Transcript ppt
ECEN5553 Telecom Systems Week #4 Readings: Read [5a] "Whatever Happened to the IPv4 Address Crisis? thru [5c] "How Can the Internet Have Too Many Routes and Not Enough Addresses" Read [6] "The Cognitive Net is Coming" Exam #1: Lecture 14, 16 September (Live) No later than 23 September (Remote DL) 4 page test. Work 3. 1-2 pages will be off Fall 2015 Exam #1 Outline: Lecture 22, 5 October (Live) No later than 12 October (Remote DL) Outlines Received due 5 October (local) 12 October (remote) 5% IEEE Ethernet 802.3 10 Mbps (1983) Coax → Twisted Pair Shared → Switched Half Duplex → Full Duplex 802.3u 100 Mbps Fast Ethernet (1995) 802.3z 1 Gbps Ethernet (1998) 802.3ae 10 Gbps Ethernet (2002) 802.3ba 40 & 100 Gbps Ethernet (2010) 802.3bs 400 Gbps Ethernet (2017?) Performance Issues Throughput Usable BW Efficiency Percent of time packets are moved Shared Ethernet Efficiency 100% under Low Load ≈ 1/(1+5*NPD) under Heavy Load Low Speed Network? This configuration... PC Server Hub PC PC 10BaseT & Shared Hub ... is as good as this one... PC Server Switched Hub PC PC 10BaseT & Switched Hub ...IF traffic mostly going to/from same machine Switched Hub better if diverse traffic flow This configuration is even better. PC 10 Mbps 1 Gbps Server Switch 100 Mbps PC 10 Mbps PC Server on a higher speed line. Shared Ethernet Efficiency Gbps has higher NPD 1.0 0.5 0.0 .01 .10 .1 1.0 NPD 1 10.0 10 100 High Speed Network? This configuration has horrible throughput. PC Server Shared Hub PC PC 1 or 10 Gbps & Shared Hub Under heavy load, too much time spent recovering from collisions. Ethernet (Shared) Hub Operates at OSI Level 1 ‘Electric Cable’ Traffic arriving at an input is immediately copied to all other ports on a bit-by bit basis. Used on LAN's. Pretty much obsolete. Repeater = single input & single output hub Not used much on Ethernet any more Generally now only used on WAN long haul May be different protocol than Ethernet Black Box Performance... From Node A Node B Node C To Node A OSI Level 1 LAN Hub Node B Node C Two packets simultaneously show up at input... Black Box Performance... From Node A Node B Node C To Node A OSI Level 1 LAN Hub Node B Node C ... will overwrite each other, i.e. garbage out. a.k.a. Shared Hub Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) Two packets simultaneously show up at input & need to exit on same output... Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) ... one will be transmitted (when allowed by MAC), the other momentarily buffered... Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) ... and then transmitted. 10BaseT & Shared Hub 53 m PC 8m PC Hub PC 26 m 17 m One big collision domain. PC 10BaseT & Half Duplex Switch 53 m PC 8m PC Switch PC 26 m 17 m PC Four smaller collision domains. Example If Box 1 & 2 are Level 1 Hubs One Big Collision Domain 15 Nodes share 10 Mbps Each node gets average of 10/15 Mbps World 10BaseT 7 Hub 1 Users Hub 2 7 Users Right Side to World gets 7/15th of available BW, on average. Example If Box 1 & 2 are Level 2 Switches Each node shares 10 Mbps with Switch Right Hand Side is on one 10 Mbps line. World 10BaseT 7 Users Sw 1 Right hand side sees increased delays. Can be alleviated with 100 Mbps Box 1 ↔ Box 2 link. Sw 2 7 Users Right Side to World gets 1/8th of available BW. _____ (Was 7/15th) Switched Hubs or Bridge On Power Up know nothing When a packet arrives at an input port... Look-Up Table consulted Source MAC address not in table? Table Updated: MAC address & Port matched Destination Packet broadcast to all outputs (a.k.a. flooding) Destination Packet MAC address not in table? MAC address in table? shipped to proper output Look-up Table update is dependent on packet arrivals Router Operates at OSI Layers 1, 2, & 3 Capable of making complex routing decisions ‘peers into’ packets and examines Layer 3 address Very useful on Large Networks with multiple end-to-end paths Routers frequently exchange connectivity info with neighboring Routers Routing Algorithms used to update Routing (Look-Up) Tables Tables updated independently of traffic Bridging versus Routing Ethernet Bridge, Switch, or Switched Hub Uses Layer 2 MAC Address Unknown Destination? Flooded Look-up Table updates are packet dependent Router Uses Layer 3 Internet Protocol Address Unknown Destination? Default location Look-up Tables updated independently of traffic Small Network? Doesn't matter Big Network? Floods not a good idea. Ethernet Switch Uses MAC Source Address to populate Look-Up Table Uses MAC Destination Address & Table for I/O Decision Bytes: 7 1 6 6 2 Pre SFD Destination Address Source Address 46-1500 Data + Padding Len 4 CRC Router Populates Look-Up table independently of traffic. Uses Destination IP Address & Table for I/O Decision Bytes: 7 1 6 6 2 MAC Destination Address MAC Source Address Does look at the MAC Address! Is this for me? 20 20 6-1460 4 IPv4 TCP Data + Padding CRC Data Network Addressing IP Address Global Information Source Global Information Sink Stays unchanged end-to-end Exception: Network Address Translation Ethernet Address Local Transmitter (MAC Source) Local Receiver (MAC Receiver) Crossing a Router (Ethernet Boundary)? MAC Header and Trailer swapped out Crossing a Switch? MAC Header and Trailer unchanged Multiplexing Sharing a chunk of Bandwidth by splitting it into channels Channel can carry one conversation FDM, TDM, & StatMux FDM Different channels use some of the frequency all of the time. frequency 1 2 3 4 5 TDM Different channels use all of the frequency some of the time. Fixed, predictable times. frequency 1 2 3 1 StatMux Different channels use all of the frequency some of the time, at random, as needed. frequency 1 3 1 2 StatMux vs. TDM & FDM uses bandwidth more efficiently for bursty traffic requires more overhead has more variable deliveries requires more complex hardware Switching: In what manner will a user get to use a channel? For the duration of the conversation? Circuit Switching For a tiny, variable length, portion of the conversation? Packet Switching Circuit vs. Packet Switching Circuit has less end-to-end delay Circuit is less complex Packet is more efficient for Bursty Traffic MULTIPLEXING SWITCHING StatMux Circuit Packet TDM FDM X X Any Switching & Multiplexing combo possible. Two marked are among most common today. LAN/MAN History: FDDI (Fiber Distributed Data Interface) Developed in ’87 – ‘88 Covered OSI Layers 1 & 2 1st 100 Mbps Line Speed Token Ring MAC Guaranteed Bandwidth Had Priorities. Originally Dual Counter-Rotating Rings Designed for Metropolitan Area Counter Rotating Fiber Rings Outside Active. Inside Hot Standby. Designed for Metropolitan Area Counter Rotating Fiber Rings 1 Line Break... Nodes 1 & 4 wrap. One big ring. 4 FDDI Status Never succeeded as a LAN NIC's Saw use mostly as a corporate backbone OSU Was too expensive backbone from 1989 - 1993 ish fairly common at Internet Exchanges Used to pass traffic from ISP A to ISP B Now too slow 1993 OSU Stillwater Network (15) (21) The Internet VAST collection of interconnected networks Key Building Block: Routers running IP (Layer 3) Router link speeds range up to 200 Gbps Hierarchical Alpha-Numeric Names [email protected] AT&T 1997 Internet Backbone UUNET 1998 Internet Backbone AT&T 2009 Internet Backbone Source: http://www.business.att.com/content/productbrochures/MIS_15906.pdf Washington D.C. Area - 2000 OSU 2009 Internet Connectivity Traceroute to WWW.CISCO.COM 3 Internal OSU-Stillwater routers 4 OneNet routers (all in OKC? Tulsa?) 3 Qwest routers dal-edge-18.inet.qwest.net Akamai Technologies (Hosting Service) (11:51 am, 9Sept15, rtt = 13 msec, 10 routers) (12:32 pm, 9Sept16, rtt = 13 msec, 10 routers) Traceroute to WWW.TULSA.COM 3 Internal OSU-Stillwater routers 3 OneNet routers (Tulsa) 5 Cogent Communications routers te0-0-1-7.rcr21.tul01.atlas.cogentco.com be2706.ccr21.mci01.atlas.cogentco.com (Kansas City?) be3035.ccr21.den01.atlas.cogentco.com be3037.ccr21.slc01.atlas.cogentco.com 4 Unified Layer routers (Hosting Service) prv-211-1-0-1.unifiedlayer.com End server (198.57.177.235) in Provo, Utah area? (12:43 pm, 9Sept16, rtt = 45 msec, 15 routers) ISP Routes Sometimes Roundabout Launched 13 September 2014, 2 miles from OSU campus 1 Scheets' home router 4 AT&T routers adsl-70-233-159-254.dsl.okcyok.sbcglobal.net ggr3.dlstx.ip.att.net 4 Cogent Communications routers Be2032.ccr22.dfw01.atlat.cogentco.com te0-0-2-1.rcr12.okc01.atlas.cogentco.com 3 ONENET routers OKC? 3 Oklahoma State routers (12:30 pm, 11Sept14, rtt = 84 msec, 15 routers) Fall 2007 Weird TraceRoute Seen by Student Tulsa to OSU Stillwater Tracert launched from Tulsa, hit Atlanta Washington, D.C. Illinois Kansas City Tulsa Oklahoma City OSU Stillwater Internet Service Provider Backbone Router Switched Network, full duplex trunks. Access lines attach to corporate routers & routers of other ISP's.