Network+ – Day 29 WAN Technologies Essentials

Circuit switching
- Requires a dedicated path for the whole session
- Example: ISDN BRI/PRI
- Pros: predictable performance
- Cons: path sits idle when no traffic; setup delay
Packet switching
- Data broken into packets, each routed independently
- Examples: Frame Relay, ATM, MPLS, the Internet
- Pros: bandwidth shared on demand, reroutes around failures
- Cons: variable delay, potential for loss

PSTN Dial-up: max $53.3\,\text{kbps}$ down / $48.0\,\text{kbps}$ up
ISDN
- BRI: $2\times64\,\text{kbps B} + 16\,\text{kbps D}$
- PRI: $23\times64\,\text{kbps B} + 64\,\text{kbps D} = 1.544\,\text{Mbps}$ (T1)
xDSL (asym & sym)
- ADSL: up to $24\,\text{Mbps}$ down / $1!!−!2\,\text{Mbps}$ up
- VDSL: up to $52\,\text{Mbps}$ (short loop)
PPP over serial/DSL
- LCP + IPCP; supports PAP, CHAP, MS-CHAP; Multilink & loop detect
Cable (DOCSIS)
- Shared coax/HFC; always-on; $100{+}\,\text{Mbps}$ possible

Satellite
- One-way (downlink only) vs. two-way (full duplex)
- High latency (≈ $500\,\text{ms}$ RTT) + weather fade
WiMAX (IEEE $802.16$ )
- Metropolitan coverage; up to $1\,\text{Gbps}$ fixed / $100\,\text{Mbps}$ mobile
Cellular
- 3G, 4G, LTE, HSPA+; LTE ≈ $100\,\text{Mbps}$ mobile / $1\,\text{Gbps}$ stationary

Fiber ring or linear, DWDM for long reach
OC levels: OC-1 $51.84\,\text{Mbps}$ , OC-3 $155.52\,\text{Mbps}$ … OC-192 $9.953\,\text{Gbps}$

CSU/DSU terminates circuit at CPE
T-Carrier
- T1 $1.544\,\text{Mbps}$ (DS1 $24\times64\,\text{kbps}$ )
- T3 $44.736\,\text{Mbps}$ (DS3 $672\,\text{DS0}$ )
E-Carrier (outside NA)
- E1 $2.048\,\text{Mbps}$ , E3 $34.368\,\text{Mbps}$

Frame Relay
- PVC identified by DLCI; CIR guarantees; FECN/BECN/DE bits manage congestion
ATM
- Fixed $53$ -byte cell ( $5$ -byte header + $48$ payload ); VPI/VCI = path + circuit
MPLS
- Inserts $32$ -bit shim label; LSR/ELSR switch on labels; unifies Frame & ATM backbones
Metro Ethernet
- Pure Ethernet hand-off at MAN speeds; service provider manages virtual circuits (E-Line, E-LAN)