L23_network_layer_01

L23_network_layer_01 - 1 The Network Layer Forwarding,...

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Unformatted text preview: 1 The Network Layer Forwarding, Routing, and Addressing (Part I) Lecture 23 6.02 Spring 2008 May 2, 2008 • Network layer functions • Difference between forwarding and routing • Link-state routing with Dijkstra’s shortest-paths alg. Data Link Physical Ethernet, WiFi, … Framing, coding, [limited] rxmits, channel access Modulation/demodulation Application HTTP, FTP, SMTP, … Transport TCP, UDP End-to-End Layer Layering in the Internet Network IP Forwarding & routing (and addressing) Everything else! Reliability, integrity, ordering, jitter ctrl, congestion response, … Today 2 Network Layer Functions • Main goal : best-effort connectivity • Addressing : How to name nodes? • Forwarding : How does switch process packet? • Routing : How to build routing tables to ensure that forwarding is correct? A B C D E F G ? Addressing • A good addressing scheme helps scalability • Influences mobility (Can nodes move a little? A lot?) • For now, assume each node has a unique arbitrary address (“just a name”) • We’ll revisit when we discuss network scalability • Hierarchical and structured addresses 3 Forwarding: It’s All in the Header • Packet header is crucial: switches look at this info to decide what to do • E.g., to send a letter via USPS, the “To” (and “From”) fields are crucial • Header depends on network layer protocol • Generally has dst address , src address, demultiplexing info (which higher layer should get packet) • Also packet length, hop limit (or “time to live”), type-of-service (e.g., priority level), checksum Example: IPv4 Header Payload TCP, UDP, ICMP, etc. Hop limit 4 Forwarding • Core function is conceptually simple • lookup(dst_addr) in routing table returns...
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This note was uploaded on 08/23/2009 for the course EECS 6.02 taught by Professor Terman during the Spring '08 term at MIT.

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L23_network_layer_01 - 1 The Network Layer Forwarding,...

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