be many megabytes
• A 100-page color presentation might be 100+ MB
• Time-sensitive printing requires consistent throughput
• Print server to printer links should be prioritized

Common Issues:

Voice over IP has largely replaced traditional telephony in enterprise environments. VoIP transforms voice communication into data packets that traverse the same LAN infrastructure as other traffic—but with stringent performance requirements.

VoIP Architecture:

IP Phones:

• Digitize voice, encode using codecs (G.711, G.722, G.729, Opus)
• Connect via Ethernet, often with passthrough for PC
• Powered via PoE (802.3af/at)
• Signaling via SIP, SCCP, or H.323

Call Control Systems:

• IP PBX: On-premises call processing (Cisco CUCM, Avaya, Asterisk)
• Cloud UC: Microsoft Teams, Zoom Phone, RingCentral
• SIP Trunk: Connection to PSTN via SIP-enabled carrier

VoIP Codecs:

Network Requirements for VoIP:

VoIP is extremely sensitive to network performance issues:

Latency:

• One-way delay should be <150ms for acceptable quality

• 300ms causes noticeable awkwardness in conversation

• LAN latency is typically negligible; WAN/internet hops add delay

Jitter:

• Variation in packet arrival times
• Causes gaps, distortion, or robotic sound
• Target: <30ms jitter buffer can compensate

Packet Loss:

• Even 1% packet loss severely degrades voice quality
• No retransmission (UDP) means lost packets = lost audio
• Target: <0.1% packet loss for high quality

QoS Requirements:

VoIP must be prioritized over bulk data traffic:

1. Classification: Identify voice traffic by DSCP marking (EF - Expedited Forwarding)
2. Prioritization: Place voice in strict priority queue
3. Bandwidth Reservation: Ensure sufficient bandwidth for call capacity
4. QoS Trust: Configure switch ports to honor markings from IP phones

Voice VLAN:

Best practice separates voice and data into distinct VLANs:

• Simplifies QoS policy application
• Isolates voice traffic from data broadcast storms
• Enables different security policies
• Facilitates 802.1X authentication for phones

Video is among the most demanding LAN applications, consuming significant bandwidth while requiring consistent performance. Video applications range from one-on-one video calls to large-scale surveillance systems with hundreds of cameras.

Video Conferencing:

Modern video conferencing platforms (Teams, Zoom, WebEx) are essential for remote collaboration:

Bandwidth Requirements:

Screen Sharing: Screen sharing can be more bandwidth-intensive than video when content changes frequently (scrolling, animations). Static content compresses well; dynamic content may use 2-5 Mbps.

Video Surveillance (CCTV):

IP-based video surveillance places sustained, predictable load on networks:

Camera Bandwidth Calculation:

Bandwidth = Resolution × Frame Rate × Color Depth × Compression Factor

Example: 1080p @ 30fps with H.264 compression

• Typical: 4-8 Mbps per camera
• High-motion scenes may spike higher

Surveillance Network Design:

• Dedicated VLAN: Separate from user traffic for security and performance
• Aggregation: Edge switches must handle aggregate camera traffic to uplinks
• Storage bandwidth: NVR/VMS servers require massive ingest capability
• Retention: 30-day retention at 4 Mbps/camera = 1.3 TB per camera

Digital Signage:

LAN-connected displays for information, advertising, and wayfinding:

• Content pushed from central management server
• Bandwidth varies: 100 Mbps burst for content updates, near-zero when static
• Often on dedicated VLAN for security
• Player devices may need PoE or nearby power

Streaming Media:

• Internal training videos, town halls, corporate communications
• Multicast delivery can dramatically reduce bandwidth for popular streams
• Consider caching proxies for repeated access to the same content

Directory services provide centralized identity management—the foundation for authentication, authorization, and policy enforcement across the LAN.

Active Directory Domain Services (AD DS):

Microsoft's Active Directory remains dominant in enterprise environments:

• User authentication: Kerberos-based single sign-on
• Computer management: Group Policy for configuration enforcement
• Resource authorization: ACLs based on AD identity
• DNS integration: AD-integrated DNS zones
• Certificate services: Enterprise PKI integration

AD Network Requirements:

Domain Controller Placement:

For reliable authentication and fast logon:

• At least one DC in each physical location
• Read-Only Domain Controllers (RODCs) for branch offices with limited security
• DNS servers colocated with DCs
• Proper site topology for replication efficiency

LDAP and Other Directory Services:

• OpenLDAP: Open-source directory for Linux environments
• Azure AD (Entra ID): Cloud-based identity for modern applications
• RADIUS: Authentication for network access (Wi-Fi, VPN, NAC)

DNS in the LAN:

DNS is the most critical network service after basic connectivity:

• Without DNS, users can't locate servers by name
• Authentication fails if DNS is unreliable
• AD-integrated DNS provides secure dynamic updates
• Split-horizon DNS may be needed for internal vs. external views

DHCP:

Dynamic Host Configuration Protocol automates IP address assignment:

• Centralized or distributed DHCP servers
• DHCP relay (IP helper) when server not on local subnet
• Lease times balanced between stability and address utilization
• DHCP snooping for security (prevent rogue DHCP servers)
• Reservations for critical devices needing stable IPs

Network management encompasses the tools and services that enable administrators to configure, monitor, and troubleshoot the LAN infrastructure itself.

Management Protocols:

Monitoring Systems:

Out-of-Band Management:

For critical infrastructure, management should not depend on the production network:

• Dedicated management VLAN: Isolated from user traffic
• Dedicated management interfaces: Separate NICs for management
• Console servers: Serial access when network is down
• Out-of-band network: Physically separate management path

Automation and Orchestration:

Modern LAN management increasingly relies on automation:

• Ansible: Agentless automation for device configuration
• Python/netmiko: Programmatic device interaction
• Terraform: Infrastructure-as-code for cloud-managed networks
• CI/CD pipelines: Automated testing and deployment of network changes

Beyond general-purpose services, many organizations run mission-critical applications on their LANs—applications where network performance directly impacts business outcomes, safety, or regulatory compliance.

Database Applications:

Database traffic has unique characteristics:

• Random I/O patterns: Unlike file streaming, databases access data unpredictably
• Latency sensitivity: Each database query may require multiple network round-trips
• Replication traffic: Synchronous replication requires very low latency between nodes
• Backup windows: Full backups move massive data volumes on schedule

Requirements:

• Low, consistent latency (<1ms ideal for on-LAN databases)
• High throughput for bulk operations
• Dedicated storage network (iSCSI, FC) for SAN-attached databases
• QoS for replication traffic in mixed environments

ERP/Business Systems:

Enterprise Resource Planning systems (SAP, Oracle, workday) are operational lifelines:

• Multi-tier architecture: Database → application servers → web frontend
• Sensitive to latency between tiers
• May have specific network requirements from vendor
• Often require session affinity (sticky connections)

Healthcare Systems:

Financial Trading:

Financial applications have extreme requirements:

• Ultra-low latency: Nanoseconds matter for high-frequency trading
• Deterministic performance: Consistent latency more important than average
• Redundancy: Zero tolerance for network failures during market hours
• Specialized NICs: Kernel bypass, timestamping, FPGA acceleration

Industrial Control (OT Networks):

• SCADA/ICS systems controlling physical processes
• Often use specialized industrial protocols (Modbus, EtherNet/IP, PROFINET)
• Strict segmentation from IT networks (Purdue Model)
• Real-time requirements: missed packets may cause equipment damage
• Long lifecycle equipment: 20+ year-old devices still in production

Virtualization and Cloud:

• vMotion/Live Migration: Moving running VMs requires high bandwidth, low latency between hosts
• Storage traffic: iSCSI, NFS, or vSAN traffic flows over LAN
• East-West traffic: VM-to-VM communication within the same data center
• Overlay networks: VXLAN/GENEVE add encapsulation overhead

We've explored the diverse applications that LANs support—from fundamental infrastructure services to demanding real-time and mission-critical applications. Understanding these applications is essential for designing networks that meet actual business needs.

What's Next:

Now that we understand LAN applications, we'll explore practical home and office LAN implementations. The next page examines how LAN concepts apply to real-world deployments—from small home networks to enterprise office environments.