Review of Important ing Concepts Review: ed communication architecture The TCP/IP protocol suite Jörg Liebeherr, 1998,1999 1 Recall the Example from last lecture Ellington.cs.virginia.edu establishes an FTP connection to neon.cs.virginia: ftp neon.cs.virginia.edu ellington Local Campus neon We will use the example to illustrate some important networking concepts Jörg Liebeherr, 1998,1999 2 1
The example: Passing a simple packet from 128.143.71.21 is not on my local network. Therefore, I need to send the packet to my default 128.143.71.21 gateway with is address on my local 128.143.137.1 network. DNS: ARP: What What The is IP is the address the IP MAC address of Therefore, I can send the packet directly. of address ARP: neon.cs.virginia.edu? The of MAC 128.143.137.1? address isof 128.143.137.1 128.143.71.21 is 00:e0:f9:23:a8:20 ARP: What is the MAC ellington.cs. ARP: address The of MAC 128.143.71.21? address of neon.cs.virginia.edu virginia.edu 128.143.137.1 is 00:20:af:03:98:28 (128.143.71.21) (128.143.137.144) router137.cs. virginia.edu (128.143.137.1) router71.cs. virginia.edu (128.143.71.1) frame frame Jörg Liebeherr, 1998,1999 3 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 Jörg Liebeherr, 1998,1999 4 2
TCP/IP Protocol Suite In this course, we will be mostly concerned with the TCP/IP protocol suite The TCP/IP protocol suite is the main characteristic for the networks that we call the Internet The TCP/IP suite has four layers: Application, Transport,, and (Data) Link Application Transport (Data) Link telnet, ftp, email TCP, UDP IP, ICMP, IGMP Device Drivers Computers (hosts) implement all four layers. Gateways (Routers ) only have the bottom two layers. Jörg Liebeherr, 1998,1999 5 Functions of the s Data Link : Service: Reliable transfer of frames over a link Functions: Synchronization, error control, flow control : Service: Moves packets inside the network Functions: Routing, addressing, congestion control Transport : Service: Controls delivery of data between hosts Functions: Connection establishment/termination, error control, flow control Application : Service: Handles details of application programs Functions: Everything is application specific Jörg Liebeherr, 1998,1999 6 3
TCP/IP Suite and OSI Reference Model You know about the OSI Reference protocol The TCP/IP protocol stack does not define the lower layers of a complete protocol stack Application Transport (Data) Link TCP/IP Suite Application Presentation Session Transport (Data) Link Physical OSI Reference Model Jörg Liebeherr, 1998,1999 7 More Information on s An entity of a particular layer can only communicate with: 1. a peer layer entity using a common protocol (Peer Protocol) 2. adjacent layers to provide services and to receive services N+1 N+1 N+1 Protocol N+1 layer N+1/N interface N N N Protocol N layer N/N-1 interface N-1 N-1 N-1 Protocol N-1 Jörg Liebeherr, 1998,1999 8 4
s in the Example FTP program TCP IP Frame is an Ethernet IP datagram Driver Open ftp session to neon FTP program Establish a connection to TCP 128.143.71.21 Open TCP connection to 128.143.71.21 IP datagram is a Send a datagram IP (which TCP Send segment IP contains datagram to 128.143.71.21 to a Send IP datagram to IP connection request) 128.143.71.21 128.143.71.21 Frame is an Send Ethernet datagram toethernet IP datagram Send Ethernet datagram 128.143.137.1 Driver Driver to 128.143.7.21 Driver ellington.cs. router71.cs. virginia.edu Send Ethernet virginia.edu 128.143.137.144 frame to 128.143.137.1 00:e0:f9:23:a8:20 00:e0:f9:23:a8:20 router137.cs. neon.cs. Send Ethernet virginia.edu virginia.edu 128.143.71.1 frame to 128.143.71.21 00:20:af:03:98:28 Jörg Liebeherr, 1998,1999 9 Encapsulation As data is moving down the protocol stack, each protocol is adding layer-specific control information Application User data TCP Application Header User data IP TCP segment Ethernet Driver Ethernet Header IP datagram Ethernet Trailer Jörg Liebeherr, 1998,1999 10 5
Encapsulation in our Example Let us look in detail at the first between ellington and router71.cs. This is the output of tcpdump -exn host 128.143.71.21 18:32:05.664412 0:a0:24:71:e4:44 0:e0:f9:23:a8:20 0800 60: 128.143.137.144.1627 > 128.143.71.21.21: S 607835:607835(0) win 8192 <mss 1460> (DF) 4500 002c 9d08 4000 8006 8bff 808f 8990 808f 4715 065b 0015 0009 465b 0000 0000 6002 2000 598e 0000 0204 05b4 b4b4 Jörg Liebeherr, 1998,1999 11 Encapsulation 6 bytes destination address source address type 4 bytes CRC Jörg Liebeherr, 1998,1999 12 6
Encapsulation: 6 bytes 00:e0:f9:23:a8:20 0:a0:24:71:e4:44 0x0800 4 bytes CRC Jörg Liebeherr, 1998,1999 13 Encapsulation: 32 bits version (4 bits) header length TTL Time-to-Live (8 bits) Identification (16 bits) Type of Service/TOS (8 bits) Protocol (8 bits) flags (3 bits) Total Length (in bytes) (16 bits) Fragment Offset (13 bits) Header Checksum (16 bits) Source IP address (32 bits) Destination IP address (32 bits) Jörg Liebeherr, 1998,1999 14 7
Encapsulation: 32 bits 0x4 0x5 0x00 44 10 9d08 010 2 0000000000000 2 128 10 0x06 8bff 128.143.137.144 128.143.71.21 Jörg Liebeherr, 1998,1999 15 Encapsulation: 32 bits Source Port Number Destination Port Number Sequence number (32 bits) header length Acknowledgement number (32 bits) 0 Flags TCP checksum kind=2 length window size urgent pointer Max. segment size Option: maximum segment size Jörg Liebeherr, 1998,1999 16 8
Encapsulation: 32 bits 1627 10 21 10 607835 10 0 10 819210 6 10 000000 2 000010 2 0x598e 0000 2 2 10 4 10 1460 10 Jörg Liebeherr, 1998,1999 17 Encapsulation: No Application Data in this frame Jörg Liebeherr, 1998,1999 18 9
Different Views of ing Different s of the protocol stack have a different view of the network. This is FTP s and TCP s view of the network. ellington.cs 128.143.137.144 FTP program neon.cs 128.143.71.21 FTP program TCP TCP IP Jörg Liebeherr, 1998,1999 19 View of IP Protocol 128.143.137.1 128.143.71.1 128.143.137.144 128.143.171.21 128.143.137.0 128.143.71.0 Jörg Liebeherr, 1998,1999 20 10
View of Hardware ellington Olsson Hall neon Gilmer Hall 100 Mbps Ethernet 10 Mbps router71 / router137 Ethernet 155 Mbps ATM 155 Mbps ATM 622 Mbps ATM Jörg Liebeherr, 1998,1999 21 11