Networking and Telecommunications

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Networking and Telecommunications

• 8. WAN Notes

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Wan Info

• Wan - wide area network
• Why? lans --gt wan
• Rutgers examples (buildings on campus, backbones,
  intercampus, internet)

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Terms

• Routing
• routing table
• ip address(32 bit)
• Mac address
• ethernet address(48 bit)

• broadcast
• load balancing
• encapsulation/de-encapsulation
• TCP/IP
• Internet

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Every Machine Uniquely identified by

• Name (fully qualified domain name)
  clam.rutgers.edu
• Ethernet address (mac address) 08002073755a
• 48bits
• 12 hex digits
• burnt into nic

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Identity!

• ip address (using tcp/ip)165.230.99.70
• 32 bits
• 4 parts (8 bits each part, 0-255)
• Decimal
• (note - ip address encapsulated within data part
  of ethernet packet)
• Configurable by system admin.

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Hardware

• transmission media
• fiber
• coax
• TP
• satellites
• microwave

• Leased lines
  
• T1 (1.544 Mbps)
• T3 (44.5 Mbps)
• 56k
• OC3 (155Mbps) OC12 (622 Mbps)
• OC192 (10 gig)
• Fractional T1
• Private Lines
• Terminal servers, mux

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More Keys

• DSL - Digital Subscriber Lines
• dedicated links. 500 meg to 9 gig or more.
• Must be close (2-3 miles) of CO
• Cable Modems - shared medium (shared bandwitch).
  CATV.
• security concerns.

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Big 4

• Repeaters, Bridges, Switches and Routers
• Intelligence ? ?
• cost increases? ? ?

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Repeater

• Dont read addresses on packet
• Boost signals
• Extend length of lan
• Often Same network/lan (subnet)
• Physical layer of OSI model (lowest)

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Bridge

• Read ethernet/mac address of EVERY packet (not ip
  address)
• Keep local traffic local
• 3 cases
• Forward packet
• Dont forward
• Not sure

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Bridge Part 2

• Splits lan into multiple segments (divide
  overburdened lan)
• Learning bridges
• Internal tables
• Data Link layer of OSI model
• Must be correctly positioned in network layout.

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Router/Gateway

• Look (read) only at packets addressed to it
• Ethernet address AND ip addresses
• Multi-protocol
• Routes based on ip address
• Multiple subnets (Multiple nics)

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Router/Gateway Continued

• Major vendors are
• Cisco
• 3com
• Bay Networks
• Pick BEST path to route packets (using routing
  tables and load balancing)
• Often used to connect buildings to backbone, and
  to internet (example rutgers)
• Upper layer of OSI model
• Routing based on ip address (and ethernet
  address)

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Switch

• Dedicated pipes
• Not shared (compared to hubs which are a shared
  medium)
• Looks at every packets, and reads MAC address
  (ethernet address)
• Can be used in a wan (ie. campus backbone) as
  well as a lan (star topology)
• Vlans - virtual lans (can be setup via switches)

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Switch Campus Backbone
Blue Buildings with Routers
Red - Switches
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Routing Protocols

• ICMP - Internet Control Message Protocol messages
  between routers
• dynamic updates.
• RIP - Routing Info Protocol
• Protocol ( hops - best path)
• lots of broadcasts on network - drawback, older
  method
• OSPF - Open Shortest Path First ( best path
  chosen from of hops and other criteria (delay,
  thru put, etc..)
• less traffic, popular today

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Other Key Concepts

• ARP - address resolution protocol
• have ip address needs ethernet address (send arp
  broadcast to all nodes on lan)
• RARP - reverse arp
• have ethernet address and need ip address.
• used by systems booting up, to obtain their own
  ip address
• rarp servers exists

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• DNS - Domain Name Service, translate names to ip
  numbers (and reverse)
• world wide set of dns services (normally unix
  machines)
• tree hierarchy
• .Edu
• .Com
• .org
• .Fr
• .De

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P

• BOOTP - when client boots up, only knows its own
  ethernet address
• May make bootp request (packet) over network
  looking for bootp server
• Bootp server has table of ethernet address, ip
  address, names, and other info
• Responds to client
• Each client has a fixed ip address per ethernet
  address, one to one correspondence
• Bootp servers are usually unix boxes

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More Concepts.

• DHCP - Dynamic Host Configuration Protocol.
• Similar to bootp, but the assigned ip addresses
  can be dynamic (changing).
• Taken from a pool of ip address....leases.
• More popular then bootp today
• DHCP servers are usually windows servers or unix.

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• NTP - network time protocol
• Keeps time in sync worldwide
• Used on pc, sun and mac clients so that time
  doesnt drift locally
• Important for networks

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Examples of Routing Packets

• Assume an ethernet network at the lowest level,
  and a tcp/ip protocol
• For any packet to be routed from Point A to Point
  B, the packets needs the following addresses
  filled in
• 1. source ethernet address
• 2. destination ethernet address
• 3. source tcp/ip address
• 4. destination tcp/ip address

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Case A

• Sending a packet between Point A and Point B and
  both systems happen to be on the same lan
  (subnet)
• 1. A system always knows its source ethernet
  address.
• Why? Its burnt in...hard coded in NIC
• 2. How does a system find its source ip address?
• hard coded in a table on the system (like
  /etc/hosts in unix)
• using bootp (from a bootp server) or dhcp (dhcp
  server)
• rarp request (given ethernet address, find ip
  address.
• RARP - Reverse Address Resolution Protocol

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• 3. Now, what about the destination ip address?
  When a user on system A runs an application to
  send a packet to system B (like email, or ftp, or
  telnet, or www), the user normally specifies the
  ip address of the destination system (thus it
  would be given) or the name of the destination
  system. If the name is supplied, a DNS server is
  contacted (Domain Name Service) whose job is to
  convert a system name to an ip number.

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• 4. What about the destination ethernet
  address? Either the sending system has the
  ethernet address of all systems on the lan stored
  in a table (like /etc/ethers in unix), or its
  loaded in cache memory, or an ARP (address
  resolution protocol). ARP is a broadcast on the
  local net, to request an ethernet address from
  the given ip address (the system with the
  matching ip address should respond).
• All this information is then filled in the
  packet, and the packet is then sent. Done.

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Case B

• Passing a packet from System A to another
  system (system B), which is on another side of a
  gateway (another lan).(could be several
  lans/gateways away...maybe far away on the
  internet).
• 1. and 2. The source ethernet address and ip
  address are obtained as above.
• 3. The destination ip address is obtained as
  above also.

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• 4. The destination ethernet address is found in
  a different manner, since the destination machine
  in not on the same subnet (lan). (A machine can
  tell the packet is going to a different subnet by
  looking at the destination ip address). Because
  of this ARP cant be used (ARP broadcasts are
  limited to a given subnet)....

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• Instead of trying to discover the
  destination ethernet address, of system b, the
  packet is sent on the network with the
  destination ethernet address of the
  gateway/router...and its the routers
  responsibility to pass on the packet. That is
  why the router only reads packets addressed to
  it. When the gateway/router receives the
  packet, it will take off its ethernet
  address.....then look inside the packet at the
  destination ip address and decide whether the
  packet goes to some local subnet or to another
  gateway/router.

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• If to another gateway/router, the routing
  tables are searched and the ethernet address of
  the next gateway is put onto the packet. If the
  packet goes to a local subnet, the gateway just
  addresses that packet to the correct system (a
  gateway/router should know the ethernet address
  of all nearby systems on all connected subnets).

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Long Distance WAN/Campus Backbones

• X.25 - old standard for packet switching network
• Gigabit Ethernet
• ATM (Asynchronous Transfer Mode)
• Fast, good for voice, data, video, speeds of 155
  and 600 Mbps
• Scalability, within lan, interconnect lans,
  campus backbone, and WAN (still expensive at lan
  level, used mostly in wan)

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Other Wan Interesting Facts

• Underwater Cables
• 1956 1st underwater cable between Europe and US.
  Handled 36 simult. Phone calls
• 1988 1st fiber underwater cable. 40,000
  simultaneous calls
• Today over 2.4 million calls per cable
• Microwave Towers
• Line of Sight, 20 to 30 miles between
• Can be interfered with bad weather

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• Satellite
• 22,300 miles above earh (geosynchronous orbit)
• Propagation delay
• 90Mbps trasmission speed, expensive, security
  issues

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Baseband vs. Broadband

• Baseband Network digital. Single signal.
• Most Lans are baseband
• Broadband Network analog. Multiple
  signals/channels. Normally Coax. Like CATV
  (Cable TV).
• Note Broadband has another definition. Any
  high speed circuit faster then a normal modem
  (56k). Like DSL or CATV.

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• THE END