3rd edition, chapter 5 - duke university.ppt

Chapter 5: The Data Link Layer
Our goals:
understand principles behind data link layer services:
error detection, correction
sharing a broadcast channel: multiple access
link layer addressing
reliable data transfer, flow control: done!
instantiation and implementation of various link layer technologies
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5: DataLink Layer
Link Layer
Introduction and services
Error detection and correction
access protocols
Link-Layer Addressing

Hubs and switches
PPP
Link Virtualization: ATM and MPLS
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5: DataLink Layer
Link Layer: Introduction
Some terminology:
hosts and routers are munication channels that connect adjacent nodes munication path are links
wired links
wireless links
LANs
layer-2 packet is a frame, encapsulates datagram
“link”
data-link layer has responsibility of
transferring datagram from one node
to adjacent node over a link
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5: DataLink Layer
Link layer: context
Datagram transferred by different link protocols over different links:
., on first link, frame relay on intermediate links, on last link
Each link protocol provides different services
., may or may not provide rdt over link
transportation analogy
trip from Princeton to Lausanne
limo: Princeton to JFK
plane: JFK to Geneva
train: Geneva to Lausanne
tourist = datagram
transport segment = communication link
transportation access = link layer protocol
travel agent = routing algorithm
Traffic lights,
Airport control,
Platform scheduling,
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5: DataLink Layer
Link Layer Services
Framing, link access:
encapsulate datagram into frame, adding header, trailer
channel access if shared medium
“MAC” addresses used in frame headers to identify source, dest
different from IP address!
Reliable delivery between adjacent nodes
we learned how to do this already (chapter 3)!
seldom used on low bit error link (fiber, some twisted pair)
wireless links: high error rates
Q: why both link-level and end-end reliability?
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5: DataLink Layer
Link Laye