Best Effort Networks, operating in layers 2, 3, and 4, are prone to delay and packet loss under congestion. These layers are used for IP traffic.
RTP Prioritization provides a strict priority queuing scheme for voice traffic. It identifies voice traffic by RTP port numbers and classifies traffic by specifying an RTP port range. If traffic matches the specified range, it is classified as voice and is placed in low latency queuing Priority Queue. If traffic does not fall within the specified port range it is classified by service policy of low latency queuing scheme.
TCP/IP Classification prioritizes packets by the packet header. There are four fragmentation methods:
1. Frame Relay Fragmentation is limited to Frame Relay connections. It enables data frames to be fragmented into smaller pieces and interleaved with real-time frames. It also enables real-time voice packets and non-real-time data packets to be carried together on lower speed links without causing excessive delay in real-time links.
2. ATM Fragmentation is limited to ATM Connections. It fragments packets into 53-byte cells for the interleaving of real-time and data packets.
3. PPP Fragmentation is limited to PPP links and splits packets into multiple smaller packets and encapsulates them into PPP frames before queuing them for transmission. Higher priority VoIP packets interrupt and transmit ahead of the larger, lower-priority data packets that were already queued and can interleave packets to minimize delay.
4. Protocol (IP) Fragmentation only transmits the layer 4 and higher protocol information in the first packet in a series of fragments.
Policy Management is another method of Layer 4 QoS. You can implement policy management on network components, such as devices, rules, actions, and policies. Policy management can actually be used on any layer of the OSI Model. Policy management controls traffic flow based on traffic conditions, schedules, and actions.