1. Networking and Telecommunications
8. WAN Notes
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2. Wan Info Wan - wide area network Why? lans --> wan
Rutgers examples (buildings on campus, backbones, intercampus, internet)
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4. 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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5. Every Machine Uniquely identified by:
Name (fully qualified domain name) clam.rutgers.edu
Ethernet address (mac address) 08:00:20:73:75:5a
48bits
12 hex digits
burnt into nic
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6. 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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7. Hardware transmission media fiber coax Leased lines: 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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8. 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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10. Big 4 Repeaters, Bridges, Switches and Routers Intelligence  
cost increases  
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11. Repeater Don’t 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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13. Bridge Read ethernet/mac address of EVERY packet (not ip address)
Keep local traffic local
3 cases
Forward packet
Don’t forward
Not sure
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14. 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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16. 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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17. 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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19. 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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22. Switch – Campus Backbone
Blue – Buildings with Routers
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Red - Switches

23. 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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24. 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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25. 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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26. 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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27. 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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28. NTP - network time protocol
Keeps time in sync worldwide
Used on pc, sun and mac clients so that time doesn’t drift locally
Important for networks
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29. 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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30. 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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31. 3. Now, what about the destination ip address
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 , 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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32. 4. What about the destination ethernet address
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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33. 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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34. 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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35. 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 it’s 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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36. 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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37. 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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40. 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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41. Satellite 22,300 miles above earh (geosynchronous orbit)
Propagation delay
90Mbps trasmission speed, expensive, security issues
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42. 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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43. THE END
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