CIS 173 Networking Week #13 Objectives Grade Homework Chapter #10 Lecture Chapter #12

Chapter 12 Wide Area & Large Scale Networks

WAN Transx. Technologies WAN Spans lg. Geo. Distance Looks & Operates like a LAN Time Delay for Transx. Expensive –Most are leased NOT purchased

WAN Transx. Technologies Connections established using special communications devices –Bridges –Gateways –Routers –Comm. Lines ISP Telco. Special Communications links used to construct a WAN –Packet Switching –Fiber Optic cable –Microwave Transmitters –Satellite Links –Cable TV coax systems

3 Primary Technologies used to Transmit Communications between LAN’s across WAN links Analog Digital Packet Switching

Analog PSTN (Public Switched Telephone Network) –Nearly 40% error rate –POTS (Plain Ol’ Telephone System) (Pg. 346, Table 12-1) –Requires modem for conversion Quality varies substantially from location to location Low quality, but inexpensive Transx. Speed slow Connection highly inconsistent –Greater distances more unreliable Line Conditioning (to sustain consistent transx. Rate) –Line testing & line Upgrades to permit a consistent transx. Rate –Improve overall signal quality

Dial-up vs. Connected Length of connection time required –Daily –Weekly –Monthly Cost of Service & usage level Avail. Of dedicated circuits, conditioning or other quality improvements Assessment of need for a 24/7 connection

Digital Connectivity DDS –Digital Data Service –Direct of Point-to-Point synchronous comm. Links –Quaranteed specified quality & transx. Rate –Nearly 99% error free –Requires Special Communications Devices CSU/DSU –Channel Service Unit/Data Service Unit Added so a bridge or router sends to this unit, this unit sends to a CSU/DSU on receiving end. That CSU/DSU sends to router or bridge on that unit.

DDS Line Types ISDN T1 T3 Switched 56K ADSL SDSL

T1 Two, 2 wire pairs Transx. Full Duplex –Bi-Directional AT SAME TIME –One Transx. & one receives Moderate number of users supported 24 individual channels –Each channel with a data rate of 64 kbps Fractional T-1

Multiplexing a.k.a. MUXING –Enables several communications streams to travel simultaneously over the same cable segment –Combines data transx. From several sources & delivers them over a single cable When received it is decoded to its original form & sent to final destination

Channel Divisions Each channel takes a data sample 8,000 times per second –Each data sample comprises 8 bits –Which produces the data rate of 64 Kbps –This is known as DS-0 Full T1 data rate with all 24 channels is known as DS-1 Table 12-2, pg. 348

T3 28 T1’s 672 Channels Supports a data rate of Mbps Fractional T3 –Data rate of 6 Mbps

Switched 56K Old technology Point-to-point Each time a connection was required a new connection path was created. –No dedicated circuits –When transx. Ended so did circuit

Packet Switching Networks Used over short & long distances Fast, Efficient, Reliable Internet is prime example Original data segmented into packets Packets labeled with sequence order & destination ID (Header) Packets sent individually toward destination Received by host Received by destination (uses sequencing info to reconstruct info to original form)

Virtual Circuits Temporary “dedicated” pathways between two points Bandwidth is allocated for specific transx. Two types: –Switched Virtual Circuits Est. when needed & terminated when complete –Permanent Virtual Circuits Similar to leased Permanent logical connection Exists even when connection is not there

Virtual Private Network Represents temporary or permanent connections across a public network –Like over the Internet Can use protocol –PPTP Point-to-Point Tunneling Protocol –Impenetrable from outside source –Win 95 with a patch or Win 98 user or WIN NT user to dial into an NT Server running RAS »Acts as a private, encrypted, dial-up session

Advanced WAN Technologies X.25 ISDN Frame Relay ATM FDDI SONET SMDS

X.25 Created in mid 1970’s Acted as an interface between public packet-switching networks & their customers It defines how devices communicate over an internetwork. Used standard telephone lines as communications links –Numerous errors –Lost data When accuracy was improved speed was lost –Connect to X.25 via DTE’s (Data Terminal Equip.) & DCE’s (Data Comm. Equip.) NIC for X.25, PAD (Packet Assembler/Disassembler), & a Gateway

ISDN Integrated Services Digital Network (1984) –To replace Analog lines –Defines single channel links of 64 Kbps In 1980’s - 10 Mbps LAN’s were good NOT GOOD TODAY (100 Mbps) –Competition form ADSL & SDSL –2-4 times faster data transx. Rates than POTS modem –Cost is reasonable only if as dial up & not dedicated link –Two formal rates BRI-(Basic Rate Interface) 2 B Channels & a D Channel –B Channel used to transx. & receive voice or data independently of each other or multiplexed together –D channel used for call setup & control PRI (Primary Rate Interface) 23 B Channels & a D Channel –Same bandwidth as a T1 Line

FRAME RELAY Point-to-Point PVC (Permanent Virtual Connection) Rast, Reliaable Digital Packet-Switching Network Does NOT use error checking –Error checking is left to devices at each end –Improves throughput Uses variable length packets or Data Link Layer of OSI Same pathway is used for all comm. –Ensures proper delivery & higher bandwidth rates –Inexpensive –Connects using a pair of CSU’s/DSU’s with router at each end. (Just like T1)

ATM Asynchronous Transfer Mode –High speed packet switching technology –Transx. Rates up to 622 Mbps –An ATM protocol data unit (PDU) is called a “cell” –53 byte length is divided into 48 data bytes & 5 header bytes Header used for sequencing & re-sequencing packets –Typical transx. Speeds are 155 Mbps (HDTV) or 622 Mbps used for 4 signals simultaneously

FDDI Fiber Distributed Data Interface –NOT a WAN technology BUT rather a method of connecting LAN’s with high-speed “ring” networks –Operates at 100 Mbps –Uses Fiber Optic media –Multiple tokens can be used –Made up of two concentric rings (opposite directions) –Limitation is NOT SPEED, BUT DISTANCE Max distance is 100 KM (62 miles) for any given ring Used for mostly relatively close LAN’s

SONET Synchronous Optical Network –Uses fiber optic media to transmit voice, data, & video at speeds in multiples of Mbps –Near faultless communications –Data rates are defined now using OC Levels Optical Carrier Levels –Basic Level is OC-1 »51.84 Mbps –Most Common Level is OC-3 » Mbps –Limit Level is OC-24 »622 Mbps

SMDS Switched Multimegabit Data Service –Inexpensive –High Speed Network Communication –Rate is to 45 Mbps –Uses a 53 byte fixed-length cell just like ATM –No error checking