As technology advances, services which requires Quality of service (QoS) increases. Network QoS mechanism focus on providing one, real time, service in addition to the normal best effort service. There is a need for low delay in real time applications, delay guarantees in video streaming applications. As a result of growing demand for QoS, Network Operators should optimize use of network resources in order to avoid over provisioning. It should also ensure committed Service Level Agreements. Major QoS components are throughput, jitter, delay and error rates. There are a no of factors which affect QoS of wireless network. They are
- Higher error rates
- Multipath Interference
- Noise, Both natural and man made such as radio, TV
- Spectrum interference like spread spectrum interference's from neighboring cells
- Mobility which affects resource utilization, management and hand over
- Limited capacity, due to cost involved in building them
Core components of Network QoS Components are
- Admission Control - In this functionality, number of flows admitted into the network are limited which is required to achieve desired QoS for each individual flow.
- Scheduling - This can affect jitter, delay and loss rate. It also helps to protect misbehaving flows.
- Buffer Management -Main objective of this is to control the buffer size. It also decides the packets which needs to be dropped. It can control packet loss rate. On of the packet drop strategies used are weighted Random Early Detection (RED).
- Congestion Control: Prevents, handles and recovers from network congestion scenarios.
QoS schemes must interact with those already in use in the Internet. Proposed Internet QoS Mechanisms are
- Differentiated Services (DiffServ)
- Integrated Services (IntServ)
- Integrated Services over Specific Link Layers (ISSLL)
- Multi-Protocol Label Switching (MPLS)
- Resource Reservation Protocol (RSVP)
IntServ ensures Guaranteed Service with quantified delay and jitter bounds for the traffic. In ensures near loss transmission, since there is no data loss from data buffers. It supports real time traffic, making the appear to be a lightly loaded which is used for delay tolerant applications. MPLS is used to carry IP traffic over fast ATM networks, since this can improve the forwarding speed of routers. Basic design principle of MPLS is that the routers at the edge of the MPLS domain mark all packets with a fixed length label which acts as shorthand for the information contained in the IP packet header. It is usually used as a Layer 2 rather than a Layer 3 solution. It cannot provide end to end QoS configurable on a flow by flow basis.