nnection points are shown and discussed in Figures 4.11 and 4.12. As illustrated, IP interconnection points are possible bottlenecks for end-to-end IP traffic. This includes also best-effort traffic from the Internet access ser- vice (access to the public Internet) and other IP traffic which is provided to customers by telecom operators with QoS guarantees (e.g. carrier-grade VoIP as a replacement for PSTN/ISDN). The interconnection points of a given telecom operator should be able to transfer the demanded traffic from/to all access networks during peak time or busy hours if one uses the traditional telecom terminology (that is, the time period in the usual weekday with the highest volume of traffic in both directions, downlink and uplink). So, peering and transit agreements of a given telecom operator (which 4.5 End-to-End QoS Network Design Regional Regional network A network B Access Transit Access network A network network B access ISP-2 network ISP-1 access (IntServ) (DiffServ) (MPLS-TE) (over provisioning) Mobile access Cable Optical (3G, 4G, 5G) access access network network BB - Backbone provider ISP - Internet service provider Figure 4.10 End-to-end QoS provision. FTTH access network has capacity, for At this interconnection point, if we example: 100 Mbit/s in DL per user, assume that 90% of the traffic in both UL and 100 Mbit/s in UL per user, and and DL goes out of the ISP-1 network, it there are 10 000 users connected to requires capacity of 800 Gbit/s X 0.9 = it, from which a maximum of 80% are 720 Gbit/s only for users from FTTH online at the same time, then the access network in this example. If the needed capacity in the access capacity at the interconnection is network will be 10000 X 100 Mbit/s X significantly below 720 Gbit/s, then the 0.8 = 800 Gbit/s in each direction (UL advertised speeds cannot be reached and DL). and we have QoS degradation. access ISP-1 ISP-2 network access (IntServ) (DiffServ) (MPLS-TE) (over provisioning) Mobile access Optical (3G, 4G, 5G) access BB - Backbone provider 