Transcript Chapter 2
Chapter 6
High-Speed LANs
Chapter 6 High-Speed LANs
1
Introduction
Fast Ethernet and Gigabit Ethernet
High-speed Wireless LANs
Chapter 6 High-Speed LANs
2
Table 6.1
Characteristics of some High-Speed LANs
Fast
Ethernet
Gigabit
Ethernet
Fibre
Channel
Wireless
LAN
Data Rate
100 Mbps
1 Gbps,
10 Gbps
100 Mbps –
3.2 Gbps
1 Mbps –
54 Mbps
Transmission
Media
UTP,
STP,
optical fibre
UTP,
shielded
cable, optical
fibre
Optical fibre,
coaxial cable,
STP
2.4 GHz,
5 GHz,
microwave
Access
Method
CSMA/CD
CSMA
Switched
CSMA/CA
Polling
Supporting
Standard
IEEE 802.3
IEEE 802.3
Fibre Channel
Association
IEEE 802.11
Chapter 6 High-Speed LANs
3
Emergence of High-Speed LANs
2 Significant trends
Computing power of PCs continues to grow
rapidly
Network computing
Examples of requirements
Centralized server farms
Power workgroups
High-speed local backbone
Chapter 6 High-Speed LANs
4
Classical Ethernet
Bus topology LAN
10 Mbps
CSMA/CD medium access control
protocol
2 problems:
A transmission from any station can be
received by all stations
How to regulate transmission?
Chapter 6 High-Speed LANs
5
Solution to First Problem
Data transmitted in blocks called
frames:
User data
Frame header containing unique address of
destination station
Chapter 6 High-Speed LANs
6
Figure 6.1
Chapter 6 High-Speed LANs
7
CSMA/CD
Carrier Sense Multiple Access/ Carrier Detection
1.
2.
3.
4.
If the medium is idle, transmit.
If the medium is busy, continue to listen
until the channel is idle, then transmit
immediately.
If a collision is detected during
transmission, immediately cease
transmitting.
After a collision, wait a random amount of
time, then attempt to transmit again (repeat
from step 1).
Chapter 6 High-Speed LANs
8
Figure 6.2
Chapter 6 High-Speed LANs
9
Figure 6.3
Chapter 6 High-Speed LANs
10
Medium Options at 10Mbps
<data rate> <signaling method> <max length>
10Base5
10 Mbps
50-ohm coaxial cable bus
Maximum segment length 500 meters
10Base-T
Twisted pair, maximum length 100 meters
Star topology (hub or multipoint repeater at central
point)
Chapter 6 High-Speed LANs
11
Hubs and Switches
Hub
Transmission from a station received by
central hub and retransmitted on all outgoing
lines
Only one transmission at a time
Layer 2 Switch
Incoming frame switched to one outgoing line
Many transmissions at same time
Chapter 6 High-Speed LANs
12
Figure 6.5
Chapter 6 High-Speed LANs
13
Bridge
Layer 2 Switch
Frame handling
done in software
Analyze and forward
one frame at a time
Store-and-forward
Frame handling
done in hardware
Multiple data paths
and can handle
multiple frames at a
time
Can do cut-through
Chapter 6 High-Speed LANs
14
Layer 2 Switches
Flat address space
Broadcast storm
Only one path between any 2 devices
Solution 1: subnetworks connected by
routers
Solution 2: layer 3 switching, packetforwarding logic in hardware
Chapter 6 High-Speed LANs
15
Figure 6.6
Chapter 6 High-Speed LANs
16
Figure 6.7
Chapter 6 High-Speed LANs
17
Figure 6.8
Chapter 6 High-Speed LANs
18
Figure 6.9
Chapter 6 High-Speed LANs
19
Figure 6.10
Chapter 6 High-Speed LANs
20
Figure 6.11
Chapter 6 High-Speed LANs
21
Benefits of 10 Gbps Ethernet over
ATM
No expensive, bandwidth consuming
conversion between Ethernet packets and
ATM cells
Network is Ethernet, end to end
IP plus Ethernet offers QoS and traffic
policing capabilities approach that of ATM
Wide variety of standard optical interfaces for
10 Gbps Ethernet
Chapter 6 High-Speed LANs
22
Wireless LAN
Forming LAN without wires has taken off big
time
Specified as IEEE 802.11
Started with link rate: 1 Mbps 54 Mbps
License-free operation
Different PHYs available 802.11b, a, g
Quality of service is being introduced thru
802.11e 4 classes
Mesh networks are formed for broader
coverage
Chapter 6 High-Speed LANs
23
IEEE 802.11 Wireless LAN
802.11b
2.4-2.5 GHz
unlicensed radio
spectrum
up to 11 Mbps
widely deployed,
using base stations
802.11a
5-6 GHz range
up to 54 Mbps
802.11g
2.4-2.5 GHz range
up to 54 Mbps
All use CSMA/CA for MAC protocol
All have infrastructure and ad-hoc
network versions
Chapter 6 High-Speed LANs
24
Infrastructure Approach
McGraw-Hill
Wireless host communicates with an access point
Basic Service Set (BSS) (a.k.a. “cell”) contains:
wireless stations
one access point (AP)
BSSs combined to form a distribution system (DS)
Chapter 6 High-Speed LANs
25 Inc., 2004
©The McGraw-Hill Companies,
Ad Hoc Approach
No AP!
Wireless stations communicate with each other
Typical usage:
“laptop” meeting in conference room, car
interconnection of “personal” devices
battlefield
IETF MANET (Mobile Ad hoc
Networks) working group
looks into this approach
Special needs such wireless routing, security
Chapter 6 High-Speed LANs
26
IEEE802.11 MAC Layer
Two medium access control
schemes
Distributed Coordination Function - DCF
Point Coordination Function - PCF
Contention Free
Services
Contention Services
Point Coordination
Function
Distributed Coordination
Function
Chapter 6 High-Speed LANs
27
IEEE 802.11: MAC protocol
Collision if 2 or more nodes transmit at same
time as the wireless channel is shared
CSMA makes sense:
get all the bandwidth if you’re the only one
transmitting
shouldn’t cause a collision if you sense another
transmission
Thus, it uses CSMA with collision avoidance
(CSMA/CA)
Not CD because detecting collision is difficult in
wireless environment
Two-handshaking
Chapter used
6 High-Speed LANs
28
DCF
Basic
access method
Contention based, distributed protocol
DCF uses CSMA/CA and a random
backoff time following a busy medium
condition
Uses RTS/CTS extension
to combat the hidden terminal problem
to reduce the BW wastage due to packet
collision
Chapter 6 High-Speed LANs
29
PCF
Contention free, centralised access protocol
Channel access is controlled using polling
Point coordinator will switch the access mode
between DCF and PCF
Unpopular with vendors, mostly not used!
Chapter 6 High-Speed LANs
30
Latest Developments
802.11 has no QoS support; 802.11e MAC
introduced in 2005
Supports 4 classes uses soft resource reservation
and backoff manipulation
802.11s taskforce working on extending
802.11 hotspots to larger wireless networks
Courtesy of
Sensors Mag
Chapter 6 High-Speed LANs
31
Summary
Wired networks has become really fast
Everything is Ethernet
End to end is Ethernet
Wireless networks supplementing wired
nets for mobility
Next: How to design and test networks
without actually deploying them?
Simulate!
Chapter 6 High-Speed LANs
32