Networking and Telecommunications

1. Networking and Telecommunications 8. WAN Notes

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

4. Terms • Routing • routing table • ip address(32 bit) • Mac address • ethernet address(48 bit) • broadcast • load balancing • encapsulation/de-encapsulation • TCP/IP • Internet

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

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.

7. 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

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.

10. Big 4 • Repeaters, Bridges, Switches and Routers • Intelligence   • cost increases  

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)

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

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.

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)

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)

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)

22. Switch – Campus Backbone Blue – Buildings with Routers 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

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

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

26. 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 P

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.

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

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

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

31. 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.

32. 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.

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.

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)....

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.

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).

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)

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

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

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.

43. THE END