Elements of Network Connectivity

• Serial and Parallel communication• Modems• Modem Pools• ISDN• DSL• Routing • Cable systems• Leased Lines• Other interconnection systems

Serial vs. Parallel

• Serial– needs one wire plus return per direction

– bits are sequenced by time slicing

– needs synchronization

– needs handshaking codes or lines

• Parallel– all bits sent at one time

– needs 1 wire per bit

– needs handshaking lines

Serial Frame (Async)

Time

Start

0 1 2 3 4 5 6 7 StopWord=01011100 Hex=5C Ascii= \

Serial Frame (Synchronous)

Bit 7 0 1 2 3 4 5 6 7 0

No start or stop bits, timing synchronized with special asciicharacters (SYN)

c07dem13 and c07dem14

Time

Parallel

0

123

45

Bits

6

7

Strobe

Time

001110

10

Pulse

Serial Communications

• Serial Data Stream (asynchronous)– 8 bits data– start/stop bits– Parity bit– baud rate– limits– Errors– c07dem10

Serial Communications

• RS-232 standard

• Modems

• PC Serial Ports

• Speeds

• Synchronous/Asynchronous– Advantages/Disadvantages

• PPP (Point to Point Protocol)

RS232 Standard

25 ping connector9 pin connectorGroundTransmitReceiveClear to SendRequest to SendCarrier DetectData Set ReadyData Terminal ReadyRing Detect

0 volts

+3 to 25Volts

-3 to 25 Volts

Modem Operation

• Modulator/Demodulator (Digital to Analog)• Use a standard (Hayes) command set.• Dialup Sequence• Training/Speed Negotiation

– Error detect and compression/decompression– Latest and greatest (??) is V.90 (56KB)

• Carrier Detect• Requirements for 56K• xDSL (Digital Subscriber Line)• ISDN (digital telephone lines)

PPP Primer

• Point to Point protocol

• Physical Layer protocol

• Authentication (PAP/CHAP)

• Addressing (dynamically assigned)

• Client Configuration

Modem Pools

• Requirements

• ISDN BRI lines (single connection)

• ISDN PRI (23 BRI) lines (equal a T1)

• Tariffs (QWest)

• Multiplexing BRI’s to save $$

• Central Office Switch

• Line selection/hunting

PPP Installation

Modem

Controller

Ethernet

$52.50per line

Modems

56K (ISDN) Modem Installation

Central O

ffice

EthernetT1’s orISDN PRI

Controller

$33.50per line

ISDN

• Handles Voice, Data, Video• Each BRI (Basic Rate Interface) has 2 64 Kbps

lines, either can be used for data or voice, combined gives 128 Kbps data.

• BRIs and PRIs (Primary Rate Interface)– BRI 64 Kbps, 128 Kbps– PRI 1544 Kbps (23 BRIs)

• Dial up standard– Each line has a phone number

DSL

• Asymmetric Digital Subscriber Line• Asymmetric (High speed downlink, slow uplink)• Uses existing telephone cabling to the DSL modem

router• Modem/router typically provides ethernet connection

to your LAN• Uses existing telephone devices for voice (single

twisted pair)• Simultaneous data and voice• Distance limitation from central office (12000 feet)

DSL

• Digital Subscriber Link– ADSL Asymmetric DSL– xDSL

• 18000 foot radius of Central Office• Speeds to 1,544 KB downstream

– 640 kbps upstream

• Simultaneous voice/data• Uses existing telephone twisted pair

More DSL

• HDSL High Speed DSL– 2 Mbps at 3 miles of cable

• VDSL Very High Speed DSL– 52 MBS downstream, 1.5-2.3 MBS upstream– 3000 foot limit

• SDSL Symmetric DSL– 1.544 MBps up and down, 11000 foot limit

Even More DSL

• Pricing: $45/month and up

• http://www.qwest.com/residential/products/dsl/index.html

• Requires:– Telephone line (POTS)– DSL Modem– External Modem requires Ethernet to the PC

Routing

• Routers operate at the Network layer• They use tables to keep track of the best path from

source to destination• They segment the network based on Network layer

traffic• They filter broadcast traffic to a single port on the

router• Routers listen on the ports and determine the best path

using OSPF (open shortest path first), RIP (Routing Information Protocol), or NSLP (NetWare Link Services Protocol) for IPX

Routing Continued

• Some protocols don’t route:– Netbeui– Local Area Transport (DEC)

• Routers can be either:– Static, addresses to other routers are fixed– Dynamic, addresses to other routers are discovered

automatically.

• Routers can use multiple links to another site to take advantage of available bandwidth on each link.

Gateways

• Gateways are like routers but switch between protocols

• Example:– Token-Ring to ethernet– IBM HDLC/SNA to Internet TCP/IP

• Because of the switching algorithms needed they are usually slow.

Radio and Satellite

• Bandwidth versus available frequencies

• High Power and Broad Bandwidth requires FCC licensed equipment

• Interference (electrical, atmospheric, animal)

• Timing problems ( 1 foot = 1 ns.)– 23500 miles to satellite ( .25 sec round trip)

Cable TV modems

• Use existing cable installation

• Uses broadband network technology via fiber optics and coaxial cable

• Asymmetric (8 MB down/1 MB up)

• Costs about $40.00/month

RAS

• Remote Access Service– NT interconnection system– Can use several different media including

dialup– Can filter specific protocols, it can audit

connections and use Callback security.– Works up to about 128 kbps.

Telco Leased Line Networks

• ISDN• DSL• T1, DS1, T3, DS3

– T1 is 1.544 Mpbs– Interfaces, CSU/DSU, Framing– CSU/DSU Channel Service Unit/Data Service Unit

• OC1, OC3, OC12– Optical Circuits, OC1 is 51.84 Mbps, OC3 is 155.52

Mbps

Leased Lines

• DS-1/T1 1.544 Mbps or 24 voice channels• DS3/T3 44.736 Mbps (28 T1s), 672 voice• Packet Switched

– Uses best route– Uses small packets

• Virtual Circuit Packet Switching– Bandwidth Allocated on demand– SVC (Switched Virtual Circuit)– PVC (Permanent Virtual Circuit)

Frame Relay

• Fast, variable length, packet switching network.

• Uses PVCs for point to point communication

• Provides customers with variable rate bandwidth, customers share bandwidth with other customers.

ATM (Asynchronous Transfer Mode)

• Used for high speed data communications primarily by common carriers (Telco).

• Uses cell relay rather than variable length frames

• ATM is expensive and fairly complicated to set up and troubleshoot.

FDDI

• Fiber Distributed Data Interface• Dual Ring (Token ring topology)

– Redundant (Fault Tolerant)

• Handles long distances (because of fiber)– 200 kilometers (124 miles)– immune to electromagnetic noise/interference

• 100 Mbps• Protocol includes built in troubleshooting• Interfaces are fairly expensive

SONET (Synchronous Optical Network)

• Fiber Optic Gigabit communications protocol.

• Standard for long distance high speed transport of data and voice

• Basic transmission unit is STS-1 at 51.84 Mbps up to STS-192 or 9,953.28 Mbps