What is a LAN ?

1
What is a LAN ?

• A LAN is a data communication system allowing a
  number of independent devices to communicate
  directly with each other, within a moderately
  sized geographic area over a physical
  communications channel of moderate data rates.
• Thus
• Communicate Directly
• Moderately Sized Geographic Area
• Moderate Data Rate

2
Basic Requirements of a LAN

• Data rate of 1 to 100 Mbps
• Geographic distances spanning at most 1-5 km
• Ability to support several hundred independent
  devices
• Simplicity, or use of the simplest mechanisms
  that have the required functionality and
  performance
• Reliability and good error characteristics

3
Basic Requirements of a LAN

• Minimal dependence on any centralized components
  or control
• Efficient use of shared resources, including the
  network channel
• Stability under high load
• Fair access (bandwidth, delay) to the network by
  all devices
• Easy installation
• Ease of reconfiguration and maintenance
• Low cost

4
LAN Extension
5
Network Topologies
B
B
B
C
C
A
A
C
A
E
D
E
D
D
E
Star Ring Dual Ring
A
D
B
F
D
B
A
C
B
A
C
E
C
F
E
Bus Tree Dual Bus
6
Network Topologies
B
A
D
A
D
B
C
F
C
E
A
B
C
Dual Bus Dual Bus Mesh
B
C
A
D
E
H
F
G
Snowflake
7
Network Topologies
G
B
???
C
H
A
F
??? ? ???
J
E
I
D
A
H
???
???
L
F
...
B
G
D
C
M
K
E
Hub or Concentrator
O
N
Bridged Ring Networks
8
Rules of Using Repeaters

• Maximum 5 sections
• Maximum 4 repeaters
• Maximum 3 sections can have hosts
• Within a whole collision domain
• Reason Propagation round trip latency lt 51.2 ms

8
9
CSMA/CD

• listen before talk
• listen while talking
• wait before talk again
• BEBA Algorithm
• n (n lt 16) collision times, more than
  16 would give error message.
• k Min (n,10) kn when nlt10,k10
  when ngt10
• r (unit slot time) 0 lt r lt 2k
  random waiting factor
• Slot time 51.2 ms.

9
10
Calculation of Slot time
????
?? ????
?? ????
???? ???
???? ???
??
??? 0.1 ms 0.1 ms 5 5 2.0 ms ????? 5.13ns/?? 0 3
00?? 300?? 3.08 ms ???(????) 0.05 ms 0.3 m
3 3 2.10 ms ???(????) 0.05 ms 0.6us 3 0 1.95
ms ???(????) 0 0.9 m 0 3 2.70 ms ???? 4.33ns/??
0 1500?? 1500?? 12.99 ms ????????? 5.13ns/?? 0 100
0?? 1000?? 10.26 ms ????? 0.1 ms 0 2 2 0.40
ms ????? 0.1 ms 0 2 2 0.40 ms ?????(????) 0.2
ms 0.4 ms 2 0 1.20 ms ?????(????) 0.2 ms 0.2
ms 0 2 0.80 ms ???? 0 0.2 ms 5 0 1.00
ms ???? 0 0.2 ms 0 5 1.00 ms ?????? 0 0.1
ms 3 0 0.30 ms (? 70 ?500???) ??????(?
50 0 2.0 ms 0 3 6.00 ms ? 94 ?
500???) ???? 0 0.2 ms 0 1 0.20 ms
?????????? 46.38 ms
11
IEEE Project 802 Standards

• IEEE 802.1 High Level Interface
• IEEE 802.1D Local Bridge (Spanning Tree
  Algorithm)
• IEEE 802.1G Remote Bridge
• IEEE 802.2 LLC (Logical Link Control)
• IEEE 802.3 CSMA/CD (Carrier Sense Multiple Access
  with Collision Detection
• IEEE 802.4 Token-Bus
• IEEE 802.5 Token-Ring
• IEEE 802.6 DQDB (Distributed Queue Dual Bus)

12
IEEE Project 802 Standards

• IEEE 802.7 Broadband Technical Advisory Group
• IEEE 802.8 Fiber Optic Technical Advisory Group
• IEEE 802.9 Integrated Voice and Data LAN Working
  Group
• IEEE 802.10 LAN Security Working Group
• IEEE 802.11 Wireless LAN
• IEEE 802.12 Demand-Priority (100VG-AnyLAN)
• IEEE 802.14 CATV Networks

13
IEEE Project 802 Standards
802.1 ??????
LLC
802.2 LLC
MAC
802.12
802.5
802.11
AX3T9.5
802.3
802.4
802.6
802.9
Token-Ring
Wireless
FDDI
CSMA/CD
Token-Bus
Isochronous
DQDB
100VG- AnyLAN
Physical
LAN
Ethernet