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Application Layer Services & Data Communications

CTS1305C Cable Run -- Week 3

Client-Server | Web/Email/File | QoS | VoIP & Streaming

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Slide 2 of 13

Client-Server Model

The Foundation of Network Services

How It Works

Client initiates requests for resources or services
Server listens on well-known ports and responds to requests
Centralized resources: easier to manage, back up, and secure
Scalable -- add more servers to handle more clients

Peer-to-peer (P2P) is the alternative: each device acts as both client and server. Used in file sharing (BitTorrent) and ad-hoc networks.

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Web Services Architecture

How the Web Delivers Content

Web Server Components

HTTP daemon (Apache, Nginx, IIS) listens on port 80/443
Serves static content: HTML, CSS, JS, images
Proxies dynamic requests to application servers
Virtual hosting: one server, multiple domains

URL Anatomy

https://www.example.com:443/path/page.html

scheme://host:port/path

                        REST APIs
                        Representational State Transfer
Uses standard HTTP methods (GET, POST, PUT, DELETE)
Returns data in JSON or XML format
Stateless -- each request carries all needed context
Powers mobile apps, SPAs, microservices

                    

Load Balancing

Distributes incoming requests across multiple servers for high availability and performance. Round-robin, least connections, and IP hash are common algorithms.

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Email Architecture

The Full Mail Delivery Pipeline

Email Security

SPF -- DNS TXT record listing authorized sending servers
DKIM -- Digital signature proving message was not altered
DMARC -- Policy defining how to handle SPF/DKIM failures
STARTTLS -- Upgrades SMTP to encrypted connection

Common Email Threats

Phishing -- spoofed sender, malicious links
Open relay -- misconfigured MTA forwarding spam
Business Email Compromise (BEC)
Attachment-based malware delivery

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File Sharing Protocols

SMB and NFS

SMB (Server Message Block)

Port 445 (TCP) -- also uses 137-139 for legacy NetBIOS
Windows-native file and printer sharing
Supports authentication, permissions, encryption (SMB3)
UNC path: \\server\share\folder
Samba implements SMB on Linux/macOS

                        NFS (Network File System)
                        Port 2049 (TCP/UDP)
Unix/Linux-native file sharing
Transparent remote file access -- appears local
NFSv4 adds security with Kerberos
Mount path: server:/export/data

                    

SMB vs NFS Comparison

Feature	SMB	NFS
Primary OS	Windows	Linux/Unix
Port	445	2049
Authentication	NTLM/Kerberos	Host-based / Kerberos (v4)
Encryption	SMB3 built-in	Kerberos or VPN tunnel
Use Case	Enterprise Windows file shares	Linux servers, NAS appliances

Slide 6 of 13

Directory Services

LDAP and Active Directory

LDAP (Port 389 / 636 LDAPS)

Lightweight Directory Access Protocol
Hierarchical database of users, groups, computers
Distinguished Name (DN): CN=jsmith,OU=IT,DC=company,DC=com
Supports search, add, modify, delete operations
LDAPS (port 636) adds TLS encryption

Active Directory (AD)

Microsoft implementation built on LDAP + Kerberos
Centralized authentication for Windows domains
Group Policy: enforce security settings at scale
Single Sign-On (SSO) across domain resources
Domain controllers replicate the directory

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Network Management -- SNMP

Traps, Polling, and MIBs

SNMP Architecture

Manager -- central station that queries and collects data
Agent -- software on each managed device
MIB -- Management Information Base: database of device variables (OIDs)

Polling vs Traps

Polling: Manager queries agents at intervals (GET requests)
Traps: Agents send unsolicited alerts when thresholds are exceeded
Best practice: combine both for comprehensive monitoring

SNMP Versions

Version	Auth	Encryption	Status
v1	Community string (plaintext)	None	Legacy -- avoid
v2c	Community string (plaintext)	None	Common but insecure
v3	Username + auth hash	AES/DES	Recommended

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Quality of Service (QoS)

Prioritizing Network Traffic

What is QoS?

QoS is a set of techniques that manage bandwidth, latency, jitter, and packet loss to ensure critical traffic gets priority.

Bandwidth -- total throughput capacity
Latency -- delay from source to destination
Jitter -- variation in latency over time
Packet loss -- percentage of dropped packets

                        QoS Mechanisms
                        Classification -- identify traffic type (VoIP, video, web)
Marking -- tag packets with priority (DSCP, CoS)
Queuing -- place packets in priority queues
Shaping -- smooth traffic bursts to match bandwidth
Policing -- drop or remark traffic exceeding limits

                    

Traffic Priority Tiers

Priority	Traffic Type	Sensitivity
Highest	VoIP / Video conferencing	Latency + jitter critical
High	Business applications (ERP, CRM)	Latency sensitive
Medium	Web browsing, email	Moderate tolerance
Low	File downloads, backups	Delay tolerant

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VoIP & SIP

Voice Over IP Networks

VoIP (Voice over IP)

Converts analog voice to digital packets
Transmitted over IP networks instead of PSTN
Uses RTP (Real-time Transport Protocol) for media
Codec compresses audio (G.711, G.729)
Requires low latency (under 150ms one-way)
Jitter buffers smooth out packet timing variations

                        SIP (Session Initiation Protocol)
                        Signaling protocol for VoIP -- sets up, manages, tears down calls
Port 5060 (unencrypted) / 5061 (TLS)
SIP INVITE initiates a call session
SIP BYE terminates the call
Works with SDP (Session Description Protocol) to negotiate media parameters

                    

VoIP Challenges

Latency degrades call quality
Jitter causes choppy audio
Packet loss creates gaps in speech
NAT traversal issues with SIP (use STUN/TURN)

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Streaming Protocols

Delivering Audio and Video Over Networks

RTSP

Port 554

Real-Time Streaming Protocol
Controls media playback (play/pause/seek)
Used by IP cameras, media servers
Does not carry the media itself

RTP/RTCP

Dynamic ports (UDP)

RTP carries the actual audio/video data
RTCP provides quality feedback (jitter, loss)
Typically used with SIP for VoIP
UDP-based for low latency

HLS / DASH

HTTP-based (TCP 80/443)

Adaptive bitrate streaming
Video split into small segments
Quality adjusts to bandwidth
Used by Netflix, YouTube, Twitch

Multicast vs Unicast

Unicast: One sender to one receiver. Each stream is a separate copy. Simple but bandwidth-heavy for many viewers.

Multicast: One sender to many receivers. Single stream, routers replicate. Efficient for IPTV, live events. Uses 224.0.0.0/4 range.

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Data Communication Concepts

How Data Flows Across Networks

Transmission Modes

Simplex: One direction only (TV broadcast, keyboard)
Half-duplex: Both directions, but only one at a time (walkie-talkie, 802.11 WiFi)
Full-duplex: Simultaneous two-way communication (telephone, modern Ethernet)

                        Bandwidth vs Throughput
                        Bandwidth: Maximum theoretical data rate (Gbps)
Throughput: Actual data rate achieved in practice
Goodput: Useful data throughput minus overhead
Throughput is always less than bandwidth due to protocol overhead, congestion, errors

                    

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Proxy Servers & Caching

Intermediaries That Optimize and Protect

Forward Proxy

Sits between clients and the internet
Clients send requests to the proxy, which fetches on their behalf
Content filtering -- block restricted sites
Caching -- store frequently accessed content locally
Anonymity -- hides client IP from destination server

                        Reverse Proxy
                        Sits in front of servers, facing the internet
Clients connect to the proxy, which forwards to backend servers
Load balancing across multiple servers
SSL termination -- handles encryption
DDoS protection and WAF integration

                    

Caching Benefits

Reduces bandwidth consumption by serving locally stored copies
Decreases load times for end users
CDNs (Content Delivery Networks) are distributed caching systems -- edge servers worldwide

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Week 3 Summary

Application Layer Services & Data Communications

Service Models

Client-server vs peer-to-peer
Web services and REST APIs
Email: MUA, MTA, MDA pipeline
File sharing: SMB and NFS

Infrastructure

Directory services: LDAP, Active Directory
SNMP: polling, traps, MIBs
Proxy and reverse proxy
Caching and CDNs

Data Communications

QoS: bandwidth, latency, jitter
VoIP: SIP signaling, RTP media
Streaming: RTSP, HLS, DASH
Simplex, half/full-duplex

Up Next

Week 4: Network Design & Security -- topologies, VLANs, firewalls, VPN, and troubleshooting.

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