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33 Cards in this Set
- Front
- Back
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Channelized T1
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A channelized T1 is a voice circuit that has 24 voice channels. Each channel contains its own signaling information, which is inserted into the data stream of the digitized voice.
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PRI
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A Primary Rate Interface is a voice circuit that has 24 channels, one of which is dedicated to signaling. Thus, the number of available voice channels is 23. The voice channels are called bearer channels,and the signaling channel is called the data channel. This type of signaling is called out-of-band signaling.
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Clear-channel T1
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A clear-channel T1 is one that is not framed in any way. There are no channels, and no organization of the bits flowing through the link. Clear-channel T1s are actually a rarity, as most data links are provisioned with ESF framing.
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AMI
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AMI is a method of encoding that inverts alternate marks. In T1 signaling, there are two possible states: mark and space. Simply put, a mark is a one, and a space is a zero. On a T1, a space is 0V, and a mark is either +5V or -5V. AMI encodes the signal such that the polarity of each mark is the opposite of the one preceding it. The risk of an all zeros signal exists, so AMI sets every eighth bit to a 1
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B8ZS
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B8ZS encoding was introduced to resolve the shortcomings of AMI. The idea behind B8ZS is that if eight zeros in a row are detected in a signal, those eight zeros are converted to a pattern including intentional BPVs. When the remote side sees this well-known pattern, it converts it back to all zeros.
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Phone audio sample rate?
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Phone audio is sampled 8,000 times per second (i.e., at 8 kHz). Each sample is converted to an 8-bit value, with one of the bits used for signaling.
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NTF
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Telecom engineers look for trouble in a line when they troubleshoot. This may sound pedantic, but when you listen to telecom engineers troubleshooting, they will use very specific terms like no trouble found (which is often abbreviated as NTF). Remember, there are more than 100 years of standards at work here.
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Frame Relay
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Frame-relay links are more flexible than point-to-point links because multiple links can be terminated at a single interface in a router. This leads to design possibilities allowing connectivity to multiple sites at a significant cost savings over point-to-point circuits.
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ACL / ACE
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The technical name for an access list is access-control list, or ACL. The individual entries in an access-control list are called access-control entries, or ACEs. The term access-control list isn't often used in practice; you'll typically hear these lists referred to simply as access lists or ACLs.
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Reflective ACL
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Reflexive access lists, covered later in this chapter, are applied in both directions.
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VLAN maps
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VLAN maps are similar in design to route maps. VLAN maps are assigned to VLANs, and can be configured to pass or drop packets based on a number of tests. VLAN maps control all traffic routed into, out of, or within a VLAN. VLAN maps have no direction.
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Port ACLs
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Port ACLs are applied to layer-2 interfaces on the switch. They cannot be applied to EtherChannels, SVIs, or any other virtual interfaces. Port ACLs can be applied to trunk interfaces, in which case they will filter every VLAN in the trunk. Standard IP, extended IP, or MAC ACLs can be assigned as port ACLs. Port ACLs can be applied only in the inbound direction.
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Router ACLs
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Router ACLs are applied to layer-3 interfaces on the switch. SVIs, layer-3 physical interfaces (configured with no switchport, for example), and layer-3 EtherChannels can have router ACLs applied to them. Standard IP and extended IP ACLs can be assigned as router ACLs, while MAC ACLs cannot. Router ACLs can be applied in both inbound and outbound directions.
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How to configure ACL to an interface?
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3750(config)#int g0/20
3750(config)# switchport 3750(config-if)# ip access-group 101 in |
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Port ACL vs. Router ACL vs. VLAN MAps
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A port ACL only filters inbound packets on a single interface, and a router ACL only filters packets as they travel into or out of a layer-3 interface. A VLAN map, on the other hand, filters every packet within a VLAN, regardless of the port type involved. For example, if you created a filter that prevented MAC address 1111.1111.1111 from talking to 2222.2222.2222, and applied it to an interface, moving the device to another interface would bypass the filter. But with a VLAN map, the filter would be applied no matter what interface was involved (assuming it was in the configured VLAN).
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Security is a _____ between ___ and ____ .
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Security is a balance between convenience and paranoia.
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Everything that's not yours...
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Everything that's not yours belongs outside the firewall
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Pain with One-time password key fobs
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"We don't want that—the key fobs are a pain, and it takes too long to log in."
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Pain with VPN
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"We like the idea, but can you make it so we don't have to enter any passwords?"
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Putting the email server inside the firewall
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"Will we have to enter more than one password? Because if we do, forget it."
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Pain with Password rotation
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"No way—we don't want to ever have to change our passwords!"
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sticky connection
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a user who connects more than once may need to connect to the same real server. load balancing
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Marking QoS
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Marking refers to deciding what priority a packet should be and labeling it accordingly
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Policing QoS
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Policing refers to the actions the router takes based on how the packets are marked.
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Weighted fair queuing (WFQ)
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Weighted fair queuing is the default queuing mechanism on 2 Mbps and slower serial links. For most implementations, the default configuration works fine. WFQ can be configured very specifically, but it usually isn't configured at all. When VoIP is involved, low-latency queuing is typically used in place of WFQ.
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Class-based weighted fair queuing (CBWFQ)
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Class-based weighted fair queuing allows you to configure classes of traffic and assign them to priorities and queues. CBWFQ is the basis for low-latency queuing.
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Priority queuing
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Priority queuing works just how it sounds: queues are created, and each class of packet is assigned to an appropriate queue based on priorities you design.
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Custom queuing
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Custom queuing is one of those features that you probably won't see much. You'll see it on Cisco exams, and you may see it on networks that had specific problems to be solved where voice was not a concern at the time of the resolution. That's not to say that custom queuing is not suitable for voice, but again, low-latency queuing is the QoS method of choice for voice-enabled networks.
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Low-latency queuing (LLQ)
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Low-latency queuing is class-based weighted fair queuing with a strict priority queue. A strict priority queue is one in which hardware is used to send packets that need to be sent with the lowest latency possible. This is especially useful for voice and video, where any latency or delay causes problems. LLQ is the preferred method of QoS for voice networks, and is the QoS method I focus on in this book.
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Traffic shaping
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Traffic shaping is slightly different from queuing. Traffic shaping monitors traffic, and, when it reaches a threshold, instead of discarding packets, keeps them until a point where bandwidth has lowered and they can be sent. The benefits are a smoother use of bandwidth (Figure 29-7) and the fact that packets are buffered and not just dropped. The downside is that traffic shaping requires memory to function because it buffers packets. Also, if the configured buffer overflows, packets will be discarded.
Traffic shaping is not really suitable for voice, as voice packets must be delivered in order and with low latency. Queuing of packets for transmission at a later time is not a viable solution for VoIP protocols. Traffic shaping can be used on data networks where TCP can assemble packets received out of order. However, in today's converged networks, traffic shaping is not often used. |
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txload 42/255, rxload 249/255
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Looking at these numbers, you can see that the transmit load (txload) is only 42 out of 255, but the receive load (rxload) is 249 out of 255. If you use some simple math (249/255 * 100), you can see that the link is 97.65 percent utilized.
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T1 Duplux? Kbps?
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T1s, like most telecom links, are full duplex. They are rated at 1.54 Mbps, and can transmit this speed in both directions simultaneously.
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how to keep Qos from dropping packets while keeping links efficient?
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Try to keep the priority queue near the level of the expected traffic peaks.
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