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Review of Important Networking Concepts Introductory material. Review of protocol architecture, protocol layers, encapsulation, network abstractions. 1 Networking Concepts • Protocol Architecture • Protocol Layers • Encapsulation • Network Abstractions 2 Communications Architecture • The complexity of the communication task is reduced by using multiple protocol layers: • Each protocol is implemented independently • Each protocol is responsible for a specific subtask • Protocols are grouped in a hierarchy • A structured set of protocols is called a communications architecture or protocol suite 3 TCP/IP Protocol Suite • The TCP/IP protocol suite is the protocol architecture of the Internet Application User-level programs Transport • The TCP/IP suite has four layers: Application, Transport, Network, and Data Link Layer • End systems (hosts) implement all four layers. Gateways (Routers) only have the bottom two layers. Operating system Network Data Link Data Link Media Access Control (MAC) Sublayer in Local Area Networks 4 Functions of the Layers • Data Link Layer: – Service: Reliable transfer of frames over a link – Functions: Framing (timing and synchronization) Media access control Error checking • Network Layer: – Service: Direct packets hop by hop from source host to destination host – Functions: Forwarding • Transport Layer: – Service: Delivery of data between hosts end to end – Functions: Connection establishment/termination error control flow control • Application Layer: – Service: Application specific (delivery of email, retrieval of HTML documents, transfer of file) – Functions: Application specific 5 Assignment of Protocols to Layers ping application HTTP Telnet FTP TCP DNS SNMP Application Layer Transport Layer UDP Routing Protocols ICMP RIP IP IGMP PIM Network Layer OSPF DHCP ARP Ethernet Network Interface Data Link Layer 6 Sending a packet from Argon to Neon Argon Neon The actual path followed by data 7 Layers in the Argon – Neon Example HTTP HTTP protocol HTTP TCP TCP protocol TCP IP Ethernet IP IP protocol Ethernet argon.tcpiplab.edu 128.143.137.144 Ethernet IP protocol Ethernet Ethernet router71.tcpip- router137.tcpiplab.edu lab.edu 128.143.137.1 128.143.71.1 00:e0:f9:23:a8:20 IP Ethernet neon.tcpip-lab.edu 128.143.71.21 8 Layers in action in the Example HTTP TCP IP Frame is an IP datagram Ethernet Send HTTP Request to neon Establish a connection to 128.143.71.21 at port 80 Open TCP connection to 128.143.71.21 port 80 is a TCP IP datagram segment for port 80 Send IP data-gram to Send a datagram (which contains a connection Send IP datagram to IP 128.143.71.21 request) to 128.143.71.21 128.143.71.21 Frame is an IP datagram Send the datagram to 128.143.137.1 Ethernet Ethernet HTTP TCP IP SendEthernet the datagram to 128.143.7.21 argon.tcpipneon.tcpip-lab.edu router71.tcpip- router137.tcpipSend Ethernet frame Send Ethernet frame lab.edu 128.143.71.21 lab.edu to 00:20:af:03:98:28 to 00:e0:f9:23:a8:20 lab.edu 128.143.137.144 128.143.137.1 128.143.71.1 00:e0:f9:23:a8:20 9 Encapsulation • As data is moving down the protocol stack, each protocol is adding layer-specific control information User data HTTP HTTP Header User data HTTP Header User data TCP TCP Header IP TCP segment IP Header Ethernet TCP Header HTTP Header User data IP datagram Ethernet Header IP Header TCP Header HTTP Header User data Ethernet Trailer Ethernet frame 10 Encapsulation – Ethernet Header 6 bytes destination address 4 bytes source address type Ethernet Header CRC IP Header TCP Header Application data Ethernet Trailer Ethernet frame 11 Encapsulation: Ethernet Header 6 bytes 00:e0:f9:23:a8:20 0:a0:24:71:e4:44 0x0800 4 bytes CRC 12 Encapsulation - IP Header 32 bits version (4 bits) header length DS Identification (16 bits) TTL Time-to-Live (8 bits) Protocol (8 bits) Total Length (in bytes) (16 bits) ECN flags (3 bits) Fragment Offset (13 bits) Header Checksum (16 bits) Source IP address (32 bits) Destination IP address (32 bits) 13 Encapsulation - IP Header 32 bits 0x4 0x5 0x0 9d08 12810 0x0 4410 0102 0x06 0000000000000 2 8bff 128.143.137.144 128.143.71.21 14 Encapsulation - TCP Header 32 bits Source Port Number Destination Port Number Sequence number (32 bits) Acknowledgement number (32 bits) header length 0 Flags TCP checksum option type Ethernet Header IP Header window size urgent pointer length Max. segment size TCP Header Application data Option: maximum segment size Ethernet Trailer Ethernet frame 15 Encapsulation and Demultiplexing: TCP Header 32 bits 162710 8010 60783510 010 610 0000002 0000102 0x598e 210 819210 00002 410 146010 16 Encapsulation - Application data Ethernet Header IP Header TCP Header Application data Ethernet Trailer Ethernet frame 17 Different Views of Networking • Different Layers of the protocol stack have a different view of the network. This is HTTP’s and TCP’s view of the network. Argon 128.143.137.144 Neon 128.143.71.21 HTTP client HTTP server HTTP server TCP client TCP server TCP server IP Network 18 Network View of IP Protocol 128.143.137.144 128.143.71.21 128.143.137.1 128.143.71.1 Router 128.143.137.0/24 Network 128.143.71.0/24 Network 19 Network View of Ethernet • Ethernet’s view of the network Argon (128.143.137.144) Router137 (128.143.137.1) Ethernet Network 20