Bài giảng Computer Networks 1 (Mạng máy tính 1) - Lecture 3: Networking Technologies - Phạm Trần Vũ
Lecture 3: Networking Technologies
Reference:
Chapter 4 - “Computer Networks”,
Andrew S. Tanenbaum, 4th Edition, Prentice Hall, 2003.
Content
ꢀ Channel allocation problem
ꢀ Multiple access protocols
ꢀ Ethernet LAN
ꢀ Wireless LAN
3
Channel Allocation Problem
ꢀ How to allocate a single broadcast channel
amongst competing users?
ꢀ Static met
ꢀ Dynamic method
4
Static Channel Allocation in LANs and
MANs
ꢀ Each user is assigned with a equal-portion
of the bandwidth
ꢀ No interfe
ꢀ Simple
network
5
Dynamic Channel Allocation in
LANs and MANs
ꢀ Five key assumptions
ꢁ
Station Model:
The model consists of N stations
ꢀ
ꢀ
Once a frame is generated, the station blocks until
the frame has been successfully transmitted
ꢁ
ꢁ
Single Channel Assumption
Collision Assumption
ꢀ
transmitted imultanousy and overlap in time
ꢁ
ꢁ
(a) Continuous Time vs (b) Slotted Time
(a) Carrier Sense vs (b) No Carrier Sense
6
Multiple Access Protocols
ꢀ ALOHA
ꢀ Carrier Sense Multiple Access Protocols
ꢀ Collision-Free Protocols
ꢀ Limited-Contention Protocols
Protocols
ꢀ Wireless LAN Protocols
7
ALOHA
ꢀ Developed by Norman Abramson, in 1970s
ꢀ Used ground-based radio broadcast
ꢀ Pure ALOHA
ꢁ
Use continuous time
ꢁ
No need for global time
ꢀ Slotted ALOHA
ꢁ
Need global time synchronisation
8
Pure ALOHA (1)
ꢀ Users can transmit whenever they have data
to send
ꢀ If there is a collision, colliding frames will be
damaged and will be destroyed
if there is a collision
ꢀ Senders wait for a random time to transmit
destroyed frames
9
Carrier Sense Multiple Access
Protocols
ꢀ
When there is data to send, a station senses
carrier first
ꢀ
ꢀ
ꢀ
If the carrier is free, it starts sending
Else, it waits until the carrier becomes free
Common carrier sense protocols
ꢁ
ꢁ
ꢁ
1-Persistent
Nonpersis
p-Persistent
14
Persistent and Nonpersistent
CSMA
Comparison of the channel utilization versus
load for various random access protocols.
15
CSMA with Collision Detection
ꢀ An improvement to CSMA
ꢀ A station stops transmitting its frame
immediate ected to
save time and bandwidth
16
Collision-Free Protocols
The basic bit-map protocol.
18
Collision-Free Protocols (2)
The binary countdown protocol. A dash indicates silence.
19
Ethernet
ꢀ Ethernet Cabling
ꢀ Manchester Encoding
ꢀ The Ethernet MAC Sublayer Protocol
ꢀ Switched Ethernet
ꢀ Fast Ethernet
ꢀ Gigabit Ethernet
20
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