Physical and Data Link Layer s (Layer 1 & 2) : Ethernet (Network Interfce Card)

1. Physical and Data Link Layers (Layer 1 & 2):Ethernet (Network Interfce Card)

2. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS • IEEE 802.1 High Level Interface • IEEE 802.2 LLC (Logical Link Control) • IEEE 802.3 CSMA/CD (Carrier Sense Multiple Access with Collision Detection) • IEEE 802.4 Token-Bus • IEEE 802.5 Token-Ring • IEEE 802.6 DQDB (Distributed Queue Dual Bus) • IEEE 802.7 Broadband Technical Advisory Group • IEEE 802.8 Fiber Optic Technical Advisory Group • IEEE 802.9 Integrated Voice and Data LAN Working Group • IEEE 802.10 LAN Security Working Group • IEEE 802.11 Wireless LAN • IEEE 802.12 Demand-Priority (100VG-AnyLAN) • IEEE 802.14 Hybrid Fiber Coaxial Network

3. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS IEEE Standard 802.3 and Ethernet

4. The Medium Access Sublayer Connecting two Hosts (Bridging) Operation of a LAN bridge from 802.3 to 802.4

5. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS IEEE Standard 802.2: Logical Link Control

6. Physical and Data Link Layer To which OSI layer does Ethernet belong?Ethernet belongs to both the Physical Layer (Layer 1) and the Data Link layer (Layer 2) in the OSI architecture. What are the standard data rates for Ethernet?The standard data rates for Ethernet are 10 Mbps, 100 Mbps, and 1 Gbps What are the IEEE standards that cover Ethernet?The following IEEE standards define Ethernet:

7. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS IEEE Standard 802.3 and Ethernet IEEE 802.3: 1-persistent CSMA/CD

8. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS IEEE Standard 802.3 and Ethernet To allow larger networks, multiple cables can be connected by repeaters. A repeater is a physical layer device. It receives, amplifies, and retransmits signals in both directions. As far as the software is concerned, a series of cable segments connected by repeaters is no different than a single cable.

9. The Medium Access Sublayer 10BASE5 10BASE2 1BASE5 10BROAD36 10BASE-T Ethernet Cheaper net StarLAN Broadband Twisted-pair coaxial cable 50ohm-10mm coaxial cable 50ohms-5mm twisted-pair unshielded coaxial cable 75ohms 2 simplex TP unshielded medium 10Mbps Manch 10Mbps Manch 1Mbps Manch 10Mbps DPSK 10Mbps Manch signals maximum segment 500m 185m 500m 1800m 100m maximum distance 2.5km 0.925km 2.5km 3.6km 1km nodes per segment 2 100 30 activity on receiver and transmitter collision detection 2 active hub inputs transmission =reception excess current Notes slot time=512 bits; gap time=96 bits; jam=32 to 48 bits

10. Ethernet • What is Ethernet?Ethernet is a Local Area Network (LAN) cabling and signaling specification for baseband networks. Ethernet uses a bus or star topology for connecting different nodes in a network.

11. Ethernet Frame (MAC Packet) • The most popular physical layer implementation • Developed in 1982, by DEC, Xerox and Intel • Uses Carrier sense, multiple access with collision detection (CSMA/CD)‏ • Initially a 10Mb/s signalling rate but developed to be as fast 1Gb/s. • Nearly the same as IEEE 802.3

12. The Medium Access Sublayer IEEE Standard 802 for LANS and MANS IEEE Standard 802.3 and Ethernet Ethernet Frame Structure (Ethernet Encapsulation) 7 1 6 6 2 4 preamble SFD DA SA type CRC Data 60 to 1514 bytes synchronize the receiver type Cyclic Redundancy Check 0800: IPv4 datagram 0806: ARP request/reply 8035: RARP request/reply 86DD: IPv6 start frame delimiter

13. Ethernet Frame (cont’d) • An Ethernet frame: • 2 byte type that indicates what kind of data follows, e.g., 0800 for an IP packet • Then the data, maximum 1500 bytes, minimum 46 bytes • Data field must be padded with extra bytes if fewer than 46 bytes are supplied

14. Ethernet Frame (cont’d) • An Ethernet frame: • 4 byte checksum, also called cyclic redundancy check (CRC)‏ • Used to check for errors in the frame

15. Ethernet Frame (cont’d) • Ethernet is a shared medium • A wishes to send to B

16. Ethernet Frame (cont’d) • Ethernet is a shared medium • A wishes to send to B • If C is already sending to D, then A must wait

17. Ethernet Frame (cont’d) • Ethernet is a shared medium • A sends packet, but keeps listening for a clash (collision detection)‏

18. Ethernet Frame (cont’d) • Ethernet is a shared medium • Random wait means one of A or C gets in next, the other sees this through its carrier sense

19. CSMA/CD IEEE Standard 802 for LANS and MANS IEEE Standard 802.3 and Ethernet

20. 1.      How two systems in an Ethernet network communicate?In a Ethernet network, a system broadcasts the data using a Ethernet frame. The destination system is specified in the Ethernet frame using its Ethernet address. All the systems in the network listen for an Ethernet frame with their Ethernet address in it. When a system receives an Ethernet frame with its address in it, it processes the frame and sends it to the higher layers (like IP) for further processing. 2.      What is a "collision"?At any one instance, in an Ethernet network, only one device can transmit. If two devices transmit at the same instance, then the signals from both devices will collide and a "collision" will occur. When a "collision" occurs, the signals will get distorted and the frame will be lost. Collisions are very common in a Ethernet network. 3.      How is "collision" handled in Ethernet networks?Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) media access control mechanism to detect and recover from a collision.

21. What is CSMA/CD?CSMA/CD is a media access control mechanism used in Ethernet to recover from frame collision. The following steps are used to recover from a collision. Step 1: Before an Ethernet device sends a frame on the Ethernet cable, it listens to find if another device is already transmitting a frame (Carrier Sense). Step 2: Once the device finds that other devices are not transmitting any frame, it starts transmitting the frame. If two devices detect that the Ethernet cable is free at the same time, then both will start transmitting the frames (Multiple Access). This will result in collision. Step 3: The Ethernet devices while transmitting the frames, also listen for the collision. (Collision Detect). Step 4: If they detect a collision, both the devices stop sending the frame (back off). Step 5: They retry the transmission after a logarithmic time-out period. This process is repeated till the frame is transmitted successfully, for a maximum of 16 times. The frame is discarded after the 16th retry.

22. Physical Layer Adressing 1.      What is an Ethernet address?Each device in an Ethernet network is uniquely identified by a 48 bit (6 bytes) address called Ethernet address. Ethernet address is also known as Media Access Control (MAC) address. Ethernet addresses are represented as six pairs of hexadecimal digits separated by a colon. Ethernet address are buried in the network adapter by the manufacturer. A Ethernet address of a device cannot be changed. Example: 00:60:08:11:B1:AB, 00:00:c0:5e:83:0e 2.      What is a broadcast address?The Ethernet address in which all the bits are 1 is known as a broadcast address. It is represented as FF:FF:FF:FF:FF:FF. A frame with this address is received and processed by all the nodes in the network.

23. LAB: Format of an Ethernet frame Using TCPDUMP read the Ethernet frames into a text file and analyse them in order to identify the fields.

24. What is MTU? • Maximum Transmission Unit (MTU) is the maximum number ofbytes that can be transmitted in a single transmission unit. • Every communication medium has a MTU. For Ethernet, the MTU of a frame is 1500. • DMTU changes for differenet physical networks

25. Ethernet Hardware • Plus several others ...

26. Ethernet Hardware • 10Base5: fat coaxial cable (yellow) with vampire taps and drop cables (blue) to the hosts, AUI plugs • 10Base2: Thinnet, simple coaxial cable, BNC connectors directly to the hosts • 10BaseT: twisted pair (UTP), RJ45 plugs, each host connects to a central hub

27. Ethernet Hardware Unshielded Twisted Pair (UTP)‏ • Category 1: No performance criteria • Category 2: Rated to 1 MHz (used for telephone wiring)‏ • Category 3: Rated to 16 MHz (used for Ethernet 10BaseT)‏ • Category 4: Rated to 20 MHz (used for Token-Ring, 10BaseT)‏ • Category 5: Rated to 100 MHz (used for 1000BaseT, 100BaseT, 10BaseT)‏

28. Ethernet Hardware Unshielded Twisted Pair (UTP)‏ • Enhanced Category 5: Rated to 200 MHz (used for 1000BaseT, 100BaseT, 10BaseT)‏ • Category 6: Rated to 250 MHz (used for 1000BaseT)‏ • Category 7: for the future, but should be shielded twisted pairs (STP), new connectors (GG45), 600MHz

29. Ethernet Hardware: Hubs • A hub simply echoes all inputs to all outputs • Provides a single collision domain • The available bandwidth shared between all the hosts

30. Ethernet Hardware: Switches • A switch understands the link layer and forwards a packet to the appropriate single output • Each output cable is now a separate collision domain • The full bandwidth available on each output • Collisions only if two hosts send to the same destination simultaneously

31. Ethernet Hardware: Switches • Switches can store and forward packets • Then there can be no collisions and we can do away with CSMA/CD • Buffers can fill up, though, then packets will be dropped

32. Ethernet Hardware • Switches can cut through, sending the start of the packet onwards before the tail has arrived • Less latency through the switch, but would forward corrupted packets

33. Ethernet Hardware: Switches • Switches can run full duplex, with independent inward and outward traffic to each host • This gives twice the total bandwidth • No collisions possible as inward and outward traffic runs over different twisted pairs

34. Ethernet Hardware: Switches • 10Mb/s, 100Mb/s, 1Gb/s, ... • These can autonegotiate to select optimum speed • Gigabit over copper: very complicated hardware • Gigabit CSMA/CD requires carrier extension to make the packets big enough • Compensates with packet bursting

35. Ethernet Hardware: Switches • 10Gb/s Ethernet coming soon • Full duplex switched only, no CSMA/CD • Mainly fibre optic, but copper is under consideration • 40Gb/s and 100Gb/s Ethernet in the planning stages • Proponents claim that Ethernet will take over the world!

36. ADSL • Another technology to send data down telephone lines, Asymmetric Digital Subscriber Line • The current technology of choice for Internet to the home

37. ADSL Modems • Analogue modems are limited to 56Kb/s, the maximum speed available from a standard analogue telephone line: all frequencies apart from a 3KHz chunk centred on the human voice are filtered out and thrown away • The telephone cable is capable of more, ADSL tries to take advantage of this • ADSL (one of a series of DSL standards) requires new hardware in the home and in the telephone exchange

38. ADSL Features • Available bandwidth decreases as cable length increases: a practical limit of about 5-6km (3-3.5 miles)‏ • Typical ADSL allows up to 8Mb/s downstream and 960Kb/s upstream • A common method of delivery of ADSL to the home is to use a modem that plugs into the USB port on a computer Then a Web browser will use HTML over HTTP over TCP over IP over PPP over AAL5 over ATM over ADSL over USB over copper!