Packet classifiers identify packets from an IP flowing within a host and router that will receive a certain level of service. To realize effective traffic control, incoming packets are mapped by classifiers into specific classes. All packets classified into the same class will receive the same treatment from the packet scheduler. The selection of a class is based on the source IP address and port number in the packet header or an additional classifier number that must be added to each packet. For example, all videos from a video conference with several sources can be classified into one class of service. But it is also possible that there is only one flow in a class of service.
Packet classification is a way of giving a class or difference to each packet, this is done to facilitate the handling of Packets by the queue. Classification is different from filtering which functions to direct and filter the flow of data packets.
Figure 43. Data Packet Classification
Figure 44. Priority Classification
1. Class Based Queue (CBQ)
The most well-known data packet classification technique is CBQ, easy to configure, allows sharing of bandwidth between classes and has user interface facilities. CBQ regulates the use of network bandwidth allocated to each user, bandwidth usage that exceeds the set value will be cut (shaping), CBQ can also be set to share and borrow bandwidth between classes if needed.
CBQ parameters:
- avpkt = Average number of packages during delivery.
- bandwidth = the bandwidth width of an ethernet card is usually 10 -- 100Mbit
- rate = Average speed of data packets when leaving qdisc, this is a parameter for setting bandwidth.
- cell = Increase the data packets issued to the ethernet card based on the number of bytes, for example 800 to 808 with a cell value of 8.
- isolated / sharing = isolated parameter sets the bandwidth to be unborrowed by other classes of the same level / siblings. Sharing parameter indicates the class bandwidth can be borrowed by other classes.
- bounded / borrow = the borrow parameter means that a class can borrow bandwidth from another class, while bounded means the opposite.
Figure 45. Bounded / Borrow
2. Buchet Token Hierarchy
HTB queuing technique is similar to CBQ only the difference lies in the options, HTB has fewer options during configuration and is more precise. HTB queuing technique provides us with traffic limitation facilities at each level or classification, unused bandwidth can be used by lower classifications. We can also see HTB as an organizational structure where each section has authority and is able to help other sections in need, HTB queuing technique is very suitable to be applied to companies with many organizational structures.
Figure 46. Data Queue on HTB
3. Admission Control
Admission control or entrance control contains a decision algorithm that a router uses to determine if there are sufficient routes to accept the QoS request for a new flow. If there are no free routes, the acceptance of the new flow will impact earlier guarantees and the new flow should be rejected. If a new flow is accepted, a reservation event in the router will assign the packet classifier and packet scheduler to reserve or reschedule the QoS request for this flow. The admission control algorithm must be consistent with the service model. Admission control is sometimes confused with policy control, which is a packet-by-packet process that is processed by the packet scheduler.