Transcript Serial vs. Parallel

Elements of Network
Connectivity
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Serial and Parallel communication
Modems
Modem Pools
ISDN
DSL
Routing
Cable systems
Leased Lines
Other interconnection systems
Serial vs. Parallel
• Serial
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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)
0 1 2 3 4 5 6 7 Stop
Start
Time
Word=01011100
Hex=5C
Ascii= \
Serial Frame (Synchronous)
Bit 7
0
1
2
3 4 5
6
7 0
Time
No start or stop bits, timing synchronized with special ascii
characters (SYN)
c07dem13 and c07dem14
Bits
Parallel
0
0
0
1
1
1
0
1
0
Pulse
1
2
3
4
5
6
7
Strobe
Time
Serial Communications
• Serial Data Stream (asynchronous)
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8 bits data
start/stop bits
Parity bit
baud rate
limits
Errors
c07dem10
Serial Communications
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RS-232 standard
Modems
PC Serial Ports
Speeds
Synchronous/Asynchronous
– Advantages/Disadvantages
• PPP (Point to Point Protocol)
RS232 Standard
+3 to 25
25 ping connector Volts
9 pin connector
Ground
0 volts
Transmit
Receive
Clear to Send
Request to Send
-3 to 25
Carrier Detect
Volts
Data Set Ready
Data Terminal Ready
Ring Detect
Modem Operation
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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)
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Carrier Detect
Requirements for 56K
xDSL (Digital Subscriber Line)
ISDN (digital telephone lines)
PPP Primer
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Point to Point protocol
Physical Layer protocol
Authentication (PAP/CHAP)
Addressing (dynamically assigned)
Client Configuration
Modem Pools
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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
Modems
Modem Controller
$52.50
per line
Ethernet
56K (ISDN) Modem Installation
Controller
Central Office
$33.50
per line
T1’s or
ISDN PRI
Ethernet
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