QoS

The Internet Engineering Task Force (IETF) defines the following two architectures for QoS: 

Integrated Services (IntServ) and

Differentiated Services (DiffServ)

IntServ uses the Resource Reservation Protocol (RSVP) to signal explicitly the QoS needs of an application's traffic along the devices in the end-to-end path through the network.
DiffServ focuses on aggregated and provisioned QoS. Instead of signaling an application's QoS requirements, DiffServ uses a DiffServ Code Point (DSCP) in the IP header to indicate the required QoS levels.

Small buffers:
        often drop packets due to bursts
        but have small delays
Large buffers:
        reduce number of packet drops (due to bursts)
        but increase delays

Traffic shaping controls the rate at which packets are sent
Two traffic shaping algorithms are:
       Leaky Bucket
      Token Bucket

Bandwidth Profile Parameters:

Ø      Committed Information Rate (CIR):
Ø      Committed Burst Size (CBS):
Ø      Excess Information Rate (EIR):
Ø      Excess Burst Size (EBS):

When using the trTCM (two-rate-three-color marking) algorithm, the “C” bucket refills constantly per CIR
"E" bucket refills the EIR.
Maximum quantity of "E" bucket or "C" bucket determined by burst size i.e. CBS/EBS.

HQoS
-The ability to provide multiple levels of packet scheduling
– The ability to support integrated class-based shaping and queuing
– The ability to apply fair queuing and drop policies on a per-class basis

The hierarchical queuing framework (HQF) defines a QoS architecture for implementing hierarchical packet scheduling and queuing.

Policing and Marking
Policing causes traffic that exceeds the configured rate to be discarded or marked down to a higher drop precedence. Marking is a way to identify packet flows to differentiate them. Packet marking allows you to partition your network into multiple priority levels or classes of service.

Queuing
Queueing is designed to accommodate temporary congestion on a network device's interface by storing excess packets in buffers until bandwidth becomes available.

The default mechanism on most interfaces is First In First Out (FIFO). Some traffic types have more demanding delay/jitter requirements. Thus, one of the following alternative queueing mechanisms should be configured or is enabled by default:

Weighted Fair Queueing (WFQ)
Class-Based Weighted Fair Queueing (CBWFQ)
Low Latency Queueing (LLQ), which is in fact CBWFQ with a Priority Queue (PQ) (known as PQCBWFQ)
Priority Queueing (PQ)
Custom Queueing (CQ)

Queueing generally happens on outbound interfaces only. A router queues packets that are going out an interface. You can police inbound traffic, but usually you cannot queue inbound to forward packets from the ingress to the egress interface;

Flow Control:

Ethernet Flow control defines a type of Ethernet packet usually referred to as a 'PAUSE' frame.
Flow control is the management of data flow between computers or devices or between nodes in a network so that the data can be handled at an efficient pace. Too much data arriving before a device can handle it causes data overflow, meaning the data is either lost or must be retransmitted.

When a network device needs to slow down a sender, it can issue a “pause frame” which tells the sender to stop transmitting frames for a period of time which is included in the pause frame

ACL
An access control list (ACL) is a set of rules (or permit or deny statements) for identifying traffic based on criteria such as source IP address, destination IP address, and port number.
ACLs are essentially used for packet filtering. A packet filter drops packets that match a deny rule and permits packets that match a permit rule. ACLs are also widely used by many modules, for example, QoS and IP routing,for traffic identification.

·   Standard ACLs: This type of AL is the simplest one since it only filters based on source IP addresses. In other words, this AL can be used only when you need to permit or deny traffic from a specific host IP address or a specific source network.

Extended ACLs: This type of AL is the most preferred one and the most advanced as well. Using this type of AL you can filter traffic based on:

    -Source IP address
    -Destination IP address
   - Protocol (TCP, UDP)
  -Port Numbers (Ftp 21, Telnet 23, etc.)