CSCI1412 - Topologies and Protocols - castlecollegeHE

enginestagNetworking and Communications

Oct 26, 2013 (3 years and 10 months ago)

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Networks 4

Topologies and
Protocols

Dr John Cowell


phones off

(please)

1

Overview


Network topologies


ring, star, bus and mesh topologies


combined topologies


Communication protocols


message switching


LAN


Ethernet, Token Ring


MAN


FDDI, DQDB


WAN


ATM, ISDN

2

3

Network Topologies


Topology means physical layout of a network


issues of:


hardware


cabling, desking


software


protocol, applications


Each workstation attached to network is known as a
node


Types of Networks


ring, star, bus, mesh/distributed


combined

4

Ring Networks


Ring must be maintained
at all times


network crashes if break in
cable ring

5


Higher speeds available at cost


Can be inflexible in wiring


Addition/deletion cause problems

Star Networks


Server dependent
-

often a mainframe


Good central control


Robust
-

no problems if cable/node breaks

6


Large
amounts of
cable

(Common) Bus Networks


Also known as
multidrop


Each node has a feed to the bus


Easy to add new nodes


Can be inflexible
-

limits to cable length


Coax connectors cause problems


only used with 10 MHz
Ethernet

7

Mesh Networks


Fully connected network


Used in WANs, not LANs


No competition for common lines


fast connections


Wasteful of connectivity potential

8

Combined Topologies

9

Combined Topologies 2


Combinations of topologies are common


‘dynamically grown’ networks


Common bus
-

backbone


LAN’s cope with most users


occasional access to mainframe is sufficient


Bridges convert between protocols

10

11

Protocols


Set of rules governing communication issues


a standard


IEEE define the 802 protocol standards


Different protocols exist for different geographical area
topologies


LANs


Ethernet (802.3), Token Bus (802.4), Token Ring (802.5), Wireless
-

WiFi
(802.11[a|b|g|n])


MAN


FDDI (802.5), DQDB (802.6)


WANs


ATM, ISDN, Frame Relay

12

Connection Strategies


Circuit switched


‘permanent’ circuit established for call duration


Message switched


a message is sent from node to node


message is stored temporarily at intermediate nodes


problem if message is too long for buffer


security issues


Packet switched
-

2 types


datagram

and
virtual circuit

13

Packet Switching


Packet switched
-

2 types


datagram


each packet transmitted separately
(e.g.
TCP/IP)


connectionless service


virtual circuit


protocols establish a circuit, used for all packets
(e.g.
ATM)


segments may be shared with other virtual circuits


connection oriented


There are possible routes between A and F


each packet may have new route


packet 1:


A


B


F

packet
2: A


C


E


F

(could arrive last of three)

packet 3:


A


C


F

14

Ethernet and Token Ring

15

Ethernet


Node connects to bus cable via a
transceiver

Sending

Network
interface card receives a frame from PC


Transceiver says when cable clear


frame is put onto cable by transceiver


transceiver listens for collision (CSMA/CD)


if collision occurs, waits random time, then tries again

Receiving

Transceiver
monitors all traffic


all incoming frames address field are read


if for node, bits are sent to NIC


NIC does error check


PC executes network software to move frame from NIC to
memory for further processing

16

Ethernet Cable Specifications


The 802.3 standard specifies limits


maximum backbone length


maximum number of nodes attached


common data rates

17



Max distance

Cable Type

Backbone

between nodes

Data Rate

10 BASE 5

50 ohm coax,

500

10 Mbps

‘Thick’


10 mm
diameter

10 BASE 2

50 ohm coax,

185

10 Mbps

‘Thin’


5 mm
diameter

10 BASE
-
T

UTP

100

10 Mbps

star topology

100 BASE
-
T

UTP

100

100 Mbps

‘Fast’

1000 BASE
-
T

UTP

100

1000 Mbps

Gigabit
Ethernet

Distance limitations


10 BASE 5 was limited to 500 metres


signals degrade in copper cable


Used
repeaters

(amplifiers) to join 500 meter sections together


maximum of four repeaters (between two nodes)


the limit comes from the collision detection protocol


if the transceiver hears a collision, it must still have part of frame to transmit, in
order to abandon it


minimum frame size of 64 bytes


maximum frame size to prevent network hogging


Faster Ethernet reduces cable length


e.g.
100 base T limited to 100 metre cables from central switch/hub

18

Token Ring


Used widely in industry


originally developed by IBM


time critical applications


Data rates of 1 Mbps, 4 Mbps, 16
Mbps


Nodes are connected in a
ring

topology


A token (special frame) is
constantly circling


If network breaks, token
disappears


need to restart (reboot) network


avoid this with wire centre hub


‘star topology’, logical ring

19

Sending Data on Token Ring


Node wishing to send frame waits for token


if token is ‘free’, it is replaced with data
frame


Frame travels around ring


each node reads destination address


destination node


copies frame


resets status bits


puts frame back on ring


transmitting node


removes frame from ring


creates a new token, and puts it on ring


waits a period before next grabbing token


prevents hogging

20

Token Ring Features


Unlike Ethernet, collisions cannot occur


a node
must

wait until the token is free


it is possible to calculate the maximum time that will pass before
any node will be able to transmit


no wasted bandwidth from collisions


Token ring uses a sophisticated priority scheme


nodes can be assigned different priorities


only nodes with high priority can seize the token


If a sending device fails, its token may continue to circulate
forever and lock the network


special monitor nodes can detect such a situation

21

FDDI and DQDB

22

Fibre Distributed Data Interface


FDDI is essentially Token Ring over fibre


covered by the same IEEE 802.5 standard


no electromagnetic interference


better security


faster data rates


100 Mbps around 200 Km ring with 200 nodes


Token is put back onto the ring immediately after a frame is
transmitted


Capacity much greater than Token Ring


Recently a CDDI (Copper Distributed Data Interface)
standard has also emerged

23

Distributed Queue Dual Bus


Attributed to the PhD thesis of Robert Newman (Uni. Western
Australia)


IEEE 802.6 is an example


High
speed MAN (2
-

300 Mbps
)


Range up to 34 miles.


Two parallel
cables, if one breaks the signal can switch to the
other bus.


Highly resistance to cable damage


24

ISDN, ATM & 10GbE

25

Integrated Services Digital Network


Now largely replaced by broadband technologies



ISDN
is digital network available over telephone


integrates voice & non
-
voice transmission


Basic installation uses three separate channels


2 B channels = 64 Kbps
-

data channels


D channel = 16 Kbps
-

control channel


can also used for telemetry


remote (water/electricity) meter reading, alarm systems


the three channels share time on a cable


time
-
division multiplexing


Industry installation uses thirty B channels +
D

26

Asynchronous Transfer Mode


ATM is a very fast packet
-
switched protocol


100 Mbps or greater, up to gigabits per second!


Uses small fixed
-
size packets


53 octets (5 header, 48 payload)


very similar to DQDB


Connection oriented


every packet with same destination travels same route


virtual circuit number in header


requires dedicated routers


CRC in header allows error checking at network nodes


Protocol optimised for multimedia


Will probably be replaced by Gigabit Ethernet technologies for
new implementations

27

10 GbE


10 Gigabit Ethernet


10 times as fast as Gb Ethernet


retains
Ethernet frame
format


Over 1.2 million ports shipped in 2008


Different standards
available


E.g. 10 GBASE
-
SR short range, 26m
-
85m. Low cost.


E.g. 10 GBASE
-
LR range up to 10km, but 25lm often achievable.


Fibre


LAN PHY, etc


Copper


10GBaseT, etc


Greatest distance between hosts currently

80 km (10GBASE
-
ZR
), but this is a de
-
facto
standard only (not part of IEEE802)


See


http://en.wikipedia.org/wiki/10_gigabit_Ethernet


http://www.ieee802.org/3/10GBT/public/nov03/10GBASE
-
T_tutorial.pdf

28

Summary


Network topologies


ring, star, bus and mesh topologies


combined topologies


Communication protocols


message switching


LAN


Ethernet, Token Ring


MAN


FDDI, DQDB


WAN


ATM, ISDN

29