Download Name: Leo Mendoza WAN (used to be slow, noisy)

Name: Leo Mendoza
WAN (used to be slow, noisy) - follows mesh topology; station -device that interfaces a user to a network;
subnet - underlying connection of nodes and telecom links;Circuit switched subnet -a subnet in which a dedicated circuit is established
between sender and reciever and all data passes over this circuit (bandwidth reserved, using Synchronous Time Division Multiplexing
[TDM])-example, telephone system (dedicated connection until termination) Packet switched subnet - subnet in which all data messages
are transmitted using fixed-size packages (packets). Datagram, form of packet switched subnet - follows its own path. Virtual circuit
packet - creates logical path throught the subnet, and all packets follow this path. Bandwith not pre-reserved, however (STDM). Broadcast
subnet - typically found in LAN. Workstation transmits data to all other workstations, and only the workstation(s) with the proper address
will accept the data.
Connection-oriented app - both sender and reciever to create a connection before data is transferred (large file transfers, banking and
business). Operate over both circuit switched and packet switched subnets.
Connectionless application - sends data with no connection (E-mail).Operates over both too, but packet switched subnet may be more
efficient.
Routing - each node in WAN is a router. Transmission line should provide the best path to the destination.The subnet is essentially a
weighted network graph. There are costs between nodes (delay, queue size, limiting speed, or $). Flooding (TTL to limit growth).
Centralized - table kept at central node. Used for routing decisions.
Dijkstra least cost routing algorithm determines least cost path between any pair of nodes. Distributed - each node has its own routing
table. Possiblity of inaccurate information. Isolated - each node uses only local info to create its own routing table. (+: routing info doesn't
have to be passed around network; -: inaccurate / dated info) Adaptive vs. Static (static simpler, but doesn't adapt to network congestion or
failures). Network Congestion - prevent w/backup nodes, links, and preallocation of resources. Handle via buffer preallocation, choke
packets, and permit systems.
Leased Data Services: Copper wire: 1 pair, modem 33.6Kbps, ADSL up to 1.544Mbps; 2 Pair, modem 56K, T1 - 1.544Mbps; Coax Cable: 40 Mbps, DS3: ~45 Mbps; Fiber Optics - OC-3: 155 Mbps, OC-12 - 622 Mbps; +: Ease of use and security, performance
(guaranteed bandwidth, minimal delay). Dialup Services - circuit switched data (connection made when cust dials out). +: Flexibility
Packet Data Services (packet-switched data) - customer gets access line to connect them to closest packet switch. +: flexibility (no prereserved bandwidth), cost
IP Address Types: A (0-127), NetID 128, HostID 16,777,216; B (128-191), NetID 16,384, HostID 65,536; C (192-223), NetID 2,097,152
HostID 256; D Multicast Address;
Subnet Masks - 32 bit value; network/subnet bits marked with 1, host bits marked with 0; TCP - transmission control protocol.
TCP – Transmission Control Protocol, at transport layer. Connection created using port numbers. Can multiplex multiple connections
(using ports) over a single IP line. Can ensure the receiver isn’t overrun with data (window field). Allows for sending of high priority data
(Urgent Pointer). IP – Internet protocol at network layer. Prepares packet for tranmission across the Internet. Header encapsulated onto
transport data packet. Datagram may get fragmented into smaller datagrams (Fragment offset, very rare). May also delete datagram (TTL).
ICMP – Internet Control Message Protocol. Used by routers and nodes error reporting for Internet Protocol. Errors inc: invalid IP, invalid
port, exceeded TTL. UDP – user datagram protocol. used in place of TCP. Used in connectionless applications. Much simpler than TCP;
ARP – address resolution protocol, translates IP address into MAC layer address so frame can be delivered to the proper workstation. ARP
table kept locally. ARP broadcasts when necessary to determine address.
IP LAN Env – ea PC has 4-byte IP address 6-byte LAN address. If packet isn’t on final LAN, then dest address identifies next router. If
packet on final lan, then dest address points to dest host (server).
BOOTP (IP address, subnet mask, IP of router, IP of name server) : request/reply model. DHCP – extension of BOOTP. When DHCP
client issues an IP request, DHCP queries static table. If(nf), selects an IP address from an available pool. Address is temporary, default
expiration – 1 hr. NAT – allows router to represent a LAN to the internet as a single IP address. Allows workstation IP addresses to hide
behind the global IP address (+ security) – (10.x.x.x; 172.16-31.x.x; 192.168.x.x). If no match is found in cache, the packet is dropped.
Fixed IP address mappings allow packets to originate from outside.
Phone: Tie line – directly connect PBX switches at 2 customer sites. VPN – monthly rate for calls between 2 locations. Guaranteed service
level.
Private line – fixed cost/mo regardless of usage, best value when lots of calls go between locations, can be imitated by VPN.
Switched service – var cost/mo, may provide special features (ex: 800), lower cost if minimal call traffic. Discounts for large call volumes,
predictable call patterns. Key System Unit (dial 9 to reach outside line).
PBX (Private Branch Exchange) is a true intelligent switching system. 4 digit special prefixes, collects dialed digits and intelligently
decides how to route call for lowest cost. Voice mail, automatic call distribution, voice response unit, permission levels, authentication
codes, data services. DID – direct inward dial trunk. 1 way, CO sends dialed number after call connect. DOD – direct outward dial trunk,
1 way outgoing trunk. PBX repeats dialed number to C.O. Centrex – commercial PBX.
DSL – problems: loop qualification, distance, crosstalk. ADSL (1.5Mbps – 7Mbps Down. 16 Kbps-640Kbps up, 4Khz analog voice).
ADSL lite, no telco visit to home (1.5 down 384 K up). VDSL, needs short copper loop (52 Mb 2 way)
Cable - +: greater bandwidth, readily available; -: coax may need upgrade, cost high, return signals noisy, not very reliable.
Data Over Cable Service Interface (DOCSIS) – cable modem term system, hybrid fiber coax network, cable modem. (27 | 40 M down)
T1 – 1.544, 24; T2 – 6.312, 96; T3 – 44.736, 672; T4 – 274.176, 2016. T1 Channelized: 24 DS0 channels of 64K. Each DS0 can carry any
service. Unchannelized T1: used as single 1.536 data circuit. Bipolar, framed. Extended Superframe (ESF) – F-bit marks 24 frame extended
superframes. Error handling: CRC. Restricted T1 – 1.344 Mbps (24 DS0 @ 56K) Frame Assembler/Disassembler (FRADs) – generate frame
relay headers/trailers and send data frames into the network. Frame Relay: Data only sent over Permanent Virtual Circuits (PVCs). No error
control done by network switches (responsibility of customer). Layer 2 protocol, so any layer 3 protocol (ex: IP) can be carried over a frame
relay network. +: guaranteed throughput and delay, very secure. -: price, inflexibility. Asyncrhonous transfer Mode (ATM): 53-byte cells
connection oriented design, scalable bandwidth hub backplane design, lan/wan convergence, adaptive to traffic, low latency. ATM devices
virtual channels must be set up, transmit in fixed len 53 byte ATM cells, each channel has QoS params. Distinguished: provides tighter
guarantees on QoS params than other services.
Smurfing: program attacks network by exploiting IP broadcast addressing operations.