A switch interface can have only one policy applied at a given time in each direction. You can apply the same policy for both inbound and outbound traffic or you can apply different QoS policy for both inbound and outbound traffic on a given interface.
QoS can be quantified by the following methods:
CoS: Class of Service. CoS is applied at Layer 2 or at frames level. A 3-bit value (known as priority bits) in the range of 0 to 7 is carried along the frames in a VLAN trunk. 0 represents the lowest priority, and 7 represents the highest priority.
CoS: Class of Service. CoS is applied at Layer 2 or at frames level. A 3-bit value (known as priority bits) in the range of 0 to 7 is carried along the frames in a VLAN trunk. 0 represents the lowest priority, and 7 represents the highest priority.
IP Precedence: IP Precedence is a 3-bit value represented in the ToS (Type of Service) byte of Layer 3 IP packets. Here also, value 0 represents the lowest priority and 7 represent the highest priority.
DSCP: DSCP stands for Differentiated Service Code Point. DSCP consists of a 3-bit Selector, and a 3-bit Drop Precedence value. DSCP is backward compatible with IP Precedence, and works at layer 3.
QoS policy is applied to an interface. You can apply one for inbound traffic, and another for outbound traffic on the same interface.
| DSCP | Codepoint Name | DSCP Bits |
|---|---|---|
| Binary | Decimal | |
| Default | 000 000 | 0 |
| AF11 | 001 010 | 10 |
| AF12 | 001 100 | 12 |
| AF13 | 001 110 | 14 |
| AF21 | 010 010 | 18 |
| AF22 | 010 100 | 20 |
| AF23 | 010 110 | 22 |
| AF31 | 011 010 | 26 |
| AF32 | 011 100 | 28 |
| AF41 | 100 010 | 34 |
| AF42 | 100 100 | 36 |
| AF43 | 100 110 | 38 |
| EF | 101 110 | 46 |
CAC: CAC mechanisms extend the capabilities of the QoS tool suite to protect voice traffic from being negatively affected by other traffic, and to keep excess voice traffic off the network. For example, if a WAN access link between the two PBXs has the bandwidth to carry only two VoIP calls, admitting a third call will impair the voice quality of all three calls. After the call is rejected, the originating gateway must find another means of handling the call.
Policing: Monitor the bit rate of the interface and discard the packet immidiately if it reaches the configured bandwidth.
Shaping: Allows excess traffic to be queued in memory buffers.
Normally Service Provider prefers Policing cause it discard the packet once reaches specific threshold, besides its not CPU intensive.
Additional notes: Call Admission Control (CAC) is a concept that applies to voice traffic only - not data traffic. CAC is a deterministic and informed decision that is made before a voice call is established and is based on whether the required network resources are available to provide suitable QoS for the new call. Though some other options such as QoS appears to be relevant answer, CAC is the best answer within the given context.
DSCP (Differentiated Services Code Point): It is associated with IPv4 and IPv6 headers.
CoS (Class of Service): It is associated with 802.1Q and used over VLAN trunk.
TID (Traffic ID): It is associated with 802.11 and used over Wi-Fi network.
EXP (EXPerimental): It is associated with MPLS label and used over MPLS WAN.
IPP (IP Precedence): It is associated with IPv4 and IPv6 headers.
Based on past experience, the following values are recommended by Cisco for interactive voice:
Delay (one way) - 150ms or less
Jitter - 30 ms or less
Loss - 1% or less
Bandwidth: 30 kbps to 320 kbps
Note that jitter is invariably smaller than the delay by a magnitude.
When migrating from internally hosted services to cloud, the following may need to be taken care of:
1. Security: The cloud services reside outside the organization, and it is possible that man-in-the-middle and other attacks might happen, particularly if you are using public Internet to connect to the Cloud. You might consider a private WAN connection for this reason.
2. Quality of Service: Usually, ISP do not provide quality of service agreement to the end users. If you organization is using time sensitive applications, connectivity via public Internet may not be desirable. In such cases, it is recommended to have a private WAN connectivity between your organization and the cloud resources.
3. SLA (Service Level Agreement): You may demand SLA from WAN providers, whereas it is difficult to negotiate the same with ISP Internet providers.
4. The cost of accessing the cloud resources via Internet is always the most cost effective solution, however, it comes with limited security and QoS. The needs of the organization are to be analyzed before making a choice.
Usually, network availability and cost are not a problem for Internet connectivity.
1.Best Effort Delivery: The best effort delivery method does not distinguish between a priority traffic and a non-priority traffic. The packets are forwarded in the order that they arrive. However, the routers or switches put their best effort to forward the packets that are received.
2.Integrated Services (IntServ) Model: The protocol that does scheduling and reserving adequate path bandwidth (end-to-end bandwidth) for application is know as Resource Reservation Protocol (RSVP). The source application requests QoS parameters through RSVP from the network devices along the route to destination. The minimum set of commonly agreed parameters is arrived at, and the source is informed of the same. RSVP enables traffic prioritization according to a pre-determined set of rules.
3.Differentiated Services Model (DiffServ): In the DiffServ model, the resources are dynamically arranged. The advantage over IntServ model is that the bandwidth utilization is more efficient in DiffServ. With IntServ, QoS is applied on a per-flow basis, whereas it is applied on a per-hop basis on DiffServ.
There are 3 basic types of QoS:
1.Best Effort Delivery: The best effort delivery method does not distinguish between a priority traffic and a non-priority traffic. The packets are forwarded in the order that they arrive. However, the routers or switches put their best effort to forward the packets that are received.
2.Integrated Services (IntServ) Model: The protocol that does scheduling and reserving adequate path bandwidth (end-to-end bandwidth) for application is know as Resource Reservation Protocol (RSVP). The source application requests QoS parameters through RSVP from the network devices along the route to destination. The minimum set of commonly agreed parameters is arrived at, and the source is informed of the same. RSVP enables traffic prioritization according to a pre-determined set of rules.
3.Differentiated Services Model (DiffServ): In the DiffServ model, the resources are dynamically arranged. The advantage over IntServ model is that the bandwidth utilization is more efficient in DiffServ. With IntServ, QoS is applied on a per-flow basis, whereas it is applied on a per-hop basis on DiffServ.
The terms are explained below:
Bandwidth - The rate at which traffic is carried by the network.
Latency - The delay in data transmission from source to destination.
Jitter - The variation in latency.
Reliability - The percentage of packets discarded by a router.
1.policy-map <policy-name>: Defines a policy map.
2.class <class-name>: Classify with a class map.
3.set ip dscp <dscp-value>: Mark the DSCP value
4.set ip ip precedence <ip-precedence-value>: Mark the ip precedence value.
5.trust {cos|dscp|ip-precedence}: Trust the inbound QoS information
6.service-policy [input|output] <policy-name>: Apply the policy map to an interface.
