麻省理工学院：《数据通信》课程教学讲义（英文版）Lectures 24&25 Higher Layer Protocols：TCP/IP and ATM

Lectures 24&25 Higher Layer Protocols: TCP/IP and atm Eytan Modiano Massachusetts Institute of Technology Laboratory for Information and Decision Systems

Lectures 24 & 25 Higher Layer Protocols: TCP/IP and ATM Eytan Modiano Massachusetts Institute of Technology Laboratory for Information and Decision Systems Eytan Modiano Slide 1

Outline Network Layer and Internetworking The TCP/IP protocol suit ATM MPLS

Outline • Network Layer and Internetworking • The TCP/IP protocol suit • ATM • MPLS Eytan Modiano Slide 2

Higher Layers Application Application irtual network service Presentation Presentation Virtual session Virtual link for end to end messages Transport Transport TCP, UDP Virtual link for end to end packet Network Network Network IP. ATM Virtual link for eliable packets Data link Data link LC DLCLDLC Control Virtual bit pipe physical nt. phys. int interface ysical link External subnet subnet External node

Higher Layers Virtual link for reliable packets Application Presentation Session Transport Network Data link Control Application Presentation Session Transport Network Data link Control Network Network DLC DLC DLC DLC Virtual bit pipe Virtual link for end to end packets Virtual link for end to end messages Virtual session Virtual network service physical phys. int. phys. int. phys. int. phys. int. interface physical interface TCP, UDP IP, ATM Physical link External subnet subnet External Site node node site Eytan Modiano Slide 3

Packet Switching Datagram packet switching Route chosen on packet-by-packet basis Different packets may follow different routes Packets may arrive out of order at the destination E.g., IP(The Internet Protocol Virtual Circuit packet switching All packets associated with a session follow the same path Route is chosen at start of session Packets are labeled with a vc# designating the route The vc number must be unique on a given link but can change from link to link Imagine having to set up connections between 1000 nodes in a mesh Unique vc numbers imply 1 Million vc numbers that must be represented and stored at each node E.g., ATM(Asynchronous transfer mode)

Packet Switching • Datagram packet switching – Route chosen on packet-by-packet basis – Different packets may follow different routes – Packets may arrive out of order at the destination – E.g., IP (The Internet Protocol) • Virtual Circuit packet switching – All packets associated with a session follow the same path – Route is chosen at start of session – Packets are labeled with a VC# designating the route – The VC number must be unique on a given link but can change from link to link Imagine having to set up connections between 1000 nodes in a mesh Unique VC numbers imply 1 Million VC numbers that must be represented and stored at each node – E.g., ATM (Asynchronous transfer mode) Eytan Modiano Slide 4

Virtual Circuits Packet Switching For datagrams, addressing information must uniquely distinguish each network node and session Need unique source and destination addresses For virtual circuits, only the virtual circuits on a link need be distinguished by addressing Global address needed to set-up virtual circuit Once established. local virtual circuit numbers can then be used to represent the virtual circuits on a given link: Vc number changes from link to link VC7 VC4 9 VC13 Merits of virtual circuits Save on route computation VC3 VC7 Need only be done once VC3 at start of session Save on header size Node 5 table More complex Less flexible (35)vc13→(5,8)Vc3 (35)Vc7→(5,8)Vc4 (6,5) Vc3→(5,8)VC7

Virtual Circuits Packet Switching • For datagrams, addressing inf ormation must uniquely distinguish each network node and session – Need unique source and destination addresses • For virtual circuits, only the virtual circuits on a link need be distinguished by addressing – Global address needed to set-up virtual circuit – Once established, local virtual circuit numbers can then be used to represent the virtual circuits on a given link: VC number changes from link to link • Merits of virtual circuits – Save on route computation Need only be done once at start of session – Save on header size – More complex – Less flexible 3 6 5 8 2 9 VC3 VC13 VC7 VC4 VC3 VC7 Node 5 table (3,5) VC13 -> (5,8) VC3 (3,5) VC7 -> (5,8) VC4 (6,5) VC3 -> (5,8) VC7 Eytan Modiano Slide 5

The TCP/P Protocol Suite Transmission Control Protocol Internet Protocol Developed by darpa to connect Universities and research labs Four Layer model Applications Telnet, FTP, email,etc Transport TCP, UDP Network IP ICMP IGMP Link D Device drivers, interface cards TCP- Transmission control protocol UDP-User Datagram Protocol IP-Internet Protoco

The TCP/IP Protocol Suite • Transmission Control Protocol / Internet Protocol • Develo ped by DARPA to connect Universities and Research Labs Four Layer model Telnet, FTP, email, etc. TCP, UDP IP, ICMP, IGMP �Device drivers, interface cards TCP - Transmission Control Protocol UDP - User Datagram Protocol IP - Internet Protocol Applications Transport Network Link Eytan Modiano Slide 6

Internetworking with TCP/IP FTP FTP Protocol > FTP client erver TCP TCP Protocol > TCP ROUTER IP Protocol IP IP Ethernet. driver Ethernet token ring i token ring Protocol :driver driver Protocol driver Ethernet token rir ng

Internetworking with TCP/IP FTP FTP Protocol FTP cli ent server TCP Protocol TCP TCP IP IP Protocol IP Protocol Ethernet Ethernet Protocol token driver token ring Protocol Ethernet driver IP ROUTER IP Ethernet driver token driver token ring ring ring Eytan Modiano Slide 7

Encapsulation user dat application Appl header user data TCP TCP header application data TCP segment TCP header application data iP datagram driver Ethernet TCP Ethernet header header header application data trailer Ethernet 14 20 20 Ethernet frame 46 to 1500 bytes

Encapsulation 14 20 20 4 Ethernet frame 46 to 1500 bytes Ethernet Ethernet Application user data Appl user data header TCP header application header IP TCP header application IP datagram TCP header application header Ethernet IP header Ethernet trailer driver IP TCP TCP segment data data data Eytan Modiano Slide 8

Bridges, Routers and Gateways a Bridge is used to connect multiple lan segments Layer 2 routing(Ethernet) Does not know iP address Varying levels of sophistication simple bridges just forward packets smart bridges start looking like routers A Router is used to route connect between different networks using network layer address Within or between Autonomous Systems Using same protocol(e.g, IP, ATM) a Gateway connects between networks using different protocols Protocol conversion Address resolution These definitions are often mixed and seem to evolve!

Bridges, Routers and Gateways • A Bridge is used to connect multiple LAN segments – Layer 2 routing (Ethernet) – Does not know IP address – Varying levels of sophistication Simple bridges just forward packets smart bridges start lo o king like routers • A Router is used to route connect between different networks using network layer address – Within or between Autonomous Systems – Using same protocol (e.g., IP, ATM) • A Gateway connects between networks using different protocols – Protocol conversion – Address resolu tion • These definitions are often mixed and seem to evolve! Eytan Modiano Slide 9

Bridges, routers and gateways Small company Another providers Frame Relay Backbone Ethernet a Router Bridge Ethernet b Gateway Gateway) ervice providers ATM backbone ATM switches (routers

Bridges, routers and gateways Ethernet A Ethernet B Bridge IP Router Small company Gateway Service provider’s ATM backbone ATM switches (routers) Gateway Another provider’s Frame Relay Backbone Eytan Modiano Slide 10