1. n Read: 4.4 n Problems: 4.1, Web 6.1 n Design #1 due 1 February (Live) u 8 February (Async DL) u Late = -1 per working day n Quiz #1 u Lecture 12, 4 February (Live) u < 11 February (Async Distance Learning) ECEN4533 Data Communications Lecture #9 28 January 2013 Dr. George Scheets

2. n Read: 5.1 - 5.4 n Problems: 5.1 - 5.3 n Design #1 due 1 February (Live) u 8 February (Async DL) u Late = -1 per working day n Quiz #1 u Lecture 12, 4 February (Live) u < 11 February (Async Distance Learning) ECEN4533 Data Communications Lecture #10 30 January 2013 Dr. George Scheets

3. n Read: 5.7 - 5.8 n Problems: None n Design #1 due 1 February (Live) u 8 February (Async DL) u Late = -1 per working day n Quiz #1 (open book & notes) u Lecture 12, 4 February (Live) u < 11 February (Async Distance Learning) ECEN4533 Data Communications Lecture #11 1 February 2013 Dr. George Scheets

4. POTS at the CO Switch n Band Pass Filter suppresses energy outside voice bandwidth (300 - 3,400 Hz) Band Pass Filter (.3 - 3.4KHz) Sampler F s = 8 KHz Twisted Pair Cable Quantize 256 levels Code 8 bits/sample 64 Kbps A/D Converter

5. Nyquist's Sampling Theorem n Want to have a shot at perfectly reconstructing a sampled signal? u Sample at a rate > twice the maximum frequency. n Example: Phone system u Maximum frequency around 3.5 KHz, fs = 8 Ksps n Example: Compact Disk u Maximum frequency around 20 KHz, fs = 44.1 Ksps

6. Video undersampling time t=0 time = 2/30 time = 1/30 30 video stills/second 27 wheel revs/second 0.9 wheel revs/still Spoke would appear to be moving backwards.

7. A/D Converter PC Dial-Up Modems & POTS n PC Bit Stream has a significant amount of energy below 0.5 KHz n Modems shift the energy into the pass band of the filter PC Quantize 256 levels Code 8 bits/sample 64 Kbps Band Pass Filter (.3 - 3.4 KHz) Sampler F s = 8 KHz Twisted Pair Cable

8. Sources of POTS delay Local Loop PCM Coder TDM Trunk POTS TSI POTS TSI Intermediate Digital Voice Switches... TDM TrunkLocal Loop PCM Coder Trunk resources are dedicated to each voice call via TDM. Source CO Destination CO

9. Example) Coding a Microphone Output time (sec) m(t) volts (air pressure) Energy from about 300 - 3,400 Hz.

10. A/D Convertor time (sec) m(t) volts (air pressure) Step #1) Sample the waveform at rate > 2*Max Frequency. Telephone voice is sampled at 8,000 samples/second. 1/8000 second

11. A/D Convertor. 1 bit/sample. time (sec) Example) N = 2. Assign 0 or 1 to voltage. 0 < Voltage < +5v, Assign Logic 1 -5v < Voltage < 0, Assign Logic 0 3.62 v, output a 1 t1 Bit Stream Out = 1111110000111...

12. A/D Convertor. 1 bit/sample. Example) N = 2. Assign 0 or 1 to voltage. Far side gets... 1111110000111 (13 samples) Need to output 13 voltages. What does a 1 represent? A 0? Receive a 1? Output +2.5 v (mid-range) Receive a 0? Output -2.5 v (mid-range) Hold the voltage until next sample 0 < Voltage < +5v, Assign Logic 1 -5v < Voltage < 0, Assign Logic 0

13. A/D Convertor. 1 bit/sample. Input to the transmitter. Output at the receiver. Considerable Round-Off error exists. +2.5 v -2.5 v

14. time (sec) Example) N = 4. Assign 00, 01, 10 or 11. 2.5 < Voltage < 5, Assign 11 0 < Voltage < 2.5, Assign 10 -2.5 < Voltage < 0, Assign 00 -5 < Voltage < -2.5, Assign 01 3.62 v, Assign 11 t1 Bit Stream Out = 11111011111100 000000101011... +2.5 v -2.5 v A/D Convertor. 2 bits/sample

15. A/D Convertor. 2 bits/sample. Input to the transmitter. Output at the receiver. Receive 11? Output 3.75v Receive 10? Output 1.25v Receive 00? Output -1.25v Receive 01? Output -3.75v Reduced Round-Off error exists. +3.75 v +1.25 v -1.25 v -3.75 v

16. Circuit Switched Voice (POTS)  Telephone System uses Pulse Code Modulation  Equal length code word assigned to all voltages  N = 256 voltage levels  Log 2 256 = 8 bits per code word  A/D Converter  samples voice 8,000 times/second  rounds off voice to one of 256 voltage levels  transmits 8 bits to far side  D/A Converter  receives 8 bit code word  outputs one of 256 voltage levels for 1/8000th sec.

17. 1/8th Second of Voice

20. Sampling & Quantizing Examples  fs = 16 KHz  4096 quantiles  256 quantiles (approximate phone quality)  32 quantiles  4 quantiles (generally 2 levels used!)  4096 quantiles  fs = 16 KHz  fs = 8 KHz (some interference)  fs = 2 KHz  fs = 1 KHz

21. SONET Hierarchy n n Basic Building Block: u u 51.84 Mbps STS-1 Frame u u 8,000 frames/second u u 810 bytes/frame, 36 bytes for OA&M n n Optical Carrier-N? u u N byte interleaved STS-1 signals (TDM) n OC-151.84 Mbps OC-3155.52 Mbps OC-12622.08 Mbps OC-482.48832 Gbps OC-1929.95328 Gbps OC-76839.81312 Gbps

22. T Carrier & SONET n Technology used in Leased Lines n Mid-1960’s (T Carrier) & Late-1980’s (SONET) technology n Covers OSI Layers 1 & 2 (not packet-aware!) n Guaranteed Bandwidth using Circuit Switching & TDM u End-to-End path mapped in advance u Provides fixed number of bytes, 8000 times second, for customer use u As they arrive, switches repetitively move input bytes to appropriate output & TDM slot

23. Leased Line Networks n Last Mile Connectivity u Fractional T-1 (4 Wire Twisted Pair) N*64 Kbps, N = 1 - 23 u T-1 (4 Wire Twisted Pair) 1.536 Mbps (24*64 Kbps) u Fractional T-3 (Coax) N T-1's, N = 1 - 27 u T-3 (Coax) 28 T-1's + Overhead (45 Mbps) n Last Mile or Long Haul Connectivity u OC- N, N = 1, 3, 12, 48, & 192 (SONET) N*51.84 Mbps (Fiber)

24. ISO OSI Seven Layer Model Leased Line (Circuit Switched, TDM) Organized around Frames:1/8000th second entity n Layer 7 Application n Layer 6 Presentation n Layer 5 Session n Layer 4 Transport n Layer 3 Network n Layer 2 Data Link SONET, T-Carrier (PPP) n Layer 1 Physical SONET, T-Carrier Carrier Switches are byte-aware, NOT packet-aware.

25. Leased Line Packet Format Data + Padding 7 20 20 6-1460 IPTCP Point-to-Point Protocol

26. Leased Line Backbone Trunks Leased Line Leased Line ‘Cloud’ Trunk capacity shared via TDM & Circuit Switching Cross-Connect

27. LAN Carrier Leased Line Network Nailed up end-to-end connectivity (a Circuit). Bit pipe. No packet processing between Routers. Cross-Connect OC-48 Trunks Leased Line T1

28. Circuit Switched connections waste bandwidth for bursty traffic. time traffic 1.536 Mbps Line Speed 146 Kbps Average Idle Time >> Active Time Load = 9.456%

29. Carrier Leased Line Network Route once (circuit setup). Path through Network nailed down. Switches forward based on Time Slots per 1/8000th sec. TDM Switch Trunks Access Line ATM Frame Relay Router

30. Long Haul U.S. Traffic n Primarily carried on fiber n Running SONET or OTN n Generally OC-48, 192, & 768; some 100 Gbps n Wavelength Division Multiplexing common u Each OC-N drives a laser u lasers tuned to different frequencies u injected onto same fiber strand n SONET BW parceled out to users u Circuit Switching u TDM

31. WDM: 32 OC-768’s (1.274 Tbps) #1 STS-768 Laser @ f1 Laser @ f2 Laser @ f32 #2 STS-768 #32 STS-768 Detector #1 Detector #2 Detector #32 #1 STS-768 #2 STS-768 #32 STS-768 Optical Combiner Optical Splitter Fiber in the ground Systems are also available that can map an arbitrary input (doesn’t have to be SONET or OTN based) onto an optical wave.

32. Leased Lines n Covers OSI Layers 1 & 2 n 64 Kbps - 10 Gbps Line Speed n TDM, Circuit Switched n Based on 1960 & 1990 technology u Switches are byte aware n Common: Corporate Connectivity n Very Common: ISP Connectivity

33. Page Info Nov 2007

35. IEEE 802.3 Ethernet n Covers OSI Layers 1 & 2 n 10 Mbps Line Speed n Packet Switch, StatMux n Based on late 1970’s technology u Computing Power & Memory was Expensive n Initially Shared System Polite Conversation (CSMA/CD) u One Node talks at a time u Need to talk? Wait til line quiet u Nobody deliberately butts in n Switched Ethernet now more common

36. ISO OSI Seven Layer Model Ethernet (Packet Switched, StatMux) n Layer 7 Application n Layer 6 Presentation n Layer 5 Session n Layer 4 Transport n Layer 3 Network n Layer 2 Data Link 802.3 n Layer 1 Physical 802.3

37. 802.3 Ethernet Frame Format MAC Destination Address MAC Source Address CRCData + Padding Bytes: 7 1 6 6 2 20 20 6-1460 4 IPTCP

38. Duplex: We're not talking apartments n Simplex Only one node can talk (one way traffic) u Commercial Radio Station n Half Duplex Only one node can talk at a time u Walkie-Talkie n Full Duplex Both nodes can talk at same time u Telephone

39. 802.3 Flow Chart (NIC) Packet to Send? No Yes Set Collision Couter = 0 Traffic on Network? Yes No Send Packet Collision? No Jam Yes Bump Collision Counter by +1 16th Collision? Drop Packet. Notify Higher Layer Yes Back-Off No

40. 802.3 Back-Off Algorithm n choose random number 1st Collision0, 1 2nd Collision0, 1, 2, 3 3rd Collision0, 1,..., 6, 7 4th Collision0, 1,..., 14, 15 10th Collision0, 1,..., 1022, 1023 15th Collision0, 1,..., 1022, 1023 16th CollisionPunt n Wait (Random Number*.0000512) seconds

41. 10Base5 & 10Base2 (Obsolete) PC Printer Logical & Physical Bus All nodes monitor traffic Nodes share 10 Mbps Coax Cable 10Base5 "Vampire Tap" 10Base2 "T" connection Images from Wikipedia

42. 10BaseT & Shared Hub PC Hub Logical Bus & Physical Star Shared hub (OSI Level 1) copies input bits to all outputs. All nodes monitor traffic.

43. 10BaseT & Shared Hub PC Hub Logical Bus & Physical Star Each PC gets 2.5 Mbps on average. Twisted Pair Cabling

44. 10BaseT & Switched Hub PC Switched Hub Logical Bus & Physical Star Switched Hub (OSI Level 1 & 2) copies packet to proper output. Only the destination monitors traffic.

45. 10BaseT & Switched Hub PC Switched Hub Logical Bus & Physical Star This system can move up to 20 Mbps

46. 10BaseT & Switched Hub PC Switched Hub Logical Bus & Physical Star Each node shares 10 Mbps with the Switched Hub.

47. 10BaseT & Switched Hub PC Switched Hub Using Half Duplex 10BaseT, a collision occurs if PC & Switched Hub simultaneously transmit. reception is screwed up

48. Full Duplex System PC Switched Hub All 10 Gbps, most 1 Gbps, & many 100 Mbps systems are Full Duplex. NIC’s are designed to simultaneously transmit & receive. Line no longer shared. No Collisions. No need for CSMA/CD.

49. Campus Network 1993

50. Ethernet Switched Hubs n On Power Up know nothing n When a packet arrives at an input port... u Look-Up Table consulted u Source MAC address not in table? F Table Updated: MAC address & Port matched u Destination MAC address not in table? F Packet broadcast to all outputs (a.k.a. flooding) u Desination MAC address in table? F Packet shipped to proper output

51. Ethernet Switched Hubs n Look-up Table updated as packets arrive u Ethernet MAC Address : Port # n Flooding does not scale well on WAN u OK on LAN with a probably a few hundred addresses u Too much unnecessary traffic on WAN with millions of addresses n Ethernet is making way into MAN & WAN u Requires modified protocols

52. Ethernet Flavors n 802.3 10 Mbps n 802.3u 100 Mbps (Fast Ethernet) n 802.3z 1 Gbps Ethernet n 802.3ae 10 Gbps Ethernet n 802.3ba 40 & 100 Gbps Ethernet

53. Shared Ethernet Trunks Access Lines Hub PC All nodes share the system's 10 Mbps. Multiple paths = feedback loop = mess. Hub

54. Switched Ethernet Trunks Access Lines Switched Hub PC Each node shares 10 Mbps with its switch. Network can move > 10 Mbps at any instant. Multiple paths usually not used. Switched Hub Switched Hub Switched Hub

55. Ethernet & Switched Hub PC Server Switched Hub 10/100 Mbps 1 Gbps 10 Gbps Different speeds are used for different connections. Server PC To the rest of the world.

56. Two Types of Addresses MAC Destination Address MAC Source Address CRCData + PaddingIPTCP Link Transmitter Link Receiver Information Source Information Sink (Destination) n Local (Layer 2 MAC) n End-to-End (Layer 3 IPv4) Exception: NAT

57. Whose Address goes where? n Generally, PC's don't directly connect to Router u Usually connected to Switched Hub n Using IPCONFIG /ALL... Ethernet MAC address (hard-wired) u 00 50 04 C1 73 50 (6 Bytes, Base 16) u Last byte is 0101 0000 n Alpha-Numeric IP Address (usually fixed) u es303f-2.ceat.okstate.edu u host name - network name n Domain Name Server u Converts alpha-numeric IP address to numeric

58. Whose Address goes where? n Numeric IP Address (assigned on Power Up) u Dynamic Host Configuration Protocol (DHCP) u 139.78.79.157 (4 Bytes, Base 10) on 31 Jan 2004 n Default Gateway (assigned on Power Up) u Dynamic Host Configuration Protocol (DHCP) u 139.78.79.254 Router IP Address u Where to send packets when destination not part of your network F ceat.okstate.edu n Generally, Router sets the network boundary

59. Packet to Print? Must know destination IP Address n At my computer's IP Layer... n Adds 20B IP Header to each packet Source IP address = My computer (Terminating) Destination IP address = Printer n Is Information Sink IP address on my network? Yes? Tell Layer 2 to use Information Sink's MAC address No? Tell Layer 2 to use Router's MAC Address

60. Shared 802.3 Ethernet Trunks Access Lines Hub PC Pr PC 10 Nodes Share 10 Mbps Printer part of "ceat.okstate.edu". R

61. Whose address goes where? MAC Destination Address MAC Source Address CRCData + PaddingIPTCP PC MACPrinter MAC Information Source (PC IP) Information Sink (Printer IP) Hub ignores packet contents, copies bits to all outputs.

62. Shared 802.3 Ethernet Trunks Hub PC Pr PC All nodes will see packets from PC to Printer. R

63. Switched Ethernet Trunks Access Lines PC Switched Hub Switched Hub Switched Hub PC Pr R Switched Hub Packet formatting same as before. Only the Printer will see packets from the PC.

64. Switched Ethernet Trunks Access Lines PC Packets need to cross a network boundary. Switched Hub Switched Hub PC Pr R Switched Hub

65. Whose address goes where? MAC Destination Address MAC Source Address CRCData + PaddingIPTCP PC MACRouter MAC Information Source (PC IP) Information Sink (Printer IP) Connection from PC to Router IP addresses don't match MAC addresses.

66. Whose address goes where? MAC Destination Address MAC Source Address CRCData + PaddingIPTCP Router MACPrinter MAC Information Source (PC IP) Information Sink (Printer IP) Connection from Router to Printer

67. Whose address goes where? MAC Destination Address MAC Source Address CRCData + PaddingIPTCP MAC addresses change when router crossed. Stay same through an Ethernet Switch. IP addresses remain unchanged end-to-end.

68. Frame Relay n Early ‘90’s technology n Covers OSI Layer 2 n N*64 Kbps or N*1.54 Mbps connections n Virtual Circuits Route once on circuit set up. n Packet Switch, StatMux Backbones n Accessed by Routers with proper interface n Being replaced by the Internet

69. Frame Relay Backbone FR Switch Trunks Leased Line Frame Relay ‘Cloud’ Trunk capacity shared via StatMux & Packet Switching

70. Frame Relay Backbone FR Switch Trunks Leased Line Corporate Routers or FRAD's usually attached to FR backbones. Corp. LAN Corp. LAN

71. ISO OSI Seven Layer Model Frame Relay Switch (Layer 1 & 2) n Layer 7 Application Word Perfect n Layer 6 Presentation Windows API n Layer 5 Session TCP, Windows n Layer 4 TransportTCP, Windows n Layer 3 Network IP, Windows n Layer 2 Data LinkFrame Relay, T Carrier or SONET n Layer 1 PhysicalT Carrier or SONET

72. Frame Relay Packet Format (Assuming Ethernet LAN) Data 3 20 20 0-1460 3 IPTCP FR Header FR Trailer Header includes 10 bit DLCI Locally Unique Address (Valid between I/O ports) Trailer includes 2 byte Frame Check Sequence Only checks for errors in FR header TCP error checking should catch any payload error

73. LAN #1 PC Server Frame Relay Connectivity FR Switch VC #2 Suppose we need to connect to three LAN's. Server VC #1 LAN #2 LAN #3

74. Frame Relay VC Set Up n Client requests connectivity from Carrier n Carrier arranges for Leased Line to nearest Point of Presence n Technician runs Routing Algorithm on a Work Station u Paths through network generated u Appropriate Switches Notified DLCI's Assigned I/O mappings updated in Switch Look-Up Tables n Source Router ships all FR traffic down same leased line u FR switches use DLCI to properly output n Note LAN #2 & #3 can communicate with each other thru edge router of LAN #1

75. LAN PC LAN Server Frame Relay Backbone FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. Reverse path DLCI's not shown. LAN Server DLCI 375 DLCI 177 DLCI 526 DLCI 617 DLCI 375

76. Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server n PC1 injects Ethernet Packet u Destination IP Address of Server (info sink) u Router Ethernet MAC Address n Router1 u Examines, processes, strips off Ethernet Header u Examines Destination IP Address & Routing Table u Sees best path is over FR network n Router1 injects FR Packet u DLCI 375 carrying Layer 3-7 info

77. LAN PC LAN Server Frame Relay Backbone 1 2 FR Switch 1 Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server 2 DLCI 375

78. Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server n FR Switch 1 u Examines FR Look Up Table u DLCI 375 on input from Router1 maps to DLCI 177 on output to FR Switch 2 n FR Switch 1 injects FR packet u DLCI 177 carrying Layer 3-7 info

79. LAN PC LAN Server Frame Relay Backbone FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server DLCI 177 1 2 1 2

80. Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server n FR Switch 2 u Examines FR Look Up Table u DLCI 177 on input from Switch1 maps to DLCI 177 on output to Router2 n FR Switch 2 injects FR packet u DLCI 177 carrying Layer 3-7 info

81. LAN PC LAN Server Frame Relay Backbone FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server DLCI 177 1 2 1 2

82. Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server n Router 2 u Strips off FR Header u Examines Destination IP Address & Routing Table u Sees best path is over Internal LAN n Router 2 injects Ethernet Packet u Server Ethernet MAC (Assuming Server is on same subnet as Router)

83. ATM n Mid ‘90’s technology n Covers OSI Layer 2, Line Speeds < OC-48 n Virtual Circuits Route once on circuit set up. n Five classes of service n Cell Switch (53 bytes), StatMux or TDM n Failed at desktop OK on Carrier WAN & Corporate Backbone n Fading from the scene Being replaced by Internet

84. ISO OSI Seven Layer Model ATM Switch n Layer 7 Application Word Perfect n Layer 6 Presentation Windows API n Layer 5 Session TCP, Windows n Layer 4 TransportTCP, Windows n Layer 3 Network IP, Windows n Layer 2 Data LinkATM, SONET or T Carrier n Layer 1 PhysicalT Carrier, or SONET

85. ATM Cell #1 Format AAL5 Data 5 20 20 8 IPTCP ATM Header Header includes 24 or 28 bit VPI & VCI Follow on cells carry remainder of the packet.

86. LAN Carrier ATM Network What appears to be nailed up end-to-end connectivity (a Virtual Circuit). Switch I/O mappings similar to Frame Relay. ATM Switch OC-48 Trunks Leased Line OC-1

87. StatMux ATM Version frequency time 1 1 3 1 Different channels use all of the frequency some of the time, at random, as needed. empty cell Can also use TDM. 2

88. 802.3 LAN OSU Campus Network ('95 - '01) ATM Switch OC-3, then OC-12 Trunks OneNet ATM-EthernetSwitch 802.3 LAN 802.3 LAN

89. ATM Network All kinds of boxes are typically hanging off carrier ATM Switches. ATM Switch Trunks Access Line Frame Relay Routers

90. ATM PVC Set Up n Client requests connectivity from Carrier n Carrier arranges for Leased Line to nearest Point of Presence n Technician runs Routing Algorithm on a Work Station u Paths through network generated u Appropriate Switches Notified VPI's and VCI's Assigned I/O mappings updated in Switch Look-Up Tables Switch Resources reserved, depending on CoS requested n Corporate ATM switch (or Router with a plug-in ATM compatible card) ships all traffic down same leased line u ATM switches use VPI & VCI to properly output

91. ATM Connection Admission Control n Procedure for setting up VC’s n End user requests call set-up Provides destination, CoS, parameters n Switches determine if resources are available Sufficient Buffer Space? Sufficient unreserved trunk bandwidth? n Call is rejected if insufficient resources

92. ATM Connection Admission Control  CBR VC’s  Reserve Peak Trunk BW  Reserve Minimal Buffer Space  VBR VC’s  Reserve Average Trunk BW  Reserve Buffers to cover bursts  ABR VC’s  Reserve Minimum Trunk BW  Reserve Buffers to cover bursts  UBR VC’s  Reserve Nothing  Allow VC establishment if spare BW & Buffers above some minimum

93. The Internet n VAST collection of interconnected networks n Mid ‘70’s technology n Key Building Block: Routers running IP (Layer 3) n Packet Switch, StatMux n Designed for data

94. Internet Service Provider Backbone Packet Switched Statmux Network. Full duplex trunks. Router Trunks Access Line

95. Washington D.C. Area - 2000

96. ISO OSI Seven Layer Model IP Router n Layer 7 Application Word Perfect n Layer 6 Presentation Windows API n Layer 5 Session TCP, Windows n Layer 4 TransportTCP, Windows n Layer 3 Network IP, Windows n Layer 2 Data LinkEthernet, FR, ATM SONET, OTN, T-Carrier, PPP, WiFi n Layer 1 PhysicalEthernet, SONET, OTN, T-Carrier, DSL, Cable Modem, WiFi

97. LAN Internet Service Provider Network Corporate Routers & Other ISP Routers attached. ISP trunks could be... Router Trunks Leased Line T1

98. Leased Lines Nailed up end-to-end connectivity (a Circuit). Bit pipe. No packet processing between Routers. Cross-Connect Trunks Leased Line ISP Router ISP Router

99. Light Path (Wave) Connectivity (OC-48, OC-192, or OC-768) Nailed up end-to-end connectivity (a Circuit). Light Path. No packet processing between Routers. Optical Switch Trunks Fiber ISP Router ISP Router

100. Internet Packet Format Traffic ?? 20 20 0-1460 ?? IPTCP Layer 2 Header Layer 2 Trailer? Probably originated on an Ethernet.

101. Internet n Router Line Speeds generally u T1 to OC-768 on the WAN, some 100 Gbps (Mostly Leased Line or Light Waves) u 10/100/1,000/10,000 Mbps (Ethernet) on the LAN u Some Ethernet making it into MAN n Hierarchical Alpha-Numeric Names username@machine.institution.domain n Datagrams u Independent I/O decisions on every packet u Not guaranteed to follow same path