Network technologies

1
Network technologies

• Avgust Jauk ltjauk_at_arnes.sigt
• ARNES

Zagreb, August 97
2
Agenda

• Internet topology
• Networks
• Modems
• Routers

3
Internet topology

• Internet - Network of Networks
• Networks
• Based on different technology
• Large or small
• Fast or slow
• Variety of connected nodes
• Interface connects node to a network
• Routers (Gateways) special nodes

4
Networks

• Collection of communicating devices that are
  interconnected and autonomous
• Different classifications
• Geographical scope LAN,MAN,WAN
• Topology star, bus, ring, tree
• Transmission media copper, fiber, radio,
  microwaves, satellites
• Ownership Private / Public

5
Network classifications (cont.)

• Technology
• Switched / Permanent links
• Physical / Virtual links
• Switching Circuit switching, Packet switching
• Packet / Frame / Cell switching
• Connection-oriented / Connectionless
• broadcast, point-to-point, NBMA
• Speed Broadband, Narowband
• . . .

6
Network Classifications (cont.)

• Broadband networks
• a network that uses high-frequency analog
  technology as a transport
• any network that operates above voice frequency
  range
• any network that operates above ISDN PRI rate
• any network that offers multimedia transport

7
Networks

• LANs
• MANs
• Wide Area Networks
• Point-to-Point Links
• NBMA Networks (Clouds - packet switching)

8
Local Area Networks (LANs)

• Ethernet
• Token Ring
• FDDI/CDDI
• ATM

9
EtherNet

• 10 Mbps
• Coax bus -or- Twisted pair / fibre to repeater
  hub
• No delivery guarantees
• Collision-Detect / Carrier Sense Multiple Access
• Inexpensive, standard

10
Ethernet

• Bus topology
• CSMA/CD (Carrier Sense Multiple Access /
  Collision Detect)

11
CSMA/CD protocol

• Listen for idle wire
• Transmit, while listening
• If garbled Collision
• back off for random, increasing time
• Retransmit up to 16 times, with ever larger
  backoff

12
Bridge function

• Router that routes on MAC address
• Automatically learns network topology
• Listens on all ports in promiscuous mode
• If broadcast, always forward (to all ports)
• If not, forward to the port it is on
• If port is unknown, forward to all ports
• Entries time out in a few seconds

13
Bridge Topology
B
14
Spanning Tree
B
B
B
15
Spanning Tree (802.1)

• Detects redundant links and shuts them down
• Reduces graph to tree

16
ARP Automatic translation of IP addresses to
ethernet addresses

• Station has IP packet
• Broadcast Who is 194.181.200.1 ?
• 194.181.200.1 replies with ethernet address
• Station builds table
• Entries time out to allow update if ethernet
  cards are switched for repair

17
Ethernet Media Types

• Yellow Coax (10Base5)
• Thin Coax (10Base2)
• Twisted pair (10BaseT)
• Fiber (10BaseF)

18
Yellow Coax

• Continuous copper core
• 50 ohms at each end
• Station transceiver drills through outer braid
  and taps core with stinger
• Up to 500 meter per cable
• Up to 100 stations
• Typical error Braid shorts when installing
  transceiver tap

19
Thin coax

• 200 meter per cable
• BNC T-connector at each station
• Max. 30 stations
• Typical error Bad crimp on BNC connector

20
Twisted pair

• Each station has two pairs (Rx and Tx) to HUB
  (multiport repeater)
• Idle station sends carrier
• Green light shows carrier on each port
• Repeater chip enables port only when good carrier
• Errors localized, easy to troubleshoot
• Typical error Bad RJ-45 crimp in cable. (Rare.)

21
TokenRing

• 4 Mbps or 16 Mbps
• Twisted pair pass-through ring or via repeater
  hub
• delivered bit
• Token Passing (like indian talking stone)
• Patent fees drive price above ethernet

22
Token ring topology

23
FDDI

• 100 Mbps over dual fiber
• Up to 20 km with single-mode fiber
• Copper version on twisted pair to concentrator
• Double token ring (opposite directions)
• When ring breaks, turns into single ring (ring
  wrap)

24
Copper FDDI

• Single-attached stations connect to hub-like
  concentrator, which is part of fiber ring
• Up to 100 meter from station to concentrator

25
Newest LAN technologies

• full duplex Ethernet flow control (802.3x)
• 100 Mbps Ethernets (100BaseT, 100VG)
• Layer two switching, VLANs
• Gigabit Ethernet
• traffic classes (IEEE 802.lp), multicast
  filtering, RSPV
• ATM LANE
• Wireless LANs

26
100 Mbit/s Ethernets

• two standards
• 100VG-AnyLAN (not really ethernet)
• fast ethernet
• Fast Ethernet
• known technology the same Media Access Control
  Layer
• hubs and repeaters
• cheaper than FDDI

27
Fast Ethernet (cont.)

• cabling
• 100Base-TX half and full duplex over 2 pairs of
  cat. 5 UTP
• transcievers based on CDDI technology
• 100Base -T4 half duplex, over 4 pairs of cat. 3
  and cat. 5 UTP
• 100Base-FX
• MII - Media Independent Interface
• Nway Autosensing (speed, duplex)

28
Layer two switching

• multiport bridges
• one/more MAC addresses per port
• modes of operation
• store and forward
• cut through

29
Layer two switching (cont.)

• Virtual LANs
• grouping of end nodes into logical LANs
• more than one logical LAN over the same physical
  LAN
• distributed over multiple switches
• VLAN setup technologies
• by switch port number
• by MAC address
• on layer three protocol basis (layer three VLANs)
• by layer three protocol type
• by layer three protocol address (IP subnet, ...)

30
VLANs (cont.)

• DHCP as an alternative technology
• policy based VLANs
• manuall/automatic setup
• how to route between VLANs?
• with a conventional router
• routing implemented in switchs HW
• map protocol address into MAC address, ATM VC,
  port number
• use of external route server

31
Gigabit Ethernet

• ongoing standardization (802.3z)
• only slightly modified MAC layer
• using Fiber Channel physical layer (PHY) for
  copper and fiber
• should work over
• fiber
• 550 m multi mode
• 3 km single mode

32
Gigabit Ethernet (cont.)

• copper
• coax 25 m
• UTP questionable (signal reflects back at RJ-45
  connectors
• use of twinax cable
• collision domain size problem (20m)
• carrier extension a special signal sent atfer a
  short frame
• actual frame and carrier extension last for 512
  bytes
• throughput drop to 300 - 400 Mbit/s (120 with 64
  byte frames)

33
Gigabit Ethernet (cont.)

• buffered distributors
• something between a repeater and switch
• full duplex links to connected nodes
• repeater it receives frames and transmit them to
  all nodes
• switch receive on multiple ports and store
  frames in buffers
• if buffers are full it uses asymmetric flow
  control to tell the transmitting nodes to stop
  sending
• no bandwidth penalty of carrier extension, but
  all transmitting nodes must implement flow
  control

34
Metropolitan Area Networks (MANs)

• FDDI
• DQDB
• SMDS

35
Wide Area Point-to-Point Links

• Dial-up links
• Analog (POTS)
• 2 wire, switched
• need for a voice-grade modem
• Digital (N-ISDN)
• 2 wire, fiber
• need for a ISDN card or TA

36
Wide Area Point-to-Point Links (cont.)

• Leased links
• Analog
• local (in the same central office), metallic
  (copper)
• 2 /4 wire
• any leased line modem
• longer distance as specified only
• 2/4 wire
• voice-grade and wide-band modems
• Digital
• PCM based digital carriers
• N-ISDN (Circuit mode)

37
Leased links (cont.)

• dark fibre or copper links
• physical wire between two points
• connect your own devices (modems, transcievers,
  )
• digital circuit
• Telekom provides their own modems
• combination voice-band intercity line
• you provide your own voice-band modems
• Telekom provides analog circuit

38
PCM based digital carriers

• Use Pulse Code Modulation
• A/D conversion of human voice
• 8000 samples per second, 8 bits each gt 64 Kbit/s
• Time Division Multiplexing (TDM) used to
  multiplex channels
• Two classes of multiplexing hierarchies
• Old hierarchies (1960s), copper based
• SONET/SDH hierarchies, fiber based

39
Old multiplexing hierarchies

• Called PDH, PCM (also TDM) hierarchies
• Different multiplexing standards in North
  America, Europe and Japan
• Terminology
• DS-n Digital Signaling, n-multiplexing level
• Tn specific type of carrier equipment
• used synonimously
• Traffic must be completely demultiplexed to get
  payload

40
Old multiplexing hierarchies (cont.)
Bit rate
(Kbit/s)
T1 (2481)8000 E1 (302)88000
41
Old multiplexing hierarchies (cont.)

• What is available to customers
• 64 Kbit/s, 2.048 Kbit/s
• fractional E1 rates using flexible multiplexers
• types of E1 links
• framed - 1984 Kbit/s (1 channel used for
  signaling)
• unframed - full 2048 Kbit/s (G.703 interface)
  old type, hard to get in international links
• E2 (8.448 Kbit/s) links - hard to get
• E3 (34.368 Kbit/s) links

42
SONET/SDH hierarchies

• SONET - Synchronous Optical Network, used in
  North America
• SDH - Synchronous Digital Hierarchy,
  international
• Completely synchronous, lower rates are directly
  accessible
• Backward compatible with old hierarchies

43
SONET/SDH hierarchies (cont.)

• Terminology
• STS-n Synchronous Transport Signal, level n,
  electrical
• OC-n Optical Carrier Signal, level n
• STM-n Synchronous Transfer Module, level n
• Base rate
• North America 51.84 Mbit/s - STS-1
• Europe 155.520 Mbit/s - STM-1 STS-3

44
SONET/SDH hierarchies (cont.)
Line rate (Kbit/s) SONET level SDH
level
51.840 OC-1
155.520 OC-3
STM-1 466.560 OC-9
622.080 OC-12
STM-4 933.120
OC-18 1.244.160 OC-24
STM-8 1.866.240
OC-36 STM-12 2.488.320
OC-48 STM-16
45
ISDN

• Integrated Services Digital Network
• Voice, Video, Data
• Narrow-band ISDN
• BRI 16 K D channel 2 x 64 K B channel
• PRI 64 K D channel 30 x 64 K B channel
• D channel is for signaling. X.25 like
• Fast call setup 1-2 seconds

46
ISDN (cont.)

• Many options -gt complex to order/configure
• IOCs (ISDN ordering codes), i.e. Intel Blue
• Bearer services
• Circuit switched voice
• speech mode
• 3.1 kHz voiceband service
• 7 kHz speech (high fidelity)
• Circuit switched data
• Packet switched data (D-channel)
• Permanent (reserved channels)

47
ISDN (cont.)

• Transferring data
• packet mode
• circuit mode
• synchronous
• asynchronous (V.110,V.120)
• Digital modems
• native ISDN
• V.34 over ISDN

48
Point-to-Point protocols

• SLIP (async)
• PPP (sync, async)
• HDLC

49
NBMA Networks (Clouds)

• based on packet switching
• X.25
• ISDN (packet mode)
• Frame Relay
• ATM

50
Clouds (cont.)

• Many things in common
• leased line to packet switch
• user sees a cloud
• any-to-any connectivity
• Permanent and switched virtual circuits

51
X.25

• Two level protocol
• HDLC error and flow control
• Packet level virtual circuits with independent
  flow control
• PVC, SVC
• old and stable protocol

52
Frame Relay

• One level protocol
• HDLC framing provides error detection only, no
  retransmissions
• No explicit flow control
• User may contract for different throughput
  classes (less than line speed)

53
ATM - LAN and WAN in one protocol ?

• Very short packets - cels (53 bytes)
• Every packet has destination address
• Different Application Adaptation Layers
• IP packet mode support
• video or voice circuit support
• SMDS
• LAN emulation

54
IP over clouds (X.25)

• No broadcast support!
• Cloud model
• treats X.25 as one interface
• address resolution by algorithm, table lookup or
  server (ARP like)
• Multiple Point-to-Point links
• each virtual circuit is treated like a
  point-to-point link
• subinterfaces are useful

55
Modems

• What are they
• Dial-up modems
• Leased line modems
• voiceband (voice-grade)
• wideband
• digital subscriber line (xDSL)
• Cable modems
• Interfaces

56
Modems (cont.)

• Enable digital communication over analog lines
• Speeds
• 1850 50 bit/s
• 1930 300 bit/s
• 1980 14.000 bit/s
• 1990 144.000 bit/s
• now 2 - 10 Mbit/s

57
Dial-up modems

• Work over PSTN
• Different standards
• speed V.21 - 300 bit/s, V22 - 1200 bit/s, V.23 -
  1200/75 bit/s, V.22bis - 2.400 bit/s, V.32 - 9600
  bit/s, V.32bis - 14.400 bit/s, V.34 - 28.800
  bit/s, V.34 - 33.600 bit/s
• error correction V.42, MNP4
• compression V.42bis, MNP5
• Flow control hardware!

58
Leased line modems

• Voiceband (voice-grade) modems

59
Leased line modems

• Voiceband (voice-grade) modems
• work in 3.1 kHz voice band (300 - 3400 Hz)
• usually dial-up modems with leased line support
• can be used over analog and digital transmission
  systems

60
Leased line modems (cont.)

• Wideband modems
• work in 60-kHz to 108 kHz group (analog!)
• dying out
• V.35 - 48 Kbit/s
• V.36 - from 48 to 72 Kbit/s
• V.37 - more than 72 Kbit/s
• the term V.35 is now used in digital transmission
  schemes!

61
Leased line modems (cont.)

• xDSL (Digital Subscriber Line) modems
• work over telephone copper pairs (2/4/8 wires)
• you may/may not use POTS over the same wires

xDSL modems conceptual model
62
xDSL modems (cont.)

• What speeds can we expect?
• operation range and speed depends on
• number of wires used
• diameter and quality of wires
• type of modulation, frequency bandwidth used
• firmware quality,

63
xDSL modems (cont.)

• practical limits on data rate in one direction on
  single UTP (24 gauge)

64
xDSL modems (cont.)

• history
• different proprietary technologies for speeds up
  to E1 (2 Mbit/s)
• first E1 modems were based on AMI encoding, using
  1.5 MHz BW, repeaters on 1-2 km
• standardisation is going on
• current products are not interoperable

65
xDSL modems (cont.)

• a lot of technologies and acronyms
• DSL Digital Subscriber Line
• DSL signifies a modem, not the line!
• DSL (without x) is a modem used for Basic Rate
  ISDN
• 160 kbps duplex, 5.5 km, 1 pair of wires
• 0-120kHZ BW gt no POTS at the same time
• ITU I431 (ANSI T1.601) standards
• used also for pair gain applications for POTS

66
xDSL modems (cont.)

• IDSL ISDN DSL
• uses ISDN technology to deliver 128 kbps data
  (ISDN routers with U interface)
• HDSL High data rate DSL
• duplex T1 (2 pairs) or E1 (3 pairs), 3.7-4.5 km
• from 80 to 240 kHz (much better than first modems
  using AMI), no POTS
• SDSL Symetric (Single pair, Single line) DSL
• HDSL over a single twisted pair
• duplex T1 or E1, appr. 3 km, no POTS

67
xDSL modems (cont.)

• UDSL Unidirectional HDSL
• not very exciting, just one proponent!
• ADSL Asymetric DSL
• using simetric signals in many pairs within a
  cable significantly limit the data rate and the
  lenght of line!
• solution asymetric transmition. ADSL uses
• high speed downstrem channel 1.5-6.1 or even 9
  Mbps
• low speed duplex channel 16-640 kbps
• each channel can be submultiplexed to form
  multiple, lower rate channels

68
ADSL (cont.)

• FDM or echo cancellation is used to divide the
  available bandwidth of a telephone line
• POTS support splitter is used to split the lower
  4 kHz
• maximum downstrem speeds (24 gauge UTP)
• T1 5.5 km, E1 4.8 km, DS2 (6.312 Mbps) 3.7 km,
  E2(8.44 Mbps) 2.7 km
• forward error correction (impulse noise)
• to facilitate transmition of digitally compresses
  video
• introduces about 20 msec of delay - bad for data
  applications

69
ADSL (cont.)

• modulation schemes
• CAP Carrierless Amplitude Phase
• simple, cheap, lower performance, not a standard
  
• DMT Discrete Multitone
• complex 256 discrete subchannels, data is
  distributed among them
• ANSI and ETSI standard, outperform CAP on speed,
  distance and resistanceto inteference
• DMT is not yet commercially available
• DWMT Discrete Wavelet Multitone
• step further in performance and complexity
• still under development
• for long-distance transmitions in environments
  with high interference

70
ADSL (cont.)

• ADSL conclusions
• it will be used for many types of applications
  (video, data, ...) with different needs
  (bandwidth, error correction, delay, ...)
  concurently.
• to achieve that goal one need a complex
  technology
• first implementations (will) have limited
  functionality

71
xDSL (cont.)

• RADSL Rate adaptive ADSL
• a version of ADSL modems test the line and
  adjust the speed according to line quality and
  length
• connection speed is determined at startup or by a
  signal from the central office. Constant
  monitoring of the line speed not decided upon
• VDSL Very high data rate DSL
• used to be called ADSL Very high speed ADSL
• first vesion of VDSL will be asymetric
• some providers and suppliers hope for fully
  simetric VDSL

72
VDSL (cont.)

• it is reffered to also as BDSL
• maximum downstrem speeds (24 gauge UTP)
• 12.96 Mbps 1.4 km, 25.82 Mbps 0.9 km, 51.84
  Mbps 0.3 km
• will operate over POTS and ISDN using passive
  splitters
• operators intend to use it to provide three
  circuit switched video channels and a single ATM
  channel

73
Cable modems

• Coax, 10Base-T technology
• Symmetric/Asymmetric
• speeds up to 30 Mbit/s
• standards under development
• HFC (Hybrid Fiber/Coax)
• bus topology, up to 2000 homes
• FTTC (Fiber To The Curb)
• a few dozen homes via copper or coax
• need for two way CATV systems!

74
Interfaces

• used to connect devices (DTE/DCE)
• V series (Data over Telephone Network)
• V.10 unbalanced interchange circuits
• V.11 balanced interchange circuits
  (differential)
• V.24 defines interchange circuits between DTE
  and DCE
• V.28 electrical characteristics of the circuits
• EIA-232 uses V.24, V.28 and ISO 2110 connector

75
Interfaces

• X series (Data Comm. Networks)
• X.26 lt-gt V.10
• X.27 lt-gt V.11
• X.21 X.27 ISO 4903 14 pin connector
• G.703 64 Kbit/s and 2Mbit/s
• Interface converters
• Clocking (DTE/DCE)
• Connectors defined in other standards (ISO, EIA)

76
Routers

• Connecting networks
• Functions
• Packet handling
• Packet forwarding
• Routing information processing
• Management
• Miscellaneous functions

77
Routers (cont.)

• Features
• diversity of ports
• concentration of ports
• switching capacity (pps)
• between different network cards
• impact of access-lists, encryption, compression,
  accounting
• protocols
• supported network protocols
• supported routing protocols

78
Routers (cont.)

• memory
• modularity, hot swappable modules
• fault-tolerant (power supply, CPU,...)
• Code runs from EPROM/FLASH/RAM
• SW upgrade
• ROM/EPROM
• FLASH
• tftp
• disk
• during normal operation

79
Routers (cont.)

• Management, Configuring
• via telnet, rsh
• SNMP
• tftp download and save config.
• Accounting
• traffic on ports
• source/destination pairs
• application (port) level

80
Routers (cont.)

• Security
• access lists
• authentication (users, routing entities)
• confidentiality
• event logging (syslog)
• QoS
• queuing techniques
• resource reservation protocol (RSVP)

81
High speed routing

• five approaches
• multigigabit routers
• peer-to-peer multilayer mapping
• switches map L3 addresses into L2 destination
  addresses (MAC, VCI/VPI)
• set up a virtual paths accross the network
• server based schemes (use of NHRP)
• route server to calculate routes
• inteligent layer 3 forwarding at the edge
• layer 2 switches in the core

82
High speed routing (cont.)

• IP address learning
• host sends ARP, gateway uses proxy ARP
• host send packet to the gateway, which forwards
  it and sends back an ICMP redirect with virtual
  IP address of the target
• limited to ethernets
• Layer 3 switching
• route lookup in hardware
• small routing tables

83
High speed routing (cont.)

• position in the network
• backbone only technologies
• some extend to the desktop
• others are only for LAN/campus environment
• support for different interfaces vary
• protocol support
• some of the implementations are IP only

84
Summary

• We have covered
• Networks
• LAN, MAN, WAN
• Point-to-Point links, Clouds
• Modems
• Interfaces
• Routers

85
Where to get more information

• RFCs, CCITT/ISO standards, other standards
• Books publishers as Addison Wesley, McGraw-Hill
• Magazines Data Communications
• Mailing lists
• Usenet News