Abstract
When we call someone over the Internet using a service such as Skype or Google talk, we may experience certain undesirable problems. For instance, we may not be able to hear the other person very well, or even worse, the call may be dropped. In order to eliminate these problems, the underlying IP network has to be able to provide quality of service guarantees. Several schemes have been developed that enable the IP network to provide such guarantees. Of these schemes, the Multi-Protocol Label Switching (MPLS) and the Differentiated Services (DiffServ) are the most widely used. In this article, some of the salient features of MPLS and DiffServ are reviewed.
TopBackground
QoS is a well-understood and studied topic within the networking community. It is typically expressed in term of the following three metrics: the end-to-end delay, the jitter, and the packet loss rate. The end-to-end delay is the amount of time it takes to transfer a packet from the transmitter to the receiver, and it consists of a) the end-to-end propagation delay, b) delays induced by transmission systems and processing times inside the routers, and c) delays a packet encounters due to queueing in the buffers of the routers. Jitter refers to the variability of the inter-arrival times of the packets at the destination, and the packet loss rate is the percent of packets that are lost.
Table 1. QoS metrics for common networking services
| Tolerance for packet loss | Tolerant | Conversational voice and video | Voicemail | Streaming audio and video | Fax |
| Intolerant | Remote app., command and control games | e-commerce
web browsing | Texting, file transfer (foreground) | File transfer (background), email |
| | Interactive
delay<<1 s | Responsive
delay ~1 s | Timely
delay ~ 10 s | Background
delay >> 10 s |
| | Tolerance for delay |
Key Terms in this Chapter
Quality of Service (QoS): It describes how well a flow of packets is served by the network. It is typically measured by different metrics, such as, end-to-end delay, jitter, packet loss rate, network availability, and bandwidth.
DiffServ: A mechanism used in the IP network to provide QoS guarantees on aggregates of flows.
Call Admission Control: This is a scheme that assures that there is sufficient bandwidth in the network for a new flow of packets.
Service Level Agreement (SLA): A contract between a network provider and a customer that spells out that spells out how much traffic per class the customer will submit, the customer’s expected QoS, and the price for the service.
Software Defined Networks (SDN): A centralized solution for managing routers and Ethernet switches.
Voice Over IP (VoIP): A telephone service implemented over the Internet. Voice is packetized into IP packets which are transmitted to the destination over the Internet. At the destination, the voice data is recovered from the packets and played back.
Open Shortest Path First (OSPF): A protocol used to construct routes through the IP network that typically minimizes the number of hops (routers).
RSVP-TE: A signaling protocol for setting connections in an MPLS network.
Network-Function Virtualization (NFV): It is a concept that uses the technologies of IT virtualization in order to virtualize networking functions that may be connected together to create communication services.
Propagation Delay: This the time it takes for a bit of data to travel across the network from one node or endpoint to another.
Explicit Route: A route through the IP network that satisfies a QoS criterion, such as, minimizations of the end-to-end delay, maximization of throughput, etc.
Enterprise Network: A privately owned and operated network.