Suntorn Witosurapot Communication networks and networking for managers Suntorn Witosurapot Contact Address: Phone: or November 2003

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 2 Chapter 3 A Small Ethernet PC Network

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 3 Review: Review: Architecture Reference Presentation OSITCP/IP Application Session Transport Network Transport Internet Data Link Physical Data Link Physical General Function Application Communication Internetworking Single Network Transmission

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 4 Review: Review: a View of Horizontal Layered Message Communication in TCP/IP PC Ethernet Switches Routers (IP) Message Web Server Message PCWeb Server

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 5 Review: Review: a View of Logical Message Communication in TCP/IP HTTP Msg Application Layer Proc Proc = Process Application Layer Proc Transport Layer Proc TCP Msg Transport Layer Proc Network Layer Proc IP Packet Network Layer Proc Network Layer Proc Client PCServerEthernet SwitchRouter Data Link Layer Proc Eth Frame Data Link Layer Proc Data Link Layer Proc Data Link Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 6 Review: Review: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process TCP Hdr IP Hdr HTTP Msg Internet Process DL Hdr TCP Hdr IP Hdr DL Hdr HTTP Msg Data Link Process

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 7 Preview: An Ethernet PC network Our goals: Understand Ethernet architecture and its components –Able to differentiate between hubs and switches and reasons for the growing dominance of switches –Understand the division of data link into the medium access control and logical link control layers

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 8 Elements of a Small Ethernet PC Network Access Router A1-44-D5-1F-AA-4C D C4-B6-9F To the Internet Ethernet Switch or Hub B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F UTP Broadband Modem Client Server

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 9 Network Interface Card (NIC) Each station must have a network interface card (NIC) This is true for both clients and servers The NIC implements LAN protocols Physical Data Link

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 10 Ethernet Standards Ethernet standards dominate in small LANs –Governs switches, wiring and NIC (network interface cards) IEEE (Institute of Electrical and Electronics Engineers) Standardization –802 LAN/MAN Standards Committee (802 Committee) creates LAN standards Working Group creates Ethernet standards So Ethernet standards are also known as standards. Physical Data Link

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 11 Ethernet Standards (cont.) Physical Layer Ethernet Standards Using UTP 10 – Base-T 10 Mbps – Base-TX, 100Base-FX 100 Mbps 10/100 operation (auto-sensing) – Base-T Gigabit Ethernet (?? Mbps) Physical Data Link T = twisted pair; F = fiber optics; T = twisted pair; F = fiber optics;

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 12 Purchasing and Installing UTP Wiring Quality Categories –Governed by the TIA/EIA-568 standard –Categories 3, 4, 5, 5e (enhanced) and 6 (released in 2002) Higher numbers indicate better quality –Category 5e is recommended for new buildings –Category 5 or 5e is required for 100Base-TX –Category 5 or 5e is required for 1000Base-TX (Gigabit Ethernet), but 5 is marginal Physical Data Link

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 13 Hubs and Switches: Available either in a form of Desktop box, or 19 ’’ Stackable/Rack-Mountable module

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 14 Hub Operation A1-44-D5-1F-AA-4C D C4-B6-9F Ethernet Hub B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F UTP Client Server Station A1-44-D5-1F-AA-4C transmits a bit. Hub broadcasts the bit out all other ports.

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 15 Hub Operation A1-44-D5-1F-AA-4C D C4-B6-9F Ethernet Hub B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F UTP Client Server While station A1-44-D5-1F-AA-4C is transmitting. If station B2-CD-13-5B-E4-65 wishes to transmit, it must wait. Waiting Transmitting

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 16 Hub Operation: Waiting to Transmit with a Hub Waiting creates latency (delay) –Becomes intolerable with many stations Not a problem for very small networksNot a problem for very small networks Speed of hub is shared by all stations—each gets only a fraction

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 17 Switch Operation A1-44-D5-1F-AA-4C on switch port 10 D C4-B6-9F on switch port 16 Ethernet Switch B2-CD-13-5B-E4-65 on switch port 13 C3-2D-55-3B-A9-4F on switch port 15 UTP Client Server switch A switch sends a frame out a single port — the one to the receiver Frame

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 18 Switch Operation A1-44-D5-1F-AA-4C on switch port 10 D C4-B6-9F on switch port 16 Ethernet Switch B2-CD-13-5B-E4-65 on switch port 13 C3-2D-55-3B-A9-4F on switch port 15 UTP Client Server simultaneous Multiple simultaneous conversations are possible! Frame

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 19 Ethernet Switching Table A1-44-D5-1F-AA-4C on switch port 10 D C4-B6-9F on switch port 16 Ethernet Switch B2-CD-13-5B-E4-65 on switch port 13 C3-2D-55-3B-A9-4F on switch port 15 UTP Client Server Frame Switching Table PortStation 10 A1-44-D5-1F-AA-4C 13 B2-CD-13-5B-E C3-2D-55-3B-A9-4F 16 D C4-B6-9F 15 C3-2D-55-3B-A9-4F

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 20 Ethernet Switches They are link-layer devices: operate on Ethernet frames, examining frame header and selectively forwarding frame based on its destination Switches isolates collision domains since it buffers frames When frame is to be forwarded on segment, bridge uses CSMA/CD to access segment and transmit

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 21 Ethernet Switches: Advantages Isolates collision domains resulting in higher total max throughput, and does not limit the number of nodes nor geographical coverage Can connect different type Ethernet since it is a store and forward device Transparent: no need for any change to hosts LAN adapters

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network Standards Layering Internet Layer Media Access Control Layer Data Link Layer Logical Link Control Layer TCP/IP Internet Layer Standards Other Internet Layer Standards Other MAC Standards (802.5, etc.) Ethernet MAC Layer Standards Physical Layer 10 Base-T 100 Base-TX 1000 Base-TX Other Physical Layer Standards (802.5, etc.)

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 23 Octet A collection of 8 bits Called a byte in computer science The term “ Octet ” is widely used in networking Octet = group of 8 bits

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 24 Ethernet Frame Preamble (7 Octets) … Begins synchronization Start of Frame Delimiter (1 Octet) Ends synchronization Signals start of content of frame FieldDescription … Synchronizes the receiver ’ s clock with the sender ’ s clock Like a boat racing calling out “ Hui, Ley, Hui ”

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 25 Ethernet Frame (cont.) Destination Address (6 Octets) Of Receiving NIC 48 Bits Expressed for humans in Hexadecimal Example: Example: A1-34-CD-7B-DF-47 Unique NIC value set at factory FieldDescription Source Address (6 Octets) Of Sending NIC 48 Bits Expressed for humans in Hexadecimal Example: Example: 34-D5-E6-6A-BD-B0 Unique NIC value set at factory

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 26 Ethernet Frame: MAC Addresses Ethernet addressesMAC addressesEthernet addresses are called MAC addresses They are station (NIC) address at the MAC layer Usually expressed for humans in hexadecimal –Base 16: Each symbol represents 4 bits (for example, 0101=5 hex) –Convert each four bits to a hex symbol between 0 and F –Put dashes between each pair –Example: A1-34-CD-7B-DF-89 Physical MAC

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 27 Ethernet Frame: Hexadecimal Notation Bits (Base 2*) Decimal (Base 10) Hexadecimal (Base 16) 0 hex 1 hex 2 hex 3 hex 4 hex 5 hex 0000 *2 4 =16 combinations For example, A1-34-CD-7B-DF hex begins with

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 28 Ethernet Frame: Hexadecimal Notation (cont.) 4 Bits (Base 2) Decimal (Base 10) Hexadecimal (Base hex 9 hex A hex B hex hex 7 hex C hex D hex E hex F hex Example: = CD-EF

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 29 Ethernet Frame (cont.) Ethernet MAC Header LLC Header IP Packet Ethernet Trailer Ethernet Data Field: LLC Frame Preamble (7 octets) Start of Frame Delimiter (1 octet) Dest. Address (6 octets) Src. Address (6 octets) Length (2 octets) Frame Check Sequence (4 octets) LLC Data Field: IP Packet Physical MAC Direction

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 30 Ethernet Frame (cont.) FieldDescription Length (2 Octets) Length of Data Field in octets 1,500 (decimal) maximum LLC Frame Containing IP Packet PAD Needed if data field < 46 octet min., (so that Data Field + PAD will be 46 Octets) Physical MAC Data Field (variable)

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 31 Ethernet Frame (cont.) FieldDescription Frame Check Sequence (4 Octets) Error detection field; If error is detected, frame is discarded The FCS field is for error checking. Both sender and receiver compute it from the other bits in the frame. If the two computed values are different, there has been an error. In case of error, the receiver discards the frame; there is no request for retransmission. Physical MAC

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 32 MAC Protocols We consider broadcast channels Problem: how to determine who gets to use the channel when there is competition for it Two basic schemes: Static channel allocation and Dynamic channel allocation Physical MAC Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Aloha Carrier Sense Multiple Access (CSMA)

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 33 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) With Hubs, NICs must engage in CSMA/CD –CSMA/CD is not used with switches Two processes Carrier Sense Multiple Access (CSMA) 1. Carrier Sense Multiple Access (CSMA) –If a NIC wishes to transmit, it must listen for traffic If there is no traffic, the NIC may transmit If there is traffic, the NIC must wait to transmit until no traffic is being transmitted; then it may send

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 34 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) (cont.) Collision Detection (CD) 2. Collision Detection (CD) If there is a collision ( by 2 or more stations transmitting at the same time ), random amount of time –All NICs stop transmitting and wait for a random amount of time –The first NIC that finishes its wait may transmit but only if there is no traffic! If there is traffic, the NIC must wait until there is no traffic

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 35 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) (cont.) Collision Detection (CD) 3. Collision Detection (CD) –If there are multiple collisions, The random wait is increased each time After 16 collisions, the sending NIC discards the frame

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 36 CSMA/CD: a few details time A B C data interframe gap (IFG): 96 bits collision enforcement jam signal: 32 bits collision backOff time: multiples of the slot time: 512 bits

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 37 CSMA/CD: Why collision occurs? A B CD t0t0 t1t1 t2t2 t3t3 A B CD A B CD A B CD

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 38 Recap: Recap: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Hubs do not implement it when talking to stations NICs implement it when talking to hub CSMA/CD with Hubs

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 39 Recap Recap: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Three basic elements for describing CSMA/CD –CSMA –CSMA — transmit only if line is clear; waiting otherwise –CD Part 1 –CD Part 1 — handling a single collision –CD Part 2 –CD Part 2 — handling of multiple collisions

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 40 NIC-Switch Communication No possibility of collisions with switches With switches, NICs operate in full-duplex mode –Turn off CSMA/CD Full Duplex –Can transmit and receive any time — called Full Duplex operation

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 41 Network Interface Cards (NICs) PC Card NICs snap into external PC card slots on notebooks. RJ-45 Jack Internal NICs fit into slots on the motherboard. Must open PC to install.

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 42 Recap Recap: Ethernet Physical Layer Standards –10Base-T, 100Base-TX, gigabit Ethernet, etc. –Media and signaling MAC Layer Standards –Frame Organization –Hub and Switch Operation –CSMA/CD versus Full-Duplex NICs Handle Both Layers, Plus LLC

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network Standards Layering Internet Layer Media Access Control Layer Data Link Layer Logical Link Control Layer TCP/IP Internet Layer Standards Other Internet Layer Standards Other MAC Standards (802.5, etc.) Ethernet MAC Layer Standards Physical Layer 10 Base-T 100 Base-TX 1000 Base-TX Other Physical Layer Standards (802.5, etc.)

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 44 Logical Link Control (LLC) Layer LLC Standard is used in all 802 LANs above –All MAC layer standards interact only with at the layer above them below –All internet layer standards interact only with at the layer below them LLC Ethernet MACWireless MAC IP MAC LLC Physical

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 45 Logical Link Control (LLC) Layer (cont.) Optional Error Correction –Error detection, and retransmission –Almost never used –NICs rarely allow user to control LLC functionality MAC LLC Physical

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 46 Ethernet Frame Organization Including LLC As noted earlier, here is how Ethernet frames are organized, including the LLC header Ethernet Header LLC Header IP or Other Packet Ethernet Trailer Ethernet Data Field: LLC Frame LLC Data Field Ethernet Frame MAC LLC Physical

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 47 Internetworking To extend / connect networks using the same or different tech. –LAN  LAN –LAN  WAN –WAN  WAN –LAN  WAN  LAN

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 48 Why not just one big LAN? Limited amount of supportable traffic: on single LAN, all stations must share bandwidth Large “collision domain” (can collide with many stations) Limited length and number of stations, e.g (Ethernet) specifies maximum cable length

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 49 Ethernet Switching Hubs Hubs can be arranged in a hierarchy (or multi-tier design), with backbone hub at its top. Each connected LAN referred to as LAN segment Hub Advantages: –simple, inexpensive device –Multi-tier provides graceful degradation: portions of the LAN continue to operate if one hub malfunctions –extends maximum distance between node pairs (100m per Hub)

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 50 Ethernet Switching Hubs: Backbone Interconnection without a backbone is not recommended due to - single point of failure at Computer Science hub - all traffic between EE and SE must path over CS segment Backbone hub  

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 51 Example: 100Mbps Ethernet Backbone strategy

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 52 Internet Access access routerDesktop access router for very small group –Usually has built-in switch to connect several PCs –The access router/switch usually has a built-in DHCP server so that all PCs can share a single IP address given to the user by the ISP 18 cm (7 in) wide

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 53 Using an Access Router Broadband Modem PC WAN Port to ISP UTP Access router has built-in switch, DHCP server for PCs and NAT Firewall (will be studied later) Auto-configured by Access Router

communiction networks and networking for managers Chapter 3 A small Ethernet PC Network 54 Linux/Windows Allows PCs to Share a Connection Broadband Modem PC With 2 NICs Other PC Or Switch ISP