CMPE 150 Introduction to Computer Networks Instructor Patrick Mantey mantey soe ucsc edu http www soe ucsc edu mantey Office Engr 2 Room 595J Office hours Tues 3 5 PM Mon 5 6 PM TA Anselm Kia akia soe ucsc edu Web site http www soe ucsc edu classes cmpe150 Winter09 Text Tannenbaum Computer Networks 4th edition available in bookstore etc Syllabus Today s Agenda Network Layer Quality of Service Internetworking IP Text Readings Today Chapter5 section 5 4 5 5 5 6 Internet Protocol Tuesday Chapter 6 Transport Layer Problem Assignment 5 On class web page this afternoon Due Tuesday February 24 Internet Layering Level 5 Application Layer rlogin ftp SMTP POP3 IMAP HTTP Level 4 Transport Layer a k a Host to Host TCP UDP Level 3 Network Layer a k a Internet IP ICMP ARP Level 2 Data Link Layer MAC sub layer a k a Network Interface or Network Access Layer Level 1 Physical Layer Leaky and Token Bucket Algorithms a Input to a leaky bucket b Output from a leaky bucket Output from a token bucket with capacities of c 250 KB d 500 KB e 750 KB f Output from a 500KB token bucket feeding a 10 MB sec leaky bucket Flow Specifications Way for user application to specify traffic patterns and desired quality of service Before connection is established or data is sent source provides flow spec to network Network can accept reject or counter offer Example flow spec language by Partridge 1992 Traffic spec maximum packet size maximum transmission rate Service desired maximum acceptable loss rate maximum delay and delay variation Admission Control 5 34 Examples of flow specification Packet Scheduling a A router with five packets queued for line O b Finishing times for the five packets Packets send in the order of their finishing fair queueing byte by byte equal priority Flow Based Algorithms Used for mulitimedia New about 1995 7 RSVP RFC 2205 Multicast routing Spanning trees Group address carried in the packet All receivers can send reservation request to sender RSVP The ReSerVation Protocol a A network b The multicast spanning tree for host 1 c The multicast spanning tree for host 2 RSVP The ReSerVation Protocol 2 a Host 3 requests a channel to host 1 b Host 3 then requests a second channel to host 2 c Host 5 requests a channel to host 1 Differentiated Services Problems with Flow base Algorithms Advance setup required Flow depends on routers not crashing Complex router to router exchanges for setup So RSVP rarely used Differentiated Services Limited to an administrative domain Class based vs flow based service Expedited Forwarding Differentiated Service where Expedited packets experience a traffic free network Assured Forwarding A possible implementation of the data flow for assured forwarding Frame Format for Label Switching and MPLS Transmitting a TCP segment using IP MPLS multiprotocol label switching and PPP Internetworking How Networks Differ How Networks Can Be Connected Concatenated Virtual Circuits Connectionless Internetworking Tunneling Internetwork Routing Fragmentation Connecting Networks A collection of interconnected networks How Networks Differ 5 43 Some of the many ways networks can differ How Networks Can Be Connected a Two Ethernets connected by a switch b Two Ethernets connected by routers Multiprotocol routers is networks differ Concatenated Virtual Circuits Internetworking using concatenated virtual circuits Connectionless Internetworking A connectionless internet Tunneling Tunneling a packet from Paris to London with source and destination same type of network Tunneling 2 Tunneling a car from France to England Internetwork Routing 1 2 level hierarchy Routing within each network interior gateway protocol Routing between networks exterior gateway protocol Within each network different routing algorithms can be used Each network is autonomously managed and independent of others autonomous system AS Internetwork Routing 2 Typically packet starts in its LAN Gateway receives it broadcast on LAN to unknown destination Gateway sends packet to gateway on the destination network using its routing table If it can use the packet s native protocol sends packet directly Otherwise tunnels it Internetwork Routing a An internetwork b A graph of the internetwork Fragmentation 1 Network specific maximum packet size Width of TDM slot OS buffer limitations Protocol number of bits in packet length field Maximum payloads range from 48 bytes ATM cells to 64Kbytes IP packets Fragmentation 2 What happens when large packet wants to travel through network with smaller maximum packet size Fragmentation Gateways break packets into fragments each sent as separate packet Gateway on the other side have to reassemble fragments into original packet 2 kinds of fragmentation transparent and nontransparent Fragmentation a Transparent fragmentation b Nontransparent fragmentation Fragmentation 2 Fragmentation when the elementary data size is 1 byte a Original packet containing 10 data bytes b Fragments after passing through a network with maximum packet size of 8 payload bytes plus header c Fragments after passing through a size 5 gateway Transparent Fragmentation Small packet network transparent to other subsequent networks Fragments of a packet addressed to the same exit gateway where packet is reassembled OK for concatenated VC internetworking Subsequent networks are not aware fragmentation occurred ATM networks through special hardware provide transparent fragmentation segmentation Problems with Transparent Fragmentation Exit gateway must know when it received all the pieces Fragment counter or end of packet bit Some performance penalty but requiring all fragments to go through same gateway May have to repeatedly fragment and reassemble through series of small packet networks Non Transparent Fragmentation Only reassemble at destination host Each fragment becomes a separate packet Thus routed independently Problems Hosts must reassemble Every fragment must carry header until it reaches destination host Keeping Track of Fragments 1 Fragments must be numbered so that original data stream can be reconstructed Tree structured numbering scheme Packet 0 generates fragments 0 0 0 1 0 2 If these fragments need to be fragmented later on then 0 0 0 0 0 1 0 1 0 0 1 1 But too much overhead in terms of number of fields needed Also if fragments are lost retransmissions can take alternate routes and get fragmented differently Keeping Track of Fragments 2 Another way is to define elementary fragment size that can pass through every
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