DOCSLIB.ORG

15-441 Computer Networking Outline Ipv4 Header – RFC791 (1981) IP

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
15-441 Computer Networking Outline Ipv4 Header – RFC791 (1981) IP Outline • IP Packet Format 15-441 Computer Networking • NAT Lecture 8 – IP Packets, Routers • IPv6 • Router Internals • Route Lookup Lecture 8: 9 -20-01 2 IPv4 Header – RFC791 (1981) IP Header Fields 32 bits 0 4 8 16 19 24 32 • Version à 4 for IPv4 type of • Header length (in 32 bit words) ver header length service length • Minimum value is 5 (header without any options) fragment 16-bit identifier flags offset • Length of entire IP packet in octets (including time to Protocol Header header) live checksum 32 bit source IP address • Identifier, flags, fragment offset à used primarily 32 bit destination IP address for fragmentation Options (if any) Padding (if any) • Time to live • Must be decremented at each router data (variable length, • Packets with TTL=0 are thrown away typically a TCP • Ensure packets exit the network or UDP segment) Lecture 8: 9 -20-01 3 Lecture 8: 9 -20-01 4 IP Header Fields IP Type of Service • Protocol • Typically ignored • Demultiplexing to higher layer protocols • TCP = 6, ICMP = 1, UDP = 17… • Values • Header checksum • 3 bits of precedence • Ensures some degree of header integrity • 1 bit of delay requirements • Relatively weak – 16 bit • 1 bit of throughput requirements • Source/Dest address • 1 bit of reliability requirements • Options • E.g. Source routing, record route, etc. • Replaced by DiffServ • Performance issues • Poorly supported Lecture 8: 9 -20-01 5 Lecture 8: 9 -20-01 6 1 ICMP: Internet Control Fragmentation Message Protocol • Used by hosts, routers, gateways to communication Type Code description • IP packets can be up to 64KB network-level information 0 0 echo reply (ping) 3 0 dest. network unreachable • Different link -layers have different MTUs • Error reporting: unreachable 3 1 dest host unreachable • Split IP packet into multiple fragments host, network, port, protocol 3 2 dest protocol unreachable • Echo request/reply (used by 3 3 dest port unreachable • IP header on each fragment ping) 3 6 dest network unknown 3 7 dest host unknown • Intermediate router may fragment as needed • Network-layer “above” IP: 4 0 source quench (congestion • ICMP msgs carried in IP control - not used) datagrams 8 0 echo request (ping) • ICMP message: type, code plus 9 0 route advertisement first 8 bytes of IP datagram 10 0 router discovery 11 0 TTL expired causing error 12 0 bad IP header Lecture 8: 9 -20-01 7 Lecture 8: 9 -20-01 8 IP Fragmentation & Reassembly Reassembly • Network links have MTU • Where to do reassembly? (max.transfer size) - largest possible link-level frame. fragmentation: • End nodes • different link types, in: one large datagram out: 3 smaller datagrams • Avoids unnecessary work where large packets different MTUs are fragmented multiple times • Large IP datagram divided (“fragmented”) within net • one datagram becomes reassembly • Dangerous to do at intermediate nodes several datagrams • IP header bits used to • How much buffer space required at routers? identify, order related • What if routes in network change? fragments • Multiple paths through network • All fragments only required to go through destination Lecture 8: 9 -20-01 9 Lecture 8: 9 -20-01 10 Fragmentation Related Fields IP Fragmentation and Reassembly • Length length ID fragflag offset • Length of IP fragment =4000 =x =0 =0 • Identification One large datagram becomes • To match up with other fragments several smaller datagrams • Flags length ID fragflag offset =1500 =x • Don’t fragment flag =1 =0 • More fragments flag length ID fragflag offset =1500 =x =1 =1480 • Fragment offset length ID fragflag offset • Where this fragment lies in entire IP datagram =1040 =x =0 =2960 • Measured in 8 octet units (13 bit field) Lecture 8: 9 -20-01 11 Lecture 8: 9 -20-01 12 2 Fragmentation is Harmful Path MTU Discovery • Uses resources poorly • Hosts dynamically discover minimum MTU of path • Forwarding costs per packet • Algorithm: • Best if we can send large chunks of data • Initialize MTU to MTU for first hop • Send datagrams with Don’t Fragment bit set • Worst case: packet just bigger than MTU • If ICMP “pkt too big” msg, decrease MTU • Poor end-to-end performance • What happens if path changes? • Loss of a fragment • Periodically (>5mins, or >1min after previous increase), • Reassembly is hard increase MTU • Buffering constraints • Some routers will return proper MTU • MTU values cached in routing table Lecture 8: 9 -20-01 13 Lecture 8: 9 -20-01 14 Outline IP Address Utilization (‘98) • IP Packet Format • Address space depletion • NAT • In danger of running out of classes A and B • 32-bit address space • IPv6 completely allocated by 2008 • Router Internals • Two solutions • NAT • Route Lookup • IPv6 Lecture 8: 9 -20-01 15 Lecture 8: 9 -20-01 16 Network Address Translation (NAT) NAT Illustration Pool of global IP • Possible solution to address space exhaustion Destination addresses Source • Kludge (but useful) G P • Sits between your network and the Internet Global Private Internet • Translates local network layer addresses to global Network IP addresses Dg Sg Data NAT Dg Sp Data • Has a pool of global IP addresses (less than number of hosts on your network) • Uses special unallocated addresses (RFC 1597) • Operation: Source (S) wants to talk to Destination (D): • Create S -S mapping locally g p • Replace Sp with Sg for outgoing packets • 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 • Replace Sg with Sp for incoming packets • How many hosts can have active transfers at one time? Lecture 8: 9 -20-01 17 Lecture 8: 9 -20-01 18 3 Problems with NAT Problems with NAT • What if we only have few (or just one) IP • Hides the internal network structure address? • Some consider this an advantage • Use Network Address & Port Translator (NAPT) • Some protocols carry addresses • NAPT translates: • E.g., FTP carries addresses in text • What is the problem? • Translates addrprivate + flow info to addrglobal + new flow info • Must update transport protocol headers • Uses TCP/UDP port numbers (port number & checksum) • Potentially thousands of simultaneous • Encryption connections with one global IP address • No inbound connections Lecture 8: 9 -20-01 19 Lecture 8: 9 -20-01 20 Outline IPv6 • IP Packet Format • Primary objective bigger addresses • Addresses are 128bit à What about header • NAT size!!! • Simplification • IPv6 • Header format helps speed processing/forwarding • Router Internals • Header changes to facilitate QoS • Removes infrequently used parts of header • Route Lookup • 40byte fixed size vs. 20+ byte variable Lecture 8: 9 -20-01 21 Lecture 8: 9 -20-01 22 IPv6 Changes IPv6 Header • IPv6 removes checksum • Relies on upper layer protocols to provide 0 4 12 16 19 24 32 integrity Version Class Flow Label • IPv6 eliminates fragmentation Payload Length Next Header Hop Limit • Requires path MTU discovery Source Address • Requires 1280 byte MTU Destination Address Lecture 8: 9 -20-01 23 Lecture 8: 9 -20-01 24 4 IPv6 Changes IPv6 Changes • TOS replaced with traffic class octet • Protocol field replaced by next header field • Flow label • Support for protocol demultiplexing as well as option processing • Identify datagrams in same “flow.” (concept of“flow” not well defined) • Option processing • Options are added using next header field • Help soft state systems • Options header does not need to be processed by • Maps well onto TCP connection or stream of every router UDP packets on host-port pair • Large performance improvement • Easy configuration • Makes options practical/useful • Additional requirements • Provides auto-configuration using hardware • Support for security MAC address to provide unique base • Support for mobility Lecture 8: 9 -20-01 25 Lecture 8: 9 -20-01 26 Transition From IPv4 To IPv6 Dual Stack Approach • Not all routers can be upgraded simultaneous • No “flag days” • How will the network operate with mixed IPv4 and IPv6 routers? • Two proposed approaches: • Dual Stack: some routers with dual stack (v6, v4) can “translate” between formats • Tunneling: IPv6 carried as payload n IPv4 datagram among IPv4 routers Lecture 8: 9 -20-01 27 Lecture 8: 9 -20-01 28 Tunneling Outline • IP Packet Format IPv6 inside IPv4 where needed • NAT • IPv6 • Router Internals • Route Lookup Lecture 8: 9 -20-01 29 Lecture 8: 9 -20-01 30 5 Router Architecture Overview What Does a Router Look Like? Two key router functions: • Line cards • Run routing algorithms/protocol (RIP, OSPF, BGP) • Network interface cards • Switching datagrams from incoming to outgoing link • Forwarding engine • Fast path routing (hardware vs. software) • Usually on line card • Backplane • Switch or bus interconnect • Processor • Handles routing protocols, error conditions Lecture 8: 9 -20-01 31 Lecture 8: 9 -20-01 32 Router Processing Network Processor • Packet arrives arrives at inbound line card • Runs routing protocol and downloads • Header processed by forwarding engine forwarding table to forwarding engines • Forwarding engine determines output line • Performs “slow” path processing card/destination • ICMP error messages • Checksum updated but not checked • IP option processing • Packet copied to outbound line card • Fragmentation • Odd situations sent to network processor • Packets destined to router Lecture 8: 9 -20-01 33 Lecture 8: 9 -20-01 34 Three Types of Switching Fabrics Switching Via Memory First generation routers: • Packet copied by system’s (single) CPU • Speed limited by memory bandwidth (2 bus crossings per datagram) Input Memory Output Port Port System Bus Modern routers: • Input port processor performs lookup, copy into memory • Cisco Catalyst 8500
Load more

Recommended publications
  • IP Datagram ICMP Message Format ICMP Message Types
    ICMP Internet Control Message Protocol ICMP is a protocol used for exchanging control messages. CSCE 515: Two main categories Query message Computer Network Error message Programming Usage of an ICMP message is determined by type and code fields ------ IP, Ping, Traceroute ICMP uses IP to deliver messages. Wenyuan Xu ICMP messages are usually generated and processed by the IP software, not the user process. Department of Computer Science and Engineering University of South Carolina IP header ICMP Message 20 bytes CSCE515 – Computer Network Programming IP Datagram ICMP Message Format 1 byte 1 byte 1 byte 1 byte VERS HL Service Total Length Datagram ID FLAG Fragment Offset 0781516 31 TTL Protocol Header Checksum type code checksum Source Address Destination Address payload Options (if any) Data CSCE515 – Computer Network Programming CSCE515 – Computer Network Programming ICMP Message Types ICMP Address Mask Request and Reply intended for a diskless system to obtain its subnet mask. Echo Request Id and seq can be any values, and these values are Echo Response returned in the reply. Destination Unreachable Match replies with request Redirect 0781516 31 Time Exceeded type(17 or 18) code(0) checksum there are more ... identifier sequence number subnet mask CSCE515 – Computer Network Programming CSCE515 – Computer Network Programming ping Program ICMP Echo Request and Reply Available at /usr/sbin/ping Test whether another host is reachable Send ICMP echo_request to a network host -n option to set number of echo request to send
    [Show full text]
  • Lesson 1 Key-Terms Meanings: Internet Connectivity Principles
    Lesson 1 Key-Terms Meanings: Internet Connectivity Principles Chapter-4 L01: "Internet of Things " , Raj Kamal, 2017 1 Publs.: McGraw-Hill Education Header Words • Header words are placed as per the actions required at succeeding stages during communication from Application layer • Each header word at a layer consists of one or more header fields • The header fields specify the actions as per the protocol used Chapter-4 L01: "Internet of Things " , Raj Kamal, 2017 2 Publs.: McGraw-Hill Education Header fields • Fields specify a set of parameters encoded in a header • Parameters and their encoding as per the protocol used at that layer • For example, fourth word header field for 32-bit Source IP address in network layer using IP Chapter-4 L01: "Internet of Things " , Raj Kamal, 2017 3 Publs.: McGraw-Hill Education Protocol Header Field Example • Header field means bits in a header word placed at appropriate bit place, for example, place between bit 0 and bit 31 when a word has 32-bits. • First word fields b31-b16 for IP packet length in bytes, b15-b4 Service type and precedence and b3-b0 for IP version • Chapter-4 L01: "Internet of Things " , Raj Kamal, 2017 4 Publs.: McGraw-Hill Education IP Header • Header fields consist of parameters and their encodings which are as per the IP protocol • An internet layer protocol at a source or destination in TCP/IP suite of protocols Chapter-4 L01: "Internet of Things " , Raj Kamal, 2017 5 Publs.: McGraw-Hill Education TCP Header • Header fields consist of parameters and their encoding which are as
    [Show full text]
  • Transport Layer Chapter 6
    Transport Layer Chapter 6 • Transport Service • Elements of Transport Protocols • Congestion Control • Internet Protocols – UDP • Internet Protocols – TCP • Performance Issues • Delay-Tolerant Networking Revised: August 2011 CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 The Transport Layer Responsible for delivering data across networks with the desired Application reliability or quality Transport Network Link Physical CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Transport Service • Services Provided to the Upper Layer » • Transport Service Primitives » • Berkeley Sockets » • Socket Example: Internet File Server » CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Services Provided to the Upper Layers (1) Transport layer adds reliability to the network layer • Offers connectionless (e.g., UDP) and connection- oriented (e.g, TCP) service to applications CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Services Provided to the Upper Layers (2) Transport layer sends segments in packets (in frames) Segment Segment CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Transport Service Primitives (1) Primitives that applications might call to transport data for a simple connection-oriented service: • Client calls CONNECT, SEND, RECEIVE, DISCONNECT • Server calls LISTEN, RECEIVE, SEND, DISCONNECT Segment CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice
    [Show full text]
  • Internet Protocol Suite
    InternetInternet ProtocolProtocol SuiteSuite Srinidhi Varadarajan InternetInternet ProtocolProtocol Suite:Suite: TransportTransport • TCP: Transmission Control Protocol • Byte stream transfer • Reliable, connection-oriented service • Point-to-point (one-to-one) service only • UDP: User Datagram Protocol • Unreliable (“best effort”) datagram service • Point-to-point, multicast (one-to-many), and • broadcast (one-to-all) InternetInternet ProtocolProtocol Suite:Suite: NetworkNetwork z IP: Internet Protocol – Unreliable service – Performs routing – Supported by routing protocols, • e.g. RIP, IS-IS, • OSPF, IGP, and BGP z ICMP: Internet Control Message Protocol – Used by IP (primarily) to exchange error and control messages with other nodes z IGMP: Internet Group Management Protocol – Used for controlling multicast (one-to-many transmission) for UDP datagrams InternetInternet ProtocolProtocol Suite:Suite: DataData LinkLink z ARP: Address Resolution Protocol – Translates from an IP (network) address to a network interface (hardware) address, e.g. IP address-to-Ethernet address or IP address-to- FDDI address z RARP: Reverse Address Resolution Protocol – Translates from a network interface (hardware) address to an IP (network) address AddressAddress ResolutionResolution ProtocolProtocol (ARP)(ARP) ARP Query What is the Ethernet Address of 130.245.20.2 Ethernet ARP Response IP Source 0A:03:23:65:09:FB IP Destination IP: 130.245.20.1 IP: 130.245.20.2 Ethernet: 0A:03:21:60:09:FA Ethernet: 0A:03:23:65:09:FB z Maps IP addresses to Ethernet Addresses
    [Show full text]
  • The Internet Protocol, Version 4 (Ipv4)
    Today’s Lecture I. IPv4 Overview The Internet Protocol, II. IP Fragmentation and Reassembly Version 4 (IPv4) III. IP and Routing IV. IPv4 Options Internet Protocols CSC / ECE 573 Fall, 2005 N.C. State University copyright 2005 Douglas S. Reeves 1 copyright 2005 Douglas S. Reeves 2 Internet Protocol v4 (RFC791) Functions • A universal intermediate layer • Routing IPv4 Overview • Fragmentation and reassembly copyright 2005 Douglas S. Reeves 3 copyright 2005 Douglas S. Reeves 4 “IP over Everything, Everything Over IP” IP = Basic Delivery Service • Everything over IP • IP over everything • Connectionless delivery simplifies router design – TCP, UDP – Dialup and operation – Appletalk – ISDN – Netbios • Unreliable, best-effort delivery. Packets may be… – SCSI – X.25 – ATM – Ethernet – lost (discarded) – X.25 – Wi-Fi – duplicated – SNA – FDDI – reordered – Sonet – ATM – Fibre Channel – Sonet – and/or corrupted – Frame Relay… – … – Remote Direct Memory Access – Ethernet • Even IP over IP! copyright 2005 Douglas S. Reeves 5 copyright 2005 Douglas S. Reeves 6 1 IPv4 Datagram Format IPv4 Header Contents 0 4 8 16 31 •Version (4 bits) header type of service • Functions version total length (in bytes) length (x4) prec | D T R C 0 •Header Length x4 (4) flags identification fragment offset (x8) 1. universal 0 DF MF s •Type of Service (8) e time-to-live (next) protocol t intermediate layer header checksum y b (hop count) identifier •Total Length (16) 0 2 2. routing source IP address •Identification (16) 3. fragmentation and destination IP address reassembly •Flags (3) s •Fragment Offset ×8 (13) e t 4. Options y IP options (if any) b •Time-to-Live (8) 0 4 ≤ •Protocol Identifier (8) s e t •Header Checksum (16) y b payload 5 •Source IP Address (32) 1 5 5 6 •Destination IP Address (32) ≤ •IP Options (≤ 320) copyright 2005 Douglas S.
    [Show full text]
  • Usenet News HOWTO
    Usenet News HOWTO Shuvam Misra (usenet at starcomsoftware dot com) Revision History Revision 2.1 2002−08−20 Revised by: sm New sections on Security and Software History, lots of other small additions and cleanup Revision 2.0 2002−07−30 Revised by: sm Rewritten by new authors at Starcom Software Revision 1.4 1995−11−29 Revised by: vs Original document; authored by Vince Skahan. Usenet News HOWTO Table of Contents 1. What is the Usenet?........................................................................................................................................1 1.1. Discussion groups.............................................................................................................................1 1.2. How it works, loosely speaking........................................................................................................1 1.3. About sizes, volumes, and so on.......................................................................................................2 2. Principles of Operation...................................................................................................................................4 2.1. Newsgroups and articles...................................................................................................................4 2.2. Of readers and servers.......................................................................................................................6 2.3. Newsfeeds.........................................................................................................................................6
    [Show full text]
  • Cisco Unified Border Element H.323-To-SIP Internetworking Configuration Guide, Cisco IOS Release 12.4T Iii
    Cisco Unified Border Element H.323-to- SIP Internetworking Configuration Guide, Cisco IOS Release 12.4T Americas Headquarters Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA http://www.cisco.com Tel: 408 526-4000 800 553-NETS (6387) Fax: 408 527-0883 THE SPECIFICATIONS AND INFORMATION REGARDING THE PRODUCTS IN THIS MANUAL ARE SUBJECT TO CHANGE WITHOUT NOTICE. ALL STATEMENTS, INFORMATION, AND RECOMMENDATIONS IN THIS MANUAL ARE BELIEVED TO BE ACCURATE BUT ARE PRESENTED WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. USERS MUST TAKE FULL RESPONSIBILITY FOR THEIR APPLICATION OF ANY PRODUCTS. THE SOFTWARE LICENSE AND LIMITED WARRANTY FOR THE ACCOMPANYING PRODUCT ARE SET FORTH IN THE INFORMATION PACKET THAT SHIPPED WITH THE PRODUCT AND ARE INCORPORATED HEREIN BY THIS REFERENCE. IF YOU ARE UNABLE TO LOCATE THE SOFTWARE LICENSE OR LIMITED WARRANTY, CONTACT YOUR CISCO REPRESENTATIVE FOR A COPY. The Cisco implementation of TCP header compression is an adaptation of a program developed by the University of California, Berkeley (UCB) as part of UCB’s public domain version of the UNIX operating system. All rights reserved. Copyright © 1981, Regents of the University of California. NOTWITHSTANDING ANY OTHER WARRANTY HEREIN, ALL DOCUMENT FILES AND SOFTWARE OF THESE SUPPLIERS ARE PROVIDED “AS IS” WITH ALL FAULTS. CISCO AND THE ABOVE-NAMED SUPPLIERS DISCLAIM ALL WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING, WITHOUT LIMITATION, THOSE OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OR ARISING FROM A COURSE OF DEALING, USAGE, OR TRADE PRACTICE. IN NO EVENT SHALL CISCO OR ITS SUPPLIERS BE LIABLE FOR ANY INDIRECT, SPECIAL, CONSEQUENTIAL, OR INCIDENTAL DAMAGES, INCLUDING, WITHOUT LIMITATION, LOST PROFITS OR LOSS OR DAMAGE TO DATA ARISING OUT OF THE USE OR INABILITY TO USE THIS MANUAL, EVEN IF CISCO OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
    [Show full text]
  • Structure of IEEE 802.11 Packets at Various Physical Layers
    Appendix A: Structure of IEEE 802.11 Packets at Various Physical Layers This appendix gives a detailed description of the structure of packets in IEEE 802.11 for the different physical layers. 1. Packet Format of Frequency Hopping Spread-spectrum Physical Layer (FHSS PHY) The packet is made up of the following elements (Figure A.1): 1.1 Preamble It depends on the physical layer and includes: – Synch: a sequence of 80 bits alterning 0 and 1, used by the physical circuits to select the correct antenna (if more than one are in use), and correct offsets of frequency and synchronization. – SFD: start frame delimiter consists of a pattern of 16 bits: 0000 1100 1011 1101, used to define the beginning of the frame. 1.2 Physical Layer Convergence Protocol Header The Physical Layer Convergence Protocol (PLCP) header is always transmitted at 1 Mbps and carries some logical information used by the physical layer to decode the frame: – Length of word of PLCP PDU (PLW): representing the number of bytes in the packet, useful to the physical layer to detect correctly the end of the packet. – Flag of signalization PLCP (PSF): indicating the supported rate going from 1 to 4.5 Mbps with steps of 0.5 Mbps. Even though the standard gives the combinations of bits for PSF (see Table A.1) to support eight different rates, only the modulations for 1 and 2 Mbps have been defined. – Control error field (HEC): CRC field for error detection of 16 bits (or 32 bits). The polynomial generator used is G(x)=x16 + x12 + x5 +1.
    [Show full text]
  • Wireless Real-Time IP Services Enabled by Header Compression
    Wireless Real-time IP Services Enabled by Header Compression Krister Svanbrof, Hans Hannu f, Lars-Erik Jonsson f, Mikael Degermarkf f Ericsson Research f Dept. of CS & EE Ericsson Erisoft AB Lulei University of Technology Box 920, SE-971 28 Lulei, Sweden SE-971 87 Lulei, Sweden Abstract - The world of telecommunications is currently A major problem with voice over IP over wireless is the going through a shift of paradigm from circuit switched, large headers of the protocols used when sending speech connection oriented information transfer towards packet data over the Internet. An IPv4 packet with speech data switched, connection-less transfer. For application will have an IP header, a UDP header, and an RTP header independence and to decrease costs for transport and making a total of 20+8+12=40 octets. With IPv6, the IP switching it is attractive to go IP all the way over the air header is 40 octets for a total of 60 octets. The size of the ' interface to the end user equipment, i.e., to not terminate speech data depends on the codec, it can be 15-30 octets. the IP protocols before the air interface. A major reason to These numbers present a major reason for terminating the avoid using voice over IP over the air interface has, up to IP protocols before the air interface: the IP/UDP/RTP now, been the relatively large overhead imposed by the headers require a higher bit rate and would cause IP/UDP/RTP headers of voice packets. This paper presents inefficient use of the expensive radio spectrum.
    [Show full text]
  • The Original Version of This Chapter Was Revised: the Copyright Line Was Incorrect
    The original version of this chapter was revised: The copyright line was incorrect. This has been corrected. The Erratum to this chapter is available at DOI: 10.1007/978-0-387-35516-0_20 H. Ural et al. (eds.), Testing of Communicating Systems © IFIP International Federation for Information Processing 2000 114 TESTING OF COMMUNICATING SYSTEMS protocols in TTCN mainly by ETSI and ITU-T. Most of the telecom vendor companies use TTCN in their internal test procedures because of its usefulness in protocol testing. Tools exist supporting the writing and execution of TTCN test cases as well as generating them from formal specifications written in SDL (Specification Description Language) or MSC (Message Sequence Chart). Telecom service providers are also executing conformance testing on the products they buy to check if it fulfills the requirements described in the protocol standards. This is a main step assuring the interoperability of the heterogeneous products built in their network. In the datacom world this kind of strict testing is not applied though interoperability of products of different vendors is becoming to be as important as for telecom networks with the growing number of datacom product vendors and the growing reliability requirements. The interoperability events use ad hoc test scenarios, and no test results are really available for the potential customers to support their decision which product to buy. This paper presents an application of the conformance testing methodology on IPv6 testing. In section two we present the main features of IPv6. Section 3 summarizes ideas why conformance testing would be useful for the Internet protocols.
    [Show full text]
  • How the Internet Works: Headers and Data; Packets and Routing 1
    Howthe Internet Works: Headers and Data; Packets and Routing 1. Transmitting Information through the Ages Howcan you get information from one place to another? How, for example, can you get an image from one place to another? Two hundred years ago, you would have todraw, paint, or print the image on paper or canvas, then carry, on foot, horseback, boat, or wagon, this analog version of view. One hundred years later,technology had advanced. By the early part of the 20th century,fax machines existed. With fax, you could drawthe image and send it overwires. What newscientific developments made that change possible? Here are a fewmilestones: YEAR WHATWHO WHERE 1800 Invents electric battery Allesandro Volta Italy 1820 Discovers electric current creates magnetism Hans O/rsted Denmark 1837 Invents electric telegraph Samuel Morse USA Before the battery,electricity was available from lightning and by shuffling across rugs on dry days, but that static electricity could not provide a steady,evenflow.Volta’sbattery made it possible to create a steady electrical current. Twenty years later,O/rsted discovered that a steady current of electricity produced a magnetic effect. Later,Morse connected a battery,aswitch, and a coil so that closing the switch at one end of the wire would create magnetism that would attract a piece of metal at the other end of the wire. By closing the switch for short and long durations, he was able to transmit bits a long distance. This system, the electric telegraph, made long-distance, all-weather,pri- vate communication possible. This technology led to the Internet.
    [Show full text]
  • 14. TCP/IP Protocol Suite Contents
    11/10/2010 14. TCP/IP Protocol Suite Contents a. TCP/IP – Internet – OSI b. Network level – IP protocol c. Addressing and sub-networks d. Other network-level protocols e. Transport level 1 11/10/2010 a. TCP/IP – Internet – OSI b. Network level – IP protocol 2 11/10/2010 Position of IPv4 in TCP/IP protocol suite IPv4 datagram format 3 11/10/2010 Service type or differentiated services The precedence subfield was part of version 4, but never used. 4 11/10/2010 Types of service Default types of service 5 11/10/2010 Values for codepoints The total length field defines the total length of the datagram including the header. 6 11/10/2010 Encapsulation of a small datagram in an Ethernet frame Protocol field and encapsulated data 7 11/10/2010 Protocol values Example 1 An IPv4 packet has arrived with the first 8 bits as shown: 01000010 Thereceiver discar ds the packtket. Why? Solution There is an error in this packet. The 4 leftmost bits (0100) show the version, which is correct. The next 4 bits (0010) show an invalid header length (2 × 4 = 8). The minimum number of bytes in the header must be 20. The packet has been corrupted in transmission. 8 11/10/2010 Example 2 In an IPv4 packet, the value of HLEN is 1000 in binary. How many bytes of options are being carried by this packet? Solution The HLEN value is 8, which means the total number of bytes in the header is 8 × 4, or 32 bytes. The first 20 bytes are the base header, the next 12 bytes are the options.
    [Show full text]