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COMPUTER SYSTEMS An Integrated Approach to Architecture and Operating Systems Chapter 13 Fundamentals of Networking and Network Protocols ©Copyright 2008 Umakishore Ramachandran and William D. Leahy Jr. 13.1 Preliminaries • Today a general purpose computer not connected to the "net" or some net is almost unthinkable. • Connecting to a network requires an I/O device which will use DMA 13.2 Basic Terminologies • Computer connected to a network is called a host • The connection is made using a device called a Network Interface Card or NIC • What exactly is the "network" shown in the diagram? • As we shall see it may be one network or a composite of multiple networks 13.2 Basic Terminologies • What is the Internet? Consider the postal system… 13.2 Basic Terminologies • Now consider an email 13.2 Basic Terminologies • Each cloud represented computers of an Internet Service Provider (ISP) • The ISP clouds are not directly connected • Instead they are connected by routers, which are special purpose computer for this purpose • How do these routers know where to send information? A universal system of addresses called Internet Protocol (or IP) Addresses is part of the answer 13.2 Basic Terminologies • We showed connecting using a cable or phone network. Connections may also be made through Local Area Networks (LAN's) • Other hardware devices – hubs/repeaters – bridges – switches – routers 13.3 Networking Software • Need to address issues such as – Arbitrary message size and physical limitations of network packets – Out of order delivery of packets – Packet loss in the network – Bit errors in transmission • Software is logically in a protocol stack configuration 13.3 Networking Software • A protocol is the set of rules used to describe all of the hardware and (mostly) software operations used to send messages from Processor A to Processor B • A protocol describes the syntax, semantics and timing of communication between two devices • Common practice is to attach headers/trailers to the actual payload forming a packet or frame. 13.3.1 Need for a Layered Protocol Stack • Good abstraction • Simpler to understand than OGP • Easier to design, analyze, implement and test • Design concept is suites or families • What do we mean by layers? Or a layered protocol? Consider the army… 13.3.1 Need for a Layered Protocol Stack General Colonel Captain Sergeant Private General Colonel Captain Sergeant Private 13.3.2 Internet Protocol Stack Application Transport Network Link Physical Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 13.3.2 Internet Protocol Stack • Application: HTTP, SMTP, FTP, etc. Shield applications using network from network details • Transport: Breaks message into packets, handles things like out of order packets, may deal with reliability • Network: Responsible for routing, does best effort delivery • Link: Moves the packet using a protocol such as Ethernet, Token Ring, and ATM • Physical: Responsible for physically (electrically, optically, etc.) moving the bits of the packet from one node to the next. 13.3.2 Internet Protocol Stack • Application: HTTP, SMTP, FTP, etc. Shield applications using network from network details • Transport: Breaks message into packets, handles things like out of order packets, may deal with reliability • Network: Responsible for routing, does best effort delivery • Link: Moves the packet using a protocol such as Ethernet, Token Ring, and ATM • Physical: Responsible for physically (electrically, optically, etc.) moving the bits of the packet from one node to the next. 13.3.2 Internet Protocol Stack Manufacturers group their protocol software together into a family and give it a nice name… • • • • • • Novell Corporation Banyan Systems Apple Computer Digital Equipment IBM “The Internet Biggie” • • • • • • Netware VINES AppleTalk DECNET SNA TCP/IP 13.3.2 Internet Protocol Stack • Layer 5: Application-Sends application specific messages • Layer 4: Transport-Sends segments • Layer 3: Network-Sends packets • Layer 2: Datalink-Sends frames • Layer 1: Physical-Sends bits 13.3.2 Internet Protocol Stack 13.4 Transport Layer • Assume – send (destination-address, message) – receive (source-address, message) • Functionality of transport layer – Support arbitrary message size at the application level – Support in-order delivery of messages – Shield the application from loss of messages – Shield the application from bit errors in transmission. 13.4 Transport Layer 13.4.1 Stop and wait protocols • Simple approach – Sender sends a packet and waits for a positive acknowledgement, commonly referred to as an ACK. – As soon as packet is received, recipient generates and sends an ACK for that packet. ACK should contain information for sender to discern unambiguously packet being acknowledged. Sequence number is unique signature of each packet. Thus, all that needs to be in ACK packet is sequence number of received packet. – Sender waits for a period of time called timeout. If within this period, it does not hear an ACK, it re-transmits the packet. Similarly, the destination may re-transmit the ACK, if it receives the same packet again (an indication to the receiver that his ACK was lost en route) 13.4.1 Stop and wait protocols 13.4.1 Stop and wait protocols 13.4.1 Stop and wait protocols RTT = Round Trip Time 13.4.2 Pipelined protocols (a) (b) 13.4.3 Reliable Pipelined Protocol 13.4.3 Reliable Pipelined Protocol Increasing sequence numbers Active window of sequence numbers Packets sent and acknowledged Packets sent but not yet acknowledged Packets that are in the active window that can be sent without waiting for any further ACKs Packets that cannot yet be sent since they are outside the active window 13.4.4 Dealing with transmission errors • Methods are needing to determine if packets are being received correctly • Examples – Checksums – Error Correcting Codes (ECC) 13.4.5 Transport protocols on the Internet Transport Features protocol Pros Cons TCP Connectionoriented; selfregulating; data flow as stream; supports windowing and ACKs Reliable; messages arrive in order; wellbehaved due to selfpolicing Complexity in connection setup and tear-down; at a disadvantage when mixed with unregulated flows; no guarantees on delay or transmission rate UDP Connection-less; unregulated; message as datagram; no ACKs or windowing Simplicity; no frills; especially suited for environments with low chance of packet loss and applications tolerant to packet loss; Unreliable; message may arrive out of order; may contribute to network congestion; no guarantees on delay or transmission rate 13.4.5 Transport protocols on the Internet Application Web browser Key requirement Reliable messaging; in order arrival of messages Transport protocol TCP Instant messaging Reliable messaging; in order arrival of messages TCP Voice over IP Electronic Mail Electronic file transfer Low latency Reliable messaging Reliable messaging; in order delivery Usually UDP TCP TCP Video over Internet Low latency File download on P2P networks Reliable messaging; in order arrival of messages Usually UDP; may be TCP TCP Network file service on LAN Reliable messaging; in order arrival of messages Remote terminal access Reliable messaging; in order arrival of messages TCP; or reliable messaging on top of UDP TCP 13.5 Network Layer • Why a separate layer? – Multiple network connections to the host – Multiple hops between source and destination – Route is not static • Transport/network layers interface – Destination address and packet size • Network layer functionality (host) – Routing algorithms – Provide a service model to the transport layer – Pass it up to transport if destination reached • Network layer functionality (Routers) – Routing algorithms 13.5.1 Routing Algorithms 13.5.1 Routing Algorithms Iteration New node Count to which least-cost route known Init 1 2 3 4 5 A AC ACB ACBD ACBDE ACBDEF B Cost/ route 2/AB 2AB 2/AB C Cost/ route 1/AC 1/AC D Cost/ route 4/AD 3/ACD 3/ACD 3/ACD E Cost/ route 5/AE 4/ACE 3/ABE 3/ABE 3ABE F Cost/ route 6/ACF 6/ACF 5/ADF 4/ABEF 4/ABEF 13.5.1 Routing Algorithms Destination A B C F A 5(EA) 3(BA) 4(ECA) 5(EFDCA) B 7(EAB) 1(EB) 5(ECB) 6(EFDCB C 6(EAC) 3(EBC) 3(EC) 4(EFDC) D 8(EACD) 4(EBEFD) 5(ECD) 2(EFD) F 9(EABEF) 2(EBEF) 7(ECBEF) 1(EF) DV Table for Node E 13.5.1 Routing on the Internet • • • Network of networks Scale, dynamism Autonomous Systems (AS) – – Allows for evolution Gateway node for inter-AS routing Details of the network layer in a gateway node 13.5.1 Hierarchical Routing Algorithms Gateway nodes use BGP Nodes within AS use LS or DV BGP Border Gateway Protocol 13.5.2 Internet Addressing Telephone Number Internet Protocol Address 24 bits 8 bits IP Network Device 13.5.2 Internet Addressing • Consider this 32 bit IP Address – (10000000 00111101 00010111 11011000)2 • Convert each 8-bit octet into a decimal number and separate each with a decimal – 128.61.23.216 • In this address the first 24 bits are network while the last 8 are the device – 128.61.23.216/24 13.5.2 Internet Addressing How many IP networks? 13.5.2 Internet Addressing How many IP networks? 13.5.2 Internet Addressing 8 bits 24 bits Device Device 16 bits 16 bits IP Network Device 24 bits 8 bits IP Network Device 13.5.3 Network Service Model Circuit Switching 13.5.3 Network Service Model MessageSwitching 13.5.3 Network Service Model Packet Switching 13.5.4 Network Layer Summary Network Terminology Circuit switching TDM FDM Definition/Use A network layer technology used in telephony. Reserves the network resources (link bandwidth in all the links from source to destination) for the duration of the call; no queuing or store-and-forward delays Time division multiplexing, a technique for supporting multiple channels on a physical link used in telephony Frequency division multiplexing, also a technique for supporting multiple channels on a physical link used in telephony Packet switching A network layer technology used in wide area Internet. It supports best effort delivery of packets from source to destination without reserving any network resources en route. Message switching Similar to packet switching but at the granularity of the whole message (at the transport level) instead of packets. Switch/Router Input buffers Output buffers Routing table A device that supports the network layer functionality. It may simply be a computer with a number of network interfaces and adequate memory to serve as input and output buffers. These are buffers associated with each input link to a switch for assembling incoming packets. These are buffers associated with each outgoing link from a switch if in case the link is busy. This is table that gives the next hop to be used by this switch for an incoming packet based on the destination address. The initial contents of the table as well as periodic updates are a result of routing algorithms in use by the network layer. 13.5.4 Network Layer Summary Network Terminology Delays Definition/Use Store and forward This delay is due to the waiting time for the packet to be fully formed in the input buffer before the switch can act on it. The delays experienced by packets in a packet-switched network Queuing This delay accounts for the waiting time experienced by a packet on either the input or the output buffer before it is finally sent out on an outgoing link. Packet loss This is due to the switch having to drop a packet due to either the input or the output buffer being full and is indicative of traffic congestion on specific routes of the network. This is the contract between the network layer and the upper layers of the protocol stack. Both the datagram and virtual circuit models used in packetswitched networks provide best effort delivery of packets. This model sets up a virtual circuit between the source and destination so that individual packets may simply use this number instead of the destination address. This also helps to simplify the routing decision a switch has to make on an incoming packet. This model does not need any call setup or tear down. Each packet is independent of the others and the switch provides a best effort service model to deliver it to the ultimate destination using information in its routing table. Service Model Virtual Circuit (VC) Datagram 13.6 Link Layer and Local Area Networks • Innovations in the link layer in the 70's led to making the internet a household term • Link layer is responsible for acquiring physical medium for transmission, and sending packet over the physical medium to destination host. • Broad Classification – Random Access: Example-Ethernet – Taking Turns: Example-Token Ring • Portion of protocol that deals with gaining access to physical medium is called the Media Access and Control (MAC) layer 13.6.1 Ethernet No collision Collision Detected Medium Idle Need to Transmit Listen for Carrier Transmit Message Medium Not Idle Abort Transmission Transmission Complete Terminologies • • • • Base band signaling Manchester encoding CSMA/CD CSMA/CA – Hidden terminal problem – RTS/CTS Joe • xBASEy • Watch – Triumph of the Nerds (PBS show) Cindy Bala 13.6.1 Manchester Encoding 0 1 1 0 0 1 0 1 1 13.6.1 Ethernet Hidden Terminal Problem 13.6.2 Token Ring Comparison Link Features Layer Protocol Pros Cons Ethernet Member of random access protocol family; opportunistic broadcast using CSMA/CD; exponential backoff on collision Token Member of taking turns ring protocol family; Token needed to transmit Simple to manage; works well in light load Too many collisions under high load Fair access to all competing stations; works well under heavy load Unnecessary latency for token acquisition under light load 13.6.3 Other link layer protocols • FDDI: Fiber Distributed Data Interface – Fiber optics based – High bandwidth backbone used to connect LAN's • ATM: Asynchronous Transfer Mode – Guarantees quality of service using link reservation and admission control to avoid congestion – Connection oriented and can have transport layer implemented on top of it – Used in MAN's and WAN's • PPP: Point to Point – Used by dial-up connections – Widespead 13.6.3 Other link layer protocols • Ethernet is really not just one protocol. As obsolescence approaches a new version is introduced and typically comes out on top • FDDI was upstaged by Gigabit Ethernet • ATM is likely to be upstaged by 10-Gigabit Ethernet 13.7 Relationship between the three layers • Both TCP and IP include error checking – They don't have to be used together • Most layers are in software but the link layer is often implemented in hardware 13.8 Data structures for packet transmission /* Packet Header Data Structure */ struct header_t { int destination_address; /* destination address */ int source_address; /* source address */ int num_packets; /* total number of */ /* packets in message */ int sequence_number; /* sequence number of */ /* this packet */ int packet_size; /* size of data */ /* contained in the */ /* packet */ int checksum; /* for integrity check of */ /* this packet */ }; 13.8 Data structures for packet transmission /* Packet Data Structure */ struct packet_t { struct header_t header; /* char *data; /* /* /* }; packet header */ pointer to the memory */ buffer containing the data */ of size packet_size */ 13.9 Message transmission time P1 P2 Protocol Protocol stack stack S msg pkt1 … pkt2 Tw pktn Network Tf R 13.9 Message transmission time Sender Overhead Time on the wire Time of Flight Receiver Overhead 13.10 Protocol Layering • Layering is a structuring tool for combating complexity of protocol stack • Allows partitioning total responsibility for message transmission and reception among various layers. • Modularity allows integration of a new module at a particular layer with minimal changes to the other layers. • It might appear that a potential downside to layering might be a performance penalty, as the message has to traverse several layers. • Judicious definition of interfaces between layers avoids such inefficiencies. 13.10.1 OSI Model 7 Application 6 Presentation 5 4 3 2 1 Session Transport Network Data Link Physical • Presentation layer subsumes user directed input/output functionalities that are common across different applications. • Session layer maintains process-to-process communication details and provides a higher-level abstraction between an application and the transport layer (e.g. Unix socket). 13.10.2 Practical issues with layering 7 Application 6 Presentation 5 4 3 2 1 Telnet, FTP, etc. 5 TCP 4 IP 3 Ethernet Card 2 Physical 1 Session Transport Network Data Link Physical 13.11 Networking Hardware • Hub/Repeater Hub 13.11 Networking Hardware • More Hubs Hub Hub Hub Hub Hub 13.11 Networking Hardware • Bridge 1 3 HUB 2 Collision domain BRIDGE HUB 4 Collision domain 13.11 Networking Hardware • Switch 13.11 Networking Hardware • VLAN 5 1 Switch Switch 6 2 4 3 8 7 13.11 Networking Hardware • NIC MAC address Header Message Payload 13.11 Networking Hardware • Router MAC address of router IP address of the destination Message Payload for destination node Payload for the router 13.11 Networking Hardware Name of Definition/Function Component Host A computer on the network; this is interchangeably referred to as node and station in computer networking parlance NIC Network Interface Card; interfaces a computer to the LAN; corresponds to layer 2 (data link) of the OSI model Port End-point on a repeater/hub/switch for connecting a computer; corresponds to layer 1 (physical) of the OSI model Collision Term used to signify the set of computers that can domain interfere with one another destructively during message transmission Repeater Boosts the signal strength on an incoming port and faithfully reproduces the bit stream on an outgoing port; used in LANs and WANs; corresponds to layer 1 (physical) of the OSI model 13.11 Networking Hardware Name of Component Hub Definition/Function Bridge Connects independent collision domains, isolating them from one another; typically 2-4 ports; uses MAC addresses to direct the message on an incoming port to an outgoing port; corresponds to layer 1 (physical) of the OSI model Similar functionality to a bridge but supports several ports (typically 432); provides expanded capabilities for dynamically configuring and grouping computers connected to the switch fabric into VLANs; corresponds to layer 1 (physical) of the OSI model Essentially a switch but has expanded capabilities to route a message from the LAN to the Internet; corresponds to layer 3 (network) of the OSI model Virtual LAN; capabilities in modern switches allow grouping computers that are physically distributed and connected to different switches to form a LAN; VLANs make higher level network services such as broadcast and multicast in Internet subnets feasible independent of the physical location of the computers; corresponds to layer 1 (physical) of the OSI model Switch Router VLAN Connects computers together to form a single collision domain, serving as a multi-port repeater; corresponds to layer 1 (physical) of the OSI model 13.12 Network Programming P1 P2 Socket 13.12.1 Unix Sockets • • • • Socket: create an endpoint of communication Bind: bind a socket to a name or an address Listen: listen for incoming connections on the socket Accept: accept an incoming connection request on a socket • Connect: send a connection request to a name (or address) associated with a remote socket • Recv: receive incoming data on a socket from a remote peer • Send: send data to a remote peer via a socket 13.13 Network Services and Higher Level Protocols P1 P2 foo (args) foo (args) RPC return Host 1 Host 2 13.13 Network Services and Higher Level Protocols User fopen Unix file system Unix file system NFS server NFS client RPC layer at client RPC layer at server Network 13.15 Historical Perspective • • • • From Telephony to Computer Networking Evolution of the Internet PC and the arrival of LAN Evolution of LAN 13.15.1 From Telephony to Computer Networking • 1875 Telephone invented…analog system • 1960 Telephone infrastructure goes digital 13.15.1 From Telephony to Computer Networking • 1940's Mainframe computers developed • 1960's Transition – Batch-oriented card-input/output – CRT I/O and timesharing 13.15.1 From Telephony to Computer Networking Digital Data Analog Data ?Missing Link? Telephone Telephone Infrastructure Infrastructure ?Missing Link? Analog Data Digital Data 13.15.1 From Telephony to Computer Networking Digital Data Analog Data MODEM Telephone Telephone Infrastructure Infrastructure MODEM Analog Data Digital Data 13.15.1 From Telephony to Computer Networking • 1968/9 Carterphone decision allowed devices which were beneficial and not harmful to the network to be connected to the Public Switched Telephone Network (PSTN). Paved the way for computers to communicate using the telephone switching infrastructure. 13.15.2 Evolution of the Internet • 1965 DoD DARPA plans first computer network • 1969 ARPANET connects 4 computers using packet switched network – Stanford Research Institute, UCLA, UC Santa Barbara, and the University of Utah – Networking luminary Leonard Kleinrock, is credited with successfully sending the first network “message” from UCLA to Stanford. 13.15.2 Evolution of the Internet • “Router” in the network was called Interface Message Processor (IMP), built by a company called BBN (which stands for Bolt, Beranak, and Newman Inc.). – IMP system architecture required a careful balance of the hardware and software that would allow it to be used as a store-and-forward packet switch among these computers. – IMP's used modems and leased telephone lines to connect to one another. • 1971 The ARPANET grows to 23 hosts connecting universities and government research centers around the country. 13.15.2 Evolution of the Internet 1973 Robert Metcalfe and David Boggs invent the Ethernet networking system at the Xerox Palo Alto Research Center. 13.15.2 Evolution of the Internet • 1973 The ARPANET goes international 13.15.2 Evolution of the Internet • 1975 Internet operations transferred to the Defense Communications Agency • 1978 Hayes Microcomputer Products releases the first mass-market modem, transmitting at 300 bps (0.3K). • 1980 John Shoch at Xerox creates the first “worm” program, with the capacity to travel through networks. • 1981 Ungermann-Bass ships the first commercial Ethernet network interface card. 13.15.2 Evolution of the Internet • 1981 ARPANET has 213 hosts. A new host is added approximately once every 20 days. • 1982 The term 'Internet' is used for the first time. • 1983 TCP/IP becomes the universal language of the Internet. Developed by Vinton Cerf and Robert Kahn • 1984 CISCO founded • Early 80's Unix and IBM OS included TCP/IP 13.15.2 Evolution of the Internet • Late 90's Internet becomes household term – Needed PC – Needed "Killer app" i.e. WWW & browsers 13.15.3 PC and the arrival of LAN • 1971 Intel introduces the first microprocessor - the Intel 4004. • 1971 The Kenbak-1, the first microcomputer, is introduced in Scientific American, selling a total of 40 units in 2 years. Used 130 IC's with a 256 byte memory and 8-bit words, processed 1000 instructions per second, and cost $750. 13.15.3 PC and the arrival of LAN • 1972 Intel launches the 8-bit 8008 - the first microprocessor which could handle both upper and lowercase characters. • 1972 Xerox develops the Xerox Alto - the first computer to use a Graphic User Interface. The Alto consists of four major parts: the graphics display, the keyboard, the graphics mouse, and the disk storage/processor box. Each Alto is housed in a beautifully formed, textured beige metal cabinet that hints at its $32,000 price tag (1979US money). With the exception of the disk storage/processor box, everything is designed to sit on a desk or tabletop 13.15.3 PC and the arrival of LAN • 1973 Robert Metcalfe and David Boggs invent the Ethernet networking system at the Xerox Palo Alto Research Center. 13.15.3 PC and the arrival of LAN • 1974 Intel introduces the 8080 microprocessor – 5 times faster than the 8008. – And the heart of the future Altair 8800. • 1975 MITS markets the Altair 8800 - the first mass-market microcomputer, launching the Personal Computer Revolution. • 1975 Bill Gates and Paul Allen form the Microsoft company to create software for the new Altair 8800. 13.15.3 PC and the arrival of LAN • 1976 Apple Computer is formed by Steve Jobs, Steve Wozniak, and Ron Wayne, and launches the Apple Computer. • 1977 Tandy Radio Shack ships its first personal computer - the TRS-80. It sells over 10,000 units, tripling expectations. • 1977 Apple Computer launches the Apple II, which sets new standards for sophisticated personal computer systems. 13.15.3 PC and the arrival of LAN • 1978 The C programming language is completed at AT&T Bell Laboratories, offering a new level of programming. • 1978 Apple and Tandy ship PCs with 5.25" floppy disks, replacing cassette tape as the standard storage medium for PCs. • 1978 Hayes Microcomputer Products releases the first mass-market modem, transmitting at 300 bps (0.3K). 13.15.3 PC and the arrival of LAN • 1978 Intel ships the Intel 8086 microprocessor, with 29,000 transistors, and running at 4.77 megahertz. • 1979 Personal Software creates VisiCalc for the Apple II, the first electronic spreadsheet program, selling over 100,000 copies. • 1979 Intel develops the 8088 microprocessor, which would later become the heart of the IBM PC. 13.15.3 PC and the arrival of LAN • 1979 Motorola develops the Motorola 68000 microprocessor, offering a new level of processing power. • 1979 Robert Metcalf founded 3COM • 1980 Seagate Technology introduces the first microcomputer hard disk, capable of holding 5 megabytes of data. • 1980 Philips introduces the first optical laser disk, with many times the storage capacity of floppy or hard disks. 13.15.3 PC and the arrival of LAN • 1980 Xerox creates Smalltalk - the first objectoriented programming language. • 1981 Ungermann-Bass ships the first commercial Ethernet network interface card. • 1981 Xerox introduces the Xerox Star 8010, the first commercial Graphic User Interface computer, for $16,000-$17,000. 13.15.3 PC and the arrival of LAN • 1981 Microsoft supplies IBM with PC-DOS (which it would also sell as MS-DOS), the OS that would power the IBM PC. • 1981 IBM brings to market the IBM PC, immediately establishing a new standard for the world of personal computers. 13.15.4 Evolution of LAN • Thicknet – Coaxial cable/Vampire taps – 10base5 (10 Mbits/sec, baseband, 500 meters) – 1979-1985 Thick Coax Segment 500 Meter Maximum MAU 15 pin AUI Connector AUI Cable (50 meter max) Ethernet Interface MAU - Medium Access Unit AUI - Attach Unit Interface Male "N" Connector 50 ohm terminator AMP Thick Coaxial (Vampire) Tap 13.15.4 Evolution of LAN • Thinnet – Coaxial cable/BNC connectors – 10base2 (10 Mbits/sec, baseband, 200 meters) 10-Base-2 Coaxial Ethernet Cable with BNC terminations – 1985-1993 Computer Terminator Terminator BNC "T" Connector 13.15.4 Evolution of LAN • Fast Ethernet – Move "ethernet" into the box – 100baseT (T for twisted pair) – RJ45 Connectors