Notes

Outline

Network Communications Chapter 12 Local Area Network Switching

Ethernet Switch

LAN Segments via a Switch Each segment uses one or more hubs

Symmetric Switching All connected segment are the same Benefits Isolate collisions Independent simultaneous transfers Reliability

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

Switch Operation Cut Through Switch 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

Source Routing

Virtual Circuit Switching Explicit connection setup (and tear-down) phase Subsequence packets follow same circuit Sometimes called connection-oriented model

Datagram Switching No connection setup phase Each packet forwarded independently Sometimes called connectionless model

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

Acknowledgements & Timeouts

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

Sliding Window Allow multiple outstanding (un-ACKed) frames Upper bound on un-ACKed frames, called window

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

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

VLAN Quasi-static switch configuration 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