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Overview
Multiplexing techniques
Space Division (SDM)
Frequency Division (FDM)
Time Division (TDM)
Addressing
Switching
Point-to-point
point-to-multipoint
space division
time division
address
frequency
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Circuit switching
- Digital Cross Connect
Origins of packet switching
Introduction to:
- Frame relay
- X.25
- Fast Packet
- ATM
Multiplexing Technologies
Multiplexing defines the means by which multiple streams of
information from multiple users share a common physical
transmission medium all of which may require some or all of the
bandwidth at any given time.
Switching takes multiple instances of a physical transmission
medium, each containing multiplexed information streams, and
rearranges the information streams between the input and output
of the switch.
Multiplexer Defined
The multiplexing function shares many inputs to a single output.
The demultiplexing function has one input which must be
distributed to many outputs.
Refer to Figure 6.1 (p. 189)
The overall speed on the access side interfaces is generally less
than that on the trunk side.
Multiplexing techniques can be used to share a physical medium
between multiple users at two different sites over a private line
with each pair of users requiring some or all of the bandwidth at
any given time.
Multiplexing Methods
Space Division Multiplexing
It can be facilitated by mechanical patch panels, or by
optical and electronic patch panels
It is being replaced by space division switching or other
types of multiplexing
An example of SDM is seen where multiple cables
interconnect equipment.
Frequency Division Multiplexing (FDM)
Many analog conversations are multiplexed onto the same cable, or radio
spectrum,by modulating each signal by a carrier frequency.
Refer to Figure 6.2 (p. 190)
FDM multiplexes 12 voice-grade, full-duplex channels into a single 48-kHz
bandwidth group by translating each voiceband signal’s carrier frequency.
One variation of FDM is Wavelength Division Multiplexing (WDM) based on
Fiber technology.
Refer to Figure 6.3 (p. 191)
Time Division Multiplexing (TDM)
TDM allows multiple users to share a digital transmission medium
by using preallocated time slots.
Refer to Figure 6.4 (p. 193)
Time slots are dedicated to a single user, whether data is being
transmitted or the user is idle. The same time slots are dedicated
to the same user in the same order for every frame transmitted.
Different time slots are dedicated to different channel sources,
such as voice channels, data, or video.
Multiplexer inputs can carry simultaneously asynchronous and
synchronous data
Time Division Multiplexing (TDM) (Continue….)
All transmissions through multiplexers are point-to-point
A single T1 circuit can be configured for 24 to 196
allocated channels.
Each channel uses 64 kbps
Refer to Figure 6.5 (p. 194)
Address or Label Multiplexing
A common name for address multiplexing is Asynchronous Time Division
Multiplexing (ATDM)
Examples: SNA, DECNET, X.25, Frame Relay, ATM
Statistical Time Division Multiplexing (STDM) dynamically assigns time slots
only to users who need data transmission.
The net effect is an increase in overall throughput for users since time slots
are “reserved” or dedicated to individual users.
Refer to Figure 6.6 (p. 194)
Concentrator is a type of block-oriented multiplexer.
Concentrators transmit blocks of information for each user as needed,
adding an address to each block to identify the user.
Address or Label Multiplexing (Continue…)
Concentrators utilizing this technique are called Asynchronous
Time Division Multiplexers (ATDMs).
The primary difference between concentrator and multiplexing is
that concentrators have additional intelligence to understand the
contents of the data being passed and can route the information
streams based upon the data within them.
Types of Multiplexers
There are four types of multiplexers used in data network
designs:
Access multiplexer
Network multiplexer
Drop-and-insert multiplexer
Aggregator multiplexor
Most forms of multiplexing are protocol-transparent and
protocol-independent.
Refer to Figure 6.7 (p. 197)
Access or Channel Bank Multiplexers
They provide the first level of user access to the multiplexer
network. These devices typically reside on the user or customer
premises
They provide network access for a variety of user asynchronous
and synchronous, low- and high-speed inputs including: Data
telephone, LAN, Low-speed video, terminal.
Access multiplexers usually provide one or more T1 trunks to the
next class of larger multiplexers, the backbone multiplexer.
Access or Channel Bank Multiplexers (continue…)
There are two versions:
Fractional T1 multiplexer
SubRate Data multiplexer
Refer to Figure 6.8 (p. 198)
Refer to Figure 6.9 (p. 199)
Both versions optimize the use of access trunks for multiple lowspeed users.
Network Multiplexers
They support T1 on the access side and T3 or higher on the
network side.
They offer larger capacity, reroute capability, and configuration
capability
Private and public data transport network backbones are built
using network multiplexers.
Refer to Figure 6.10 (p. 200)
Aggregator Multiplexers
They combine multiple T1 channels into higher-bandwidth pipes
for transmission.
M12 Multiplexer: 4 DS1s to the rate of DS2
M13 Multiplexer: 28 DS1s to the rate of DS3
M23 Multiplexer: 7 DS2s to the rate of DS3
M22 and M44 Multiplexers: configuration management and rerouting
capability of 22 and 44 channels
MX3 Multiplexer: different combinations of DS1s and DS2s to the rate of
DS3
Note that syncrhonization of the aggregate circuits within many of
these multiplexers is not supported by many vendors
Drop-and-Insert Multiplexer
They are special-purpose multiplexers designed to drop and insert
low-speed channels in and out of a high-speed multiplexed
channel like a T1.
Channel speeds dropped and inserted are typically 56 or 64kbps.
Each DS0 is demultiplexed and remultiplexed for transmission.
Refer to Figure 6.12 (p. 202)
Switching Techniques
Space Division Switching
It delivers a signal from one physical interface to another physical
interface.
Classical space division switch fabrics have been built from
electromechanical and electronic elements with the crosspoint
function.
Refer to Figure 6.15 (p. 207)
Time Division Switching
The operation of current digital telephone switches may be viewed
as being made up of an interconnected network of special-purpose
computers called Time Division Switches (TDS).
The TDS is effectively a very special-purpose computer designed
to operate at very high speeds.
Refer to Figure 6.16 (p. 208)
Address Switching
Address switching operates on a data stream in which data is
organized into packets, each with a header and a payload. The
header contains address information that is used in switching
decisions at each node.
All possible connection topologies can be implemented: point-topoint, point-to-multipoint, multipoint-to-point, and multipoint-tomultipoint.
Refer to Figure 6.17 (p. 208)
Frequency/Wavelength Switching
It translates signals from one carrier frequency (wavelength) to
another.
Currently Optical Fiber networks use this method
The optical end system nodes transmit on at least one wavelength
 and receive on at least one wavelength. The wavelengths for
transmission and reception are currently tunable in a time frame
on the order of milliseconds, with an objective of microseconds.
Refer to Figure 6.18 (p. 210)
The Matrix Switch
They provide a simplistic form of T1 multiplexing and offer the
capability to switch ports similar to a cross-connect.
They are composed of a high-speed bus for connection between
ports.
They are controlled and switched through a central networkmanagement center, and can manage the entire network from a
single point.
The drawback is the possibility of failure, which would bring down
the entire network.
Refer to Figure 6.20 (p. 212)
Packet Switching Technologies
Packet-switching allows multiple users to share data-network facilities and
bandwidth, rather than providing specific amounts of dedicated bandwidth to
each user.
The traffic passed by packet-switched networks is “bursty” in nature, and
therefore can be aggregated statistically to maximize the use of on-demand
bandwidth resources.
Due to the connectionless characteristic of packet switching, the intelligence
of the network nodes will route packets around failed links.
Quick interview of packet switching technologies
X.25
Frame relay
- Fast Packet
- ATM
X.25
Access speeds range up to 56 kbps
Contains error detection and correction
Connectionless service using connection-oriented virtual circuits
Good for time-insensitive data transmission but poor for connectionoriented and time-sensitive voice and video.
Employs a queuing scheme for buffering and transmission of data
Allows numerous virtual circuits on the same physical path, and can
transport packet sizes up to 4,096 bytes
Permanent Virtual Circuits and Switched Virtual Circuits are supported.
Traffic can be prioritized
Old technology
Frame Relay
It is a connection-oriented service employing PVCs and SVCs.
Frames can vary in size and bandwidth
Multiple sessions can take place over a single physical circuit
It is only a transport service (no error control or correction)
It must be transmitted over reliable fiber-optic transmission media with low
bit-error ratios
Fast Packet
It is not a defined standard, protocol, or service.
Fast packet is a backbone technology which combines attributes of both
circuit switching and packet switching.
It can accommodate both delay-sensitive traffic as well as data traffic not
affected by variable delay.
It offers low network delay and high network resources efficiency
It provides protocol transparency
Fast packet technologies typically use advanced fiber-optic transport media,
such as T3 and SONET.
Asynchronous Transfer Mode (ATM)
ATM is another form of fast packet switching.
Fixed size packets called cells
It provides two types of connection:
Virtual channel
Virtual path
It allows for the transmission for data, voice, and video traffic simultaneously
over high-bandwidth circuits.
Full dublex 155.52 Mbps
Asymmetrical transmission from subscriber to network at 155.52 Mbps in one
direction and 622.08 Mbps in the other
Full-dublex 622.08 Mbps service.
Cisco
Switching Technologies
Objectives
Describe layer-2 switching
Describe address learning in layer-2 Switches
Understand when a layer-2 switch will forward or filter a
frame
Describe network loop problems in layer-2 switched
networks
Describe the Spanning-Tree Protocol
List the LAN switch types and describe how they work
with layer-2 switches
Layer-2 Switching
Hardware based
Provides the following:
Hardware-based bridging (MAC)
Wire speed
Low latency
Low cost
Layer-2 Switching
Limitations
Bridging vs LAN Switching
Three Switch Functions at Layer 2
Address Learning
How Switches Learn Hosts’ Locations
Layer-2 Switching
Forward/Filter Decisions
Broadcast & Multicast Frames
Loop Avoidance
Broadcast Storms
Multiple Frame Copies
Spanning-Tree Protocol (SPT)
Purpose
History
STP Operations
Function
How does it do this?
Selecting a Root Bridge
Process
Spanning-Tree Port States
Port states
Convergence
Selecting the Designated Port
Process
Spanning-Tree Operations
LAN Switch Types
Store and Forward
Cut-through
FragmentFree
Spanning Tree Example
Different Switching Modes within a
Frame
Summary
Described layer-2 switching
Described address learning in layer-2 Switches
Stated when a layer-2 switch will forward or filter a
frame
Described network loop problems in layer-2 switched
networks
Described the Spanning-Tree Protocol
Listed the LAN switch types and describe how they
work with layer-2 switches
Cisco
Internet Protocol
Objectives
Describe the different classes of IP addresses
Perform subnetting for an internetwork
Configure IP address in an internetwork
Verify IP addresses and configuration
The DoD and OSI Models
Process/Application Layer Protocols
Telnet
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Line Printer Daemon (LPD)
Process/Application Layer Protocols
X Window
Simple Network Management Protocol (SNMP)
Domain Name Service (DNS)
Dynamic Host Configuration Protocol (DHCP)
Host-to Host Layer Protocols
Purpose
Protocols
Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
The TCP/IP Protocol Suite
TCP Segment Format
UDP Segment
Key Concepts
TCP
Sequenced
Reliable
Connection-oriented
Virtual circuit
UDP
Unsequenced
Unreliable
Connectionless
Low overhead
Port Numbers
Purpose
Port Numbers:
< 1024: “Well-known port numbers”

Defined in RFC 1700; linked to specific applications or
protocols
> 1024: Dynamically assigned

Used by upper layers to communicate between hosts
Port Numbers for TCP & UDP
Internet Layer Protocols
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
IP Header
The Protocol Field in an IP Header
Local APR Broadcast
RARP Broadcast
Summary of the Three Classes of
Networks
IP Addressing
What is it?
Terminology
Bit: one digit: 1 or 0
Byte: 7 or 8 digits
Octet: Always 8 bits (base-8 addressing)
Network Address: Used to send packets to a remote network
Broadcast Address: Sends information to all nodes on a network
 All networks: 255.255.255.255
 All nodes: 172.16.255.255
 All subnets & hosts: 10.255.255.255
Hierarchical IP Addressing Scheme
IP addresses = 32 bits
Divided into 4 sections or octets or bytes
Each byte containing 8 bits
Depicting IP addresses:
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Dotted decimal: 172.16.30.56
Binary: 10101100.00010000.00011110.00111000
Hexadecimal: 82 39 1E 38
Network Addressing
Background
Network Address Range: Class A
Network Address Range: Class B
Network Address Range: Class C
Network Address Ranges: Classes D & E
Network Addresses: Special Purpose
Class A Addresses
Structure
Network.node.node.node
Class A Valid Host IDs
10.0.0.0
All host bits off
10.255.255.255
All host bits on
Valid hosts = 10.0.0.1 - 10.255.255.254

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0’s & 255s are valid hosts but hosts bits cannot all be off
or on at the same time!
224-2 = 222
Class B Addresses
Structure
Network.Network.node.node
Class B Valid Host IDs
172.16.0.0
All host bits off
172.16.255.255
All host bits on
Valid hosts = 172.16.0.1 - 172.16.255.254

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0’s & 255s are valid hosts but hosts bits cannot all be off
or on at the same time!
216-2 = 214
Class C Addresses
Structure
Network.Network.Network.node
Class C Valid Host IDs
192.168.100.0 All host bits off
192.168.100.255
All host bits on
Valid hosts = 192.168.100.1 - 192.168.100.254


0’s & 255s are valid hosts but hosts bits cannot all be off
or on at the same time!
28-2 = 26
Subnetting
Benefits
Creating subnetworks
Understanding the Powers of 2
Subnet Masks
Subnetting Class C Addresses
Class C address = 8 bits
Subnetting =
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10000000 = 128
11000000 = 192
11100000 = 224
11110000 = 240
11111000 = 248
11111100 = 252
11111110 = 254
Rules
Cannot have only 1 bit for subnetting
 Subnets 128 & 254 are illegal
The Binary Method
The Alternate Method
1. How many subnets does the subnet mask produce?
2. How many valid hosts per subnet?
3. What are the valid subnets?
4. What are the valid hosts in each subnet?
5. What is the broadcast address of each subnet?
Subnetting Practice Examples
Class C
Class B
Class A
Summary
Described the different classes of IP addresses
Performed subnetting for an internetwork
Configured IP address in an internetwork
Verified IP addresses and configuration