TDC 461 Basic Communications Systems Local Area Networks 29 May, 2001

Agenda Local Area Networks –Components –Topologies –Transmission Media –Network Interface Cards (NICs) –Network Operating System software Client vs Server functions Peer-to-Peer vs. Server- based Local Area Network Technologies –Ethernet –Token Ring LAN Interconnection –LAN Switches –Routers

What is a LAN? Key Elements: –

LAN Components Workstations (PCs, etc.) – Interconnecting Cable – Network Operating System (NOS) Software

LAN Topologies How are Workstations connected together? –

Bus Topology

Bus Topology Example: 10Base5 Ethernet

Ring Topology

Dual Ring Example: Fiber Distributed Data Interface (FDDI) GOLDMAN: LAN Self-healing FDDI dual- attached adapters Self healed after Link Failure link failure

Star Topology

Star Topology Example: 10BaseT Ethernet

LAN Cable LAN Cable can be of several types: –

Twisted Pair Unshielded Twisted Pair (UTP) –Similar to telephone cable, but Usually 4-pair cable is used UTP Category ratings –Category Mbps up to 100 meters –Category Mbps up to 100 meters –Category Mbps up to 100 meters Shielded Twisted Pair (STP) –

Coaxial Cable LAN coaxial cable is similar to Cable TV cable (and can be identical) –Construction –Advantages –Disadvantages

Coaxial Cable

Fiber Optic Cable Transmits data using light rather than electricity –Structure –Advantages –Disadvantages

Fiber Optic Cable

LAN Hardware Cabling and NIC card specs dictated by standards document for the particular LAN Access Method: –Ethernet –Token Ring –ARCNet –Fiber Distributed Data Interface (FDDI) –etc.

NIC Card Sales - 1Q 1998 (percentage of 10.9 millions units sold) Source: In-Stat

Network Operating Systems Popular NOSes: – NOS determines workstation role: –

Installed LAN Servers 2Q 1998 Source: Dataquest

New Servers Deployed Jan-June 1998 Source: Network World

File Servers A File Server Shared files accessed via –

Network Drives

Security Login (Log on) Network Manager controls access rights for each user to each resource.

File Servers

Example: Get File Open File File Opened Read Data Data Close File File Closed

NOS Types Peer-to-Peer NOS – Dedicated Server NOS –

LAN Standards IEEE 802 Committee Standards – Ethernet – Token Ring

LAN Standards IEEE 802 Standards include –Physical (Layer 1) Cable Types Maximum length restrictions Data rate and bit encodings –Medium Access Control (Layer 2) Access control protocol (determines which device can transmit when Frame header/trailer format

Ethernet Physical Standards: –10Base5 (1985) 10 Mbps Thick Coaxial Cable (Bus) –10Base2 (1988) 10 Mbps Thin Coaxial Cable (Bus) –10BaseT (1990) 10 Mbps Twisted Pair (Star)

Ethernet Physical Standards: –100BaseT (1995) 100 Mbps Twisted Pair (Star) –100BaseF (1995) 100 Mbps Fiber (Star) –1000BaseX (1998) 1 Gbps Fiber (Star)

Ethernet IEEE Naming System: – –Example: 10Base5 10 Mbps data rate Baseband signal type Longest cable length = 500 meters

Ethernet IEEE Naming System: – –Example: 10Base5 10 Mbps data rate Baseband signal type Longest cable length = 500 meters

10Base5 Ethernet

10Base2 Ethernet

10BaseT Ethernet

100BaseT Ethernet (Fast Ethernet) Requires high-quality (Category 5) twisted pair cabling Requires 100 Mbps NIC cards in PC workstations Requires 100 Mbps hub

100BaseT Ethernet (Fast Ethernet)

Switched Ethernet Switched vs. shared Bandwidth to desktop Additional hardware –Switches Switched 10 Switched 100

Gigabit Ethernet Requires fiber optic cabling Requires Gigabit NIC cards in PC workstations Requires Gigabit Ethernet hub or Gigabit Ethernet switch

1000BaseX Ethernet

Ethernet MAC Protocol Medium Access Control (MAC) layer protocol is identical for all Ethernets: –Ethernet Frame format –Carrier Sense Multiple Access with Collision Detection (CSMA/CD) used to determine which workstation can send at any given time.

Ethernet Frame Format

Ethernet Frame Header: –Preamble - 8 bytes - alternating 1/0 bits for clock synchronization –Dest. Address - 6 bytes –Source Address - 6 bytes –Length - 2 bytes - Packet length Trailer: –CRC - 4 bytes - Cyclic Redundancy Check

MAC Protocol

Carrier Sense Multiple Access with Collision Detection To transmit data packet: –First, listen to see if any other station is transmitting (Carrier Sense) –When network is quiet, start transmitting

Carrier Sense Multiple Access with Collision Detection Station Backoff –Each station involved in collision: –As number of collisions grows, range of random values (N) increases (“exponential backoff”)

Ethernet Enhancements Switched Ethernet – Full-duplex Ethernet –

Ethernet Switches Ethernet Switch –

Switches vs. Routers How is Switch different than a Router? –Addressing Switch uses layer 2 MAC addresses Router uses layer 3 IP address –Speed & security Switch forwards packets fast (~ nsec). Router takes more time (~1-50 msec) and provides other security features

Switched Ethernet

Switches vs. Hubs How is Switch different than a Hub? –Broadcasting (and Security) Hub broadcasts every packet to every device Switch forwards packet out single port –Matching Data Rates All ports on hub must run at same data rate Switch ports can run at different rates (can buffer incoming packet at one data rate and re-transmit at another data rate).

Full-Duplex Ethernet Full-Duplex Ethernet allows a workstation to send and receive data simultaneously. Requirements –Must have a full-duplex NIC card –Must be connected to Ethernet switch

Switched Hierarchy Switches allow network manager to put bandwidth where it is needed. –Some users get 10 Mbps shared (hub) –Some users get 10 Mbps dedicated (switch) –Some users get 100 Mbps shared (hub) –Some users get 100 Mbps dedicated (switch)

Token Ring Physical Layout: –Dual Ring of Stars Medium Access Control Protocol –Token Passing

Token Ring Advantages over Ethernet: – Disadvantages over Ethernet: –

Token Ring Frames

Access Control Byte

Token Ring Operation