Test on Aaron's Worthless Words

IIUC Update - Passed!

Wed, 09 Feb 2011 00:00:00 +0000

I passed the IIUC yesterday, so now I’m a CCNA Voice. It’s kind of belittling to get a CCNA-level certification at this point in my career, but I didn’t want to be completely left behind, so I figured I should move into some voice stuff before I’m left in the dust.

The exam was probably the best Cisco exam I’ve ever taken. Of all the exams I’ve taken in the last few years, this is the only one that didn’t have questions with huge misspellings or grammatical errors. I was really taken aback at that since a good portion of the questions from some of my recent CCNP exams were plain unreadable. I think I remember leaving a comment on one IIUC question about the word “an” being left out of a description, but that was no big deal. I’m not that obesessive-compulsive.

CME Exercise #1

Thu, 07 Oct 2010 00:00:00 +0000

I tried something like this earlier this year with STP. It got rave reviews (from my mother), so I figured I try it again.

Below is a list of requirements for configuring a router as a call processor. In a lab or in your head, configure the router to support the features as listed. This isn’t a contest or anything like that. If you get it right, a virtual thumbs up is all I can afford to give you. There are some licensing issues for running this stuff in GNS3/dynamips, so I can’t help you out on that. I’ll just hint that GNS3 and dynamips will bind to real networks and that copies of a compatible IP softphone are available.

IIUC Notes - Voice Ports and Dial Peers

Mon, 04 Oct 2010 00:00:00 +0000

More of my IIUC study notes. As always, feel free to correct. I really need to have a real post, don’t I?

show voice port summary

Shows the voice ports available for use

R1#show voice port summary
                                          IN       OUT
PORT           CH   SIG-TYPE   ADMIN OPER STATUS   STATUS   EC
============== == ============ ===== ==== ======== ======== ==
50/0/1         1      efxs     up    up   on-hook  idle     y
50/0/1         2      efxs     up    up   on-hook  idle     y
50/0/2         1      efxs     up    up   on-hook  idle     y
50/0/2         2      efxs     up    up   on-hook  idle     y
50/0/3         1      efxs     up    up   on-hook  idle     y
50/0/4         1      efxs     up    up   on-hook  idle     y
50/0/5         1      efxs     up    up   on-hook  idle     y

An ephone-dn shows up as efxs, so all these are ephone-dns.
Channels are numbered 0-23; timeslots are numbered 1-24

FXS Ports

IIUC Notes - More Phone Features

Sat, 02 Oct 2010 00:00:00 +0000

Here are some more notes from my IIUC studies. As always, corrections requested.

Paging

Broadcasts messages to a group for a one-way communication
Paging groups are used to limit which phones get the broadcast
Paging can be unicast or multicast
- Unicast groups limited to 10 members
- Multicast requires mcast support on the network
Paging configurations can be unicast, multicast, or multiple-group

! Unicast Paging
! When 1044 is dialed, ephone 1 is paged
R1(config)#ephone-dn 44
R1(config-ephone-dn)#number 1044
R1(config-ephone-dn)#paging
R1(config-ephone-dn)#exit
R1(config)#ephone 1
R1(config-ephone)#paging-dn 44

IIUC Notes - Phone Features

Fri, 01 Oct 2010 00:00:00 +0000

Here are some more notes from my IIUC studies. As always, corrections requested.

Local Directory

Allows users to look up names
Allows names to show up when dialing or receiving a call
Most phones have a directory button; some have a menu options for the directory

R1(config)#ephone-dn 1
R1(config-ephone-dn)#name Roger Smith

Directory entries can be added manually

R1(config-telephony)#directory entry 1 1700 Corporate Fax
R1(config-telephony)#directory entry 2 1701 HR Fax

By default, sorting is done alphabetically by first name.
Sorting can be changed

R1(config-telephony)#directory last-name-first

IIUC Notes - Getting Phones on the LAN

Thu, 30 Sep 2010 00:00:00 +0000

More study notes. Correct if wrong, though I hope I get some of it right since I already since I’m an R&S guy. :$

**Switchport Configuration
**

switchport mode access: This config makes the port an access port that carries the primary and voice VLAN traffic
switchport mode trunk: This config akes the port a trunk unconditionally, but it will still send DTP messages
switchport nonegotiate: This config keeps the port from sending DTP messages.
switchport mode dynamic auto: If the port receives DTP messages, it will become a trunk. If not, it will be an access port.
switchport mode dynamic desirable: The port actively sends DTP messages trying to become a trunk. This is the default configuration on a Cisco switch.

Cisco IP Phone Boot Process

IIUC Notes - Assigning Ephone-dns to Ephone Buttons

Thu, 23 Sep 2010 00:00:00 +0000

These are some of my notes on my IIUC studies. Since I am a novice as voice stuff, please let me know what I get wrong.

An ephone is a representation of a phone. It’s basically a structure of features that a phone will have.

Configuration in CME:

R1(config)#ephone 34 <– This is just a tag and has nothing to do with an extension or phone
R1(config-ephone)#mac-address 1111.2222.3333 <– Assigns this ephone to the phone with that MAC address

IIUC Notes - Powering Cisco Phones

Tue, 21 Sep 2010 00:00:00 +0000

Feel free to correct anything that is wrong or incomplete.

Power over Ethernet (PoE)
- Can provide power to a Cisco phone, access point, security camera, etc., through the network cabling, eliminating the need to plug the phone into the wall for power.
- Generic term for providing power on the Ethernet cable
- Provides centralized power that can be put on a UPS
- Allows devices to be located away from power outlets
- Removes cabling clutter at the user’s desk
- Can be provided through PoE-enabled switches, power panels or inline couplers (power injectors)
- Oversubscription is common
  - If every device on a switch asks for full power, the switch may not be able to handle the load.
- Of course, devices can be powered with a power brick at the desk
802.3af

IIUC Notes - VoIP Structures

Tue, 21 Sep 2010 00:00:00 +0000

Feel free to correct. No need to sugar-coat it; I’m pretty new at this stuff. :)

Advantages of VoIP
- Reduces costs of communications: Eliminates/reduces long distance and international call tolls
- Reduces costs of cabling: No need for second network of phone lines
- Integrates all voice into one large network: All your remote offices can be implemented/maintained/controlled centrally
- Provides mobility: Moves, adds, and changes (MACs) are (nearly) eliminated since your phone is just a network node
- Allows use of IP Softphones
- Unifies emails, voice mails, and faxes: All these can be treated as a single box for user messages
- Increases productivity: Ringing multiple devices at the same time eliminates phone tag. <— pushing it, eh?
- Enhances communications: Applications can be launched/updated from a voice call through application servers
- Provides open, compatible standards: You can connect different vendor devices into the same VoIP network. <— I’ve never seen that happen
Cisco VoIP Structure

IIUC Notes - Old School Voice Stuff

Wed, 08 Sep 2010 00:00:00 +0000

These are the notes I’ve taken as I read through the study materials. Feel free to correct anything you see.

Analog phone signaling
- Misc
  - Ground = positive = tip
  - Battery = negative = ring
  - Signaling uses specific frequencies for specific events
- Loop start signaling
  - When a circuit in the phone is completed (i.e., you take it off-hook), the CO detects it and provides services.
  - Susceptible to glare, where the phone requests dialtone at the same time that the CO sends a call.
    - Can connect two different calls if in a business with multiple lines
- Ground start signaling
  - The circuit is temporarily completed to signal the CO for services
  - Doesn’t connect any call to any phone directly
  - Used in PBXes.
- Supervisory signaling
  - On-hook: Circuit is open
  - Off-hook: Circuit is completed
  - Ringing: AC current generated by CO to tell the phone to ring
- Informational signaling
  - Gives information for the caller to use
  - Dial tone
  - Busy
  - Ringback: the ring you hear when you call
  - Confirmation: the call is being attempted
  - Congestion: no lines available to make the call
  - Receiver off-hook
  - Reorder: can’t make the call
  - No such number: can’t find the endpoint
- Address signaling
  - Used to send digits
  - Dual-tone multifrequency (DTMF): uses two electrical signals to indicate a digit; touch tone
  - Pulse: flashes the circuit to indicate a digit; rotary dial
- Disadvantages of analog signaling
  - Attenuation
  - Repeaters can’t differentiate between call and noise
  - One cable pair for each call; think about a pair for each call taking place in Manhattan right now
Digitizing voice

Some Cisco Testing Advice

Sat, 24 Jul 2010 00:00:00 +0000

If you follow the blog, you know I’ve had quite an adventure getting my CCNP. Finally, this past Monday, after what seemed liked years of struggling, I finished up my ROUTE test and got the email telling me I’d made it. I’ve learned a lot over the course, but, more than the technical details, I learned more about how to prepare for the exams. It’s too bad I hit the moment of enlightenment after I reached the end of the line. Well, at least this line; there will be others very soon.

ROUTE Notes - Further IGP Redistribution

Sun, 18 Jul 2010 00:00:00 +0000

As always, corrections are requested.

Study Questions

I’ve got IGRP and EIGRP both configured with the same AS number. What’s special about this configuration?

If both use the same AS number, then they automatically redistribute their routes into each other without using the redistribute command.

When redistributing one IGP into another, where’s a good place to filter routes?

There’s no one good place, but at the router(s) that’s doing the redistribution is a good start. There’s no need to send an IGP a bunch of routes it doesn’t need.

ROUTE Notes - Even More IGP Redistribution

Sat, 17 Jul 2010 00:00:00 +0000

I didn’t do so well on IGP redistribution the last time out, so here’s some more stuff to study. As always, feel free to correct.

Study Questions

What three things are needed to be able to redistribute one routing protocol into another?

1. One or more links into each routing protocol 2. A proper, working config for each protocol 3. The addition of the redistribute command to one or more of the protocols

ROUTE - Epic Fail (#1?)

Thu, 08 Jul 2010 00:00:00 +0000

I took the ROUTE test today and failed like I usually do. That makes me 3-4 on these P-level tests if you’re scoring at home. Don’t worry, though. I’m not giving up. :)

In atypical fashion, I must say that the ROUTE test was a good test. Let me say that again. The ROUTE test was a good test. I said good, though…not great. There were a few problems with it that I’ll get to, but, overall, this is the best test I’ve ever taken for a Cisco cert. The questions were very well-written and there were no obvious omissions or wrong details. I failed this test because I simply didn’t put in enough work.

ROUTE Notes - EIGRP Neighbor Relationships

Thu, 17 Jun 2010 00:00:00 +0000

Or neighborships, as they call it in the book. What a terrible word.

Study Questions

What settings must match between two routers in order to become EIGRP neighbors?

Both routers must be in the same primary subnet Both routers must be configured to use the same k-values Both routers must in the same AS Both routers must have the same authentication configuration (within reason) The interfaces facing each other must not be passive

Stubby Post - show ip protocols

Thu, 10 Jun 2010 00:00:00 +0000

I’ve seen and used the command before, but I’ve never really seen any use of the show ip protocols command until tonight while reading up for my ROUTE test. There’s a lot of good information in the output, and, from the way the book is reading, this is a great candidate for use in a lab question.

To check it out a bit, I set up a small network with four routers connected only to a single Ethernet segment. I set up one router to run EIGRP, OSPF, and BGP to each one of the other routers just so I could see the output for the different routing protocols. Here’s what puked out after struggling with GNS for a few minutes.

SWITCH - Epic Fail

Thu, 06 May 2010 00:00:00 +0000

I did my standard 2ish-hour drive to the closest testing center today to take the SWTCH test (642-813). Utter failure. That’s 3 for those scoring at home.

The test was the absolute worst I’ve ever taken. I know that I complain a lot, but this is totally justified in my eyes. My 4th grade spelling tests were better than this. I’ve seen kindergarten plays with better production value.

First of all, it was poorly written. Whoever wrote those questions has a few pieces of information about English sentence structure missing from their skill set. A sentence needs a verb, right? Well, a lot of the sentences were missing those. It’s kind of important to know what the whole point of the sentence is, or is that too much to ask? The “drag this over here” exercise questions all started with the same 13-word phrase that left the question so long that it was unreadable. A couple of commas would have been nice in some. Others I just had to infer from the answers what they were trying to ask.

ONT - Epic Fail Part 2

Fri, 19 Mar 2010 00:00:00 +0000

I took the ONT again today. The stench of failure is upon me for a second time, and I’m beginning to think I’m not the god-like person that everyone thinks I am. I went into the test very confidently. I did extra time on my weak points from the last attempt and knew it inside and out. I put hours and hours of lab time in and got other books and online materials involved. I was absolutely convinced that I would blow this thing away, but, alas, it was not to be.

ONT - Epic Fail

Tue, 16 Feb 2010 00:00:00 +0000

I failed the ONT test today. It was an utter lack of subject matter knowledge that did me in from the beginning. When the first three questions mention things that I’ve never even heard, it’s going to be a long test. I’ll take blame on it for sure, but the test was a lot darker than I imagined it would be.

I heard from a couple people that the ONT test was the easiest of the 4 CCNP test. I must say today’s test was a LOT harder than the ISCW test I took back in December. Most of the questions were fair, but there were a few that were down-right evil or unanswerable. Without giving too much away, there were some matching questions that had multiple items with multiple answers, rendering the answer to a guess. I even ran into a CLI question about the WLC, which surely wasn’t mentioned anywhere I studied, and I don’t have a spare sitting around on which to test. The icing, though, was the number of questions about FRTS; I know I need to understand it, but the magical question dice landed on that topic way too many times in my opinion.

ONT Notes - WLAN Management

Sat, 13 Feb 2010 00:00:00 +0000

Elements of Cisco Unified Wireless Network

Client devices - Cisco compatible extensions on WLAN clients
Mobility platform - allows configuration of LWAPs through WLCs
Network unification - integration into the rest of the network with WLCs doing RF management, IPS, etc.
World-class network management - centralized management through WCS
Unified advanced services - supports advanced technologies and threat detection

WLAN Implementation

Autonomous and LWAP

Category	Autonomous	LWAP
Access Point	Autonomous APs	LWAPs
Control	Individual configurations	Configuration through WLCs
Dependency	Independent operations	Dependent on WLC
Management	CiscoWorks WLSE and WDS	WCS
Redundancy	Through APs	Through WLCs

Wireless LAN Services Engine (WLSE)

ONT Notes - 802.1x and Encryption on LWAPs

Fri, 12 Feb 2010 00:00:00 +0000

Traditional WLAN weaknesses
- SSID for security
- Vulnerable to rogue APs
- MAC filtering for security
- WEP
WEP weaknesses
- Disribution of static keys is not scalable
- WEP keys can be cracked easily
- Vulnerable to dictionary attacks
- No protection against rogue APs
Benefits of 802.1x
- Centralized authentication through Radius via AAA
- Mutual authentication between client and auth server
- Can use multiple encryption algorithms (AES, WPA, TKIP, WEP)
- Automatic dynamic WEP keys
- Roaming
Requirements of 802.1x
- EAP-capable client (supplicant)
- 802.1x-capable AP (authenticator)
- EAP-capable auth server

Table 1. Characteristics of the EAP variants

ONT Notes - QoS On Wireless Networks

Thu, 11 Feb 2010 00:00:00 +0000

Wireless LANs (WLANs)
- Extensions to wired LANs
- Carrier sense multiple access collision avoidance (CSMA/CA) as media access method
- Uses distributed coordinated function (DCF) for collision avoidance
- DCF is based on RF carrier sense, inter-frame spacing (IFS), and random wait timers
Wifi QoS standards
- 802.11e
  - IEEE standard
  - 0-7 priority levels
- Wifi Multimedia (WMM)
  - Four access categories
    - Platinum (voice) - 6 or 7 802.11e
    - Gold (video) - 4 or 5 802.11e
    - Silver (BE) - 0 or 3 802.11e
    - Bronze (Background) - 1 or 2 802.11e
- WMM and 802.11e replace DCF with EDCF
Cisco Split-MAC
- Splits functions between Lightweight access points (LWAPs) and WLAN controllers (WLCs)
- LWAPs handle real-time functions
  - Beacon generation
  - Probe transmission and response
  - Power management
  - 802.11e/WMM scheduling and queuing
  - Packet buffering
  - Encryption/decryption
  - Control frame/message processing
- WLCs handle non-real-time functions
  - Association/disassociation/reassociation
  - 802.11e/WMM resource reservation
  - 802.1x EAP
  - Key management
  - Authentication
  - Fragmentation
  - Ethernet-WLAN bridging
End-to-end QoS
- Step 1: WLC copies DSCP from switch to outer DSCP and outer 802.1p and sends to LWAP over LWAPP tunnel
- Step 2: LWAP copies outer DSCP from WLC to 802.11e/WMM field and sent to client
- Step 3: LWAP copies 802.11e/WMM value from the client to outer DSCP and sends it to WLC
- Step 4: WLC copies outer DSCP from WLAP to 802.1p (CoS) fields and sends it to the switch
Web interface (do you even need to know this?)
- Controller>QoS Profiles
  - Per-User Bandwidth Contracts - set avg data rate, burst data rate, avg real-time rate, and burst real-time rate
  - Over the Air QoS
    - Maximum RF usage per AP (%)
    - Queue Depth - queue size before dropping packets
    - Wired QoS Protocol - 802.1p or None
- Controller>WLANs>Edit
  - For each WLAN ID, set the QoS value: plat, gold, silver, bronze
  - WMM Policy
    - Disabled - 802.11e/WMM QoS requests are ignored
    - Allowed - 802.11e/WMM QoS requests are sent
    - Required - 802.11e/WMM QoS requests are required

ONT Notes - AutoQoS

Wed, 10 Feb 2010 00:00:00 +0000

AutoQoS benefits
- Automates QoS for most deployments
- Protects business-critical apps to maximize availability
- Simplifies QoS deployments
- Reduces configuration errors
- Cheaper, faster, and simpler deployments
- Follows DiffServ
- Allows complete control over QoS configs
- Allows modification of auto-generated configs
AutoQoS phases of evolution
- AutoQoS VOIP - Early version that configures the basics without discovery
- AutoQoS for Enterprise - Second version that only runs on routers and uses two-step process
  - Autodiscovery using NBAR
  - Generation of class maps
AutoQoS key elements
- Application classification
- Policy generation
- Configuration
- Monitoring and reporting
- Consistency
Interfaces that you can configure AutoQoS on
- Serial ifs with PPP and HDLC
- FR point-to-point subifs (NOT multipoint)
- ATM point-to-point subifs
- FR-to-ATM links
Prerequsites
- No Qos policy already configured on if
- CEF enabled on if
- Correct bandwidth configured on if
- IP address on low-speed if
Configuring AutoQoS Enterprise on a router (NOT a switch)
- auto qos discovery - begins discovery process
- auto qos - generates and applies MQC-based policies
Configuring AutoQoS VOIP
- auto qos voip [ trust | cisco-phone ]
Verifying AutoQoS on router
- show auto discovery qos - get autodiscovery results
- show auto qos - examine configuration generated
  - Number of classes
  - Classification options
  - Marking options
  - Queuing mechanisms
  - Other QoS mechanisms
  - If, subif, PVC where policy is applied
- show policy-map interface - look at if stats
Verify AutoQoS VOIP
- show auto qos
- show policy-map interface
- show mls qos maps - shows CoS to DSCP mappings
Possible issues with AutoQoS
- Too many traffic classes - manually consolidate some
- Configuration doesn’t change - rerun AutoQoS
- Configuration may not fit your situation - fine-tune it by hand
Fine-tuning AutoQoS
- Use QPM
- CLI
- copy policy into editor, change, reapply
AutoQoS can match on characteristics besides ACLs and NBAR
- match input interface
- match cos
- match ip precedence
- match ip dscp
- match ip rtp

ONT Notes - Pre-classify and End-to-end QoS

Thu, 04 Feb 2010 00:00:00 +0000

VPNs (Didn’t ISCW cover this?)
- Provide
  - Confidentiality
  - Integrity
  - Authentication
- Types
  - Remote-access
    - Client-initiated
    - NAS-initiated
  - Site-to-site
    - LAN-to-LAN
    - Extranet
L3 Tunneling protocols
- GRE
- IPSec
Pre-classify allows traffic to be classified before being sent across a tunnel or crypto-ed.
- qos pre-classify
- Provides a view into the original IP headers
- To classify on pre-tunnel header, apply the policy to the tunnel interface WITHOUT pre-classify.
- To classify on post-tunnel header, apply the policy to the physical interface WITHOUT pre-classify.
- To classify on pre-tunnel header, apply the policy to the physical interface WITH pre-classify.
SLA - agreement with provider to guarantee QoS mechanisms across their network based on your markings.
- Assures availability, loss, throughput, delay, and jitter.
End-to-end QoS
- To be effective, each hop in the path must have QoS configured similarly.
- Necessary in three locations
  - Campus - within the customer network
  - The edges - customer facing the provider, provider facing customer
  - On the provider network
QoS tasks
- Campus access switches
  - Speed/duplex settings
  - Classification
  - Trust
  - Phone/access switch configs
  - Multiple queues on switch ports, including priority for VOIP
- Campus distribution
  - L3 policing and marking
  - Multiple queues on switch ports, including priority for VOIP
  - WRED
- WAN edge
  - SLA definitions
  - LLQ
  - LFI
  - WRED
  - Shaping
- Provider cloud
  - Capacity planning
  - PHB
  - LLQ
  - WRED
Enterprise campus QoS implementation
- Implement multiple queues to avoid congestion
- Assign VOIP and video to highest priority queue
- Esablish trust boundaries
- Use policing to rate-limit excess traffic
- Use hardware QoS when possible
Control Plane Policing (CoPP)
- Applies QoS policy to traffic destined for the router
  - Routing protocols
  - Management protocols
- Can be used to avoid DOS attacks
- Applied to control-plane in global config

ONT Notes - Congestion Avoidance, Policing, Shaping, and Link Efficiency

Wed, 03 Feb 2010 00:00:00 +0000

Tail drop drawbacks
- TCP synchronization - Dropping TCP packets from different flows can cause them all to window down and back up again at the same time in cycles.
- TCP starvation - Non-TCP or aggressive flows can starve everyone else out when TCP throttles back.
- No differentiated drop - Tail drop doesn’t care who you are, so you get dropped if the queue is full.
RED - Random Early Detection
- Avoids tail drop by randomly dropping packets from the queue before it gets full
- Only dropped TCP flows slow down instead of everyone who has sent a packet since the queue filled
- Queues are smaller.
- Link utilization is more efficient
- Configured with
  - Minimum threshold - start dropping when the queue is this size
  - Maximum threshold - if the queue is this big, start tail dropping
  - Mark probability denominator (MPD) - 1/MPD is the ratio of packets to drop when between the thresholds
WRED - Weighted RED
- Based on IP precedence or DSCP values
- Less-important packets are dropped more aggressively than important packets
- Applied to an interface, VC or a class within a policy map
CBWRED - Class based WRED
- Configured with CBWFQ
Policing
- Limits subrate bandwidth (give you 100kbps on a T1)
- Limits traffic of certain applications
- Any traffic that exceeds police is dropped or re-classified; it’s a hard limit
- Inbound or outbound
Shaping
- Sets a limit but buffers any in excess
- Requires memory to store the buffer
- Buffers = delay and/or jitter
- Outbound only
- Can respond to network signals like BECNs and FECNs
Token and bucket
- The queue is a bucket; if a byte of data needs to be sent, it needs a token.
- If there are enough tokens, the traffic is considered conforming.
- If there aren’t enough tokens, the traffic is considered exceeding, which triggers the drop (policing), re-classify (policing), or buffer (shaping).
Frame relay traffic shaping (FRTS)
- Only controls frame relay traffic
- Applied on subif or DLCI
- Support fragmentation and interleaving
- Reacts to FECNs and BECNs
Compression
- Removed redundancy and patterns in data
- Less data = less latency
- Hardware compression or hardware-assisted compression does not involve the main CPU
- Software compression does
- Payload compression
- Header compression
Link fragmentation and interleaving
- Small data might be waiting for larger data pieces to finish sending
- Chunks data into smaller fragments so they don’t have to wait
- Interleaving shuffles flows in the Tx queue

ONT Notes - Queuing

Sun, 24 Jan 2010 00:00:00 +0000

Here are some more notes from my studies. Of course, no one cares about them but me, but it’s my blog. I’m sure someone will find it useful. Please help to correct dumbass mistakes.

Congestion
- Speed mismatch - traffic leaves a lower-bandwidth interface than the one it came in on
- Aggregation problem - lots of links with one egress of equal bandwidth
- Confluence problem - a bunch of traffic needs to egress out of the same interface
Queuing

ONT Notes – Classification, Marking, and NBAR

Fri, 22 Jan 2010 00:00:00 +0000

Here’s another set of notes from my ONT studies. I’m sure someone will find it useful. Please help to correct dumbass mistakes.

Classification is done with traffic desriptors
- Ingress interface
- CoS value on ISL or 802.1P frames
- Source/destination IP address
- IP Precedence or DSCP value
- MPLS EXP
- Application type
Layer 3 QoS
- Type of Service (ToS) is 8-bit field.
- First 3 bits of ToS are the IP precedence.
- First 6 bits of ToS are the DSCP value.
- Last 2 bits of ToS are explicit congestion notification (ECN).
Layer 2 QoS

ONT Notes - Intro to QoS

Thu, 21 Jan 2010 00:00:00 +0000

I’ll try to keep it a little shorter this time.

Major issues for converged enterprise networks

Available bandwidth: competition among applications
- Fixes
  - Increase bandwidth: More power!
  - Properly queue based on classification and marking: QoS
  - Compress: cRTP, TCP header compression, etc.
Delay: Lead time to get a packet to the destination
- Types of delay
  - Processing delay: routing, switch delay
  - Queuing delay: how long a frame stays in an output queue
  - Serialization delay: how long to put the frame on the wire
  - Propagation delay: the time to cross the physical medium
Jitter (delay variation): Variation is the delay
- Different delays mean different arrival times
- De-jitter buffers save up packets to reduce jitter (like the old CD writers)
- Fixes
  - More bandwidth
  - Prioritize sensitive data and forward first
  - Remark (reclassify) packets based on sensitivity
  - Enable L2 payload compression: make sure compression delay isn’t worse than the jitter
  - Use header compression
Packet loss: Packets are lost in the network somewhere
- Fixes
  - More bandwidth
  - Increase buffers space: more room for the queue on the interface
  - Provide guaranteed bandwidth: Queuing and QoS
  - Congestion avoidance
    - Random Early Detection (RED) and weighted RED (WRED) drop packets before the queue is full
    - Selective dropping is better than FIFO or LIFO dropping

QoS History

ONT Notes - VOIP Networks

Sun, 10 Jan 2010 00:00:00 +0000

Here are some of the notes I’ve been taking while reading over the ONT book. I hope it benefits somebody. Feel free to correct any stupid mistakes as a paraphrase to avoid a lawsuit.

There’s way too much info here. I’ll refine the process a little better for the next topics.

Benefits of Packet Telephony Networks

More efficient use of bandwidth and equipment - Packet telephony networks don’t dedicate channels or a static bandwidth to a call; it’s just another network application.
Consolidate network expense - The common infrastructure (IP-based networks) keeps you from having to support another distinct network for voice like in traditional PBX implementations.
Improved employee productivity - The phone can be used for more than just phone calls by utilizing the XML interface to run applications or provide content from the network.
Access to new communications devices - IP phones can communicate with computers, network gear, PDAs, etc., and not just the PBX.

Packet Telephony Components

ISCW Down, Three To Go

Thu, 10 Dec 2009 00:00:00 +0000

I took and passed the ISCW test today. I was super-nervous going into it, which is weird for me, but I finally calmed down after the first few questions. Here’s my take. I don’t want to get into any trouble so I’m not going to include very much detail.

The testing center wasn’t very good at all. It’s in an old building on the busiest road in town, and the noise from the street was barely dampened by the 1960s building materials. I can tell you that there are three different pipes in the walls since their vibrations resonated through the room every time somebody flushed or brewed some coffee. There was also a little foot traffic, which can be expected anywhere; they were working through some software problems on another testing station and were very respectful, so it wasn’t too bad. The worst part of the whole ordeal, though, was the Microsoft class I sat through while taking the test. They were across the hall, but it sounded like they were in the room with me. Usually, you hear the instructor yelling at the top of his lungs so the whole class can hear, but I could hear questions being asked and papers being moved. I think I can go pass a test of AD replication, though. I certainly won’t be using that facility for any more tests.