Chapter 8 - Test 3 Flashcards
What are the four types of WAN services?
- circuit-switched
- dedicated circuit
- packet-switched
- virtual private network.
Describe common carriers.
- private companies such as att, Bell canada, Sprint, and BellSouth that provide communication services to the public
- you do not lease physical cables, lease circuits that provide certain transmission characteristics.
Describe local exchange carriers.
-common carriers that provide local telephone services.
Describe local exchange carriers.
-common carriers that provide local telephone services.
Describe interexchange carriers(IXCs).
-common carriers that provide long-distance services.
What federal government agency regulates data and voice communications in the US?
- Federal Communications Commission.
- Canada: Canadian Radio-Television and Telecommunications Commission(CRTC)
Describe circuit-switched networks.
- Oldest and simplest approach to WAN circuits.
- operate over the public switched telephone network(PSTN)
What architecture do circuit switched services use?
- cloud architecture.
- users lease connection points into the common carrier’s network which is called the clud.
How do circuit-switched services operate?
- person dials telephone number of the destination computer and establishes a temporary circuit between the two computers.
- computers exchange data and then the circuit is disconnected.
What are the two basic types of circuit-switched services?
-POTS and ISDN
Describe POTS.
- Plain old telephone service
- dial up services
- use telephone line and a modem.
- 33 kbps to 56 kbps data rate.
Describe ISDN
- integrated services digital network
- combines voice, video and data over the same digital circuit.
- original= narrowband ISDN.
How does ISDN work?
- telephone lines.
- special equipmetn to connect their computers into PSTN.
- ISDN network terminator that functions like a hub and a NIC(terminal adapter), also called an ISDN modem.
- each computer attached to the NT-1/NT-2 needs a unique service profile identifier (SPID)
How does ISDN work?
- telephone lines.
- special equipmetn to connect their computers into PSTN.
- ISDN network terminator that functions like a hub and a NIC(terminal adapter), also called an ISDN modem.
- each computer attached to the NT-1/NT-2 needs a unique service profile identifier (SPID) to aidentify it.
Describe Basic rate interface(BRI).
-2B+D. provides a communication circuit with two 64 Kbps digitaion transmission channels and one 16 Kbps control signalling channel.
Describe Primary rate interface(PRI).
- 23B+D. offered to commercial customers.
- 23 64-Kbps B channels plus 1 64 Kbps D channe.
- almost same capacity as a T1 circuit (1.544 Mbps).
What are two problems with circuit-switched networks?
- need separate connection for each connection.
- data rates are slow ranging from 56Kbps to 128 Kbps or 1.5Mbps
Describe dedicated-circuits.
- user leases circuits from the common carrier for his or her exclusive use 24 hours per day, 7 days per week.
- also called private line services.
what type of connections are dedicated connections?
- point to point
- from one building in one city to another building.
- carrier installs the circuit connections at the two end points of the circuit and makes the connection between them.
What type of equipment is included in dedicated-circuit networks?
- multiplexers or channel service unit (CSU)
- and/or a data service unit(DSU.
- equivalent of a NIC in a LAN.
how are dedicated circuits billed?
- flat fee per month
- user has unlimited use of the circuit.
What are the three basic dedicated-circuit network architectures?
-ring, star, mesh.
What is a distributed star architecture?
-series of star networks that are connected by a mesh or ring architecture.
Describe a ring architecture.
- connects all computers in a closed loop with each computer linked to the next.
- circuits are full-duplex or half-duplex.
What are disadvantages to the ring architecture?
-messages can take a long time to travel from the sender to the receiver resulting in traffic delayrs
What happens if there is a failure?
-traffic will be routed away from the failed circuit, but it will double the traffic.
Describe the star architecture.
-connects all computers to one central computer that routes messages to the appropriate computer.
Describe the star architecture.
-connects all computers to one central computer that routes messages to the appropriate computer.
What are the advantages of a star topology?
- easy to manage because central computer receives and routes all messages in the network
- faster because any message needs to travel through at most two circuits.
What are disadvantages to the star network?
- susceptible to traffic problems because one computer processs all the messages on the network.
- central computer fails, entire network fails.
What are disadvantages to the star network?
- susceptible to traffic problems because one computer processs all the messages on the network.
- central computer fails, entire network fails.
Describe a dedicated-circuit mesh architecture.
- full-mesh: every computer is connected to every other computer. Extremely high cost.
- partial-mesh: many but not all computers are connected.
What is the advantage of mesh networks?
- combine the performance benefits of both ring and star networks.
- mesh networks provide relatively short routes through the network and provide many possible routes through the network to prevent any one circuit or computer from becoming overloaded.
What is a drawback of mesh networks?
- use decentralized routing so that each computer in the network performs its own routing.
- requires more processing by each computer in the network than in star or ring networks.
- transmission o fnetwork status information wastes network capacity.
What are the two types of dedicated circuit services in use?
- T carrier services
- Synchronous optical network(SONET services.
- each has their own data link protocols.
Describe T-carrier services.
- most commonly used form of dedicated-circuits services in North America today.
- costs are fixed amount per month
Describe a T1 service.
- also called a DS1 circuit.
- data arate of 1.544 Mbps.
- used to transmit both data and voice.
- Inverse TDM provideds 24 64 Kbpos circuits.
- enables 24 simultaneous voice channels.
Describe a T3 circuit.
- transmission rate of 44.736 Mbps.
- equals capacity of 28 T1 circuits.
- popular for corporate MANs and WANs.
Describe Fractional T1
-FT1
-offers portions of a 1.544 Mbps T1 circuit for a fraction of its full cost.
-most common FT1 services provide 128, 256, 384, 512, and 768 Kbps.
DS0=64Kbps.
Describe Fractional T1
-FT1
-offers portions of a 1.544 Mbps T1 circuit for a fraction of its full cost.
-most common FT1 services provide 128, 256, 384, 512, and 768 Kbps.
DS0=64Kbps.
Describe SONET.
- American standard(ANSI) for high-speed dedicated-circuit services.
- OC-1: optical carrier level 1=51.84Mbps.
- OC-3072
- each level above OC-1 created by an inverse multiplexer.
Describe SONET.
- American standard(ANSI) for high-speed dedicated-circuit services.
- OC-1: optical carrier level 1=51.84Mbps.
- OC-3072
- each level above OC-1 created by an inverse multiplexer.
Describe packet-switched networks.
-enable multiple connections to exist simultaneously between computers over the same physical circuit.
How doe packet-switched services work?
- user buys a connection
- pays fixed fee for the connection based on type and capacity and is charged for the number of packets transmitted.
What is a PAD?
- packet assembly/disassembly device.
- user’s connection into the network
- owned and operated by the customer or by the common carrier.
- converts sender’s data into the network layer and data link layer packets used by the packet network and sends them through the packet-switched network.
What are the advantages of packet-switched networks?
- different locations can have different connection speeds into the common carrier cloud.
- PAD compensates for differences in transmission speed between sender and receiver.
- allow packets from separate messages with different destinations to be interleaved for transmission.
What are the advantages of packet-switched networks?
- different locations can have different connection speeds into the common carrier cloud.
- PAD compensates for differences in transmission speed between sender and receiver.
- allow packets from separate messages with different destinations to be interleaved for transmission.
Describe datagram.
- connectionless services
- adds a destination address and sequence number to each packet in addition to information about the data stream to which the packet belongs.
Describe a virtual circuit routing method as it relates to packet-switched circuits.
- packet-switched network establishes what appears to be one ended to end circuit between the sender and receiver.
- all packets for that transmission take the same route over the cirtual circuit that has been set up.
Describe a PVC.
- permanent virtual circuit
- defined for frequent and consistent use by the network.
- do not change unless the network manager changes the network.
Describe a PVC.
- permanent virtual circuit
- defined for frequent and consistent use by the network.
- do not change unless the network manager changes the network.
What’s the difference between PVC’s and dedicated circuits?
-PVC’s are software based instead of hardware circuits.
What are the two types of data rates negotiated in PVCs?
- committed information rate(CIR): data rate the PVC must guarantee to transmit.
- maximum allowable rate(MAR): maixmum rate that the network will attempt to provide over and above the CIR.
What can potentially happen to packets above CIR?
-marked as discard eligible(DE) and can be discarded if network becomes overloaded.
Describe POP
- point of presence
- organizations usually lease a dedicated circuit to a packet-switched network point of presence.
- POP is location at which the packet-switched network or any common carrier network connects into the local telephone exchange.
What are the four types of packet switched services?
-ATM, frame relay IP/MPLS, and ethernet services.
Describe ATM.
- Asynchronous Transfer Mode.
- works similar to ethernet and TCP/IP networks
- uses different layer 2 and layer 3 protocols.
- typically uses SONET at layer 2.
How does ATM work?
-usually performs encapsulation, ethernet frames are surround by an ATM layer-3 packet and a sonet frame.
What is ATM considered?
- unreliable packet service
- no error control in the network
- responsibility is on source and destination.
What else does ATM provide?
- extensive QoS information enables setting very precise priorities.
- scalable: easy to multiplex basic ATM circuits into faster circuits.
Describe Frame relay.
-transmits data slower than ATM, sometimes called “poor man’s ATM”
How does frame relay work?
- performs encapsulation of packets so packets are delivered unchanged through the network
- unreliable packet service.
- checks for errors but discards them. No error control
How does frame relay work?
- performs encapsulation of packets so packets are delivered unchanged through the network
- unreliable packet service.
- checks for errors but discards them. No error control.
Describe ethernet services.
- bypass the PSTN by laying their own gigabit Ethernet fiber-optic networks in large cities.
- committed information rate (CIR) of 1Mbps to 40Gbps. in 1 Mbps increments at a lower cost than traditional packet-switched networks.
Describe MPLS.
- multi protocol lable switching.
- designed to work with a variety of commonly used layer-2 protocols.
- inserts 4-byte header that contains its own information between the layer-2 and layer-3 IP packet.
How does MPLS work?
- customer connects to common carrier’s network.
- carrier’s switch converts incoming layer 2 or 3 address into an MPLS address label.
What is an advantage of MPLS?
- operates faster than traditional routing.
- common carriers in US and canada have diffrenet way of charging for MPLS services, common to use full mesh design.
- fewer hops and less time to reach destination.
What is an advantage of MPLS?
- operates faster than traditional routing.
- common carriers in US and canada have diffrenet way of charging for MPLS services, common to use full mesh design.
- fewer hops and less time to reach destination.
Describe a VPN.
- provides equivalent of a private packet-switched network over the public internet.
- series of PVCs that run over the internet so that the network acts like a set of dedicated circuits over a private packet network.
How do VPNs work?
- lease an internet connection.
- pay common carrier for the circuit and ISP for internet access.
- connect a VPN gateway to each internet access circuit to provide access from your switches to the VPN.
- create PVCs through the internet that are called tunnels.
How do VPNs work?
- lease an internet connection.
- pay common carrier for the circuit and ISP for internet access.
- connect a VPN gateway to each internet access circuit to provide access from your switches to the VPN.
- create PVCs through the internet that are called tunnels.
Describe VPN software.
-used on home computers or laptops to provide the same secure tunnels to people working from offsite.
Describe layer-2 VPNs.
- uses layer-2 packet to select the VPN tunnel and encapsulates the entire packet starting with the layer-2 packet.
- L2TP: layer 2 VPN
Describe layer-3 VPNs.
- uses layer-3 packet(IP to select the VPN tunnel and encapsulates the entire packet starting with the layer-3 packet.
- discards the incoming layer-2 packet and generates an entirely new layer-2 packet at the destination
- IPsec is a layer 3 VPN.
What are the advantages of VPNs?
-low-cost and flexibility.
Describe an extranet VPN?
-VPN connects several different organizations, often customers and suppliers over the internet.
Describe an access VPN.
-enables employees to access an organization’s networks from a remote location.
Describe an access VPN.
-enables employees to access an organization’s networks from a remote location.
Describe an ESP.
- Encapsulating security payload.
- encapsulates ip, tcp and http packet which then is itself encapsulated with another transport and network layer protocols.
Describe an ESP.
- Encapsulating security payload.
- encapsulates ip, tcp and http packet which then is itself encapsulated with another transport and network layer protocols.
Describe latency.
-speed of a device to convert input packets to output packets.
