Category Archives: VoIP – CCNA / CCNP Voice

Quick Interview Review Cisco Commands

Quick Interview Review Cisco Commands

CBWFQ + LLQ – VoIP/Voice priority traffic – Bandwidth management template

Low-Latency Queuing (Congestion Management and Queuing)

Neither WFQ nor CBWFQ can provide guaranteed bandwidth and low-delay guarantee to selected applications such as VoIP; that is because those queuing models have no priority queue. Certain applications such as VoIP have a small end-to-end delay budget and little tolerance to jitter (delay variation among packets of a flow).

LLQ includes a strict-priority queue that is given priority over other queues, which makes it ideal for delay and jitter-sensitive applications. Unlike the plain old PQ, whereby the higher-priority queues might not give a chance to the lower-priority queues and effectively starve them, the LLQ strict-priority queue is policed. This means that the LLQ strict-priority queue is a priority queue with a minimum bandwidth guarantee, but at the time of congestion, it cannot transmit more data than its bandwidth permits. If more traffic arrives than the strict-priority queue can transmit (due to its strict bandwidth limit), it is dropped. Hence, at times of congestion, other queues do not starve, and get their share of the interface bandwidth to transmit their traffic.

Figure 4-6 shows an LLQ. As you can observe, LLQ is effectively a CBWFQ with one or more strict-priority queues added. Please note that it is possible to have more than one strict priority queue. This is usually done so that the traffic assigned to the two queues—voice and video traffic, for example—can be separately policed. However, after policing is applied, the traffic from the two classes is not separated; it is sent to the hardware queue based on its arrival order (FIFO).

LLQ

As long as the traffic that is assigned to the strict-priority class does not exceed its bandwidth limit and is not policed and dropped, it gets through the LLQ with minimal delay. This is the benefit of LLQ over CBWFQ.

Benefits of LLQ

LLQ offers all the benefits of CBWFQ, including the ability of the user to define classes and guarantee each class an appropriate amount of bandwidth and to apply WRED to each of the classes (except to the strict-priority queue) if needed. In the case of LLQ and CBWFQ, the traffic that is not explicitly classified is considered to belong to the class-default class. You can make the queue that services the class-default class a WFQ instead of FIFO, and if needed, you can apply WRED to it.

The benefit of LLQ over CBWFQ is the existence of one or more strict-priority queues with bandwidth guarantees for delay- and jitter-sensitive traffic. The advantage of LLQ over the traditional PQ is that the LLQ strict-priority queue is policed. That eliminates the chance of starvation of other queues, which can happen if PQ is used. As opposed to the old RTP priority queue, the LLQ strict-priority is not limited to accepting RTP traffic only. You can decide and assign any traffic you want to the LLQ strict-riority queue using special IOS keywords, using access lists, or using Network Based Application Recognition (NBAR) options. Finally, like many other queuing mechanisms, LLQ is not restricted to certain platforms or media types.

Configuring and Monitoring LLQ

Configuring LLQ is almost identical to configuring CBWFQ, except that for the strict-priority queue(s), instead of using the keyword/command bandwidth, you use the keyword/command priority within the desired class of the policy map. You can reserve bandwidth for the strict-priority queue in two ways: you can specify a fixed amount, or you can specify a percentage of the interface bandwidth. The following command syntax is used to do just that in the appropriate order:

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The burst amount (bytes) is specified as an integer between 32 and 2,000,000; it allows a temporary burst above the policed bandwidth. Note that if the percent option is used, the reservable amount of bandwidth is limited by the value of max-reserved-bandwidth on the interface configuration, which is 75 percent by default.

Example 4-7 shows implementation of LLQ using a policy map called enterprise. The policy map assigns a class called voice to the strict-priority queue with a bandwidth guarantee of 50 Kbps. Classes business and class-default form the CBWFQ component of this LLQ.

Example 4-7 A Policy Map to Implement LLQ

A Policy Map to Implement LLQ

You can use the show policy-map interface interface command to see the packet statistics for all classes used within a policy map that is applied to an interface using the service-policy command. Example 4-8 shows (partial) output of this command for the serial 1/0 interface of a router.

Example 4-8 Sample Output of the show policy-map interface Command

Sample Output of the show policy-map interface Command

QoS template – bandwidth dependency calculation:

Cisco QoS features like LLQ and CBWFQ let us to prioritize and guarantee delay and bandwidth for defined class of traffic.
CBWFQ configuration allows to configure the BW requirements for specific class of service. First we have to defined the class and match the specific type of traffic, then assign BW limit in the policy that will be reserverd during interface congestion. Standard bandwidth command with BW in Kbps under class can be used for above. The drawback of this type of configuration is need to adjust the BW speed definition each time once we have changed the access speed.

IOS allows to tune the QoS configuration to define kind of QoS template that will use BW class ratio accross function similar devices without need for reconfiguration of BW parameters each time when access speed change. LLQ defines the priority queue for the delay sensetive traffic. Additionaly for business critical traffic CBWFQ needs to be configured. We have two options to confgure the QoS template: bandwidth percent and bandwidth remaining percent per class options.

I have defined 4 classes that will be used to presents configuration options.
class-map match-all TELNET
match protocol telnet
class-map match-all HTTP
match protocol http
class-map match-all SMTP
match protocol smtp
class-map match-all VoIP
match protocol rtp

Option 1 – bandwidth percent
First option to define BW template is to use bandwidth percent command instead of just bandwidth under class in policy map configuration. BW will be calculated based on the interface’s BW, so in case Fast Ethernet it will be 100Mbps. Priority percent 10 for PQ or bandwidth percent 10 in CBWFQ it’s 10% of 100Mbps.

By default, available interface BW is defined based on the physical port speed unless you configure the bandwidth command under interface to set access speed to something less (SLA access). Additionaly Cisco IOS has Default Class (class-default) with reserved the 25% of interface BW that match all undefined traffic (you can change it with max-reserved-bandwidth command under interface mode).

Let’s configure the first policy based on option 1:
R1(config)#policy-map LLQ
R1(config-pmap)#class VoIP
R1(config-pmap-c)#priority percent 10
R1(config-pmap-c)#class HTTP
R1(config-pmap-c)#bandwidth percent 10
R1(config-pmap-c)#class SMTP
R1(config-pmap-c)#bandwidth percent 50
R1(config-pmap-c)#class TELNET
R1(config-pmap-c)#bandwidth percent 30

The first way choice is to configure the bandwidth percent to fil 100% of interface speed, but due to class-default the available BW to share is 75%. In the above example we have defined 4 classed and assigned 100% of interface BW, here let’s try to assign the LLQ policy to the inerface:
R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#int fa0/0
R1(config-if)#service-policy output LLQ
I/f FastEthernet0/0 class TELNET requested bandwidth 30%, available only 5%
R1(config-if)#

We can observe the error message that is saying that we have just 5% of available BW, this is due to 25% reserved for default class. OK so let change reserved BW for TELNET to 5%, assign policy to the interface and see the policy.
R1#show policy-map interface fastEthernet 0/0
FastEthernet0/0
Service-policy output: LLQ
Class-map: VoIP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol rtp
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth 10 (%)
Bandwidth 10000 (kbps) Burst 250000 (Bytes)
(pkts matched/bytes matched) 0/0
(total drops/bytes drops) 0/0
Class-map: HTTP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol http
Queueing
Output Queue: Conversation 265
Bandwidth 10 (%)
Bandwidth 10000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: SMTP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol smtp
Queueing
Output Queue: Conversation 266
Bandwidth 50 (%)
Bandwidth 50000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: TELNET (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol telnet
Queueing
Output Queue: Conversation 267
Bandwidth 5 (%)
Bandwidth 5000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any

Policy has been defined for Fast Ethernet so LLQ and CBWFQ have 75Mbps traffic reserved, below BW calculation details:

VoIP = 100Mbps * 0,1 = 10Mbps
HTTP = 100Mbps * 0,1 = 10Mbps
SMTP = 100Mbps * 0,5 = 50Mbps
TELNET = 100Mbps * 0,05 = 5Mbps

Option 2 – bandwidth remaining percent
Second option to define BW is to use bandwidth remaining percent command. The idea of this type of configuration is to first reserve the BW for the PQ thru priority percent command and next divides the available remaining BW between defined classes.
Let’s configure below:
R1(config)#policy-map LLQ
R1(config-pmap)#class VoIP
R1(config-pmap-c)#priority percent 10
R1(config-pmap-c)#class HTTP
R1(config-pmap-c)#bandwidth remaining percent 10
R1(config-pmap-c)#class SMTP
R1(config-pmap-c)#bandwidth remaining percent 50
R1(config-pmap-c)#class TELNET
R1(config-pmap-c)#bandwidth remaining percent 40
R1(config-pmap-c)#int fa0/0
R1(config-if)#service-policy output LLQ

For class VoIP priority percent 10 will be equal 100Mbps*0,1=10Mbps, BW Remaining is = (100-10)Mbps * 0,75= 67,5Mbps. So BW Remaining will be used as reference for all classes.
For class HTTP bandwidth remaining percent 10 will be equal BW Remaining*0,1 = 67,5Mbps*0,1= 6,75 Mbps.
For class SMTP bandwidth remaining percent 50 will be equal BW Remaining*0,5 = 33,75 Mbps.
For class TELNET bandwidth remaining percent 40 will be equal BW Remaining*0,4 = 27 Mbps.
By default Burst for Strict Priority queue is equal 20% of the PQ’s BW so 20% of 10Mbps, (10000000bitów/8)*0,2=250000B

R1#show policy-map interface fa0/0
FastEthernet0/0
Service-policy output: LLQ
Class-map: VoIP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol rtp
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth 10 (%)
Bandwidth 10000 (kbps) Burst 250000 (Bytes)
(pkts matched/bytes matched) 0/0
(total drops/bytes drops) 0/0
Class-map: HTTP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol http
Queueing
Output Queue: Conversation 265
Bandwidth remaining 10 (%)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: SMTP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol smtp
Queueing
Output Queue: Conversation 266
Bandwidth remaining 50 (%)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: TELNET (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol telnet
Queueing
Output Queue: Conversation 267
Bandwidth remaining 40 (%)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: class-default (match-any)
30 packets, 2851 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any

Above examples are Cisco recommended ways to deploye CE QoS configuration for different access speed port.

CUCME/CME VBOX GNS3 IP Communicator basic LAB (VoIP)

 

VoIP on GNS3/Packet Tracer / Cisco IP Communicator and Cisco Unified Communications Manager Express CUCME

ISDN2 and ISDN30

https://networkengineer.me/2014/03/03/e1e-carrier-isdn-pri-integrated-services-digital-network-private-rate-interface/

Integrated Services for Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network

The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI), Primary Rate Interface (PRI),

ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kilobit/s

Primary Rate Interface

The other ISDN access available is the Primary Rate Interface (PRI), which is carried over an E1 (2048 kbit/s) in most parts of the world. An E1 is 30 ‘B’ channels of 64 kbit/s, one ‘D’ channel of 64 kbit/s and a timing and alarm channel of 64 kbit/s.

In North America PRI service is delivered on one or more T1 carriers (often referred to as 23B+D) of 1544 kbit/s (24 channels). A PRI has 23 ‘B’ channels and 1 ‘D’ channel for signalling (Japan uses a circuit called a J1, which is similar to a T1). Inter-changeably but incorrectly, a PRI is referred to as T1 because it uses the T1 carrier format. A true T1 (commonly called “Analog T1” to avoid confusion) uses 24 channels of 64 kbit/s of in-band signaling. Each channel uses 56 kb for data and voice and 8 kb for signaling and messaging. PRI uses out of band signaling which provides the 23 B channels with clear 64 kb for voice and data and one 64 kb ‘D’ channel for signaling and messaging. In North America, Non-Facility Associated Signalling allows two or more PRIs to be controlled by a single D channel, and is sometimes called “23B+D + n*24B”. D-channel backup allows for a second D channel in case the primary fails. NFAS is commonly used on aT3.

PRI-ISDN is popular throughout the world, especially for connecting PBXs to PSTN.

While the North American PSTN can use PRI or Analog T1 format from PBX to PBX, the POTS or BRI can be delivered to a business or residence. North American PSTN can connect from PBX to PBX via Analog T1, T3, PRI, OC3, etc…

Even though many network professionals use the term “ISDN” to refer to the lower-bandwidth BRI circuit, in North America BRI is relatively uncommon whilst PRI circuits serving PBXs are commonplace.

Bearer channels

The bearer channel (B) is a standard 64 kbit/s voice channel of 8 bits sampled at 8 kHz with G.711 encoding. B-Channels can also be used to carry data, since they are nothing more than digital channels.

Each one of these channels is known as a DS0.

Most B channels can carry a 64 kbit/s signal, but some were limited to 56K because they traveled over RBS lines. This was commonplace in the 20th century, but has since become less so.

Signaling channel

The signaling channel (D) uses Q.931 for signaling with the other side of the link.

United Kingdom

In the United KingdomBritish Telecom (BT) provides ISDN2 (BRI) as well as ISDN30 (PRI). 

In ISDN, there are two types of channels, B (for “bearer”) and D (for “data”). B channels are used for data (which may include voice), and D channels are intended for signaling and control (but can also be used for data).

There are two ISDN implementations. Basic Rate Interface (BRI), also called basic rate access (BRA) — consists of two B channels, each with bandwidth of 64 kbit/s, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D. Primary Rate Interface (PRI), also called primary rate access (PRA) in Europe — contains a greater number of B channels and a D channel with a bandwidth of 64 kbit/s. The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B+1D, with an aggregate bit rate of 1.544 Mbit/s (T1); in Europe, India and Australia it is 30B+1D, with an aggregate bit rate of 2.048 Mbit/s (E1).

 

WHAT IS THE DIFFERENCE BETWEEN ISDN2 AND ISDN30?

  • ISDN2 is also called Basic Rate Interface or BRI for short.
  • ISDN30 is also called Primary Rate Interface or PRI for short.

ISDN2 has a minimum installation of 2 channels
ISDN30 has a minimum installation of 8 channels.

ISDN2 doesn’t have a maximum number of channels, but rarely goes over 8. This is because at 8 channels, ISDN30 becomes cheaper. The only exception might be in more remote locations where ISDN30 isn’t available.

So typically if you want 2/4/6/8 channels you’ll go for ISDN2, if you want 8 or more channels you’ll go for ISDN30. Simple*.

The functionality of ISDN2e and ISDN30 is very similar. ISDN2e is supplied in multiples of two lines. You can expand further in multiples of two, but each expansion requires a visit from BT (two week lead-time) plus system programming. If you require 6 lines or less on your telephone system and it is likely that this figure will not increase, then ISDN2e is usually adequate. For larger organisations, the correct solution is ISDN30. ISDN30 is delivered as ‘a site connection’, you merely specify how many lines you want (eight is the minimum). One advantage of ISDN30 is the use of fibre optic cable, which is more reliable than traditional copper wire. (note ISDN30 is quite often now supplied on copper).

UC500 (Unified Communications 500) / SPA504G IP Phones

Telephony System/VoIP/SIP/Cisco/Mitel/Polycom/Avaya/Linksys

E1(E-Carrier) – ISDN PRI (Integrated Services Digital Network – Private Rate Interface)/SIP Trunking

What is Cisco Collaboration?

Cisco Unified Communications Manager Express/CUCM/CUCM Business Edition