FALLSEM2013 14 CP1853 07 Aug 2013 RM02 Chenming Hu Ch4 Slides
FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
-
Upload
selvamrock85 -
Category
Documents
-
view
219 -
download
0
Transcript of FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
1/26
Switching
Unit -I
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
2/26
Switching Networks
In the switched network methodology, the network consists ofa set of interconnected nodes, among which information is
transmitted from source to destination via different routes,
which is controlled by the switching mechanism.
Nodes not concerned with content of data End devices that wish to communicate with each other are
called stations-
Computer, terminal, phone, etc.
The switching devices are called nodes. Some nodes connect to other nodes and some are to connected
to some stations.
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
3/26
Simple Switched Network
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
4/26
Nodes
Nodes may connect to other nodes only, or to stationsand other nodes
Node to node links usually multiplexed.
Node-station links are generally dedicated point-to-point links.
Network is usually not fully connected.
Some redundant connections are desirable for reliability
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
5/26
Simple Switched Network
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
6/26
Taxonomy of Switched Networks
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
7/26
Circuit Switching
A switching technology that establishes an electricalconnection between stations using a dedicated path.
Dedicated communication path between two stations
Three phasesEstablish
Transfer
Disconnect
Must have switching capacity and channel capacityto establish connection
Must have intelligence to work out routing
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
8/26
Circuit Switching
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
9/26
Circuit Switching
InefficientChannel capacity dedicated for duration of connection
If no data, capacity wasted
Set up (connection) takes time Once connected, transfer is transparent
Circuit switching designed for voice
Resources dedicated to a particular call
Much of the time a data connection is idle
Data rate is fixed
Both ends must operate at the same rate
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
10/26
Public Circuit Switched Network
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
11/26
Telecommunication Components
SubscriberDevices attached to network
Subscriber lineThe link between the subscriber and the network
Known as Local Loop or Subscriber loop
Few km up to few tens of km Exchange
Switching centers in the network.
A switching center that directly supports subscribers is known as anend office.
TrunksBranches between exchanges
Trunks carry multiple voice frequency circuits using either FDM orsynchronous TDM
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
12/26
Circuit Establishment
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
13/26
Circuit Switch Elements
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
14/26
Circuit Switching Concepts
Digital SwitchProvide transparent signal path between devices
Network Interface Element
- represents the functions and hardware needed to connect digitaldevices, such as data processing devices and digital telephones.
Control Unit
Establish connections
Generally on demand
Handle and acknowledge requests
Determine if destination is free construct path
Maintain connection
Disconnect
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
15/26
Characteristics of Circuit Switching
BlockingA network is unable to connect stations because all paths
are in use
Used on voice systems
Short duration calls
Non-blocking
Permits all stations to connect (in pairs) at once
Used for some data connections
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
16/26
Packet Switching Principles
In a packet-switched network, there is no resourcereservation; resources are allocated on demand.
Data transmitted in small packets
Typically 1000 octets
Longer messages split into series of packetsEach packet contains a portion of user data plus some
control info
Control info
Routing (addressing) info
Packets are received, stored briefly (buffered) andpast on to the next node
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
17/26
Use of Packets
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
18/26
Advantages
Line efficiencySingle node to node link can be shared by many packets
over time
Packets queued and transmitted as fast as possible
Data rate conversion
Each station connects to the local node at its own speed
Nodes buffer data if required to equalize rates
Packets are accepted even when network is busyDelivery may slow down
Priorities can be used
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
19/26
Packet Switching Technique
Station breaks long message into packets Packets sent one at a time to the network
Packets handled in two ways
Datagram ApproachVirtual circuit Approach
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
20/26
Datagram Approach
Each packet treated independently Packets can take any practical route
Packets may arrive out of order
Packets may go missing
Up to receiver to re-order packets and recover from
missing packets.
A switch in a datagram network uses a routing table
that is based on the destination address.
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
21/26
A datagram network with four switches
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
22/26
Datagram
Diagram
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
23/26
Virtual Circuit Approach
Preplanned route established before any packets sent Call request and call accept packets establish
connection (handshake)
Each packet contains a virtual circuit identifierinstead of destination address
No routing decisions required for each packet
Clear request to drop circuit
Not a dedicated path
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
24/26
Virtual
Circuit
Diagram
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
25/26
Virtual Circuits v Datagram
Virtual circuitsNetwork can provide sequencing and error control
Packets are forwarded more quickly
No routing decisions to make
Less reliable Loss of a node looses all circuits through that node
Datagram
No call setup phase
Better if few packetsMore flexible
Routing can be used to avoid congested parts of the network
-
7/27/2019 FALLSEM2013 14 CP0180 07 Aug 2013 RM01 Circuit and Packet Swicthing1
26/26
Cell Switching
Cell Switching is a connection oriented switching technique in
which message is transmitted in the form of packets of same size.
Cell switching is similar to packet switching as it operates in a
similar way to packet switching but uses small fixed length cells
for data transport.
Used in Asynchronous Transfer Mode networks.
Cell switching can handle multiple data types, i.e. voice, video and
data. Moreover, cell switching is typically a high bandwidth and
high speed technology.
Cell switching is essentially an attempt to combine the best of
circuit switching and packet switching