WANs Flashcards
Circuit-Switched Connection
Connection is brought up only when needed, like making a phone call
On-demand bandwidth can provide cost savings for customers who only need periodic connectivity to a remote site
Packet-Switched Connection
Always on like a dedicated leased line, but multiple customers share the bandwidth
SLAs used to guarantee a certain quality
(5Mbps at least 80% of the time)
Virtual circuits are represented as dashed lines
WAN Physical Media
UTP/STP (analog/digital)
Ex: T1, DSL, Dial-up, ISDN
Coaxial (RG-6)
Ex: cable modems
Fiber Optic Cable
High bandwidth, long distance, no EMI
Electric Power Lines
BPL (Broadband over Power Lines)
Up to 2.7Mbps
WAN Wireless Media
Cellular (See other flash cards)
WiMAX (Worldwide Interoperability for Microwave Access)
Alternative to DSL/Cellular
Wireless fixed location service
802.16
Satellite
HughesNet Gen5
VSAT (Very Small Aperture Terminal)
Used for remote areas (expensive too)
Starlink (Smaller coverage area, more satellites, faster)
High-Frequency Radio
Dedicated Leased Line
Logical connection that connects two sites through a service provider’s facility or telephone company’s central office
More expensive than other WAN tech because customer doesn’t share bandwidth
Point-to-point connection between two sites
(All bandwidth online is available at all times)
Digital circuits are measured in 64kbps channels called DS0 (Digital Signal 0)
CSU/DSU (Channel Service Unit/Data Service Unit)
Terminates the digital signals at customer location
Common circuits:
T1, E1, T3, E3
Metro Ethernet
Service providers are beginning to offer Ethernet interfaces to their customers
Less expensive & more common than specialized serial ports used in CSU/DSU
Tech used by service provider is hidden from customer
Only need to connect their network’s router to Smart Jack
PPP
Point-to-Point Protocol
Commonly used Layer 2 protocol on dedicated leased lines to simultaneously transmit multiple Layer 3 protocols (IP, IPX)
Each layer 3 control protocol runs an instance of PPP’s LCP (Link Control Protocol)
PPP: LCP
Link Control Protocol (Used in PPP)
Multilink interface
Allows multiple physical connections to be bonded together into a logical interface
(Can combine multiple T1s, T3s, etc) - Similar to link aggregation
Looped link detection
Layer 2 loop can be detected & prevented
Error detection
Frames containing errors can be detected & discarded
Authentication
Device on another end can authenticate the link
PPP Authentication: PAP
Password Authentication Protocol
Performs one-way authentication between client/server
Credentials sent in clear text (not secure)
PPP Authentication: CHAP
Challenge-Handshake Authentication Protocol
Performs one-way authentication using a three-way handshake
Credentials are hashed before transmission
PPP Authentication: MS-CHAP
Microsoft Challenge-Handshake Authentication Protocol
Microsoft-enhanced version of CHAP, includes two-way authentication
PPPoE
PPP over Ethernet
Commonly used with DSL modems
Encapsulates PPP frames within Ethernet frames
Allows for authentication over ethernet
ADSL
Asymmetric Digital Subscriber Line
Max distance to DSLAM: 18,000 ft
Voice & data on same line
Downstream: up to 8 Mbps
Upstream: up to 1.544 Mbps
SDSL
Symmetric Digital Subscriber Line
Max distance to DSLAM: 12,000 ft
NO simultaneous voice & data on same line
Downstream: 1.168 Mbps
Upstream: 1.168 Mbps
VDSL
Very High-Bit Rate DSL
Max distance to DSLAM: 4,000 ft
Downstream: up to 52 Mbps
Upstream: up to 12 Mbps
Cable Modems
HFC (Hybrid Fiber-Coax) distribution network is a cable TV infrastructure containing both fiber/coax
Specific frequency ranges used for upstream/downstream data transmission
Determined by DOCSIS (Data-over-cable service interface specification)
Satellite Modems
Used in remote/rural locations where other connections are unavailable
Provides relatively fast speeds like DSL, but low bandwidth usage limits & high cost (especially when over limit)
Issues: Weather conditions can cause loss of connectivity
Delays (time to satellite & back = > 0.25 sec)
POTS
Plain Old Telephone Service
PSTN (Public Switched Telephone Network) consists of telephone carriers around the world
Analog connections (voice and/or data) using PSTN are POTS connections
53.3 Kbps max bandwidth
(Can only access one 64 Kbps channel at a time)
ISDN (2 Channels)
Integrated Services Digital Network
Supports multiple Bearer (B) channels - 64 Kbps
Older tech used to carry voice/video/data
Delta (D) channel existed for 64Kbps signaling data
BRI (Basic Rate Interface)
Two 64Kbps B channels with 16Kbps D channel
PRI (Primary Rate Interface)
1.472Mbps data pather over 23 B channels
64Kbps D channel
Frame Relay
Losing market share due to cable & DSL
Frame relay sites connected to virtual circuits
VCs = point-to-point or point-to-multipoint
Low cost, widely available
Always-on or On-demand
Layer 2 tech
SONET
Synchronous Optical Network
Layer 1 tech using fiber as media
Transports layer 2 encapsulation (like ATM)
High data rates (155Mbps to 10Gbps)
Covers large distances (20km to 250km)
Physical topology = bus or ring
ATM (& cell size [header/payload])
Asynchronous Transfer Mode (Fiber & SONET networks!)
Layer 2 WAN tech operating using PVCs & SVCs (Permanent Virtual Circuits & Switched Virtual Circuits)
Similar to frame relay, except all frames are transferred as fixed-length “cells” as its PDU (protocol data unit)
Fixed-length cells of 53-bytes used to increase speed of transmissions
(5-byte header & 48-byte payload)
ATM Virtual Circuits
UNI (User-Network Interface)
Used to connect ATM switches & endpoints
NNI (Network-Node Interface)
Used to connect ATM switches together
MPLS
Multiprotocol Label Switching
Supports multiple protocols on the same network (used by ISPs, not end-users)
Support both frame relay & ATM on same backbone
Allows traffic to be dynamically routed based on load conditions & path availability
Label switching is more efficient than Layer 3 IP routing
