1. Network Communications Chapter 12
Local Area Network Switching

2. Ethernet Switch
A B C D
DA= B
Switch
Figure 12.1
Figure 12.2: Symbol

3. LAN Segments via a Switch
Each segment uses one or more hubs
Figure 12.3

4. Symmetric Switching All connected segment are the same Benefits
Isolate collisions
Independent simultaneous transfers
Reliability
Figure 12.4

5. Asymmetric Switching Allows different speed segments
Use old hardware/cables along with new equipment
Don’t mix speeds on the same segment
Figure 12.5

6. Switch Operation Cut Through Switch Store-and-Forward
No per link frame checking (done end-to-end)
Reads only the header
Short frame processing delay
Store-and-Forward
Full error checking per link
More reliable
Longer frame processing delay

7. Source Routing

8. Virtual Circuit Switching
Explicit connection setup (and tear-down) phase
Subsequence packets follow same circuit
Sometimes called connection-oriented model 1 3 2 5 11 4 7
Switch 3
Host B
Switch 2
Host A
Switch 1
Analogy: phone call
Each switch maintains a VC table

9. Datagram Switching No connection setup phase
Each packet forwarded independently
Sometimes called connectionless model 1 3 2
Switch 3
Host B
Switch 2
Host A
Switch 1
Host C
Host D
Host E
Host F
Host G
Host H
Analogy: postal system
Each switch maintains a forwarding (routing) table

10. Delay calculation Timelines Acknowledgements & Timeouts Stop-and-Wait
Sliding Window

11. Acknowledgements & Timeouts

12. Stop-and-Wait Problem: keeping the pipe full Example
Sender
Receiver
Problem: keeping the pipe full
Example
1.5Mbps link x 45ms RTT = 67.5Kb (8KB)
1KB frames imples 1/8th link utilization

13. Sliding Window Allow multiple outstanding (un-ACKed) frames
Upper bound on un-ACKed frames, called window
Sender
Receiver T
ime …

14. Figure 12.6: Connecting buildings
Switch Architecture
Layer 2 Switch
Data Link Level
MAC Addresses Based
Layer 3 Switch
IP Address Based
Layer 4
Transport Layer (UDP, TCP)
NAT & Packet Filtering
Figure 12.6: Connecting buildings

15. Firewall NAT (Network Address Translation) Packet Filtering
Accept/reject/modify
Rule-based
Port/Protocol/Application
Proxy Server
Application Surrogate
Allows Controlled Access
Figure 12.7

16. VLAN Quasi-static switch configuration Maintained by administrator
Connect specific LAN segments to form a VLAN
Isolate all VLANs from each other
Maintained by administrator
Subject to hacking (lock equipment cabinets)
Complex to maintain in a large multi-switch environment