DOCSLIB.ORG

Adaptive Header Compression for Wireless Networks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Adaptive Header Compression for Wireless Networks Adaptive Header Compression for Wireless Networks Changli Jiao Loren Schwiebert Golden Richard Dept. of Elec. and Computer Eng. Dept. of Computer Science Dept. of Computer Science Wayne State University Wayne State University University of New Orleans Detroit, MI 48202 Detroit, MI 48202 New Orleans, LA 70148 Email: [email protected] Email: [email protected] Email: [email protected] Abstract is called error propagation. When the packet error rate is TCP/IP header compression has long been used to send high, e.g., over a wireless channel, this might also result in information efficiently and to improve the response time of senders not receiving ACKs, which is assumed as network communication systems. It is also well known that errors congestion and which deteriorates TCP performance [2]. on the link where header compression is used can dete- In order to solve this problem, the ”twice” algorithm [2] riorate the performance. In addition, the recently noticed was designed to repair the desynchronization. When a high frequency of some computer networking problems can packet cannot be decompressed correctly, it is assumed that make the performance of header compression even worse. one or more previous packets, which carry the same delta These problems include packet reordering and packet er- values, are lost. The decompressor will apply these values rors that avoid link layer error detection. In this paper, we two or more times. If the result can pass the TCP check- analyze the influence of these problems on existing header sum, the packet is considered as correctly decompressed. compression algorithms. We also propose an adaptive The twice algorithm improves the performance of header header compression that gives better performance. compression in certain circumstances. Window based LSB [3] is an encoding method for delta 1 Previous Work values. If the compressor can ensure that the decompres- Van Jacobson proposed a TCP/IP header compression sor has received a group of packets, it can then transfer algorithm [5] for low-speed links. TCP/IP packets with the delta values as the differences from that of the group, compressed headers normally traverse a single link, with a which are expected to occupy fewer bits. TCP Aware RO- compressor on one side and a decompressor on the other. bust Header Compression (TAROC) [4] uses the sliding The idea is to avoid transferring redundant information window of the TCP sender to decide which packets have whenever possible. The decompressor should use infor- already been received. A new packet cannot be transferred mation already known to recover the headers. The TCP/IP without getting all the acknowledgments for the previous header fields can be divided into several groups. Constant window. Hence, the compressor tracks the size of the slid- fields, which usually do not change during the lifetime of ing window according to the arriving sequence of packets. a connection, can be eliminated from most packets. In- stead, a unique value, the Compression Identifier (CID), is 2 New Challenges assigned and added to the packet header to identify these Packet reordering, due to packets of one connection fol- fields. Inferable fields can be inferred from other fields lowing different paths, may seem uncommon. Bennett et and need not be transferred. Delta fields are expected to al. showed that reordering is not necessarily a rare occur- change only slightly from the previous packet. These fields rence in the Internet [1]. Even when a consistent path is are transferred using only the differences, which can be ex- chosen, the existence of multiple paths between routing pressed with fewer bits and are referred to as ”delta” val- neighbors, or within the data path of a single router, can ues. Random fields are transferred without change. cause packet reordering. Some header compression algo- Correctly decompressed packets refresh the information rithms are thus challenged since they assume that the pack- on the decompressor side, based on which following pack- ets arrive in order or with minor reordering. ets can be recovered. A corrupted packet is dropped and Cyclic Redundancy Check (CRC) is very powerful in makes the decompressor desynchronized. Thus, subse- error detection and is the usual error detection method quent packets received by the decompressor may also be used in the link layer. TCP/UDP checksum was thus ar- dropped even though they are transmitted correctly, which gued as unnecessary. But both experiment and tracing ¡ This material is based upon work supported by the National Science analysis have shown that there are a wide variety of error Foundation under Grant No. 0086020. sources which cannot be detected by link-level CRCs [8]. In TCP/UDP, these errors can be detected only by Internet will potentially make the decompressor work incorrectly. checksum [6] [7]. The error detection performance should We define error masking probability as the probability be analyzed for header compression algorithms. that errors passing link layer CRC are not detected by the TCP checksum and thus passed to a higher layer. Error 3 Header Compression Performance masking probability of VJ header compression needs fur- Both VJ and twice compression algorithm prohibit neg- ther consideration. But it is clear that the error masking ative delta values, since these packets could be sent due probability of the twice algorithm is higher than that of to the desynchronization. Full headers are sent to re- VJ compression. If the delta values are applied once and fresh the decompressor, but packet reordering also triggers the TCP checksum is not correct, the actual reason may this. This introduces errors on estimating compression ef- be some errors in the data payload or other bytes in the ficiency, which increases with more reordering. The error header of the packet. The more times the delta value is on the estimate also increases with the compression ratio. applied or the more educated guesses for the acknowledg- A packet error means that packets cannot be decom- ment stream [2], the more likely that an error can be passed pressed, which includes physically corrupted ones as well to the layer above TCP. as uncorrupted packets influenced by error propagation. Assume every bit has the same probability to be corrupted 4 Adaptive Header Compression and any error will be detected by the error detection mech- We propose an adaptive header compression algorithm. anism. Also assume all original packet lengths are ¢¡¤£ Define a semi-compressed packet as one with all header ¡§¦ fields compressed except delta fields. Define two variables, bytes, compressed are ¥ bytes. In order to get Figure 1, we also make a random selection on when a full header windowSize and distance. The delta fields are coded us- packet will be sent by the compressor. For the VJ algo- ing Window based LSB based on the previous windowSize rithm, packet error probability increases almost linearly packets. After every distance compressed packets, a semi- until a full header packet is received. If packets are of the compressed packets is sent. The value of windowSize and distance are determined by the average BER of the link and VJ header compression 1.2 twice header compression the average packet size. The higher the BER, the bigger TAROC header compression without header compression the windowSize and the smaller the distance. Conversely, 1 the lower the BER, the smaller the windowSize and the 0.8 bigger the distance. By changing these two variables, we 0.6 can make the packet error probability less than that with- 0.4 out header compression. In this way, the channel usage probability of packet not delivered to the upper layer 0.2 and TCP performance can be improved. A wireless chan- nel is usually modeled as in good and bad states follow- 0 10 20 30 40 50 60 70 80 90 100 packet transferred on the link ing a Markov chain. If we can get some indications as the ¡ wireless channel is in bad state, a semi-compressed packet Figure 1: Packet error prob. comparison, ¨ © should be sent immediately after this to refresh the decom- same size and there is no reordering/loss before the com- pressor, which also lowers the packet error probability. pressor, the twice algorithm always recovers the loss on the link between the compressor and decompressor. But, References even for applications with same length packets, reordering [1] J. Bennett, C. Partridge, and N. Schectman. Packet reordering is not pathological network behavior, 1999. makes delta values irregular, which causes the twice al- [2] M. Degermark, M. Engan, B. Nordgren, and S. Pink. Low-loss gorithm to not perform well. When applying delta values TCP/IP header compression for wireless networks. In MobiCom, multiple times can not decompress the packet, the error 1996. probability increases almost linearly just as in VJ header [3] C. Bormann (ed.) et al. RObust Header Compression (ROHC). In- compression. If the algorithm can decompress a subse- ternet Draft (work in progress) draft-ietf-rohc-rtp-09.txt, Internet En- gineering Task Force, February 2001. quent packet, the error probability will become low again. [4] H. Liao et al. TCP-Aware RObust Header Compression (TAROC). Otherwise, the probability can drop only when a packet Internet Draft (work in progress) draft-ietf-rohc-tcp-taroc-01.txt, In- with a full header is received by the decompressor. The- ternet Engineering Task Force, March 2001. oretically, TAROC will work perfectly if the compressor [5] V. Jacobson. IP headers for low-speed serial links. RFC 1144, Inter- knows when the sender changes the window size, which net Engineering Task Force, February 1990. [6] J. Postel. Transmission Control Protocol. RFC 793, Internet Engi- is not an easy task. TAROC uses the packet arrival se- neering Task Force, September 1981. quence as the window size indication.
Load more

Recommended publications
  • 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]
  • 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]
  • 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]
  • 2045 Innosoft Obsoletes: 1521, 1522, 1590 N
    Network Working Group N. Freed Request for Comments: 2045 Innosoft Obsoletes: 1521, 1522, 1590 N. Borenstein Category: Standards Track First Virtual November 1996 Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract STD 11, RFC 822, defines a message representation protocol specifying considerable detail about US-ASCII message headers, and leaves the message content, or message body, as flat US-ASCII text. This set of documents, collectively called the Multipurpose Internet Mail Extensions, or MIME, redefines the format of messages to allow for (1) textual message bodies in character sets other than US-ASCII, (2) an extensible set of different formats for non-textual message bodies, (3) multi-part message bodies, and (4) textual header information in character sets other than US-ASCII. These documents are based on earlier work documented in RFC 934, STD 11, and RFC 1049, but extends and revises them. Because RFC 822 said so little about message bodies, these documents are largely orthogonal to (rather than a revision of) RFC 822. This initial document specifies the various headers used to describe the structure of MIME messages. The second document, RFC 2046, defines the general structure of the MIME media typing system and defines an initial set of media types.
    [Show full text]
  • TSD Header and Footer Formal-T
    Remote Public Access Connectivity Information September 2011 Technology Services Division TABLE OF CONTENTS 1. Overview of Connectivity Options 3 Option #1 – SSL-Enabled TN3270 Option #2 – Business-to-Business Virtual Private Network (VPN) 2. SSL-Enabled TN3270 Specifications 5 3. Business-to-Business Virtual Private Network (VPN) Specifications 6 4. Glossary of Acronyms & Definitions 10 Remote Public Access Connectivity Information September 2011 Page 2 1. Overview of Connectivity Options The North Carolina Administrative Office of the Courts (AOC) has two options for the public to access the enterprise server. This document provides an overview of these options. Also, estimated costs have been provided where it is realistic to do so. Actual costs may vary. OPTION #1 – SSL-Enabled TN3270 This option is designed to provide a connection for individual workstations using an SSL- enabled TN3270 client over the Internet. It is a standards-based solution that utilizes various protocols for authentication and encryption. This option may be the most affordable choice for small businesses and individuals. Basic Customer Requirements: • An Internet connection • SSL-enabled TN3270 client software installed on each workstation requiring access NOTE: Many vendors sell SSL-enabled TN3270 client software. The approximate cost is $50 to $300 per workstation. The cost depends on which vendor you select and how many licenses you need. To find a vendor, you can google “TN3270 Emulation Software.” Many vendors also offer free 30-day trials. OPTION #2 – Business-to-Business Virtual Private Network (VPN) This option is designed for business-to-business (or site-to-site) VPN connections and is not intended to provide connections for individual workstations.
    [Show full text]
  • SMS Service Reference
    IceWarp Unified Communications SMS Service Reference Version 10.4 Printed on 16 April, 2012 Contents SMS Service 1 About .............................................................................................................................................................................. 3 Why Do I Need SMS Service? ............................................................................................................................. 3 What Hardware Will I Need? ............................................................................................................................. 3 Why Would I Want More Than One SMS Gateway? .......................................................................................... 4 GSM Service ................................................................................................................................................................... 5 Tested and Supported Products ........................................................................................................................ 5 HTTP Gateway ................................................................................................................................................................ 6 Tested Products ................................................................................................................................................. 6 Reference ......................................................................................................................................................................
    [Show full text]
  • Module 6 Internet Layer Meghanathan Dr
    Module 6 Internet Layer Meghanathan Dr. Natarajan Meghanathan Associate ProfessorCopyrights of Computer Science Jackson StateAll University, Jackson, MS 39232 E-mail: [email protected] Module Topics • 6.1 IP Header • 6.2 IP Datagram Fragmentation • 6.3 IP Datagram Forwarding • 6.4 IP Auxiliary Protocols and Meghanathan Technologies Copyrights – ARP, DHCP, ICMP, VPN, NA(P)T All • 6.5 IPv6 Natarajan Meghanathan Copyrights All Natarajan 6.1 IP Header Meghanathan Copyrights All Natarajan IP Header Format (v4) © 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved. IP Header Format • VERS – Each datagram begins with a 4-bit protocol version number • H.LEN – 4-bit header length field specifies the number of 32-bit quantities in the header. The header size should be a multiple of 32. • The minimum integer value for the IP header length is 5 as the top 5 32-bit rows of the IP header are mandatory for inclusion. Hence, the minimum size of the IP header is 5 * 32-bits = 5 * 4 bytes = 20 bytes. • The maximum integer value for the IP header length (with 4 bits for the field) would be 15, necessitating the Options field to be at most 10 32- bit rows. The maximum size of theMeghanathan IP header is 15 * 32-bits = 15 * 4 bytes = 60 bytes. Copyrights • SERVICE TYPE – used to specify whether the sender prefers the datagram to be sentAll over a path that has minimum delay or maximum throughput, etc. A routerNatarajan that has multiple paths to the destination, can apply these service type preferences to select the most suitable path.
    [Show full text]
  • Ipv6 Header Format: • Traffic Class: Similar Role As TOS Field in Ipv4
    CS 422 Park IPv6 header format: versiontraffic class flow label 4 8 20 payload length next header hop limit 16 8 8 source address 128 destination address 128 • traffic class: similar role as TOS field in IPv4 • flow label: flow label + source address → per-flow traffic management → significant extra bits • next header: similar to IPv4 protocol field → plus double duty for option headers • note missing fields CS 422 Park • Dynamically assigned IP addresses → share an IP address pool → reusable → e.g., DHCP (dynamic host configuration protocol) → UDP-based client/server protocol (ports 67/68) → note: process/daemon based service → used by access ISPs, enterprises, etc. → where are the IP address savings? Old days of non-permanent dial-up modems ::: CS 422 Park • Network address translation (NAT) → dynamically assigned + address translation → private vs. public IP address → private: Internet routers discard them → e.g., 192.168.0.0 is private → 10.x.x.x are also private → useful for home networks, small businesses → also industry and university research labs CS 422 Park Example: network testbed intranet (HAAS G50) • intranet NICs have 10.0.0.0/24 addresses → each interface: a separate subnet • only one of the routers connected to Internet CS 422 Park • NAPT (NAT + port) → variant of NAT: borrow src port field as address bits Ex.: 192.168.10.10 and 192.168.10.11 both map to 128.10.27.10 but → 192.168.10.10 maps to 128.10.26.10:6001 → 192.168.10.11 maps to 128.10.26.10:6002 What about port numbers of 192.168.10.10 and 192.168.10.11? → e.g., client process
    [Show full text]
  • IP Packet Switching Reading: Sect 4.1.1 – 4.1.4, 4.3.5
    IP Packet Switching Reading: Sect 4.1.1 – 4.1.4, 4.3.5 COS 461: Computer Networks Spring 2011 Mike Freedman hp://www.cs.princeton.edu/courses/archive/spring11/cos461/ 2 Goals of Today’s Lecture • Connecvity – Circuit switching – Packet switching • IP service model – Best‐effort packet delivery – IP as the Internet’s “narrow waist” – Design philosophy of IP • IP packet structure – Fields in the IP header – Traceroute using TTL field – Source‐address spoofing 3 Recall the Internet layering model host host HTTP message HTTP HTTP TCP segment TCP TCP router router IP packet IP packet IP packet IP IP IP IP Ethernet Ethernet SONET SONET Ethernet Ethernet interface interface interface interface interface interface 4 Review: Circuit Switching ‐ Mulplexing a Link • Time‐division • Frequency‐division – Each circuit allocated – Each circuit allocated certain me slots certain frequencies time frequency time 5 Circuit Switching (e.g., Phone Network) 1. Source establishes connecon to desnaon – Node along the path store connecon info – Nodes may reserve resources for the connecon 2. Source sends data over the connecon – No desnaon address, since nodes know path 3. Source tears down connecon when done 6 Circuit Switching With Human Operator “Operator, please Telephone connect me to switch 555-1212” 7 Advantages of Circuit Switching • Guaranteed bandwidth – Predictable performance: not “best effort” • Simple abstracon – Reliable communicaon channel between hosts – No worries about lost or out‐of‐order packets • Simple forwarding – Forwarding based on me slot
    [Show full text]