Communication Networks
Chapter 3
Types of Communication
N t
Networks
k
Traditional
di i l
Traditional local area network (LAN)
( )
Traditional wide area network (WAN)
Higher speed
Higher-speed
High-speed local area network (LAN)
Metropolitan area network (MAN)
High-speed
High speed wide area network (WAN)
Speed and Distance of
C
Communications
i ti Networks
N t k
Ch
Characteristics
t i ti off WANs
WAN
Covers large
C l geographical
hi l areas
Circuits provided by a common carrier
Consists of interconnected switching nodes
Traditional WANs provide modest capacity
64,000 bps common
Business subscribers using T-1 service – 1.544 Mbps
common
Higher-speed WANs use optical fiber and
transmission technique known as asynchronous
transfer mode (ATM)
10s and 100s of Mbps common
M-Taiwan Project
NTD: 30 billion to construct NTD: 7 billion for content
a fiber infrastructure services/applications
Ch
Characteristics
t i ti off LANs
LAN
Like
ik WAN, LAN interconnects
i a variety
i off
devices and provides a means for
information exchange among them
Traditional LANs
Provide data rates of 1 to 20 Mbps
High-speed LANS
Provide data rates of 100 Mbps to 1 Gbps
Differences between LANs and
WANs
WAN
Scope off a LAN is
i smaller
ll
LAN interconnects devices within a single
g
building or cluster of buildings
LAN is usually owned by organization that
owns the attached devices
For WANs,
A most off network
k assets are not
owned by same organization
Internal data rate of LAN is much greater,
such as 100Mbps to 10Gbps
Th N
The Need
d ffor MAN
MANs
A MAN occupies i a middle
iddl ground d bbetween
t LAN
LANs
and WANs
T diti l point-to-point
Traditional i tt i t andd switched
it h d network
t k
techniques used in WANs are inadequate for
growing needs of organizations
Need for private and public networks that provide
high capacity and low costs over a large area (on a
metropolitan scale)
Headquarter
Taipei City Data Center
Branch Office
S it hi Terms
Switching T
S it hi Nodes:
Switching N d
Intermediate switching device that moves data
Not concerned with content of data
Stations:
End devices that wish to communicate
Each station is connected to a switching node
Communications Network:
A collection
ll i off switching
i hi nodes
d
Switched Network
Some nodes connect only to other nodes (e.g., 5 and 7)
Some nodes connect to one or more stations
Node-station links are usually dedicated point-to-point links
Node-node links are usuallyy multiplexed
p links
Frequency-division multiplexing (FDM)
Time-division multiplexing (TDM)
Not a direct
di li
linkk between
b
every node pair
stations
nodes
Techniques Used in Switched
N t
Networks
k
Circuit
i i switching
i hi
Dedicated communications ppath between two
stations
E.g., public telephone network
Packet switching
Message is broken into a series of packets
Each node determines next leg of transmission
for each packet
E.g., IP
IP-based
based data network
Ph
Phases off Ci
Circuit
it Switching
S it hi
Ci it establishment
Circuit t bli h t
An end to end circuit is established through switching
nodes
Information Transfer
Information transmitted through the network
Data may be analog voice, digitized voice, or binary
data
Circuit disconnect
Circuit is terminated
Each node deallocates dedicated resources
Characteristics of Circuit
S it hi
Switching
C be
Can b inefficient
i ffi i
Channel capacity dedicated for duration of connection
Utilization not 100%
Delay prior to signal transfer for establishment
Once established, network is transparent to users
Information
o a o transmitted
a s ed at
a fixed
ed data
da a rate
a e with
w
only propagation delay
Components of Public
T l
Telecommunications
i ti Network
N t k
Subscribers - devices that attach to the network; mostly telephones
Subscriber line - link between subscriber and network
Also called subscriber loop or local loop
Exchanges - switching centers in the network
A switching centers that support subscribers is an end office
Trunks - branches between exchanges
H P
How Packet
k tSSwitching
it hi Works
W k
Data
D t is
i transmitted
t itt d in
i blocks,
bl k called
ll d packets
k t
Before sending, the message is broken into a series of
packets
Typical packet length is 1,000 octets (bytes)
Packets consists of a p portion of data pplus a p
packet
header that includes control information
At each node en route, packet is received, stored briefly
andd passed
d tto the
th nextt noded
P k tS
Packet Switching
it hi Advantages
Ad t
Line efficiency is greater
Many packets over time can dynamically share the
same node-to-node
node to node link
Packet-switching networks can carry out data-rate
conversion
Two stations with different data rates can exchange
information
Unlike circuit-switching networks that block calls
when traffic is heavy, packet-switching still
accepts packets, but with increased delivery delay
Priorities can be used
Disadvantages of Packet
S it hi
Switching
Eachh packet
E k t switching
it hi noded introduces
i t d a delay
d l
Overall packet delay can vary substantially
This
hi is
i referred
f d to as jitter
ji
Caused by differing packet sizes, routes taken and
varying delay in the switches
Each packet requires overhead information
Includes destination and sequencing information
Reduces communication capacity
More processing required at each node
Packet Switching Networks -
D t
Datagram
Each
E h packet
k treated d iindependently,
d d l without
ih
reference to previous packets
Each node chooses next node on packet’s path
Packets don’t necessarilyy follow same route and
may arrive out of sequence
Exit node restores packets to original order
Responsibility of exit node or destination to detect
loss of packet and how to recover
Packet Switching Networks –
D t
Datagram
Advantages:
d
Call setupp pphase is avoided
Because it’s more primitive, it’s more flexible
Datagram delivery is more reliable
Packet Switching Networks –
Vi t l Circuit
Virtual Ci it
Preplanned
P l d route
t established
t bli h d before
b f packets
k t sentt
All packets between source and destination follow
thi route
this t
Routing decision not required by nodes for each
packet
k t
Emulates a circuit in a circuit switching network
b t is
but i nott a dedicated
d di t d pathth
Packets still buffered at each node and queued for
output over a line
Packet Switching Networks –
Vi t l Circuit
Virtual Ci it
Advantages:
d
Packets arrive in original
g order
Packets arrive correctly
Packets transmitted more rapidly without
routing decisions made at each node
Effect of Packet Size on
T
Transmission
i i
Effect of Packet Size on
T
Transmission
i i
Breaking up packets decreases transmission time
because transmission is allowed to overlap
Figure 3.9a
Entire message (40 octets) + header information
(3 octets) sent at once
Transmission time: 129 octet-times
Figure 3.9b
Message broken into
2 packets (20 octets) + header (3 octets)
Transmission time: 92 octet-times
Effect of Packet Size on
T
Transmission
i i
Figure
g 3.9c
Message broken into
5 packets (8 octets) + header (3 octets)
Transmission time: 77 octet-times
Figure 3.9d
Message broken into
12 packets (4 octets) + header (3 octets)
Transmission time: 84 octet-times
Making the packets too small, transmission time starts
increases
E h packet
Each k requires
i a fixed
fi d header;
h d the h more packets,
k
the more headers
Asynchronous
y Transfer Mode (ATM)
( ) is a network
of Virtual Circuit with a 53-octet packet size
Asynchronous Transfer Mode
(ATM):
(ATM)
Also kknown as cell
Al ll relay
l
Operates at high data rates
Resembles packet switching
Involves transfer of data in discrete chunks, like packet
switching
it hi
Allows multiple logical connections to be multiplexed
over a single physical interface
Minimal error and flow control capabilities
reduces overhead processing and size
Fixed-size cells simplify processing at ATM nodes
ATM T
Terminology
i l
Vi
Virtual
l channel
h l connection
i (VCC)
Logical connection in ATM
Basic unit of switching in ATM network
Analogous to a virtual circuit in packet switching
networks
k
Exchanges variable-rate, full-duplex flow of fixed-size
cells
ll
Virtual path connection (VPC)
Bundle of VCCs that have the same end points
ATM Connection Relationships
Ad t
Advantages off Vi
Virtual
t l Paths
P th
Simplified
i lifi d networkk architecture
hi
Increased network performance and
reliability
R d d processing
Reduced i andd short
h t connection
ti
setup time
Enhanced network services
C ll Establishment
Call E t bli h t
Vi t l Channel
Virtual Ch l Connection
C ti Uses
U
B t
Between endd users
Can carry end-to-end user data or control
signaling
i li between
b two users
Between an end user and a network entity
Used for user-to-network control signaling
Between two network entities
Used for network traffic management and
routing functions
Virtual Path/Virtual Channel
Ch
Characteristics
t i ti
Q lit off service
Quality i
Specified by parameters such as cell loss ratio and cell
delay variation
Switched and semipermanent virtual channel
connections
Cell sequence integrity
Traffic parameter negotiation and usage
monitoring
Virtual channel identifier restriction within a VPC
ATM Cell
C ll Header
H d Format
F t
Generic
G i flow
fl control
t l (GFC) – 4 bits,
bit usedd only
l in
i
user-network interface
Used to alleviate short-term
short term overload conditions in
network
Virtual path identifier (VPI) – 8 bits at the user-
user
network interface, 12 bits at network-network
interface
Routing field
Virtual channel identifier ((VCI)) – 8 bits
Used for routing to and from end user
ATM Cell
C ll Header
H d Format
F t
P l d type
Payload t (PT) – 3 bits
bit
Indicates type of information in information
fi ld
field
Cell loss priority (CLP) – 1 bit
Provides guidance to network in the event of
congestion
Header error control (HEC) – 8 bit
Error code
ATM Cell Format
ATM S
Service
i C Categories
t i
Real-time
l i service
i
Constant bit rate (CBR)
( )
Real-time variable bit rate (rt-VBR)
Non real time service
Non-real-time
Non-real-time variable bit rate (nrt-VBR)
Available bit rate (ABR)
Unspecified bit rate (UBR) – Best
Best-Effort
Effort
Service
E
Examples
l off CBR Applications
A li ti
Videoconferencing
id f i
Interactive audio (e.g., telephony)
Audio/video distribution (e.g., television,
di t
distance learning,
l i pay-per-view)
i )
Audio/video retrieval ((e.g.,
g , video-on-
demand, audio library)
E
Examples
l off UBR applications
li ti
Text/data/image
/d /i transfer,
f messaging,
i
distribution, retrieval
Remote terminal (e.g., telecommuting)
