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Networking Essentials

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									Networking Essentials

  Chapter 9 – Communication
            Circuits



        RVCC - CISY 219 - Fall 2004 - TWE   1
 Terms You Should Know
Circuit – the path over which two-way
communication takes place (line)
Link – a segment of a circuit between
two points (nodes)
Node – (1) a functional unit that
connects two links; (2) an end point on
a circuit or a junction point of two or
more circuits

            RVCC - CISY 219 - Fall 2004 - TWE   2
Figure 9-1   Links are segments of a circuit. Nodes
connect links or lines or may be an end point on a link.




                     RVCC - CISY 219 - Fall 2004 - TWE     3
    Terms You Should Know
Channel - a subdivision of a circuit
which is a one way path for
communication
Forward Channel – high speed for data
Reverse Channel - low speed for
control
Broadband (imprecise term)
   On a LAN, a multi-channel, analog circuit
    using COAX
   On a WAN, a high speed circuit, 256Kbps
    or more
                RVCC - CISY 219 - Fall 2004 - TWE   4
   Point-to-Point Circuits
A circuit connecting two and only two
nodes
Example is a standard telephone call




            RVCC - CISY 219 - Fall 2004 - TWE   5
     Multi-Point Circuits
Several nodes are connected to the
same circuit
Less expensive than having separate
point-to-point circuits
Useful for handling low volume traffic
from multiple nodes; line sharing
without impact
Normally found in WANs

            RVCC - CISY 219 - Fall 2004 - TWE   6
Figure 9-2  Types of circuits with nodes A, B, C, D, and
the host computer.




                     RVCC - CISY 219 - Fall 2004 - TWE     7
 2-wire and 4-wire Circuits
Normally, 2 wires are required to carry
a communication in one direction
2-wire is inherently half-duplex while 4-
wire is full-duplex
Using analog multiplexing techniques,
a 2-wire circuit can provide full duplex
service (e.g., DSL)


             RVCC - CISY 219 - Fall 2004 - TWE   8
 2-wire and 4-wire Circuits
Normally, in a 4-wire circuit, 2 wires
provide transmission in one direction;
the other 2 wires in the other direction
2-wire is common; your telephone
4-wire circuits are consider special
services and must be ordered and
leased from the Carrier


             RVCC - CISY 219 - Fall 2004 - TWE   9
         Analog Circuits
Requires modems in pairs to transmit and
receive data
Limited in speed; more susceptible to errors
than digital
Sub-voice – telegraph, teletypewriter; low
speed, 45-200bps; alarms
Voice-grade – for voice and data up to
56Kbps
Wide-band – multiplex voice and data; 48000
Hz subdivided into 4 Hz channels

              RVCC - CISY 219 - Fall 2004 - TWE   10
         Digital Circuits
Designed for digital traffic end to end
Pulses are easier to detect and
regenerate (than sine waves)
Lower error rate than Analog
No conversion (modem) necessary
CSU/DSU interface to Carrier circuit



             RVCC - CISY 219 - Fall 2004 - TWE   11
Figure 9-3   Amplification of an analog signal.




                  RVCC - CISY 219 - Fall 2004 - TWE   12
Figure 9-4   Regeneration of a digital signal.




                  RVCC - CISY 219 - Fall 2004 - TWE   13
       T-Carrier Systems
A family of high speed, digital
transmission systems
Each member is designated by its
speed (or capacity)
T1 = 1.544 Mbps; T2 = 6.312 Mbps; T3 =
44.73 Mbps; T4 = 274.170 Mbps
T1 and T3 used by carrier and customer
T2 and T4 used for inter-office trunking
            RVCC - CISY 219 - Fall 2004 - TWE   14
       T-Carrier Systems
T1 uses standard pairs of copper cable
T1 has 24 circuits of 64 Kbps each and
an 8 Kbps signaling (control) channel
T’s are subdivided by multiplexing
T3 has 28 channels each at T1 speed
T1 channels on a T3 can be further
subdivided like a T1


            RVCC - CISY 219 - Fall 2004 - TWE   15
          Fractional T1
Offers lower capacity circuits than a full
T1 (64, 128,…Kbps) which can be used
separately or combined
Essentially offers one or more channels
for customer defined use (voice,
data,…)
Breakpoint between Fractional T1 and
full T1 is 768 Kbps

             RVCC - CISY 219 - Fall 2004 - TWE   16
Digital Subscriber Line (DSL)
Designed to compete with CATV
Digital service end to end over copper
wire ( 2 pair )
Point-to-point from customer to CO
over local loop
VERY sensitive to distance
Actual speeds depend on distance from
CO, quality of wire in local loop, and
overall quality of the circuit
            RVCC - CISY 219 - Fall 2004 - TWE   17
Digital Subscriber Line (DSL)
ADSL – Asymmetric DSL; more
bandwidth downstream; channelized to
support voice and data streams
G.Lite ADSL – lower speeds and less
cost than ADSL
SDSL – Symmetric DSL; equal speeds
in both directions/
VDSL – Very high speed DSL – T3
speeds over short distances
           RVCC - CISY 219 - Fall 2004 - TWE   18
Figure 9-5  An ADSL circuit is divided into several channels, and
uses a much wider frequency range than a standard telephone circuit.




                        RVCC - CISY 219 - Fall 2004 - TWE        19
       Cable TV (CATV)
High Speed Digital transmission
Originally designed for one-way
transmission (TV channels)
Requires a “modem” (splits service)
Shared medium for data transfers, but
less restrictive in distance than DSL



            RVCC - CISY 219 - Fall 2004 - TWE   20
       Satellite Circuits
DSS – Digital Satellite Services
Competitor with CATV and DSL for high
speed data transfer
Receive only – requires phone line for
upstream communication to Internet
Huge propagation delay (.5 sec) and so
unsuitable for interactive apps


            RVCC - CISY 219 - Fall 2004 - TWE   21
         Private Circuits
Installed, maintained and owned by a
company other than a carrier
Typically used for Campus LANs
Circuit is exclusively available for the
owner’s use




             RVCC - CISY 219 - Fall 2004 - TWE   22
          Leased Circuits
    Installed, maintained and owned by
    Carrier
    Used when:
    Impossible to install private circuits
    Cost of leased < cost of dial-up time
    4 wire service is required
    High speed needed
    Carrier does maintenance (fixes,…)
    Lease rate depends on speed and
    distance
                RVCC - CISY 219 - Fall 2004 - TWE   23
      Circuit Switching
A dedicated connection exists between
two stations
Call Setup – find the path between A and
B and dedicate the circuit
Call Tear-down – release all equipment
and channels
Paths through the “cloud” vary from
connection to connection and so quality
of the circuit varies
            RVCC - CISY 219 - Fall 2004 - TWE   24
Figure 9-6  Circuit switching networks build temporary
connections between devices that wish to communicate.




                    RVCC - CISY 219 - Fall 2004 - TWE   25
        Packet Switching
Circuit switching is inefficient for data because
of long idle times and variance in quality
(speed)
Packet Switching segments messages into
packets (packetizing) and sends to the
Network
PAD (Packet Assembly/Disassembly) breaks
message in packets, adds headers and sends
through the network
PAD receives packets, reassembles into
message; removes all headers
Packets from several PCs can share the
connection to the PAD
               RVCC - CISY 219 - Fall 2004 - TWE   26
Figure 9-7    Packets from the three PCs are interspersed
on the circuit.




                     RVCC - CISY 219 - Fall 2004 - TWE   27
Packet Switching Connection
           Types
SVC (Switched Virtual Circuit) – users
dials into PDN (Packet Data Network)
which established a VC to the receiver
for the duration of the session
PVC (Private Virtual Circuit) – always
on VC between end points; for high
volume, frequent use
Datagram Service – for single packet
messages; traverse network at high
speeds
           RVCC - CISY 219 - Fall 2004 - TWE   28
      Some Good News
We will be skipping Sections 9-8
 through 9-13; they won’t be
 covered in the homework or in
 any test




           RVCC - CISY 219 - Fall 2004 - TWE   29

								
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