计算机网络ch4_2014

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Computer Networking
Chapter 4
The Network Layer
Interplay between routing and forwarding
routing algorithm
local forwarding table header value output link
The Network Layer
Chapter 4: Network Layer
4.5 Routing algorithms
• Link state • Distance Vector • Hierarchical routing
4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.4 IP: Internet PTM VBR
ATM ABR ATM UBR
yes
yes yes
yes
no no
no (inferred via loss) no congestion no congestion yes no
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Computer Networking
Chapter 4
3rd important function in some network architectures:
• ATM, frame relay, X.25
Before datagrams flow, two hosts and intervening routers establish virtual connection
transport segment from sending to receiving host on sending side encapsulates segments into datagram on receiving side, delivers segments to transport layer network layer protocols in every host, router Router examines header fields in all IP datagram passing through it
• Routers get involved
Network and transport layer connection service:
• Network: between two hosts • Transport: between two processes
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call setup before data can flow, teardown for each call each packet carries VC identifier (not destination host ID) every router on source-dest path maintains “state” for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC
0100 0101 0111 1001 3 2 2 1
value in arriving packet’s header
0111
1
3 2
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Computer Networking
Chapter 4
The Network Layer
Connection setup
• to get circuit-like performance.
Page
• transport-layer connection only involved two end systems
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Computer Networking
Computer Networking
Chapter 4
The Network Layer
Network layer connection and connection-less service
Datagram network provides network-layer connectionless service VC (Virtual Circuit ) network provides network-layer connection service Analogous to the transport-layer services, but:
Chapter goals:
understand principles behind network layer services:
routing (path selection) dealing with scale how a router works advanced topics: IPv6, mobility
instantiation and implementation in the Internet
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Computer Networking
Chapter 4
The Network Layer
Overview
network layer services routing principle: path selection hierarchical routing 层次路由选择 IP Internet routing protocols reliable transfer • intra-domain • inter-domain what’s inside a router? IPv6 mobility
Datagram format IPv4 addressing ICMP IPv6
4.6 Routing in the Internet
Link state Distance Vector Hierarchical routing
RIP OSPF BGP
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Computer Networking
Chapter 4
The Network Layer
Network layer
application transport
network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical
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Computer Networking
Chapter 4
The Network Layer
Chapter 4: Network Layer
4.5 Routing algorithms
4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.4 IP: Internet Protocol
The Network Layer
Virtual circuits 虚电路
“source-to-dest. path behaves much like telephone circuit” • performance-wise • network actions along source-to- dest. path
• • • • Datagram format IPv4 addressing ICMP IPv6
4.6 Routing in the Internet
• RIP • OSPF • BGP
4.7 Broadcast and multicast routing
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Guarantees ?
Network Service Architecture Model
Congestion Bandwidth Loss Order Timing feedback no yes yes no no
Internet best effort none
ATM CBR constant rate guaranteed rate guaranteed minimum none
Computer Networking
Chapter 4
The Network Layer
Network service model
Q: What
transporting datagram from sender to Example services for a flow of receiver? In-order datagram delivery guaranteed delivery Guaranteed minimum Guaranteed delivery bandwidth to flow with bounded delay Restrictions on changes in inter(within 40 ms) packet spacing
Computer Networking
Chapter 4
The Network Layer